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   38981篇
  免费   16703篇
  国内免费   838篇
  2023年   157篇
  2022年   489篇
  2021年   907篇
  2020年   2502篇
  2019年   4083篇
  2018年   4165篇
  2017年   4349篇
  2016年   4510篇
  2015年   4764篇
  2014年   4449篇
  2013年   4933篇
  2012年   2894篇
  2011年   2462篇
  2010年   3625篇
  2009年   2279篇
  2008年   1399篇
  2007年   882篇
  2006年   847篇
  2005年   784篇
  2004年   685篇
  2003年   663篇
  2002年   578篇
  2001年   566篇
  2000年   482篇
  1999年   373篇
  1998年   119篇
  1997年   90篇
  1996年   100篇
  1995年   93篇
  1994年   73篇
  1993年   78篇
  1992年   176篇
  1991年   132篇
  1990年   129篇
  1989年   150篇
  1988年   107篇
  1987年   116篇
  1986年   118篇
  1985年   123篇
  1984年   74篇
  1983年   83篇
  1982年   63篇
  1981年   66篇
  1980年   64篇
  1979年   94篇
  1978年   80篇
  1977年   61篇
  1976年   68篇
  1974年   65篇
  1973年   66篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
122.
Although Ficus (Moraceae) is a keystone plant genus in the tropics, providing resources to many frugivorous vertebrates, its population genetic structure, which is an important determinant of its long‐term survival, has rarely been investigated. We examined the population genetic structure of two dioecious fig species (Ficus hispida and Ficus exasperata) in the Indian Western Ghats using co‐dominant nuclear microsatellite markers. We found high levels of microsatellite genetic diversity in both species. The regression slopes between genetic relationship coefficients (fij) and spatial distances were significantly negative in both species indicating that, on average, individuals in close spatial proximity were more likely to be related than individuals further apart. Mean parent–offspring distance (σ) calculated using these slopes was about 200 m in both species. This should be contrasted with the very long pollen dispersal distances documented for monoecious Ficus species. Nevertheless, overall population genetic diversity remained large suggesting immigrant gene flow. Further studies will be required to analyze broader scale patterns.  相似文献   
123.
The initial time of synthesis of globin polypeptide chains in differentiating red cells has been delineated. Three analytical techniques were used, namely, SDS-polyacrylamide gel electrophoresis, acid urea polyacrylamide gel electrophoresis, and two-dimensional gel electrophoresis. The results indicate that globin peptide chains are synthesized in proerythroblasts at the initial time when globin mRNA first enters into the cytoplasm, and there is no apparent time gap between these two events.  相似文献   
124.
125.
R. M. Chan  H. R. Graham  C. L. Birmingham 《CMAJ》1983,129(11):1201-1202
A case is presented of toxic shock syndrome in a patient with systemic lupus erythematosus. Toxic shock syndrome is rarely reported in patients who are immunosuppressed, perhaps because such patients are often treated vigorously with antibiotics at the earliest sign of infection. The association in this case may have been coincidental.  相似文献   
126.
127.
Space use including territoriality and spatial arrangement within a population can reveal important information on the nature, dynamics, and evolutionary maintenance of alternative strategies in color polymorphic species. Despite the prevalence of color polymorphic species as model systems in evolutionary biology, the interaction between space use and genetic structuring of morphs within populations has rarely been examined. Here, we assess the spatial and genetic structure of male throat color morphs within a population of the tawny dragon lizard, Ctenophorus decresii. Male color morphs do not differ in morphology but differ in aggressive and antipredator behaviors as well as androgen levels. Despite these behavioral and endocrine differences, we find that color morphs do not differ in territory size, with their spatial arrangement being essentially random with respect to each other. There were no differences in genetic diversity or relatedness between morphs; however, there was significant, albeit weak, genetic differentiation between morphs, which was unrelated to geographic distance between individuals. Our results indicate potential weak barriers to gene flow between some morphs, potentially due to nonrandom pre‐ or postcopulatory mate choice or postzygotic genetic incompatibilities. However, space use, spatial structure, and nonrandom mating do not appear to be primary mechanisms maintaining color polymorphism in this system, highlighting the complexity and variation in alternative strategies associated with color polymorphism.  相似文献   
128.
129.
130.
Studies on the synthesis and secretion of the sex-dependent urinary protein, alpha2mu-globulin, have been extended by establishing its sequential passage from the rough to the smooth endoplasmic reticulum and Golgi-rich fractions of the liver of adult male rats. After injection of 14C-labeled amino acids, the maximum radioactivity of alpha2mu occurred at 20 min in the rough, 25 min in the smooth microsomes and 30 or 35 min in the Golgi-rich fractions. Radioactive alpha2mu-globulin appeared in the bloodstream and kidneys after a lag of 20--25 min. Results indicate that alpha2mu-globulin follows a secretory pathway similar to that of serum albumin.  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