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   7394篇
  免费   556篇
  国内免费   547篇
  8497篇
  2024年   10篇
  2023年   104篇
  2022年   254篇
  2021年   445篇
  2020年   255篇
  2019年   323篇
  2018年   283篇
  2017年   244篇
  2016年   315篇
  2015年   434篇
  2014年   533篇
  2013年   546篇
  2012年   662篇
  2011年   564篇
  2010年   334篇
  2009年   351篇
  2008年   379篇
  2007年   305篇
  2006年   283篇
  2005年   208篇
  2004年   219篇
  2003年   214篇
  2002年   136篇
  2001年   136篇
  2000年   128篇
  1999年   144篇
  1998年   84篇
  1997年   70篇
  1996年   81篇
  1995年   70篇
  1994年   62篇
  1993年   31篇
  1992年   62篇
  1991年   43篇
  1990年   40篇
  1989年   22篇
  1988年   24篇
  1987年   28篇
  1986年   16篇
  1985年   33篇
  1984年   9篇
  1983年   5篇
  1982年   2篇
  1981年   3篇
  1980年   1篇
  1979年   2篇
排序方式: 共有8497条查询结果,搜索用时 15 毫秒
41.
We present a multimodal in vivo skin imaging instrument that is capable of simultaneously acquiring multiphoton and reflectance confocal images at up to 27 frames per second with 256 × 256 pixel resolution without the use of exogenous contrast agents. A single femtosecond laser excitation source is used for all channels ensuring perfect image registration between the two‐photon fluorescence (TPF), second harmonic generation (SHG), and reflectance confocal microscopy (RCM) images. Images and videos acquired with the system show that the three imaging channels provide complementary information in in vivo human skin measurements. In the epidermis, cell boundaries are clearly seen in the RCM channel, while cytoplasm is better seen in the TPF imaging channel, whereas in the dermis, SHG and TPF channels show collagen bundles and elastin fibers, respectively. The demonstrated fast imaging speed and multimodal imaging capabilities of this MPM/RCM instrument are essential features for future clinical application of this technique. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
42.
以肠炎沙门氏菌脂多糖为抗原,用酶标法测定Vi多糖菌苗免疫血清的抗LPS抗体。各Vi多糖菌苗组免疫后1月,6月的抗LPS水平均显著高于免前(P<0.0001),对照组无显著差异(p>0.1)。两30μg菌苗组抗LPS阳转率均约为15%。提纯Vi多糖菌苗所含的微量伤寒LPS,也可能为接种者提供一定的保护作用。  相似文献   
43.
为研究浙江西门岛海洋特别保护区大型底栖动物功能群的变化规律及其与环境因子的关系,作者分别于2010年4月(春季)、11月(秋季),2011年8月(夏季)和2012年2月(冬季)进行了4个航次的大型底栖动物调查,共鉴定出大型底栖动物78种,根据其食性类型划分为浮游生物食者、植食者、肉食者、杂食者、碎屑食者5种功能群.各功能群平均密度从高到低依次为浮游生物食者>肉食者>植食者>碎屑食者>杂食者,平均生物量从高到低依次为浮游生物食者>碎屑食者>肉食者>杂食者>植食者.单因素方差分析结果表明,大型底栖动物各功能群的密度和生物量季节间均无显著性差异.典范对应分析结果表明,影响大型底栖动物功能群的主要环境因子包括温度、溶解氧、溶解态无机磷和表层沉积物的中值粒径,排序轴对功能群-环境关系的贡献率计算结果表明环境变量可以较好地解释功能群的变化情况.  相似文献   
44.
