全文获取类型
收费全文 | 299485篇 |
免费 | 36375篇 |
国内免费 | 191篇 |
出版年
2016年 | 3204篇 |
2015年 | 4750篇 |
2014年 | 5566篇 |
2013年 | 7659篇 |
2012年 | 8786篇 |
2011年 | 8688篇 |
2010年 | 5909篇 |
2009年 | 5464篇 |
2008年 | 7750篇 |
2007年 | 7848篇 |
2006年 | 7419篇 |
2005年 | 7320篇 |
2004年 | 7144篇 |
2003年 | 7141篇 |
2002年 | 6726篇 |
2001年 | 11281篇 |
2000年 | 11373篇 |
1999年 | 9285篇 |
1998年 | 3506篇 |
1997年 | 3636篇 |
1996年 | 3606篇 |
1995年 | 3492篇 |
1994年 | 3485篇 |
1993年 | 3448篇 |
1992年 | 8221篇 |
1991年 | 7986篇 |
1990年 | 7782篇 |
1989年 | 7708篇 |
1988年 | 7262篇 |
1987年 | 7218篇 |
1986年 | 6670篇 |
1985年 | 6829篇 |
1984年 | 5717篇 |
1983年 | 5135篇 |
1982年 | 4101篇 |
1981年 | 3937篇 |
1980年 | 3574篇 |
1979年 | 5927篇 |
1978年 | 4639篇 |
1977年 | 4436篇 |
1976年 | 4231篇 |
1975年 | 4587篇 |
1974年 | 5037篇 |
1973年 | 4926篇 |
1972年 | 4586篇 |
1971年 | 4137篇 |
1970年 | 3648篇 |
1969年 | 3667篇 |
1968年 | 3271篇 |
1967年 | 2823篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
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
2.
Hyuck Choi Byung-Chul Jeong Sung-Woong Hur Jung-Woo Kim Keun-Bae Lee Jeong-Tae Koh 《PloS one》2015,10(10)
Craniofacial bone defects are observed in a variety of clinical situations, and their reconstructions require coordinated coupling between angiogenesis and osteogenesis. In this study, we explored the effects of cartilage oligomeric matrix protein-angiopoietin 1 (COMP-Ang1), a synthetic and soluble variant of angiopoietin 1, on bone morphogenetic protein 2 (BMP2)-induced cranial bone regeneration, and recruitment and osteogenic differentiation of perivascular pericytes. A critical-size calvarial defect was created in the C57BL/6 mouse and COMP-Ang1 and/or BMP2 proteins were delivered into the defects with absorbable collagen sponges. After 3 weeks, bone regeneration was evaluated using micro-computed tomography and histologic examination. Pericyte recruitment into the defects was examined using immunofluorescence staining with anti-NG2 and anti-CD31 antibodies. In vitro recruitment and osteoblastic differentiation of pericyte cells were assessed with Boyden chamber assay, staining of calcified nodules, RT-PCR and Western blot analyses. Combined administration of COMP-Ang1 and BMP2 synergistically enhanced bone repair along with the increased population of CD31 (an endothelial cell marker) and NG2 (a specific marker of pericyte) positive cells. In vitro cultures of pericytes consistently showed that pericyte infiltration into the membrane pore of Boyden chamber was more enhanced by the combination treatment. In addition, the combination further increased the osteoblast-specific gene expression, including bone sialoprotein (BSP), osteocalcin (OCN) and osterix (OSX), phosphorylation of Smad/1/5/8, and mineralized nodule formation. COMP-Ang1 can enhance BMP2-induced cranial bone regeneration with increased pericyte recruitment. Combined delivery of the proteins might be a therapeutic strategy to repair cranial bone damage. 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