全文获取类型
收费全文 | 80986篇 |
免费 | 1431篇 |
国内免费 | 545篇 |
专业分类
测绘学 | 2004篇 |
大气科学 | 5782篇 |
地球物理 | 15670篇 |
地质学 | 28354篇 |
海洋学 | 7101篇 |
天文学 | 18692篇 |
综合类 | 190篇 |
自然地理 | 5169篇 |
出版年
2021年 | 684篇 |
2020年 | 767篇 |
2019年 | 853篇 |
2018年 | 1714篇 |
2017年 | 1691篇 |
2016年 | 1991篇 |
2015年 | 1189篇 |
2014年 | 2047篇 |
2013年 | 3964篇 |
2012年 | 2128篇 |
2011年 | 2904篇 |
2010年 | 2681篇 |
2009年 | 3398篇 |
2008年 | 3113篇 |
2007年 | 3192篇 |
2006年 | 2975篇 |
2005年 | 2361篇 |
2004年 | 2367篇 |
2003年 | 2302篇 |
2002年 | 2143篇 |
2001年 | 1916篇 |
2000年 | 1776篇 |
1999年 | 1666篇 |
1998年 | 1608篇 |
1997年 | 1601篇 |
1996年 | 1326篇 |
1995年 | 1300篇 |
1994年 | 1209篇 |
1993年 | 1095篇 |
1992年 | 1030篇 |
1991年 | 1029篇 |
1990年 | 1113篇 |
1989年 | 1004篇 |
1988年 | 941篇 |
1987年 | 1048篇 |
1986年 | 967篇 |
1985年 | 1223篇 |
1984年 | 1372篇 |
1983年 | 1341篇 |
1982年 | 1244篇 |
1981年 | 1166篇 |
1980年 | 1069篇 |
1979年 | 1012篇 |
1978年 | 998篇 |
1977年 | 935篇 |
1976年 | 865篇 |
1975年 | 797篇 |
1974年 | 864篇 |
1973年 | 873篇 |
1972年 | 559篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
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
73.
D. H. Lumb A. Finoguenov R. Saxton B. Aschenbach P. Gondoin M. Kirsch I. M. Stewart 《Experimental Astronomy》2003,15(2):89-111
We describe measurements of the mirror vignetting in the XMM-Newton Observatory made in-orbit, using observations of SNR G21.5-09
and SNR 3C58 with the EPIC imaging cameras. The instrument features that complicate these measurements are briefly described.
We show the spatial and energy dependences of measured vignetting, outlining assumptions made in deriving the eventual agreement
between simulation and measurement. Alternate methods to confirm these are described, including an assessment of source elongation
with off-axis angle, the surface brightness distribution of the diffuse X-ray background, and the consistency of Coma cluster
emission at different position angles. A synthesis of these measurements leads to a change in the XMM calibration data base,
for the optical axis of two of the three telescopes, by in excess of 1 arcmin. This has a small but measureable effect on
the assumed spectral responses of the cameras for on-axis targets.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
74.
75.
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
76.
Using photoclinometry, topographic profiles across europan ridges have been produced. These profiles allow the identification of bulges in the terrain adjacent to the ridges. The bulges are assumed to have been produced by flexure of the elastic lithosphere due to the load of the ridges, which lie along cracks in the crust. The distance from the crack to these “fore-bulges” depends on the thickness of the elastic plate being flexed. Based on a survey of ridges in Galileo images with resolution <300 m/pixel, the thickness of the elastic lithosphere has been determined by this method at a wide variety of sites along the leading and trailing hemispheres of Europa. The average thickness is about 200 m. The elastic lithosphere underneath smooth dilational bands tends to be thicker than plains morphology, an effect that is pronounced at Thynia Linea and Astypalaea Linea. Among the ridges investigated here, more recent loading correlates with a thicker elastic lithosphere, which may either reflect an intrinsically thicker layer, or less viscous relaxation over the shorter time period. 相似文献
77.
78.
The occultation of Io by Ganymede as observed on 10 June 1985 is reported. The middle of the occultation minimum was found to occur at 14h 14m 5.7s UT. In the plane perpendicular to the line of sight the centres of the two satellite disks passed to within ~ 2530 km of each other, at a relative velocity, in this plane, of about 11 kms–1. The values of these last two quantities, however, depend on what assumptions are made about the light distribution over io's disk. 相似文献
79.
80.
This paper presents an on-line trained neural net work controller for ship track-keeping problems. Following a brief review of the ship track-keeping control development since the 1980's, an analysis of various existing backpropagation-based neural controllers is provided. We then propose a single-input multioutput (SIMO) neural control strategy for situations where the exact mathematical dynamics of the ship are not available. The aim of this study is to build an autonomous neural controller which uses rudder to regulate both the tracking error and heading error. During the whole control process, the proposed SIMO neural controller adapts itself on-line from a direct evaluation of the control accuracy, and hence the need for a “teacher” or an off-line training process can be removed. With a relatively modest amount of quantitative knowledge of the ship behavior, the design philosophy enables real time control of a nonlinear ship model under random wind disturbances and measurement noise. Three different track-keeping tasks have been simulated to demonstrate the effectiveness of the training method and the robust performance of the proposed neural control strategy 相似文献