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641.
In behavioral, biomedical, and psychological studies, structural equation models (SEMs) have been widely used for assessing relationships between latent variables. Regression-type structural models based on parametric functions are often used for such purposes. In many applications, however, parametric SEMs are not adequate to capture subtle patterns in the functions over the entire range of the predictor variable. A different but equally important limitation of traditional parametric SEMs is that they are not designed to handle mixed data types—continuous, count, ordered, and unordered categorical. This paper develops a generalized semiparametric SEM that is able to handle mixed data types and to simultaneously model different functional relationships among latent variables. A structural equation of the proposed SEM is formulated using a series of unspecified smooth functions. The Bayesian P-splines approach and Markov chain Monte Carlo methods are developed to estimate the smooth functions and the unknown parameters. Moreover, we examine the relative benefits of semiparametric modeling over parametric modeling using a Bayesian model-comparison statistic, called the complete deviance information criterion (DIC). The performance of the developed methodology is evaluated using a simulation study. To illustrate the method, we used a data set derived from the National Longitudinal Survey of Youth. 相似文献
642.
Christine M. Guardino Christine Dunkel Schetter Julienne E. Bower Michael C. Lu Susan L. Smalley 《Psychology & health》2013,28(3):334-349
This randomised controlled pilot trial tested a six-week mindfulness-based intervention in a sample of pregnant women experiencing high levels of perceived stress and pregnancy anxiety. Forty-seven women enrolled between 10 and 25 weeks gestation were randomly assigned to either a series of weekly Mindful Awareness Practices classes (n = 24) with home practice or to a reading control condition (n = 23). Hierarchical linear models of between-group differences in change over time demonstrated that participants in the mindfulness intervention experienced larger decreases from pre-to post-intervention in pregnancy-specific anxiety and pregnancy-related anxiety (PRA) than participants in the reading control condition. However, these effects were not sustained through follow-up at six weeks post-intervention. Participants in both groups experienced increased mindfulness, as well as decreased perceived stress and state anxiety over the course of the intervention and follow-up periods. This study is one of the first randomised controlled pilot trials of a mindfulness meditation intervention during pregnancy and provides some evidence that mindfulness training during pregnancy may effectively reduce PRA and worry. We discuss some of the dilemmas in pursuing this translational strategy and offer suggestions for researchers interested in conducting mind-body interventions during pregnancy. 相似文献
643.
644.
Judith S. Brook Lu Zheng Martin Whiteman David W. Brook 《The Journal of genetic psychology》2013,174(2):228-241
This study examined the relation among parenting factors, marital relations, and toddler aggression. A structured questionnaire was administered to both parents of 254 2-year-olds. The authors used correlation and hierarchical multiple regression analyses to assess the extent to which certain personality traits, drug use, parenting style, and marital conflicts were related to the toddlers' aggressive behavior. Results showed that the maternal child-rearing and parental aggression domains had a direct effect on toddler aggression. The domain of maternal child rearing also served as a mediator for the domains of marital relations, paternal child rearing, parental aggression, and parental drug use. The findings indicated that maternal child-rearing practices, personality attributes, and drug use were more important than paternal attributes in relation to toddler aggression. Implications for prevention among families at risk are discussed. 相似文献
645.
This research examined the impact of dialectical thinking (DT) on perceived training outcomes in commercial leadership training using a quasi‐experimental design. Study 1 found that high‐DT individuals had better perceived on‐site training outcomes when compared with individuals with low DTs, regardless of training methods. But there was no significant difference between low and high DTs on subsequent behavioral improvements. It was also found that self‐reported training outcomes were consistent with others' observation. To further validate the on‐site effect of DT, we introduced a cognitive style manipulation prior to training to increase DT levels among trainees in Study 2. Individuals following the cognitive style manipulation reported significantly better perceived training outcomes. The implications of this research for field training are discussed. 相似文献
646.
