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   590698篇
  免费   62424篇
  国内免费   282篇
  2018年   7082篇
  2017年   6798篇
  2016年   10360篇
  2015年   16013篇
  2014年   17021篇
  2013年   21707篇
  2012年   23363篇
  2011年   21075篇
  2010年   14518篇
  2009年   13347篇
  2008年   16796篇
  2007年   16885篇
  2006年   15818篇
  2005年   20289篇
  2004年   18732篇
  2003年   16690篇
  2002年   13821篇
  2001年   23008篇
  2000年   22561篇
  1999年   18761篇
  1998年   6760篇
  1997年   7025篇
  1996年   6717篇
  1995年   6257篇
  1994年   6070篇
  1993年   6134篇
  1992年   16178篇
  1991年   15916篇
  1990年   15263篇
  1989年   15014篇
  1988年   13927篇
  1987年   13304篇
  1986年   12431篇
  1985年   12369篇
  1984年   10215篇
  1983年   8622篇
  1982年   6526篇
  1981年   5846篇
  1980年   5602篇
  1979年   9469篇
  1978年   7569篇
  1977年   6756篇
  1976年   6353篇
  1975年   7212篇
  1974年   7558篇
  1973年   7484篇
  1972年   6753篇
  1971年   6257篇
  1970年   5266篇
  1969年   5154篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
131.
Forty-two white-rot fungi isolated in South America were incubated with long fibre sugar cane bagasse (LFB). The residual composition of LFB was determined after white-rot decay at 30 and 60 days. The ratio of residual lignin to residual lignin to residual cellulose (RL/RC) of untreated material (LFB) was 0.48. After white-rot-decay, the residual material with lower RL/RC ratios indicated that mainly lignin was degraded. In only 30 days, Phlebia sp. MVHC 5535, Athelia sp. MVHC 5509 and Spongipellis pachyodon MVHC 5019 caused a decrease in the RL/RC ratio to 0.36, 0.37 and 0.38, respectively, while it took 60 days for Ganoderma applanatum MVHC 5347, Hyphodontia sp. MVHC 5544, Panus tigrinus MVHC 5400, Stereum sp. MVHC 5113, Phellinus punctatus MVHC 5346 and MVHC 6388 to reach a ratio lower than 0.40. No correlation was found between the amount of some ligninolytic enzymes secreted and the residual composition of bagasse after white-rot fungi fermentation. Most of the fungal strains caused an increase in the relative amount of residual cellulose, indicating that hemicellulose was the preferred energy source.  相似文献   
132.
The neutrophil-stimulating properties of 38 S. aureus strains and 32 S. epidermidis strains were studied in the reaction of luminol-mediated chemiluminescence. All S. aureus strains and 29 S. epidermidis strains were found to possess neutrophil-stimulating activity, the mean activity index for S. aureus being significantly higher. The stimulating activity of the strains varied within a wide range (the variation coefficient was 120.0 +/- 21.9%) and did not correlate with the content of protein A in bacterial cells and the degree of their hydrophoby. The opsonization of staphylococci with normal human serum enhanced the neutrophil reaction 1.5- to 100-fold and simultaneously leveled out the chemiluminescence indices in experiments with different strains (the variation coefficient was 8.0 +/- 1.5%). The nature of the neutrophil-stimulating effect of staphylococci and its relationship to the exploratory reactions of phagocytes are discussed.  相似文献   
133.
134.
A chronic implant for recording of cochlear potentials in primates   总被引:1,自引:0,他引:1  
A new technique for the continuous recording of peripheral bioelectrical activity in the auditory system of primates is described. Because of basic differences in the anatomy of the temporal bone, the approach to the round window of the cochlea is more difficult in most primates than in lower animals. A relatively simple surgical approach, which made possible the placement of an electrode into the perilymph of the inner ear via the well-demarcated horizontal semicircular canal was therefore developed and is described in detail. The bared tip of a Teflon-coated wire was cemented into the canal opening with carboxylate cement, and the wire attached to a permanent electrical connector on the skull. Cochlear microphonic and action potentials of 50 to 100 μV amplitude were thus recorded on a continuing basis at the same time that behavioral studies of primate auditory acuity were conducted.  相似文献   
135.
136.
137.
Histone deacetylase from calf thymus   总被引:4,自引:0,他引:4  
  相似文献   
138.
A new gas-liquid chromatographic method was developed for the determination of diethylether in whole blood. Ether was quantitated by peak area ratio analysis with n-propanol as the internal standard using a flame ionization detector. Blood ether concentrations were determined in cats undergoing inhalational anesthesia by ether in oxygen. In normal spontaneously breathing cats, anesthesia began at ether concentrations of about 0.6 g/l, and respiratory arrest occurred at 2.4 g/l and above. Mean arterial blood pressure was well maintained throughout the entire anesthetic range. In spinal artificially respired animals, mean arterial blood pressure correlated inversely with blood ether concentration. The data suggest that decline in blood pressure may be a useful sign of ether toxicity in spinal cats.  相似文献   
139.
Intraperitoneal stimulation of adoptively sensitized rats with bacterial antigen promotes the localization of lymphoblasts at the site of antigen deposition. Lymphoblast extravasation activity (LEA) is generated only when specifically immune donor lymphocytes and the recipients of these cells share at least on Ag-B haplotype. However, if the specificity criteria for its formation are satisfied, LEA promotes the local development of lymphoblasts of all available specificities and irrespective of their Ag-B genotype. Allogeneic lymphoblasts do not participate actively in the delayed inflammatory reaction even when they are passively recruited into exudates. The results suggest that LEA is a T cell-derived mediator that amplifies the delayed type hypersensitivity reaction by directing recently activated lymphocytes into lesions.  相似文献   
140.
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