全文获取类型
收费全文 | 78855篇 |
免费 | 1150篇 |
国内免费 | 597篇 |
专业分类
测绘学 | 1873篇 |
大气科学 | 5256篇 |
地球物理 | 14555篇 |
地质学 | 31095篇 |
海洋学 | 6699篇 |
天文学 | 16951篇 |
综合类 | 289篇 |
自然地理 | 3884篇 |
出版年
2022年 | 458篇 |
2021年 | 748篇 |
2020年 | 864篇 |
2019年 | 959篇 |
2018年 | 4045篇 |
2017年 | 3744篇 |
2016年 | 3141篇 |
2015年 | 1125篇 |
2014年 | 1877篇 |
2013年 | 3215篇 |
2012年 | 2875篇 |
2011年 | 4790篇 |
2010年 | 4232篇 |
2009年 | 4933篇 |
2008年 | 4153篇 |
2007年 | 4664篇 |
2006年 | 2603篇 |
2005年 | 2039篇 |
2004年 | 1941篇 |
2003年 | 2014篇 |
2002年 | 1773篇 |
2001年 | 1406篇 |
2000年 | 1316篇 |
1999年 | 1114篇 |
1998年 | 1111篇 |
1997年 | 1079篇 |
1996年 | 928篇 |
1995年 | 868篇 |
1994年 | 821篇 |
1993年 | 700篇 |
1992年 | 658篇 |
1991年 | 669篇 |
1990年 | 723篇 |
1989年 | 587篇 |
1988年 | 571篇 |
1987年 | 638篇 |
1986年 | 600篇 |
1985年 | 779篇 |
1984年 | 789篇 |
1983年 | 763篇 |
1982年 | 733篇 |
1981年 | 649篇 |
1980年 | 668篇 |
1979年 | 586篇 |
1978年 | 565篇 |
1977年 | 535篇 |
1976年 | 499篇 |
1975年 | 506篇 |
1974年 | 482篇 |
1973年 | 517篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
31.
The growth of Glasgow from a small town into a heavily industrialised conurbation depended greatly on its local geological riches. Extensive mining and quarrying of a range of minerals took place from the 18th century onwards. The early underground stoop and room (pillar and stall) workings, and the backfilled quarries, together with variably consolidated natural superficial deposits, have bequeathed to the city a heritage of unwanted engineering problems which cannot easily be quantified. Recent work by the British Geological Survey (BGS) illustrates the scale of both geological and man-made problems. 相似文献
32.
V. Parro J.A. Rodríguez-Manfredi C. Compostizo E. Vez M. Moreno-Paz P. Fernández-Calvo J. Pérez-Mercader J. Gómez-Elvira 《Planetary and Space Science》2005,53(7):729-737
Recent findings by the MER rover opportunity confirming the presence of iron minerals that can only be formed in the presence of water emphasize the study of analogous environments to Mars on Earth. The study of chemolithoautotrophic communities living in acidic iron-rich habitats is highly relevant in order to identify Mars analog environment-specific biomarkers. Iron oxidizing bacteria like Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans have ways of life for which it is feasible to identify a past or present hypothetical niche on Mars. We have developed a strategy for biomarker identification based on: (i) search for biosignatures on acid and metal-rich environments; (ii) development of an immunosensor microarray; and (iii) integration into an instrument for autonomous and remote operation. The instrument that we have built, called Signs Of LIfe Detector (SOLID), is capable of processing a variety of samples for the detection of specific biomarkers. Antibodies against several bacterial strains have been developed and tested in a microarray biosensor on SOLID. Tests with field samples have been successfully performed, allowing the detection of L. ferrooxidans, A. ferrooxidans present in sediment samples. 相似文献
33.
We consider the particular solutions of the evolutionary system of equations in elements that correspond to planar and spatial circular orbits of the singly averaged Hill problem. We analyze the stability of planar and spatial circular orbits to inclination and eccentricity, respectively. We construct the instability regions of both particular solutions in the plane of parameters of the problem. 相似文献
34.
Summary. Asymptotic ray theory (ART) fails in transition regions near critically reflected, bottom glancing or caustic-forming rays in a vertically inhomogeneous layered earth. These deficiencies are repaired here by replacing the transitional ray fields with guided modes plus truncation remainders. Exact ray-mode equivalences and their high-frequency asymptotic approximations are formulated, and their validity and efficiency are verified by numerical comparisons for SH motion in a two-layer earth model comprised of an inhomogeneous sediment above an homogeneous semi-infinite bedrock. 相似文献
35.
Homogenous isotropic cosmologies in the presence of a cosmological constant A are studied in the modified Brans-Dicke theory.
A class of exact solutions are obtained in Dicke's revised units for empty space as well as for the models filled with dust
or radiation. Behaviour of these models near the singularity are discussed. 相似文献
36.
A numerical scheme is developed in order to simulate fluid flow in three dimensional (3‐D) microstructures. The governing equations for steady incompressible flow are solved using the semi‐implicit method for pressure‐linked equations (SIMPLE) finite difference scheme within a non‐staggered grid system that represents the 3‐D microstructure. This system allows solving the governing equations using only one computational cell. The numerical scheme is verified through simulating fluid flow in idealized 3‐D microstructures with known closed form solutions for permeability. The numerical factors affecting the solution in terms of convergence and accuracy are also discussed. These factors include the resolution of the analysed microstructure and the truncation criterion. Fluid flow in 2‐D X‐ray computed tomography (CT) images of real porous media microstructure is also simulated using this numerical model. These real microstructures include field cores of asphalt mixes, laboratory linear kneading compactor (LKC) specimens, and laboratory Superpave gyratory compactor (SGC) specimens. The numerical results for the permeability of the real microstructures are compared with the results from closed form solutions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
37.
M.S. Hanner E. Tedesco A.T. Tokunaga G.J. Veeder D.F. Lester F.C. Witteborn J.D. Bregman J. Gradie L. Lebofsky 《Icarus》1985,64(1):11-19
The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ~2 × 105 g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ~0.04 at 1.25 μm and ~0.05 at 2.2 μm. 相似文献
38.
N. I. Kobanov 《Solar physics》1990,125(1):25-30
Using a differential method we have carried out observations of oscillations in six sunspots. Spectral lines Fe i 5434 Å and Fe i 5576 Å were used. Horizontal waves are not observed in the sunspot umbra photosphere. Results obtained indicate that, at least, the sunspot umbra oscillates as a single whole. 相似文献
39.
N. N. Chugai 《Astronomy Letters》2006,32(11):739-746
I study the question of whether the asymmetry of 56Ni ejecta that results in the asymmetry of the Hα emission line at the nebular epoch of the type-IIP supernova SN 2004dj can account for the recently detected polarization of the supernova radiation. I have developed a model of the Hα profile and luminosity with nonthermal ionization and excitation in a spherically symmetric envelope for an asymmetric bipolar 56Ni distribution. I have calculated the polarized radiation transfer against the background of the recovered electron density distribution. The observed polarization is shown to be reproduced at the nebular epoch around day 140 for the same parameters of the envelope, and the 56Ni distribution for which the evolution of the Hα luminosity and profile is explained. Yet the model polarization decreases with time more slowly than is observed. The origin of the additional component responsible for the early polarization on day 107 is discussed. 相似文献
40.