全文获取类型
收费全文 | 139814篇 |
免费 | 1808篇 |
国内免费 | 1867篇 |
专业分类
测绘学 | 4230篇 |
大气科学 | 10462篇 |
地球物理 | 27500篇 |
地质学 | 51839篇 |
海洋学 | 11447篇 |
天文学 | 27664篇 |
综合类 | 2425篇 |
自然地理 | 7922篇 |
出版年
2021年 | 902篇 |
2020年 | 1057篇 |
2019年 | 1119篇 |
2018年 | 7802篇 |
2017年 | 7040篇 |
2016年 | 5917篇 |
2015年 | 2025篇 |
2014年 | 2969篇 |
2013年 | 5598篇 |
2012年 | 4376篇 |
2011年 | 7728篇 |
2010年 | 6725篇 |
2009年 | 8164篇 |
2008年 | 6952篇 |
2007年 | 7576篇 |
2006年 | 4180篇 |
2005年 | 3749篇 |
2004年 | 3924篇 |
2003年 | 3729篇 |
2002年 | 3336篇 |
2001年 | 2709篇 |
2000年 | 2655篇 |
1999年 | 2204篇 |
1998年 | 2251篇 |
1997年 | 2121篇 |
1996年 | 1895篇 |
1995年 | 1764篇 |
1994年 | 1587篇 |
1993年 | 1455篇 |
1992年 | 1400篇 |
1991年 | 1280篇 |
1990年 | 1470篇 |
1989年 | 1236篇 |
1988年 | 1160篇 |
1987年 | 1351篇 |
1986年 | 1195篇 |
1985年 | 1486篇 |
1984年 | 1700篇 |
1983年 | 1552篇 |
1982年 | 1455篇 |
1981年 | 1375篇 |
1980年 | 1228篇 |
1979年 | 1188篇 |
1978年 | 1234篇 |
1977年 | 1077篇 |
1976年 | 1036篇 |
1975年 | 986篇 |
1974年 | 943篇 |
1973年 | 983篇 |
1971年 | 608篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
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
43.
The discovery of binaries among the population of transneptunian objects isa landmark advance in the study of this remote region of the solar system.Determination of binary orbits will enable direct determination of systemmasses, fundamental for determination of density, internal structure, and bulkcomposition. The mere existence of binaries with the observed separations andapparent masses constrains models of planetary formation. 相似文献
44.
45.
46.
47.
M.P. Collings J.W. Dever H.J. Fraser M.R.S. McCoustra 《Astrophysics and Space Science》2003,285(3-4):633-659
The interaction of carbon monoxide (CO) with vapour-deposited water(H2O) ices has been studied using temperature programmed desorption (TPD) and Fourier transform reflection-absorption infrared
spectroscopy (FT-RAIRS) over a range of astrophysically relevant temperatures. Such measurements have shown that CO desorption
from amorphous H2Oices is a much more complex process than current astrochemical models suggest. Re-visiting previously reported laboratory
experiments (Collings et al., 2003), a rate model has been constructed to explain, in a phenomenological manner, the desorption
of CO over astronomically relevant time scales. The model presented here can be widely applied to a range of astronomical
environments where depletion of CO from the gas phase is relevant. The model accounts for the two competing processes of CO
desorption and migration, and also enables the entrapment of some of the CO in the ice matrix and its subsequent release as
the water ice crystallises and then desorbs. The astronomical implications of this model are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
48.
Impulsive acoustic waveforms are characterized by a different set of derived quantities than are continuous waveforms. This note presents commonly accepted definitions, units, and symbols used to describe the magnitude of impulsive underwater signals 相似文献
49.
Kunde Yang Yuanliang Ma Chao Sun Miller J.H. Potty G.R. 《Oceanic Engineering, IEEE Journal of》2004,29(4):964-972
This paper discusses the results of geoacoustic inversion carried out using explosive charge data from the Asian Seas International Acoustic Experiment (ASIAEX) East China Sea (ECS) Experiment. A multifrequency incoherent matched-field inversion processor and a genetic algorithm (GA) are used for the inversion. A multistep matched field inversion approach is presented, which makes use of the varying sensitivities of wave fields at various frequencies to reduce the inversion problem into a sequence of smaller inversions with fewer unknowns to estimate at each stage. Different parameters are estimated using data at different frequencies according to their sensitivities. Inversion results for different areas in the ECS region are summarized and compared with core data. 相似文献
50.
We report multi-frequency and multi-epoch radio continuum observations with multi-spatial resolution for the low-luminosity active galactic nucleus (LLAGN) NGC 266. In the centimetre regime, we find diffuse components with Very Large Array (VLA) observations, and a variable compact core with a rising spectrum with Very Long Baseline Array (VLBA) observations. Although the spectral index of the rising spectrum is consistent with the prediction of the simple advection-dominated accretion flow (ADAF) model, the observed radio power is slightly high compared with that of the model prediction. A spectral break at centimetre-to-millimetre wavelengths is inferred from the upper limits of flux densities from Nobeyama Millimetre Array (NMA) and James Clerk Maxwell Telescope (JCMT) data at millimetre and submillimetre wavelengths, respectively. More complicated considerations are required for the theoretical model to interpret such observed radio properties. 相似文献