全文获取类型
收费全文 | 2328篇 |
免费 | 152篇 |
学科分类
生物科学 | 2480篇 |
出版年
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 25篇 |
2018年 | 29篇 |
2017年 | 22篇 |
2016年 | 39篇 |
2015年 | 51篇 |
2014年 | 68篇 |
2013年 | 121篇 |
2012年 | 101篇 |
2011年 | 95篇 |
2010年 | 71篇 |
2009年 | 59篇 |
2008年 | 106篇 |
2007年 | 136篇 |
2006年 | 101篇 |
2005年 | 114篇 |
2004年 | 115篇 |
2003年 | 111篇 |
2002年 | 118篇 |
2001年 | 102篇 |
2000年 | 99篇 |
1999年 | 87篇 |
1998年 | 38篇 |
1997年 | 25篇 |
1996年 | 25篇 |
1995年 | 16篇 |
1994年 | 27篇 |
1993年 | 22篇 |
1992年 | 72篇 |
1991年 | 27篇 |
1990年 | 44篇 |
1989年 | 35篇 |
1988年 | 53篇 |
1987年 | 28篇 |
1986年 | 29篇 |
1985年 | 18篇 |
1984年 | 12篇 |
1983年 | 22篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 17篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1975年 | 11篇 |
1974年 | 12篇 |
1973年 | 18篇 |
1971年 | 8篇 |
排序方式: 共有2480条查询结果,搜索用时 15 毫秒
41.
A Ca2+, calmodulin-dependent protein kinase from rat brain with a MW of 640,000 phosphorylated calmodulin-sensitive phosphodiesterase from the brain cytosol. The Km of the enzyme for the phosphodiesterase was 5.0 microM and the Vmax was 212 nmol/mg/min. The amount of phosphate incorporated into the phosphodiesterase was 0.7 mol/mol subunit. Phosphorylation of the phosphodiesterase enhanced the enzyme activity by about 20% for hydrolysis of a higher concentration of cyclic AMP. 相似文献
42.
The effect of reovirus double-stranded RNA (dsRNA) and 5'-O-monophosphate form of 2',5'-oligoadenylate (pA(2'p5'A)2) on the translation and degradation of reovirus messenger RNA and on protein phosphorylation was examined in extracts prepared from interferon-treated mouse L fibroblasts. The following results were obtained. 1) The enhanced degradation of reovirus [3H]mRNA observed in the presence of either dsRNA or the 5'-O-triphosphate form of 2',5'-oligoadenylate (pppA(2'p5'A)3) was completely blocked by pA(2'p5'A)2. 2) The dsRNA-dependent phosphorylation of protein P1 and the alpha subunit of eukaryotic initiation factor (eIF-2) depended in a similar manner upon the concentration of dsRNA and was optimal at low dsRNA concentrations (0.1 to 1 microgram/ml). However, high concentrations of dsRNA (greater than 100 micrograms/ml) drastically reduced the phosphorylation of both P1 and eIF-2 alpha. Neither P1 nor eIF-2 alpha phosphorylation was affected by either pA(2'p5'A)2 or pppA(2'p5'A)3. 3) The translation of reovirus mRNA in vitro was inhibited by the addition of either low concentrations of dsRNA or pppA(2'p5'A)3. Whereas pA(2'p5'A)2 completely reversed the pppA(2'p5'A)3-mediated inhibition of translation, the inhibition mediated by low concentrations of dsRNA was only partially reversed by pA(2'p5'A)2. Under conditions where the pppA-(2'p5'A)3mediated degradation of reovirus mRNA was blocked, the translation of reovirus mRNA was still inhibited by low but not by high concentrations of dsRNA in a manner that correlated with the activation of P1 and eIF-2 alpha phosphorylation. These results suggest that the pppA(2'p5'A)n-dependent ribonuclease is not required and that protein phosphorylation may indeed be sufficient for the dsRNA-dependent inhibition of reovirus mRNA translation in cell-free systems derived from interferon-treated mouse fibroblasts. 相似文献
43.
