全文获取类型
收费全文 | 1979篇 |
免费 | 131篇 |
国内免费 | 175篇 |
专业分类
2285篇 |
出版年
2024年 | 9篇 |
2023年 | 70篇 |
2022年 | 66篇 |
2021年 | 98篇 |
2020年 | 95篇 |
2019年 | 114篇 |
2018年 | 97篇 |
2017年 | 74篇 |
2016年 | 63篇 |
2015年 | 63篇 |
2014年 | 118篇 |
2013年 | 135篇 |
2012年 | 87篇 |
2011年 | 86篇 |
2010年 | 69篇 |
2009年 | 69篇 |
2008年 | 86篇 |
2007年 | 89篇 |
2006年 | 82篇 |
2005年 | 75篇 |
2004年 | 63篇 |
2003年 | 49篇 |
2002年 | 55篇 |
2001年 | 47篇 |
2000年 | 32篇 |
1999年 | 27篇 |
1998年 | 36篇 |
1997年 | 35篇 |
1996年 | 32篇 |
1995年 | 26篇 |
1994年 | 20篇 |
1993年 | 25篇 |
1992年 | 27篇 |
1991年 | 18篇 |
1990年 | 11篇 |
1989年 | 21篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1974年 | 4篇 |
1971年 | 2篇 |
排序方式: 共有2285条查询结果,搜索用时 0 毫秒
31.
猪伪狂犬病毒(PRV)是一种良好的兽用活病毒疫苗载体。但以PRV基因缺失疫苗株TK-/gE-/LacZ+为载体表达PRRSV GP5的重组病毒TK-/gE-/GP5+免疫实验动物后难以激发抗PRRSV的中和抗体。为了进一步增强这种重组病毒的免疫效力,用具有更好免疫原性的修饰的ORF5基因(ORF5m)代替天然ORF5基因,构建了表达PRRSV的修饰型GP5m蛋白的重组伪狂犬病毒TK-/gE-/GP5m+。经PCR、Southern blot、Western blot 证实构建正确,并能表达具有活性的GP5m蛋白。将TK-/gE-/GP5m+与TK-/gE-/GP5+分别免疫Balb/c小鼠,结果TK-/gE-/GP5m+免疫小鼠不仅产生了较高水平的抗PRRSV的中和抗体(3/6只达到了1∶16),而且在诱导PRRSV特异性细胞免疫方面也显著优于TK-/gE-/GP5+,表明TK-/gE-/GP5m+是一种极有希望的PRRSV和PRV二价基因工程候选疫苗。 相似文献
32.
Determination of PRKAG1 coding sequence and mapping of PRKAG1 and PRKAG2 relatively to porcine back fat thickness QTL 总被引:1,自引:0,他引:1
PRKAG1, PRKAG2 and PRKAG3 encode three isoforms of AMP-activated protein kinase gamma chain. A major effect on meat quality and a medium effect on back fat thickness of the RN- mutation in the PRKAG3 gene has previously been reported. We have now mapped PRKAG1 and PRKAG2 at expected locations on SSC5 and SSC18 by analysis of radiation hybrids (IMpRH panel). PRKAG2 has been mapped in a region where no quantitative trait loci (QTL) has been reported. PRKAG1 has been mapped close to (but probably outside) a region containing a QTL influencing fatness traits. We have determined the full coding sequence of PRKAG1. No missense mutation was identified when comparing the coding sequence of one Meishan and one Large White boars. Further work is, however, required to determine if a polymorphism in PRKAG1 could be responsible for a part of the variability observed on fatness traits. 相似文献
33.
Hidehiko Kumagai Hideyuki Suzuki Hiroki Shigematsu Tatsurokuro Tochikura 《Bioscience, biotechnology, and biochemistry》2013,77(9):2481-2487
An enzyme that catalyzes the synthesis of S-carboxymethyl- l-cysteine from 3-chloro- l-alanine (3-Cl-Ala) and thioglycolic acid was found in Escherichia coli W3110 and was designated as S- carboxymethyl-l-cysteine synthase. It was purified from the cell-free extract to electrophoretic homogeneity and was crystallized. The enzyme has a molecular weight of 84,000 and gave one band corresponding to a molecular weight of 37,000 on SDS-polyacrylamide gel electrophoresis. The purified enzyme catalyzed the β-replacement reactions between 3-CI-AIa and various thiol compounds. The apparent Km values for 3-Cl-Ala and thioglycolic acid were 40 mM and 15.4 mM. The enzyme showed very low activity as to the α,β-elimination reaction with 3-Cl-Ala and l-serine. It was not inactivated on the incubation with 3-Cl-Ala. The absorption spectrum of the enzyme shows a maximum at 412 nm, indicating that it contains pyridoxal phosphate as a cofactor. The N-terminal amino acid sequence was determined and the corresponding sequence was detected in the protein sequence data bank, but no homogeneous sequence was found. 相似文献
34.
