全文获取类型
收费全文 | 101627篇 |
免费 | 1827篇 |
国内免费 | 895篇 |
专业分类
测绘学 | 2472篇 |
大气科学 | 7016篇 |
地球物理 | 20458篇 |
地质学 | 36186篇 |
海洋学 | 8790篇 |
天文学 | 23410篇 |
综合类 | 271篇 |
自然地理 | 5746篇 |
出版年
2022年 | 549篇 |
2021年 | 960篇 |
2020年 | 1059篇 |
2019年 | 1114篇 |
2018年 | 2565篇 |
2017年 | 2378篇 |
2016年 | 2956篇 |
2015年 | 1748篇 |
2014年 | 2919篇 |
2013年 | 5296篇 |
2012年 | 3104篇 |
2011年 | 4228篇 |
2010年 | 3655篇 |
2009年 | 4925篇 |
2008年 | 4414篇 |
2007年 | 4227篇 |
2006年 | 3987篇 |
2005年 | 3141篇 |
2004年 | 3081篇 |
2003年 | 2872篇 |
2002年 | 2678篇 |
2001年 | 2466篇 |
2000年 | 2340篇 |
1999年 | 1936篇 |
1998年 | 2031篇 |
1997年 | 1941篇 |
1996年 | 1596篇 |
1995年 | 1631篇 |
1994年 | 1389篇 |
1993年 | 1278篇 |
1992年 | 1241篇 |
1991年 | 1154篇 |
1990年 | 1300篇 |
1989年 | 1104篇 |
1988年 | 1016篇 |
1987年 | 1270篇 |
1986年 | 1039篇 |
1985年 | 1332篇 |
1984年 | 1456篇 |
1983年 | 1406篇 |
1982年 | 1272篇 |
1981年 | 1199篇 |
1980年 | 1058篇 |
1979年 | 986篇 |
1978年 | 1005篇 |
1977年 | 904篇 |
1976年 | 885篇 |
1975年 | 835篇 |
1974年 | 822篇 |
1973年 | 834篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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
52.
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
53.
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
54.
MohammedHazaea HUKe MohammedMattash CHENBing M.O.AI-JabaliAref MohammedAbdussalam 《东北亚地学研究》2004,7(2):181-184
The chemical composition of several thermal springs around Changbaishan area has been investigated. Cenozoic basaltic rocks are widely distributed in Northeast China and geothermal characteristics have been described. About one hundred hot springs exist around Changhaishan Volcano at the border between China and D.P.R.Korea with high temperature about 82~C. The pH values of the spring water range from 6.9 to 7.1 and the total flow rate is about 4.8 L/sec. The chemical composition of the thermal springs is sodium carbonate; the high-mineral contents of thermal water are believed to have medicinal properties. Bathhouses are already built along the hot springs to take the advantage of the supposed healing properties. The high quality of those hot springs is believed to be utilitized for mineral water. The chemical equilibrium temperatures were estimated at about 160℃ based on the Na-K-Ca geochemical thermometer. 相似文献
55.
56.
57.
58.
Rostov State Pedagogical Institute; All-Union Scientific Research Institute Gradient. Translated from Astrofizika, Vol. 33, No. 3, pp. 379–393, November–December, 1990. 相似文献
59.
M. A. Mansour 《Astrophysics and Space Science》1990,166(2):269-275
The interaction of free convection with thermal radiation of the oscillatory flow past a vertical plate is studied. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. 相似文献
60.
It is shown that the kinematical parameters associated with the congruence formed by tachyonic motion can be defined in the manner of Greenberg, but not that of Ehlers. The space-like counterpart of Raychaudhuri's equation has also been obtained. 相似文献