全文获取类型
收费全文 | 20941篇 |
免费 | 2104篇 |
国内免费 | 2047篇 |
专业分类
25092篇 |
出版年
2024年 | 81篇 |
2023年 | 322篇 |
2022年 | 722篇 |
2021年 | 1155篇 |
2020年 | 816篇 |
2019年 | 1025篇 |
2018年 | 933篇 |
2017年 | 711篇 |
2016年 | 924篇 |
2015年 | 1320篇 |
2014年 | 1512篇 |
2013年 | 1703篇 |
2012年 | 1859篇 |
2011年 | 1759篇 |
2010年 | 1041篇 |
2009年 | 951篇 |
2008年 | 1079篇 |
2007年 | 911篇 |
2006年 | 889篇 |
2005年 | 606篇 |
2004年 | 578篇 |
2003年 | 560篇 |
2002年 | 476篇 |
2001年 | 365篇 |
2000年 | 322篇 |
1999年 | 298篇 |
1998年 | 219篇 |
1997年 | 154篇 |
1996年 | 152篇 |
1995年 | 135篇 |
1994年 | 115篇 |
1993年 | 94篇 |
1992年 | 127篇 |
1991年 | 115篇 |
1990年 | 92篇 |
1989年 | 96篇 |
1988年 | 71篇 |
1987年 | 65篇 |
1986年 | 56篇 |
1985年 | 61篇 |
1984年 | 59篇 |
1983年 | 49篇 |
1982年 | 41篇 |
1979年 | 37篇 |
1977年 | 25篇 |
1976年 | 27篇 |
1975年 | 30篇 |
1974年 | 30篇 |
1973年 | 36篇 |
1972年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Li‐Yuan Wang Lin Zeng Yan‐Sheng Shi Zheng‐Liang Qiu Hua‐Hu Ye Xiao‐Fei Zhang Qing‐Bin Lu Michael Kosoy Wei Liu Wu‐Chun Cao 《Molecular ecology》2013,22(8):2118-2127
Bartonella quintana is a bacterium that causes a broad spectrum of diseases in humans including trench fever. Humans were previously considered to be the primary, if not the only, reservoir hosts for B. quintana. To identify the animal reservoir and extend our understanding of the ecological and evolutionary history of B. quintana, we examined blood samples from macaques and performed multilocus sequence typing (MLST) analysis. We demonstrated the prevalence of B. quintana infection was common in macaques from main primate centres in mainland China. Overall, 18.0% (59/328) of rhesus macaques and 12.7% (39/308) of cynomolgus macaques were found to be infected with B. quintana by blood culture and/or polymerase chain reaction. The infection was more frequently identified in juvenile and young monkeys compared with adult animals. In contrast with the relatively low level of sequence divergence of B. quintana reported in humans, our investigation revealed much higher genetic diversity in nonhuman primates. We identified 44 new nucleotide variable sites and 14 novel sequence types (STs) among the B. quintana isolates by MLST analysis. Some STs were found only in cynomolgus macaques, while some others were detected only in rhesus macaques, suggesting evidence of host‐cospeciation, which were further confirmed by phylogenetic analysis and Splits decomposition analysis. Our findings suggest that trench fever may primarily be a zoonotic disease with macaques as the natural hosts. 相似文献
962.
Miaorong Huang Zicong Li Xiaoling Huang Wenchao Gao Cailin Zhu Hui Xu Yujuan Yuan Liang Shuai Ruiai Chen Zhenfang Wu Dewu Liu 《Transgenic research》2013,22(4):779-790
Cellulose is the main non-starch polysaccharides (NSP) in plant cell walls and acts as anti-nutritional factor in animal feed. However, monogastric animals do not synthesize enzymes that cleave such plant structural polysaccharides and thus waste of resources and pollute the environment. We described the vectors construction and co-expressions of a multi-functional cellulase EGX (with the activities of exo-β-1,4-glucanase, endo-β-1,4-glucanase, and endo-β-1,4-xylanase activities) from mollusca, Ampullaria crossean and a β-glucosidase BGL1 from Asperjillus niger in CHO cells and the transgenic mice. The recombinant enzymes were synthesised, secreted by the direction of pig PSP signal peptide and functionally active in the eukaryote systems including both of CHO cells and transgenic mice by RT-PCR analysis, western blot analysis and cellulolytic enzymes activities assays. Expressions were salivary glands-specific dependent under the control of pig PSP promoter in transgenic mice. 2A peptide was used as the self-cleaving sequence to mediate co-expression of the fusion genes and the cleavage efficiency was very high both in vitro and in vivo according to the western blot analysis. In summary, we have demonstrated that the single ORF containing EGX and BGL1 were co-expressed by 2A peptide in CHO cells and transgenic mice. It presents a viable technology for efficient disruption of plant cell wall and liberation of nutrients. To our knowledge, this is the first report using 2A sequence to produce multiple cellulases in mammalian cells and transgenic animals. 相似文献
963.
