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   32278篇
  免费   3833篇
  国内免费   1020篇
  2023年   181篇
  2022年   443篇
  2021年   803篇
  2020年   544篇
  2019年   689篇
  2018年   738篇
  2017年   613篇
  2016年   904篇
  2015年   1318篇
  2014年   1484篇
  2013年   1748篇
  2012年   1991篇
  2011年   1936篇
  2010年   1156篇
  2009年   1092篇
  2008年   1421篇
  2007年   1241篇
  2006年   1227篇
  2005年   1032篇
  2004年   909篇
  2003年   836篇
  2002年   753篇
  2001年   2507篇
  2000年   2300篇
  1999年   1678篇
  1998年   574篇
  1997年   566篇
  1996年   511篇
  1995年   472篇
  1994年   372篇
  1993年   315篇
  1992年   847篇
  1991年   696篇
  1990年   575篇
  1989年   485篇
  1988年   361篇
  1987年   288篇
  1986年   235篇
  1985年   200篇
  1984年   103篇
  1983年   89篇
  1982年   72篇
  1981年   53篇
  1980年   52篇
  1979年   50篇
  1978年   43篇
  1977年   42篇
  1976年   38篇
  1973年   34篇
  1972年   36篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
951.
The cytology and developmental attributes of 18 deficiency mutations in the 3A1–3C6 region of the salivary gland X chromosome of Drosophila melanogaster have been investigated. The cytological limits of several older deficiencies have been revised and clarified and several new deficiencies are characterized. The deficiency mutants, with one possible exception, show a lethal phase in the late embryonic period or the early first larval instar. In contrast, the earliest acting point mutation lethals exposed by these deficiencies generally exhibit a somewhat later, post-embryonic lethality, perhaps indicating that the deficiencies are having some cumulative or synergistic impact on development. However, even with this difference in time of lethality, it is still possible to conclude that it is not the absolute size of the deficiency but rather the character of the loci deleted that determines the impact on development. Observations on the morphology of lethal embryos shows that while this analysis is internally consistent, it does not agree with earlier work. None of the 3A1–3C6 deficiencies causes any major teratologies during embryogenesis. Furthermore, the "earliest acting" gene in this region does not lie in band 3C1 but is most likely associated with bands 3A8–10.  相似文献   
952.
953.
954.
The Raman spectroscopic lines of liquid cultures of Rhizobium japonicum have been compared with electron microscopic examinations and growth measurements of these cells. The results showed that the significant Raman lines are related to the reproduction activities of the procaryotic cells.  相似文献   
955.
ZAK (sterile alpha motif and leucine zipper containing kinase AZK), a serine/threonine kinase with multiple biochemical functions, has been associated with various cell processes, including cell proliferation, cell differentiation, and cardiac hypertrophy. In our previous reports, we found that the activation of ZAKα signaling was critical for cardiac hypertrophy. In this study, we show that the expression of ZAKα activated apoptosis through both a FAS‐dependent pathway and a mitochondria‐dependent pathway by subsequently inducing caspase‐3. ZAKβ, an isoform of ZAKα, is dramatically expressed during cardiac hypertrophy and apoptosis. The interaction between ZAKα and ZAKβ was demonstrated here using immunoprecipitation. The results show that ZAKβ has the ability to diminish the expression level of ZAKα. These findings reveal an inherent regulatory role of ZAKβ to antagonize ZAKα and to subsequently downregulate the cardiac hypertrophy and apoptosis induced by ZAKα.  相似文献   
956.
957.
958.
959.
Cerebral glucose metabolism is a reliable index of neural activity and may provide evidence for brain function in healthy adults. We studied the correlation between cerebral glucose metabolism and age under the resting-state in both sexes with position emission tomography. Statistical test of age effect on cerebral glucose metabolism was performed using the statistical parametric mapping software with a voxel-by-voxel approach ( family wise error corrected, -voxel threshold). The subjects consisted of 108 females (mean S.D. = 4510 years) and 126 males (mean S.D. = 4911 years). We showed here that brain activity in the frontal and temporal lobes in both sexes decreased significantly with normal aging. The glucose metabolism in the caudate bilaterally showed a negative correlation with age in males, but not in females. Few regions in males were shown with an increased glucose metabolism with age. Although the mechanisms of brain aging are still unknown, a map of brain areas susceptible to age was described in this report.  相似文献   
960.
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