全文获取类型
收费全文 | 29578篇 |
免费 | 4954篇 |
国内免费 | 7589篇 |
专业分类
测绘学 | 4388篇 |
大气科学 | 6625篇 |
地球物理 | 5919篇 |
地质学 | 11097篇 |
海洋学 | 4034篇 |
天文学 | 4141篇 |
综合类 | 2097篇 |
自然地理 | 3820篇 |
出版年
2024年 | 129篇 |
2023年 | 329篇 |
2022年 | 899篇 |
2021年 | 1073篇 |
2020年 | 1247篇 |
2019年 | 1470篇 |
2018年 | 1208篇 |
2017年 | 1378篇 |
2016年 | 1442篇 |
2015年 | 1618篇 |
2014年 | 1724篇 |
2013年 | 1989篇 |
2012年 | 1848篇 |
2011年 | 1889篇 |
2010年 | 1503篇 |
2009年 | 1999篇 |
2008年 | 1980篇 |
2007年 | 2139篇 |
2006年 | 2037篇 |
2005年 | 1880篇 |
2004年 | 1755篇 |
2003年 | 1505篇 |
2002年 | 1328篇 |
2001年 | 1177篇 |
2000年 | 1083篇 |
1999年 | 960篇 |
1998年 | 1003篇 |
1997年 | 631篇 |
1996年 | 538篇 |
1995年 | 496篇 |
1994年 | 455篇 |
1993年 | 371篇 |
1992年 | 233篇 |
1991年 | 208篇 |
1990年 | 135篇 |
1989年 | 103篇 |
1988年 | 99篇 |
1987年 | 61篇 |
1986年 | 40篇 |
1985年 | 37篇 |
1984年 | 24篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1973年 | 6篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
31.
同时采用4个台站的国际超导重力仪长期连续重力观测资料和国际地球自转服务中心提供的同步地球自转参数,研究了极移引起的地球重力场变化特征。利用自回归模型估计了各序列的功率谱密度和积谱密度,结果表明极移导致的重力效应的主要能量集中在Chandler摆动和周年项附近,叠积后实际重力观测与极移重力信号理论值之间的差异分别为0.4%和3.9%,说明超导重力仪可有效监测极移导致的重力变化。 相似文献
32.
空间数据仓库的认知过程 总被引:3,自引:3,他引:0
从理论上探讨了空间数据仓库的认知过程.主要是十一个层次的世界模型通过十个算子转换的过程,对十一个层次世界及十个算子概念进行了较详细地讨论,并用代数系统对其进行了定义。 相似文献
33.
An elastoplastic model for sands is presented in this paper, which can describe stress–strain behaviour dependent on mean effective stress level and void ratio. The main features of the proposed model are: (a) a new state parameter, which is dependent on the initial void ratio and initial mean stress, is proposed and applied to the yield function in order to predict the plastic deformation for very loose sands; and (b) another new state parameter, which is used to determine the peak strength and describe the critical state behaviour of sands during shearing, is proposed in order to predict simply negative/positive dilatancy and the hardening/softening behaviour of medium or dense sands. In addition, the proposed model can also predict the stress–strain behaviour of sands under three-dimensional stress conditions by using a transformed stress tensor instead of ordinary stress tensor. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
34.
In the frame of 2D-static problems one approaches the problem of elastic-NRT (not-resisting tension) semi-plane loaded on its limit line. This problem is intended to model the stress situation induced in the soil by a foundation structure. The solution, in terms of activated stress field, is searched for in the class of stress fields satisfying equilibrium and admissibility conditions, by applying an energy approach. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
35.
Numerical simulations of the evolving activity of comet Hale-Bopp are presented, assuming a porous, spherical nucleus, 20
km in radius, made of dust and gas-laden amorphous ice. The main effects included are: crystallization of amorphous ice and
release of occluded gas, condensation, sublimation and flow of gases through the pores, changing pore sizes, and flow of dust
grains. The model parameters, such as initial pore size and porosity, emissivity, dust grain size, are varied in order to
match the observed activity. In all cases, a sharp rise in the activity of the nucleus occurs at a large heliocentric distance
pre-perihelion, marked by a few orders of magnitude increase in the CO and the CO2 fluxes and in the rate of dust emission. This is due to the onset of crystallization, advancing down to a few meters below
the surface, accompanied by release of the trapped gases. A period of sustained, but variable, activity ensues. The emission
of water molecules is found to surpass that of CO at a heliocentric distance of 3 AU. Thereafter the activity is largely determined
by the behaviour of the dust. If a dust mantle is allowed to build up, the water production rate does not increase dramatically
towards perihelion; if most of the dust is ejected, the surface activity increases rapidly, producing a very bright comet.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
36.
The problem of clock synchronization: A relativistic approach 总被引:2,自引:0,他引:2
Sergei A Klioner 《Celestial Mechanics and Dynamical Astronomy》1992,53(1):81-109
The problem of synchronization of the Earth-based clocks has been discussed in the framework of General Relativity Theory. The synchronization is considered as the transformation of the observers' proper time scales to the coordinate time scale of local inertial geocentric reference system, which is single for all the observers. The formulas for the relativistic corrections occurring in some methods of Earth-based clock synchronization (transported clock, duplex communication via geostationary satellite and meteor-burst link, LASSO experiments) have been derived enabling one to attain the accuracy of 0.1 ns. 相似文献
37.
本文在已有数据处理方法的基础上,利用近代数值逼近理论,给出了从时空域角度描述地壳垂直运动过程的一种具体的函数解析形式。最后给出了一个实际算例。 相似文献
38.
Hai-Ning LiNational Astronomical Observatories Chinese Academy of Sciences Beijing lhnDepartment of Astronomy Beijing Normal University Beijing 《中国天文和天体物理学报》2003,3(5)
We present a quantitative estimate of the relativistic corrections to the thermal SZ power spectrum produced by the energetic electrons in massive clusters. The corrections are well within 10% for current experiments with working frequencies below v < 100 GHz, but become non-negligible at high frequencies v > 350 GHz. Moreover, the corrections appear to be slightly smaller at higher l or smaller angular scales. We conclude that there is no need to include the relativistic corrections in the theoretical study of the SZ power spectrum especially at low frequencies unless the SZ power spectrum is used for precision cosmology. 相似文献
39.
40.