全文获取类型
收费全文 | 11419篇 |
免费 | 866篇 |
国内免费 | 541篇 |
专业分类
12826篇 |
出版年
2024年 | 23篇 |
2023年 | 115篇 |
2022年 | 276篇 |
2021年 | 442篇 |
2020年 | 326篇 |
2019年 | 404篇 |
2018年 | 447篇 |
2017年 | 354篇 |
2016年 | 482篇 |
2015年 | 711篇 |
2014年 | 758篇 |
2013年 | 906篇 |
2012年 | 1074篇 |
2011年 | 935篇 |
2010年 | 546篇 |
2009年 | 509篇 |
2008年 | 594篇 |
2007年 | 520篇 |
2006年 | 442篇 |
2005年 | 388篇 |
2004年 | 355篇 |
2003年 | 294篇 |
2002年 | 253篇 |
2001年 | 201篇 |
2000年 | 187篇 |
1999年 | 170篇 |
1998年 | 86篇 |
1997年 | 97篇 |
1996年 | 92篇 |
1995年 | 76篇 |
1994年 | 72篇 |
1993年 | 72篇 |
1992年 | 89篇 |
1991年 | 87篇 |
1990年 | 66篇 |
1989年 | 53篇 |
1988年 | 47篇 |
1987年 | 48篇 |
1986年 | 36篇 |
1985年 | 39篇 |
1984年 | 22篇 |
1983年 | 21篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1979年 | 11篇 |
1978年 | 15篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1972年 | 12篇 |
1971年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
玉米种子萌发成苗不同阶段需水阈值的研究 总被引:7,自引:0,他引:7
用渗透势不同的聚乙二醇(PEG)6000模拟外界环境水分条件,对玉米不同品种的种子在萌动、萌发及成苗三个阶段需水的量化研究表明,种苗的抗旱性随吸水进程的推进而减弱;种子在萌动、萌发及胚芽伸长至一定长度的时间(t)与外界环境水势(w)之间存在着1/t=a+bw的关系,据此推算出不同品种在不同成苗阶段的需水阈值,发现不同品种在同一成苗过程中对环境水分条件的反应不同,它们的抗旱性也不同。 相似文献
72.
73.
74.
MCM genes encode a family of evolutionarily conserved proteins required for DNA replication. In Saccharomyces cerevisiae, where they were first identified, MCM genes interact genetically with each other. Allele specificity in these interactions suggests that MCM proteins physically associate with one another and that this association is essential for function. We describe here an analysis of physical interactions among three Drosophila MCM proteins. Using specific antibodies we detect Drosophila MCMs almost exclusively in 600-kDa protein complexes. Co-immunoprecipitation data demonstrate the existence of at least two distinct types of 600-kDa complexes, one that contains DmCDC46 and one that appears to contain both DmMCM2 and Dpa (a CDC54 homologue). These complexes are stable throughout embryonic division cycles, are resistant to treatments with salt and detergent, and are present during development in tissues undergoing mitotic DNA replication as well as endoreplication. When extracts are prepared under low salt conditions all three MCM proteins co-immunoprecipitate. Consequently, we suggest that the 600-kDa complexes interact in a higher order complex. 相似文献
75.
桃花营养元素的分析与开发探讨 总被引:2,自引:0,他引:2
桃花含有较高的蛋白质和人体必需的各种氨基酸、维生素和微量元素。由于桃树在我国分布范围广泛,产花量大且需要人工疏花,使桃花的开发利用具有良好的条件。 相似文献
76.
77.
云南普通马矮型马蛋白多态性及其品种分化关系 总被引:3,自引:1,他引:2
本文运用蛋白电泳技术对来自云南省文山州马关县和麻栗坡县的21匹普通马和14匹矮型马进行了分析。共分析遗传座位44个,其中有10个座位检测到多态性。根据分子钟假说和相应的公式,推算两者的分歧时间约为18.5万年。 相似文献
78.
Identification and analysis of a retinoblastoma binding motif in the replication protein of a plant DNA virus: requirement for efficient viral DNA replication. 总被引:22,自引:3,他引:19 下载免费PDF全文
Geminiviruses are plant DNA viruses with small genomes whose replication, except for the viral replication protein (Rep), depends on host proteins and, in this respect, are analogous to animal DNA tumor viruses, e.g. SV40. The mechanism by which these animal viruses create a cellular environment permissive for viral DNA replication involves the binding of a virally encoded oncoprotein, through its LXCXE motif, to the retinoblastoma protein (Rb). We have identified such a LXCXE motif in the Rep protein of wheat dwarf geminivirus (WDV) and we show its functional importance during viral DNA replication. Using a yeast two-hybrid system we have demonstrated that WDV Rep forms stable complexes with p130Rbr2, a member of the Rb family of proteins, and single amino acid changes within the LXCXE motif abolish the ability of WDV Rep to bind to p130Rbr2. The LXCXE motif is conserved in other members of the same geminivirus subgroup. The presence of an intact Rb binding motif is required for efficient WDV DNA replication in cultured wheat cells, strongly suggesting that one of the functions of WDV Rep may be the linking between viral and cellular DNA replication cycles. Our results point to the existence of a Rb-like protein(s) in plant cells playing regulatory roles during the cell cycle. 相似文献
79.
Allergenic and antigenic proteins released in the apertural sporoderm during the activation process in grass pollen grains 总被引:2,自引:0,他引:2
Jesús Márquez Juan A. Seoane-Camba María Suárez-Cervera 《Sexual plant reproduction》1997,10(5):269-278
A combination of transmission electron microscopy with immunocytochemical methods was used to localize antigenic and allergenic proteins during the maturation and activation processes of Poaceae pollen grains. The intine undergoes a series of modifications that play a decisive role in these processes. Allergenic and antigenic proteins were detected particularly in the intine of activated in vitro grass pollen grains. Labelling of antigenic proteins was more abundant and less specific than that of allergenic proteins. At the time of hydration, the operculum was lifted up, the intine was swollen and labelling of allergenic proteins appeared highly localized in the Zwischenkörper. No significant labelling was observed when the Zwischenkörper gelatinized. Immunolocalization of allergenic proteins in the activated Zwischenkörper indicated the presence of proteins related to activation of the pollen grains. This confirms that the intine function is involved in the processes of pollen tube formation and fertilization, and also suggests the possible mechanism activated in the pollen grains when allergenic proteins reach the mucosa of sensitive subjects. 相似文献
80.
The power of heteronuclear NMR spectroscopy to study macromoleculesand their complexes has been amply demonstrated over the last decade. Theobstacle to routinely applying these techniques to the study of DNA has beenthe synthesis of 13C,15N-labeled DNA. Here wepresent a simple and efficient method to generate isotope-labeled DNA forNMR studies that is as easy as that for isotope labeling of RNA. The methodwas used to synthesize a uniformly13 C,15N-labeled 32-nucleotide DNA that binds tohuman basic fibroblast growth factor with high affinity and specificity.Isotope-edited experiments were applied to the13 C,15N-labeled DNA bound to unlabeled protein,and the 13 C,15N-labeled DNA was also examined incomplex with 15N-labeled protein. The NMR experiments showthat the DNA adopts a well-defined stable structure when bound to theprotein, and illustrate the potential of13 C,15N-labeled DNA for structural studies ofDNA–protein complexes. 相似文献