全文获取类型
收费全文 | 29885篇 |
免费 | 616篇 |
国内免费 | 359篇 |
专业分类
测绘学 | 808篇 |
大气科学 | 2174篇 |
地球物理 | 6021篇 |
地质学 | 10314篇 |
海洋学 | 2702篇 |
天文学 | 6991篇 |
综合类 | 69篇 |
自然地理 | 1781篇 |
出版年
2021年 | 255篇 |
2020年 | 298篇 |
2019年 | 362篇 |
2018年 | 693篇 |
2017年 | 664篇 |
2016年 | 849篇 |
2015年 | 534篇 |
2014年 | 815篇 |
2013年 | 1523篇 |
2012年 | 940篇 |
2011年 | 1270篇 |
2010年 | 1113篇 |
2009年 | 1487篇 |
2008年 | 1315篇 |
2007年 | 1331篇 |
2006年 | 1314篇 |
2005年 | 999篇 |
2004年 | 991篇 |
2003年 | 897篇 |
2002年 | 855篇 |
2001年 | 689篇 |
2000年 | 727篇 |
1999年 | 635篇 |
1998年 | 631篇 |
1997年 | 583篇 |
1996年 | 452篇 |
1995年 | 473篇 |
1994年 | 483篇 |
1993年 | 372篇 |
1992年 | 370篇 |
1991年 | 308篇 |
1990年 | 375篇 |
1989年 | 327篇 |
1988年 | 312篇 |
1987年 | 340篇 |
1986年 | 289篇 |
1985年 | 383篇 |
1984年 | 422篇 |
1983年 | 399篇 |
1982年 | 378篇 |
1981年 | 304篇 |
1980年 | 334篇 |
1979年 | 269篇 |
1978年 | 260篇 |
1977年 | 254篇 |
1976年 | 227篇 |
1975年 | 238篇 |
1974年 | 214篇 |
1973年 | 217篇 |
1972年 | 135篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
51.
Daniel P. Glavin Jason P. Dworkin Andrew Aubrey Oliver Botta James H. Doty Zita Martins Jeffrey L. Bada 《Meteoritics & planetary science》2006,41(6):889-902
Abstract— Amino acid analyses of the Antarctic CM2 chondrites Allan Hills (ALH) 83100 and Lewis Cliff (LEW) 90500 using liquid chromatography‐time of flight‐mass spectrometry (LC‐ToF‐MS) coupled with UV fluorescence detection revealed that these carbonaceous meteorites contain a suite of indigenous amino acids not present in Antarctic ice. Several amino acids were detected in ALH 83100, including glycine, alanine, β‐alanine, γ‐amino‐n‐butyric acid (γ‐ABA), and α‐aminoisobutyric acid (AIB) with concentrations ranging from 250 to 340 parts per billion (ppb). In contrast to ALH 83100, the CM2 meteorites LEW 90500 and Murchison had a much higher total abundance of these amino acids (440–3200 ppb). In addition, ALH 83100 was found to have lower abundances of the α‐dialkyl amino acids AIB and isovaline than LEW 90500 and Murchison. There are three possible explanations for the depleted amino acid content in ALH 83100: 1) amino acid leaching from ALH 83100 during exposure to Antarctic ice meltwater, 2) a higher degree of aqueous alteration on the ALH 83100 parent body, or 3) ALH 83100 originated on a chemically distinct parent body from the other two CM2 meteorites. The high relative abundance of ?‐amino‐n‐caproic acid (EACA) in the ALH 83100 meteorite as well as the Antarctic ice indicates that Nylon‐6 contamination from the Antarctic sample storage bags may have occurred during collection. 相似文献
52.
53.
54.
55.
56.
This paper proposes a multi‐level parallelized substructuring–frontal combined algorithm for the analysis of the problem of thermo/hydraulic/mechanical behaviour of unsaturated soil. Temperature, displacement, pore water pressure and pore air pressure are treated as the primary variables in a non‐linear analysis. Details are given firstly of the substructuring–frontal combined approach. The incorporation of the algorithm in a multi‐level parallel strategy is then discussed. The parallel processing can thus be carried out at different substructural levels. The method thus developed impacts, in a positive way, on both computer storage requirement and execution time. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
57.
58.
Sarah Church Peter Ade James Bock Melanie Bowden John Carlstrom Ken Ganga Walter Gear James Hinderks Wayne Hu Brian Keating John Kovac Andrew Lange Eric Leitch Olivier Mallie Simon Melhuish Anthony Murphy Ben Rusholme Creidhe OSullivan Lucio Piccirillo Clem Pryke Andy Taylor Keith Thompson 《New Astronomy Reviews》2003,47(11-12):1083
QUEST on DASI is a ground-based, high-sensitivity, high-resolution (ℓmax2500) experiment designed to map CMB polarization at 100 and 150 GHz and to measure the power spectra from E-modes, B-modes from lensing of the CMB, and B-modes from primordial gravitational waves. The experiment comprises a 2.6 m Cassegrain optical system, equipped with an array of 62 polarization-sensitive bolometers (PSBs), located at the South Pole. The instrument is designed to minimize systematic effects; features include differencing of pairs of orthogonal PSBs within a single feed, a rotatable achromatic waveplate, and axisymmetric rotatable optics. In addition the South Pole location allows both repeatable and highly controlled observations. QUEST on DASI will commence operation in early 2005. 相似文献
59.
60.