全文获取类型
收费全文 | 87021篇 |
免费 | 7804篇 |
国内免费 | 42篇 |
专业分类
94867篇 |
出版年
2023年 | 284篇 |
2022年 | 711篇 |
2021年 | 1557篇 |
2020年 | 884篇 |
2019年 | 1112篇 |
2018年 | 1443篇 |
2017年 | 1248篇 |
2016年 | 2149篇 |
2015年 | 3648篇 |
2014年 | 4075篇 |
2013年 | 4854篇 |
2012年 | 6588篇 |
2011年 | 6513篇 |
2010年 | 4196篇 |
2009年 | 3820篇 |
2008年 | 5470篇 |
2007年 | 5460篇 |
2006年 | 5286篇 |
2005年 | 5062篇 |
2004年 | 4924篇 |
2003年 | 4713篇 |
2002年 | 4447篇 |
2001年 | 907篇 |
2000年 | 666篇 |
1999年 | 1005篇 |
1998年 | 1250篇 |
1997年 | 844篇 |
1996年 | 764篇 |
1995年 | 668篇 |
1994年 | 632篇 |
1993年 | 680篇 |
1992年 | 595篇 |
1991年 | 544篇 |
1990年 | 498篇 |
1989年 | 427篇 |
1988年 | 446篇 |
1987年 | 366篇 |
1986年 | 335篇 |
1985年 | 427篇 |
1984年 | 546篇 |
1983年 | 423篇 |
1982年 | 516篇 |
1981年 | 500篇 |
1980年 | 429篇 |
1979年 | 314篇 |
1978年 | 345篇 |
1977年 | 293篇 |
1976年 | 289篇 |
1975年 | 230篇 |
1974年 | 259篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Michael Jamieson 《BMJ (Clinical research ed.)》1980,281(6253):1466
102.
103.
Steven I. Higgins Robert B. O’Hara Olga Bykova Michael D. Cramer Isabelle Chuine Eva‐Maria Gerstner Thomas Hickler Xavier Morin Michael R. Kearney Guy F. Midgley Simon Scheiter 《Journal of Biogeography》2012,39(12):2132-2145
Aim To develop a physiologically based model of the plant niche for use in species distribution modelling. Location Europe. Methods We link the Thornley transport resistance (TTR) model with functions which describe how the TTR’s model parameters are influenced by abiotic environmental factors. The TTR model considers how carbon and nutrient uptake, and the allocation of these assimilates, influence growth. We use indirect statistical methods to estimate the model parameters from a high resolution data set on tree distribution for 22 European tree species. Results We infer, from distribution data and abiotic forcing data, the physiological niche dimensions of 22 European tree species. We found that the model fits were reasonable (AUC: 0.79–0.964). The projected distributions were characterized by a false positive rate of 0.19 and a false negative rate 0.12. The fitted models are used to generate projections of the environmental factors that limit the range boundaries of the study species. Main conclusions We show that physiological models can be used to derive physiological niche dimensions from species distribution data. Future work should focus on including prior information on physiological rates into the parameter estimation process. Application of the TTR model to species distribution modelling suggests new avenues for establishing explicit links between distribution and physiology, and for generating hypotheses about how ecophysiological processes influence the distribution of plants. 相似文献
104.
105.
106.
K Murray S Stahl P G Ashton-Rickardt 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1989,324(1224):461-476
The simplest application of the modern genetic manipulation methods to vaccine development is the expression in microbial cells of genes from pathogens that encode surface antigens capable of inducing neutralizing antibodies in the host of the pathogen involved. This procedure has been exploited successfully for development of a vaccine against hepatitis B virus (HBV) that is now widely used. Similar approaches have been directed towards formulations for immunization against several other animal and human diseases and some of these preparations are now presently in trials. Of no less importance is the impact of biotechnology in providing reagents for fundamental studies of topics such as the determination of virulence, antigenic variation, virus receptors and the immunological response to viral antigens. The core antigen of HBV is a good example of a product of genetic engineering that is a valuable diagnostic reagent, and that is finding important use in immunological studies of particular pertinence to vaccine development. 相似文献
107.
108.
Michael J. Gentle 《Behavioural processes》1981,6(2):109-120
The oral behaviour of adult Brown Leghorn hens was recorded in response to oral stimulation with water, 2 M sodium chloride, 2 M acetic acid and 0.1 M quinine hydrochloride before and after surgical ablation of either the anterior telencephalon or the entire telencephalon and/or the diencephalon. It was found that beak wiping behaviour could be abolished by the removal of the anterior telencephalon. Head shaking behaviour was abolished only by the complete removal of the forebrain (telencephalon and diencephalon) whereas beak and tongue movements persisted after forebrain removal. Although these three behaviour patterns occur together in response to the stimulus, they appear to be controlled in different areas of the brain. The results are discussed in relation to the current work on the control of oral behaviour in mammals. 相似文献
109.
110.