Selectins play a major role in the inflammatory reaction by initiating neutrophil attachment to activated vascular endothelium. Some heparin preparations can interact with L- and P-selectin; however, the determinants required for inhibiting selectin-mediated cell adhesion have not yet been characterized. We now report that carboxyl-reduced and sulfated heparin (prepared by chemical modifications of porcine intestinal mucosal heparin leading to the replacement of carboxylates by O-sulfate groups) and trestatin A sulfate (obtained by sulfation of trestatin A, a non-uronic pseudo-nonasaccharide extracted from Streptomyces dimorphogenes) exhibit strong anti-P-selectin and anti-L-selectin activity while lacking antithrombin-mediated anticoagulant activity. In vitro experiments revealed that both compounds inhibited P-selectin- and L-selectin-mediated cell adhesion under laminar flow conditions. Moreover, carboxyl-reduced and sulfated heparin and trestatin A sulfate were also active in vivo, as assessed by experiments showing 1) that microinfusion of trestatin A sulfate reduced by 96% leukocyte rolling along rat mesenteric postcapillary venules and 2) that both compounds inhibited (by 58-81%) neutrophil migration into thioglycollate-inflamed peritoneum of BALB/c mice. These results indicate that nonanticoagulant sulfated saccharides targeted at P-selectin and L-selectin may have therapeutic potential in inflammatory disorders.  相似文献   
45.
46.
47.
The immunological characteristics of SARS-CoV spike protein were investigated by administering mice with plasmids encoding various S gene fragments. We showed that the secreting forms of S1, S2 subunits and the N-terminus of S1 subunit (residues 18-495) were capable of eliciting SARS-CoV specific antibodies and the region immediate to N-terminus of matured S1 protein contained an important immunogenic determinant for elicitation of SARS-CoV specific antibodies. In addition, mice immunized with plasmids encoding S1 fragment developed a Th1-mediated antibody isotype switching. Another interesting finding was that mouse antibodies elicited separately by plasmids encoding S1 and S2 subunits cooperatively neutralized SARS-CoV but neither the S1 nor S2 specific antibodies did, suggesting the possible role of both S1 and S2 subunits in host cell docking and entry. These results provide insights into understanding the immunological characteristics of spike protein and the development of subunit vaccines against SARS-CoV.  相似文献   
48.
We have generated a number of mAb against various epitopes on the external envelope glycoprotein, gp46, of human T cell leukemia virus type I (HTLV-I) from a WKA rat immunized with a recombinant vaccinia virus containing the HTLV-I env gene. Among these mAb, one group of mAb, represented by a mAb designated LAT-27, could neutralize the infectivity of HTLV-I, as determined by a HTLV-I-mediated cell fusion inhibition assay. LAT-27 also interfered with transformation of normal T lymphocytes by HTLV-I in vitro. An antibody-binding assay using overlapping synthetic oligopeptides showed that LAT-27 bound specifically to 10-mer peptides that contained the gp46 amino acid sequence 191-196 (Leu-Pro-His-Ser-Asn-Leu). Antibodies from HTLV-I+ humans interfered with the binding of LAT-27 to gp46 Ag. Sera from rabbits immunized with a LAT-27-reactive peptide, 190-199, conjugated with OVA, but not sera from OVA-immunized rabbits, reacted with gp46 Ag and neutralized infectivity of HTLV-I. These results show that the HTLV-I neutralization epitope recognized by LAT-27 locates to the gp46 amino acids 191-196, and that immunization with a peptide containing the LAT-27 epitope can elicit an HTLV-I neutralizing antibody response.  相似文献   
49.
Human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) hold great potential for their therapeutic use in various clinical diseases. Many publications have reported on human blood-derived alternatives to animal serum for culturing mesenchymal stem cells, such as human serum, allogenic umbilical cord blood serum, and human platelet derivatives. However, it is not clear whether human umbilical cord blood plasma (UCBP), as the surplusage of umbilical cord blood mesenchymal stem cell extraction, could be used. In this study, in order to make the best of umbilical cord blood, the human UCBP was dialyzed to replace fetal bovine serum (FBS) in the culture medium. hUC-MSCs were cultured in the new medium. Cell growth rate, specific biomarkers, and differentiation properties were detected to characterize the cell proliferation and MSC-specific properties. The hUC-MSCs cultured in such derived medium were verified with proliferation rate, cluster differentiation markers, cell cycle, as well as differentiation capabilities. Such dialyzed human UCBP is fully comparable with, if not superior to, FBS in deriving and culturing hUC-MSCs.  相似文献   
50.
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