This article proposes an intuitive approach for predictive discriminant analysis with mixed continuous, dichotomous, and ordered categorical variables that are defined via an underlying multivariate normal distribution with a threshold specification. The classification rule is based on the comparison of the observed data logarithm probability density functions. To reduce the computational burden, the analysis is conducted in the context of a confirmatory factor analysis model with independent error measurements. Identification of the dichotomous and ordered categorical variables is discussed. Results are obtained by implementations of a Monte Carlo expectation maximization (MCEM)algorithm and a path sampling procedure. Probabilities of misclassification are estimated via the idea of the “jackknife” method. A real example is given to illustrate the proposed method. 相似文献
647.
648.
Po H. Lu Grace J. Lee Todd A. Tishler Michael Meghpara Paul M. Thompson George Bartzokis 《Brain and cognition》2013
Background
To assess the hypothesis that in a sample of very healthy elderly men selected to minimize risk for Alzheimer’s disease (AD) and cerebrovascular disease, myelin breakdown in late-myelinating regions mediates age-related slowing in cognitive processing speed (CPS).Materials and methods
The prefrontal lobe white matter and the genu of the corpus callosum myelinate later in brain development (late-myelinating white matter; LMWM) and are more vulnerable to breakdown due to the effects of normal aging. An in vivo MRI biomarker of myelin integrity (transverse relaxation rates; R2) of LMWM was obtained for 38 very healthy elderly adult men (mean age = 66.3 years; SD = 6.0; range = 55–76). To evaluate regional specificity, we also assessed a contrasting early-myelinating region (splenium of the corpus callosum; SWM), which primarily contains axons involved in visual processing. CPS was assessed using the Trail Making Test.Results
LMWM R2 and CPS measures were significantly correlated (r = .515, p = .0009), but no significant association between R2 and CPS was detected in the splenium (p = .409). LMWM R2, but not SWM R2, was a significant mediator of the relationship between age and CPS (p = .037).Conclusions
In this very healthy elderly sample, age-related slowing in CPS is mediated by myelin breakdown in highly vulnerable late-myelinating regions but not in the splenium. 相似文献649.
Peiqing La Fuan Wei Xuefeng Lu Ting Shi Chenggang Chu Yupeng Wei 《Philosophical Magazine Letters》2013,93(8):478-486
The microstructures of 304 stainless steels with different amounts of nanocrystalline and microcrystalline austenite prepared by an aluminothermic reaction casting, without and with annealing at 1073?K for 8?h, have been investigated by X-ray diffraction, an electron probe micro-analyser, a transmission electron microscope and a scanning electron microscope. The steels, both without and with annealing, consisted of different dual nanocrystalline and microcrystalline austenite combinations and a little nanocrystalline δ ferrite, while the average grain size of the nanocrystalline austenite increased from 19 to 26?nm and volume fraction of the microcrystalline austenite increased from 17 to 30% after annealing. The tensile strength of the steel was dramatically increased from 500 to 1000?MPa and the tensile elongation ratio increased from 8 to 12% after annealing. However, the tensile strength was decreased to 600?MPa and the tensile elongation ratio increased from 12 to 22% after an annealing at 1273?K. The combination of dual nanocrystalline and microcrystalline austenite obtained after the annealing at 1073?K results in the best tensile properties. 相似文献
650.
The mechanical properties of α-Al2O3(0001) have been investigated using the technique of nanoindentation with a Berkovich indenter. Coupled with the Hertzian contact theory, a theoretical shear strength of 28?±?2?GPa was determined from the onset of pop-in events on load–displacement curves during loading, and the intrinsic hardness 30?±?3?GPa was obtained by analysis of the so-called indentation size effect, based on the concept of geometrically necessary dislocations. The predicted values of the shear strength, hardness and elastic modulus are in good agreement with available experimental data. The importance of experimentally calibrating the area function over the contact depth range prior to nanoindentation tests is emphasized. 相似文献