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   429097篇
  免费   44957篇
  国内免费   200篇
  2016年   4692篇
  2015年   6231篇
  2014年   7339篇
  2013年   10988篇
  2012年   11913篇
  2011年   12366篇
  2010年   8394篇
  2009年   7739篇
  2008年   11045篇
  2007年   11744篇
  2006年   11034篇
  2005年   10514篇
  2004年   10553篇
  2003年   10321篇
  2002年   10078篇
  2001年   17563篇
  2000年   17629篇
  1999年   14283篇
  1998年   5083篇
  1997年   5383篇
  1996年   5125篇
  1995年   4833篇
  1994年   4748篇
  1993年   4750篇
  1992年   12450篇
  1991年   12253篇
  1990年   12266篇
  1989年   12012篇
  1988年   11339篇
  1987年   10666篇
  1986年   9976篇
  1985年   10422篇
  1984年   8595篇
  1983年   7397篇
  1982年   5724篇
  1981年   5117篇
  1980年   4790篇
  1979年   8223篇
  1978年   6428篇
  1977年   6031篇
  1976年   5793篇
  1975年   6249篇
  1974年   6788篇
  1973年   6690篇
  1972年   6245篇
  1971年   5631篇
  1970年   4879篇
  1969年   4858篇
  1968年   4527篇
  1967年   3892篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
972.
973.
974.
The first 46 amino acids (aa) of the N terminus of the rabbit heart (RH) L-type cardiac Ca(2+) channel alpha(1C) subunit are crucial for the stimulating action of protein kinase C (PKC) and also hinder channel gating (Shistik, E., Ivanina, T., Blumenstein, Y., and Dascal, N. (1998) J. Biol. Chem. 273, 17901-17909). The mechanism of PKC action and the location of the PKC target site are not known. Moreover, uncertainties in the genomic sequence of the N-terminal region of alpha(1C) leave open the question of the presence of RH-type N terminus in L-type channels in mammalian tissues. Here, we demonstrate the presence of alpha(1C) protein containing an RH-type initial N-terminal segment in rat heart and brain by using a newly prepared polyclonal antibody. Using deletion mutants of alpha(1C) expressed in Xenopus oocytes, we further narrowed down the part of the N terminus crucial for both inhibitory gating and for PKC effect to the first 20 amino acid residues, and we identify the first 5 aa as an important determinant of PKC action and of N-terminal effect on gating. The absence of serines and threonines in the first 5 aa and the absence of phosphorylation by PKC of a glutathione S-transferase-fusion protein containing the initial segment suggest that the effect of PKC does not arise through a direct phosphorylation of this segment. We propose that PKC acts by attenuating the inhibitory action of the N terminus via phosphorylation of a remote site, in the channel or in an auxiliary protein, that interacts with the initial segment of the N terminus.  相似文献   
975.
976.
A large and increasing number of women in the western world will at some point during their life be investigated morphologically for some type of breast lesion. Fine Needle Aspiration (FNA) is one morphological method which is considered to be the fastest, cheapest and the most patient-friendly approach. However, the frequency of conclusive samples using this method varies and is often too low, especially when performed by unexperienced operators. In this study we have developed and tested a new semi-automated instrument (“CytoTest”) designed for FNA which is intended to improve the efficacy of the technique by increasing the percentage of conclusive samples. A total of 443 consecutive aspiration procedures on palpable breast lesions were performed to compare this new “CytoTest” equipment with the standard protocol using the same type of needles. We conclude that by increasing the extent and frequency of the reciprocatory motions used by an experienced sampling operator as well as enhancing the ejection pressure, the cellular yield can be increased almost three folded compared to the standard protocol. For cases with high amounts of non-diagnostic material (such as blood or cystic fluid) which were discarded, up to four times more sample could be obtained. Furthermore, the frequency of sparse samples under 1 mg was halved with use of the “CytoTest”.  相似文献   
977.
A number of motile strains of Azospirillum brasilense, A. lipoferum, and A. irakense, were found to possess tyrosinase activity both on the surface of and inside the cells. A. brasilense Sp245, Sp7, and A. irakense KBC-1 each possessed two forms of tyrosinase of different molecular masses; A. lipoferum 43, A. lipoferum 59b, and A. irakense KA-3 each had a single tyrosinase form of approximately the same molecular mass; and A. brasilense Sp107 possessed a single form of tyrosinase different from all the other forms.  相似文献   
978.
979.
ANDERSON and POSPAHALA (1970) investigated the estimation of wildlife population size using the belt or line transect sampling method and devised a correction for bias, thus leading to a class of estimators with desirable characteristics. This work was given a basic and rigorous mathematica framework by BURNHAM and ANDERSON (1976). In the present article we use this mathematical framework to develop an estimator of population size and density using weighted least squares. The approach is a two-stage Method.  相似文献   
980.
Lysine-mediated inhibition of postexponential growth in Saccharomyces cerevisiae occurred when glucose, fructose, or maltose, but not lactate, pyruvate, or ethanol, was used as the carbon source. Arginine starvation is not responsible for the inhibitory effect, since neither the intracellular pool of glucose-grown (inhibited) cells nor that of lactate-grown (noninhibited) cells contained arginine.  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