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   1098篇
  免费   86篇
  国内免费   201篇
  2024年   6篇
  2023年   6篇
  2022年   12篇
  2021年   34篇
  2020年   14篇
  2019年   24篇
  2018年   16篇
  2017年   16篇
  2016年   21篇
  2015年   44篇
  2014年   55篇
  2013年   60篇
  2012年   96篇
  2011年   86篇
  2010年   78篇
  2009年   63篇
  2008年   76篇
  2007年   71篇
  2006年   55篇
  2005年   53篇
  2004年   63篇
  2003年   47篇
  2002年   56篇
  2001年   33篇
  2000年   22篇
  1999年   18篇
  1998年   23篇
  1997年   9篇
  1996年   7篇
  1995年   6篇
  1994年   18篇
  1993年   12篇
  1992年   11篇
  1991年   12篇
  1990年   10篇
  1989年   14篇
  1988年   7篇
  1987年   6篇
  1985年   9篇
  1984年   7篇
  1983年   9篇
  1982年   7篇
  1979年   6篇
  1975年   4篇
  1974年   7篇
  1973年   5篇
  1970年   5篇
  1965年   5篇
  1963年   4篇
  1961年   4篇
排序方式: 共有1385条查询结果,搜索用时 15 毫秒
1.
2.
A nasal, so called ethmoidal, tumor from a fallow deer is described. It appears to be the first reported case of that species. The etiology is discussed.  相似文献   
3.
The amount and nature of glutathione transferases in rat liver microsomes were determined using immunological techniques. It was shown that cytosolic glutathione transferase subunits A plus C, and B plus L were present at levels of 2.4 ± 0.6 and 1.5 ± 0.1 μg/mg microsomal protein, respectively. These levels are 10-times higher than those for non-specific binding of cytosolic components judging from the distribution of lactate dehydrogenase, a cytosolic marker. The possibility that a portion of these glutathione transferases is functionally localized on the endoplasmic reticulum is discussed. A previously described microsomal glutathione transferase which is distinct from the cytosolic enzymes is present in an amount of 31 ± 6 μg/mg microsomal protein.  相似文献   
4.
5.
Summary The pineal organ of the sardine, Sardina pilchardus sardina, was investigated light and electron microscopically. The pineal parenchyma contains sensory cells, supporting cells, and ganglion cells, and the overlying tissues appear specialized for light penetration. The ganglion cells are arranged in 3 groups, their axons giving rise to the tractus epiphyseos. The sensory cell is of a photoreceptor type found in several other teleost species. No definitive evidence of a secretion was educed but some indications of an endocrine function are reported and discussed.The pineal receptor cell of neonates of Mugil spp. which have a pigment-free spot above the pineal organ, was investigated electron microscopically and found to have the same organization as that of adult Mugil auratus.Supported by grants from the Helge Ax:son Johnsons Stiftelse, Stockholm, and from the Kungliga Vetenskapsakademien, Stockholm, Sweden. This is gratefully acknowledged.The animal material has been provided by the Stazione Zoologica di Napoli.  相似文献   
6.
对我国52种微茎类吸虫的18项成虫形态学特征进行主成分分析,结果表明:卵巢位置、子宫延伸位置等7项性状对第一主成分贡献较大,提示描述器官位置的指标是重要的分类依据。52个虫种在前三个主成分上的排序图显示应将其划分成4个亚科。  相似文献   
7.
Formalin fixation strongly influences biomechanical properties of the spine   总被引:7,自引:0,他引:7  
As fresh human cadaveric spine specimens for in vitro testing are hard to obtain and carry a potential risk of infection, the possibility of using embalmed spine specimens has been considered. The cross-linking effect of formalin fixation, however, raises uncertainties regarding the biomechanical likeness of preserved specimens. They have been reported to be stiffer, but no quantitative data exist.

The purpose of this study was to determine the biomechanical differences between fresh and formalin-fixed spine specimens, using L1–2 motion segments from six 16-week-old calf spines. The range of motion and neutral zone were determined in flexion-/extension, left/right axial rotation, and right/left lateral bending.

The range of motion decreased in the formalin fixed specimens by as much as 80%, and the neutral zone by as much as 96%. The results of this study therefore imply that, for biomechanical testing, formalin-fixed specimens are not representative of the in vivo conditions.  相似文献   

8.
Abstract: This article evaluates the influence of an opening of the blood-brain barrier (BBB) on compounds in brain extracellular fluid. The concentrations of amino acids and some other primary amines were determined in dialysates sampled from the right parietal cortex of rats before and after an intracarotid infusion of protamine sulfate. Extravasated plasma proteins were visualized by Evans blue/albumin and immunohistochemistry. CSF albumin— an indicator of blood-CSF barrier opening—was quantified with immunoelectrophoresis. The brains were macroscopically edematous after 10 mg but not after 5 mg of protamine sulfate. The higher dose led to a 50% death rate. The concentrations of amino acids did not change 10 min after the BBB opening. No significant alterations in the amino acid concentrations were observed after the lower dose. The concentrations of glutamate, aspartate, GABA, glycine, taurine, and phosphoethanolamine increased significantly within 50–80 min after the infusion of 10 mg of protamine sulfate. CSF albumin levels were significantly increased 1 h after infusion. We conclude that a dysfunction of the BBB, of a degree known to induce brain edema (10 mg of protamine sulfate), significantly increases the extracellular concentration of excitatory amino acids, GABA, taurine, and phosphoethanolamine in the extracellular space.  相似文献   
9.
    
Major virulence determinants of group A streptococci, such as M-protein, immunoglobulin Fc-receptors (FcRA, EmmL) and C5a peptidase, appear to be genetically co-regulated, their genes being located within a vir regulon. We studied the organization of these genes in a group A, type M15 strain of Streptococcus pyogenes, previously defined as OF, by hybridization analysis of chromosomal DNA and of an S. pyogenes gene library in Escherichia coli, and by gene sequencing. Within the vir regulon, in addition to the virR and scpA genes, three so-called emm-related genes were found: fcrA, emmL and enn. Whereas IgG Fc-binding proteins were encoded by fcrA and emmL, the product of enn was not identified. The presence of three emm-related genes in this region is reminescent of vir regulon organization in OF+ rather than OF strains as earlier defined by others. Furthermore, analysis of the deduced product of the emmL gene showed deletions and amino acid substitutions within the PGTS-rich domain and membrane anchor, which thus resembles corresponding products of OF+ rather than OF strains. In view of these findings, the opacity factor (OF) activity of the strain was tested using growth supernatant, with negative outcome. However, a concentrated SDS cell extract revealed definite OF activity. One of two other type M15 reference strains also showed definite OF activity in SDS extracts. We therefore propose that type M15 strains belong to the OF+ category but often show low levels of expression of OF.  相似文献   
10.
本文就萤叶甲亚科中柱萤叶甲属鞘翅具黑色刻点的种类进行研究,共记述4种,我国已记录3种,其中1种为新种。  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