全文获取类型
收费全文 | 39956篇 |
免费 | 4135篇 |
国内免费 | 11篇 |
专业分类
44102篇 |
出版年
2023年 | 175篇 |
2022年 | 349篇 |
2021年 | 670篇 |
2020年 | 486篇 |
2019年 | 566篇 |
2018年 | 701篇 |
2017年 | 631篇 |
2016年 | 1043篇 |
2015年 | 1727篇 |
2014年 | 1881篇 |
2013年 | 2329篇 |
2012年 | 2865篇 |
2011年 | 2783篇 |
2010年 | 1849篇 |
2009年 | 1609篇 |
2008年 | 2246篇 |
2007年 | 2234篇 |
2006年 | 2125篇 |
2005年 | 1894篇 |
2004年 | 1887篇 |
2003年 | 1680篇 |
2002年 | 1650篇 |
2001年 | 651篇 |
2000年 | 607篇 |
1999年 | 620篇 |
1998年 | 432篇 |
1997年 | 352篇 |
1996年 | 339篇 |
1995年 | 350篇 |
1994年 | 308篇 |
1993年 | 305篇 |
1992年 | 413篇 |
1991年 | 354篇 |
1990年 | 349篇 |
1989年 | 363篇 |
1988年 | 364篇 |
1987年 | 334篇 |
1986年 | 268篇 |
1985年 | 298篇 |
1984年 | 303篇 |
1983年 | 269篇 |
1982年 | 257篇 |
1981年 | 231篇 |
1980年 | 209篇 |
1979年 | 215篇 |
1978年 | 181篇 |
1977年 | 183篇 |
1976年 | 182篇 |
1975年 | 198篇 |
1973年 | 164篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Ulrike Rosenfellner Franz Zehetner Martin H. Gerzabek 《Soil & Sediment Contamination》2009,18(6):685-687
Data from eight published studies were combined to show that the influence of traffic density on Pb contents in roadside soils increases with proximity to the road. 相似文献
72.
73.
74.
Michael Gewecke Martin Woike 《Ethology : formerly Zeitschrift fur Tierpsychologie》1978,47(3):293-298
Analysis of the flight behaviour of siskins (Carduelis spinus) was made possible by tethering them with a harness to a flight balance in a wind tunnel. It could be shown that the breast feathers work as an air-current sense organ influencing the siskins' flight pattern and the aerodynamic parameters. 相似文献
75.
76.
John A. Nyakatura Vivian R. Allen Jonas Laustr?er Amir Andikfar Marek Danczak Hans-Jürgen Ullrich Werner Hufenbach Thomas Martens Martin S. Fischer 《PloS one》2015,10(9)
Orobates pabsti, a basal diadectid from the lower Permian, is a key fossil for the understanding of early amniote evolution. Quantitative analysis of anatomical information suffers from fragmentation of fossil bones, plastic deformation due to diagenetic processes and fragile preservation within surrounding rock matrix, preventing further biomechanical investigation. Here we describe the steps taken to digitally reconstruct MNG 10181, the holotype specimen of Orobates pabsti, and subsequently use the digital reconstruction to assess body mass, position of the centre of mass in individual segments as well as the whole animal, and study joint mobility in the shoulder and hip joints. The shape of most fossil bone fragments could be recovered from micro-focus computed tomography scans. This also revealed structures that were hitherto hidden within the rock matrix. However, parts of the axial skeleton had to be modelled using relevant isolated bones from the same locality as templates. Based on the digital fossil, mass of MNG 10181 was estimated using a model of body shape that was varied within a plausible range to account for uncertainties of the dimension. In the mean estimate model the specimen had an estimated mass of circa 4 kg. Varying of the mass distribution amongst body segments further revealed that Orobates carried most of its weight on the hind limbs. Mostly unrestricted joint morphology further suggested that MNG 10181 was able to effectively generate propulsion with the pelvic limbs. The digital reconstruction is made available for future biomechanical studies. 相似文献
77.
Rachel M. Haywood Andrew W. D. Claxson Geoffrey E. Hawkes David P. Richardson Declan P. Naughton Gregory Coumbarides Jane Hawkes Edward J. Lynch Martin C. Grootveld 《Free radical research》1995,22(5):441-482
High field (400 and 600 MHz) proton NMR spectroscopy has been employed to investigate the thermally-induced autoxidation of glycerol-bound polyunsaturated fatty acids present in intact culinary frying oils and fats. Heating of these materials at 180°C for periods of 30, 60 and 90 min. generated a variety of peroxidation products, notably aldehydes (alkanals, trans-2-alkenals and alka-2, 4-dienals) and their conjugated hydroperoxydiene precursors. Since such aldehydes appear to be absorbed into the systemic circulation from the gut in vivo, the toxicological significance of their production during standard frying practices is discussed. 相似文献
78.
79.
80.