全文获取类型
收费全文 | 748篇 |
免费 | 56篇 |
国内免费 | 33篇 |
专业分类
837篇 |
出版年
2023年 | 6篇 |
2022年 | 21篇 |
2021年 | 21篇 |
2020年 | 15篇 |
2019年 | 22篇 |
2018年 | 20篇 |
2017年 | 13篇 |
2016年 | 16篇 |
2015年 | 48篇 |
2014年 | 41篇 |
2013年 | 48篇 |
2012年 | 58篇 |
2011年 | 45篇 |
2010年 | 31篇 |
2009年 | 22篇 |
2008年 | 38篇 |
2007年 | 42篇 |
2006年 | 35篇 |
2005年 | 22篇 |
2004年 | 21篇 |
2003年 | 25篇 |
2002年 | 32篇 |
2001年 | 15篇 |
2000年 | 20篇 |
1999年 | 13篇 |
1998年 | 13篇 |
1997年 | 15篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 10篇 |
1972年 | 2篇 |
1970年 | 2篇 |
1968年 | 3篇 |
1967年 | 3篇 |
1966年 | 8篇 |
排序方式: 共有837条查询结果,搜索用时 19 毫秒
51.
Novel bacterial sulfur oxygenase reductases from bioreactors treating gold-bearing concentrates 总被引:1,自引:0,他引:1
Chen ZW Liu YY Wu JF She Q Jiang CY Liu SJ 《Applied microbiology and biotechnology》2007,74(3):688-698
The microbial community and sulfur oxygenase reductases of metagenomic DNA from bioreactors treating gold-bearing concentrates
were studied by 16S rRNA library, real-time polymerase chain reaction (RT-PCR), conventional cultivation, and molecular cloning.
Results indicated that major bacterial species were belonging to the genera Acidithiobacillus, Leptospirillum, Sulfobacillus, and Sphingomonas, accounting for 6.3, 66.7, 18.8, and 8.3%, respectively; the sole archaeal species was Ferroplasma sp. (100%). Quantitative RT-PCR revealed that the 16S rRNA gene copy numbers (per gram of concentrates) of bacteria and archaea
were 4.59 × 109 and 6.68 × 105, respectively. Bacterial strains representing Acidithiobacillus, Leptospirillum, and Sulfobacillus were isolated from the bioreactors. To study sulfur oxidation in the reactors, pairs of new PCR primers were designed for
the detection of sulfur oxygenase reductase (SOR) genes. Three sor-like genes, namely, sor
Fx, sor
SA, and sor
SB were identified from metagenomic DNAs of the bioreactors. The sor
Fx is an inactivated SOR gene and is identical to the pseudo-SOR gene of Ferroplasma acidarmanus. The sor
SA and sor
SB showed no significant identity to any genes in GenBank databases. The sor
SB was cloned and expressed in Escherichia
coli, and SOR activity was determined. Quantitative RT-PCR determination of the gene densities of sor
SA and sor
SB were 1,000 times higher than archaeal 16S rRNA gene copy numbers, indicating that these genes were mostly impossible from
archaea. Furthermore, with primers specific to the sor
SB gene, this gene was PCR-amplified from the newly isolated Acidithiobacillus sp. strain SM-1. So far as we know, this is the first time to determine SOR activity originating from bacteria and to document
SOR gene in bioleaching reactors and Acidithiobacillus species. 相似文献
52.
53.
The OspF family of phosphothreonine lyase, including SpvC from Salmonella, irreversibly inactivates the dual-phosphorylated host MAPKs (pT-X-pY) through beta elimination. We determined crystal structures of SpvC and its complex with a phosphopeptide substrate. SpvC adopts a unique fold of alpha/beta type. The disordered N terminus harbors a canonical D motif for MAPK substrate docking. The enzyme-substrate complex structure indicates that recognition of the phosphotyrosine followed by insertion of the threonine phosphate into an arginine pocket places the phosphothreonine into the enzyme active site. This requires the conformational flexibility of pT-X-pY, which suggests that p38 (pT-G-pY) is likely the preferred physiological substrate. Structure-based biochemical and enzymatic analysis allows us to propose a general acid/base mechanism for beta elimination reaction catalyzed by the phosphothreonine lyase. The mechanism described here provides a structural understanding of MAPK inactivation by a family of pathogenic effectors conserved in plant and animal systems and may also open a new route for biological catalysis. 相似文献
54.
Isolation of Laribacter hongkongensis, a novel bacterium associated with gastroenteritis, from drinking water reservoirs in Hong Kong 总被引:1,自引:0,他引:1
Lau SK Woo PC Fan RY Ma SS Hui WT Au SY Chan LL Chan JY Lau AT Leung KY Pun TC She HH Wong CY Wong LL Yuen KY 《Journal of applied microbiology》2007,103(3):507-515
AIMS: Freshwater fish has been found to be the reservoir of Laribacter hongkongensis, a recently discovered bacterium associated with community-acquired gastroenteritis. However, little is known about the ecology of this bacterium in the aquatic environment. We carried out a surveillance study to investigate the presence of L. hongkongensis in water and freshwater fish from 10 drinking water reservoirs in Hong Kong. METHODS AND RESULTS: Using membrane filtration, L. hongkongensis was isolated from the waters of six reservoirs, with numbers ranging from 1 to 12 CFU l(-1). Higher recovery rates were observed in summer and during days of higher water and ambient temperatures. Of 27 freshwater fish collected from the reservoirs, L. hongkongensis was recovered from the intestines of two fish, a Goldfish and a Nile tilapia. Overall, 35 different pulsed-field gel electrophoresis patterns are found among the 59 isolates recovered from water and the two isolates from freshwater fish. CONCLUSIONS: The present report represents the first to demonstrate the presence of L. hongkongensis in natural water environments. SIGNIFICANCE AND IMPACT OF THE STUDY: Although it is unlikely that treated, drinking water is an important source of L. hongkongensis-associated gastroenteritis, one should be aware of the possibility of other contaminated water as a source of human infection. 相似文献
55.
