全文获取类型
收费全文 | 315757篇 |
免费 | 38190篇 |
国内免费 | 1531篇 |
出版年
2016年 | 3833篇 |
2015年 | 5661篇 |
2014年 | 6607篇 |
2013年 | 8721篇 |
2012年 | 9926篇 |
2011年 | 9589篇 |
2010年 | 6507篇 |
2009年 | 6064篇 |
2008年 | 8292篇 |
2007年 | 8321篇 |
2006年 | 7832篇 |
2005年 | 7626篇 |
2004年 | 7390篇 |
2003年 | 7421篇 |
2002年 | 6997篇 |
2001年 | 12205篇 |
2000年 | 12205篇 |
1999年 | 9958篇 |
1998年 | 3774篇 |
1997年 | 3926篇 |
1996年 | 3866篇 |
1995年 | 3717篇 |
1994年 | 3680篇 |
1993年 | 3595篇 |
1992年 | 8566篇 |
1991年 | 8294篇 |
1990年 | 8066篇 |
1989年 | 7904篇 |
1988年 | 7444篇 |
1987年 | 7347篇 |
1986年 | 6797篇 |
1985年 | 6920篇 |
1984年 | 5773篇 |
1983年 | 5190篇 |
1982年 | 4117篇 |
1981年 | 3952篇 |
1980年 | 3588篇 |
1979年 | 5951篇 |
1978年 | 4652篇 |
1977年 | 4448篇 |
1976年 | 4260篇 |
1975年 | 4605篇 |
1974年 | 5056篇 |
1973年 | 4956篇 |
1972年 | 4621篇 |
1971年 | 4176篇 |
1970年 | 3666篇 |
1969年 | 3688篇 |
1968年 | 3288篇 |
1967年 | 2834篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
ObjectiveWe investigated whether glutamate, NMDA receptors, and eukaryote elongation factor-2 kinase (eEF-2K)/eEF-2 regulate P-glycoprotein expression, and the effects of the eEF-2K inhibitor NH125 on the expression of P-glycoprotein in rat brain microvessel endothelial cells (RBMECs).MethodsCortex was obtained from newborn Wistar rat brains. After surface vessels and meninges were removed, the pellet containing microvessels was resuspended and incubated at 37°C in culture medium. Cell viability was assessed by the MTT assay. RBMECs were identified by immunohistochemistry with anti-vWF. P-glycoprotein, phospho-eEF-2, and eEF-2 expression were determined by western blot analysis. Mdr1a gene expression was analyzed by RT-PCR.ResultsMdr1a mRNA, P-glycoprotein and phospho-eEF-2 expression increased in L-glutamate stimulated RBMECs. P-glycoprotein and phospho-eEF-2 expression were down-regulated after NH125 treatment in L-glutamate stimulated RBMECs.ConclusionseEF-2K/eEF-2 should have played an important role in the regulation of P-glycoprotein expression in RBMECs. eEF-2K inhibitor NH125 could serve as an efficacious anti-multidrug resistant agent. 相似文献
2.
While supertrees have been built for many vertebrate groups (notably birds, mammals and dinosaurs), invertebrates have attracted relatively little attention. The paucity of supertrees of arthropods is particularly surprising given their economic and ecological importance, as well as their overwhelming contribution to biodiversity. The absence of comprehensive archives of machine-readable source trees, coupled with the need for software implementing repeatable protocols for managing them, has undoubtedly impeded progress. Here we present a supertree of Achelata (spiny, slipper and coral lobsters) as a proof of concept, constructed using new supertree specific software (the Supertree Toolkit; STK) and following a published protocol. We also introduce a new resource for archiving and managing published source trees. Our supertree of Achelata is synthesised from morphological and molecular source trees, and represents the most complete species-level tree of the group to date. Our findings are consistent with recent taxonomic treatments, confirming the validity of just two families: Palinuridae and Scyllaridae; Synaxidae were resolved within Palinuridae. Monophyletic Silentes and Stridentes lineages are recovered within Palinuridae, and all sub-families within Scyllaridae are found to be monophyletic with the exception of Ibacinae. We demonstrate the feasibility of building larger supertrees of arthropods, with the ultimate objective of building a complete species-level phylogeny for the entire phylum using a divide and conquer strategy. 相似文献
3.
Tom P. Moorhouse Cecilia A. L. Dahlsj? Sandra E. Baker Neil C. D'Cruze David W. Macdonald 《PloS one》2015,10(10)
Tourism accounts for 9% of global GDP and comprises 1.1 billion tourist arrivals per annum. Visits to wildlife tourist attractions (WTAs) may account for 20–40% of global tourism, but no studies have audited the diversity of WTAs and their impacts on the conservation status and welfare of subject animals. We scored these impacts for 24 types of WTA, visited by 3.6–6 million tourists per year, and compared our scores to tourists’ feedback on TripAdvisor. Six WTA types (impacting 1,500–13,000 individual animals) had net positive conservation/welfare impacts, but 14 (120,000–340,000 individuals) had negative conservation impacts and 18 (230,000–550,000 individuals) had negative welfare impacts. Despite these figures only 7.8% of all tourist feedback on these WTAs was negative due to conservation/welfare concerns. We demonstrate that WTAs have substantial negative effects that are unrecognised by the majority of tourists, suggesting an urgent need for tourist education and regulation of WTAs worldwide. 相似文献
4.
5.
6.
7.
8.
9.
10.
B. Oderfeld-Nowak W. Jegliski M. Skup J. Skangiel-Kramska M. Zaremba D. Koczyk 《Journal of neurochemistry》1993,61(1):116-119
Abstract: The glial fibrillary acidic protein (GFAP) content was investigated using immunoblotting techniques in the septum and hippocampus of the rat after bilateral lateral fimbria transection. Seven days after surgery GFAP content increased significantly both in the septum (140% of control) and hippocampus (120% in dorsal, the less denervated, and 145% in the most denervated ventral part), indicating the occurrence of reactive gliosis. The GM1 treatment caused statistically significant attenuation of GFAP increment in all hippocampal parts. In contrast, GM1 treatment has no influence on the increase of GFAP content in the septum. Results suggest a differential effect of GM1 on the two gliotic reactions formed as a consequence of the lesion at the level of the source of innervation (septum) and the target (hippocampus). 相似文献