全文获取类型
收费全文 | 18126篇 |
免费 | 1657篇 |
国内免费 | 1922篇 |
专业分类
21705篇 |
出版年
2024年 | 38篇 |
2023年 | 134篇 |
2022年 | 375篇 |
2021年 | 545篇 |
2020年 | 416篇 |
2019年 | 562篇 |
2018年 | 569篇 |
2017年 | 437篇 |
2016年 | 667篇 |
2015年 | 1023篇 |
2014年 | 1196篇 |
2013年 | 1198篇 |
2012年 | 1578篇 |
2011年 | 1478篇 |
2010年 | 956篇 |
2009年 | 889篇 |
2008年 | 1156篇 |
2007年 | 1080篇 |
2006年 | 1008篇 |
2005年 | 934篇 |
2004年 | 850篇 |
2003年 | 831篇 |
2002年 | 683篇 |
2001年 | 512篇 |
2000年 | 424篇 |
1999年 | 414篇 |
1998年 | 189篇 |
1997年 | 182篇 |
1996年 | 143篇 |
1995年 | 117篇 |
1994年 | 100篇 |
1993年 | 64篇 |
1992年 | 114篇 |
1991年 | 116篇 |
1990年 | 70篇 |
1989年 | 76篇 |
1988年 | 57篇 |
1987年 | 53篇 |
1986年 | 42篇 |
1985年 | 49篇 |
1984年 | 40篇 |
1983年 | 24篇 |
1982年 | 24篇 |
1979年 | 21篇 |
1978年 | 25篇 |
1977年 | 24篇 |
1976年 | 24篇 |
1974年 | 25篇 |
1973年 | 19篇 |
1971年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Characterization of humoral responses in mice immunized with plasmid DNAs encoding SARS-CoV spike gene fragments 总被引:11,自引:0,他引:11
Zeng F Chow KY Hon CC Law KM Yip CW Chan KH Peiris JS Leung FC 《Biochemical and biophysical research communications》2004,315(4):1134-1139
The immunological characteristics of SARS-CoV spike protein were investigated by administering mice with plasmids encoding various S gene fragments. We showed that the secreting forms of S1, S2 subunits and the N-terminus of S1 subunit (residues 18-495) were capable of eliciting SARS-CoV specific antibodies and the region immediate to N-terminus of matured S1 protein contained an important immunogenic determinant for elicitation of SARS-CoV specific antibodies. In addition, mice immunized with plasmids encoding S1 fragment developed a Th1-mediated antibody isotype switching. Another interesting finding was that mouse antibodies elicited separately by plasmids encoding S1 and S2 subunits cooperatively neutralized SARS-CoV but neither the S1 nor S2 specific antibodies did, suggesting the possible role of both S1 and S2 subunits in host cell docking and entry. These results provide insights into understanding the immunological characteristics of spike protein and the development of subunit vaccines against SARS-CoV. 相似文献
112.
113.
Yuanyuan Yu Jiugang Yuan Qiang Wang Xuerong Fan Ping Wang Xuejiao Sun 《Engineering in Life Science》2013,13(2):194-200
Cellulases can penetrate into the fiber, causing tensile strength loss of the cellulosic fibers or fabrics. To minimize the tensile strength loss, we have immobilized cellulases on Eudragit S‐100. The characteristics of covalent Eudragit cellulase were evaluated using gel filtration analysis and UV spectra. Gel filtration analysis revealed that the cellulases were covalently bound to the polymer. Covalent Eudragit cellulase was loaded with the enzyme of about 40% and had a relative activity about 80% at a Eudragit S‐100 concentration of 15 g/L. When cellulase is bound to the polymer, the solubility profile becomes similar to the one of Eudragit. In addition, the effects of the enzyme on the cotton yarns and fabric using cellulases have been investigated. Native and immobilized cellulases caused improvements in whiteness and wrinkle recovery angle of the fabric in comparison to the control samples. The bending stiffness results show that native and immobilized cellulase treated cotton fabric has an improved softness than the control samples. It was found that using the immobilized cellulase reduced the weight and tensile strength, because the hydrolytic attack is only limited to the surfaces of cotton fibers. 相似文献
114.
115.
