全文获取类型
收费全文 | 2806篇 |
免费 | 88篇 |
国内免费 | 2篇 |
专业分类
2896篇 |
出版年
2020年 | 28篇 |
2019年 | 30篇 |
2018年 | 42篇 |
2017年 | 55篇 |
2016年 | 61篇 |
2015年 | 31篇 |
2014年 | 42篇 |
2013年 | 342篇 |
2012年 | 84篇 |
2011年 | 87篇 |
2010年 | 57篇 |
2009年 | 66篇 |
2008年 | 70篇 |
2007年 | 70篇 |
2006年 | 81篇 |
2005年 | 95篇 |
2004年 | 79篇 |
2003年 | 81篇 |
2002年 | 75篇 |
2001年 | 39篇 |
2000年 | 35篇 |
1999年 | 46篇 |
1998年 | 54篇 |
1997年 | 36篇 |
1996年 | 42篇 |
1995年 | 37篇 |
1994年 | 36篇 |
1993年 | 36篇 |
1992年 | 31篇 |
1991年 | 37篇 |
1990年 | 35篇 |
1989年 | 44篇 |
1988年 | 35篇 |
1987年 | 32篇 |
1986年 | 30篇 |
1984年 | 43篇 |
1983年 | 35篇 |
1982年 | 47篇 |
1981年 | 37篇 |
1980年 | 41篇 |
1979年 | 42篇 |
1978年 | 45篇 |
1977年 | 36篇 |
1976年 | 39篇 |
1975年 | 34篇 |
1974年 | 43篇 |
1973年 | 36篇 |
1971年 | 26篇 |
1969年 | 33篇 |
1968年 | 26篇 |
排序方式: 共有2896条查询结果,搜索用时 15 毫秒
161.
162.
163.
164.
Metalogical properties that have traditionally been studied in the deductive system context (see, e.g., [21]) and transferred later to the institution context [33], are here formulated in the -institution context. Preservation under deductive equivalence of -institutions is investigated. If a property is known to hold in all algebraic -institutions and is preserved under deductive equivalence, then it follows that it holds in all algebraizable -institutions in the sense of [36]. 相似文献
165.
Volume Contents
Contents Volume 112 2003 相似文献166.
G.D., a 79 year-old female, presents with a severe and slowly progressive amnesia although she remains entirely independent in daily life and is perfectly well spatially oriented. Her amnesia is relatively isolated and her deficit does not embrace other cognitive domains. G.D. underwent extensive neuropsychological evaluation including language, executive functions, perceptual, and memory tests. Based on clinical observation, the purpose of this study was to determine whether there was a dissociation between her autobiographical and semantic memory. Results point out a severely degraded semantic knowledge of famous public events and persons while autobiographical memory of personally experienced and relevant information remains intact. Results from this study and from previous studies seem to suggest that relative sparing of hippocampal structures may be related to the preservation of autobiographical memory. 相似文献
167.
Sinai et al (1998 Nature 395 497-500) showed that less distance is perceived along a ground surface that spans two differently textured regions than along a surface that is uniformly textured. We examined the effect of texture continuity on judged distance using computer-generated displays of simulated surfaces in five experiments. Discontinuities were produced by using different textures, the same texture reversed in contrast, or the same texture shifted horizontally. The simulated surface was either a ground plane or a frontoparallel plane. For all textures and both orientations, less distance was judged in the discontinuous conditions than in continuous conditions. We propose that when a surface contains a texture discontinuity, a small area adjacent to the perceived boundary is excluded from judged distances. 相似文献
168.
In the current study, we explored observers' use of two distinct analyses for determining their direction of motion, or heading: a scene-based analysis and a motion-based analysis. In two experiments, subjects viewed sequentially presented, paired digitized images of real-world scenes and judged the direction of heading; the pairs were presented with various interstimulus intervals (ISIs). In Experiment 1, subjects could determine heading when the two frames were separated with a 1,000-ms ISI, long enough to eliminate apparent motion. In Experiment 2, subjects performed two tasks, a path-of-motion task and a memory-load task, under three different ISIs, 50 ms, 500 ms, and 1,000 ms. Heading accuracy decreased with an increase in ISI. Increasing memory load influenced heading judgments only for the longer ISI when motion-based information was not available. These results are consistent with the hypothesis that the scene-based analysis has a coarse spatial representation, is a sustained temporal process, and is capacity limited, whereas the motion-based analysis has a fine spatial resolution, is a transient temporal process, and is capacity unlimited. 相似文献
169.
170.
Kang SY Lee KY Park MJ Kim YC Markelonis GJ Oh TH Kim YC 《Neurobiology of learning and memory》2003,79(1):11-18
We previously reported that a total methanolic extract of the underground part of Angelica gigas Nakai (Umbelliferae) (here-in-after abbreviated AG) significantly inhibited acetylcholinesterase (AChE) activity. We characterized 12 coumarin derivatives including both decursin and decursinol from extracts of AG. In this study, we evaluated the anti-amnestic activity of decursin, a major coumarin constituent isolated from AG, in vivo using ICR mice with amnesia induced by scopolamine (1 mg/kg body weight, s.c.). Decursin, when administered to mice at 1 and 5 mg/kg body weight i.p., significantly ameliorated scopolamine-induced amnesia as measured in both the passive avoidance test and the Morris water maze test. Moreover, decursin significantly inhibited AChE activity by 34% in the hippocampus of treated mice. These results indicate that decursin may exert anti-amnestic activity in vivo through inhibition of AChE activity in the hippocampus. 相似文献