全文获取类型
收费全文 | 13834篇 |
免费 | 1290篇 |
国内免费 | 7篇 |
专业分类
15131篇 |
出版年
2022年 | 108篇 |
2021年 | 235篇 |
2020年 | 121篇 |
2019年 | 171篇 |
2018年 | 231篇 |
2017年 | 203篇 |
2016年 | 296篇 |
2015年 | 519篇 |
2014年 | 640篇 |
2013年 | 755篇 |
2012年 | 1014篇 |
2011年 | 1014篇 |
2010年 | 657篇 |
2009年 | 588篇 |
2008年 | 797篇 |
2007年 | 785篇 |
2006年 | 728篇 |
2005年 | 667篇 |
2004年 | 708篇 |
2003年 | 640篇 |
2002年 | 648篇 |
2001年 | 154篇 |
2000年 | 105篇 |
1999年 | 151篇 |
1998年 | 179篇 |
1997年 | 124篇 |
1996年 | 103篇 |
1995年 | 97篇 |
1994年 | 127篇 |
1993年 | 111篇 |
1992年 | 104篇 |
1991年 | 93篇 |
1990年 | 84篇 |
1989年 | 78篇 |
1988年 | 65篇 |
1987年 | 76篇 |
1986年 | 70篇 |
1985年 | 95篇 |
1984年 | 125篇 |
1983年 | 82篇 |
1982年 | 122篇 |
1981年 | 90篇 |
1980年 | 86篇 |
1979年 | 71篇 |
1978年 | 82篇 |
1977年 | 61篇 |
1976年 | 72篇 |
1975年 | 63篇 |
1974年 | 72篇 |
1973年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
The use of a cotton gauze swab and subsequent culture of the swab was found to be a more sensitive method for isolating Salmonella from liquid milk than the revised procedure of North. The swab method was found to be as sensitive as the North procedure for recovering Salmonella when incubated at 37 C but more sensitive when incubated at 43 C. Incubation of the swab cultures at the elevated temperature of 43 C gave good results when Salmonella was present at levels as low as one per liter. Swabs exposed to milk contaminated with 100 Salmonella per liter remained positive even when subsequently washed for 2 hr in noncontaminated milk. Bismuth sulfite agar and Brilliant Green sulfadiazine agar were equally effective for isolating Salmonella from broth cultures; use of both media resulted in maximal isolations. 相似文献
93.
94.
Immunological and Biophysical Separation of Dengue-2 Antigens 总被引:12,自引:1,他引:11
Robert D. Cardiff Walter E. Brandt Thomas G. McCloud Daniel Shapiro Philip K. Russell 《Journal of virology》1971,7(1):15-23
Antigenic compositions of slowly sedimenting dengue-2 hemagglutinin (SHA) and soluble complement-fixing antigen (SCF) were compared with the virion (rapidly sedimenting hemagglutinin, RHA) by radioimmune precipitation (RIP), RIP inhibition, kinetic neutralization, and neutralization blocking tests with the use of hyperimmune mouse ascitic fluids. RHA and SHA were unable to inhibit completely the RIP of each other by anti-RHA, and neutralization by anti-RHA was not blocked by SHA. This indicated that SHA is serologically related, but not identical, to RHA. SHA differed from RHA in that SHA lacked the “core” polypeptide but contained the two envelope polypeptides. In addition, SHA contained a polypeptide with a molecular weight of 16,500 daltons and a suggestion of several other proteins. These data, when considered with other evidence, suggest that SHA is a special form of “incomplete virus.” SCF was unable to inhibit the RIP of SHA or RHA or to block neutralizing antibodies. Further, anti-SCF did not neutralize RHA or precipitate significant levels of SHA or RHA. Polyacrylamide gel electrophoresis separated SCF from structural polypeptides by molecular size. This evidence suggests that SCF is a nonstructural antigen. 相似文献
95.
