全文获取类型
收费全文 | 121377篇 |
免费 | 1951篇 |
国内免费 | 943篇 |
专业分类
测绘学 | 3123篇 |
大气科学 | 8767篇 |
地球物理 | 23573篇 |
地质学 | 44520篇 |
海洋学 | 10152篇 |
天文学 | 26688篇 |
综合类 | 395篇 |
自然地理 | 7053篇 |
出版年
2021年 | 891篇 |
2020年 | 1011篇 |
2019年 | 1052篇 |
2018年 | 4349篇 |
2017年 | 4147篇 |
2016年 | 3944篇 |
2015年 | 1841篇 |
2014年 | 2951篇 |
2013年 | 5516篇 |
2012年 | 3742篇 |
2011年 | 6052篇 |
2010年 | 5366篇 |
2009年 | 6539篇 |
2008年 | 5728篇 |
2007年 | 6046篇 |
2006年 | 3985篇 |
2005年 | 3647篇 |
2004年 | 3485篇 |
2003年 | 3307篇 |
2002年 | 2979篇 |
2001年 | 2640篇 |
2000年 | 2488篇 |
1999年 | 2139篇 |
1998年 | 2179篇 |
1997年 | 2105篇 |
1996年 | 1713篇 |
1995年 | 1723篇 |
1994年 | 1524篇 |
1993年 | 1407篇 |
1992年 | 1359篇 |
1991年 | 1292篇 |
1990年 | 1443篇 |
1989年 | 1268篇 |
1988年 | 1172篇 |
1987年 | 1369篇 |
1986年 | 1163篇 |
1985年 | 1491篇 |
1984年 | 1669篇 |
1983年 | 1587篇 |
1982年 | 1521篇 |
1981年 | 1385篇 |
1980年 | 1257篇 |
1979年 | 1173篇 |
1978年 | 1182篇 |
1977年 | 1064篇 |
1976年 | 1047篇 |
1975年 | 940篇 |
1974年 | 1008篇 |
1973年 | 967篇 |
1972年 | 618篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The 362.156 GHz absorption spectrum of H2O2 in the Mars atmosphere was observed on September 4 of 2003, employing the James Clerk Maxwell Telescope (JCMT) sub-millimeter facility on Mauna Kea, Hawaii. Radiative transfer analysis of this line absorption yields an average volume mixing ratio of 18±0.4 ppbv within the lower (0-30 km) Mars atmosphere, in general accordance with standard photochemical models (e.g., Nair et al., 1994, Icarus 111, 124-150). Our derived H2O2 abundance is roughly three times greater than the upper limit retrieved by Encrenaz et al. (2002, Astron. Astrophys. 396, 1037-1044) from infrared spectroscopy, although part of this discrepancy may result from the different solar longitudes (Ls) of observation. Aphelion-to-perihelion thermal forcing of the global Mars hygropause generates substantial (>200%) increases in HOx abundances above ∼10 km altitudes between the Ls=112° period of the Encrenaz et al. upper limit measurement and the current Ls=250° period of detection (Clancy and Nair, 1996, J. Geophys. Res. 101, 12785-12590). The observed H2O2 line absorption weakens arguments for non-standard homogeneous (Encrenaz et al., 2002, Astron. Astrophys. 396, 1037-1044) or heterogeneous (Krasnopolsky, 2003a, J. Geophys. Res. 108; 2003b, Icarus 165, 315-325) chemistry, which have been advocated partly on the basis of infrared (8 μm) non-detections for Mars H2O2. Observation of Mars H2O2 also represents the first measurement of a key catalytic specie in a planetary atmosphere other than our own. 相似文献
52.
The UBV photometric observations of RT Per, from Sanwal and Chaubey (1981), were analyzed by the Wilson and Devinney code (1971). The light curves include reflection effects that for the first time has been suggested by Dugan (1911). RT Per has a semi-detached configuration where the lower-mass component is in contact with its respective Roche surface. The higher-mass component very nearly fills its Roche lobe. It has the characteristic of an Algol type system. The absolute dimensions for the primary and secondary of this system were calculated from its spectral types and by combining the photometric solution with inferred component radial velocities (Lu, 1990). 相似文献
53.
54.
55.
Long-term changes in growth of Norwegian spring-spawning herring 总被引:3,自引:1,他引:2
56.
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
57.
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
58.
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
59.
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
60.