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   360680篇
  免费   28058篇
  国内免费   92篇
  2018年   4183篇
  2017年   4035篇
  2016年   5094篇
  2015年   4959篇
  2014年   6609篇
  2013年   9473篇
  2012年   11067篇
  2011年   11919篇
  2010年   8300篇
  2009年   7314篇
  2008年   10597篇
  2007年   11075篇
  2006年   10583篇
  2005年   9878篇
  2004年   10101篇
  2003年   9733篇
  2002年   9712篇
  2001年   15832篇
  2000年   15711篇
  1999年   12022篇
  1998年   3817篇
  1997年   3774篇
  1996年   3427篇
  1995年   3164篇
  1992年   9532篇
  1991年   9726篇
  1990年   9487篇
  1989年   9491篇
  1988年   8753篇
  1987年   8245篇
  1986年   7531篇
  1985年   7852篇
  1984年   6333篇
  1983年   5319篇
  1982年   3614篇
  1981年   3180篇
  1980年   3132篇
  1979年   5962篇
  1978年   4646篇
  1977年   4230篇
  1976年   3993篇
  1975年   4803篇
  1974年   5315篇
  1973年   5269篇
  1972年   4790篇
  1971年   4485篇
  1970年   3896篇
  1969年   3795篇
  1968年   3554篇
  1967年   3201篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Oligosaccharide chains of agalactoorosomucoid, α1-acid glycoprotein from which sialic acid and galactose have been sequentially removed, terminate in N-acetylglucosaminyl residues. This protein is rapidly transferred from the circulation into the liver by a route distinct from that previously demonstrated for a number of galactosyl terminating glycoproteins.  相似文献   
993.
T-cell phenotype that regulates isoproterenol-induced lymphocyte-dependent hyperplasia of mouse salivary glands and conditions of its activation has been investigated. Stimulated Thy-1 and Ly-1-positive cell populations proliferated in the medium supplemented with both interleukin-1 (IL-1) and interleukin-2 (IL-2). The inhibiting population was Thy-1 and Ly-2-positive, proliferating only in IL-2-containing medium. Both regulatory cell properties and the character of their activation are similar to those of lymphocytes that regulate syngeneic mixed lymphocyte culture. The regularities shown may reflect important processes of cell proliferation regulation in multicellular organisms.  相似文献   
994.
995.
The influence of endosymbiotic bacterium Wolbachia on the recombination processes in the sex chromosome of Drosophila melanogaster on the region between white and cut genes has been studied. The analysis of the crossing-over frequency in various variants of strain crossing, infected and noninfected, with bacteria has been carried out. The results have shown the absence of the influence of infection with Wolbachia on the frequency of crossing-over in the studied region of the X chromosome of D. melanogaster.  相似文献   
996.
997.
Recent data have demonstrated that differences in sIg density on B lymphocytes distinguish functionally distinct subpopulations of these cells. Other reports suggest that cyropreservation may change the frequency of sIg-bearing lymphocytes. To determine if cryopreservation alters either the frequency of sIg cells or the distribution of sIg density, PBM from normals and patients with CLL and LCL were analyzed using the FACS. Aliquots of Ficoll-Hypaque-separated PBM were controlled-rate frozen (1 °C/min) in 7.5% Me2SO in RPMI 1640 and thawed in a 37 °C water bath on the same day. Fresh and frozen-thawed PBM aliquots were labeled with fluorescein conjugates of F(ab′) fragments of affinity chromatography-purified anti-Fab or class-specific anti-μ, anti-δ, anti-γ, or anti-α. Histograms of relative cell fluorescence, reflecting sIg density, were prepared for each aliquot with the FACS. The frequency of sIg-bearing PBM labeled with each reagent was not significantly altered by freezing. Likewise, FACS profiles demonstrated that the distribution of sIg density on normal and CLL PBM was unchanged after freezing. However, the fluorescence peak produced by frozen-thawed unlabeled cells was occasionally slightly broader than that of fresh cells, suggesting increased autofluorescence induced by freezing. These data indicate that frozen cell preparations may be utilized for the study of B-lymphocyte subsets as determined by sIg density.  相似文献   
998.
Summary In comparison with intact yeast, dehydrated-rehydrated cells of Saccharomyces cerevisiae show significantly higher ethanol production from exogenous substrate under both anaerobic and aerobic conditions, particularly when low concentration (0.1%) of glucose are used. For populations with a higher percentage of viable rehydrated cells (above 70%) a more notable decrease in the Pasteur effect (the difference between the quantity of ethanol formed under anaerobic and aerobic conditions) is observed.  相似文献   
999.
Testes, collected from 11 species of demersal and platform associated pelagic fishes, were examined microscopically for petroleum induced lesions. The fish were taken from 19 oil and gas production platforms and four control sites from the north-central Gulf of Mexico, during two periods, spring and late summer. The status of the spermatogenic cycle at the time specimens were collected correlated well with the known spawning times for the respective species of fish with one exception. Histopathological evaluation revealed acidophilic granular cells, chromatophores, degeneration and focal leucocytic aggregations as the most prominent and abundant conditions in testes, with encapsulated cysts, protozoa and helminths being observed only rarely. No evidence of adverse effects on gonadal morphology was found.  相似文献   
1000.
We screened a total of 460 stool samples from humans with and without underlying disease for the black yeast and neurotrope, Exophiala dermatitidis using conventional and molecular identification procedures. Sixteen (3.5%) samples were positive. Twelve out of the sixteen positive samples where the fungus was recovered were from individuals who had diarrhoea at the moment of isolation. Two asymptomatic positive cases were within the age bracket of 21–30. Susceptibility testing of the strains using the CLSI M38 protocol suggests that almost all the strains were susceptible to amphotericin B, 5 fluorocytosine, itraconazole, fluconazole and voriconazole. Considering the health risk currently posed by this organism in Asia, especially among healthy younger subjects of the population and the scarcity of data on this fungus in Africa in general and Nigeria in particular, some recommendations were suggested.  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