K Higashi K Fukunaga K Matsui M Maeyama E Miyamoto 《Biochimica et biophysica acta》1983,747(3):232-240
Myosin light-chain kinase was purified from porcine myometrium to apparent homogeneity at about 262-fold with an Mr of 130 000 as determined by SDS-polyacrylamide gel electrophoresis and a sedimentation coefficient of 4.5 S. The approximate content of the soluble myosin light-chain kinase was estimated to be about 0.85 microM. The purified enzyme exhibited strict substrate specificity only for 20-kDa myosin light chain and Ka values of 0.6 nM and 0.3 microM for calmodulin and Ca2+, respectively. The enzyme was phosphorylated by the catalytic subunit of cyclic AMP-dependent protein kinase, which resulted in a decrease in the affinity for calmodulin of 4-7-fold without effect on the Vmax. The maximal amount of phosphate incorporated into the enzyme was 0.5-0.8 and 1.0-1.4 mol per mol of the enzyme in the presence and absence of Ca2+ and calmodulin, respectively. In the presence of a subsaturating concentration of calmodulin, the enzyme showed a lower sensitivity for Ca2+ by phosphorylation. 相似文献
44.
Abstract: The higher-molecular-weight elongation factor-1 (EF-1H) of the chick brain was observed to contain three subunits (denominated α, β, and γ), contrary to a previous report that the brain EF-1H consisted of aggregates of low-molecular-weight elongation factor- 1 (EF-1L). Crude EF-1H, obtained from 20-day embryonic brain, was treated with 0.4 M ammonium chloride and 0.1 mM GTP, and EF-1βγ, was obtained using a DEAE-Sephadex column equilibrated in 0.025 mM GTP. Both EF-1β, and EF-1γ, were isolated by means of a DE-52 column equilibrated in 6 M urea and were found to have molecular weights of 2.8 and 4.8 × 104, respectively. EF-1β and EF-1γ were also obtained from young rat and calf brains by the same procedures. The molecular weight of the isolated EF-1α was 5 × 104. It was found that EF-1β stimulated the two EF-1α-dependent reactions, i.e., phenylalanyl-tRNA binding (reaction 1) and polyphenylalanine synthesis (reaction 2), and also stimulated the nucleotide exchange reaction in the EF- 1α-guanine nucleotide binary complex (reaction 3). The degrees of stimulation of reactions 1, 2, and 3 by the addition of EF-1β were 2 to 3 times, about 18 times, and 2 to 3 times as much as with EF-1α alone, respectively. The amino acid compositions of EF-1α -1β, and -1γ and EF-2 were very similar to those of other eukaryotic tissues. Thus the constituents and properties of EFs of the brain were found to be basically similar to those of other tissues of eukaryotes, although EF-1β, and EF-1, had not been reported in the brain. A possible physiological significance of EF-1β during brain development is also discussed. 相似文献
45.
Alleviation of Aluminum Stress and Stimulation of Tea Pollen Tube Growth by Fluorine 总被引:2,自引:0,他引:2
Aluminum (Al) and fluorine (F) were found to affect tea pollentube growth on an agar medium. Not only was the growth stronglyrepressed by increasing Al content of the medium but it wasalso distinctly affected by declining pH from 5.2 to 4.4. Additionof 0.2 mM Al as Al2(SO4)3 to a pH 4.6 medium containing 1.2%agar, 8% sucrose and 17 ppm boron remarkably repressed tea pollentube growth. However, NaF added to medium containing Al clearlyalleviated the growth inhibition. This effect was observed with0.2 mM and 0.4 HIM NaF, and the presence of 0.6 mM and 1.2 DIMNaF with 0.2 mM Al even produced a stimulatory effect. Treatmentwith NaF alone significantly stimulated growth at pH 4.6 and5.2. These results indicate that Al-F complexes have a favorablerather than adverse effect on tea pollen tube growth. (Received November 22, 1982; Accepted April 20, 1983) 相似文献
46.
Serologic classification of Herpes simplex viruses 总被引:4,自引:0,他引:4
47.
48.
49.
50.
Power requirements in the agitation of non-Newtonian fermentation broths with and without aeration were measured by a strain gage-type dynamometer. Broth from the production of gluc-amylase by Endomyces species and carboxymethyl cellulose solutions were used as non-Newtonian fluids. In gas–liquid agitation systems, the correlation between Pg and P02 ND3/Q0.56 observed by Michel and Miller was found to be applicable to non-Newtonian fluids in laminar and transition regions. This was particularly true for fluids with apparent viscosities larger than 300 cp. The impeller diameter and impeller blade width had considerable effects on power consumption in a nongassed system. It was suggested, therefore, that Pg/P0 should be correlated by a dimensionless term involving some impeller-size factors. 相似文献