全文获取类型
收费全文 | 30938篇 |
免费 | 2547篇 |
国内免费 | 20篇 |
出版年
2023年 | 140篇 |
2022年 | 370篇 |
2021年 | 742篇 |
2020年 | 406篇 |
2019年 | 500篇 |
2018年 | 652篇 |
2017年 | 540篇 |
2016年 | 877篇 |
2015年 | 1414篇 |
2014年 | 1577篇 |
2013年 | 1867篇 |
2012年 | 2541篇 |
2011年 | 2414篇 |
2010年 | 1563篇 |
2009年 | 1467篇 |
2008年 | 1965篇 |
2007年 | 1964篇 |
2006年 | 1837篇 |
2005年 | 1761篇 |
2004年 | 1634篇 |
2003年 | 1538篇 |
2002年 | 1429篇 |
2001年 | 294篇 |
2000年 | 215篇 |
1999年 | 341篇 |
1998年 | 396篇 |
1997年 | 271篇 |
1996年 | 247篇 |
1995年 | 175篇 |
1994年 | 188篇 |
1993年 | 193篇 |
1992年 | 142篇 |
1991年 | 131篇 |
1990年 | 154篇 |
1989年 | 144篇 |
1988年 | 111篇 |
1987年 | 110篇 |
1986年 | 66篇 |
1985年 | 126篇 |
1984年 | 133篇 |
1983年 | 85篇 |
1982年 | 100篇 |
1981年 | 96篇 |
1980年 | 74篇 |
1979年 | 58篇 |
1978年 | 47篇 |
1977年 | 46篇 |
1976年 | 38篇 |
1975年 | 25篇 |
1974年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Deborah F. Tate Leslie Lytle Kristen Polzien Molly Diamond Kelsey R. Leonard John M. Jakicic Karen C. Johnson Christine M. Olson Kevin Patrick Laura P. Svetkey Rena R. Wing Pao‐Hwa Lin Mathilda Coday Melissa N. Laska Gina Merchant Sara J. Czaja Richard Schulz Steven H. Belle 《Obesity (Silver Spring, Md.)》2019,27(7):1085-1098
992.
Zachary A. Bornholdt Andrew S. Herbert Chad E. Mire Shihua He Robert W. Cross Anna Z. Wec Dafna M. Abelson Joan B. Geisbert Rebekah M. James Md Niaz Rahim Wenjun Zhu Viktoriya Borisevich Logan Banadyga Bronwyn M. Gunn Krystle N. Agans Ariel S. Wirchnianski Eileen Goodwin Kevin Tierney John M. Dye 《Cell host & microbe》2019,25(1):49-58.e5
993.
994.
995.
Marjorie C. Sorensen Tanmay Dixit Kevin J. Kardynal Jason Newton Keith A. Hobson Staffan Bensch Susanne Jenni‐Eiermann Claire N. Spottiswoode 《Ecology and evolution》2019,9(14):8294-8304
Migration can influence host–parasite dynamics in animals by increasing exposure to parasites, by reducing the energy available for immune defense, or by culling of infected individuals. These mechanisms have been demonstrated in several comparative analyses; however, few studies have investigated whether conspecific variation in migration distance may also be related to infection risk. Here, we ask whether autumn migration distance, inferred from stable hydrogen isotope analysis of summer‐grown feathers (δ2Hf) in Europe, correlates with blood parasite prevalence and intensity of infection for willow warblers (Phylloscopus trochilus) wintering in Zambia. We also investigated whether infection was correlated with individual condition (assessed via corticosterone, scaled mass index, and feather quality). We found that 43% of birds were infected with Haemoproteus palloris (lineage WW1). Using generalized linear models, we found no relationship between migration distance and either Haemoproteus infection prevalence or intensity. There was spatial variation in breeding ground origins of infected versus noninfected birds, with infected birds originating from more northern sites than noninfected birds, but this difference translated into only slightly longer estimated migration distances (~214 km) for infected birds. We found no relationship between body condition indices and Haemoproteus infection prevalence or intensity. Our results do not support any of the proposed mechanisms for migration effects on host–parasite dynamics and cautiously suggest that other factors may be more important for determining individual susceptibility to disease in migratory bird species. 相似文献
996.
Angela M. Mech Kathryn A. Thomas Travis D. Marsico Daniel A. Herms Craig R. Allen Matthew P. Ayres Kamal J. K. Gandhi Jessica Gurevitch Nathan P. Havill Ruth A. Hufbauer Andrew M. Liebhold Kenneth F. Raffa Ashley N. Schulz Daniel R. Uden Patrick C. Tobin 《Ecology and evolution》2019,9(21):12216-12230
- 相似文献
997.
Quercus wutaishansea populations on the Loess Plateau are currently becoming more dominant in natural secondary forests, whereas Pinus tabulaeformis is declining. In the present paper, the diameter class (instead of age) was used to classify the different growth stages as juvenile, subadult, or adult, and the univariate function g(r) was used to analyze the dynamic changes in spatial patterns and interspecific associations in three 1‐ha tree permanent plots on the Loess Plateau, NW China. Our results suggested that the niche breadth changed with the development stage. The diameter distribution curve was consistent with the inverted “J” type, indicating that natural regeneration was common in all three plots. There was a close relationship between the spatial pattern and scale, which showed significant aggregation at small distances, and became more random as distance increased, but in the Pinus + Quercus mixed forests, the whole species were aggregated at distances up to 50 m. The degree of spatial clumping decreased from juvenile to subadult and from subadult to adult. The spatial pattern also differed at different growth stages, likely due to strong intraspecific competition. Associations among different growth stages were positively correlated at small scales. Our study is important to the understanding of the development of the Q. wutaishansea forests; thus, the spatial dynamic change features should be received greater attention when planning forest management and developing restoration strategies on the Loess Plateau. 相似文献
998.
999.
1000.
Kevin Ni Amar Gill Danting Cao Kengo Koike Kelly S. Schweitzer Stavros Garantziotis Irina Petrache 《Biochemistry and Biophysics Reports》2019
During inflammation, the covalent linking of the ubiquitous extracellular polysaccharide hyaluronan (HA) with the heavy chains (HC) of the serum protein inter alpha inhibitor (IαI) is exclusively mediated by the enzyme tumor necrosis factor α (TNFα)-stimulated-gene-6 (TSG-6). While significant advances have been made regarding how HC-modified HA (HC-HA) is an important regulator of inflammation, it remains unclear why HC-HA plays a critical role in promoting survival in intraperitoneal lipopolysaccharide (LPS)-induced endotoxemia while exerting only a modest role in the outcomes following intratracheal exposure to LPS. To address this gap, the two models of intraperitoneal LPS-induced endotoxic shock and intratracheal LPS-induced acute lung injury were directly compared in TSG-6 knockout mice and littermate controls. HC-HA formation, endogenous TSG-6 activity, and inflammatory markers were assessed in plasma and lung tissue. TSG-6 knockout mice exhibited accelerated mortality during endotoxic shock. While both intraperitoneal and intratracheal LPS induced HC-HA formation in lung parenchyma, only systemically-induced endotoxemia increased plasma TSG-6 levels and intravascular HC-HA formation. Cultured human lung microvascular endothelial cells secreted TSG-6 in response to both TNFα and IL1β stimulation, indicating that, in addition to inflammatory cells, the endothelium may secrete TSG-6 into circulation during systemic inflammation. These data show for the first time that LPS-induced systemic inflammation is uniquely characterized by significant vascular induction of TSG-6 and HC-HA, which may contribute to improved outcomes of endotoxemia. 相似文献