全文获取类型
收费全文 | 28999篇 |
免费 | 549篇 |
国内免费 | 250篇 |
专业分类
测绘学 | 567篇 |
大气科学 | 2218篇 |
地球物理 | 5924篇 |
地质学 | 10159篇 |
海洋学 | 2404篇 |
天文学 | 6430篇 |
综合类 | 57篇 |
自然地理 | 2039篇 |
出版年
2021年 | 201篇 |
2020年 | 235篇 |
2019年 | 250篇 |
2018年 | 551篇 |
2017年 | 522篇 |
2016年 | 625篇 |
2015年 | 503篇 |
2014年 | 669篇 |
2013年 | 1378篇 |
2012年 | 810篇 |
2011年 | 1139篇 |
2010年 | 1011篇 |
2009年 | 1369篇 |
2008年 | 1169篇 |
2007年 | 1160篇 |
2006年 | 1078篇 |
2005年 | 911篇 |
2004年 | 917篇 |
2003年 | 872篇 |
2002年 | 813篇 |
2001年 | 753篇 |
2000年 | 679篇 |
1999年 | 620篇 |
1998年 | 624篇 |
1997年 | 616篇 |
1996年 | 501篇 |
1995年 | 459篇 |
1994年 | 424篇 |
1993年 | 377篇 |
1992年 | 358篇 |
1991年 | 329篇 |
1990年 | 348篇 |
1989年 | 320篇 |
1988年 | 280篇 |
1987年 | 355篇 |
1986年 | 290篇 |
1985年 | 405篇 |
1984年 | 460篇 |
1983年 | 448篇 |
1982年 | 399篇 |
1981年 | 349篇 |
1980年 | 359篇 |
1979年 | 328篇 |
1978年 | 357篇 |
1977年 | 304篇 |
1976年 | 301篇 |
1975年 | 302篇 |
1974年 | 260篇 |
1973年 | 270篇 |
1972年 | 181篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
An updated Lagrangian finite-element formulation has been developed for time-dependent problems of soil consolidation involving finite deformations. Large plastic strains as well as rotations occur in such problems and nominal stress measures are introduced in the formulation to redefine stresses. This leads to corrective terms for equilibrium and yield violations in addition to geometric stiffening terms in the governing integral equations. The soil is considered to be either a linear elastic or an elastoplastic, critical-state material. Some simple numerical examples are studied to validate the formulation, followed by a detailed analysis of the problem of penetration of a pile into soil. The results of this problem are viewed with emphasis on the physical interpretation and practical significance. 相似文献
32.
33.
34.
35.
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
36.
37.
N. Ivanova K. Belczynski J. M. Fregeau F. A. Rasio 《Monthly notices of the Royal Astronomical Society》2005,358(2):572-584
We study the evolution of binary stars in globular clusters using a new Monte Carlo approach combining a population synthesis code ( startrack ) and a simple treatment of dynamical interactions in the dense cluster core using a new tool for computing three- and four-body interactions ( fewbody ). We find that the combination of stellar evolution and dynamical interactions (binary–single and binary–binary) leads to a rapid depletion of the binary population in the cluster core. The maximum binary fraction today in the core of a typical dense cluster such as 47 Tuc, assuming an initial binary fraction of 100 per cent, is only ∼ 5–10 per cent. We show that this is in good agreement with recent Hubble Space Telescope observations of close binaries in the core of 47 Tuc, provided that a realistic distribution of binary periods is used to interpret the results. Our findings also have important consequences for the dynamical modelling of globular clusters, suggesting that 'realistic models' should incorporate much larger initial binary fractions than has usually been the case in the past. 相似文献
38.
Lawrence M. Mayer Peter T. Rahaim William Guerin Stephen A. Macko Les Watling Franz E. Anderson 《Estuarine, Coastal and Shelf Science》1985,20(4):491-503
A variety of measures of organic matter concentration and quality were made on samples collected from the top few mm of intertidal mudflat sediment over the course of a year, in order to assess the relative importance of biological and sedimentological influences on sedimentary organic matter. Winter and summer were times of relatively fine-grained sediment accumulation, caused by biological deposition or stabilization processes and resulting in higher organic matter concentrations. Stable carbon isotope and Br:C ratios indicated a planktonic source of bulk organic matter. Ratios of organic carbon to specific surface area of the sediments were consistent with an organic monolayer coverage of sediment grains. Correction for changing grain size during the year showed no change in the organic concentration per unit surface area, in spite of organic matter inputs by in situ primary production, buildup of heterotroph biomass and mucus coatings, and biodeposition of organic-rich seston. There were also no indications of changes in bulk organic quality, measured as hydrolyzable carbohydrates and amino acids, in response to these biological processes. It is concluded that biological processes on a seasonal time scale affect the bulk organic matter of these sediments via a modulation of grain size rather than creation or decay of organic matter. 相似文献
39.
We present new 1.45-1.75 μm spectra of Europa's dark non-ice material with a spectral resolution (λ/δλ) of 1200, obtained by using adaptive optics on the Keck telescope to spatially separate the spectrum of the non-ice material from that of the surrounding ice-rich regions. Despite the great increase in spectral resolution over the previous best spectra of the non-ice material, taken with Galileo's near-infrared mapping spectrometer (NIMS) with λ/δλ=66, no new fine-scale spectral structure is revealed. The smoothness of the spectra is inconsistent with available laboratory spectra of crystalline hydrated salts at Europa temperatures, but is more consistent with various combinations of non-crystalline hydrated salts and/or hydrated sulfuric acid, as have been matched to the lower-resolution NIMS spectra. 相似文献
40.