35.
36.
Zhang X Wang H Shi Y Peng W Zhang S Zhang W Xu J Mei Y Feng Z 《Cell biology international》2012,36(6):589-594
BPD (bronchopulmonary dysplasia) is predominantly characterized by persistent abnormalities in lung structure and arrested lung development, but therapy can be palliative. While promising, the use of BMSC (bone marrow-derived mesenchymal stem cell) in the treatment of lung diseases remains controversial. We have assessed the therapeutic effects of BMSC in vitro and in vivo. In vitro co-culturing with injured lung tissue increased the migration-potential of BMSC; and SP-C (surfactant protein-C), a specific marker of AEC2 (type II alveolar epithelial cells), was expressed. Following intraperitoneal injection of BMSC into experimental BPD mice on post-natal day 7, it was found that BMSC can home to the injured lung, express SP-C, improve pulmonary architecture, attenuate pulmonary fibrosis and increase the survival rate of BPD mice. This work supports the notion that BMSC are of therapeutic benefit through the production of soluble factors at bioactive levels that regulate the pathogenesis of inflammation and fibrosis following hyperoxia. 相似文献
37.
在体外系统中,发现超氧化物歧化酶(SOD)具有切割超螺旋DNA的活性. 猪血和牛血Cu/Zn-SOD以及烟草Mn-SOD都能将超螺旋DNA转变为非超螺旋结构的缺刻环状DNA,进一步产生线状DNA. 它们只作用于超螺旋DNA而不作用于线状DNA. 这个事实排除了SOD样品中污染核酸酶的可能性. 用H2O2、胍基抑制或蛋白酶降解的实验结果表明,这两种酶的活性中心处于酶蛋白的不同部位. 相似文献
38.
Vega-Rocha S Byeon IJ Gronenborn B Gronenborn AM Campos-Olivas R 《Journal of molecular biology》2007,367(2):473-487
Circoviruses are the smallest circular single-stranded DNA viruses able to replicate in mammalian cells. Essential to their replication is the replication initiator, or Rep protein that initiates the rolling circle replication (RCR) of the viral genome. Here we report the NMR solution three-dimensional structure of the endonuclease domain from the Rep protein of porcine circovirus type 2 (PCV2), the causative agent of postweaning multisystemic wasting syndrome in swine. The domain comprises residues 12-112 of the full-length protein and exhibits the fold described previously for the Rep protein of the representative geminivirus tomato yellow leaf curl Sardinia virus. The structure, however, differs significantly in some secondary structure elements that decorate the central five-stranded beta-sheet, including the replacement of a beta-hairpin by an alpha-helix in PCV2 Rep. The identification of the divalent metal binding site was accomplished by following the paramagnetic broadening of NMR amide signals upon Mn(2+) titration. The site comprises three conserved acidic residues on the exposed face of the central beta-sheet. For the 1:1 complex of the PCV2 Rep nuclease domain with a 22mer double-stranded DNA oligonucleotide chemical shift mapping allowed the identification of the DNA binding site on the protein and aided in constructing a model of the protein/DNA complex. 相似文献
39.
40.
Tungtrakoolsub P Noda T Morozumi T Hamasima N Kobayashi E Ueda J Watanabe T 《Animal genetics》2008,39(1):22-27
The porcine MX1 and MX2 promoters were characterized in this study. Sequencing of the 332-bp MX1 promoter region identified 15 substitutions and insertions at three positions in 21 pigs from 15 breeds, in which nine genotypes were classified. Among the nine genotypes, no statistically significant differences in the promoter activities were observed after interferon (IFN- α 2b) treatment of transiently transfected cells containing constructs with luciferase reporter plasmids. The 341-bp MX2 promoter region contained regulatory sequences for ISRE, GC box, Sp1 and AP-1, as well as a TATA box. Nucleotide sequences of the MX2 promoter region revealed four substitutions and one deletion, in which six genotypes were classified. Among the six genotypes, a statistically significant difference ( P < 0.05) in MX2 promoter activities after IFN- α 2b treatment was detected in transiently transfected cells. 相似文献