MOTIVATION: Due to advances in experimental technologies, such as microarray, mass spectrometry and nuclear magnetic resonance, it is feasible to obtain large-scale data sets, in which measurements for a large number of features can be simultaneously collected. However, the sample sizes of these data sets are usually small due to their relatively high costs, which leads to the issue of concordance among different data sets collected for the same study: features should have consistent behavior in different data sets. There is a lack of rigorous statistical methods for evaluating this concordance or discordance. METHODS: Based on a three-component normal-mixture model, we propose two likelihood ratio tests for evaluating the concordance and discordance between two large-scale data sets with two sample groups. The parameter estimation is achieved through the expectation-maximization (E-M) algorithm. A normal-distribution-quantile-based method is used for data transformation. RESULTS: To evaluate the proposed tests, we conducted some simulation studies, which suggested their satisfactory performances. As applications, the proposed tests were applied to three SELDI-MS data sets with replicates. One data set has replicates from different platforms and the other two have replicates from the same platform. We found that data generated by SELDI-MS showed satisfactory concordance between replicates from the same platform but unsatisfactory concordance between replicates from different platforms. AVAILABILITY: The R codes are freely available at http://home.gwu.edu/~ylai/research/Concordance. 相似文献
56.
She Yang Gao Xiang Jing Xin Wang Jing Dong Yibei Cui Jinzi Xue Huidan Li Zhengke Zhu Derui 《Journal of applied phycology》2022,34(3):1281-1291
Journal of Applied Phycology - A new strain of Eustigmatophyceae, Vischeria sp. WL1, which accumulates oil droplets in the cells, was isolated from a large biological soil crust in the arid steppes... 相似文献
57.
Longbiao Guo Jie Qiu Zujing Han Zihong Ye Chao Chen Chuanjun Liu Xiufang Xin Chu‐Yu Ye Ying‐Ying Wang Hongqing Xie Yu Wang Jiandong Bao She Tang Jie Xu Yijie Gui Fei Fu Weidi Wang Xingchen Zhang Qianhua Zhu Xuanmin Guang Chongzhi Wang Haifeng Cui Daguang Cai Song Ge Gerald A. Tuskan Xiaohan Yang Qian Qian Sheng Yang He Jun Wang Xue‐Ping Zhou Longjiang Fan 《The Plant journal : for cell and molecular biology》2015,83(4):600-609
58.
59.
The effects of Aluminum (Al) exposure on immune functions of cultured splenic T and B lymphocytes of rats were studied. The lymphocytes were isolated from spleen of healthy male Wistar rats weighing 110-120 g. The cultured cells in RPMI-1640 medium were exposed to 0 (control group), 0.035 (low-dose group), 0.07 (medial-dose group), and 0.14 (high-dose group) mg/mL Al(3+) as aluminum trichloride (AlCl(3)) in an incubator under 5% CO(2) at 37°C for 24 h. The T and B lymphocyte proliferation was measured with a tetrazolium dye colorimetric assay. The levels of interleukin (IL)-2, IL-6, and tumor necrosis factor (TNF)-α were determined by iodine [(125)I] IL-2, IL-6, and TNF-α radioimmunoassay kits, respectively. The proportions of CD3(+), CD4(+), and CD8(+) T lymphocytes were measured with a flow cytometer. The results showed that the T and B lymphocyte proliferation, the levels of IL-2, IL-6, TNF-α, the proportions of CD3(+) and CD4(+) T lymphocytes, and the ratio of CD4(+)/CD8(+) T lymphocytes were lowered by Al treatments, while the proportion of CD8(+) T lymphocytes was increased. These findings indicate that Al exposure can inhibit the immune functions of splenic T and B lymphocytes of rats in vitro. 相似文献
60.
Analysis of known sulfur oxygenase-reductases (SORs) and the SOR-like sequences identified from public databases indicated that they all possess three cysteine residues within two conserved motifs (V-G-P-K-V-C(31) and C(101)-X-X-C(104); numbering according to the Acidianus tengchongensis numbering system). The thio-modifying reagent N-ethylmaleimide and Zn(2+) strongly inhibited the activities of the SORs of A. tengchongensis, suggesting that cysteine residues are important. Site-directed mutagenesis was used to construct four mutant SORs with cysteines replaced by serine or alanine. The purified mutant proteins were investigated in parallel with the wild-type SOR. Replacement of any cysteine reduced SOR activity by 98.4 to 100%, indicating that all the cysteine residues are crucial to SOR activities. Circular-dichroism and fluorescence spectrum analyses revealed that the wild-type and mutant SORs have similar structures and that none of them form any disulfide bond. Thus, it is proposed that three cysteine residues, C(31) and C(101)-X-X-C(104), in the conserved domains constitute the putative binding and catalytic sites of SOR. Furthermore, enzymatic activity assays of the subcellular fractions and immune electron microscopy indicated that SOR is not only present in the cytoplasm but also associated with the cytoplasmic membrane of A. tengchongensis. The membrane-associated SOR activity was colocalized with the activities of sulfite:acceptor oxidoreductase and thiosulfate:acceptor oxidoreductase. We tentatively propose that these enzymes are located in close proximity on the membrane to catalyze sulfur oxidation in A. tengchongensis. 相似文献