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   18973篇
  免费   1379篇
  国内免费   1250篇
  21602篇
  2024年   41篇
  2023年   255篇
  2022年   540篇
  2021年   925篇
  2020年   565篇
  2019年   806篇
  2018年   801篇
  2017年   562篇
  2016年   830篇
  2015年   1103篇
  2014年   1347篇
  2013年   1449篇
  2012年   1678篇
  2011年   1518篇
  2010年   970篇
  2009年   935篇
  2008年   1043篇
  2007年   974篇
  2006年   795篇
  2005年   682篇
  2004年   528篇
  2003年   519篇
  2002年   439篇
  2001年   344篇
  2000年   301篇
  1999年   291篇
  1998年   166篇
  1997年   160篇
  1996年   155篇
  1995年   118篇
  1994年   85篇
  1993年   71篇
  1992年   110篇
  1991年   85篇
  1990年   68篇
  1989年   52篇
  1988年   43篇
  1987年   43篇
  1986年   38篇
  1985年   51篇
  1984年   8篇
  1983年   17篇
  1982年   9篇
  1981年   11篇
  1980年   7篇
  1979年   7篇
  1978年   6篇
  1977年   5篇
  1974年   5篇
  1969年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The chemoattractant receptor-homologous molecule expressed on T(H)2 cells (CRTH-2), also found on eosinophils and basophils, is a prostaglandin D2 receptor involved in the recruitment of these cell types during an inflammatory response. In this report, we describe the synthesis and optimization of a ramatroban isostere that is a selective and potent antagonist of CRTH-2 which may be useful in the treatment of certain diseases.  相似文献   
102.
Currently, three predominant subtypes of influenza virus are prevalent in pig populations worldwide: H1N1, H3N2, and H1N2. European avian-like H1N1 viruses, which were initially detected in European pig populations in 1979, have been circulating in pigs in eastern China since 2007. In this study, six influenza A viruses were isolated from 60 swine lung samples collected from January to April 2011 in eastern China. Based on whole genome sequencing, molecular characteristics of two isolates were determined. Phylogenetic analysis showed the eight genes of the two isolates were closely related to those of the avian-like H1N1 viruses circulating in pig populations, especially similar to those found in China. Four potential glycosylation sites were observed at positions 13, 26, 198, 277 in the HA1 proteins of the two isolates. Due to the presence of a stop codon at codon 12, the isolates contained truncated PB1-F2 proteins. In this study, the isolates contained 591Q, 627E and 701N in the polymerase subunit PB2, which had been shown to be determinants of virulence and host adaptation. The isolates also had a D rather than E at position 92 of the NS1, a marker of mammalian adaptation. Both isolates contained the GPKV motif at the PDZ ligand domain of the 3′ end of the NS1, a characteristic marker of the European avian-like swine viruses since about 1999, which is distinct from those of avian, human and classical swine viruses. The M2 proteins of the isolates have the mutation (S31N), a characteristic marker of the European avian-like swine viruses since about 1987, which may confer resistance to amantadine and rimantadine antivirals. Our findings further emphasize the importance of surveillance on the genetic diversity of influenza A viruses in pigs, and raise more concerns about the occurrence of cross-species transmission events.  相似文献   
103.
104.
105.
SAR studies on amides, ureas, and vinylogous amides derived from pyrrolidine led to the discovery of several potent hNK(1) antagonists. One particular vinylogous amide (45b) had excellent potency, selectivity, pharmacokinetic profile, and functional activity in vivo. An in vivo rhesus macaque brain receptor occupancy PET study for compound 45b revealed an estimated Occ(90) approximately 300 ng/ml.  相似文献   
106.
Transient receptor potential melastatin 7 (TRPM7) channels are divalent cation-selective ion channels that are permeable to Ca(2+) and Mg(2+). TRPM7 is ubiquitously expressed in vertebrate cells and contains both an ion channel and a kinase domain. TRPM7 plays an important role in regulating cellular homeostatic levels of Ca(2+) and Mg(2+) in mammalian cells. Although studies have shown that the kinase domain of TRPM7 is required for channel activation and can phosphorylate other target proteins, a systematic analysis of intact TRPM7 channel phosphorylation sites expressed in mammalian cells is lacking. We applied mass spectrometric proteomic techniques to identify and characterize the key phosphorylation sites in TRPM7 channels. We identified 14 phosphorylation sites in the cytoplasmic domain of TRPM7, eight of which have not been previously reported. The identification of phosphorylation sites using antibody-based immunopurification and mass spectrometry is an effective approach for defining the phosphorylation status of TRPM7 channels. The present results show that TRPM7 channels are phosphorylated at multiple sites, which serves as a mechanism to modulate the dynamic functions of TRPM7 channels in mammalian cells.  相似文献   
107.
体细胞克隆技术是将已分化的体细胞移到去核的成熟卵母细胞中,通过体外激活和培养,再移植入受体母畜子宫内,繁殖出具有相同基因型后代的一种技术。该技术可以大幅提升繁殖效率,并提供高质、充足和营养丰富的动物食品。近年来,美国、日本和欧洲等国家相继宣布体细胞克隆动物食品可以上市。然而,目前体细胞克隆效率相当低下,即使是出生的克隆动物也往往伴随发育畸形或高死亡率等现象,在对克隆动物发育异常知之甚少的情况下,宣布克隆动物产品上市是否为时过早?以下综述了克隆牛肉、奶及其产品安全。  相似文献   
108.
Chronic inflammation is closely associated with metabolic disorders such as obesity and type 2 diabetes, however, the underlying mechanism is unclear. Toll-like receptors (TLRs) play a key role in innate immune response as well as inflammatory signals. Here, we observed that mRNA level of TLR4 was induced during adipocyte differentiation and remarkably enhanced in fat tissues of obese db/db mice. In addition, activation of TLR4 with either LPS or free fatty acids stimulated NFkappaB signaling and expression of inflammatory cytokine genes, such as TNFalpha and IL-6 in 3T3-L1 adipocytes. Furthermore, we discovered that TLR4 activation in 3T3-L1 adipocytes provoked insulin resistance. Taken together, these results suggest that activation of TLR4 in adipocyte might be implicated in the onset of insulin resistance in obesity and type 2 diabetes.  相似文献   
109.
双探针原位杂交揭示稻属BB、cc 和EE基因组之间的分化 李常宝1 张大明1* 葛颂1 卢宝荣2 洪德元1  相似文献   
110.
从江浙蝮蛇中分离纯化的碱性磷脂酶A2在pH9.5,0.05mmol/LCHES缓冲液中,用汽相悬滴扩散的方法,获得了适用于高分辨率X射线结构分析的单晶.经X200B面探测器分析,表明该晶体属于正交晶系,P2I2I2I空间群,晶胞参数为a=97.13,b=103.69,c=23.27.并收集了一套衍射数据,独立衍射点数12001个,数据完整度为86.2%,Rmerge为0.0459.最高分辨率达2.0,根据分子量与晶胞体积估算,一个不对称单位含两个分子.  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