全文获取类型
收费全文 | 4989篇 |
免费 | 257篇 |
国内免费 | 9篇 |
出版年
2023年 | 51篇 |
2022年 | 99篇 |
2021年 | 124篇 |
2020年 | 92篇 |
2019年 | 112篇 |
2018年 | 137篇 |
2017年 | 124篇 |
2016年 | 191篇 |
2015年 | 271篇 |
2014年 | 321篇 |
2013年 | 346篇 |
2012年 | 413篇 |
2011年 | 401篇 |
2010年 | 260篇 |
2009年 | 225篇 |
2008年 | 277篇 |
2007年 | 262篇 |
2006年 | 207篇 |
2005年 | 187篇 |
2004年 | 169篇 |
2003年 | 142篇 |
2002年 | 130篇 |
2001年 | 101篇 |
2000年 | 96篇 |
1999年 | 73篇 |
1998年 | 31篇 |
1997年 | 29篇 |
1996年 | 21篇 |
1995年 | 25篇 |
1994年 | 15篇 |
1993年 | 11篇 |
1992年 | 30篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 27篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1972年 | 8篇 |
排序方式: 共有5255条查询结果,搜索用时 15 毫秒
61.
62.
Some chemical and physical properties of extracellular polysaccharides produced by Butyrivibrio fibrisolvens strains. 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Most strains of Butyrivibrio fibrisolvens are known to produce extracellular polysaccharides (EPs). However, the rheological and functional properties of these EPs have not been determined. Initially, 26 strains of Butyrivibrio were screened for EP yield and apparent viscosities of cell-free supernatants. Yields ranged from less than 1.0 to 16.3 mg per 100 mg of glucose added to the culture. Viscosities ranged from 0.71 to 5.44 mPa.s. Five strains (CF2d, CF3, CF3a, CE51, and H10b) were chosen for further screening. The apparent viscosity of the EP from each of these strains decreased by only 50 to 60% when the shear rate was increased from 20 to 1,000 s-1. Strain CE51 produced the EP having the highest solution viscosity. A detailed comparison of shear dependency of the EP from strain CF3 with xanthan gum showed that this EP was less shear sensitive than xanthan gum and, at a shear rate of 1,000 s-1, more viscous. EPs from strains CF3 and H10b were soluble over a wide range of pH (1 to 13) in 80% (vol/vol) ethanol-water or in 1% (wt/vol) salt solutions. The pH of 1% EP solutions was between 4.5 and 5.5. Addition of acid increased solution viscosities, whereas addition of base decreased viscosity. EPs from strains CF3, CE51, and H10b displayed qualitatively similar infrared spectra. Calcium and sodium were the most abundant minerals in the three EPs. The amounts of magnesium, calcium, and iron varied considerably among the EPs, but the potassium contents remained relatively constant. 相似文献
63.
Two soluble serine proteases Do and So from Escherichia coli were found to distinctively cleave the purified, 39 kDa Ada protein into fragments with sizes of 12-31 kDa. Protease So appears to generate a C-terminal 19 kDa polypeptide, similarly to OmpT protease. In addition, the purified 19 kDa C-terminal half of Ada protein can be further processed mainly to an 18 kDa fragment by protease So and to a 12 kDa by protease Do. These results suggest that proteases Do and So are involved in endogenous cleavage of Ada protein, which may play a role in down-regulating the adaptive response to alkylating agents. 相似文献
64.
65.
The complex sterol mixture isolated from was found to contain a low level of Δ4-3-keto steroids, 5β-stanols and 4α-methyl sterols in addition to regular (4-demethyl) sterols. The following new marine sterols were isolated and identified using MS and 360 MHz NMR: 5β-cholest-22E-en-3β-ol, 24S-methyl-5β-cholest-22E-en-3β-ol, 24-methylene-5β-cholestan-3β-ol, both epimers at C-24 of 4α-methyl-24-ethyl-5α-cholest-22E-en-3β-ol, 4α, 22ξ, 23ξ-(or 24ξ-)trimethyl-5α-cholest-8(14)-en-3β-ol and (22S, 23S, 24S)-4α-24-dimethyl-22, 23-methylene-5α-cholestan-3β-ol. The latter sterol and 23-demethylgorqosterol have opposite configurations at C-22, C-23, and C-24; the Δ8(14) sterol has an unprecedented side chain. 相似文献
66.
