全文获取类型
收费全文 | 5116篇 |
免费 | 473篇 |
国内免费 | 903篇 |
出版年
2023年 | 75篇 |
2022年 | 104篇 |
2021年 | 241篇 |
2020年 | 186篇 |
2019年 | 230篇 |
2018年 | 201篇 |
2017年 | 147篇 |
2016年 | 224篇 |
2015年 | 297篇 |
2014年 | 381篇 |
2013年 | 405篇 |
2012年 | 516篇 |
2011年 | 508篇 |
2010年 | 329篇 |
2009年 | 278篇 |
2008年 | 336篇 |
2007年 | 298篇 |
2006年 | 285篇 |
2005年 | 212篇 |
2004年 | 200篇 |
2003年 | 195篇 |
2002年 | 171篇 |
2001年 | 126篇 |
2000年 | 99篇 |
1999年 | 93篇 |
1998年 | 65篇 |
1997年 | 46篇 |
1996年 | 43篇 |
1995年 | 21篇 |
1994年 | 35篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1980年 | 7篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 5篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有6492条查询结果,搜索用时 967 毫秒
1.
Bing Xia Haiping Ke Wei Jiang Masayori Inouye 《The Journal of biological chemistry》2002,277(8):6005-6011
The 5'-end region of cspA mRNA contains a Cold Box sequence conserved among several cold-shock mRNAs. This region forms a stable stem-loop structure followed by an AU-rich sequence. Here we show that the Cold Box region is essential for the normal scale of cspA mRNA induction after cold shock because a deletion of the stem-loop significantly destabilizes the mRNA and reduces the cold shock-induced cspA mRNA amount by approximately 50%. The AU-rich track, however, slightly destabilizes the mRNA. The integrity of the stem is essential for the stabilizing function, whereas that of the loop sequence is less important. Overexpression of a mutant cspA mRNA devoid of both the AUG initiation codon and the coding sequence results in a severe growth inhibition at low temperature along with a derepression of the chromosomal cspA expression. Furthermore, the overexpressed RNA is stably associated with the 30 S and 70 S ribosomes. Our results demonstrate that the AUG initiation codon and the coding region containing the downstream box are not required for cspA mRNA to bind ribosomes and that the 5'-untranslated region by itself has a remarkable affinity to ribosomes at low temperature. 相似文献
2.
3.
4.
The effect of lysolecithin (lysophosphatidylcholine) on the relaxation of rabbit aortic strip closely resembled that produced by acetylcholine (ACh) which releases the endothelium-derived relaxing factor (EDRF). Relaxation induced by lysolecithin depended on the presence of endothelium and was inhibited by hemoglobin and methylene blue. It appeared to be mediated by the second messenger, c-GMP. Lysolecithin induced relaxation was slower but more persistent than that resulting from the endothelium-derived relaxing factor (EDRF) produced by acetylcholine (ACh). Like lysolecithin, Triton X-100, a non-ionic detergent, also preferentially relaxed aortic strips with intact endothelium. The results demonstrate the importance of phospholipids derived from cell membranes in vascular smooth muscle relaxation. Endothelium-derived relaxing factors appear as a group of heterogeneous substances. 相似文献
5.
An endogenous circadian rhythm in the transpiration of Tamarix aphylla (L.) Karst. was found for plants grown in continuous light under laboratory conditions. The mean period (±SD) was 21.7±2.3 h (n = 121). No such rhythm was observed in continuous darkness, except for one small hump at the time of the first cycle. The influence of NaCl, Cd(NO3 )2 and LiCi on the rhythmic behaviour of young T. aphylla plants was investigated. NaCl concentrations of up to 150 m M reduced the overall transpiration rates of the plants, but did not change the period of the rhythm. The amplitude and the mesor of the oscillations were inversely correlated with the NaCl concentration. A similar influence was found for Cd(NO3 )2 , but with concentrations that were approximately three orders of magnitude smaller than those of the NaCl treatments. The rhythmic behaviour of the plants was not altered by 10 m M LiCl. It is suggested that the described rhythm of transpiration may have a dual effect: (a) it might cause a partial closure of the stomates during midday hours and (b) it might serve as a possible synchronizer ("master clock") for other rhythmic phenomena in the plants. 相似文献
6.
