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   2220篇
  免费   134篇
  2023年   10篇
  2021年   34篇
  2020年   15篇
  2019年   25篇
  2018年   36篇
  2017年   27篇
  2016年   45篇
  2015年   62篇
  2014年   87篇
  2013年   149篇
  2012年   134篇
  2011年   127篇
  2010年   87篇
  2009年   66篇
  2008年   126篇
  2007年   122篇
  2006年   130篇
  2005年   112篇
  2004年   85篇
  2003年   104篇
  2002年   87篇
  2001年   59篇
  2000年   58篇
  1999年   55篇
  1998年   20篇
  1997年   25篇
  1996年   31篇
  1995年   20篇
  1994年   13篇
  1993年   15篇
  1992年   38篇
  1991年   46篇
  1990年   27篇
  1989年   28篇
  1988年   22篇
  1987年   23篇
  1986年   26篇
  1985年   22篇
  1984年   18篇
  1983年   20篇
  1982年   14篇
  1981年   17篇
  1979年   6篇
  1978年   7篇
  1977年   14篇
  1976年   6篇
  1975年   10篇
  1974年   11篇
  1973年   5篇
  1968年   5篇
排序方式: 共有2354条查询结果,搜索用时 15 毫秒
41.
The isolation of Chlamydia pneumoniae, especially from elderly persons, is generally not easy. Recently, we succeeded in isolating a chlamydial strain, which was designated KKpn-15, from a 57-year-old man suffering from acute bronchitis. It was compared with well established strains of C. pneumoniae, C. trachomatis and C. psittaci, and its biological properties, such as the morphology of elementary bodies (EBs) and inclusions, and the immunochemistry of EB proteins, were investigated. Based on the results obtained in the present study, it was confirmed that the new chlamydial strain, KKpn-15, is a member of the C. pneumoniae strain and that the organisms of KKpn-15 are useful as an antigen for the serodiagnosis and epidemiology of C. pneumoniae infection.  相似文献   
42.
Abstract: Compositions of neutral and sulfated glucuronyl glycosphingolipids purified from human motor and sensory nerves and myelins were studied. Higher neutral glycosphingolipids (fraction B), which were separated from GazlCer (fraction A), were analyzed by TLC and TLC-immunostaining. Both nerve myelins contained paragloboside (nLc4Cer) and nLc6Cer dominantly as major higher glycosphingolipids and very little globoside (Gb4Cer), whereas both nerves contained Gb4Cer and nLc4Cer. Besides these major glycosphingolipids, a neutral glycolipid containing asialoGMI (Gg4Cer) epitope and other minor components such as ceramide trihexoside and ceramide dihexoside were detected in both nerves and their myelins. Furthermore, sulfated glucuronyl nLc4Cer and n Lc6Cer, which were monoclonal antibody HNK-1 reactive glycolipids, were detected in both nerves and myelins.  相似文献   
43.
Adeno-associated virus (AAV)-based gene therapy holds promise as a fundamental treatment for genetic disorders. For clinical applications, it is necessary to control AAV release timing to avoid an immune response to AAV. Here we propose an ultrasound (US)-triggered on-demand AAV release system using alginate hydrogel microbeads (AHMs) with a release enhancer. By using a centrifuge-based microdroplet shooting device, the AHMs encapsulating AAV with tungsten microparticles (W-MPs) are fabricated. Since W-MPs work as release enhancers, the AHMs have high sensitivity to the US with localized variation in acoustic impedance for improving the release of AAV. Furthermore, AHMs were coated with poly-l -lysine (PLL) to adjust the release of AAV. By applying US to the AAV encapsulating AHMs with W-MPs, the AAV was released on demand, and gene transfection to cells by AAV was confirmed without loss of AAV activity. This proposed US-triggered AAV release system expands methodological possibilities in gene therapy.  相似文献   
44.
45.
Methyl , a 3-O hexyl analogue of the octaosyl component of fungal lipooligosaccharide HS-142-1, was stereo- and regioselectively synthesized as a potent antagonist for the tetrameric atrial natriuretic peptide (ANP) receptors.  相似文献   
46.
47.
