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   746890篇
  免费   89256篇
  国内免费   524篇
  836670篇
  2016年   7678篇
  2015年   11111篇
  2014年   12950篇
  2013年   18695篇
  2012年   20739篇
  2011年   21094篇
  2010年   14141篇
  2009年   13206篇
  2008年   18731篇
  2007年   19428篇
  2006年   18300篇
  2005年   17693篇
  2004年   17339篇
  2003年   16966篇
  2002年   16579篇
  2001年   33835篇
  2000年   34530篇
  1999年   27499篇
  1998年   9514篇
  1997年   10179篇
  1996年   9584篇
  1995年   9069篇
  1994年   8920篇
  1993年   9016篇
  1992年   22919篇
  1991年   22403篇
  1990年   21586篇
  1989年   21178篇
  1988年   19672篇
  1987年   18841篇
  1986年   17755篇
  1985年   17892篇
  1984年   14921篇
  1983年   12878篇
  1982年   10016篇
  1981年   9214篇
  1980年   8580篇
  1979年   14316篇
  1978年   11445篇
  1977年   10485篇
  1976年   9901篇
  1975年   11000篇
  1974年   11861篇
  1973年   11663篇
  1972年   10794篇
  1971年   9813篇
  1970年   8364篇
  1969年   8184篇
  1968年   7413篇
  1967年   6383篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
The Caenorhabditis elegans excretory cell extends tubular processes, called canals, along the basolateral surface of the epidermis. Mutations in the exc-5 gene cause tubulocystic defects in this canal. Ultrastructural analysis suggests that exc-5 is required for the proper placement of cytoskeletal elements at the apical epithelial surface. exc-5 encodes a protein homologous to guanine nucleotide exchange factors and contains motif architecture similar to that of FGD1, which is responsible for faciogenital dysplasia. exc-5 interacts genetically with mig-2, which encodes Rho GTPase. These results suggest that EXC-5 controls the structural organization of the excretory canal by regulating Rho family GTPase activities.  相似文献   
83.
The dynamic mechanical properties of lung tissue and its contents of collagen and elastic fibers were studied in strips prepared from mice instilled intratracheally with saline (C) or silica [15 (S15) and 30 days (S30) after instillation]. Resistance, elastance, and hysteresivity were studied during oscillations at different frequencies on S15 and S30. Elastance increased from C to silica groups but was similar between S15 and S30. Resistance was augmented from C to S15 and S30 and was greater in S30 than in S15 at higher frequencies. Hysteresivity was higher in S30 than in C and S15. Silica groups presented a greater amount of collagen than did C. Elastic fiber content increased progressively along time. This increment was related to the higher amount of oxytalan fibers at 15 and 30 days, whereas elaunin and fully developed elastic fibers were augmented only at 30 days. Silicosis led not only to pulmonary fibrosis but also to fibroelastosis, thus assigning a major role to the elastic system in the silicotic lung.  相似文献   
84.
85.
The actions of a series of 15 Ca2+ channel antagonists including D-600, nifedipine, and diltiazem were examined against K+ depolarization and muscarinic receptor induced responses in guinea pig bladder smooth muscle. Responses of bladder are very dependent upon extracellular Ca2+ and sensitive to the Ca2+ channel antagonists, the tonic component more than the phasic component of response. Regardless of stimulant, K+ or methylfurmethide (MF), or component of response, the same rank order of antagonist activities is expressed, suggestive of a single structure-activity relationship and the existence of a single category of binding site which may, however, exist in several affinity states. High affinity binding of [3H]nitrendipine (KD = 1.1 X 10(-10) M) occurs in bladder membranes, and similar high affinity binding was found in microsomal preparations from other smooth muscles including guinea pig and rat lung, rat vas deferens, uterus, and stomach. [3H]nitrendipine binding in the bladder was sensitive to displacement by other 1,4-dihydropyridines, paralleling their pharmacologic activities and showing excellent agreement with binding data previously obtained for guinea pig ileal smooth muscle. Comparison of pharmacologic data for inhibition of K+- and MF-induced responses by a common series of Ca2+ channel antagonists in bladder and ileum revealed excellent correlations. Neither pharmacologic nor binding studies suggest significant differences in Ca2+ channel antagonist properties in smooth muscle from bladder and intestine.  相似文献   
86.
1. Seasonal regulation of energy economy was studied in farm-raised blue foxes (Alopex lagopus) and raccoon dogs (Nyctereutes procyonoides; Gray, 1834). 2. Both species exhibited marked seasonal changes in body weight, body energy content, food intake and locomotor activity. Seasonal changes in food efficiency were also evident. 3. The results emphasize the important role of both energy intake and energy expenditure in the regulation process. 4. It can be concluded that regulation of seasonal energy balance is a dynamic process with various interactions between different factors.  相似文献   
87.
88.
89.
90.
D Bell 《BMJ (Clinical research ed.)》1985,290(6480):1450-1451
  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