全文获取类型
收费全文 | 13860篇 |
免费 | 1038篇 |
国内免费 | 1篇 |
出版年
2023年 | 113篇 |
2022年 | 168篇 |
2021年 | 343篇 |
2020年 | 240篇 |
2019年 | 322篇 |
2018年 | 390篇 |
2017年 | 311篇 |
2016年 | 457篇 |
2015年 | 707篇 |
2014年 | 763篇 |
2013年 | 883篇 |
2012年 | 1062篇 |
2011年 | 1061篇 |
2010年 | 635篇 |
2009年 | 532篇 |
2008年 | 718篇 |
2007年 | 738篇 |
2006年 | 715篇 |
2005年 | 555篇 |
2004年 | 563篇 |
2003年 | 476篇 |
2002年 | 441篇 |
2001年 | 226篇 |
2000年 | 224篇 |
1999年 | 188篇 |
1998年 | 149篇 |
1997年 | 105篇 |
1996年 | 96篇 |
1995年 | 78篇 |
1994年 | 79篇 |
1993年 | 87篇 |
1992年 | 127篇 |
1991年 | 102篇 |
1990年 | 87篇 |
1989年 | 99篇 |
1988年 | 91篇 |
1987年 | 73篇 |
1986年 | 78篇 |
1985年 | 71篇 |
1984年 | 61篇 |
1983年 | 60篇 |
1982年 | 51篇 |
1981年 | 48篇 |
1979年 | 56篇 |
1978年 | 38篇 |
1977年 | 39篇 |
1976年 | 42篇 |
1975年 | 38篇 |
1974年 | 32篇 |
1973年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
Alba Luengo Zhaoqi Li Dan Y. Gui Lucas B. Sullivan Maria Zagorulya Brian T. Do Raphael Ferreira Adi Naamati Ahmed Ali Caroline A. Lewis Craig J. Thomas Stefani Spranger Nicholas J. Matheson Matthew G. Vander Heiden 《Molecular cell》2021,81(4):691-707.e6
- Download : Download high-res image (172KB)
- Download : Download full-size image
13.
J. Paupério J. S. Herman J. Melo‐Ferreira M. Jaarola P. C. Alves J.B. Searle 《Molecular ecology》2012,21(24):6015-6032
Species are generally described from morphological features, but there is growing recognition of sister forms that show substantial genetic differentiation without obvious morphological variation and may therefore be considered ‘cryptic species’. Here, we investigate the field vole (Microtus agrestis), a Eurasian mammal with little apparent morphological differentiation but which, on the basis of previous sex‐linked nuclear and mitochondrial DNA (mtDNA) analyses, is subdivided into a Northern and a Southern lineage, sufficiently divergent that they may represent two cryptic species. These earlier studies also provided limited evidence for two major mtDNA lineages within Iberia. In our present study, we extend these findings through a multilocus approach. We sampled 163 individuals from 46 localities, mainly in Iberia, and sequenced seven loci, maternally, paternally and biparentally inherited. Our results show that the mtDNA lineage identified in Portugal is indeed a distinct third lineage on the basis of other markers as well. In fact, multilocus coalescent‐based methods clearly support three separate evolutionary units that may represent cryptic species: Northern, Southern and Portuguese. Divergence among these units was inferred to have occurred during the last glacial period; the Portuguese lineage split occurred first (estimated at c. 70 000 bp ), and the Northern and Southern lineages separated at around the last glacial maximum (estimated at c. 18 500 bp ). Such recent formation of evolutionary units that might be considered species has repercussions in terms of understanding evolutionary processes and the diversity of small mammals in a European context. 相似文献
14.
Cortinarius sarcoflammeus is proposed as a new species belonging to subgenus Dermocybe, on the basis of its morphological, chemical and ecological characters. The strong red-orange colour of the context and stipe
base, large spores, sphagnicolous habitat and high dermorubin content are characteristic for the new species. Holotypes of
C. huronensis and C. huronensis var. olivaceus have been examined for comparison, and their differences discussed. Photographs and line drawings of C. sarcoflammeus are added.
Received February 13, 2001 Accepted March 23, 2001 相似文献
15.
16.
Margarida A. Ferreira M.Aurea Cruz Costa A.Correia Alves M.Helena Lopes 《Phytochemistry》1973,12(2):433-435
7-MethyljugIone, 8,8′-dihydroxy-4,4′-dimethoxy-6,6′-dimethyl-2,2′-binaphthyl-1,1′-quinone, 2-methylnaphthazarin, mamegakinone and euclein have been isolated from Euclea pseudebenus. Euclein is the 3,6′-dimer of 7-methyljuglone. 相似文献
17.
18.
Rafael L. X. Consani Mariana R. Carmignani Marcelo F. Mesquita Lourenço Correr‐Sobrinho Ricardo D. Guiraldo 《Gerodontology》2010,27(3):236-242
doi:10.1111/j.1741‐2358.2009.00333.x Effect of microwave treatment on the shear bond strength of different types of commercial teeth to acrylic resin Objective: The purpose of this study was to verify the effect of microwave treatment on the shear bond strength of commercial types of teeth to acrylic resin, when the glossy ridge laps were unmodified (groups 1 and 5), bur abraded (groups 2 and 6), bur grooved (groups 3 and 7) or etched by monomer (groups 4 and 8). Background: Controversial findings have shown that mechanical or chemical changes in ridge‐lap surface of the tooth increase or decrease the bond strength between tooth and acrylic resin, and the microwave disinfection may cause different changes on this bond strength. Materials and methods: Eighty specimens (n = 10) were made with the acrylic resin bonded to tooth glossy ridge lap, polymerised in water at 74°C for 9 h, and deflasked after flask cooling. Specimens of the groups 5, 6, 7 and 8 were individually immersed in 150 ml of water and submitted to microwave treatment in an oven at 650 W for 3 min. Control specimens (groups 1, 2, 3 and 4) were not microwave treated. Shear bond strength test was performed in an Instron machine with a cross‐speed of 1 mm/min. Collected data were submitted to anova and Tukey’s test (α = 0.05). Results: Microwave treatment decreased the shear bond strength values of the tooth/resin bond. In the microwaved and non‐microwaved procedures, mechanical retention improved the shear bond strength when compared with the control and monomer treatments. Conclusion: Shear bond strength of the tooth/resin bond was influenced by the microwave treatment and different commercial teeth association, and was lower for the Biotone tooth. 相似文献
19.
20.
Plasma hormones in pre- and postmenopausal breast cancer 总被引:1,自引:0,他引:1