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   352546篇
  免费   38971篇
  国内免费   1534篇
  2021年   3127篇
  2018年   3659篇
  2017年   3312篇
  2016年   4773篇
  2015年   6691篇
  2014年   7822篇
  2013年   10400篇
  2012年   11928篇
  2011年   11827篇
  2010年   7890篇
  2009年   7190篇
  2008年   10058篇
  2007年   10390篇
  2006年   9576篇
  2005年   9125篇
  2004年   8823篇
  2003年   8408篇
  2002年   8292篇
  2001年   18445篇
  2000年   18612篇
  1999年   14324篇
  1998年   4407篇
  1997年   4637篇
  1996年   4437篇
  1995年   4115篇
  1994年   4043篇
  1993年   3837篇
  1992年   11548篇
  1991年   11174篇
  1990年   10739篇
  1989年   10288篇
  1988年   9513篇
  1987年   8877篇
  1986年   8102篇
  1985年   7979篇
  1984年   6416篇
  1983年   5570篇
  1982年   4110篇
  1981年   3591篇
  1980年   3350篇
  1979年   6105篇
  1978年   4562篇
  1977年   4120篇
  1976年   3759篇
  1975年   4328篇
  1974年   4495篇
  1973年   4389篇
  1972年   4084篇
  1971年   3496篇
  1970年   3168篇
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
991.
The structure of the c-myc oncogene in 17 cervical tumors and patient-matched nontumor tissues from Chinese patients residing in Taiwan was analysed. In contrast to recent reports on Mexican patients, none of the samples showed rearrangements and sequence amplification in the c-myc gene. The discrepancy may be explained by different carcinogenesis mechanisms being in operation in different geographic regions. Although no structural alterations in the c-myc gene were found in seven cervical carcinoma cell lines analysed, Northern blot analysis indicated different levels of c-myc gene expression which may be related to the presence of human papillomavirus (HPV) sequence in the cell and suggests a possible c-myc-hpv interaction in some stages of the transformation process.  相似文献   
992.
Effect of membrane additives on vesicle fusion   总被引:1,自引:0,他引:1  
A large variety of alkyl derivatives were found to either slow or block the low-temperature induced fusion of dipalmitoylphosphatidylcholine small unilamellar vesicles (DPPC SUV) when incorporated into the SUV bilayer at five mol%. Only corn oil was fusogenic.  相似文献   
993.
The patterns of EMG activity in the biceps and triceps muscles were recorded during horizontal oscillatory movements of the forearm. Subjects showed increased frequency of oscillation as they voluntarily reduced movement amplitude. EMG burst duration was significantly correlated with wavelength of oscillation in every case. In almost half the cases burst intensity was also positively correlated with wavelength. Subjects seemed to be using one or both these methods to control amplitude. A model was developed in three stages which satisfactorily accounted for the data.  相似文献   
994.
Vitronectin is a cell-adhesive glycoprotein in serum and plasma, also termed serum spreading factor and complement S-protein. It consists of a mixture of a polypeptide of molecular weight 75 kilodalton (kDa) and its nicked product of 65 kDa plus 10 kDa. By a quantitative immunoblotting assay, human blood samples could be classified into three distinct vitronectin types; type I (58% of the population) was 75 kDa rich and 65 kDa poor, type II (35% of the population) contained approximately equal amounts of 75 kDa and 65 kDa, and type III (5% of the population) was 75 kDa poor and 65 kDa rich. The vitronectin type did not correlate with age, sex, or ABO blood type.  相似文献   
995.
996.
997.
A method for the extraction and quantitative determination of both the mass and radioactivity of glycolic acid from -14C-labeled leaf tissue is described. The recoveries of both mass and radioactivity from standard [1-14C]glycolic acid solutions averaged 98 percent, and recovery of radioactivity added to plant samples as [1-14C]glycolic acid was over 90 percent after the complete procedure. The method was reliable with total samples containing as little as 130 nmol of glycolic acid. The mass of glycolic acid recovered from sunflower leaf tissue was proportional to the amount of tissue extracted. In experiments with different plant material, the amount of glycolic acid varied between 530 and 1120 nmol/dm-2 of leaf tissue. The specific radioactivity of the glycolic acid in sunflower leaf tissue during photosynthesis in -14CO(2) was never more than 20 percent of the specific radioactivity of the -14CO(2) supplied.  相似文献   
998.
999.
Intermittent illumination increased H2 and C2H4 yields per unit of light from growing cells and from nitrogren-starved cells by 1.7- and 1.35-fold, respectively, as compared with continuous illumination.  相似文献   
1000.
The release of alanine by rat diaphragm muscle in vitro.   总被引:13,自引:10,他引:3       下载免费PDF全文
Z discs were isolated from Lethocerus flight muscle by removing the contractile proteins from myofibrils with a solution of high ionic strength. The protein composition of the Z discs was analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis; the major proteins were alpha-actinin, actin and tropomyosin. Z lines were selectively removed from intact myofibrils by digestion with crude lipase and chymotrypsin, but not by purified lipase.  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