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   5240篇
  免费   502篇
  国内免费   1篇
  5743篇
  2023年   21篇
  2022年   42篇
  2021年   88篇
  2020年   36篇
  2019年   61篇
  2018年   49篇
  2017年   41篇
  2016年   110篇
  2015年   227篇
  2014年   251篇
  2013年   321篇
  2012年   379篇
  2011年   362篇
  2010年   268篇
  2009年   235篇
  2008年   360篇
  2007年   332篇
  2006年   367篇
  2005年   337篇
  2004年   318篇
  2003年   345篇
  2002年   282篇
  2001年   62篇
  2000年   41篇
  1999年   70篇
  1998年   100篇
  1997年   60篇
  1996年   53篇
  1995年   53篇
  1994年   40篇
  1993年   49篇
  1992年   41篇
  1991年   33篇
  1990年   26篇
  1989年   30篇
  1988年   26篇
  1987年   19篇
  1986年   28篇
  1985年   21篇
  1984年   17篇
  1983年   19篇
  1982年   18篇
  1981年   23篇
  1980年   22篇
  1979年   9篇
  1978年   10篇
  1977年   8篇
  1976年   5篇
  1973年   6篇
  1968年   5篇
排序方式: 共有5743条查询结果,搜索用时 11 毫秒
71.
72.
73.
To date, no vaccine that is safe and effective against herpes simplex virus 2 (HSV-2) disease has been licensed. In this study, we evaluated a DNA prime-formalin-inactivated-HSV-2 (FI-HSV2) boost vaccine approach in the guinea pig model of acute and recurrent HSV-2 genital disease. Five groups of guinea pigs were immunized and intravaginally challenged with HSV-2. Two groups were primed with plasmid DNAs encoding the secreted form of glycoprotein D2 (gD2t) together with two genes required for viral replication, either the helicase (UL5) and DNA polymerase (UL30) genes or the single-stranded DNA binding protein (UL29) and primase (UL52) genes. Both DNA-primed groups were boosted with FI-HSV2 formulated with monophosphoryl lipid A (MPL) and alum adjuvants. Two additional groups were primed with the empty backbone plasmid DNA (pVAX). These two groups were boosted with MPL and alum (MPL-alum) together with either formalin-inactivated mock HSV-2 (FI-Mock) or with FI-HSV2. The final group was immunized with gD2t protein in MPL-alum. After challenge, 0/9 animals in the group primed with UL5, UL30, and gD2t DNAs and all 10 animals in the mock-immunized control group (pVAX-FI-Mock) developed primary lesions. All mock controls developed recurrent lesions through day 100 postchallenge. Only 1 guinea pig in the group primed with pVAX DNA and boosted with FI-HSV2 (pVAX-FI-HSV2 group) and 2 guinea pigs in the group primed with UL5, UL30, and gD2t DNAs and boosted with FI-HSV2 (UL5, UL30, gD2t DNA-FI-HSV2 group) developed recurrent lesions. Strikingly, the UL5, UL30, gD2t DNA-FI-HSV2 group showed a 97% reduction in recurrent lesion days compared with the mock controls, had the highest reduction in days with recurrent disease, and contained the lowest mean HSV-2 DNA load in the dorsal root ganglia.  相似文献   
74.
75.
The interactions of metabolites of the antidiabetic vanadium-containing drug bis(maltolato)oxovanadium(IV) (BMOV) with lipid interface model systems were investigated and the results were used to describe a potentially novel mechanism by which these compounds initiate membrane-receptor-mediated signal transduction. Specifically, spectroscopic studies probed the BMOV oxidation and hydrolysis product interaction with interfaces created from cetyltrimethylammonium bromide (CTAB) which mimics the positively charged head group on phosphatidylcholine. 1H and 51V NMR spectroscopies were used to determine the location of the dioxobis(maltolato)oxovanadate(V) and the maltol ligand in micelles and reverse micelles by measuring changes in the chemical shift, signal linewidth, and species distribution. Both micelles and reverse micelles interacted similarly with the complex and the ligand, suggesting that interaction is strong as anticipated by Coulombic attraction between the positively charged lipid head group and the negatively charged complex and deprotonated ligand. The nature of the model system was confirmed using dynamic light scattering studies and conductivity measurements. Interactions of the complex/ligand above and below the critical micelle concentration of micelle formation were different, with much stronger interactions when CTAB was in the form of a micelle. Both the complex and the ligand penetrated the lipid interface and were located near the charged head group. These studies demonstrate that a lipid-like interface affects the stability of the complex and raise the possibility that ligand exchange at the interface may be important for the mode of action for these systems. Combined, these studies support recently reported in vivo observations of BMOV penetration into 3T3-L1 adipocyte membranes and increased translocation of a glucose transporter to the plasma membrane.  相似文献   
76.