Radiolarians of several radiolarites sections of the Pindos-Olonos zone, southern Peloponnesus, lead to propose direct datations of mesozoic sediments. The acuity of such datations allow to distinguish two periods for depositionof radiolarites s.s. in the tethyan region. The first period would be Upper Jurassic and general in tethyan realm, radiolarites depositing under various latitudes (0–35°N). This would be the result of a strong ocean surface current. The second period would be Upper Cretaceous (Vraconian—Coniacian) and be geographically much more restricted (0–15°N). This could result from a weaker current. The absence of radiolaritic sedimentation is possibly the result of the destruction or insulation of the accurate basins during the obduction of ophiolites on the apulo-african realm. The inventory of Late Cretaceous radiolarian fauna, rarely done on alpine series so far, shows similar result to those obtained in Central American and California. 相似文献
67.
The method of administration of [D-Ala5,D-Trp8] somatostatin is of central importance in determining the degree and duration of suppression of insulin and glucagon release. The analog decreased insulin levels in rats when injected by s.c. or i.v. routes, with a nadir 15 minutes following injection. After i.v. injection, insulin levels rapidly returned to basal values while s.c. injection produced significant suppression for 60 minutes. Neither type of injection altered glucagon levels. Intravenous infusion resulted in inhibition of both insulin and glucagon release, with rebound hyperglucagonemia, but not hyperinsulinemia in the post-infusion period. Plasma glucose levels reflected these hormonal changes. Thus, dramatic alterations in the specificity of this somatostatin analog may be achieved by employing different methods of administration. 相似文献
68.
The effects of an inhibitor of RNA synthesis, cordycepin, and an inhibitor of protein synthesis, cycloheximide, on aldosterone-induced changes in lipid metabolism and phospholipid fatty acid composition have been studied in the toad urinary bladder. At the concentrations employed, the inhibitors abolish the hormone-induced increases in total lipid synthesis, phospholipid fatty acid specific activities, and weight percentage of phospholipid long-chain polyunsaturated fatty acids as well as blocking the aldosterone-mediated increase in sodium transport. 相似文献
69.
J P Leroux J C Marchand R Hong Tuan Ha P Cartier 《European journal of biochemistry》1975,58(2):367-373
Viable human polymorphonuclear leukocytes isolated from peripheral blood were incubated for 1 h at 37 degrees C with variable concentrations of insulin in a saline medium buffered at pH 7.4. The hormone increased glucose consumption by about 40% without influencing the permeability of the membranes to glucose, whose uptake followed a passive diffusion process. The measurement of intermediates localized activation of glycolysis by insulin, down to 0.36 nM, at the phosphofructokinase step. However, the spectrophotometric measurement showed no activation of phosphofructokinase after preincubation with insulin of either intact granulocytes or crude or ultracentrifuged homogenates. The level of cyclic AMP, which is known to activate phosphofructokinase, was not modified by insulin; cyclic GMP did not activate the enzyme in the granulocyte extracts: neither of the two nucleotides can therefore be considered as a direct messenger of the action of insulin on phosphofructokinase. An important fraction of the extra glucose consumed under the influence of insulin was recovered as neither glycogen nor lactate, nor was it oxidized in the Krebs cycle. It might be assumed to have been converted into glycerolipids. However, insulin produced no detectable accumulation of triglycerides and activated neither the pentose phosphate pathway nor oxidative decarboxylation of pyruvate. The fate of the extra glucose consumed under the influence of insulin therefore remains questionable. 相似文献
70.