全文获取类型
收费全文 | 7730篇 |
免费 | 408篇 |
国内免费 | 98篇 |
专业分类
测绘学 | 214篇 |
大气科学 | 887篇 |
地球物理 | 2050篇 |
地质学 | 3021篇 |
海洋学 | 475篇 |
天文学 | 1185篇 |
综合类 | 75篇 |
自然地理 | 329篇 |
出版年
2023年 | 37篇 |
2022年 | 57篇 |
2021年 | 132篇 |
2020年 | 156篇 |
2019年 | 132篇 |
2018年 | 412篇 |
2017年 | 411篇 |
2016年 | 493篇 |
2015年 | 331篇 |
2014年 | 419篇 |
2013年 | 540篇 |
2012年 | 484篇 |
2011年 | 428篇 |
2010年 | 372篇 |
2009年 | 398篇 |
2008年 | 283篇 |
2007年 | 217篇 |
2006年 | 215篇 |
2005年 | 389篇 |
2004年 | 355篇 |
2003年 | 241篇 |
2002年 | 153篇 |
2001年 | 113篇 |
2000年 | 96篇 |
1999年 | 83篇 |
1998年 | 82篇 |
1997年 | 108篇 |
1996年 | 62篇 |
1995年 | 79篇 |
1994年 | 78篇 |
1993年 | 45篇 |
1992年 | 34篇 |
1991年 | 38篇 |
1990年 | 67篇 |
1989年 | 32篇 |
1988年 | 24篇 |
1987年 | 43篇 |
1986年 | 28篇 |
1985年 | 37篇 |
1984年 | 42篇 |
1983年 | 34篇 |
1982年 | 41篇 |
1981年 | 45篇 |
1980年 | 19篇 |
1979年 | 29篇 |
1978年 | 22篇 |
1977年 | 25篇 |
1975年 | 17篇 |
1974年 | 19篇 |
1973年 | 22篇 |
排序方式: 共有8236条查询结果,搜索用时 359 毫秒
21.
We present solutions for the effective stress induced by gas flow through a porous solid into a borehole resulting from sudden pressure reduction. Tensile effective stress that exceeds the strength of the solid will lead to borehole failure. This has applications to the intentional creation of cavities, relevant to the efficient recovery of coalbed methane, and the avoidance of borehole stability problems in conventional gas production. 相似文献
22.
Arnaud M. Aubourg E. Bareyre P. Br';ehin S. Caridroit R. de Kat J. Dispau G. Djidi K. Gros M. Lachièze-Rey M. Laigneau Y. Laurent B. Lesquoy E. Lavocat Ph. Magneville C. Mazeau B. Milsztajn A. Moscoso L. Pasquaud J. Paul B. Perrin P. Petibon J. Piret Y. Queinnec F. Rich J. Spiro M. de Trogoff J. Vigroux L. Zylberajch S. Ansari R. Cavalier F. Moniez M. Beaulieu J. P. Ferlet R. Grison Ph. Vidal-Madjar A. Adrianzyk G. Berger J. P. Burnage R. Delclite J. C. Kohler D. Magnan R. Richaud A. Guibert J. Moreau O. Tajahmady F. Baranne A. Maurice E. Prévôt L. Gry C. 《Experimental Astronomy》1994,4(3-4):265-278
A 20cm
2
CCD mosaic camera has been especially built to search for dark galactic halo objects by the gravitational microlensing effect. The sensitive area is made of 16 edge-buttable CCDs developped by Thomson-CTS, with 23×23 µm
2
pixels. The 35 kg camera housing and mechanical equipment is presented. The associated electronics and data acquisition system are described in a separate paper. The camera resides at the focal plane of a 40 cm, f/10, Ferson reflector. The instrument has been in operation since December 1991 at the La Silla Observatory (ESO). 相似文献
23.