We have cloned a novel cDNA (Spa-1) which is little expressed in the quiescent state but induced in the interleukin 2-stimulated cycling state of an interleukin 2-responsive murine lymphoid cell line by differential hybridization. Spa-1 mRNA (3.5 kb) was induced in normal lymphocytes following various types of mitogenic stimulation. In normal organs it is preferentially expressed in both fetal and adult lymphohematopoietic tissues. A Spa-1-encoded protein of 68 kDa is localized mostly in the nucleus. Its N-terminal domain is highly homologous to a human Rap1 GTPase-activating protein (GAP), and a fusion protein of this domain (SpanN) indeed exhibited GAP activity for Rap1/Rsr1 but not for Ras or Rho in vitro. Unlike the human Rap1 GAP, however, SpanN also exhibited GAP activity for Ran, so far the only known Ras-related GTPase in the nucleus. In the presence of serum, stable Spa-1 cDNA transfectants of NIH 3T3 cells (NIH/Spa-1) hardly overexpressed Spa-1 (p68), and they grew as normally as did the parental cells. When NIH/Spa-1 cells were serum starved to be arrested in the G1/G0 phase of the cell cycle, however, they, unlike the control cells, exhibited progressive Spa-1 p68 accumulation, and following the addition of serum they showed cell death resembling mitotic catastrophes of the S phase during cell cycle progression. The results indicate that the novel nuclear protein Spa-1, with a potentially active Ran GAP domain, severely hampers the mitogen-induced cell cycle progression when abnormally and/or prematurely expressed. Functions of the Spa-1 protein and its regulation are discussed in the context of its possible interaction with the Ran/RCC-1 system, which is involved in the coordinated nuclear functions, including cell division.  相似文献   
48.
The fast atom bombardment (FAB) collision induced dissociation (CID)-mass spectrometry/mass spectrometry (MS/MS) technique was successfully applied to characterize and identify the structures of the immunoreactive trisulfated and tetrasulfated tetrasaccharides that were obtained from the chondroitin sulfate in a shark fin using a treatment with chondroitinase ABC.Abbreviations FABMS fast atom bombardment mass spectrometry - CID collision induced dissociation - MS/MS mass spectrometry/mass spectrometry - UA2S-GalNAc6S 2-acetamido-2-deoxy-3-O-(2-O-sulfo--d-gluco-4-enepyranosyluronic acid)-6-O-sulfo-d-galactose - UA-GalNAc4S 2-acetamido-2-deoxy-3-O-(-d-gluco-4-enepyranosyluronic acid)-4-O-sulfo-d-galactose - UA-GalNAcDiS 2-acetamido-2-deoxy-3-O-(-d-gluco-4-enepyranosyluronic acid)-4,6-di-O-sulfo-d-galactose  相似文献   
49.
The glycopeptides 1 and 2 ), carrying the core structure of serine-linked cell-surface proteoglycans were synthesized in a stereocontrolled manner. The carbohydrate key imidate xylosyl donors 3 and glycotetraosyl donors 4 and 5, as well as a tetrapeptide glycosyl acceptor 6, were coupled in the crucial glycosylation step. In these reactions, the application of either trimethylsilyl trifluoromethanesulfonate (TMSOTf) or borontrifluoride etherate (BF3-Et2O) as catalysts proved to be highly efficient. The serine linked glycopeptides 34, 36 and 37 thus obtained yielded target compounds 1 and 2 on complete deprotection.  相似文献   
50.
Rat erythrocyte phosphatidylethanolamine (PE) consists of 60% alkenylacyl, 5% alkylacyl and 35% diacyl types. The fatty acid at the 2-position of these types is mainly composed of arachidonic acid. When intact rat erythrocytes were incubated with exogenous arachidonic acid, about 90% of the arachidonic acid incorporated into the PE fraction was found in the 2-position of the diacyl type. The rates of incorporation of arachidonic acid into alkenylacyl-, alkylacyl- and diacylPE were 78, 134 and 1360 pmol/h per mumol of the corresponding PE, respectively. The substrate specificities of endogenous phospholipase A2 and acyl-CoA:lysophospholipid acyltransferase were observed. DiacylPE was hydrolysed rapidly by endogenous phospholipase A2, while alkenylacyl- and alkylacylPE were poor substrates for the enzyme. The selective transfer of arachidonic acid into the 2-position of 1-acyl-lysoPE was observed. 1-Alkenyl- and 1-alkyl-lysoPE were also poor substrates for acyl-CoA:lysophospholipid acyltransferase. The acyltransferase activities with the lysoPE analogues were higher than the phospholipase A2 activities with PE analogues. These results suggest that the different incorporation rates of arachidonic acid into alkenylacyl-, alkylacyl- and diacylPE are based on the substrate specificity of endogenous phospholipase A2.  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