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   142276篇
  免费   9548篇
  国内免费   37篇
  2022年   690篇
  2021年   1816篇
  2020年   1388篇
  2019年   1491篇
  2018年   3087篇
  2017年   2769篇
  2016年   4024篇
  2015年   5846篇
  2014年   6071篇
  2013年   8117篇
  2012年   9880篇
  2011年   9191篇
  2010年   5953篇
  2009年   4780篇
  2008年   7373篇
  2007年   7176篇
  2006年   6951篇
  2005年   6386篇
  2004年   6334篇
  2003年   5809篇
  2002年   5541篇
  2001年   2754篇
  2000年   2442篇
  1999年   2196篇
  1998年   1508篇
  1997年   1055篇
  1996年   1114篇
  1995年   1058篇
  1994年   1014篇
  1993年   969篇
  1992年   1462篇
  1991年   1310篇
  1990年   1219篇
  1989年   1305篇
  1988年   1139篇
  1987年   1102篇
  1986年   1035篇
  1985年   1156篇
  1984年   1084篇
  1983年   936篇
  1982年   930篇
  1981年   844篇
  1980年   774篇
  1979年   922篇
  1978年   798篇
  1977年   789篇
  1975年   810篇
  1974年   875篇
  1973年   831篇
  1969年   732篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
83.
Plots of fresh pulverized fuel ash (PFA, an industrial waste) were inoculated with soils from existing PFA sites and fertilizers in a factorial design, then left unmanaged for 12 years during which time the floral development and soil chemistry were monitored annually. For the first 3 years, the site supported a sparse mix of chenopods (including the scarce Chenopodium glaucum ) and halophytes. As salinity declined, ruderals, legumes, and grasses plus the fire-site moss Funaria hygrometrica colonized, followed by Festuca arundinacea grassland (NVC community MG12) and Hippophae rhamnoides scrub. Dactylorhiza incarnata (orchidacea) appeared after 7 years, but only in plots that had received soil from existing orchid colonies. Four years later, a larger second generation of Dactylorhiza appeared, but only in the central zone of the site where vegetation was thinnest. By year 12, the site was dominated by coarse grasses and scrub, with early successional species persisting only in the sparsely vegetated center, where nitrate levels were lowest. This edge effect is interpreted as centripetal encroachment, a process of potentially wider concern for the conservation of low-fertility habitat patches. Overall, seed bank inoculation seems to have introduced few but desirable species ( D. incarnata , Pyrola rotundifolia , some halophytes, and annuals), whereas initial application of organic fertilizer had long-lasting (≥10 years) effects on cover and soil composition.  相似文献   
84.
85.
The in vitro determination of the effects of some pharmacological agents on the outer diameter and axial tension of human Fallopian tube ampullar segments showed that some drugs may act on the circular and longitudinal smooth muscle layers relatively separately. PGF2 alpha elicited an excitatory response in both muscle layers while norepinephrine and isoproterenol decreased the activity. Oxytocin and indomethacin had relatively limited effects on the spontaneous motility of the ampullar segments. The calcium antagonist verapamil inhibited the spontaneous periodic activity.  相似文献   
86.
87.
A strain of 1,507 typised donors enables 15.97 average donors to be selected for a thrombocyte transfusion in one of 75 patients selected at random with HLA antibodies being previously determined (1 to 66 donors per patient). HLA compatible donors were found for 72 patients (97.33 per cent). More than 5 HLA compatible donors could be found for 58 patients. The high number of compatible donors is based on the fact that among 1,507 donors there were 156 HLA homozygotes and 556 donors with 3 HLA-A or B-antigens respectively. Compatibility in the ABO-system was not taken into account.  相似文献   
88.
Lateral membrane heterogeneity, in the form of lipid rafts and microdomains, is currently implicated in cell processes including signal transduction, endocytosis, and cholesterol trafficking. Various biophysical techniques have been used to detect and characterize lateral membrane domains. Among these, Förster resonance energy transfer (FRET) has the crucial advantage of being sensitive to domain sizes smaller than 50-100 nm, below the resolution of optical microscopy but, apparently, similar to those of rafts in cell membranes. In the last decade, several formalisms for the analysis of FRET in heterogeneous membrane systems have been derived and applied to the study of microdomains. They are critically described and illustrated here.  相似文献   
89.
90.
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