全文获取类型
收费全文 | 73477篇 |
免费 | 938篇 |
国内免费 | 405篇 |
专业分类
测绘学 | 1708篇 |
大气科学 | 4777篇 |
地球物理 | 13724篇 |
地质学 | 29302篇 |
海洋学 | 6094篇 |
天文学 | 15423篇 |
综合类 | 262篇 |
自然地理 | 3530篇 |
出版年
2022年 | 440篇 |
2021年 | 727篇 |
2020年 | 767篇 |
2019年 | 904篇 |
2018年 | 3965篇 |
2017年 | 3680篇 |
2016年 | 2957篇 |
2015年 | 966篇 |
2014年 | 1633篇 |
2013年 | 2873篇 |
2012年 | 2709篇 |
2011年 | 4563篇 |
2010年 | 4108篇 |
2009年 | 4716篇 |
2008年 | 3936篇 |
2007年 | 4553篇 |
2006年 | 2410篇 |
2005年 | 1853篇 |
2004年 | 1797篇 |
2003年 | 1919篇 |
2002年 | 1671篇 |
2001年 | 1318篇 |
2000年 | 1149篇 |
1999年 | 1000篇 |
1998年 | 978篇 |
1997年 | 982篇 |
1996年 | 739篇 |
1995年 | 770篇 |
1994年 | 692篇 |
1993年 | 594篇 |
1992年 | 565篇 |
1991年 | 567篇 |
1990年 | 584篇 |
1989年 | 536篇 |
1988年 | 490篇 |
1987年 | 544篇 |
1986年 | 558篇 |
1985年 | 661篇 |
1984年 | 701篇 |
1983年 | 696篇 |
1982年 | 642篇 |
1981年 | 602篇 |
1980年 | 581篇 |
1979年 | 553篇 |
1978年 | 508篇 |
1977年 | 499篇 |
1976年 | 453篇 |
1975年 | 467篇 |
1974年 | 443篇 |
1973年 | 510篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
81.
In connection with the celebration of the centennial of the Institute of Electrical and Electronics Engineers (UEEE) in 1984, the history of electrical engineering in relation to the world's oceans is traced, with emphasis on the 20-year period from the 1960's to the present. Note is taken of the breadth of the cross-disciplinary interests involved, as exemplified by the active participation of a score of IEEE Societies and Professional Groups, how they organized to cooperate, the periodic meetings and annual conferences they sponsored, the publications they undertook, the tokens of recognition they adopted, and how they adapted to changes in emphasis to reflect shifts in the areas of technology served. Finally, an assessment is made of the future of the recently organized IEEE Oceanic Engineering Society. 相似文献
82.
A numerical scheme is developed in order to simulate fluid flow in three dimensional (3‐D) microstructures. The governing equations for steady incompressible flow are solved using the semi‐implicit method for pressure‐linked equations (SIMPLE) finite difference scheme within a non‐staggered grid system that represents the 3‐D microstructure. This system allows solving the governing equations using only one computational cell. The numerical scheme is verified through simulating fluid flow in idealized 3‐D microstructures with known closed form solutions for permeability. The numerical factors affecting the solution in terms of convergence and accuracy are also discussed. These factors include the resolution of the analysed microstructure and the truncation criterion. Fluid flow in 2‐D X‐ray computed tomography (CT) images of real porous media microstructure is also simulated using this numerical model. These real microstructures include field cores of asphalt mixes, laboratory linear kneading compactor (LKC) specimens, and laboratory Superpave gyratory compactor (SGC) specimens. The numerical results for the permeability of the real microstructures are compared with the results from closed form solutions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
83.
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
84.
N. I. Kobanov 《Solar physics》1990,125(1):25-30
Using a differential method we have carried out observations of oscillations in six sunspots. Spectral lines Fe i 5434 Å and Fe i 5576 Å were used. Horizontal waves are not observed in the sunspot umbra photosphere. Results obtained indicate that, at least, the sunspot umbra oscillates as a single whole. 相似文献
85.
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
86.
87.
88.
89.
90.
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