全文获取类型
收费全文 | 107567篇 |
免费 | 1800篇 |
国内免费 | 857篇 |
专业分类
测绘学 | 2399篇 |
大气科学 | 7649篇 |
地球物理 | 21083篇 |
地质学 | 38813篇 |
海洋学 | 9602篇 |
天文学 | 24261篇 |
综合类 | 272篇 |
自然地理 | 6145篇 |
出版年
2022年 | 663篇 |
2021年 | 1136篇 |
2020年 | 1230篇 |
2019年 | 1393篇 |
2018年 | 2875篇 |
2017年 | 2686篇 |
2016年 | 3203篇 |
2015年 | 1657篇 |
2014年 | 3055篇 |
2013年 | 5505篇 |
2012年 | 3342篇 |
2011年 | 4400篇 |
2010年 | 3959篇 |
2009年 | 5076篇 |
2008年 | 4416篇 |
2007年 | 4457篇 |
2006年 | 4255篇 |
2005年 | 3088篇 |
2004年 | 3032篇 |
2003年 | 2868篇 |
2002年 | 2844篇 |
2001年 | 2476篇 |
2000年 | 2492篇 |
1999年 | 1981篇 |
1998年 | 1996篇 |
1997年 | 1909篇 |
1996年 | 1654篇 |
1995年 | 1629篇 |
1994年 | 1401篇 |
1993年 | 1303篇 |
1992年 | 1251篇 |
1991年 | 1279篇 |
1990年 | 1258篇 |
1989年 | 1134篇 |
1988年 | 1048篇 |
1987年 | 1239篇 |
1986年 | 1123篇 |
1985年 | 1323篇 |
1984年 | 1515篇 |
1983年 | 1465篇 |
1982年 | 1344篇 |
1981年 | 1276篇 |
1980年 | 1147篇 |
1979年 | 1106篇 |
1978年 | 1099篇 |
1977年 | 970篇 |
1976年 | 928篇 |
1975年 | 903篇 |
1974年 | 934篇 |
1973年 | 995篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
561.
N. Callegari Jr S. Ferraz-Mello T. A. Michtchenko 《Celestial Mechanics and Dynamical Astronomy》2006,94(4):381-397
This paper considers the dynamics of two planets, as the planets B and C of the pulsar PSR B1257+12, near a 3/2 mean-motion resonance. A two-degrees-of-freedom model, in the framework of the general three-body planar problem, is used and the solutions are analyzed through surfaces of section and Fourier techniques in the full phase space of the system.On the possibility of existence of a fourth planet in distant orbit, see Wolszczan et al., 2000 相似文献
562.
The evolution of a homogeneous, isotropic cosmological model driven by a nonminimally coupled scalar field is studied. The
potential for the quintessential inflation model proposed by Peebles and Vilenkin is selected as a scalar potential. Possible
scenarios for the cosmological dynamics are described in the conformal Einstein and Jordan representations. It is shown that,
unlike in models with a minimal scalar field, here a class of solutions exists for which the scalar field is fixed at finite
values during cosmological expansion.
__________
Translated from Astrofizika, Vol. 49, No. 3, pp. 487–498 (August 2006). 相似文献
563.
In recent years, high‐molecular‐weight anionic polyacrylamides (PAMs) have been tested on a variety of soils, primarily in temperate climates. However, little information is available regarding the effectiveness of PAM for preventing soil loss through runoff in tropical settings. Screening tests were performed using three negatively charged PAMs and one positively charged PAM on five Hawaii soils (two Oxisols, one Vertisol, and two Aridisols) to determine erosion loss, sediment settling, and aggregate stability. A laboratory‐scale rainfall simulator was used to apply erosive rainfall at intensities from 5 to 8·5 cm h?1 at various PAM doses applied in both dry and solution forms. Soil detachment due to splash and runoff, as well as the runoff and percolate water volumes, were measured for initial and successive storms. The impact of PAM on particle settling and aggregate stability was also evaluated for selected soil‐treatment combinations. Among the PAMs, Superfloc A‐836 was most effective, and significantly reduced runoff and splash sediment loss for the Wahiawa Oxisol and Pakini Andisol at rates varying between 10 and 50 kg ha?1. Reduced runoff and splash sediment loss were also noted for PAM Aerotil‐D when applied in solution form to the Wahiawa Oxisol. Significant reductions in soil loss were not noted for either the Lualualei Vertisol or the Holomua Oxisol. It is believed that the high montmorillonite content of the Lualualei Vertisol and the low cation‐exchange capacity of the Holomua Oxisol diminished the effectiveness of the various PAMs tested. The polymers were also found to enhance sediment settling of all soils and helped improve their aggregate stability. This screening study shows the potential use of PAM for tropical soils for applications such as infiltration enhancement, runoff reduction, and enhanced sedimentation of detention ponds. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
564.
