全文获取类型
收费全文 | 747篇 |
免费 | 56篇 |
国内免费 | 33篇 |
出版年
2023年 | 5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836条查询结果,搜索用时 15 毫秒
61.
Fusicoccin (FC) treatment prevents dark‐induced stomatal closure, the mechanism of which is still obscure. By using pharmacological approaches and laser‐scanning confocal microscopy, the relationship between FC inhibition of dark‐induced stomatal closure and the hydrogen peroxide (H2O2) levels in guard cells in broad bean was studied. Like ascorbic acid (ASA), a scavenger of H2O2 and diphenylene iodonium (DPI), an inhibitor of H2O2‐generating enzyme NADPH oxidase, FC was found to inhibit stomatal closure and reduce H2O2 levels in guard cells in darkness, indicating that FC‐caused inhibition of dark‐induced stomatal closure is related to the reduction of H2O2 levels in guard cells. Furthermore, like ASA, FC not only suppressed H2O2‐induced stomatal closure and H2O2 levels in guard cells treated with H2O2 in light, but also reopened the stomata which had been closed by darkness and reduced the level of H2O2 that had been generated by darkness, showing that FC causes H2O2 removal in guard cells. The butyric acid treatment simulated the effects of FC on the stomata treated with H2O2 and had been closed by dark, and on H2O2 levels in guard cells of stomata treated with H2O2 and had been closed by dark, and both FC and butyric acid reduced cytosol pH in guard cells of stomata treated with H2O2 and had been closed by dark, which demonstrates that cytosolic acidification mediates FC‐induced H2O2 removal. Taken together, our results provide evidence that FC causes cytosolic acidification, consequently induces H2O2 removal, and finally prevents dark‐induced stomatal closure. 相似文献
62.
Nazina TN Grigor'ian AA Feng Ts Shestakova NM Babich TL Pavlova NK Ivoĭlov VS Ni F Wang J She Y Xiang T Mei B Luo Z Beliaev SS Ivanov MV 《Mikrobiologiia》2007,76(3):340-353
Microbiological technology for the enhancement of oil recovery based on the activation of the stratal microflora was tested in the high-temperature horizons of the Kongdian bed (60 degrees C) of the Dagang oil field (China). This biotechnology consists in the pumping of a water-air mixture and nitrogen and phosphorus mineral salts into the oil stratum through injection wells in order to stimulate the activity of the stratal microflora which produce oil-releasing metabolites. Monitoring of the physicochemical, microbiological, and production characteristics of the test site has revealed large changes in the ecosystem as a result of the application of biotechnology. The cell numbers of thermophilic hydrocarbon-oxidizing, fermentative, sulfate-reducing, and methanogenic microorganisms increased 10-10 000-fold. The rates of methanogenesis and sulfate reduction increased in the near-bottom zone of the injection wells and of some production wells. The microbial oil transformation was accompanied by the accumulation of bicarbonate ions, volatile fatty acids, and biosurfactants in the formation waters, as well as of CH4 and CO2 both in the gas phase and in the oil. Microbial metabolites promoted the additional recovery of oil. As a result of the application of biotechnology, the water content in the production liquid from the test site decreased, and the oil content increased. This allowed the recovery of more than 14000 tons of additional oil over 3.5 years. 相似文献
63.
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
64.
65.
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
66.
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
67.
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
68.
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
69.
70.