全文获取类型
收费全文 | 565篇 |
免费 | 22篇 |
国内免费 | 42篇 |
专业分类
丛书文集 | 9篇 |
教育与普及 | 5篇 |
现状及发展 | 42篇 |
综合类 | 573篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 10篇 |
2018年 | 11篇 |
2017年 | 5篇 |
2016年 | 21篇 |
2015年 | 16篇 |
2014年 | 32篇 |
2013年 | 27篇 |
2012年 | 34篇 |
2011年 | 43篇 |
2010年 | 36篇 |
2009年 | 37篇 |
2008年 | 46篇 |
2007年 | 42篇 |
2006年 | 34篇 |
2005年 | 28篇 |
2004年 | 29篇 |
2003年 | 23篇 |
2002年 | 26篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 15篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1985年 | 5篇 |
排序方式: 共有629条查询结果,搜索用时 15 毫秒
601.
1Cr18Ni9Ti不锈钢的表面Co基材料的激光熔覆,在熔覆层表面形成了致密的微结构,基体与熔覆层间的热影区内,基体元素的固溶度明显增加,位错能降低,在热影响区还发现了孪晶产生,根据M谱研究确诊有多种Fe、C固溶相的存在。 相似文献
602.
《科学通报(英文版)》1992,37(19):1627-1627
603.
Hult M Elleby B Shafqat N Svensson S Rane A Jörnvall H Abrahmsen L Oppermann U 《Cellular and molecular life sciences : CMLS》2004,61(7-8):992-999
Interconversion between cortisone and the glucocorticoid receptor ligand cortisol is carried out by 11-hydroxysteroid dehydrogenase (11-HSD)isozymes and constitutes a medically important example of pre-receptor control of steroid hormones. The enzyme 11-HSD type 1 (11-HSD1) catalyzes the conversion of cortisone to its active receptor-binding derivative cortisol, whereas 11-HSD type 2 performs the reverse reaction. Specific inhibitors against the type 1 enzyme lower intracellular levels of glucocorticoid hormone, with an important clinical application in insulin resistance and other metabolic disorders. We report here on the in vitro oxysterol-metabolizing properties of human and rodent 11-HSD1. The enzyme, either as full-length, membrane-attached, or as a transmembrane domain-deleted, soluble form, mediates exclusively conversion between 7-ketocholesterol and 7-hydroxycholesterol with similar kcat values as observed with glucocorticoid hormones. Thus, human, rat, and mouse 11-HSD1 have dual enzyme activities like the recently described 7-hydroxysteroid dehydrogenase/11-hydroxysteroid dehydrogenase from hamster liver, but differ fundamentally from the latter in that 7-OH rather than 7-OH dehydrogenase constitutes the second activity. These results demonstrate an enzymatic origin of species differences in 7-oxysterol metabolism, establish the origin of endogenous 7-OH cholesterol in humans, and point to a possible involvement of 11-HSD1 in atherosclerosis.Received 30 December 2003; received after revision 16 February 2004; accepted 16 February 2004 相似文献
604.
605.
606.
The Sox genes of allotetraploids and their original maternal red crucian carp (Carassius caassius red var.) and original paternal common carp (Cyprinus carpio L.) were detected by PCR with the designed primers based on the conserved HMG-box sequence in different species. Sequencing of Sox genes indicated that two Sox9 genes (Atsox9a and Atsox9b) existed in allotetraploids, while only one Sox9 gene existed in red crucian carp (Rcsox9a) and common carp (Ccsox9b). All of the four Sox9 genes contained an intron in the HMG-box, with the sizes of 413 bp, 703 bp, 401 bp and 714 bp, respectively. Moreover, the introns obeyed the rule of “GT-AG”. A high similarity was observed between introns of Atsox9a and Rcsox9a (94.4%), Atsox9b and Ccsox9b (97.8%). Interestingly, the deduced amino acid sequences of their corresponding exons all shared 100% identity. Thus, introns of the HMG-domain of Sox9s in allotetraploids and their original parents have not only the length polymorphism but also intron variability. Our results provide significant molecular evidence for the origin and evolution of allotetraploids. 相似文献
607.
采用固相法,制备了Mg4Nb2O9微波介质陶瓷,研究了银粉与Mg4Nb2O9陶瓷粉体的化学兼容性和微波介电性能.通过X射线衍射谱(XRD)、扫描电镜(SEM)等分析测试手段,对材料的晶相组成、显微结构进行了研究.采用V2O5、Li2CO3复合掺杂来降低Mg4Nb2O9陶瓷的烧结温度,以便能够与银粉匹配共烧.结果表明,1.5%V2O5和1.5%Li2CO3(VLi)共掺杂可使925℃烧结无第二相生成.该陶瓷良好的整体微波介电性能可用于微波材料. 相似文献
608.
用紫外-可见分光光度计对Na2S与Na2[Fe(CN)5NO]反应得到的紫色混合水溶液的稳定性进行跟踪检测,结果表明此紫色化合物极不稳定.进一步用显微熔点测定仪、红外光谱等仪器对该紫色混合液的分解产物-黄色针状晶体进行了鉴定,最终确定该晶体为黄血盐Na4[Fe(CN)6].3H2O.这一研究对Na2[Fe(CN)5NO]鉴定S2-的实验现象有更进一步的解释. 相似文献
609.
Comparative studies of the genes involved in sex determination in the three extant classes of mammals, and other vertebrates,
has allowed us to identify genes that are highly conserved in vertebrate sex determination and those that have recently evolved
roles in one lineage. Analysis of the conservation and function of candidate genes in different vertebrate groups has been
crucial to our understanding of their function and positioning in a conserved vertebrate sex-determining pathway. Here we
review comparisons between genes in the sex-determining pathway in different vertebrates, and ask how these comparisons affect
our views on the role of each gene in vertebrate sex determination. 相似文献
610.
设计合成了基于双酚芴衍生物有机化合物1,该凝胶因子能够在甲苯中形成有机凝胶.分别用紫外可见吸收光谱、红外光谱、扫描电镜和接触角等技术对凝胶因子自组装过程进行了表征.结果表明,自组装过程形成了具有一定的疏水性的膜结构,其接触角为106°,氢键作用是该体系自组装的主要驱动力. 相似文献