全文获取类型
收费全文 | 201842篇 |
免费 | 9323篇 |
国内免费 | 9781篇 |
出版年
2024年 | 144篇 |
2023年 | 1317篇 |
2022年 | 1854篇 |
2021年 | 5676篇 |
2020年 | 3980篇 |
2019年 | 4927篇 |
2018年 | 15322篇 |
2017年 | 13169篇 |
2016年 | 11715篇 |
2015年 | 7719篇 |
2014年 | 8668篇 |
2013年 | 9237篇 |
2012年 | 14605篇 |
2011年 | 21580篇 |
2010年 | 17198篇 |
2009年 | 13102篇 |
2008年 | 15486篇 |
2007年 | 16392篇 |
2006年 | 5069篇 |
2005年 | 4320篇 |
2004年 | 4221篇 |
2003年 | 3977篇 |
2002年 | 3258篇 |
2001年 | 2309篇 |
2000年 | 2022篇 |
1999年 | 1851篇 |
1998年 | 1118篇 |
1997年 | 1111篇 |
1996年 | 1030篇 |
1995年 | 887篇 |
1994年 | 858篇 |
1993年 | 705篇 |
1992年 | 920篇 |
1991年 | 737篇 |
1990年 | 535篇 |
1989年 | 500篇 |
1988年 | 417篇 |
1987年 | 402篇 |
1986年 | 300篇 |
1985年 | 324篇 |
1984年 | 184篇 |
1983年 | 197篇 |
1982年 | 112篇 |
1981年 | 96篇 |
1980年 | 67篇 |
1979年 | 88篇 |
1978年 | 63篇 |
1975年 | 68篇 |
1972年 | 307篇 |
1971年 | 300篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
根瘤菌资源数据库(RRDB)的建立 总被引:1,自引:1,他引:0
在总结我室多年对根瘤菌资源调查与分类研究的基础上,建立了根瘤菌资源数据库(RRDB)。此库依据根瘤菌研究特点而设计,包括:基本信息、采集信息、保藏信息、回接信息、参考文献、性状信息、菌株说明等七个子库。目前收录了来自国内21个省或地区及国外部分研究单位提供的;并经全面性状分析与分类研究的286个菌株的信息,每个菌株设有寄主来源、固氮酶活性、碳源、氮源的利用等321个数据项。该库具有数据维护、查询检索、数据统计、输出打印等功能,引入并连接了聚类分析软件包-MINTS系统,可以满足当前研究的需要。 相似文献
992.
马铃薯Y病毒组病毒高产量提取方法的建立 总被引:11,自引:0,他引:11
本文报道了高产量提取芜菁花叶病毒(TuMV)、莴苣花叶病毒(LMV)、芋花叶病毒(DMV)和大豆花叶病毒(SMV)的提取方法。本方法通过使用高盐浓度的磷酸盐缓冲液以及在缓冲液中加入氯化镁和脲,并用TritonX-100作为澄清剂,替代常规使用的氯仿和正丁醇,成功的提取到了大量病毒粒子,上述四种病毒提取的得率分别是TuMV为173.3mg/kg病叶,LMV为96mg/kg病叶,SMV为199.2mg/kg病叶,DMV为176.6mg/kg病叶。 相似文献
993.
原生质体诱变选育无孢平菇 总被引:7,自引:0,他引:7
用紫外线照射紫孢侧耳(Pleurotus sapidus)双核菌丝原生质体,再生后筛选生长势好的菌株, 通过出菇试验得到了生产性状与紫孢侧耳一致的无孢和少孢平菇新品种。Abstract: This paper reported isolation and regeneration of the dikaryocyte protoplasts from Pleurotus sapidus, and the protoplasts were treated by U.V-irradiation for selection spore less mutants. 相似文献
994.
995.
996.
