全文获取类型
收费全文 | 6269篇 |
免费 | 443篇 |
国内免费 | 2篇 |
出版年
2023年 | 23篇 |
2022年 | 82篇 |
2021年 | 159篇 |
2020年 | 73篇 |
2019年 | 98篇 |
2018年 | 137篇 |
2017年 | 122篇 |
2016年 | 201篇 |
2015年 | 290篇 |
2014年 | 326篇 |
2013年 | 420篇 |
2012年 | 529篇 |
2011年 | 604篇 |
2010年 | 318篇 |
2009年 | 280篇 |
2008年 | 372篇 |
2007年 | 436篇 |
2006年 | 365篇 |
2005年 | 328篇 |
2004年 | 305篇 |
2003年 | 315篇 |
2002年 | 302篇 |
2001年 | 54篇 |
2000年 | 28篇 |
1999年 | 42篇 |
1998年 | 47篇 |
1997年 | 43篇 |
1996年 | 32篇 |
1995年 | 31篇 |
1994年 | 18篇 |
1993年 | 21篇 |
1992年 | 15篇 |
1991年 | 14篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 12篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1975年 | 12篇 |
1973年 | 9篇 |
1972年 | 12篇 |
1969年 | 10篇 |
1968年 | 13篇 |
1967年 | 7篇 |
1966年 | 11篇 |
排序方式: 共有6714条查询结果,搜索用时 15 毫秒
41.
Summary A method based on absorption of Fe(III) at 300 nm was developed and then applied to bacterial leaching of iron-containing metal sulphides. 相似文献
42.
Evelina L Zdorovenko Evgeny Vinogradov Galina M Zdorovenko Buko Lindner Olga V Bystrova Alexander S Shashkov Klaus Rudolph Ulrich Z?hringer Yuriy A Knirel 《European journal of biochemistry》2004,271(23-24):4968-4977
The core structure of the lipopolysaccharide (LPS) isolated from a rough strain of the phytopathogenic bacterium Pseudomonas syringae pv. phaseolicola, GSPB 711, was investigated by sugar and methylation analyses, Fourier transform ion-cyclotron resonance ESI MS, and one- and two-dimensional 1H-, 13C- and 31P-NMR spectroscopy. Strong alkaline deacylation of the LPS resulted in two core-lipid A backbone undecasaccharide pentakisphosphates in the ratio approximately 2.5 : 1, which corresponded to outer core glycoforms 1 and 2 terminated with either L-rhamnose or 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo), respectively. Mild acid degradation of the LPS gave the major glycoform 1 core octasaccharide and a minor truncated glycoform 2 core heptasaccharide, which resulted from the cleavage of the terminal Kdo residues. The inner core of P. syringae is distinguished by a high degree of phosphorylation of L-glycero-D-manno-heptose residues with phosphate, diphosphate and ethanolamine diphosphate groups. The glycoform 1 core is structurally similar but not identical to one of the core glycoforms of the human pathogenic bacterium Pseudomonas aeruginosa. The outer core composition and structure may be useful as a chemotaxonomic marker for the P. syringae group of bacteria, whereas a more conserved inner core structure appears to be representative for the whole genus Pseudomonas. 相似文献
43.
Summary The ability of time-averaged restrained molecular dynamics (TARMD) to escape local low-energy conformations and explore conformational space is compared with conventional simulated-annealing methods. Practical suggestions are offered for performing TARMD calculations with ligand-receptor systems, and are illustrated for the complex of the immunosuppressant FK506 bound to Q50R,A95H,K98I triple mutant FKBP-13. The structure of 13C-labeled FK506 bound to triple-mutant FKBP-13 was determined using a set of 87 NOE distance restraints derived from HSQC-NOESY experiments. TARMD was found to be superior to conventional simulated-annealing methods, and produced structures that were conformationally similar to FK506 bound to wild-type FKBP-12. The individual and combined effects of varying the NOE restraint force constant, using an explicit model for the protein binding pocket, and starting the calculations from different ligand conformations were explored in detail.Abbreviations DG
distance geometry
- dmFKBP-12
double-mutant (R42K,H87V) FKBP-12
- FKBP-12
FK506-binding protein (12 kDa)
- FKBP-13
FK506-binding protein (13 kDa)
- HSQC
heteronuclear single-quantum coherence
- KNOE
force constant (penalty) for NOE-derived distance restraints
- MD
molecular dynamics
- NOE
nuclear Overhauser effect
- SA
simulated annealing
- TARMD
molecular dynamics with time-averaged restraints
- tmFKBP-13
triple-mutant (Q50R,A95H,K98I) FKBP-13
- wtFKBP-12
wild-type FKBP-12 相似文献
44.
45.
Factors involved in capillary growth in the heart 总被引:6,自引:0,他引:6
Olga Hudlická Margaret D. Brown Helene Walter Jacqueline B. Weiss Anita Bate 《Molecular and cellular biochemistry》1995,147(1-2):57-68
Growth of capillaries in the heart occurs under physiological circumstances during endurance exercise training, exposure to high altitude and/or cold, and changes in cardiac metabolism or heart rate elicited by modification of thyroid hormone levels. Capillary growth in all these conditions can be linked with increased coronary blood flow, decreased heart rate, or both. This paper brings evidence that, although increased blood flow due to long-term administration of coronary vasodilators results in capillary growth, a long-term decrease in heart rate induced by electrical bradycardial pacing in rabbits and pigs, or by chronic administration of a bradycardic drug, alinidine, in rats, stimulates capillary growth with little or no change in coronary blood flow. Decreased heart rate results in increased capillary wall tension, increased end-diastolic volume and increased force of contraction, and thus stretch of the capillary wall. This could lead to release of various growth factors possibly stored in the capillary basement membrane. Correlation was found between capillary density (CD) and the levels of low molecular endothelial cell stimulating angiogenic factor (ESAF) both in rabbit and pig hearts with CD increased by pacing. There was no relation between expression of mRNA for basic fibroblast growth factor and CD in sham-operated and paced rabbit hearts. In contrast, mRNA for TGFß was increased in paced hearts, and the possible role of this factor in the regulation of capillary growth induced by bradycardia is discussed. 相似文献
46.
