全文获取类型
收费全文 | 258625篇 |
免费 | 5295篇 |
国内免费 | 3359篇 |
专业分类
测绘学 | 6973篇 |
大气科学 | 19200篇 |
地球物理 | 54245篇 |
地质学 | 89778篇 |
海洋学 | 21587篇 |
天文学 | 56289篇 |
综合类 | 1037篇 |
自然地理 | 18170篇 |
出版年
2021年 | 2241篇 |
2020年 | 2602篇 |
2019年 | 2887篇 |
2018年 | 3560篇 |
2017年 | 3303篇 |
2016年 | 5747篇 |
2015年 | 4242篇 |
2014年 | 6943篇 |
2013年 | 14299篇 |
2012年 | 6518篇 |
2011年 | 7897篇 |
2010年 | 6963篇 |
2009年 | 9576篇 |
2008年 | 8422篇 |
2007年 | 7921篇 |
2006年 | 9692篇 |
2005年 | 7754篇 |
2004年 | 7648篇 |
2003年 | 7152篇 |
2002年 | 6729篇 |
2001年 | 5988篇 |
2000年 | 5968篇 |
1999年 | 5212篇 |
1998年 | 5242篇 |
1997年 | 5031篇 |
1996年 | 4670篇 |
1995年 | 4430篇 |
1994年 | 4112篇 |
1993年 | 3843篇 |
1992年 | 3656篇 |
1991年 | 3600篇 |
1990年 | 3759篇 |
1989年 | 3518篇 |
1988年 | 3311篇 |
1987年 | 3847篇 |
1986年 | 3406篇 |
1985年 | 4233篇 |
1984年 | 4734篇 |
1983年 | 4422篇 |
1982年 | 4315篇 |
1981年 | 3921篇 |
1980年 | 3648篇 |
1979年 | 3515篇 |
1978年 | 3487篇 |
1977年 | 3280篇 |
1976年 | 3041篇 |
1975年 | 2962篇 |
1974年 | 2920篇 |
1973年 | 3084篇 |
1972年 | 2027篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
661.
H. -U. Zimmermann 《Astrophysics and Space Science》1995,228(1-2):331-347
Results from ROSAT observations of recent supernova events are discussed in the light of a model, where the soft X-rays originate in the shock interaction of the expanding supernova ejecta with the circumstellar material, left from heavy mass loss of the progenitor object. Special attention is given to the observations of SN1993J in M81, where lightcurves and spectral measurements allow a more detailed analysis and comparison to numerical model calculations. 相似文献
662.
B. D. F. Methley 《The Photogrammetric Record》1994,14(83):793-803
A case is made for the development of an inexpensive and portable data capturing unit which could be used with existing mirror stereoscopes and which could provide an accuracy sufficient for most digital map databases. The results of simulation experiments to test the accuracy of the system are presented. 相似文献
663.
Evaluation of Fluorobenzoate Tracers in Surface Soils 总被引:2,自引:0,他引:2
Dan B. Jaynes 《Ground water》1994,32(4):532-538
664.
Abstract— A whole rock sample from the H3 chondrite Sainte Rose, which was discovered in 1983, was dated with the 40Ar-39Ar technique. From the K/Ca spectrum and from an analysis of the 39Ar recoil effect we conclude that this meteorite has at least two distinguishable K-carriers: a low temperature, high-K/Ca, fine-grained carrier with a typical grain size of about 2 μm and a high temperature, low-K/Ca, more coarse-grained carrier. The K-Ar clocks of both were started 4.40 ± 0.01 Ga ago. 相似文献
665.
666.
Robe's restricted three-body problem is reanalyzed with a view to incorporate a new assumption, namely that the configuration of the fluid body is that described by an hydrostatic equilibrium figure (Roche's ellipsoid). In the concomitant gravitational field a full treatment of the buoyancy force is given. The pertinent equations of motion are derived, the linear stability of the equilibrium solution is studied and the connection between the effect of the buoyancy forces and a perturbation of the Coriolis force is pointed out. 相似文献
667.
The restricted problem of 2 + 2 bodies when one of the infinitesimal masses is further acted upon by the light pressure of the two primaries, is considered. The stationary solutions of this problem are found out. A short discussion is devoted to the stability of these solutions. 相似文献
668.
Perspectives for the Radio-Optical Telescope 54/32/2.6 are given for scientific research in radioastronomy. Its characteristics and potential scientific fields are summarized in the frame of the present French-Armenian collaboration. A 3-phase upgrade plan including a detailed technical evaluation of the antenna is presented.Published in Astrofizika, Vol. 38, No. 4, pp. 645–648, October–December, 1995. 相似文献
669.
We have studied the influence of the magnetic helicity on solar particle propagation using the IMF data observed by the HELIOS spacecraft in the range 0.31–0.95 AU, during eight solar proton events. For this, we have derived power and helicity spectra of the turbulence of the magnetic field during the time of the events. These are used to compute the particle pitch-angle scattering coefficients according to the quasi-linear theory (QLT) treatment of particle propagation in turbulent magnetic fields. The results show that in all the cases the helicity effects are negligible and the particle's mean free paths deduced from the pitch-angle diffusion coefficients are the same regardless of whether or not helicity effects are included in the calculations. The computed mean free paths are quite different in each case.Deceased 10 April, 1995. 相似文献
670.
The testing of a synthetic aperture technique, the ETAM algorithm, is extended and its performance for CW pseudorandom signals and broadband ship noise is examined. The results show the limitations of the technique and are of special interest for operational systems development. In the CW experiments, the transmitted signal was generated with high temporal coherence, and loss of the spatial and temporal coherence of the received signal was introduced only by the medium and the stability of the towed array. In the experiments that included the pseudorandom signal and the ship noise, the temporal coherence of the transmitted signals was deliberately chosen to be poor in order to study the effects and the performance of this algorithm with broadband signals. The related experimental results show that for received signals, which have their segments over the synthesizing period highly cross-correlated, a synthetic aperture array gain was achieved that corresponds to the length of an equivalent fully populated array 相似文献