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   4813篇
  免费   398篇
  国内免费   2篇
  5213篇
  2023年   17篇
  2022年   40篇
  2021年   75篇
  2020年   43篇
  2019年   61篇
  2018年   71篇
  2017年   78篇
  2016年   133篇
  2015年   184篇
  2014年   230篇
  2013年   294篇
  2012年   332篇
  2011年   312篇
  2010年   258篇
  2009年   196篇
  2008年   281篇
  2007年   295篇
  2006年   239篇
  2005年   242篇
  2004年   258篇
  2003年   256篇
  2002年   218篇
  2001年   83篇
  2000年   66篇
  1999年   68篇
  1998年   83篇
  1997年   44篇
  1996年   36篇
  1995年   36篇
  1994年   32篇
  1993年   39篇
  1992年   55篇
  1991年   52篇
  1990年   35篇
  1989年   35篇
  1988年   35篇
  1987年   25篇
  1986年   18篇
  1985年   22篇
  1984年   23篇
  1983年   15篇
  1982年   22篇
  1981年   19篇
  1978年   12篇
  1977年   13篇
  1975年   12篇
  1974年   16篇
  1973年   11篇
  1972年   15篇
  1970年   11篇
排序方式: 共有5213条查询结果,搜索用时 0 毫秒
101.
HCMV infection represents a life-threatening condition for immunocompromised patients and newborn infants and novel anti-HCMV agents are clearly needed. In this regard, a series of 1-[ω-(phenoxy)alkyl]uracil derivatives were synthesized and examined for antiviral properties. Compounds 17, 20, 24 and 28 were found to exhibit highly specific and promising inhibitory activity against HCMV replication in HEL cell cultures with EC50 values within 5.5–12 μM range. Further studies should be undertaken to elucidate the mechanism of action of these compounds and the structure–activity relationship for the linker region.  相似文献   
102.
Many organs of higher organisms are heavily branched structures and arise by an apparently similar process of branching morphogenesis. Yet the regulatory components and local interactions that have been identified differ greatly in these organs. It is an open question whether the regulatory processes work according to a common principle and how far physical and geometrical constraints determine the branching process. Here, we review the known regulatory factors and physical constraints in lung, kidney, pancreas, prostate, mammary gland and salivary gland branching morphogenesis, and describe the models that have been formulated to analyse their impacts.  相似文献   
103.
Because of its fundamental relevance to scientific innovation, artistic expression, and human ingenuity, creativity has long been the subject of systematic psychological investigation. Concomitantly, the far-reaching effects of stereotypes on various cognitive and social processes have been widely researched. Bridging these two literatures, we show in a series of two studies that stereotypes related to creativity can both enhance and diminish individuals’ performance on a divergent thinking task. Specifically, Study 1 demonstrated that participants asked to take on a stereotypically uninhibited perspective performed significantly better on a divergent thinking task than those participants who took on a stereotypically inhibited perspective, and a control group. Relatedly, Study 2 showed that the same effect is found within-subjects, with divergent thinking significantly improving when participants invoke an uninhibited stereotype. Moreover, we demonstrate the efficacy of Latent Semantic Analysis as an objective measure of the originality of ideas, and discuss implications of our findings for the nature of creativity. Namely, that creativity may not be best described as a stable individual trait, but as a malleable product of context and perspective.  相似文献   
104.
105.
Streptococcus pneumoniae bacteria can be characterized into over 90 serotypes according to the composition of their polysaccharide capsules. Some serotypes are common in nasopharyngeal carriage whereas others are associated with invasive disease, but when carriage serotypes do invade disease is often particularly severe. It is unknown whether disease severity is due directly to the capsule type or to other virulence factors. Here, we used a clinical pneumococcal isolate and its capsule-switch mutants to determine the effect of capsule, in isolation from the genetic background, on severity of meningitis in an infant rat model. We found that possession of a capsule was essential for causing meningitis. Serotype 6B caused significantly more mortality than 7F and this correlated with increased capsule thickness in the cerebrospinal fluid (CSF), a stronger inflammatory cytokine response in the CSF and ultimately more cortical brain damage. We conclude that capsule type has a direct effect on meningitis severity. This is an important consideration in the current era of vaccination targeting a subset of capsule types that causes serotype replacement.  相似文献   
106.
107.
Culicoides boyi Nielsen, Kristensen & Pape 2015 (Diptera: Ceratopogonidae), described in Denmark in 2015, is reported in France. This species is closely related to Culicoides pulicaris (Linnaeus 1758) and can only be distinguished from this species by a subtle variation in spot wing pattern and by calculation of maxillary palpal ratio.  相似文献   
108.
Climate change has consequences for terrestrial functioning, but predictions of plant responses remain uncertain because of the gaps in the representation of nutrient cycles and C–N–P interactions in ecosystem models. Here, we review the processes that are included in ecosystem models, but focus on coupled C–N–P cycle models. We highlight important plant adjustments to climate change, elevated atmospheric CO2, and/or nutrient limitations that are currently not—or only partially—incorporated in ecosystem models by reviewing experimental studies and compiling data. Plant adjustments concern C:N:P stoichiometry, photosynthetic capacity, nutrient resorption rates, allocation patterns, symbiotic N2 fixation and root exudation (phosphatases, carboxylates) and the effect of root exudation on nutrient mobilization in the soil rhizosphere (P solubilization, biochemical mineralization of organic P and priming effect). We showed that several plant adjustments could be formulated and calibrated using existing experimental data in the literature. Finally, we proposed a roadmap for future research because improving ecosystem models necessitate specific data and collaborations between modelers and empiricists.  相似文献   
109.
110.
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