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   11071篇
  免费   1003篇
  国内免费   1篇
  12075篇
  2022年   109篇
  2021年   197篇
  2020年   113篇
  2019年   150篇
  2018年   195篇
  2017年   155篇
  2016年   270篇
  2015年   498篇
  2014年   539篇
  2013年   613篇
  2012年   840篇
  2011年   763篇
  2010年   511篇
  2009年   464篇
  2008年   696篇
  2007年   650篇
  2006年   596篇
  2005年   605篇
  2004年   589篇
  2003年   572篇
  2002年   505篇
  2001年   112篇
  2000年   91篇
  1999年   102篇
  1998年   170篇
  1997年   121篇
  1996年   120篇
  1995年   110篇
  1994年   94篇
  1993年   72篇
  1992年   85篇
  1991年   68篇
  1990年   74篇
  1989年   58篇
  1988年   73篇
  1987年   47篇
  1986年   61篇
  1985年   69篇
  1984年   80篇
  1983年   59篇
  1982年   60篇
  1981年   72篇
  1980年   56篇
  1979年   54篇
  1978年   53篇
  1977年   47篇
  1976年   38篇
  1974年   40篇
  1973年   42篇
  1970年   33篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Bacterial resistance to antimicrobial agents is a growing problem worldwide. Not only is issue compounded by the fact that there are fewer pharmaceutical companies conducting research to discover novel antimicrobials than in the past but development time lines have stretched so that a dozen years from discovery to the market is now the standard. Eleven antibacterial drugs in late stage clinical development are discussed. Whereas many of these may successfully deal with resistant strains of Gram-positive pathogens, there is very little in development to address the gorwing unmet medical need of multi-drug resistant Gram-negative infections.  相似文献   
53.
The identification of angiogenic growth factors, such as vascular endothelial growth factor and fibroblast growth factor, has fueled interest in using such factors to induce therapeutic angiogenesis. The results of numerous animal studies and clinical trials have offered promise for new treatment strategies for various ischemic diseases. Increased understanding of the cellular and molecular biology of vessel growth has, however, prompted investigators and clinicians alike to reconsider the complexity of therapeutic angiogenesis. The realization that formation of a stable vessel is a complex, multistep process may provide useful insights into the design of the next generation of angiogenesis therapy.  相似文献   
54.
Focal adhesion regulation of cell behavior   总被引:23,自引:0,他引:23  
Focal adhesions lie at the convergence of integrin adhesion, signaling and the actin cytoskeleton. Cells modify focal adhesions in response to changes in the molecular composition, two-dimensional (2D) vs. three-dimensional (3D) structure, and physical forces present in their extracellular matrix environment. We consider here how cells use focal adhesions to regulate signaling complexes and integrin function. Furthermore, we examine how this regulation controls complex cellular behaviors in response to matrices of diverse physical and biochemical properties. One event regulated by the physical structure of the ECM is phosphorylation of focal adhesion kinase (FAK) at Y397, which couples FAK to several signaling pathways that regulate cell proliferation, survival, migration, and invasion.  相似文献   
55.
56.
57.
Animals evolve their sensory systems and foraging behaviours to adapt and colonize new and challenging habitats such as the dark cave environment. Vibration attraction behaviour (VAB) gives fish the ability to locate the source of a water disturbance in the darkness. VAB evolved in the blind Mexican cave tetra, Astyanax mexicanus. VAB is triggered in cavefish by vibration stimuli peaking at 35 Hz, which is within the main spectrum of water fluctuations produced by many prey crustaceans and insects. VAB has a genetic component and is correlated to an increased number of head mechanosensory neuromasts in the eye orbital region when compared to surface fish. Previous competitive prey capture assays have supported the advantage of VAB for foraging in the dark. Despite its putative adaptive function, VAB has been described as absent in some Astyanax cave populations (Tinaja and Molino) but present in others (Pachón, Piedras, Toro and Sabinos). Here we have tested the occurrence of VAB in the field and in multiple cave populations using a vibrating device in natural pools. Our results confirmed the presence of VAB in caves such as Pachón, Toro and Sabinos but showed that VAB is also present in the Tinaja and Molino cave populations, previously reported as VAB-negative in laboratory experiments. Thus, VAB is available throughout the range of hypogean A. mexicanus. However, and most notably, within a given cave the levels of VAB were highly variable among different pools. Fish at one pool may express no VAB, while fish at another nearby pool of the same cave may actively show VAB. While a variety of environmental conditions may foster this diversity, we found that individuals inhabiting pools with a high abundance of organic matter have reduced expression of VAB. In contrast, in pools with little organic debris where fish probably depend more on hunting than on scavenging, VAB is enhanced. Our results suggest that expression of VAB is a plastic trait whose variability can depend on local conditions. Such plasticity may be required within and among caves where high environmental variability between pools results in a diverse availability of food.  相似文献   
58.
59.
60.
Travellers' malaria is an exciting topic. It is a field in flux with evolving options for chemoprophylaxis, self-diagnosis, self-treatment, risk/strategy analyses and surveillance. Ideologies vary and experts differ but debate is needed and can bring change. The launch of a new thematic series in the Malaria Journal -- " Travellers' malaria " -- creates an ideal forum to bring together research papers, reviews, opinion papers and commentaries, and will hopefully stimulate debate.  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