全文获取类型
收费全文 | 29428篇 |
免费 | 393篇 |
国内免费 | 323篇 |
专业分类
测绘学 | 617篇 |
大气科学 | 1821篇 |
地球物理 | 5264篇 |
地质学 | 11291篇 |
海洋学 | 2973篇 |
天文学 | 6904篇 |
综合类 | 68篇 |
自然地理 | 1206篇 |
出版年
2022年 | 300篇 |
2021年 | 461篇 |
2020年 | 509篇 |
2019年 | 556篇 |
2018年 | 1096篇 |
2017年 | 1040篇 |
2016年 | 1152篇 |
2015年 | 547篇 |
2014年 | 1046篇 |
2013年 | 1690篇 |
2012年 | 1158篇 |
2011年 | 1438篇 |
2010年 | 1284篇 |
2009年 | 1563篇 |
2008年 | 1335篇 |
2007年 | 1399篇 |
2006年 | 1306篇 |
2005年 | 769篇 |
2004年 | 708篇 |
2003年 | 664篇 |
2002年 | 690篇 |
2001年 | 622篇 |
2000年 | 573篇 |
1999年 | 463篇 |
1998年 | 482篇 |
1997年 | 454篇 |
1996年 | 392篇 |
1995年 | 350篇 |
1994年 | 379篇 |
1993年 | 298篇 |
1992年 | 297篇 |
1991年 | 286篇 |
1990年 | 322篇 |
1989年 | 221篇 |
1988年 | 225篇 |
1987年 | 268篇 |
1986年 | 209篇 |
1985年 | 314篇 |
1984年 | 276篇 |
1983年 | 258篇 |
1982年 | 275篇 |
1981年 | 203篇 |
1980年 | 243篇 |
1979年 | 195篇 |
1978年 | 211篇 |
1977年 | 165篇 |
1976年 | 163篇 |
1975年 | 172篇 |
1974年 | 167篇 |
1973年 | 166篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
301.
302.
303.
304.
305.
Distribution of forms of sulfur in peats from saline environments in the Florida Everglades 总被引:1,自引:0,他引:1
Although there is published information on the mechanism of sedimentary pyrite formation resulting from bacterial reduction of sulfate, little is known about the distribution of forms of sulfur, including organic, in peats. In order to increase understanding of the geochemistry of sulfur in coals, we have determined distributions of forms of sulfur in five cores of saline peat and one of brackish peat, all from areas near the Shark River and Whitewater Bay in the coastal swamps of south Florida. All concentrations vary widely with depth. Total sulfur concentrations range up to 6% of dry solids. Minor amounts of sulfur are present as H2S, S0, SO42−, and acid-soluble sulfide, but the principal forms are usually pyritic and organic. The ratio, organic/pyritic, is highly variable, but at a majority of levels in a profile is considerably greater than unity. It is inferred that topochemical factors are important in determining the distribution of sulfur forms in any element of volume. 相似文献
306.
Zagidullin A. A. Usanin V. S. Petrova N. K. Nefedyev Yu. A. Andreev A. O. Gudkova T. V. 《Astronomy Reports》2020,64(12):1093-1106
Astronomy Reports - The work is devoted to the study of the physical libration of the Moon. Interest in the traditional topic related to the rotation of the Moon is stirred up by the activity of... 相似文献
307.
Dolgikh G. I. Dolgikh S. G. Vasilevskaya L. N. Lisina I. A. 《Doklady Earth Sciences》2020,490(1):18-22
Doklady Earth Sciences - The interaction between the atmosphere and the lithosphere in the minute range of periods is considered. The technique of assessment of the influence of atmospheric... 相似文献
308.
We solve a plane problem of linear baroclinic seiches in closed rotating basins of variable depth with two-layer density stratification.
In the long-wave approximation, we get a boundary-value problem for a system of ordinary differential equations and propose
a numerical procedure for finding internal seiches. The analytic solutions of the problem are obtained for a basin of constant
depth. The numerical analysis of seiches is performed for the distributions of depth corresponding to the zonal and meridional
sections of the Black Sea and model basins including the cases of a shelf zone and an underwater ridge. It is shown that the
baroclinic seiches become more intense in shallow-water regions and that the intense longshore currents caused by Earth’s
rotation are formed in the shelf zones and over the underwater ridges. 相似文献
309.
An intergral model of a transient vertical impulse–buoyant jet is suggested. The model contains a universal equation describing the propagation of the upper boundary of the convection front depending on the strength of the point source of buoyancy and momentum. The convective regime of jet propagation is considered, which includes a class of self-similar solutions corresponding to the buoyancy sources, whose strength varies with time following power and exponential laws. The obtained numerical solutions are compared with available experimental data on the profiles of vertical velocity and buoyancy on the jet axis. 相似文献
310.
Wind erosion of soil is an appreciable but unstudied event following fires in cold desert. We examined aeolian transport of sediment for 1 year following fire in semi-arid shrub steppe on loess soils in southern Idaho, USA. Sediment collectors were used to determine horizontal mass transport of soil and saltation sensors and anemometers were used to determine saltation activity (fraction of time having saltation) and threshold wind speed in an area burned in August and an unburned control site. Horizontal mass transport (per 30-day period) was negligible in the unburned area, but in the burned area was 5.40 kg m?1 in October and decreased to 2.80 kg m?1 in November and 0.32 kg m?1 in December. Saltation activity was high enough to determine threshold wind speeds only in the burn site during fall, when values ranged from 10.0 to 10.6 m s?1. Sediment flux and saltation activity in the burned site became much less pronounced following the emergence of herbaceous vegetation in the spring. Post-fire sediment flux in the shrub steppe we examined was of greater magnitude but shorter duration than post-fire fluxes in warm deserts or sandier regions that experience more frequent wind erosion. 相似文献