Histidyl-Transfer Ribonucleic Acid Synthetase in Positive Control of the Histidine Operon in Salmonella typhimurium 总被引:15,自引:9,他引:6 下载免费PDF全文
James H. Wyche Bert Ely Thomas A. Cebula Michael C. Snead Philip E. Hartman 《Journal of bacteriology》1974,117(2):708-716
Autolysin-like enzymes appear to be responsible for cell separation in Agmenellum quadruplicatum. Mutants that are impaired in cell separation and grow as chains exhibit reduced cell lytic activity. Lysozyme, extracted autolysin, and antibiotics that affect peptidoglycan synthesis phenotypically suppress chain formation. Various aspects of the regulation of the cell separation process were also examined. Studies involving antibiotic inhibitors of macromolecular synthesis and general growth inhibitors provided no evidence for the active regulation of the cell separation process during the latter portion of the division cycle. Evidence was obtained, however, for the partial restriction of peptidogly-can hydrolysis by unknown secondary modifications. The thin electron-dense layer of peptidoglycan along the sides of cells was much more resistant to hydrolysis by egg-white lysozyme than was the septum between daughter cells. The middle portion of the septum was more sensitive than was the layer immediately adjacent to the cytoplasmic membrane. Under conditions that would not osmotically stabilize spheroplasts, lysozyme facilitates rapid cell separation in chain-forming mutants with little leakage of cellular protein or loss of viability. 相似文献
96.
A new minimal medium for enterobacteria has been developed. It supports growth of Escherichia coli and Salmonella typhimurium at rates comparable to those of any of the traditional media that have high phosphate concentrations, but each of the macronutrients (phosphate, sulfate, and nitrogen) is present at a sufficiently low level to permit isotopic labeling. Buffering capacity is provided by an organic dipolar ion, morpholinopropane sulfonate, which has a desirable pK (7.2) and no apparent inhibitory effect on growth. The medium has been developed with the objectives of (i) providing reproducibility of chemical composition, (ii) meeting the experimentally determined nutritional needs of the cell, (iii) avoiding an unnecessary excess of the major ionic species, (iv) facilitating the adjustment of the levels of individual ionic species, both for isotopic labeling and for nutritional studies, (v) supplying a complete array of micronutrients, (vi) setting a particular ion as the crop-limiting factor when the carbon and energy source is in excess, and (vii) providing maximal convenience in the manufacture and storage of the medium. 相似文献
97.
RNA, poly(G) and poly(A) were reacted with benz[a]anthracene 5,6-oxide or with 7,12-dimethylbenz[a]anthracene 5,6-oxide and hydrolysates of the alkylated polymers examined using a combination of Sephadex LH20 column chromatography and thin-layer chromatography on silica gel. The results show that two RNA products are formed in reactions with benz[a]anthracene 5,6-oxide, one resulting from reaction with guanine and the other from reaction with adenine. With 7,12-dimethylbenz[a]anthracene 5,6-oxide, six RNA products appeared to be formed, two resulting from reactions with guanine and three from alkylation of adenine; the other product has not been identified. 相似文献
98.
Hydrostatic pressure was found to cause a marked narrowing of pH ranges for growth and reductions in growth yields for a variety
of bacteria. In many cases, reduced yields under pressure could be directly related to increased sensitivities to metabolic
acids that accumulated in the enclosed culture vessels used. Magnesium and calcium ions partially reversed increases in sensitivities
of representative gram-positive and gram-negative bacteria to low, but not high, pH. Growth inhibition of these organisms
at both extremes of pH was associated with enhanced loss of K+ from pressurized cells. Inhibited cells in alkaline media also lysed under pressure, but microscopically observable lysis
was clearly a secondary phenomenon because it occurred slowly. Apparent volumes for growth-inhibitory protonation-deprotonation
reactions were calculated on the basis of measured shifts in inhibitory pH with pressure. The values ranged from 99 to 431
ml/mole, and their magnitudes indicated that growth inhibition by acids or bases involves cooperative changes in polymeric
interactions such as those which accompany protein denaturation. 相似文献
99.
Bilayers of human erythrocyte apoprotein-lipid complexes were made by dipping a mica plate through monolayers of the complex formed at the air-water interface. Stearic acid and erythrocyte lipid alone served as controls. Freeze-fracture images of the complex at high lipid surface pressures (30 dynes/cm) showed particles (average diameter, 109 Å ± 18 Å) similar to those of erythrocyte ghosts (average diameter, 102 Å ± 19 Å). Control surfaces were smooth. We conclude that part or all of the protein molecule penetrated into the lipid bilayer and that erythrocyte apoprotein-lipid complexes yield fracture faces similar to the native erythrocyte membrane. 相似文献
100.
Use of Erythrocytes Sensitized with Purified Pneumococcal Polysaccharides for the Assay of Antibody and Antibody-producing Cells 总被引:53,自引:2,他引:51 下载免费PDF全文
A method was described for the sensitization of erythrocytes with purified type-specific pneumococcal polysaccharide antigens using chromium chloride as a coupling agent. Erythrocytes so sensitized can be used in routine passive hemagglutination and hemolysis tests as well as in the technique of localized hemolysis-in-gel for the detection of specific antibody and specific antibody-producing cells, respectively. 相似文献