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   15197篇
  免费   1453篇
  国内免费   2篇
  2023年   43篇
  2022年   130篇
  2021年   294篇
  2020年   148篇
  2019年   223篇
  2018年   281篇
  2017年   238篇
  2016年   499篇
  2015年   782篇
  2014年   828篇
  2013年   1005篇
  2012年   1269篇
  2011年   1131篇
  2010年   738篇
  2009年   722篇
  2008年   906篇
  2007年   931篇
  2006年   860篇
  2005年   846篇
  2004年   790篇
  2003年   788篇
  2002年   740篇
  2001年   141篇
  2000年   87篇
  1999年   157篇
  1998年   195篇
  1997年   142篇
  1996年   118篇
  1995年   125篇
  1994年   114篇
  1993年   111篇
  1992年   100篇
  1991年   81篇
  1990年   78篇
  1989年   65篇
  1988年   65篇
  1987年   50篇
  1986年   63篇
  1985年   68篇
  1984年   83篇
  1983年   46篇
  1982年   76篇
  1981年   56篇
  1980年   62篇
  1979年   41篇
  1977年   34篇
  1976年   23篇
  1974年   30篇
  1972年   22篇
  1971年   22篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
131.
Hexadecane mineralization by a bacterial consortium isolated from a non heavily contaminated coastal seawater was largely increased by an enrichment with Inipol EAP 22 (10% w/w). In the conditions of the experiment, the efficiency of this oleophilic nutrient is linked to the organic N and P sources (urea and lauryl-phosphate) and, to a lesser extent, to the presence of a readily available carbon source (oleic acid). Otherwise, the micro emulsion nature of the formulation and its physical properties seem to play a major role in accelerating hexadecane mineralization.  相似文献   
132.
The nucleotide sequence data reported in this paper have been submitted to the EMBL/GenBank nucleotide sequence database and have been assigned the accession number Z48631. The name listed for this sequence was officially assigned by the WHO Nomenclature Committee in November 1994. This follows the agreed policy that, subject to the conditions stated in the most recent Nomenclature Report (Bodmer et al. 1994), names will be assigned to new sequences as they are identified. Lists of such new names will be published in the following WHO Nomenclature Report  相似文献   
133.
134.
135.
    
Interactions between the Streptococcus milleri-group organisms (SMG; S. intermedius, S. constellatus and S. anginosus) and Eikenella corrodens were investigated. Coaggregation reactions occurred frequently between S. anginosus (83% of strain combinations) or S. constellatus (87%) and E. corrodens isolates, but were infrequent between S. intermedius and E. corrodens (28%). No enhancement of enzyme activities against lipid, phosphate, peptide and saccharide substrates tested were detected with combinations of species in comparison to the species alone. Exponential growth of S. constellatus and S. intermedius, in mixed culture with E. corrodens, occurred within 6h post inoculation, in comparison to 25h without E. corrodens. No growth stimulation of S. anginosus was observed. It is concluded that both coaggregation and growth stimulation occur between E. corrodens and SMG isolates, and may be important mechanisms in the establishment of mixed infections involving these bacteria.  相似文献   
136.
Recombinant human interleukin 1α (rh IL-1α) and etoposide (VP-16) synergize for direct growth inhibition of several human tumor cell linesin vitro. Our previous studies demonstrated that VP-16 increased the number of membrane-associated IL-1 receptors (IL-1Rs) and also enhanced the internalization of receptor-bound rh IL-1α. The purposes of this study were to test our hypothess that these events were critical to the synergy between rhIL-1α and VP-16, to determine whether rhIL-1α and VP-16 synergize to increase superoxide (SO) anion radical productionin vitro since SO anion has been implicated in the toxic effects of IL-1, and to investigate the antitumor efficacy of the combinaton against tumors in vivo. A375/C6 melanoma cells and OVCAR-3 ovarian carcinoma cells were tested with IL-1 receptor antagonist (IL-1ra) before exposure to rhIL-1α, VP-16 and rhIL-1α plus VP-16. The synergistic or antagonistic effects were assessed by MTT assay. SO production was measured by reduction of cytochrome C. Athymic female mice bearing the A375/C6 melanoma were treated by rhIL-1α, VP-16, and rhIL-1α+VP-16. The antitumor effects were evaluated by quantitating tumor growth and survival time. Pretreatment with the IL-1ra abrogated the synergistic effects of rhIL-1α and VP-16. The production of SO radical by A375/C6 cells was increased 2.5 fold by the combination of rhIL-1α and VP-16, and the addition of exogenous SOD blocked the synergy between rhIL-1α and VP-16. However, when A375/S0D15 cells which over-expressed manganese superoxide dismutase (MnSOD) after MnSOD cDNA transfecton were exposed to rhIL-1α and VP-16, in vitro antagonism was observed. In vivo studies demonstrated that the combination of rhIL-1α and VP-16 delayed tumor growth better than either agent alone, although long-term survival was not improved because of substantial toxicity. Our results suggest that the synergistic antitumor effects of IL-1α and VP-16 may be due to IL-1R modulation and increased internalization of IL-1-IL-1R complex by VP-16 treatment, as well as to a subsequent increase in SO anion radical production from the tumor cells exposed to both drugs. Thus, the combnation of IL-1α and VP-16 might prove useful for the treatment of malignant diseasein vivo, if the increased toxicity can be reduced or managed. The US Government’s right to retain a non-exclusive royalty-free license on and to any copyright is acknowledged.  相似文献   
137.
138.
Two experiments were conducted to compare the utility of in vitro- and in vivo-derived bovine blastocysts for the isolation of pluripotent epiblasts. In experiment 1, the inner cell masses (ICMs) of in vivo-collected blastocysts yielded a higher proportion of epiblasts after culture on STO feeder cells than ICMs from in vitro-produced blastocysts (P = .0157). In experiment 2, ICMs of in vivo-collected blastocysts that hatched on day 8 yielded a greater proportion of epiblasts after culture on STO feeder cells than ICMs from in vitro-produced blastocysts that hatched on day 8. The difference was reversed but smaller for blastocysts that hatched on day 9 (Interaction, P = .0125). Epiblasts from blastocysts that hatched on day 8 regardless of their source generated more differentiated cell lines in extended culture than did blastocysts that hatched on day 9. Extended epiblast culture yielded cells identifiable as products of the three embryonic germ layers that included epithelial cells, fibroblasts, neuronal cells, hepatocyte-like cells, and macrophage-like cells. Alkaline phosphatase activity combined with cell morphology identified the bovine epiblast cells and distinguished them from trophectoderm and endoderm that frequently contaminated epiblast cell cultures. In vivo-derived blastocysts, especially from early-hatching blastocysts, were a superior source of pluripotent epiblasts. Epiblast cells in this study all differentiated or senesced indicating that standard conditions for mouse embryonic stem cell culture do not maintain bovine epiblast cells in an undifferentiated state. © 1995 wiley-Liss, Inc.
  • 1 This artilce is a US Government work and, as such, is in the public domain in the United States of America.
  •   相似文献   
    139.
    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