全文获取类型
收费全文 | 81027篇 |
免费 | 1574篇 |
国内免费 | 2099篇 |
专业分类
测绘学 | 2877篇 |
大气科学 | 6143篇 |
地球物理 | 16010篇 |
地质学 | 31778篇 |
海洋学 | 6194篇 |
天文学 | 14644篇 |
综合类 | 2396篇 |
自然地理 | 4658篇 |
出版年
2022年 | 352篇 |
2021年 | 607篇 |
2020年 | 625篇 |
2019年 | 734篇 |
2018年 | 5909篇 |
2017年 | 5156篇 |
2016年 | 4096篇 |
2015年 | 1268篇 |
2014年 | 1669篇 |
2013年 | 2998篇 |
2012年 | 2886篇 |
2011年 | 5126篇 |
2010年 | 4228篇 |
2009年 | 5162篇 |
2008年 | 4350篇 |
2007年 | 4826篇 |
2006年 | 2657篇 |
2005年 | 2099篇 |
2004年 | 2200篇 |
2003年 | 2043篇 |
2002年 | 1825篇 |
2001年 | 1413篇 |
2000年 | 1413篇 |
1999年 | 1160篇 |
1998年 | 1196篇 |
1997年 | 1110篇 |
1996年 | 902篇 |
1995年 | 896篇 |
1994年 | 812篇 |
1993年 | 683篇 |
1992年 | 690篇 |
1991年 | 614篇 |
1990年 | 721篇 |
1989年 | 600篇 |
1988年 | 578篇 |
1987年 | 666篇 |
1986年 | 546篇 |
1985年 | 712篇 |
1984年 | 823篇 |
1983年 | 740篇 |
1982年 | 733篇 |
1981年 | 640篇 |
1980年 | 666篇 |
1979年 | 549篇 |
1978年 | 517篇 |
1977年 | 538篇 |
1976年 | 471篇 |
1975年 | 462篇 |
1974年 | 469篇 |
1973年 | 490篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
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
32.
TANGYa XIEJiasui SUNHui 《山地科学学报》2004,1(1):38-45
Dry valleys are a striking geographic landscape in Hengduan Mountains Region and are characterized by low rainfall, desert type of vegetation and fragile environment. Past efforts and resources have been concentrated mainly on rehabilitation of degraded ecosystem and fragile environment, particularly reforestation, while socio-economic development has been largely overlooked. Despite successes in pocket areas, the overall trend of unsustainability and environmental deterioration are continuing. It is important to understand that uplift of the Tibetan Plateau is the root cause of development of dry valleys, and development and formation of dry valleys is a natural process. Human intervention has played a secondary role in development of dry valleys and degradation of dry valleys though human intervention in many cases has speeded up environmental degradation of the dry valleys. It is important to understand that dry valleys are climatic enclaves and an integrated approach that combines rehabilitation of degraded ecosystems and socio-economic development should be adopted if the overall goal of sustainable development of dry valleys is to be achieved. Promotion of niche-based cash crops, rural energy including hydropower, solar energy, biogas and fuelwood plantation is recommended as the priority activities. 相似文献
33.
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.
Faith Vilas David J. Tholen Larry A. Lebofsky Humberto Campins Glenn J. Veeder Richard P. Binzel Alan T. Tokunaga 《Icarus》1985,63(2):201-205
Visual and infrared observations were made of Amor asteroid 1982 DV during its discovery apparition. Broadband visual and near-infrared photometry shows that it is an S-class asteroid. Narrowband spectrophotometry shows an absorption feature due to olivine or pyroxene or both centered at 0.93 μm. Applying a nonrotating thermal model to 10-μm photometry, the geometric albedo is calculated to be approximately 0.27. The geometric albedo for a slowly rotating, rocky surface was calculated for 1 night to be 0.15, consistent with S-class asteroid albedos. Thus, 1982 DV is either one of the most reflective S-class asteroids known, or a significant amount of bare rock is exposed on the asteroid's surface. For the nonrotating model, ellipsoidal dimensions for 1982 DV are 3.5 × 1.4 × 1.4 km. 相似文献
38.
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
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.