To improve the management of leishmaniasis, new drugs and/or alternative therapeutic strategies are required. Combination therapy of antileishmanial drugs is currently considered as one of the most rational approaches to lower treatment failure rate and limit drug resistance spreading. Nicotinamide (NAm), also known as vitamin B3 that is already is used in human therapy, exerts in vitro antileishmanial activity. Drug combination studies, performed on L. infantum axenic amastigotes, revealed that NAm significantly improves the antileishmanial activity of trivalent antimony in a synergistic manner while it shows additive activity with amphotericin B and slightly antagonizes pentamidine activity. NAm also significantly increases the toxicity of pentavalent antimony against the intracellular forms of L. infantum, L. amazonensis and L. braziliensis. The potential of NAm to be used as adjuvant during leishmaniasis chemotherapy is further discussed.  相似文献   
77.
Classical genetic studies discovered loss of genes from the ancient sex chromosome systems of several animals (genetic degeneration), and complete genome sequencing confirms that the heterogametic sex is hemizygous for most sex-linked genes. Genetic degeneration is thought to result from the absence of recombination between the sex chromosome pair (reviewed by [1]) and is very rapid after sex chromosome-autosome fusions in Drosophila [2-4]. Plant sex chromosome systems allow study of the time course of degeneration, because they evolved from a state wholly without sex chromosomes (rather than after a large genome region fused to a preexisting sex chromosome), and, in several taxa, recombination stopped very recently. However, despite increasing genetic and physical mapping of plant nonrecombining sex-determining regions [5-8], it remains very difficult to discover sex-linked genes, and it is unclear whether Y-linked genes are losing full function. We therefore developed a high-throughput method using RNA-Seq to identify sex linkage in Silene latifolia. Recombination suppression between this plant's XY sex chromosome pair started only about 10 million years ago [9]. Our approach identifies several hundred new sex-linked genes, and we show that this young Y chromosome retains many genes, yet these already have slightly reduced gene expression and are accumulating changes likely to reduce protein functions.  相似文献   
78.
Background information. CRISP2 (cysteine‐rich secretory protein 2) is a sperm acrosome and tail protein with the ability to regulate Ca2+ flow through ryanodine receptors. Based on these properties, CRISP2 has a potential role in fertilization through the regulation of ion signalling in the acrosome reaction and sperm motility. The purpose of the present study was to determine the expression, subcellular localization and the role in spermatogenesis of a novel CRISP2‐binding partner, which we have designated SHTAP (sperm head and tail associated protein). Results. Using yeast two‐hybrid screens of an adult testis expression library, we identified SHTAP as a novel mouse CRISP2‐binding partner. Sequence analysis of all Shtap cDNA clones revealed that the mouse Shtap gene is embedded within a gene encoding the unrelated protein NSUN4 (NOL1/NOP2/Sun domain family member 4). Five orthologues of the Shtap gene have been annotated in public databases. SHTAP and its orthologues showed no significant sequence similarity to any known protein or functional motifs, including NSUN4. Using an SHTAP antiserum, multiple SHTAP isoforms (~20–87 kDa) were detected in the testis, sperm, and various somatic tissues. Interestingly, only the ~26 kDa isoform of SHTAP was able to interact with CRISP2. Furthermore, yeast two‐hybrid assays showed that both the CAP (CRISP/antigen 5/pathogenesis related‐1) and CRISP domains of CRISP2 were required for maximal binding to SHTAP. SHTAP protein was localized to the peri‐acrosomal region of round spermatids, and the head and tail of the elongated spermatids and sperm tail where it co‐localized with CRISP2. During sperm capacitation, SHTAP and the SHTAP—CRISP2 complex appeared to be redistributed within the head. Conclusions. The present study is the first report of the identification, annotation and expression analysis of the mouse Shtap gene. The redistribution observed during sperm capacitation raises the possibility that SHTAP and the SHTAP—CRISP2 complex play a role in the attainment of sperm functional competence.  相似文献   
79.
Eleven homoisoflavonoids and two xanthones were isolated and characterized from the bulbs of Ledebouria graminifolia. Five of the homoisoflavonoids are new compounds and were identified as: 5-hydroxy-7-methoxy-3-(4'-hydroxybenzyl)-4-chromanone, 5-hydroxy-6,7-dimethoxy-3-(4'-hydroxybenzyl)-4-chromanone, 5,7,8-trimethoxy-3-(4'-hydroxybenzyl)-4-chromanone, 5-hydroxy-3',4',7-trimethoxyspiro[2H-1-benzopyran-7'-bicyclo[4.2.0]octa-trien]-4-one, 5,7-dihydroxy-3',4'-dimethoxyspiro[2H-1-benzopyran-7'-bicyclo[4.2.0]octa-trien]-4-one. Structures were elucidated by extensive 1D, and 2D NMR spectroscopy and HRMS. A method for tissue culture was developed and the bulbs of mature plants were found to contain all the compounds isolated from the wild specimens of L. graminifolia.  相似文献   
80.
Recent advances in legume transformation   总被引:29,自引:0,他引:29       下载免费PDF全文
  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