全文获取类型
收费全文 | 6858篇 |
免费 | 1293篇 |
国内免费 | 1909篇 |
专业分类
测绘学 | 628篇 |
大气科学 | 1419篇 |
地球物理 | 1548篇 |
地质学 | 3494篇 |
海洋学 | 1044篇 |
天文学 | 288篇 |
综合类 | 708篇 |
自然地理 | 931篇 |
出版年
2024年 | 40篇 |
2023年 | 149篇 |
2022年 | 264篇 |
2021年 | 380篇 |
2020年 | 326篇 |
2019年 | 337篇 |
2018年 | 408篇 |
2017年 | 357篇 |
2016年 | 418篇 |
2015年 | 335篇 |
2014年 | 477篇 |
2013年 | 477篇 |
2012年 | 428篇 |
2011年 | 449篇 |
2010年 | 471篇 |
2009年 | 432篇 |
2008年 | 406篇 |
2007年 | 405篇 |
2006年 | 361篇 |
2005年 | 301篇 |
2004年 | 222篇 |
2003年 | 220篇 |
2002年 | 198篇 |
2001年 | 204篇 |
2000年 | 226篇 |
1999年 | 295篇 |
1998年 | 197篇 |
1997年 | 201篇 |
1996年 | 179篇 |
1995年 | 151篇 |
1994年 | 157篇 |
1993年 | 113篇 |
1992年 | 81篇 |
1991年 | 78篇 |
1990年 | 49篇 |
1989年 | 36篇 |
1988年 | 43篇 |
1987年 | 28篇 |
1986年 | 37篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 4篇 |
1976年 | 7篇 |
1966年 | 3篇 |
1958年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
251.
任基 《成都信息工程学院学报》1990,(1)
本文介绍了一种新的标定流气式正比计数管的方法。此方法的特点是把正比管作为吸收体,利用He气对光子较为透明的原理,标定正比管的探测效率。方法简便实用,并对P-10(90%Ar+10%CH_4)为工作气体的正比管进行了标定。 相似文献
252.
Enhancements for the Bragg reflection are introduced for three sets of 2D higher order Boussinesq equations to improve the prediction of the Bragg reflection. The extension of the approach to other sets of Boussinesq equations is discussed. The analytical solutions for the Bragg reflection over an infinite number of sinusoidal bars are derived for these Boussinesq models and compared to the exact theoretical solution in order to determine the optimized values of the parameters in the new enhancement terms. Numerical simulations are also carried out for the Bragg reflection over a finite number of sand bars and compared with corresponding measurements to validate the enhancements. Comparisons with other forms of Boussinesq models are made to discuss the applicability of different forms of Boussinesq models to rapidly varying topography with sand bars. The effects of the mild slope assumption on the prediction of Bragg reflection and of wave reflection on a plane self are also discussed. 相似文献
253.
Félix Darve Stein Sture René de Borst Andrew J. Whittle Ian M. Smith 《国际地质力学数值与分析法杂志》2009,33(3):n\a-n\a
254.
The raindrop impact and overland flow are two major factors causing soil detachment and particle transportation. In this study, the turbulent characteristics of the shallow rain‐impacted water flow were investigated using a 2‐D fibre‐optic laser Doppler velocimetry (FLDV) and an artificial rainfall simulator. The fluctuating turbulent shear stress was computed using digital data processing techniques. The experimental data showed that the Reynolds shear stress follows a probability distribution with heavy tails. The tail probability increases with an increase of rainfall intensity or raindrop diameter, and it decreases with an increase of Reynolds number. A modified empirical equation was derived using both the raindrop diameter and rainfall intensity as independent variables to provide a better prediction of the Darcy‐Weisbach friction coefficient f under rainfall conditions. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
255.
256.
Emergy analysis is effective for analyzing ecological economic systems. However, the accuracy of the approach is af-fected by the diversity of economic level, meteorological and hydrological parameters... 相似文献
257.
The temperature curve in the solar chromosphere has puzzled astronomers for a long time.Referring to the structure of supergranular cells,we propose an in ductive heating model.It mainly includes the following three steps.(1) A small-scale dynamo exists in the supergranulation and produces alternating small-scale magnetic fluxes;(2) The supergranular flow distributes these small-scale fluxes according to a regular pattern;(3) A skin effect occurs in the alternating and regularly-distributed magnetic fields.The induced current is concentrated near the transition region and heats it by resistive dissipation. 相似文献
258.
Comparisons of drought variability between central High Asia and monsoonal Asia: Inferred from tree rings 总被引:1,自引:0,他引:1
Keyan Fang Xiaohua Gou Fahu Chen Fen Zhang Yingjun Li Jianfeng Peng 《Frontiers of Earth Science》2010,4(3):277-288
Severe drought is a serious natural disaster that frequently strikes East Asia, highlighting the need to understanding its
drought regime and the associations with Asian monsoon. Tree-ring-based drought reconstructions provide invaluable paleoclimatic
archives for detecting regional and large-scale drought variability and their potential forcings. We herein reviewed many
drought reconstructions from central High Asia and monsoonal Asia and compared their similarities and differences, as well
as their linkages to Asia monsoon. We compared the decadal-scale variability of six drought reconstructions for the central
High Asia, where differing drought variations were found between the western and eastern portions. Seven drought reconstructions
were reviewed for monsoonal Asia, from which a difference in drought variability was observed between the northern and southern
parts. Therefore, we compared the drought variations of the four sub-regions of western and eastern parts of central High
Asia, as well as northern and southern portions of monsoonal Asia. ENSO activity and sea surface temperature of western Pacific
and northern Indian Oceans, coupled with Asian monsoon, play an important role in modulating drought variability of much area
of the East Asia. An improved denser multi-index tree-ring network of longer length for East Asia is necessary for the establishment
of more reliable large-scale drought reconstruction. 相似文献
259.
China Ocean Engineering - This study aimed to restore the ultimate strength of dented stainless-steel hemispheres with a radius of 90 mm and a thickness of 0.86 mm. All of the hemispheres were... 相似文献
260.
<正>Erratum to:Chinese Journal of Oceanology and Limnology Vol.31 No.6,P.1190-1195,2013http://dx.doi.org/10.1007/s00343-013-3049-3The supporting grant information on the footnote of the original version of this article needs to be altered and updated.The new information is given below. 相似文献