全文获取类型
收费全文 | 63379篇 |
免费 | 799篇 |
国内免费 | 373篇 |
专业分类
测绘学 | 1592篇 |
大气科学 | 4510篇 |
地球物理 | 11689篇 |
地质学 | 24975篇 |
海洋学 | 5271篇 |
天文学 | 13137篇 |
综合类 | 212篇 |
自然地理 | 3165篇 |
出版年
2021年 | 407篇 |
2020年 | 419篇 |
2019年 | 463篇 |
2018年 | 3786篇 |
2017年 | 3517篇 |
2016年 | 2642篇 |
2015年 | 756篇 |
2014年 | 1084篇 |
2013年 | 2142篇 |
2012年 | 2202篇 |
2011年 | 4213篇 |
2010年 | 3927篇 |
2009年 | 4466篇 |
2008年 | 3601篇 |
2007年 | 4267篇 |
2006年 | 1655篇 |
2005年 | 1815篇 |
2004年 | 1657篇 |
2003年 | 1681篇 |
2002年 | 1450篇 |
2001年 | 1092篇 |
2000年 | 1024篇 |
1999年 | 819篇 |
1998年 | 820篇 |
1997年 | 834篇 |
1996年 | 681篇 |
1995年 | 672篇 |
1994年 | 606篇 |
1993年 | 556篇 |
1992年 | 504篇 |
1991年 | 490篇 |
1990年 | 499篇 |
1989年 | 483篇 |
1988年 | 459篇 |
1987年 | 543篇 |
1986年 | 477篇 |
1985年 | 596篇 |
1984年 | 650篇 |
1983年 | 594篇 |
1982年 | 534篇 |
1981年 | 592篇 |
1980年 | 487篇 |
1979年 | 456篇 |
1978年 | 441篇 |
1977年 | 432篇 |
1976年 | 383篇 |
1975年 | 377篇 |
1974年 | 374篇 |
1973年 | 379篇 |
1971年 | 223篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
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
72.
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
73.
74.
75.
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
76.
An algorithm for considering time-correlated errors in a Kalman filter is presented. The algorithm differs from previous implementations
in that it does not suffer from numerical problems; does not contain inherent time latency or require reinterpretation of
Kalman filter parameters, and gives full consideration to additive white noise that is often still present but ignored in
previous implementations. Simulation results indicate that the application of the new algorithm yields more realistic and
therefore useful state and covariance information than the standard implementation. Results from a field test of the algorithm
applied to the problem of kinematic differential GPS demonstrate that the algorithm provides slightly pessimistic covariance
estimates whereas the standard Kalman filter provides optimistic covariance estimates. 相似文献
77.
78.
79.
D. Montes M. C. Gálvez M. J. Fernández-Figueroa I. Crespo-Chacón 《Astrophysics and Space Science》2006,304(1-4):367-369
High resolution echelle spectroscopic observations taken with the FEROS spectrograph at the 2.2 m telescope ESO confirm the binary nature of the flare M3.5V star LU Vel (GJ 375, RE J0958-462) previously reported by Christian and Mathioudakis (2002). Emission of similar intensity from both components is detected in the Balmer, Na i D1&D2, He i D3, Ca ii H&K, and Ca ii IRT lines. We have determined precise radial velocities by cross correlation with radial velocity standard stars, which have allowed us to obtain for the first time the orbital solution of the system. The binary consists of two near-equal M3.5V components with an orbital period shorter than 2 days. We have analyzed the behaviour of the chromospheric activity indicators (variability and possible flares). In addition, we have determined its rotational velocity and kinematics. 相似文献
80.
Measurements of 18O concentrations in precipitation, soil solution, spring and runoff are used to determine water transit time in the small granitic Strengbach catchment (0·8 km2; 883–1146 m above sea level) located in the Vosges Mountains of northeastern France. Water transit times were calculated by applying the exponential, exponential piston and dispersion models of the FlowPC program to isotopic input (rainfall) and output (spring and stream water) data sets during the period 1989–95. The input function of the model was modified compared with the former version of the model and estimated by a deterministic approach based on a simplified hydrological balance. The fit between observed and calculated output data showed marked improvements compared with results obtained using the initial version of the model. An exponential piston version of the model applied to spring water indicates a 38·5 month mean transit time, which suggests that the volume in the aquifer, expressed in water depth, is 2·4 m. A considerable thickness (>45 m) of fractured bedrock may be involved for such a volume of water to be stored in the aquifer. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献