全文获取类型
收费全文 | 92449篇 |
免费 | 1574篇 |
国内免费 | 2188篇 |
专业分类
测绘学 | 2961篇 |
大气科学 | 6349篇 |
地球物理 | 18186篇 |
地质学 | 37132篇 |
海洋学 | 7408篇 |
天文学 | 17123篇 |
综合类 | 2493篇 |
自然地理 | 4559篇 |
出版年
2022年 | 741篇 |
2021年 | 1110篇 |
2020年 | 1152篇 |
2019年 | 1224篇 |
2018年 | 6889篇 |
2017年 | 6026篇 |
2016年 | 4967篇 |
2015年 | 1544篇 |
2014年 | 2415篇 |
2013年 | 3682篇 |
2012年 | 3700篇 |
2011年 | 5921篇 |
2010年 | 5009篇 |
2009年 | 5838篇 |
2008年 | 4985篇 |
2007年 | 5621篇 |
2006年 | 3231篇 |
2005年 | 2213篇 |
2004年 | 2220篇 |
2003年 | 2105篇 |
2002年 | 1877篇 |
2001年 | 1564篇 |
2000年 | 1415篇 |
1999年 | 1047篇 |
1998年 | 1109篇 |
1997年 | 1108篇 |
1996年 | 875篇 |
1995年 | 866篇 |
1994年 | 778篇 |
1993年 | 675篇 |
1992年 | 664篇 |
1991年 | 633篇 |
1990年 | 731篇 |
1989年 | 623篇 |
1988年 | 583篇 |
1987年 | 669篇 |
1986年 | 522篇 |
1985年 | 690篇 |
1984年 | 794篇 |
1983年 | 706篇 |
1982年 | 690篇 |
1981年 | 638篇 |
1980年 | 649篇 |
1979年 | 528篇 |
1978年 | 567篇 |
1977年 | 517篇 |
1976年 | 471篇 |
1975年 | 457篇 |
1974年 | 458篇 |
1973年 | 527篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
We discuss long-time changes of polar activity of the Sun using the new observational data sets in the optical range during
1872–2001. A study of the secular and cycle variations of the magnetic activity at the high-latitude regions is the main goal
that includes polar magnetic field reversals during 1872–2001 and secular changes of the duration of polar activity cycles.
The secular increase of the area of polar zones during the minimum activity in the last 120 years and as consequence a decrease
of coronal temperature of the Sun in the high-latitude zones during the last 50 years. Correlation between the polar cycles
of Caii-K bright points with the Wolf sunspot numbers cycles, W(t), and the 22-year polar magnetic cycles of Caii-K bright points at the high latitudes during 1905–1995 is discussed. 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.
W. H. Jefferys G. F. Benedict P. D. Hemenway P. J. Shelus R. L. Duncombe 《Celestial Mechanics and Dynamical Astronomy》1985,37(3):299-305
The Hubble Space Telescope (HST), a large optical telescope having an aperture of 2.4 meters and a length of 8.8 meters, is being developed by the National Aeronautics and Space Administration. This telescope will be placed into earth orbit by the space shuttle. Astrometric observations with the HST are made using a Fine Guidance Sensor which is capable of measuring the position of one object relative to another with an accuracy of ±0.002 arcseconds. The astrometric user of HST will be provided with an Astrometric Data Reduction Software package (ADRS). The variety of astrometric problems to be investigated with HST is discussed. 相似文献
35.
36.
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
37.
38.
39.
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
40.
Transport by southeastern rivers has insignificant influence on the lead concentration of southeastern shelf waters. If the rate of mobilization and transport of lead by these rivers is representative of uncontaminated fluvial transport during the Pleistocene, only about 5% of the prehistoric output of lead to the North Atlantic can be accounted for by river input.Lead concentrations in southeastern shelf waters are similar to those of North Atlantic Water from the upper 1000 m, which is probably similar to the intrusion source water for the shelf. Atmospheric inputs to the shelf of the same magnitude as observed for the Western North Atlantic are difficult to reconcile given the residence time of shelf waters and their lead concentration unless the rate of loss of lead to shelf sediments is about the same as the atmospheric flux. 相似文献