A novel mammalian Ras GTPase-activating protein which has phospholipid-binding and Btk homology regions. 总被引:8,自引:2,他引:6 下载免费PDF全文
M Maekawa S Li A Iwamatsu T Morishita K Yokota Y Imai S Kohsaka S Nakamura S Hattori 《Molecular and cellular biology》1994,14(10):6879-6885
We have previously purified a novel GTPase-activating protein (GAP) for Ras which is immunologically distinct from the known Ras GAPs, p120GAP and neurofibromin (M. Maekawa, S. Nakamura, and S. Hattori, J. Biol. Chem. 268:22948-22952, 1993). On the basis of the partial amino acid sequence, we have obtained a cDNA which encodes the novel Ras GAP. The predicted protein consists of 847 amino acids whose calculated molecular mass, 96,369 Da, is close to the apparent molecular mass of the novel Ras GAP, 100 kDa. The amino acid sequence shows a high degree of similarity to the entire sequence of the Drosophila melanogaster Gap1 gene. When the catalytic domain of the novel GAP was compared with that of Drosophila Gap1, p120GAP, and neurofibromin, the highest degree of similarity was again observed with Gap1. Thus, we designated this gene Gap1m, a mammalian counterpart of the Drosophila Gap1 gene. Expression of Gap1m was relatively high in brain, placenta, and kidney tissues, and it was expressed at low levels in other tissues. A recombinant protein consisting of glutathione-S-transferase and the GAP-related domain of Gap1m stimulated GTPase of normal Ras but not that of Ras having valine at the 12th residue. Expression of the same region in Saccharomyces cerevisiae suppressed the ira2- phenotype. In addition to the GAP catalytic domain, Gap1m has two domains with sequence closely related to those of the phospholipid-binding domain of synaptotagmin and a region with similarity to the unique domain of Btk tyrosine kinase. These results clearly show that Gap1m is a novel Ras GAP molecule of mammalian cells. 相似文献
997.
998.
The distribution and abundance of nitric oxide synthase (NOS)-containing neurons and their terminals in the gastrointestinal tract of the guinea-pig were examined in detail using NADPH diaphorase histochemistry and NOS immunohistochemistry. NOS-containing cell bodies were found in the myenteric plexus throughout the gastrointestinal tract and in the submucous plexus of the stomach, colon and rectum. NOS-containing neurons comprised between 12% (in the duodenum) and 54% (in the esophagus) of total myenteric neurons. In the ileum, NOS neurons represented 19% of total myenteric neurons. Most of the NOS neurons throughout the gastrointestinal tract possessed lamellar dendrites and a single axon. NOS-containing terminals were abundant in the circular muscle, including that of the sphincters, but were rare in the longitudinal muscle, except for the taeniae of the caecum. The muscularis mucosae of the esophagus, stomach, colon and rectum received a medium to dense innervation by NOS terminals. Within myenteric ganglia, NOS-containing terminals were extremely sparse in the esophagus, stomach and duodenum, common in the ileum and distal colon and extremely dense in the proximal colon and rectum. The submucous plexus in the ileum and large intestine contained a sparse plexus of NOS-containing terminals. NOS terminals were not observed in the mucosa of any region. We conclude that throughout the gastrointestinal tract of the guinea-pig, NOS neurons are inhibitory motor neurons to the circular muscle; in the ileum and large intestine, NOS neurons may also function as interneurons. 相似文献
999.
1000.
Specificities of human, rat and E. coli O6-methylguanine-DNA methyltransferases towards the repair of O6-methyl and O6-ethylguanine in DNA. 总被引:1,自引:1,他引:0 下载免费PDF全文
The behaviour of highly purified bacterial expressed rat O6-methylguanine-DNA methyltransferase (MGMT) towards the repair of CGCm6GAGCTCGCG and CGCe6GAGCTCGCG (km6G/ke6G = 1.45, where k is the second order repair rate constant determined, m6G and e6G are O6-methyl and O6-ethylguanine) is similar to that of E. coli 39kD Ada protein (km6G/ke6G = 1.6). However, the human MGMT is very different (km6G/ke6G = 163). The preferential repair of O6-ethylguanine lesion by the rat MGMT appears not to be related to the lack of the initiator methionine in the expressed protein since similar results were obtained from N-terminal Glutathione-S-transferase (GST) fused protein (GSTMGMT) which retains the methionine. The possible relationship between these findings and the differences observed in the primary amino acid sequence of these proteins is discussed. In addition the preferential repair of O6-ethylguanine substrate by the 39kD Ada protein as compared to the catalytic C-terminus alone (different by 134 times) suggests that the N-terminus plays a crucial role in the repair of O6-ethylguanine. This is in contrast to the minor effects of the GST domain when fused to the N-terminus of mammalian MGMT. 相似文献