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   292984篇
  免费   34552篇
  国内免费   149篇
  2018年   2399篇
  2016年   3089篇
  2015年   4036篇
  2014年   4916篇
  2013年   6742篇
  2012年   7707篇
  2011年   7914篇
  2010年   5205篇
  2009年   5037篇
  2008年   7154篇
  2007年   7326篇
  2006年   7215篇
  2005年   6924篇
  2004年   6790篇
  2003年   6620篇
  2002年   6468篇
  2001年   17262篇
  2000年   17449篇
  1999年   13302篇
  1998年   3863篇
  1997年   4127篇
  1996年   3851篇
  1995年   3488篇
  1994年   3466篇
  1993年   3541篇
  1992年   10388篇
  1991年   10316篇
  1990年   9804篇
  1989年   9635篇
  1988年   8990篇
  1987年   8356篇
  1986年   7557篇
  1985年   7407篇
  1984年   5824篇
  1983年   5074篇
  1982年   3612篇
  1981年   3179篇
  1980年   3030篇
  1979年   5349篇
  1978年   4115篇
  1977年   3749篇
  1976年   3300篇
  1975年   3778篇
  1974年   3949篇
  1973年   3894篇
  1972年   3422篇
  1971年   3185篇
  1970年   2823篇
  1969年   2741篇
  1968年   2413篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
831.
832.
833.
The howler monkey possesses unique anatomical adaptations associated with its arboreal habit. The behavioral elements are described by locomotor pattern, substrate, timing and rhythm of movement. The most significant motor adaptations are correlated clearly and directly with musculoskeletal features of the lower limb. The orientation of the joints within the limb, the shape of the joint surfaces, their bony environments, and the important planes of muscular control are the foundations for the observable locomotor behaviors.  相似文献   
834.
835.
The influence of diazepam (1; 5; 10 mg/kg, i. p.), chlorpromazine (1 mg/kg) and amphetamine (1; 5 mg/kg) on the Fourier's spectral EEG power of sensomotor cortex and dorsal hippocampus and conflict behavior freely moving albino and cotton (Sigmondon hispidus) rats was studied. Effects of diazepam (5 mg/kg) in cotton rats were similar, but influence on the theta-activity was more expressed. Correlation between slowing of theta-activity and extent of anxiolytic effect in conflict situation was showed. On the basis of the results obtained the authors discuss possible mutual relations between the influence of diazepam on EEG and anxiolytic effect of benzodiazepines.  相似文献   
836.
837.
Purification and partial characterization of goose ceruloplasmin   总被引:2,自引:0,他引:2  
The preparation and properties of ceruloplasmin from goose blood plasma are described. Ammonium sulfate was used to precipitate the crude protein followed by adsorption and elution from DEAE-Sephadex A-50. Further treatment with an ethanol-chloroform mixture and Sephadex G-200 yielded an intensely blue protein possessing a high degree of chemical purity and biological activity. Goose ceruloplasmin, existing in two forms, appears to be a single polypeptide, apparent Mr121,300, with an A610/A280 ratio of 0.07. Copper represented 0.32%, which corresponded to six atoms of copper per protein molecule. Although the amount of EPR-detectable copper was the same as in mammalian ceruloplasmins there were some differences in EPR parameters, mainly in A parallel. Goose ceruloplasmin's amino acid composition, although similar in many residues to human ceruloplasmin, was lower in tyrosine, cystine/cysteine, and acidic amino acids. Valine was found as the N-terminal amino acid. Hexose, hexosamine, sialic acid, and fucose accounted for 6.65% of the weight. Goose protein contained only half the sialic acid of human ceruloplasmin. Two values for Km using either p-phenylenediamine (0.64 and 0.053 mM) or o-dianisidine (0.76 and 0.15 mM) were evaluated from Lineweaver-Burk plots. EPR studies on reactions with water radiolysis products at cryogenic temperatures allowed us to discover that goose ceruloplasmin, like human and bovine ceruloplasmins, possesses superoxide dismutase activity.  相似文献   
838.
839.
Down-regulation of murine collagen-induced arthritis by a T cell hybridoma   总被引:1,自引:0,他引:1  
T cell hybridoma cell lines were generated by somatic cell fusion of BW 5147 myeloma cells and splenic cells from mice suppressed for collagen-induced arthritis (CIA). Two cell lines were characterized for their cell surface phenotype, antigen recognition and capacity to down-regulate the erythema and edema associated with CIA. Cell line T101N was determined to portray the cell surface phenotype Ly1+2- L3T4- Thy1+ by a direct binding assay. Cell line T104B1 was determined to express only the Thy1+ alloantigen. Panning studies, measurement of IL-2 production in vitro and the suppression of antibodies to type I and type II collagen in vivo indicate that the hybridoma cells are not isotype specific in their recognition of the polymorphic interstitial collagens. Down-regulation of the erythema and edema of CIA occurred on injection of 1 X 10(5) T101N cells but not T104B1 cells. Histology of the tarsus region of the hind paw of CIA mice 33 days after the administration of T101N cells showed contrasting histopathology compared to that of CIA mice. The joints of CIA mice given T101N cells showed aligned articular surfaces resembling normal joint structure and only residual pannus. The data indicate that collagen-specific cloned T cell lines can modulate the gross pathology and joint architecture of joints exhibiting CIA.  相似文献   
840.
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