全文获取类型
收费全文 | 32028篇 |
免费 | 425篇 |
国内免费 | 372篇 |
专业分类
测绘学 | 1221篇 |
大气科学 | 2437篇 |
地球物理 | 6203篇 |
地质学 | 11292篇 |
海洋学 | 2484篇 |
天文学 | 7638篇 |
综合类 | 143篇 |
自然地理 | 1407篇 |
出版年
2021年 | 279篇 |
2020年 | 276篇 |
2019年 | 324篇 |
2018年 | 816篇 |
2017年 | 778篇 |
2016年 | 1019篇 |
2015年 | 590篇 |
2014年 | 957篇 |
2013年 | 1687篇 |
2012年 | 1037篇 |
2011年 | 1277篇 |
2010年 | 1074篇 |
2009年 | 1386篇 |
2008年 | 1203篇 |
2007年 | 1159篇 |
2006年 | 1177篇 |
2005年 | 978篇 |
2004年 | 869篇 |
2003年 | 867篇 |
2002年 | 856篇 |
2001年 | 770篇 |
2000年 | 743篇 |
1999年 | 672篇 |
1998年 | 617篇 |
1997年 | 629篇 |
1996年 | 568篇 |
1995年 | 534篇 |
1994年 | 506篇 |
1993年 | 428篇 |
1992年 | 384篇 |
1991年 | 411篇 |
1990年 | 411篇 |
1989年 | 387篇 |
1988年 | 359篇 |
1987年 | 432篇 |
1986年 | 361篇 |
1985年 | 444篇 |
1984年 | 478篇 |
1983年 | 462篇 |
1982年 | 444篇 |
1981年 | 356篇 |
1980年 | 360篇 |
1979年 | 311篇 |
1978年 | 306篇 |
1977年 | 294篇 |
1976年 | 258篇 |
1975年 | 254篇 |
1974年 | 281篇 |
1973年 | 305篇 |
1972年 | 194篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
REDUCE programs for algebraic computation in General Relativity are presented which use the metric tensor as input. The programs calculate — according to the user's option — the CHRISTOFFEL symbols, the RIEMANN tensor, the RICCI tensor, the RICCI scalar, the EINSTEIN tensor and the WEYL tensor. 相似文献
202.
K. M. Evans 《Geological Journal》1983,18(4):297-305
The Lynton Beds represent shallow marine sediments with a restricted fauna dominated by brachiopods. The age indicated by the brachiopod fauna is late Emsian, although the possibility of a younger date for the uppermost horizons cannot be discounted. 相似文献
203.
Numerical modelling of deep sea air-lift 总被引:2,自引:0,他引:2
Deep sea air-lifting of solid particles from depth of 1600 m is simulated with a mathematical model of the three-phase flow in an upward pipe. The computations are carried out for an axisymmetric domain in a transient way. Phase distributions, pressure and velocity profiles together with flow rates for all phases are presented and analysed. The influence of the pipe diameter on the air-lift efficiency was studied for air-lift pipes of different lengths and found to be significant. The lifting efficiency increases with the increase of the pipe diameter due to the reduction of the wall friction influence on the flow. In addition, the efficiency also increases with the increase of the solid particles volume fraction at the inlet. The presented numerical model can be utilized during various stages of the design of the air-lift pumps to help answer fundamental questions on the process, and during their operation to select optimal process parameters and to address possible problems. 相似文献
204.
205.
From prints of the Palomar Observatory Sky Survey the widths of the equatorial dust layers of a sample of 39 galaxies seen on edge are obtained to be in the range 500 ≤ D ≤ 1600 pc. The width of a dust layer seems to be correlated with the luminosity of the galaxy. The dust lanes of field galaxies are obviously broader than those of the members of the Virgo cluster. This result may be interpreted as a dust deficiency caused by stripping of interstellar matter resulting from galactic collisions and interaction of the galaxies with the intracluster medium. 相似文献
206.
Solar wind propagation from the point of measurement to an arbitrary target in the heliosphere is an important input for heliospheric, planetary and cometary studies. In this paper a new kinematic propagation method, the magnetic lasso method is presented. Compared to the simple ballistic approach our method is based on reconstructing the ideal Parker spiral connecting the target with the Sun by testing a previously defined range of heliographic longitudes. The model takes into account the eventual evolution of stream–stream interactions and handles these with a simple model based on the dynamic pressure difference between the two streams. Special emphasis is given to input data cleaning by handling interplanetary coronal mass ejection events as data gaps due to their different propagation characteristics. The solar wind bulk velocity is considered radial and constant. Density and radial magnetic field are propagated by correcting with the inverse square of the radial distance. The model has the advantage that it can be coded easily and fitted to the problem; it is flexible in selecting and handling input data and requires little running time. 相似文献
207.
208.
209.
A new version of the magnetic-tape catalog of ABELL clusters of galaxies is used to obtain redshift estimators and to generate two samples of clusters. A procedure for searching for superclusters of galaxies is applied and the results are given in tabular and graphic form. For a lmited homogeneous sample (distance 60–275 Mpc, galactic latitude B > 35°), 12 multiplets, having member clusters with known redshifts, are found. It is shown that the spatial covariance function for rich clusters has the form ξ = (r0/r)γ with r0 = 22.4 ± 1.8 Mpc and γ = 1.90 ± 0.25 for 3 Mpc ≲ r ≲ 80 Mpc. 相似文献
210.