Noboru Tomiya Juliette G. Jardim Jennifer Hou Rebecca Pastrana-Mena Rhoel R. Dinglasan Yuan C. Lee 《Bioorganic & medicinal chemistry》2013,21(17):5275-5281
We have synthesized poly-γ-glutamic acid (PGA) modified with a synthetic trivalent glyco-ligand (TriGalNAc) for the hepatocyte asialoglycoprotein receptor (ASGP-R). We investigated in vivo distribution of unmodified PGA and TriGalNAc-modified PGA (TriGalNAc-PGA) in mice after intravenous injection. Most of unmodified PGA administered was transported to the bladder over 20–80 min, suggesting a rapid excretion of unmodified PGA into urine. In contrast, TriGalNAc-PGA was found exclusively in the liver over the same period of time. We further synthesized TriGalNAc-PGA–primaquine conjugate (TriGalNAc-PGA–PQ), and investigated binding, uptake, and catabolism of the conjugate by rat hepatocytes. Our studies indicated that approximately 250 ng per million cells of the conjugate bound to one million rat hepatocytes at 0 °C, and approximately 2 μg per million cells of the conjugate was taken up over 7 h incubation at 37 °C. Furthermore, our results suggested that TriGalNAc-PGA–PQ was almost completely degraded over 24 h, and small degradation products were secreted into cell culture medium.The results described in this report suggest that the TriGalNAc ligand can serve as an excellent targeting device for delivery of PGA-conjugates to the liver hepatocytes, and rat hepatocytes possess sufficient capacity to digest PGA even modified with other substituents. 相似文献
964.
Kang Jin Xiaopan Zhang Chunhua Ma Yingying Xu Yumei Yuan Wenfang Xu 《Bioorganic & medicinal chemistry》2013,21(9):2663-2670
Aminopeptidase N (APN/CD13), as a zinc-containing ectoenzyme, plays a critical role in the process of tumor angiogenesis, invasion and metastasis. Through the docking-based virtual screening of chemical databases and the further activity assay, we discovered that compound 10c exhibits potent and selective inhibitory ability towards APN. In addition, a series of indoline-2,3-dione derivates have been designed and synthesized as APN inhibitors. The results of preliminary activity evaluation showed that compound 12a (IC50 = 0.074 ± 0.0026 μM) exhibited the best inhibitory activity against APN, which could be used for further anticancer agent research. 相似文献
965.
966.
锌指核酸酶技术在基因定点修饰中具有效率高和特异性好等特点,并成功应用于数十种生物。目前,该技术是否能应用羊上尚未报道。为了敲除转基因山羊标记基因 (EGFP),构建了一对针对EGFP外显子上的锌指核酸酶表达载体,将其电转染至转EGFP基因胎儿成纤维细胞中,研究了锌指核酸酶突变EGFP基因的效率和方式,利用基因显微注射单细胞获得获得的转基因 (EGFP) 细胞系作为锌指核酸酶的靶细胞。结果显示,通过锌指核酸酶的突变作用,转染后的细胞发绿色荧光比例下降,测序结果显示在EGFP外显子中插入1个碱基G,导致编码EGFP基因的阅读框改变,从而起到基因突变的作用。结果表明,文中构建的锌指核酸酶对EGFP基因有突变作用,可以为以后获得无标记基因供核细胞进行体细胞核移植生产克隆羊奠定基础。 相似文献
967.
968.
969.
970.