全文获取类型
收费全文 | 19077篇 |
免费 | 1777篇 |
国内免费 | 1613篇 |
出版年
2024年 | 44篇 |
2023年 | 224篇 |
2022年 | 494篇 |
2021年 | 894篇 |
2020年 | 639篇 |
2019年 | 789篇 |
2018年 | 831篇 |
2017年 | 592篇 |
2016年 | 835篇 |
2015年 | 1213篇 |
2014年 | 1410篇 |
2013年 | 1530篇 |
2012年 | 1742篇 |
2011年 | 1634篇 |
2010年 | 1064篇 |
2009年 | 815篇 |
2008年 | 1070篇 |
2007年 | 879篇 |
2006年 | 790篇 |
2005年 | 725篇 |
2004年 | 665篇 |
2003年 | 662篇 |
2002年 | 550篇 |
2001年 | 239篇 |
2000年 | 201篇 |
1999年 | 220篇 |
1998年 | 161篇 |
1997年 | 108篇 |
1996年 | 97篇 |
1995年 | 98篇 |
1994年 | 108篇 |
1993年 | 66篇 |
1992年 | 96篇 |
1991年 | 82篇 |
1990年 | 62篇 |
1989年 | 61篇 |
1988年 | 56篇 |
1987年 | 37篇 |
1986年 | 48篇 |
1985年 | 53篇 |
1984年 | 43篇 |
1983年 | 33篇 |
1982年 | 38篇 |
1981年 | 37篇 |
1980年 | 29篇 |
1979年 | 26篇 |
1978年 | 26篇 |
1976年 | 30篇 |
1974年 | 31篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 207 毫秒
101.
102.
103.
昆虫是森林生态系统中的重要组成部分。由于森林中枯枝落叶较多,生境复杂,为昆虫提供了良好的繁殖和栖息场所;因而在森林中昆虫的种类多,数量大。大多数昆虫都以森林 相似文献
104.
105.
David A. Raftos Dan L. Stillman Edwin L. Cooper 《In vitro cellular & developmental biology. Plant》1990,26(10):962-970
Summary Pharyngeal explants and circulatory hemocytes from the tunicateStyela clava were cultured in a medium containing tunicate plasma, artificial seawater, RPMI 1640, and antibiotics. Pharnngeal tissue
remained viable and proliferated for up to 72 d in vitro. Proliferative activity maintained the pool of hemocytes within explants
and facilitated the migration of pharyngeal hemocytes from explants into culture supernatants. The diversity of morphologically
distinct cell types within the hemocyte pool of pharyngeal cultures indicated that cell division was followed by regulated
differentiation. In contrast to pharyngeal cultures, suspensions of circulatory hemocytes did not survive for prolonged periods
in vitro. Proliferative activity could not be detected in circulatory hemocyte cultures. These results are discussed in terms
of the differentiation state of hemocytes and the efficacy of culture conditions.
This study was supported by the National Science Foundation, Washington, DC (grant DCB 85 19848) and by BRSG funds from UCLA
Schools of Medicine and Dentistry. Flow cytometric facilities were sponsored in part by a Johnson Cancer Center Core Grant
(CA 16042). David A. Raftos is a Fulbright Postdoctoral Fellow and recipient of a Frederik B. Bang Scholarship in Marine Invertebrate
Immunology administered by the American Association of Immunologist. Dan L. Stillman was supported by an REU supplement from
the National Science Foundation. 相似文献
106.