Yannick Giraud-Héraud Jean Kaplan François De Volnay Martin Charling Tao Sylvaine Turck-Chièze 《Solar physics》1990,128(1):21-33
The Saclay solar evolution code is used to check the effect of WIMPs on solar evolution. In this paper we study the effects of various types of Cosmion-matter interactions, give constraints on the crosssections compatible with the measured neutrino rate of 2 SNU on chlorine, and relate these constraints to ongoing dark matter detection experiments.Unité associée au CNRS UA 280, F-75251 Paris Cedex 05, France.On leave from LPC, Collège de France. 相似文献
24.
The trans-Neptunian belt has been subject to a strong depletion that has reduced its primordial population by a factor of one hundred over the solar system's age. One by-product of such a depletion process is the existence of a scattered disk population in transit from the belt to other places, such as the Jupiter zone, the Oort cloud or interstellar space. We have integrated the orbits of the scattered disk objects (SDOs) so far discovered by 2500 Myr to study their dynamical time scales and the probability of falling in each of the end states mentioned above, paying special attention to their contribution to the Oort cloud. We found that their dynamical half-time is close to 2.5 Gyr and that about one third of the SDOs end up in the Oort cloud. 相似文献
25.
Gérard Daigne Patrick Charlot Christine Ducourant Jean-François Lestrade 《Astrophysics and Space Science》2003,286(1-2):255-260
The question of positioning the optical counterparts of the ICRF quasars is outlined in the perspective of future space astrometry
missions, which ultimately will bring a new realization of the ICRS in the optical range. Ground-based interferometry with
a dual-field observing mode (PRIMA/VLTI),together with the missions DIVA and FAME, will have a key role in building an extragalactic
reference frame in the optical/near-IR range with about the same accuracy as that of the present (VLBI) primary frame.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
26.
27.
Szilárd Csizmadia Zsolt Kővári Péter Klagyivik 《Astrophysics and Space Science》2006,304(1-4):355-357
We carried out optical and Hα photometry of two contact binaries (V861 Herculis, EQ Tauri). The light curve modeling revealed stellar spots in both contact systems and strong Hα excess in the position of the observed stellar spots. A correlation was found between the V−R and R−Hα colour indices of V861 Her. 相似文献
28.
In view of rapid developments in iterative solvers, it is timely to re‐examine the merits of using mixed formulation for incompressible problems. This paper presents extensive numerical studies to compare the accuracy of undrained solutions resulting from the standard displacement formulation with a penalty term and the two‐field mixed formulation. The standard displacement and two‐field mixed formulations are solved using both direct and iterative approaches to assess if it is cost‐effective to achieve more accurate solutions. Numerical studies of a simple footing problem show that the mixed formulation is able to solve the incompressible problem ‘exactly’, does not create pressure and stress instabilities, and obviate the need for an ad hoc penalty number. In addition, for large‐scale problems where it is not possible to perform direct solutions entirely within available random access memory, it turns out that the larger system of equations from mixed formulation also can be solved much more efficiently than the smaller system of equations arising from standard formulation by using the symmetric quasi‐minimal residual (SQMR) method with the generalized Jacobi (GJ) preconditioner. Iterative solution by SQMR with GJ preconditioning also is more elegant, faster, and more accurate than the popular Uzawa method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
29.
During a campaign of optical observations at high latitude, a bi-dimensional study of the wave structure of the OH layer has been performed in December 1981 from Sodankyla (Finland). This site is one of the three stations of the EISCAT ionosphere sounding system. It has been found that a wave field covering an area of 1 million km2 may extend to latitudes as high as 70°N. The OH wave structure shows many similarities with noctilucent clouds. The fairly large horizontal wavelength, of the order of 40 km cannot easily be explained by a wave motion at an interface. The observed wave structure seems to be a result of the propagation of an internal gravity wave in the 80–100 km region. This wave structure was often recorded during the same time as an active aurora was present. As a result, it appears that the perturbation might be correlated with particle precipitations at auroral latitudes. 相似文献
30.