全文获取类型
收费全文 | 134746篇 |
免费 | 10958篇 |
国内免费 | 13783篇 |
专业分类
159487篇 |
出版年
2024年 | 346篇 |
2023年 | 1788篇 |
2022年 | 4028篇 |
2021年 | 6736篇 |
2020年 | 4705篇 |
2019年 | 5880篇 |
2018年 | 5543篇 |
2017年 | 4149篇 |
2016年 | 5774篇 |
2015年 | 8382篇 |
2014年 | 9916篇 |
2013年 | 10454篇 |
2012年 | 12660篇 |
2011年 | 11492篇 |
2010年 | 7258篇 |
2009年 | 6461篇 |
2008年 | 7403篇 |
2007年 | 6683篇 |
2006年 | 5825篇 |
2005年 | 4670篇 |
2004年 | 3946篇 |
2003年 | 3673篇 |
2002年 | 3102篇 |
2001年 | 2442篇 |
2000年 | 2168篇 |
1999年 | 2096篇 |
1998年 | 1302篇 |
1997年 | 1241篇 |
1996年 | 1156篇 |
1995年 | 981篇 |
1994年 | 943篇 |
1993年 | 716篇 |
1992年 | 936篇 |
1991年 | 713篇 |
1990年 | 536篇 |
1989年 | 511篇 |
1988年 | 410篇 |
1987年 | 380篇 |
1986年 | 315篇 |
1985年 | 340篇 |
1984年 | 179篇 |
1983年 | 186篇 |
1982年 | 128篇 |
1981年 | 106篇 |
1980年 | 70篇 |
1979年 | 96篇 |
1977年 | 65篇 |
1975年 | 61篇 |
1974年 | 60篇 |
1973年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Isolation of two novel myb-like genes from Arabidopsis and studies on the DNA-binding properties of their products 总被引:2,自引:0,他引:2
Two novel myb-like genes (atmyb6 and atmyb7) were isolated from an Arabidopsis thaliana cDNA library. The entire proteins or the Myb domains encoded by the genes were expressed as fusion proteins in Escherichia coli. The DNA-binding domain of the murine c-Myb was also expressed in the same way for use in comparative studies. The fusion proteins were examined for their DNA-binding activity using the animal c-Myb DNA-binding site (MBS) and the binding site of the maize P gene product (PBS). The Myb domain of Atmyb6 bound to PBS more efficiently than to MBS. Complete Atmyb6 and Atmyb7 proteins preferentially bound to PBS but not MBS. This suggests that the in vitro binding consensus sequences for both Atmyb6 and Atmyb7 are similar to PBS. The binding of the Myb domain of Atmyb6 to both PBS and MBS raises the possibility that the protein recognizes multiple sequences in vivo. The third α-helix and three adjacent amino acids in the third repeat (R3) of c-Myb were replaced with the analogous sequence of Atmyb6 to create a chimeric Myb protein. This chimeric protein bound to PBS with a low affinity but failed to bind to MBS. Thus the binding pattern of the chimeric Myb protein is similar to that of the Atmyb6. This result suggests that the last 20 amino acids in the R3 repeat of Atmyb6 play a major role in DNA-binding. 相似文献
92.
93.
Microbial uptake of radiolabeled substrates: estimates of growth rates from time course measurements. 下载免费PDF全文
W K Li 《Applied microbiology》1984,47(1):184-192
The uptake of [3H]glucose and a mixture of 3H-labeled amino acids was measured, in time course fashion, in planktonic microbial assemblages of the eastern tropical Pacific Ocean. The average generation times of those portions of the assemblages able to utilize these substrates were estimated from a simple exponential growth model. Other workers have independently used this model in its integrated or differential form. A mathematical verification and an experimental demonstration of the equivalence of the two approaches are presented. A study was made of the size distribution of heterotrophic activity, using time course measurements. It was found that the size distribution and the effect of sample filtration before radiolabeling were dependent on time of incubation. In principle, it was possible to ascribe these time dependences to differences in the specific growth rate and initial standing stock of the microbial assemblages. 相似文献
94.
95.
96.
Rotating disk voltammetry was used in this work to study the rates of reaction of ferricytochrome c with two very strong reductants, methyl and benzyl viologen. The rates of reaction for these reductants were found to be 4.0 × 107 and 5.4 × 107m?1s?1 at 24°C for benzyl and methyl viologen, respectively. The versatility of this method was demonstrated by the ease with which the activation parameters were obtained. The ΔH≠ and ΔS≠ were found to be 4.0 kcal/mol and ?10.6 cal/mol-K, respectively, for benzyl viologen. All the observed reaction rates were corrected for coulombic effects by the method of Wherland and Gray, and the electrostatically corrected rate constants were compared with the Marcus and Hopfield theories for electron transfer. The agreement was excellent for the tunneling theory but there were some discrepancies with the absolute Marcus theory. The relative Marcus approach worked quite well and, by taking into account the nonadiabaticity of the electron transfer, reasonable values were obtained for the absolute Marcus theory when realistic values of the self-exchange constants were used. 相似文献
97.
本文介绍用二相分配法制备蚕豆叶片原生质膜上的Ca~(2+)·Mg~(2+)-ATPase,用以研究镧系,稀土离子对此酶活性的影响。初步证实Pr~(3+)、Nd~(3+)对依赖于CaM的以及不依赖于CaM的蚕豆叶片原生质膜上Ca~(2+)·Mg~(2+)-ATPase活性的抑制不是CaM专一的。 相似文献
98.
99.
100.
本文选用金黄地鼠的微血管,利用显微高速摄影技术,放大微观流场和血细胞,连续地“冻结”短瞬间的变化状态,把物理图象呈现在胶片上,经图像分析和数据处理,从定性及定量方面研究血液微流变学,为生命科学和医学研究提供了又一种新的方法。 相似文献