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   58196篇
  免费   6176篇
  国内免费   338篇
  2021年   508篇
  2019年   451篇
  2018年   736篇
  2017年   688篇
  2016年   927篇
  2015年   1120篇
  2014年   1410篇
  2013年   1663篇
  2012年   1870篇
  2011年   2026篇
  2010年   1301篇
  2009年   1283篇
  2008年   1713篇
  2007年   1712篇
  2006年   1707篇
  2005年   1470篇
  2004年   1403篇
  2003年   1360篇
  2002年   1317篇
  2001年   4754篇
  2000年   4287篇
  1999年   3123篇
  1998年   976篇
  1997年   937篇
  1996年   815篇
  1995年   729篇
  1994年   623篇
  1993年   554篇
  1992年   1950篇
  1991年   1692篇
  1990年   1540篇
  1989年   1386篇
  1988年   1189篇
  1987年   1126篇
  1986年   952篇
  1985年   906篇
  1984年   647篇
  1983年   573篇
  1979年   661篇
  1978年   478篇
  1977年   437篇
  1975年   509篇
  1974年   597篇
  1973年   583篇
  1972年   592篇
  1971年   558篇
  1970年   545篇
  1969年   543篇
  1968年   449篇
  1966年   421篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
In 0.05--0.1 mmol.l-1 concentration, bilirubin inhibits ADP-activated respiration of isolated liver mitochondria; it has no effect on respiration in the absence of ADP. Bilirubin-induced inhibition of respiration is not abolished by serum albumin, but bilirubin bound to serum albumin and the photodegradation products of bilirubin have no inhibitory effect.  相似文献   
72.
73.
The biological activity of the filtrates of 29 C. difficile strains was studied in vivo (suckling white mice) and in vitro (cell cultures of different species and origin). The action of the filtrates on the experimental models in vivo was evaluated from the cytotoxic effect index, while in vitro the intensity of the cytotoxic effect was evaluated from the percentage of dead cells in the monolayer. The results of the comparative determination of toxicity characteristics in vivo and in vitro demonstrated that cell cultures were more sensitive experimental models than suckling white mice. The use of cell cultures permitted the quantitative evaluation of the cytotoxic activity of the filtrates under study, as well as the detection of their cell-directed action at minimal concentrations.  相似文献   
74.
75.
76.
The genetic structure of 65 chicken populations was studied using 29 simple sequence repeat loci. Six main clusters which corresponded to geographical origins and histories were identified: Brown Egg Layers; predominantly Broilers; native Chinese breeds or breeds with recent Asian origin; predominantly breeds of European derivation; a small cluster containing populations with no common history and populations that had breeding history with White Leghorn. Another group of populations that shared their genome with several clusters was defined as 'Multi-clusters'. Gallus gallus gallus (Multi-clusters), one of the subspecies of the Red Jungle Fowl, which was previously suggested to be one of the ancestors of the domesticated chicken, has almost no shared loci with European and White Egg layer populations. In a further sub-clustering of the populations, discrimination between all the 65 populations was possible, and relationships between each were suggested. The genetic variation between populations was found to account for about 34% of the total genetic variation, 11% of the variation being between clusters and 23% being between populations within clusters. The suggested clusters may assist in future studies of genetic aspects of the chicken gene pool.  相似文献   
77.
We conducted a multicenter evaluation of the analytical and clinical performance of the automated Bayer Immuno 1 complexed PSA (cPSA) assay, and compared assay performance to the Bayer Immuno 1 PSA assay. We sought to determine whether measurements of cPSA could be of clinical utility in the management of patients with prostate cancer. Results of the 10-day imprecision across three evaluation sites produced total CV < 2.50% and an analytical sensitivity of 0.02 microgram/L. There was an increased trend in clinical sensitivity for prostate cancer with increasing stage of disease (71-86%). Clinical specificity for patients with benign urogenital disease was 74.8%, and for other nonprostate diseases ranged from 91.1-100%. Retrospective serial monitoring of 155 patients with prostate cancer demonstrated concordance of cPSA measurements to clinical status for 97% of the patients analyzed. Results from the clinical studies using the Bayer Immuno 1 cPSA assay were comparable to results obtained with the Bayer Immuno 1 PSA assay. The Bayer Immuno 1 cPSA assay demonstrates analytical performance and clinical effectiveness in the management of prostate cancer patients during the course of disease and therapy.  相似文献   
78.
79.
Electron microscopy of mouse neocortex was carried out during rehabilitation following long-term protein-caloric deficiency. Food rehabilitation led to partial recovery of brain ultrastructure, however, a high neuronal level of secondary lysosoms and lipofuscin bodies was preserved, with the changes in the spine apparatus and synaptic contacts persisting in neuropile. Carnitine addition to food during rehabilitation increased the number of free ribosomes in cortical neurons. A substantial development of granular endoplasmic reticulum was observed. A greater number of spine apparatus cisterns was detected, however, like in conventional rehabilitation, the width of synaptic clefts and postsynaptic densities remained narrower than in control mice.  相似文献   
80.
This study has demonstrated that aneurysms occur in about 50 percent of the rat femoral arteries subjected to microvascular anastomosis. These aneurysms are consistent histologically--being characterized by medial necrosis, loss of elastic lamellae, and subintimal hyperplasia. Mechanical trauma is implicated as a factor in their pathogenesis, though further study in necessary to define the exact etiology.  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