首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   10172篇
  免费   597篇
  国内免费   7篇
  2023年   136篇
  2022年   171篇
  2021年   219篇
  2020年   321篇
  2019年   317篇
  2018年   519篇
  2017年   551篇
  2016年   496篇
  2015年   309篇
  2014年   366篇
  2013年   1341篇
  2012年   702篇
  2011年   705篇
  2010年   444篇
  2009年   295篇
  2008年   572篇
  2007年   487篇
  2006年   444篇
  2005年   338篇
  2004年   261篇
  2003年   250篇
  2002年   211篇
  2001年   114篇
  2000年   132篇
  1999年   90篇
  1998年   58篇
  1997年   46篇
  1996年   47篇
  1995年   44篇
  1994年   37篇
  1993年   43篇
  1992年   52篇
  1991年   54篇
  1990年   45篇
  1989年   44篇
  1988年   43篇
  1987年   31篇
  1986年   30篇
  1985年   30篇
  1984年   29篇
  1983年   22篇
  1981年   19篇
  1980年   17篇
  1979年   26篇
  1976年   20篇
  1971年   17篇
  1970年   16篇
  1968年   20篇
  1966年   16篇
  1965年   18篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This study uses a social-ecological approach to the development of delinquency. The authors emphasize that a balance between eliminating risk and enhancing protection across domains is essential in reducing problems and promoting competence. The cumulative risk and promotive effects of temperament, family and school factors in preadolescence were examined on different groups of delinquents (based on self-report) in early adolescence. Data from the first two waves of the TRAILS study (N = 2,230) were used. The results provide evidence for a compensatory model that assumes main effects of risk and promotive factors on problem behavior. Accumulation of risks in preadolescence promoted being a serious delinquent in early adolescence, with the strongest effects for temperament. Accumulation of promotive effects decreased being a delinquent and supported being a non-delinquent. Furthermore, evidence is found for a counter-balancing effect of cumulative promotive and risk factors. Exposure to more promotive domains in the relative absence of risk domains decreased the percentage of serious delinquents. Our results did not support a protective model. Implications for prevention and intervention are discussed.  相似文献   
992.
When people scan mental images, their response times increase linearly with increases in the distance to be scanned, which is generally taken as reflecting the fact that their internal representations incorporate the metric properties of the corresponding objects. In view of this finding, we investigated the structural properties of spatial mental images created from nonvisual sources in three groups (blindfolded sighted, late blind, and congenitally blind). In Experiment 1, blindfolded sighted and late blind participants created metrically accurate spatial representations of a small-scale spatial configuration under both verbal and haptic learning conditions. In Experiment 2, late and congenitally blind participants generated accurate spatial mental images after both verbal and locomotor learning of a full-scale navigable space (created by an immersive audio virtual reality system), whereas blindfolded sighted participants were selectively impaired in their ability to generate precise spatial representations from locomotor experience. These results attest that in the context of a permanent lack of sight, encoding spatial information on the basis of the most reliable currently functional system (the sensorimotor system) is crucial for building a metrically accurate representation of a spatial environment. The results also highlight the potential of spatialized audio-rendering technology for exploring the spatial representations of visually impaired participants.  相似文献   
993.
Working memory was designed to explain four benchmark memory effects: the word length effect, the irrelevant speech effect, the acoustic confusion effect, and the concurrent articulation effect. However, almost all research thus far has used tests that emphasize forward recall. In four experiments, we examine whether each effect is observable when the items are recalled in reverse order. Subjects did not know which recall direction would be required until the time of test, ensuring that encoding processes would be identical for both recall directions. Contrary to predictions of both the primacy model and the feature model, the benchmark memory effect was either absent or greatly attenuated with backward recall, despite being present with forward recall. Direction of recall had no effect on the more difficult conditions (e.g., long words, similar-sounding items, items presented with irrelevant speech, and items studied with concurrent articulation). Several factors not considered by the primacy and feature models are noted, and a possible explanation within the framework of the SIMPLE model is briefly presented.  相似文献   
994.
Ellipsis refers to an element that is absent from the input but whose meaning can nonetheless be recovered from context. In this cross-modal priming study, we examined the online processing of Sluicing, an ellipsis whose antecedent is an entire clause: The handyman threw a book to the programmer but I don’t know which book the handyman threw to the programmerellipsis. To understand such an elliptical construction, the listener arguably must ‘fill in’ the missing material (“the handyman threw___ to the programmer”) based on that which occurs in the antecedent clause. We aimed to determine the point in time in which reconstruction of the sluiced sentence is attempted and whether such a complex antecedent is re-accessed by the ellipsis. Out of the two antecedent constituents for which we probed, only the Object (programmer) was found active in the elliptical clause, confirming that an antecedent is attributed to the sluice in real time. Possible reasons for the non-observation of the Subject (handyman) are considered. We also suggest that ellipses are detected earlier in coordinated than subordinated sentences.  相似文献   
995.
