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   463860篇
  免费   56917篇
  国内免费   291篇
  521068篇
  2018年   4109篇
  2017年   3756篇
  2016年   5854篇
  2015年   8853篇
  2014年   9909篇
  2013年   13760篇
  2012年   16012篇
  2011年   16042篇
  2010年   10586篇
  2009年   9820篇
  2008年   13954篇
  2007年   14459篇
  2006年   13089篇
  2005年   12903篇
  2004年   12587篇
  2003年   11965篇
  2002年   11472篇
  2001年   21760篇
  2000年   21857篇
  1999年   17558篇
  1998年   6424篇
  1997年   6612篇
  1996年   6419篇
  1995年   5792篇
  1994年   5856篇
  1993年   5674篇
  1992年   13737篇
  1991年   13033篇
  1990年   12750篇
  1989年   12584篇
  1988年   11235篇
  1987年   10862篇
  1986年   9913篇
  1985年   9723篇
  1984年   8267篇
  1983年   7124篇
  1982年   5590篇
  1981年   5063篇
  1980年   4693篇
  1979年   7724篇
  1978年   5949篇
  1977年   5452篇
  1976年   5087篇
  1975年   5380篇
  1974年   5832篇
  1973年   5671篇
  1972年   5110篇
  1971年   4739篇
  1970年   3935篇
  1969年   3859篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
A multi-sample slippage test based on ordered observations has been given. The test statistic is based on the sum of ranks of the sample. The probability distribution of the test statistic has been worked out for small sample and it turns out to be chi-square distribution for large sample. The analytical procedure has been explained by a numerical example.  相似文献   
994.
We describe the use of a suprahyoid flap for reconstruction in the lower anterior neck. It has been most useful for immediately closing pharyngostomes and for resurfacing defects from the excision of squamous cell carcinoma of the larynx or other neoplasms involving the skin. This flap provides a good deal of viable tissue, it can easily be rotated without a delay procedure, and the donor area is closed by direct suture. We present our experience with 22 cases.  相似文献   
995.
The cat hindlimb contains several long, biarticular strap muscles composed of parallel muscle fascicles that attach to short tendons. Three of these muscles--sartorius, tenuissimus, and semitendinosus--were studied by dissecting individual gold-stained fibers and determining the surface distribution of acetylcholinesterase-stained end-plate zones. In each muscle, fascicles were composed of muscle fibers that ran only part of the fascicle length and tapered to end as fine strands that interdigitated with other tapering fibers within the muscle mass. Most muscle fibers measured 2-3 cm in length. Fascicles of muscle fibers were crossed by short transverse bands of endplates (1 mm wide by 1-5 mm long) that were spaced at fairly regular intervals from the origin to the insertion of the muscle. The endplate pattern suggested that the fiber fascicles were organized into multiple longitudinal strips. In the sartorius, the temporospatial distribution of electromyographic (EMG) activity evoked by stimulating fine, longitudinal branches of the parent nerve confirmed that each strip was selectively innervated by a small subset of the motor axons. These axons appeared to distribute their endings throughout the entire length of the fascicles, providing for synchronous activation of their in-series fibers.  相似文献   
996.
Cardiac sarcolemma preparations of both pig and rat ventricles were found to possess two sets of taurine-binding components. The two proteins from pig heart were solubilized with the detergent Ammonyx-Lo. Characterization of these solubilized proteins revealed that both components are glycoproteins and retain the binding properties observed for the membrane isolate. However, the characterization also revealed several differences between the proteins including their binding specificities, their affinities for taurine, their binding isotherms, and their molecular sizes. Possible functions of these two taurine-binding proteins are discussed.  相似文献   
997.
