全文获取类型
收费全文 | 135497篇 |
免费 | 2738篇 |
国内免费 | 1463篇 |
专业分类
测绘学 | 3487篇 |
大气科学 | 10102篇 |
地球物理 | 27821篇 |
地质学 | 47203篇 |
海洋学 | 11809篇 |
天文学 | 29756篇 |
综合类 | 399篇 |
自然地理 | 9121篇 |
出版年
2021年 | 1035篇 |
2020年 | 1246篇 |
2019年 | 1309篇 |
2018年 | 2829篇 |
2017年 | 2655篇 |
2016年 | 3579篇 |
2015年 | 2299篇 |
2014年 | 3473篇 |
2013年 | 7087篇 |
2012年 | 3736篇 |
2011年 | 5252篇 |
2010年 | 4490篇 |
2009年 | 6134篇 |
2008年 | 5614篇 |
2007年 | 5223篇 |
2006年 | 5076篇 |
2005年 | 4264篇 |
2004年 | 4245篇 |
2003年 | 4002篇 |
2002年 | 3767篇 |
2001年 | 3364篇 |
2000年 | 3304篇 |
1999年 | 2815篇 |
1998年 | 2812篇 |
1997年 | 2719篇 |
1996年 | 2368篇 |
1995年 | 2239篇 |
1994年 | 2046篇 |
1993年 | 1883篇 |
1992年 | 1778篇 |
1991年 | 1666篇 |
1990年 | 1820篇 |
1989年 | 1590篇 |
1988年 | 1472篇 |
1987年 | 1757篇 |
1986年 | 1547篇 |
1985年 | 1931篇 |
1984年 | 2159篇 |
1983年 | 2062篇 |
1982年 | 1929篇 |
1981年 | 1783篇 |
1980年 | 1600篇 |
1979年 | 1482篇 |
1978年 | 1545篇 |
1977年 | 1401篇 |
1976年 | 1334篇 |
1975年 | 1263篇 |
1974年 | 1274篇 |
1973年 | 1275篇 |
1972年 | 808篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
151.
The dynamics of the vortex lattice in the inner crust of a neutron star is considered. A general equation of motion is obtained
and solved under the assumption that there are regions of pinned and of free vortices. By comparing these solutions with observational
data for the Vela pulsar, the relative moments of inertia of regions of relaxation with the corresponding characteristic times
are calculated for two model stars with different equations of state. It is shown that the theory can be reconciled with observations
of the relaxation of pulsar angular velocity only for model stars with extremely stiff equations of state.
Translated from Astrofizika, Vol. 40, No. 1, pp. 67–76, January–March, 1997. 相似文献
152.
R. Sarmiento M. Gallardo A. Laquidara J. Reyna Almandos 《Astrophysics and Space Science》1997,256(1-2):359-363
This work presents preliminaries spectroscopic results about ionized xenon and xenon-helium mixture using a capillary pulsed discharge under several experimental results. 相似文献
153.
Harker David E. Woodward Charles E. McMURTRY Craig W. Goetz J. A. Pipher J. L. Forrest W. J. 《Earth, Moon, and Planets》1997,78(1-3):259-264
We present 1- to 5-μm broadband and CVF images of comet Hale-Bopp taken 1997 February 10.5 UT, 50 days before perihelion.
All the images exhibit a nonspherical coma with a bright “ridge” in the direction of the dust tail approximately 10″ from
the coma. Synthetic aperture spectrophotometry implies that the optically important grains are of a radius ≤0.4 μm; smallest
radius for any comet seen to date. The variation of the integrated surface brightness with radial distance from the coma (ρ)
in all the images closely follows the “steady state” ρ−1 model for comet dust ablation (Gehrz and Ney, 1992). The near-infrared colors taken along the dust tail are not constant
implying the dust grain properties vary with coma distance.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
154.
Solar scintillations were investigated as a method of detecting seeing-dependent wavefront curvature variations for solar adaptive optics. The method is applicable to full-disk averaged, adaptive corrections of large-scale near-field seeing distortions. As a test case, seeing measurements were carried out on a single small adaptive mirror, representing one element of what would be a large multielement adaptive array. All observations showed a greater than 5× reduction of seeing distortions as a result of this wavefront correction. 相似文献
155.
T. H. BELL S. E. JOHNSON B. DAVIS A. FORDE N. HAYWARD C. WILKINS 《Journal of Metamorphic Geology》1992,10(3):295-307
Extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non-coaxial ductile deformation of the matrix subsequent to their growth. This has been demonstrated for all tectonic environments so far investigated. The work also has provided new insights and data on metamorphic, structural and tectonic processes including: (1) the intimate control of deformation partitioning on metamorphic reactions; (2) solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones, and relative plate motion; and (3) a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens. 相似文献
156.
J. Wirsich 《Astrophysics and Space Science》1997,250(2):271-295
Using the chromospheric UV flux based on IUE data, we have undertaken a wavelength calculation of the rates of photodissociation and the a abundances of the relevant molecules CO, SiS, HCN and C2H2 for the inner region of the circumstellar shell of the carbon-rich star TX Psc. Shielding by heavy elements and dust was taken into account. Further, for CO, the line self-shielding as an additional shielding process was included. We find that the large influence of the shielding prevents the molecules from photodissociation in the internal layer of the shell of TX Psc. The possibility of detecting C2H2 via the equivalent widths of the infrared lines in the circumstellar shell is discussed. Finally, we estimate the antenna temperature and the luminosity of the fine-structure lines of [CI]609µ and [CII]158µ of the envelope of TX Psc, respectively. 相似文献
157.
Several temperature-depth profiles measured in Kasai and in Shaba provinces of Zaire using mining exploration boreholes exhibit a significant negative temperature gradient near the surface. This anomalous curvature which extends to 100–200 m depth could reflect the effect of variations in surface conditions. Applying the theory of heat conduction in a semi-infinite homogeneous medium, these profiles indicate a surface warming by 3–4°C. This warming is related to the effect of the environmental changes associated with the mining exploitation and the urbanization during the last 40–90 years. 相似文献
158.
159.
Angela C. Taylor 《New Astronomy Reviews》2003,47(11-12):925
We discuss two experiments – the Very Small Array (VSA) and the Arcminute MicroKelvin Imager (AMI) – and their prospects for observing the CMB at high angular multipoles. Whilst the VSA is primarily designed to observe primary anisotropies in the CMB, AMI is designed to image secondary anisotropies via the Sunyaev–Zel’dovich effect. The combined ℓ-range of these two instruments is between ℓ=150 and 10,000. 相似文献
160.
We have derived the galaxy luminosity function in various regions of the cluster of galaxies Abell 496 from a wide field image
in the I band. A Schechter function fit in the 17≤ IAB ≤22(–19.5≤ MIAB ≤ –14.5) magnitude interval gives a steep power law index, which is somewhat steeper in the outer regions than in the inner
zones. This result agrees with previous findings obtained by several teams on the Coma cluster and can be interpreted as due
to the fact that faint galaxies are accreted by large ones in the central regions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献