Mutagenicity of azo dyes: structure-activity relationships. 总被引:10,自引:0,他引:10
Azo dyes are extensively used in textile, printing, leather, paper making, drug and food industries. Following oral exposure, azo dyes are metabolized to aromatic amines by intestinal microflora or liver azoreductases. Aromatic amines are further metabolized to genotoxic compounds by mammalian microsomal enzymes. Many of these aromatic amines are mutagenic in the Ames Salmonella/microsomal assay system. The chemical structure of many mutagenic azo dyes was reviewed, and we found that the biologically active dyes are mainly limited to those compounds containing p-phenylenediamine and benzidine moieties. It was found that for the phenylenediamine moiety, methylation or substitution of a nitro group for an amino group does not decrease mutagenicity. However, sulfonation, carboxylation, deamination, or substitution of an ethyl alcohol or an acetyl group for the hydrogen in the amino groups leads to a decrease in the mutagenic activity. For the benzidine moiety, methylation, methoxylation, halogenation or substitution of an acetyl group for hydrogen in the amino group does not affect mutagenicity, but complexation with copper ions diminishes mutagenicity. The mutagenicity of benzidine or its derivatives is also decreased when in the form of a hydrochloride salt with only one exception. Mutagenicity of azo dyes can, therefore, be predicted by these structure-activity relationships. 相似文献
116.
胰岛素抵抗(IR)是许多疾病的独立危险因素。胰岛素抵抗与脂肪代谢紊乱非常密切,研究发现它在脂肪肝的发生、发展过程中起了很大的作用。近年来,越来越多的人已经意识到脂肪肝与胰岛素抵抗之间的密切关系。在胰岛素抵抗与脂肪肝的研究中关于瘦素及瘦素抵抗在胰岛素抵抗及脂肪肝的关系中的作用是研究比较多的,本文主要介绍了胰岛素抵抗、脂肪肝的发生机制及瘦素、瘦素抵抗在其中的催化作用。 相似文献
117.
棘白菌素类化合物纽莫康定B_0生产菌株Glarea lozoyensis,在其连续传代和发酵过程中都观察到菌株的变异,给科研、生产带来极大困扰。因此,采用低温冷冻保藏对G.lozoyensis Q1进行长期保存。采用单因素实验法研究了低温保护剂类型、保藏温度以及低温保护剂浓度对G.lozoyensis Q1菌体形态和发酵性能的影响。以作用于全细胞的80 g/L甘油和作用于细胞壁外的200 g/L PEG-6000作为低温保护剂,在-80℃保藏3个月后,纽莫康定B_0产量达到1.6 g/L,与保藏前基本一致。并且,当菌体保藏过后菌丝形态能维持一定褶皱的实验组产量均能保持在1 g/L以上,当表面趋于光滑时产量急剧下降,仅为初始的25%左右。结果表明,以甘油及PEG-6000作为冷冻保护剂,在-80℃条件下可实现G.lozoyensis Q1长期保藏。 相似文献
118.
Sang-Yeop Lee Young-Ho Yoon Si-Hoon Kim Se-Ra Lee Jeong-Min Chu Seung Il Kim Tae-Hong Kang Jin Woong Chung Vladimir Larionov Sun-Hee Leem 《Genes & genomics.》2012,34(6):647-652
CHO (Chinese Hamster ovary) cells are widely used for biotechnology and biomedical purposes, and now the EST library database of CHO cells is built. Based on this, the construction of the hamster genome library is under exertion. Though the transformation-associated recombination (TAR) cloning method is accounted as an innovative cloning technology without the construction of the genome library in human and mouse, there has been no trial to isolate the genomic fragment from hamster genome by TAR cloning. In this study, approximately 31 kb of hamster genomic fragment was isolated from the normal human/hamster mono-chromosomal somatic cell line (UV5HL9-5B) using universal hooks of rodent repeats sequence of B1 and B2 by TAR cloning. This fragment was analyzed by bioinformatics tools related to the genome alignment for the similarity analysis among rodent and primate, and was classified into rodents by phylogenetic analysis. One putative gene was found in this region which has homology with the human c14orf4 gene. A zinc finger protein domain was found in the translated hamster ORF. Therefore, we suggest that TAR cloning technique can be applied in CHO cells using mouse genomic information, and it can lead to the establishment of the hamster genome database. 相似文献
119.
叶绿体基因组进化的速率和方式 总被引:1,自引:0,他引:1
叶绿体是植物细胞重要的细胞器,叶绿体基因组被广泛用于系统进化的研究。对叶绿体基因组进化的速度和方式进行了介绍,并对造成其特异的点突变的原因进行了一定的分析。 相似文献
120.