全文获取类型
收费全文 | 44010篇 |
免费 | 115篇 |
国内免费 | 188篇 |
专业分类
系统科学 | 464篇 |
丛书文集 | 785篇 |
教育与普及 | 111篇 |
理论与方法论 | 193篇 |
现状及发展 | 20173篇 |
研究方法 | 1736篇 |
综合类 | 20251篇 |
自然研究 | 600篇 |
出版年
2013年 | 289篇 |
2012年 | 628篇 |
2011年 | 1240篇 |
2010年 | 294篇 |
2008年 | 765篇 |
2007年 | 881篇 |
2006年 | 833篇 |
2005年 | 865篇 |
2004年 | 834篇 |
2003年 | 843篇 |
2002年 | 754篇 |
2001年 | 1377篇 |
2000年 | 1327篇 |
1999年 | 819篇 |
1994年 | 393篇 |
1992年 | 784篇 |
1991年 | 620篇 |
1990年 | 722篇 |
1989年 | 640篇 |
1988年 | 601篇 |
1987年 | 685篇 |
1986年 | 687篇 |
1985年 | 833篇 |
1984年 | 634篇 |
1983年 | 570篇 |
1982年 | 526篇 |
1981年 | 574篇 |
1980年 | 610篇 |
1979年 | 1456篇 |
1978年 | 1148篇 |
1977年 | 1104篇 |
1976年 | 851篇 |
1975年 | 925篇 |
1974年 | 1306篇 |
1973年 | 1118篇 |
1972年 | 1093篇 |
1971年 | 1272篇 |
1970年 | 1688篇 |
1969年 | 1334篇 |
1968年 | 1202篇 |
1967年 | 1283篇 |
1966年 | 1134篇 |
1965年 | 796篇 |
1959年 | 456篇 |
1958年 | 723篇 |
1957年 | 506篇 |
1956年 | 464篇 |
1955年 | 404篇 |
1954年 | 399篇 |
1948年 | 299篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
991.
Ann-Karin Haas Gunnar Kleinau Inna Hoyer Susanne Neumann Jens Furkert Claudia Rutz Ralf Schülein Marvin C. Gershengorn Gerd Krause 《Cellular and molecular life sciences : CMLS》2011,68(1):159-167
The thyrotropin receptor (TSHR) exhibits elevated cAMP signaling in the basal state and becomes fully activated by thyrotropin.
Previously we presented evidence that small-molecule ligands act allosterically within the transmembrane region in contrast
to the orthosteric extracellular hormone-binding sites. Our goal in this study was to identify positions that surround the
allosteric pocket and that are sensitive for inactivation of TSHR. Homology modeling combined with site-directed mutagenesis
and functional characterization revealed seven mutants located in the allosteric binding site that led to a decrease of basal
cAMP signaling activity. The majority of these silencing mutations, which constrain the TSHR in an inactive conformation,
are found in two clusters when mapped onto the 3D structural model. We suggest that the amino acid positions identified herein
are indicating locations where small-molecule antagonists, both neutral antagonists and inverse agonists, might interfere
with active TSHR conformations. 相似文献
992.
Q.Xia Y.P.Wu 《复旦学报(自然科学版)》2007,46(5)
1 Results In order to overcome the inherent incompatibility of PC with graphite in the lithium ion battery system, improve their electrochemical performance at low temperature,phenyl tris-2-methoxydiethoxy silane (PTMS) has been studied as an additive to the PC-based electrolyte of lithium ion batteries with graphite anode. From the cyclic voltammogram for the graphite anode in the PC-based electrolyte,we find that in the case of the electrolyte without the additive,there is a large irreversible peak ne... 相似文献
993.
994.
Jérémie Gautheron Gilles Courtois 《Cellular and molecular life sciences : CMLS》2010,67(18):3101-3113
Ubiquitination has emerged over the years as the most sophisticated way to modify proteins to affect their fate and function.
In particular, it has been reported to be instrumental in regulating several steps of the NF-κB signalling pathway which controls
inflammation, immunity, adhesion and cell survival. Integrating ubiquitination into NF-κB activation requires the regulatory
subunit of IKK, NEMO, which not only displays affinity for polyubiquitin chains, but is also posttranslationally modified
by a complex set of reactions involving ubiquitin. Here, we examine how studies of the NEMO/ubiquitin relationship have provided
novel insights into the IKK activation process and have uncovered molecular mechanisms that should represent in the future
attractive targets for specifically modulating NF-κB function. 相似文献
995.
996.
997.
998.
Mark C. Hove Bernard E. Sietman Matthew S. Berg Erika C. Frost Kiru Wolf Tony R. Brady 《Journal of Natural History》2016,50(9-10):523-542
Managing a rare species can be improved with knowledge of its natural history. The sheepnose (Plethobasus cyphyus) is a freshwater mussel recently listed by the US as federally endangered. We used standard methods to study P. cyphyus brooding behaviour, host fishes in the laboratory and under natural conditions, and glochidial morphology. We monitored a population of P. cyphyus in the Chippewa River, WI during spring and summer 2007–2009 and 2011 and found brooding animals between mid-May and early August. Gravid individuals ranged between 5 and 27 yr (mean age ± 1 s.d. = 13 ± 4 yr). Plethobasus cyphyus brooded glochidia in outer gills, which varied in colour from red, orange, pink, cream, or white. We observed mature glochidia more commonly in individuals with cream or white gills and these glochidia were released in a clear, adhesive, mucus matrix. In laboratory trials we found several minnow and topminnow species (29 spp.) served as productive suitable native hosts. The mean number of juvenile mussels released per cyprinid per day was significantly higher for trials conducted at 22–25°C compared with those at 18–20°C, and 83% of trials conducted at 18–20°C using suitable host species produced no juveniles. Glochidia had a unique outline and shell morphometrics that distinguished P. cyphyus from seven other Chippewa River mussel species that produce similar sized glochidia. Using morphometrics we determined that mimic shiners (Notropis volucellus) were natural hosts for P. cyphyus, round pigtoe (Pleurobema sintoxia), and Wabash pigtoe (Fusconaia flava). Releasing mucus-bound glochidia has evolved in a variety of mussel species and may be more common than is currently realized. Our data show that P. cyphyus is a cyprinid host specialist, and propagation efforts for this species can be strengthened through improved access to mature glochidia by using females with cream-coloured gills and increased juvenile production through warmer fish holding temperatures. 相似文献
999.
1000.
桥梁结构在各种荷载作用下产生的内力和弯矩影响着桥梁的性能.桥梁弯曲、扭转和挠度等过大时会导致结构的破坏,这在结构设计阶段就应加以分析.本文提出一种有限条简化分析方法,可以较好地分析桥梁的挠度、弯曲和扭转变形.通过对一座简支板梁桥模型的分析,与现行有限元方法的分析结果进行了比较.结果表明,本方法能够较好地处理边界条件,只需要很少的输入工作就可以得到正确的分析结果,从而为结构工程师提供了一种用于分析板梁桥在交通荷载作用下行为的有效工具. 相似文献