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   1110031篇
  免费   117994篇
  国内免费   2996篇
  2018年   11460篇
  2017年   10678篇
  2016年   15183篇
  2015年   20321篇
  2014年   23988篇
  2013年   33548篇
  2012年   37989篇
  2011年   38933篇
  2010年   26246篇
  2009年   24118篇
  2008年   34283篇
  2007年   35174篇
  2006年   32985篇
  2005年   31559篇
  2004年   31276篇
  2003年   29728篇
  2002年   28968篇
  2001年   45565篇
  2000年   45064篇
  1999年   36387篇
  1998年   14105篇
  1997年   14170篇
  1996年   13409篇
  1995年   12596篇
  1994年   12139篇
  1993年   12074篇
  1992年   30055篇
  1991年   29567篇
  1990年   28938篇
  1989年   28176篇
  1988年   25928篇
  1987年   24710篇
  1986年   23261篇
  1985年   23234篇
  1984年   19210篇
  1983年   16794篇
  1982年   12823篇
  1981年   11678篇
  1980年   10777篇
  1979年   18029篇
  1978年   14397篇
  1977年   13060篇
  1976年   12324篇
  1975年   13921篇
  1974年   14999篇
  1973年   14762篇
  1972年   13425篇
  1971年   12111篇
  1970年   10587篇
  1969年   10347篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Recent experimental evidence suggests that coordinated expression of ion channels plays a role in constraining neuronal electrical activity. In particular, each neuronal cell type of the crustacean stomatogastric ganglion exhibits a unique set of positive linear correlations between ionic membrane conductances. These data suggest a causal relationship between expressed conductance correlations and features of cellular identity, namely electrical activity type. To test this idea, we used an existing database of conductance-based model neurons. We partitioned this database based on various measures of intrinsic activity, to approximate distinctions between biological cell types. We then tested individual conductance pairs for linear dependence to identify correlations. Contrary to experimental evidence, in which all conductance correlations are positive, 32% of correlations seen in this database were negative relationships. In addition, 80% of correlations seen here involved at least one calcium conductance, which have been difficult to measure experimentally. Similar to experimental results, each activity type investigated had a unique combination of correlated conductances. Finally, we found that populations of models that conform to a specific conductance correlation have a higher likelihood of exhibiting a particular feature of electrical activity. We conclude that regulating conductance ratios can support proper electrical activity of a wide range of cell types, particularly when the identity of the cell is well-defined by one or two features of its activity. Furthermore, we predict that previously unseen negative correlations and correlations involving calcium conductances are biologically plausible.  相似文献   
72.
Formation of rings from Drosophila DNA fragments   总被引:1,自引:0,他引:1  
  相似文献   
73.
74.
75.
76.
77.
Four myeloid cell lines (M1, WEHI-3B D+, FDC-P1, and 32D) were screened for the presence of J11d antigen. One of these cell lines, the myeloid leukemia M1, was found to express a high level of J11d antigen on the cell surface. Recombinant mouse leukemic inhibitory factor (rm-LIF), recombinant human LIF (rh-LIF), and steroids (hydrocortisone and dexamethasone) could induce M1 cells to undergo monocytic differentiation. The level of J11d antigen was greatly reduced after treatment of the cells with LIF or steroids. Western blotting revealed that the apparent molecular weight of the J11d antigen on M1 cells was 45-48 kDa. Furthermore, the level of J11d mRNA was also reduced during LIF-induced differentiation of M1 cells.  相似文献   
78.
79.
80.
Censuses of buffalo and wildebeest in the Serengeti-Mara region have been carried out by various workers at intervals since 1958. The methods of these censuses, which normally employ a total count, are described and the errors inherent in such techniques are analysed in detail. After the appropriate corrections had been made the results showed that both populations have increased considerably over the years 1961–1971.  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