全文获取类型
收费全文 | 6140篇 |
免费 | 1037篇 |
国内免费 | 1482篇 |
专业分类
测绘学 | 1033篇 |
大气科学 | 1077篇 |
地球物理 | 1115篇 |
地质学 | 3014篇 |
海洋学 | 733篇 |
天文学 | 102篇 |
综合类 | 567篇 |
自然地理 | 1018篇 |
出版年
2024年 | 22篇 |
2023年 | 96篇 |
2022年 | 234篇 |
2021年 | 306篇 |
2020年 | 254篇 |
2019年 | 315篇 |
2018年 | 322篇 |
2017年 | 300篇 |
2016年 | 330篇 |
2015年 | 342篇 |
2014年 | 384篇 |
2013年 | 467篇 |
2012年 | 418篇 |
2011年 | 424篇 |
2010年 | 445篇 |
2009年 | 467篇 |
2008年 | 463篇 |
2007年 | 458篇 |
2006年 | 356篇 |
2005年 | 320篇 |
2004年 | 269篇 |
2003年 | 236篇 |
2002年 | 289篇 |
2001年 | 249篇 |
2000年 | 191篇 |
1999年 | 156篇 |
1998年 | 93篇 |
1997年 | 72篇 |
1996年 | 69篇 |
1995年 | 64篇 |
1994年 | 49篇 |
1993年 | 44篇 |
1992年 | 39篇 |
1991年 | 28篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 20篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1979年 | 4篇 |
1958年 | 3篇 |
1957年 | 3篇 |
1954年 | 1篇 |
1943年 | 1篇 |
1937年 | 1篇 |
1934年 | 1篇 |
排序方式: 共有8659条查询结果,搜索用时 31 毫秒
1.
Mobile Agent技术是一门新兴的技术,具有移动性、智能性和异步计算的特点,已成为计算机网络和分布式系统最具活力的发展方向.现对Mobile Agent的概念、系统结构及其关键技术进行了分析和探讨. 相似文献
2.
3.
This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
4.
应用拉格朗日插值法拟合鱼类体长与体重之间的函数关系 ,使用计算机VB语言进行编写程序 ,与常用的线性回归法、Ricker法进行比较 ,得出体长与体重的关系式为Pn(x) =∑nk=0yklk(x)=∑nk=0(∏nj=0j≠kx-xjxk-xj)yk 。 相似文献
5.
Zhang Qing Wang Li-fan Hu Jing-yao P. A. Mazzali Wang Zhen-ru 《Chinese Astronomy and Astrophysics》1995,19(4):426-431
We present the modeling of the ultraviolet and optical spectra obtained simultaneously on 1993 April 15 with the HST and at Lick Observatory. A Monte Carlo code is employed in the modeling and a comparison is made between models reported by different groups. With an atmosphere similar to the Sun in chemical composition, the observed spectral lines are well reproduced by a power law density structure of index around 20 except the strong H and HeI λ5876 lines which have peculiar absorption profiles. The photospheric velocity is found to be 9500 km/s and the blackbody temperature of the spectrum is 7990 K. For H and HeI λ5876, we suggest a two-component density structure which has a smoother layer located immediately outside the steeply decreasing inner envelope. The power law indices are most probably 20 and 3, respectively, with the transition point at about 13 000 km/s. In addition, this outer smooth layer serves to flatten the far UV spectrum as observed. 相似文献
6.
Observation of fluid parcel pathways in the Kuroshio Stream revealed a striking crossstream pattern associated with the Kuroshio‘‘ s meanders. In order to understand the observed pattern, a two-dimensional kinematic model of a meandering jet was developed which could be used to examine the relationship between streamfunction patterns and fluid parcel trajectories. The experiments designed to investigate the dependence of the water exchanges between the Kuroshio water and its surroundings on the characteristics of the Kuroshio‘‘s meanders involved the downstream speed,phase speed and the amplitude of other propagating waves. The results suggested that fluid parcels could cross the meandering jet to and fro; and that the water exchanges between the Kuroshio and its surroundings increased with a) increasing meander amplitude, b) decreasing downstream speed, and c) increasing wave phase speed. The results also showed that when the meandering jet was disturbed by other propagating waves, more effective water exchanges could be induced. 相似文献
7.
8.
9.
Development of a 3D GIS and its application to karst areas 总被引:1,自引:0,他引:1
There is a growing interest in modeling and analyzing karst phenomena in three dimensions. This paper integrates geology,
groundwater hydrology, geographic information system (GIS), database management system (DBMS), visualization and data mining
to study karst features in Huaibei, China. The 3D geo-objects retrieved from the karst area are analyzed and mapped into different
abstract levels. The spatial relationships among the objects are constructed by a dual-linker. The shapes of the 3D objects
and the topological models with attributes are stored and maintained in the DBMS. Spatial analysis was then used to integrate
the data in the DBMS and the 3D model to form a virtual reality (VR) to provide analytical functions such as distribution
analysis, correlation query, and probability assessment. The research successfully implements 3D modeling and analyses in
the karst area, and meanwhile provides an efficient tool for government policy-makers to set out restrictions on water resource
development in the area. 相似文献
10.
Unconsolidated sand, gravel and clay deposits near Beihai and in the Leizhou Peninsula in southern China form an unconfined
aquifer, aquitard and a confined aquifer. Water and soil samples were collected from the two aquifers in the coastal Beihai
area for the determination of chemical compositions, minerals and soluble ions. Hydrogeochemical modeling of three flow paths
through the aquitard are carried out using PHREEQC to determine water–rock interactions along the flow paths. The results
indicate that the dissolution of anorthite, fluorite, halite, rhodochrosite and CO2, and precipitation of potash feldspar and kaolinite may be occurring when groundwater leaks through the aquitard from the
unconfined aquifer to the confined aquifer. Cation exchanges between Na and Ca can also happen along the flow paths. 相似文献