全文获取类型
收费全文 | 176385篇 |
免费 | 14258篇 |
国内免费 | 273篇 |
出版年
2023年 | 776篇 |
2022年 | 736篇 |
2021年 | 3139篇 |
2020年 | 2040篇 |
2019年 | 2573篇 |
2018年 | 3590篇 |
2017年 | 3164篇 |
2016年 | 4789篇 |
2015年 | 7437篇 |
2014年 | 8059篇 |
2013年 | 10150篇 |
2012年 | 12648篇 |
2011年 | 12111篇 |
2010年 | 7807篇 |
2009年 | 7205篇 |
2008年 | 9988篇 |
2007年 | 9865篇 |
2006年 | 9352篇 |
2005年 | 8634篇 |
2004年 | 8456篇 |
2003年 | 7900篇 |
2002年 | 7454篇 |
2001年 | 3074篇 |
2000年 | 2690篇 |
1999年 | 2638篇 |
1998年 | 2153篇 |
1997年 | 1537篇 |
1996年 | 1420篇 |
1995年 | 1412篇 |
1994年 | 1169篇 |
1993年 | 1210篇 |
1992年 | 1616篇 |
1991年 | 1491篇 |
1990年 | 1357篇 |
1989年 | 1357篇 |
1988年 | 1228篇 |
1987年 | 1187篇 |
1986年 | 1060篇 |
1985年 | 1245篇 |
1984年 | 1224篇 |
1983年 | 1087篇 |
1982年 | 1086篇 |
1981年 | 981篇 |
1980年 | 971篇 |
1979年 | 865篇 |
1978年 | 812篇 |
1977年 | 707篇 |
1976年 | 666篇 |
1974年 | 712篇 |
1973年 | 701篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
M Górska 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1992,47(46-48):1069-1071
102.
103.
104.
105.
Céline Fouquet Bénédicte M. Babayan Aurélie Watilliaux Bruno Bontempi Christine Tobin Laure Rondi-Reig 《PloS one》2013,8(6)
We investigated the neural bases of navigation based on spatial or sequential egocentric representation during the completion of the starmaze, a complex goal-directed navigation task. In this maze, mice had to swim along a path composed of three choice points to find a hidden platform. As reported previously, this task can be solved by using two hippocampal-dependent strategies encoded in parallel i) the allocentric strategy requiring encoding of the contextual information, and ii) the sequential egocentric strategy requiring temporal encoding of a sequence of successive body movements associated to specific choice points. Mice were trained during one day and tested the following day in a single probe trial to reveal which of the two strategies was spontaneously preferred by each animal. Imaging of the activity-dependent gene c-fos revealed that both strategies are supported by an overlapping network involving the dorsal hippocampus, the dorsomedial striatum (DMS) and the medial prefrontal cortex. A significant higher activation of the ventral CA1 subregion was observed when mice used the sequential egocentric strategy. To investigate the potential different roles of the dorsal hippocampus and the DMS in both types of navigation, we performed region-specific excitotoxic lesions of each of these two structures. Dorsal hippocampus lesioned mice were unable to optimally learn the sequence but improved their performances by developing a serial strategy instead. DMS lesioned mice were severely impaired, failing to learn the task. Our data support the view that the hippocampus organizes information into a spatio-temporal representation, which can then be used by the DMS to perform goal-directed navigation. 相似文献
106.
Caitlin M. Cossaboom Laura Córdoba Dianjun Cao Yan-Yan Ni Xiang-Jin Meng 《Journal of virology》2012,86(23):13124-13125
Hepatitis E virus (HEV) is a single-strand positive-sense RNA virus in the family Hepeviridae. The disease caused by HEV, hepatitis E, is an important public health problem in developing countries of Asia and Africa and is also endemic in many industrialized countries, including the United States. HEV has been identified from several other animal species in addition to humans, including the pig, chicken, mongoose, deer, rabbit, ferret, bat, and fish. Here we report the complete genome sequence of the first strain of HEV from rabbits in the United States. Sequence and phylogenetic analyses revealed that the U.S. rabbit HEV is a distant member of the zoonotic genotype 3 HEV, thus raising a concern for potential zoonotic human infection. A unique 90-nucleotide insertion within the X domain of the ORF1 was identified in the rabbit HEV, and this insertion may play a role in the species tropism of HEV. 相似文献
107.
In the development of the horseshoe crab, Limulus polyphemus, the fertilized egg undergoes a complicated cleavage (Stages 1–3) resulting in blastoderm formation (Stage 4). Stage 1 involves intralecithal cleavage and consists of nine discrete surface modifications (events) which have been briefly described with light microscopy by Brown and Barnum ('83). Since in Stage 1 the cortical reaction (events 1–4) has already been examined with ultrastructural methods, the objectives of the present study were to examine with scanning electron microscopy: (1) the first two of three intermittent granulations (events 5 and 7), and (2) the associated events characterized by smooth surfaces (events 4, 6, and 8). The first granulation occurs 2 1/2 to 3 hours after fertilization (22°C) and lasts approximately 1 1/2 hours. The second granulation appears approximately 5 hours after fertilization and lasts about 3 hours. The dynamic changes that occur during the two granulations involve the transformation of a smooth appearing embryonic surface, liberally coated with microvilli, into a granule-dominated surface on which microvilli are greatly reduced in number. Also of considerable interest are the numerous projections which begin to appear on the surface near the end of the second granulation (event 7) and dominate the surface of the following smooth step stage (event 8). Hypotheses on the significance of these dynamic changes and surface modifications involve relationships to the cell cycle, possible mechanisms for membrane storage, and secretory function. 相似文献
108.
Effect of pharmacological agents on the activity of the circular and longitudinal smooth muscle layers of human fallopian tube ampullar segments 总被引:1,自引:0,他引:1
The in vitro determination of the effects of some pharmacological agents on the outer diameter and axial tension of human Fallopian tube ampullar segments showed that some drugs may act on the circular and longitudinal smooth muscle layers relatively separately. PGF2 alpha elicited an excitatory response in both muscle layers while norepinephrine and isoproterenol decreased the activity. Oxytocin and indomethacin had relatively limited effects on the spontaneous motility of the ampullar segments. The calcium antagonist verapamil inhibited the spontaneous periodic activity. 相似文献
109.
110.
Dominant males of nonseasonally breeding species should have more opportunity than seasonal breeders to monopolize access to estrous females and thus enhance their reproductive success. They may also use other strategies for maximizing reproductive success such as producing offspring by relatively high ranking females. To test these hypotheses, the paternity of 35 (80%) of 44 Macaca fascicularis offspring, born over a 28-month period, was established using electrophoretically and serologically defined genetic markers. The social ranks of each of the seven potential fathers and 26 potential mothers were determined by recording outcomes of dyadio agonistic interactions. No evidence could be found to support either hypothesis. Further, in view of previously reported significant, positive correlations between male social rank and sexual activity rates in this study group, sexual activity rates do not appear to predict the number of offspring a male sires in this species. 相似文献