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   532712篇
  免费   48123篇
  国内免费   973篇
  2018年   16862篇
  2017年   15731篇
  2016年   13482篇
  2015年   7538篇
  2014年   8429篇
  2013年   11516篇
  2012年   17681篇
  2011年   27796篇
  2010年   22639篇
  2009年   18375篇
  2008年   23488篇
  2007年   26035篇
  2006年   12118篇
  2005年   12597篇
  2004年   12598篇
  2003年   12155篇
  2002年   11658篇
  2001年   17727篇
  2000年   17692篇
  1999年   13943篇
  1998年   5040篇
  1997年   5294篇
  1996年   4928篇
  1995年   4621篇
  1994年   4488篇
  1993年   4562篇
  1992年   11636篇
  1991年   11596篇
  1990年   11299篇
  1989年   10924篇
  1988年   10510篇
  1987年   10100篇
  1986年   9372篇
  1985年   9234篇
  1984年   7764篇
  1983年   6735篇
  1982年   5185篇
  1981年   4619篇
  1980年   4467篇
  1979年   7422篇
  1978年   5862篇
  1977年   5393篇
  1976年   5201篇
  1975年   5610篇
  1974年   6306篇
  1973年   6169篇
  1972年   6373篇
  1971年   5800篇
  1970年   4650篇
  1969年   4579篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Reconstruction of bony structures of the face is always a problem as big as the defect and the function that must be replaced. Everything from simple grafts to sophisticated distant bone flaps has been used. Based on the studies of Cutting et al., Psillakis et al., and Casanova et al., we have developed the full-thickness galeoparietal bone flap, initially for mandibular reconstruction, but of great use for all maxillofacial reconstructions. From July of 1987 to December of 1988, 14 patients have been operated on. The experience with this flap is shown in four patients as follows: primary reconstruction of a mandible as a result of ameloblastoma, secondary reconstruction of a mandible with associated old fractures and malalignment of segments, bilateral malar reconstruction in a patient with Treacher Collins syndrome, and severe sequelae of an already treated Romberg case. Small variations could be made to best accommodate the technique used to the defect we were treating. Some technical details, the experience, the results, and possible sequelae or complications are also discussed.  相似文献   
52.
53.
54.
55.
56.
An agar-degrading marine bacterium identified as a Microscilla species was isolated from coastal California marine sediment. This organism harbored a single 101-kb circular DNA plasmid designated pSD15. The complete nucleotide sequence of pSD15 was obtained, and sequence analysis indicated a number of genes putatively encoding a variety of enzymes involved in polysaccharide utilization. The most striking feature was the occurrence of five putative agarase genes. Loss of the plasmid, which occurred at a surprisingly high frequency, was associated with loss of agarase activity, supporting the sequence analysis results.  相似文献   
57.
Expression of the glycoprotein clusterin is markedly increased following tissue injury. One function of clusterin is to promote cell interactions which are perturbed in these pathologic settings. Clusterin causes cell aggregation and adhesion in vitro yet the molecular mechanism for this effect is not known. In order to identify the active site(s) of clusterin, 34 peptides, each 15 amino acid residues in length, were synthesized from hydrophilic regions of human clusterin. When studied individually, none of the peptides caused aggregation of LLC-PK1 cells, a porcine renal epithelial cell line. However, two out of the 34 peptides inhibited clusterin-induced cell aggregation in a dose-dependent manner. Scrambled versions of these two 'active' peptides did not inhibit cell aggregation. Seven peptides promoted cell adhesion. In conclusion, these findings provide evidence for novel amino acid sequences mediating clusterin-induced renal cell interactions.  相似文献   
58.
59.
Self-consistent steady-state axisymmetric configurations of a plasma envelope with a uniform anisotropic conductivity around a rotating magnetized spherical body are considered. A set of electrodynamic and magnetohydrodynamic equations is analyzed under the assumption that the mass velocity of a moving weakly ionized plasma has only the azimuthal component. The equations describing the profile of the angular frequency of the rotating plasma envelope, the magnetic field, the conduction currents, and the plasma density distribution are solved in the limit of a strong anisotropy of the conductivity of a weakly ionized gas. The applicability of the results obtained to a qualitative interpretation of the phenomena occurring in the plasmaspheres of magnetized planets is discussed.  相似文献   
60.
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