JOHN  C. D.; LAUCHLI  A. 《Annals of botany》1980,46(4):395-400
Respiratory gas exchange and incorporation of 14C-leucine intoprotein were studied in proximal root segments from 25-day-oldmaize plants grown for the last ten days in 50 mM Na2SO4. 14C-leucineincorporation, and oxygen uptake in the presence of glucose,were as large in Na2SO4-grown tissues tested under saline conditionsas in tissues exposed to non-saline solutions throughout Thisadaptation was attributed to an increased metabolic capacityof Na2SO4-treated tissues, because these tissues, when returnedto non-saline solutions, evolved oxygen and incorporated 14C-leucinefaster than tissues exposed continuously to non-saline solutions. These changes are interpreted as a ‘compensation’for the inhibitory effects found when non-adapted tissues wereexposed to 50 mM Na2SO4. Moreover, we have related them to ultrastructuralchanges observed previously in xylem parenchyma cells of thesetissues, and to the possible involvement of these xylem parenchymacells in the re-absorption of sodium from the ascending xylemfluid Zea mays L., maize, salt-stress, respiration, protein synthesis  相似文献   
998.
We have characterized the effects of the T199S, T199A, and K70A mutations on the biochemical activity and in vivo functioning of Escherichia coli DnaK. Threonine-199 is the site of autophosphorylation of DnaK, and the lysine residue of bovine Hsc70 corresponding to K70 of DnaK has been shown to be essential for the hydrolysis of ATP. The dnaK alleles T199A and K70A are completely unable, and the T199S allele is only partially able, to complement the defects of a DeltadnaK mutant. The ATPase activities of the DnaK T199A and DnaK K70A proteins are nearly abolished, while the ATPase activity of the DnaK T199S protein has a steady-state rate similar to that of wild-type DnaK. The DnaK T199S protein also retains approximately 13% of the autophosphorylation activity of wild-type DnaK, while the autophosphorylation activities of the T199A and K70A derivatives are completely abolished. All four DnaK proteins bind a model peptide substrate, and the wild-type, T199A, and T199S DnaK proteins release the peptide with similar kinetics upon the addition of ATP. The DnaK K70A protein, in contrast, does not release the peptide upon the addition of ATP. ATP induces a conformational change in the wild-type, T199A, and T199S DnaK proteins but not in the DnaK K70A protein. The T199A and K70A mutations both disrupt the ATPase activity of DnaK but have profoundly different effects on the ATP-induced conformational change and peptide release activities of DnaK, implying that the two mutations affect different steps in the functional cycle of DnaK. The DnaK T199S protein represents a new class of DnaK mutant, one which has near-normal levels of ATPase activity and undergoes an ATP-induced conformational change that results in the release of peptide but which is not able to fully complement loss of DnaK function in the cell.  相似文献   
999.
1000.
The major cell surface glycoprotein components of four new cell lines derived from human squamous cell carcinomas of the head and neck (TR126, TR131, TR138, TR146, Rupniak, H. T. et al., JNCI 75, 621-635, 1985) were identified by three complementary labelling methods. The profile of labelled glycoprotein components was very similar in the four cell lines, although quite large quantitative differences in individual bands were seen. Two galactoproteins, designated GPC-130 and GPC-80 (apparent molecular weight X 10(-3)) were labelled by galactose oxidase/NaB [3H]4 but in all four lines only GPC-130 was prominent. The cell surface galactose and N-Acetylgalactosaminyl residues of glycoproteins were quite highly sialylated, as the galactose oxidase/NaB [3H]4 reaction was increased by between 3- and 6-fold after neuraminidase treatment. The neuraminidase-galactose oxidase/NaB [3H]4 and NaIO4/NaB [3H]4 methods identified a complex profile of glycoprotein components, with very high molecular weight sialogalactoconjugates being prominent. The major sialoglycoproteins were GPC-205, GPC-175, GPC-155, GPC-90 and GPC-70 and in addition, GPC-130 and GPC-80 showed enhanced labelling. Lactoperoxidase catalyzed the iodination of a similar profile of high molecular weight glycoprotein components, with GPC-205 and GPC-175 being prominent in TR126, TR131 and TR146 but less evident in TR138. Overall, the profile of labelled glycoprotein components was similar to the pattern seen in the well differentiated transitional carcinoma lines RT112 and RT4 (Steele, J. G. et al., Biochim. Biophys. Acta. 732, 219-228, 1983).  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