Intercontinental spread of promiscuous mercury-resistance transposons in environmental bacteria 总被引:4,自引:0,他引:4
Olga Yurieva Gennady Kholodii Leonid Minakhin Zhosephine Gorlenko Eza Kalyaeva Sofia Mindlin & Vadim Nikiforov 《Molecular microbiology》1997,24(2):321-329
We demonstrate that horizontal spread of mer operons similar to worldwide spread of antibiotic-resistance genes in medically important bacteria occurred in bacteria found in ores, soils and waters. The spread was mediated by different transposons and plasmids. Some of the spreading transposons were damaged in different ways but this did not prevent their further spread. Certain transposons are mosaics composed of segments belonging to distinct sequence types. These mosaics arose as a result of homologous and site-specific recombination. Our data suggest that the mercury-resistance operons of Gram-negative environmental bacteria can be considered as a worldwide population composed of a relatively small number of distinct recombining clones shared, at least partially, by environmental and clinical bacteria. 相似文献
47.
TNF-alpha in smoke inhalation lung injury 总被引:2,自引:0,他引:2
Hales Charles A.; Elsasser T. H.; Ocampo Peter; Efimova Olga 《Journal of applied physiology》1997,82(5):1433-1437
Hales, Charles A., T. H. Elsasser, Peter Ocampo, and OlgaEfimova. TNF- in smoke inhalation lung injury.J. Appl. Physiol. 82(5):1433-1437, 1997.Adult respiratory distress syndrome is a majorcause of morbidity in fire victims. Tumor necrosis factor- (TNF-)is edematogenic and has been associated with the etiology of otherforms of adult respiratory distress syndrome. In the sheep lymphfistula model, we measured TNF- after 48 (n = 7) or 128 (n = 3) breaths of cotton smoke andcompared this with sham controls (n = 5) or controls in which left atrial pressure was elevated to 20 mmHg(n = 5) to increase lymph flow in the absence of inflammation. Smoke induced a rise in lymph flow and pulmonary arterial pressure with either no fall in lymph-to-plasma protein ratio (128 breaths) or a modest fall in lymph-to-plasma proteinratio (48 breaths), consistent with a change in microvascular permeability as well as a rise in microvascular pressure.Lymph concentration of TNF- fell in both groups, although lymph flux (concentration × flow) transiently rose in both. In neither case did TNF- flux exceed that induced by left atrial pressure elevation. TNF- was detectable in only one out of five sheep in alveolar lavage. Thus, by utilizing a sensitive and specific radioimmunoassay, we were unable to demonstrate a role for TNF- in smoke-induced microvascular lung injury in sheep. 相似文献
48.
In vitro pollen germination of five species and two interspecific hybrids from the genus Brassica was tested in four media. Genetically fixed differences in the demands for optimal pollen germination among species were found. The experiments were designed to define optimal content of mineral salts, sugar, and PEG for every investigated species or hybrids. The differences found among species are discussed in relation to the evolutionary trend. 相似文献
49.
Alexander V. Itkes Kyril T. Turpaev Olga N. Kartasheva Constantin A. Kafiam Evgenii S. Severin 《Molecular and cellular biochemistry》1984,59(1-2):165-171
Summary Dihydrofolate synthetase (EC 6.3.2.12) from N. gonorrhoeae was isolated and enzyme characteristics were determined. The purified enzyme was found quite stable when stored at –60 °C. About 50% of the enzyme activity wag destroyed within 6 weeks when kept at 4 °C. Maximum velocity was observed at pH 9.3. The enzyme required a monovalent cation, K+ or NH4
+ , and divalent cation, Mg2+ or Mn2+ for its function. ATP at 5 mM concentration gave maximum activity. Km values for dihydropteroate and L-glutamate at pH 9.3 were 3.5 × 10–5 M and 6.5 × 10–4 M, respectively. Patterns of product inhibition by dihydrofolate were found to be non-competitive with respect to dihydropteroate, having a Ki value of 5.1 ± 0.8 × 10–4 M, and competitive with respect to L-glutamate, having a Ki value of 6.2 × 10–4 M. 相似文献
50.
Summary Isolated nuclei of rat hepatocytes were incubated with 0.05% sodium heparinate for 2 to 10 min. Alterations in the nuclei were controlled biochemically, determining the amounts of DNA and histones, and by cytophotometric methods determining the amounts of total and nonhistone proteins and DNA. Under the selected experimental conditions 95% of histones are bound already after 5-min incubation with heparin; nonhistone proteins of cell nuclei remain unchanged. The blockade of histones is followed by DNA diffusion into the incubation medium. Experiments with nuclear staining with alcian blue proved the specificity of heparin binding with histones and showed that heparin-histone complex remains in the nuclei, and its histones lose their extractability with 0.25 n HCl. 相似文献