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   50285篇
  免费   4168篇
  国内免费   2860篇
  57313篇
  2024年   91篇
  2023年   551篇
  2022年   1361篇
  2021年   2189篇
  2020年   1445篇
  2019年   1934篇
  2018年   1841篇
  2017年   1309篇
  2016年   1985篇
  2015年   2886篇
  2014年   3391篇
  2013年   3793篇
  2012年   4224篇
  2011年   3925篇
  2010年   2397篇
  2009年   2097篇
  2008年   2610篇
  2007年   2351篇
  2006年   2040篇
  2005年   1712篇
  2004年   1481篇
  2003年   1419篇
  2002年   1169篇
  2001年   1034篇
  2000年   939篇
  1999年   877篇
  1998年   480篇
  1997年   455篇
  1996年   435篇
  1995年   393篇
  1994年   368篇
  1993年   270篇
  1992年   444篇
  1991年   421篇
  1990年   327篇
  1989年   314篇
  1988年   270篇
  1987年   221篇
  1986年   183篇
  1985年   212篇
  1984年   147篇
  1983年   128篇
  1982年   106篇
  1981年   114篇
  1979年   114篇
  1978年   91篇
  1977年   71篇
  1975年   88篇
  1974年   89篇
  1973年   81篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Summary The HPV oncoproteins E6 and E7 are consistently expressed in HPV-associated cancer cells and are responsible for their malignant transformation. Therefore, HPV E6 and E7 are ideal target antigens for developing vaccines and immunotherapeutic strategies against HPV-associated neoplasms. Recently, it has been demonstrated that codon optimization of the HPV-16 E7 gene resulted in highly efficient translation of E7 and increased the immunogenicity of E7-specific DNA vaccines. Since vaccines targeting E6 also represent an important strategy for controlling HPV-associated lesions, we developed a codon-optimized HPV-16 E6 DNA vaccine (pNGVL4a-E6/opt) and characterized the E6-specific CD8+ T cell immune responses as well as the protective and therapeutic anti-tumor effects in vaccinated C57BL/6 mice. Our data indicated that transfection of human embryonic kidney cells (293 cells) with pNGVL4a-E6/opt resulted in highly efficient translation of E6. In addition, vaccination with pNGVL4a-E6/opt significantly enhanced E6-specific CD8+ T cell immune responses in C57BL/6 mice. Mice vaccinated with pNGVL4a-E6/opt are able to generate potent protective and therapeutic antitumor effects against challenge with E6-expressing tumor cell line, TC-1. Thus, DNA vaccines encoding a codon-optimized HPV-16 E6 may be a promising strategy for improving the potency of prophylactic and therapeutic HPV vaccines with potential clinical implications.  相似文献   
182.
广东省曲江县发现鳄蜥   总被引:5,自引:2,他引:5  
报道了首次发现于广东的鳄蜥的形态结构特征,并将它与广西的鳄蜥进行了比较。  相似文献   
183.
To synthesize and secrete heterologous proteins in an attenuated Vibrio anguillarum strain for potential multivalent live vaccine development, different antigen-delivery systems based on bacterial-originated secretion signal peptides (SPs) were designed and identified in this work. Four SPs were derived from hemolysin of Escherichia coli, RTX protein of V. cholerae, hemolysin of V. anguillarum, zinc-metalloprotease of V. anguillarum, respectively, and their abilities to support secretion of green fluorescent protein (GFP) in an attenuated V. anguillarum strain MVAV6203 were assayed. Immunodetection of GFP showed that the capability of the tested signal leaders to direct secretion of GFP varied greatly. Although all the four signal peptide-fused GFPs could be expressed correctly and trapped intracellularly in recombinant strains, only the EmpA signal peptide could confer efficient secretion to GFP. For the investigation of its potential application in live bacteria carrier vaccines, a heterologous protein EseB of Edwardsiella tarda was fused to the SP(empA) antigen-delivery system and introduced into the strain MVAV6203. Further analysis of EseB demonstrated that the constructed SP(empA) antigen-delivery system could be used to secrete foreign protein in attenuated V. anguillarum and be available for carrier vaccines development.  相似文献   
184.
185.
186.
Scrub typhus is the most common endemic vector-borne disease in Taiwan. We identified a total of 4,857 laboratory-confirmed cases during 2006–2016 with hyperendemic foci on offshore islands, including Penghu (778 cases, 16.0%) and Kinmen (716 cases, 14.7%), and eastern Taiwan, including Taitung (628 cases, 12.9%) and Hualien (508 cases, 10.5%). Scrub typhus cases occur year-round throughout Taiwan, with a summer peak in June and July. A total of 545 O. tsutsugamushi isolates were successfully obtained from patients infected in diverse geographic areas, including Taiwan and three offshore islands, and the complete open reading frame of the 56 kDa type-specific antigen gene (tsa56) sequence of these isolates was examined. High phylogenetic diversity was found in these isolates, which could be grouped into 36 distinct sequence types. Most isolates belonged to the Karp (49.9%; 272/545), followed by the TW-22 (17.8%; 97/454) and Kawasaki (14.7%; 80/545) genotypes. In conclusion, our data indicate the widespread presence of tsa56 genotypes closely related to Thailand and Korean strains and the presence of the unique endemic strains TW-12, TW-22, TW-29, and TW-36 in Taiwan.  相似文献   
187.
Tumor acidic microenvironment is the main feature of many solid tumors.As a part of the tumor microenvironment,it has a profound impact on the occurrence and de...  相似文献   
188.
Although cisplatin is one of the chemotherapeutics most frequently used in oral squamous cell carcinoma (OSCC) treatment,it exerts multiple side effects and poo...  相似文献   
189.
采用全基因分段合成和补丁连接相结合的方法构建了人甲状旁腺素 (hPTH) (1~ 34)肽基因 ,并利用GST融合表达系统 ,在大肠杆菌中克隆和可溶性表达了hPTH(1~ 34)肽基因。融合蛋白表达量占菌体总蛋白质的 2 5 %以上 ,经高密度发酵、亲和纯化后 ,在每升发酵液中得到了 10 g融合蛋白。融合蛋白经肠激酶一步加工并亲合纯化和反相脱盐后 ,最终可以得到约 0 .6g /L人甲状旁腺素 (1~ 34)肽纯品 ,样品的理论回收值达到了4 8.75 %。产物的纯度和性质经HPLC、毛细管电泳、质谱分析、N端测序等得到证明 ,并与化学合成产物的结果相吻合。兔肾皮质细胞测活表明 ,重组产物与化学合成人甲状旁腺素 (1~ 34)肽具有相近的腺苷酸环化酶激活活性。  相似文献   
190.
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