棕色固氮菌缺失nifZ基因的突变种固氮酶MoFe蛋白的纯化和性质 总被引:1,自引:0,他引:1
采用 52℃下加热 6 min,后经 DEAE- 52、Sephacryls S- 2 0 0和 Q- Sepharose等柱层析方法 ,分离纯化了棕色固氮菌 (Azotobacter vinelandii)缺失 nif Z基因突变种固氮酶 Mo Fe(Δnif Z Mo Fe)蛋白 ,其纯度达到电泳纯。Δnif Z Mo Fe蛋白的固氮活性为 2 83nmol C2 H2 还原 / (min·mg蛋白 ) ,远低于野生种 Mo Fe蛋白。Δnif Z Mo Fe蛋白对氧更敏感 ;热稳定性略低于野生种。Δnif Z Mo Fe蛋白的可见光吸收光谱与野生种 Mo Fe蛋白极为相似。其圆二色谱和磁圆二色谱在 450~ 550 nm与野生种 Mo Fe蛋白显著不同 ,表明其 P- cluster及其周围环境与野生种 Mo Fe蛋白有所差异。这亦可能是造成缺失 nif Z突变种 Mo Fe蛋白固氮活性低的原因。 相似文献
107.
108.
Interactions between the ankyrin repeat-containing protein Akr1p and the pheromone response pathway in Saccharomyces cerevisiae. 总被引:4,自引:2,他引:2
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Akr1p, which contains six ankyrin repeats, was identified during a screen for mutations that displayed synthetic lethality with a mutant allele of the bud emergence gene BEM1. Cells from which AKR1 had been deleted were alive but misshapen at 30 degrees C and inviable at 37 degrees C. During a screen for mutants that required one or more copies of wild-type AKR1 for survival at 30 degrees C, we isolated mutations in GPA1, which encodes the G alpha subunit of the pheromone receptor-coupled G protein. (The active subunit of this G protein is G beta gamma, and G alpha plays an inhibitory role in G beta gamma-mediated signal transduction.) AKR1 could serve as a multicopy suppressor of the lethality caused by either loss of GPA1 or overexpression of STE4, which encodes the G beta subunit of this G protein, suggesting that pheromone signaling is inhibited by overexpression of Akr1p. Mutations in AKR1 displayed synthetic lethality with a weak allele of GPA1 and led to increased expression of the pheromone-inducible gene FUS1, suggesting that Akr1p normally (and not just when overexpressed) inhibits signaling. In contrast, deletion of BEM1 resulted in decreased expression of FUS1, suggesting that Bem1p normally facilitates pheromone signaling. During a screen for proteins that displayed two-hybrid interactions with Akr1p, we identified Ste4p, raising the possibility that an interaction between Akr1p and Ste4p contributes to proper regulation of the pheromone response pathway. 相似文献
109.
Two Chains of Rhamnogalacturonan II Are Cross-Linked by Borate-Diol Ester Bonds in Higher Plant Cell Walls 总被引:21,自引:4,他引:17
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Polysaccharide moiety of the boron-polysaccharide complex (T. Matoh, K. Ishigaki, K. Ohno, J. Azuma [1993] Plant Cell Physiol 34: 639-642) isolated from radish (Raphanus sativus) roots has been shown to be rhamnogalacturonan II by glycosyl-linkage analysis and the presence of diagnostic monosaccharides, including apiose, aceric acid, 2-O-methylfucose, and 3-deoxy-D-manno-2-octulosonic acid. Removal of boron from the complex reduced the molecular weight by one-half without causing a significant increase in the number of reducing end groups, indicating that boron, as boric acid, links two rhamnogalacturonan II chains together to form the boron-polysaccharide complex. 相似文献
110.
We calculate the membrane-induced interaction between inclusions, in terms of the membrane stretching and bending moduli and the spontaneous curvature. We find that the membrane-induced interaction between inclusions varies nonmonotonically as a function of the inclusion spacing. The location of the energy minimum depends on the spontaneous curvature and the membrane perturbation decay length, where the latter is set by the membrane moduli. The membrane perturbation energy increases with the inclusion radius. The Ornstein-Zernike theory, with the Percus-Yevick closure, is used to calculate the radial distribution function of inclusions. We find that when the spontaneous curvature is zero, the interaction between inclusions due to the membrane deformation is qualitatively similar to the hard-core interaction. However, in the case of finite spontaneous curvature, the effective interaction is dramatically modified. 相似文献