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   3970篇
  免费   300篇
  2023年   37篇
  2022年   101篇
  2021年   132篇
  2020年   136篇
  2019年   129篇
  2018年   164篇
  2017年   141篇
  2016年   207篇
  2015年   249篇
  2014年   263篇
  2013年   320篇
  2012年   352篇
  2011年   299篇
  2010年   169篇
  2009年   173篇
  2008年   188篇
  2007年   182篇
  2006年   157篇
  2005年   139篇
  2004年   106篇
  2003年   97篇
  2002年   89篇
  2001年   58篇
  2000年   62篇
  1999年   63篇
  1998年   9篇
  1997年   12篇
  1996年   12篇
  1995年   16篇
  1994年   5篇
  1993年   8篇
  1992年   16篇
  1991年   17篇
  1990年   15篇
  1989年   16篇
  1988年   10篇
  1987年   10篇
  1986年   8篇
  1985年   9篇
  1984年   12篇
  1983年   7篇
  1982年   8篇
  1981年   5篇
  1980年   9篇
  1979年   8篇
  1978年   7篇
  1971年   6篇
  1970年   3篇
  1968年   3篇
  1967年   4篇
排序方式: 共有4270条查询结果,搜索用时 31 毫秒
151.
152.
Neuroblasts from the subventricular zone (SVZ) migrate to striatum following stroke, but most of them die in the ischaemic milieu and this can be related to exacerbated microglial activation. Here, we explored the effects of the non-steroidal anti-inflammatory indomethacin on microglial activation, neuronal preservation and neuroblast migration following experimental striatal stroke in adult rats. Animals were submitted to endothelin-1 (ET-1)-induced focal striatal ischaemia and were treated with indomethacin or sterile saline (i.p.) for 7 days, being perfused after 8 or 14 days. Immunohistochemistry was performed to assess neuronal loss (anti-NeuN), microglial activation (anti-Iba1, ED1) and migrating neuroblasts (anti-DCX) by counting NeuN, ED1 and DCX-positive cells in the ischaemic striatum or SVZ. Indomethacin treatment reduced microglia activation and the number of ED1+ cells in both 8 and 14 days post injury as compared with controls. There was an increase in the number of DCX+ cells in both SVZ and striatum at the same survival times. Moreover, there was a decrease in the number of NeuN+ cells in indomethacin-treated animals as compared with the control group at 8 days but not after 14 days post injury. Our results suggest that indomethacin treatment modulates microglia activation, contributing to increased neuroblast proliferation in the SVZ and migration to the ischaemic striatum following stroke.  相似文献   
153.
154.
In the present work, we propose to design drugs that target the enzyme dihydrofolate redutase (DHFR) as a means of a novel drug therapy against plague. Potential inhibitors of DHFR from Yersinia pestis (YpDHFR) were selected by virtual screening and subjected to docking, molecular dynamics (MD) simulations, and Poisson–Boltzmann surface area method, in order to evaluate their interactions in the active sites of YpDHFR and human DHFR (HssDHFR). The results suggested selectivity for three compounds that were further used to propose the structures of six new potential selective inhibitors for YpDHFR.  相似文献   
155.
156.
157.
158.
Surprising invariance relationships have emerged from the study of social interaction, whereby a cancelling‐out of multiple partial effects of genetic, ecological or demographic parameters means that they have no net impact upon the evolution of a social behaviour. Such invariants play a pivotal role in the study of social adaptation: on the one hand, they provide theoretical hypotheses that can be empirically tested; and, on the other hand, they provide benchmark frameworks against which new theoretical developments can be understood. Here we derive a novel invariant for dispersal evolution: the ‘constant philopater hypothesis’ (CPH). Specifically, we find that, irrespective of variation in maternal fecundity, all mothers are favoured to produce exactly the same number of philopatric offspring, with high‐fecundity mothers investing proportionally more, and low‐fecundity mothers investing proportionally less, into dispersing offspring. This result holds for female and male dispersal, under haploid, diploid and haplodiploid modes of inheritance, irrespective of the sex ratio, local resource availability and whether mother or offspring controls the latter's dispersal propensity. We explore the implications of this result for evolutionary conflict of interests – and the exchange and withholding of contextual information – both within and between families, and we show that the CPH is the fundamental invariant that underpins and explains a wider family of invariance relationships that emerge from the study of social evolution.  相似文献   
159.
African mole-rats are fossorial rodents that consist of five chisel-tooth digging genera (Heterocephalus, Heliophobius, Georychus, Fukomys, and Cryptomys) and one scratch digger (Bathyergus). They are characterized by striking physiological, morphological, and behavioral adaptations intimately related to their subterranean life. The influence of their mode of life in shaping the cranial morphology has yet to be evaluated in comparison to other Ctenohystrica, especially fossorial genera, which include the subterranean genera Spalacopus and Ctenomys. In our study, we seek to determine to what extent subterranean life affects the morpho-functional properties of the skull among fossorial ctenohystricans. 3D geometric morphometric analyses were performed on 277 skulls, encompassing 63 genera of Ctenohystrica, and complemented by biomechanical studies. African mole-rats and other subterranean Ctenohystrica, especially chisel-tooth diggers, have a short snout, a wide cranium with enlarged zygomatic arches, and a strongly hystricognathous mandible. Even if convergences are also manifest between most fossorial Ctenohystrica, subterranean rodents departed from the main ctenohystrican allometric trends in having a skull shape less size-dependent, but under stronger directional selection with intense digging activity as a major constraint. African mole-rats, notably chisel-tooth diggers, show important mechanical advantage for the temporalis muscles favoring higher forces at the bite point, while mechanical advantage of the superficial masseter muscles is lower compared to other Ctenohystrica. If subterranean species can be clearly discriminated based on their skull morphology, the intrinsic mosaic of anatomical characters of each genus (e.g., skull, teeth, and muscles) can be understood only in the light of their ecology and evolutionary history.  相似文献   
160.
Bioprocess and Biosystems Engineering - Hybrid semi-parametric modeling, combining mechanistic and machine-learning methods, has proven to be a powerful method for process development. This paper...  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