Synchronized human lymphocytes were exposed to 5-bromo-2-deoxyuridine (BrdUrd) for incorporation in either G-or R-bands. The substituted bands were revealed by monoclonal anti-BrdUrd antibodies disclosed with either gold-labeled antibodies or with the protein A-gold complex. Sharp G-or R-banding, specific for electron microscopy (EM), was obtained. These banding patterns, referred to as GB-AAu (G-bands by BrdUrd using Antibodies and gold [Au]) and RB-AAu (R-bands by BrdUrd using Antibodies and gold [Au]), resemble dynamic band patterns (GBG and RBG) much more than they do morphologic band patterns (GTG and RHG). The G- and R- band patterns allow accurate chromosome identification and karyotyping. An actual karyotype of human GB-AAu-banded chromosomes at the 750 band level, photographed in the EM, is presented. The method produces excellent band separation and band contrast. Variations in band staining intensities were noted and correlated with BrdUrd enrichment. The C-band regions were positively stained after GB-AAu banding while they were negatively stained after RB-AAu banding. Telomeres appeared heterogeneous after GB-AAu banding suggesting that part of the telomeric bands might be late replicating. 相似文献
7.
High-resolution dynamic and morphological G-bandings (GBG and GTG): a comparative study 总被引:3,自引:0,他引:3
Summary A high-resolution replication banding technique, dynamic GBG banding (G-bands after 5-bromodeoxyuridine [BrdUrd] and Giemsa), showed that, at a resolution of 850 bands/genome, GBG banding and GTG banding (G-bands after trypsin and Giemsa) produce almost identical patterns. RBG band (R-bands after BrdUrd and Giemsa) and RHG band (R-bands after heat denaturation and Giemsa) patterns were previously shown to be only 75%–85% coincident; thus GTG banding more accurately reflects replication patterns than does RHG banding. BrdUrd synchronization uses high concentrations of BrdUrd both to substitute early replicating DNA and to arrest cells before the late bands replicate. Release from the block is via a low thymidine concentration. The banding is revealed by the fluorochrome-photolysis-Giemsa (FPG) technique and produces the GBG banding that includes concomitant staining of constitutive heterochromatin. As opposed to other replication G-banding procedures, BrdUrd synchronization and GBG banding produces a reproducible replication band pattern. The discordance between homologs after GBG banding is similar to that after GTG banding and no lateral asymmetry of the constitutive heterochromatin has been observed. Also, BrdUrd synchronization neither significantly depresses the mitotic index, nor induces chromosome breaks. Thus, GBG banding seems as clinically useful as GTG banding and provides important information regarding replication time. 相似文献
8.
9.
水生观赏植物的调查和研究 总被引:2,自引:0,他引:2
倪学明;赵家荣;於炳;周远捷 《武汉植物学研究》1992,10(1):92-100
水生绿化观赏植物是美化园林水景的重要植物材料,作者通过几年的调查研究和引种栽培,提出了28种(其中荷花含18个品种,睡莲含20个品种)水生绿化观赏植物,同时介绍了20种(其中荷花含6个品种)观赏价值较高的水生绿化观赏植物。 相似文献
10.
青龙河底栖无脊椎动物群落结构及其水质评价 总被引:17,自引:3,他引:14
本文论述了青龙河底栖生物种类、数量、分布和结构等特点及其与环境因子间的关系。应用Beck、Gleason、Shannon、Simpson等生物指数对水质状况进行评价。结果表明青龙河除个别断面受污染外,大部分河段属尚清洁水。 相似文献