Referring to studies about addictive behaviors, the objective of this article is to present the validation of a new tool for the assessment of the addictive behaviors with or without substances: the Addictive Intensity Evaluation Questionnaire (AIEQ). Twelve different versions of the AIEQ have been administered to 354 participants in order to assess their addictive behaviors. The study of the factorial structure of the questionnaire and its reliability allow us considering the psychometric qualities of the AIEQ as satisfactory. The results suggest the existence of a continuum between the absence of addiction and the severe forms of addiction. The discussion section proposes a classification based on the severity of the addictive behaviors and applications of the use of the AIEQ.  相似文献   
996.
This article outlines the struggle between the power of the health care professional and the rights of the individual to choose freely a modality of treatment. Nurses are instrumental in assisting patients in making the best decision for a therapy they will have to assume for the rest of their lives. In guiding patients' decision, nurses must take into account these unavoidable contingencies: changes in lifestyle, nutritional restrictions, level of acceptance, compliance issues, ease of training and availability of support/facilities. Ensuring that the patient makes an informed decision is therefore an ongoing challenge for nurses as they are taking part in a delicate balancing act between not directly influencing the patient's decision while making sure the patient is accurately informed.  相似文献   
997.
Single crystals of 6H–SiC were implanted at room temperature with 4-MeV Au ions to a fluence of 1015?cm?2. Raman spectra showed that full amorphization was achieved. The recrystallization process was studied by micro-Raman spectrometry after isochronal thermal annealing between 700 and 1500°C. The spectra permitted the evolution upon annealing of Si–C bonds, and also of Si–Si and C–C bonds, to be followed. Amorphous phase relaxation takes place below 700°C; then recrystallization of the 6H polytype sets in at 700°C. At 900°C crystallites with different crystalline states are formed. Moreover, Raman spectra provide evidence of graphitic nanocluster formation at 1500°C.  相似文献   
998.
The metallic glass Pd40Cu30Ni10P20 in as-cast or pre-annealed states was shot-peened successively at room temperature or at 77 K. The structural state of the glass was characterized by the relaxation spectrum measured in a differential scanning calorimeter. Mechanically induced relaxation of the as-cast glass and mechanically induced rejuvenation of pre-annealed samples are both more evident at 77 K than at 298 K, enabling deductions about the underlying mechanisms. The relaxation spectrum of the glass as a function of temperature displays two broad maxima, which occurring at the higher temperature is attributed to the part of the free-volume distribution associated with flow defects. In samples shot-peened at 77 K, the stored energy after deformation can be as high as 20% of the cold work. Shot-peening simultaneously generates flow defects within shear bands and destroys them in the matrix between bands: whose effect dominates is principally dependent on the initial state of relaxation of the glass. Shot-peening of partially crystallized samples appears capable of breaking up and dispersing crystallites without inducing any further significant crystallization.  相似文献   
999.
The work-hardening behaviour of virgin martensitic steel has been investigated in a strictly un-aged state and after various ageing conditions. At room temperature (RT), the un-aged alloy shows astonishing tensile performances (ultimate tensile stress?=?1600?MPa/uniform elongation?=?15%) but unexpected serrations. These serrations can be suppressed by static ageing (at RT or higher) while maintaining the initial work-hardening rate (ageing at RT). Parallel investigations using atom probe tomography reveal that the distribution of carbon at the atomic scale evolves from purely homogeneous for virgin martensite to partly segregated at a very fine scale (5–10?nm) after static ageing. This particular mechanical behaviour can therefore be associated with a very local decrease in available carbon in solid solution due to redistribution and segregations on defects (nanotwins) that occurs rapidly, even after few days at RT.  相似文献   
1000.
Owing to their very high strength, nanocrystalline metals have been extensively studied over the recent years. The direct Hall–Petch law, empirically proportioning the material strength to the inverse square root of its grain size has been shown to break down below a grain size of the order of tenths of nanometers. This phenomenon has been widely rationalized as a gradual switch from intragrain mediated deformation mechanisms to grain boundary mediated deformation mechanisms. This transition has been observed in many finite element simulations, despite the intrinsic restriction of necessarily limiting the nanocrystalline representative assembly to only a few grains. Such a limitation is generally overlooked, and its influence on an uniaxial tension test – when compared to a complete sample of millions of grains – ignored. We propose here to quantify the approximation done by considering a finite number of grains by means of a simple analytical model based on the early work of Stevens [R.N. Stevens, Philos. Mag. 23 (1971) p. 265]. The finite element approximation is demonstrated to be relatively good, even down to only three grains in width, and a method to “correct” the stress-strain curves of small representative volumes is proposed.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号