全文获取类型
收费全文 | 17860篇 |
免费 | 1412篇 |
国内免费 | 1591篇 |
专业分类
20863篇 |
出版年
2024年 | 43篇 |
2023年 | 227篇 |
2022年 | 607篇 |
2021年 | 1004篇 |
2020年 | 660篇 |
2019年 | 794篇 |
2018年 | 762篇 |
2017年 | 522篇 |
2016年 | 745篇 |
2015年 | 1113篇 |
2014年 | 1331篇 |
2013年 | 1384篇 |
2012年 | 1661篇 |
2011年 | 1472篇 |
2010年 | 898篇 |
2009年 | 818篇 |
2008年 | 903篇 |
2007年 | 798篇 |
2006年 | 722篇 |
2005年 | 671篇 |
2004年 | 518篇 |
2003年 | 475篇 |
2002年 | 371篇 |
2001年 | 297篇 |
2000年 | 278篇 |
1999年 | 271篇 |
1998年 | 170篇 |
1997年 | 158篇 |
1996年 | 181篇 |
1995年 | 136篇 |
1994年 | 154篇 |
1993年 | 98篇 |
1992年 | 113篇 |
1991年 | 108篇 |
1990年 | 79篇 |
1989年 | 72篇 |
1988年 | 48篇 |
1987年 | 55篇 |
1986年 | 38篇 |
1985年 | 28篇 |
1984年 | 37篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1979年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
Ikegaya H Zheng HY Saukko PJ Varesmaa-Korhonen L Hovi T Vesikari T Suganami H Takasaka T Sugimoto C Ohasi Y Kitamura T Yogo Y 《American journal of physical anthropology》2005,128(1):185-193
The JC virus (JCV) genotyping method was used to gain insights into the population history of the Saami and the Finns, both speaking Finno-Ugric languages and living in close geographic proximity. Urine samples from Saami and Finns, collected in northern and southern Finland, respectively, were used to amplify a 610-bp JCV-DNA region containing abundant type-specific mutations. Based on restriction site polymorphisms in the amplified fragments, we classified JCV isolates into one of the three superclusters of JCV, type A, B, or C. All 15 Saami isolates analyzed and 41 of 43 Finnish isolates analyzed were classified as type A, the European type, and two samples from Finns were classified as type B, the African/Asian type. We then amplified and sequenced a 583-bp JCV-DNA region from the type A isolates of Saami and Finns. According to type-determining nucleotides within the region, we classified type A isolates into EU-a1, -a2, or -b. Most type A isolates from Saami were classified as EU-a1, while type A isolates from Finns were distributed among EU-a1, EU-a2, and EU-b. This trend in the JCV-genotype distribution was statistically significant. On a phylogenetic tree based on complete sequences, most of the type A isolates from Saami were clustered in a single clade within EU-a1, while those from Finns were distributed throughout EU-a1, EU-a2, and EU-b. These findings are discussed in the context of the population history of the Saami and the Finns. This study provides new complete JCV DNA sequences derived from populations of anthropological interest. 相似文献
212.
Dai X Chen Q Lian M Zhou Y Zhou M Lu S Chen Y Luo J Gu X Jiang Y Luo M Zheng X 《Biochemical and biophysical research communications》2005,332(2):593-601
Human secreted proteins play a very important role in signal transduction. In order to study all potential secreted proteins identified from the human genome sequence, systematic production of large amounts of biologically active secreted proteins is a prerequisite. We selected 25 novel genes as a trial case for establishing a reliable expression system to produce active human secreted proteins in Escherichia coli. Expression of proteins with or without signal peptides was examined and compared in E. coli strains. The results indicated that deletion of signal peptides, to a certain extent, can improve the expression of these proteins and their solubilities. More importantly, under expression conditions such as induction temperature, N-terminus fusion peptides need to be optimized in order to express adequate amounts of soluble proteins. These recombinant proteins were characterized as well-folded proteins. This system enables us to rapidly obtain soluble and highly purified human secreted proteins for further functional studies. 相似文献
213.
214.
Wang Ting-Ting Zhu Chen-Ye Zheng Shuang Meng Cai-Cai Wang Tian-Tian Meng Dan-Hua Li Yi-Jun Zhu Hao-Miao Wang Feng-Shan Sheng Ju-Zheng 《Applied microbiology and biotechnology》2018,102(11):4785-4797
Applied Microbiology and Biotechnology - Avibacterium paragallinarum is a Gram-negative bacterium that causes infectious coryza in chicken. It was reported that the capsule polysaccharides... 相似文献
215.
Zou Shu-Ping Zheng Yu-Guo Wu Qun Wang Zhi-Cai Xue Ya-Ping Liu Zhi-Qiang 《Applied microbiology and biotechnology》2018,102(2):733-742
Applied Microbiology and Biotechnology - Enantioselective hydrolysis of epoxides by epoxide hydrolase (EH) is one of the most attractive approaches for the synthesis of chiral epoxides. So far,... 相似文献
216.
217.
218.
219.
The genome of the metal sulfide-oxidizing, thermoacidophilic strain Metallosphaera cuprina Ar-4 has been completely sequenced and annotated. Originally isolated from a sulfuric hot spring, strain Ar-4 grows optimally at 65°C and a pH of 3.5. The M. cuprina genome has a 1,840,348-bp circular chromosome (2,029 open reading frames [ORFs]) and is 16% smaller than the previously sequenced Metallosphaera sedula genome. Compared to the M. sedula genome, there are no counterpart genes in the M. cuprina genome for about 480 ORFs in the M. sedula genome, of which 243 ORFs are annotated as hypothetical protein genes. Still, there are 233 ORFs uniquely occurring in M. cuprina. Genome annotation supports that M. cuprina lives a facultative life on CO(2) and organics and obtains energy from oxidation of sulfidic ores and reduced inorganic sulfuric compounds. 相似文献
220.
Tissue-specific and expression of porcine growth hormone gene in BAC transgenic mice 总被引:1,自引:0,他引:1
Tong J Lillico SG Bi MJ Qing T Liu XF Wang Y Zheng M Wang M Dai YP Whitelaw CB Li N 《Transgenic research》2011,20(4):933-938
One of the primary goals of traditional livestock breeding is to improve growth rate and optimise body size. Growth rate can be significantly increased by integrating a growth hormone (GH) transgene under the control of a ubiquitous promoter, but while such animals do demonstrate increased growth there are also serious deleterious side-effects to the animals health. Here we report the generation and initial characterization of transgenic mice that carried a porcine BAC encoding the porcine GH gene. We show that GH expression is restricted specifically to the pituitary, is associated with elevated IGF-1 levels, and results in growth enhancement. No negative effects to the health of the transgenic animals were detected. This initial characterisation supports the use of BAC pGH transgene in livestock studies. 相似文献