565.
566.
567.
568.
Near the inner edge of the Edgeworth-Kuiper Belt (EKB) are Pluto and Charon, which are known to have N2- and H2O-dominated surface ices, respectively. Such non-polar and polar ices, and perhaps mixtures of them, also may be present on other trans-Neptunian objects. Pluto, Charon, and all EKB objects reside in a weak, but constant UV-photon and energetic ion radiation environment that drives chemical reactions in their surface ices. Effects of photon and ion processing include changes in ice composition, volatility, spectra, and albedo, and these have been studied in a number of laboratories. This paper focuses on ice processing by ion irradiation and is aimed at understanding the volatiles, ions, and residues that may exist on outer solar system objects. We summarize radiation chemical products of N2-rich and H2O-rich ices containing CO or CH4, including possible volatiles such as alcohols, acids, and bases. Less-volatile products that could accumulate on EKB objects are observed to form in the laboratory from acid-base reactions, reactions promoted by warming, or reactions due to radiation processing of a relatively pure ice (e.g., CO → C3O2). New IR spectra are reported for the 1–5 mu;m region, along with band strengths for the stronger features of carbon suboxide, carbonic acid, the ammonium and cyanate ions, polyoxymethylene, and ethylene glycol. These six materials are possible contributors to EKB surfaces, and will be of interest to observers and future missions. 相似文献
569.
Miquel A. Andreu 《Celestial Mechanics and Dynamical Astronomy》2003,86(2):107-130
The computation of translunar Halo orbits of the real Earth–Moon system (REMS) has been an open problem for a long time, but now, it is possible to compute Halo orbits of the REMS in a systematic way. In this paper, we describe the method used for the numerical computation of Halo orbits for a time span longer than 41 years. Halo orbits of the REMS are computed from quasi-periodic Halo orbits of the quasi-bicircular problem (QBCP). The QBCP is a model for the dynamics of a spacecraft in the Earth–Moon–Sun system. It is a Hamiltonian system with three degrees of freedom and depending periodically on time. In this model, Earth, Moon and Sun are moving in a self-consistent motion close to bicircular. The computed Halo orbits of the REMS are compared with the family of Halo orbits of the QBCP. The results show that the QBCP is a good model to understand the main features of the Halo family of the REMS. 相似文献
570.
Churyumov K. I. Klesachonok V. V. Mussaev F. A. Bikmaev I. F. Galazutdinov G. H. 《Earth, Moon, and Planets》1997,78(1-3):105-110
We present the results of the preliminary study of the comet Hale-Bopp spectrum obtained April 17, 1997 by K. Churyumov and F. Mussayev with the help of the 1-meter Zeiss reflector and the echelle spectrometer (spectral resolutionλ/Δ λ ≈ 50000), CCD and the long slit, oriented along the radius-vector(“Sun-comet direction”). Energy distributions for three selected regions including the C3, C2 (0-0) and CN(Δ ν = 0) molecules emissions of the comet Hale-Bopp spectrum were built. The rotational lines of the CN(Δ ν = 0) band were identified. The nature of the high emission peak near λ 4020 Å in the C3 band is discussed. The presence of the cometary continuum of the nonsolar origin is assumed. 相似文献