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   811875篇
  免费   83749篇
  国内免费   309篇
  895933篇
  2018年   8118篇
  2017年   7729篇
  2016年   10879篇
  2015年   13891篇
  2014年   16494篇
  2013年   23882篇
  2012年   26753篇
  2011年   27593篇
  2010年   18801篇
  2009年   17368篇
  2008年   24709篇
  2007年   25667篇
  2006年   23997篇
  2005年   23097篇
  2004年   22848篇
  2003年   21981篇
  2002年   21472篇
  2001年   34884篇
  2000年   34322篇
  1999年   27746篇
  1998年   10369篇
  1997年   10397篇
  1996年   9977篇
  1995年   9185篇
  1994年   8868篇
  1993年   8872篇
  1992年   22474篇
  1991年   22036篇
  1990年   21468篇
  1989年   20921篇
  1988年   19218篇
  1987年   18430篇
  1986年   17209篇
  1985年   17095篇
  1984年   14087篇
  1983年   12338篇
  1982年   9387篇
  1981年   8535篇
  1980年   7922篇
  1979年   13063篇
  1978年   10347篇
  1977年   9320篇
  1976年   8916篇
  1975年   9935篇
  1974年   10619篇
  1973年   10478篇
  1972年   9548篇
  1971年   8538篇
  1970年   7449篇
  1969年   7347篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Mycotoxins are fungal metabolite which may in some cases exhibit a high health hazard potential. Mycotoxins can show carcinogenic, mutagenic, toxic, teratogenic or immunotoxic effects. Mycotoxin exposure in the workplace may occur through inhalation and skin contact,e.g. during occupational handling of organic matter such as livestock feed, food products, or waste. Various studies suggest that both acute and chronic effects can occur, depending at least on the exposure level. The magnitude of the potential health risks associated with a respiratory or dermal intake of mycotoxins has largely remained unclear to date. However, according to the directive 2000/54/EC on biological agents and the corresponding German Biological Agents Ordinance, employers are also required to consider the potential hazards posed by toxic effects of biological agents when assessing workplace risks. The aim of this article, therefore, is to present some basis information that should facilitate an evaluation of the significance of mycotoxins in the context of assessing workplace risks. It also provides suggestions for occupational health and safety measures.  相似文献   
995.
Abstract. Objectives: The ADAMs (a disintegrin and metalloproteinase) enzymes compose a family of membrane‐bound proteins characterized by their multi‐domain structure and ADAM‐12 expression is elevated in human non‐small cell lung cancers. The aim of this study was to investigate the roles played by ADAM‐12 in critical steps of bronchial cell transformation during carcinogenesis. Materials and methods: To assess the role of ADAM‐12 in tumorigenicity, BEAS‐2B cells were transfected with a plasmid encoding human full‐length ADAM‐12 cDNA, and then the effects of ADAM‐12 overexpression on cell behaviour were explored. Treatment of clones with heparin‐binding epidermal growth factor (EGF)‐like growth factor (HB‐EGF) neutralizing antibodies as well as an EGFR inhibitor allowed the dissection of mechanisms regulating cell proliferation and apoptosis. Results: Overexpression of ADAM‐12 in BEAS‐2B cells promoted cell proliferation. ADAM‐12 overexpressing clones produced higher quantities of HB‐EGF in their culture medium which may rely on membrane‐bound HB‐EGF shedding by ADAM‐12. Targeting HB‐EGF activity with a neutralizing antibody abrogated enhanced cell proliferation in the ADAM‐12 overexpressing clones. In sharp contrast, targeting of amphiregulin, EGF or transforming growth factor‐α failed to influence cell proliferation; moreover, ADAM‐12 transfectants were resistant to etoposide‐induced apoptosis and the use of a neutralizing antibody against HB‐EGF activity restored rates of apoptosis to be similar to controls.Conclusions: ADAM‐12 contributes to enhancing HB‐EGF shedding from plasma membranes leading to increased cell proliferation and reduced apoptosis in this bronchial epithelial cell line.  相似文献   
996.
997.
Electron micrographs of skin from xanthic (gold) sailfin mollies revealed numerous xanthophores, as well as scattered melanophores. The melanophores were seen to contain premelanosomes in various stages of development. This is consistent with the fact that xanthic mollies have been shown to be tyrosinase positive. Melanosomes in xanthic mollies appear to develop by one of two pathways: 1) from an endoplasmic reticulum-derived vesicle which develops an internal lamellar framework, and 2) by fusion of multiple Golgi-derived vesicles which lack an internal lamellar framework. Analysis of the pigments in the skin of the xanthic mollies identified four colorless pteridine pigments (xanthopterin, isoxanthopterin, neopterin, and pterin) and a carotenoid with an absorbance spectrum similar to beta-carotene. It appears that, unlike some other poeciliid fishes, sailfin mollies do not use pteridine pigments for orange coloration. Rather, they appear to rely primarily on carotenoids.  相似文献   
998.
999.
1000.
The test for the evaluation of the toxicity of different types of pertussis preparations as manifested by their in vitro influence on mouse thymic cells (T test) has been finally worked out. The use of the T test has made it possible to reveal the nonstandard character of the production lots of adsorbed diphtheria-pertussis-tetanus vaccines, both whole-cell vaccine and Japanese acellular vaccine. The degree of the in vitro damaging action of pertussis preparations on mouse thymic cells greatly depends on the residual content of Bordetella pertussis nontoxoidized toxin which, in contrast to B. pertussis lipopolysaccharide and filamentous hemagglutinin, produces pronounced cytotoxic action on mouse thymic cells.  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