全文获取类型
收费全文 | 333274篇 |
免费 | 37198篇 |
国内免费 | 189篇 |
专业分类
370661篇 |
出版年
2018年 | 2845篇 |
2017年 | 2702篇 |
2016年 | 3886篇 |
2015年 | 5350篇 |
2014年 | 6251篇 |
2013年 | 8773篇 |
2012年 | 10005篇 |
2011年 | 9978篇 |
2010年 | 6816篇 |
2009年 | 6147篇 |
2008年 | 8879篇 |
2007年 | 9333篇 |
2006年 | 8607篇 |
2005年 | 8309篇 |
2004年 | 8031篇 |
2003年 | 7790篇 |
2002年 | 7794篇 |
2001年 | 18158篇 |
2000年 | 18380篇 |
1999年 | 14111篇 |
1998年 | 4235篇 |
1997年 | 4497篇 |
1996年 | 4307篇 |
1995年 | 4008篇 |
1994年 | 3940篇 |
1993年 | 3778篇 |
1992年 | 11489篇 |
1991年 | 11132篇 |
1990年 | 10689篇 |
1989年 | 10249篇 |
1988年 | 9486篇 |
1987年 | 8850篇 |
1986年 | 8086篇 |
1985年 | 7962篇 |
1984年 | 6396篇 |
1983年 | 5562篇 |
1982年 | 4105篇 |
1981年 | 3592篇 |
1980年 | 3355篇 |
1979年 | 6113篇 |
1978年 | 4569篇 |
1977年 | 4124篇 |
1976年 | 3762篇 |
1975年 | 4331篇 |
1974年 | 4500篇 |
1973年 | 4391篇 |
1972年 | 4090篇 |
1971年 | 3498篇 |
1970年 | 3168篇 |
1969年 | 2969篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Morphological pathway of flagellar assembly in Salmonella typhimurium. 总被引:14,自引:0,他引:14
The process of flagellar assembly was investigated in Salmonella typhimurium. Seven types of flagellar precursors produced by various flagellar mutants were purified by CsCl density gradient protocol. They were characterized morphologically by electron microscopy, and biochemically by two-dimensional gel electrophoresis. The MS ring is formed in the absence of any other flagellar components, including the switch complex and the putative export apparatus. Four proteins previously identified as rod components, FlgB, FlgC, FlgF, FlgG, and another protein, FliE, assemble co-operatively into a stable structure. The hook is formed in two distinct steps; formation of its proximal part and elongation. Proximal part formation occurs, but elongation does not occur, in the absence of the LP ring. FlgD is necessary for hook formation, but not for LP-ring formation. A revised pathway of flagellar assembly is proposed based on these and other results. 相似文献
922.
Thrombin is released as a soluble enzyme from the surface of platelets and tissue-factor-bearing cells to trigger fibrin polymerization during thrombosis under flow conditions. Although isotropic fibrin polymerization under static conditions involves protofibril extension and lateral aggregation leading to a gel, factors regulating fiber growth are poorly quantified under hemodynamic flow due to the difficulty of setting thrombin fluxes. A membrane microfluidic device allowed combined control of both thrombin wall flux (10−13 to 10−11 nmol/μm2 s) and the wall shear rate (10-100 s−1) of a flowing fibrinogen solution. At a thrombin flux of 10−12 nmol/μm2 s, both fibrin deposition and fiber thickness decreased as the wall shear rate increased from 10 to 100 s−1. Direct measurement and transport-reaction simulations at 12 different thrombin flux-wall shear rate conditions demonstrated that two dimensionless numbers, the Peclet number (Pe) and the Damkohler number (Da), defined a state diagram to predict fibrin morphology. For Da < 10, we only observed thin films at all Pe. For 10 < Da < 900, we observed either mat fibers or gels, depending on the Pe. For Da > 900 and Pe < 100, we observed three-dimensional gels. These results indicate that increases in wall shear rate quench first lateral aggregation and then protofibril extension. 相似文献
923.
924.
925.
926.
927.
928.
929.
H J Gabius A Bardosi S Gabius K P Hellmann M Karas H Kratzin 《Biochemical and biophysical research communications》1989,163(1):506-512
A Ca2+-dependent sialic acid-binding protein was purified on fetuin-Sepharose from various types of human tissue. The molecular mass was determined to be 10,315 Da by laser desorption mass spectrometry. Partial sequence analysis after cyanogen bromide cleavage that yielded one N-terminus accessible for Edman degradation revealed an identity to an internal stretch following the only methionine residue within a putative amino acid sequence (Mr 10,048), deduced from the cDNA of a cell cycle-specific gene. The reported biochemical identification is a prerequisite to infer the biological role of the so far undetected gene product. Initial glycohistochemical studies with sialic acid-(BSA-biotin) raised evidence for nuclear localization of sialic acid-binding sites that might reflect, at least in part, detection of this protein. 相似文献
930.
The results of a detailed analysis of 100 supernumerary limbs generated by 180° ipsilateral rotation (on the same limb stump) of regeneration blastemas is presented. The limbs were analyzed in terms of their position of origin, frequency, cartilage structure by Victoria blue staining, and muscle structure by serial sections. Single, double, or triple supernumeraries can be produced at no unique position of origin, although the posterodorsal quadrant was preferred. Four classes of supernumerary limbs were generated by such operations—normal; double dorsal or double ventral; part normal/part mirror imaged; part normal/part inverted in approximately equal frequencies. After amputation of these supernumeraries the same muscle patterns are faithfully regenerated. A hypothesis to explain the production of these abnormal limbs is proposed based on the observed phenomenon of fusion of supernumerary blastemata, but their regenerative behaviour presents problems for current models of pattern formation. Similar results have been obtained with developing limb buds and the relation between development and regeneration is discussed. 相似文献