全文获取类型
收费全文 | 84581篇 |
免费 | 27790篇 |
国内免费 | 54942篇 |
专业分类
测绘学 | 12769篇 |
大气科学 | 25849篇 |
地球物理 | 20883篇 |
地质学 | 64941篇 |
海洋学 | 23601篇 |
天文学 | 1306篇 |
综合类 | 7945篇 |
自然地理 | 10019篇 |
出版年
2024年 | 829篇 |
2023年 | 2169篇 |
2022年 | 4113篇 |
2021年 | 5017篇 |
2020年 | 5087篇 |
2019年 | 8043篇 |
2018年 | 7652篇 |
2017年 | 7292篇 |
2016年 | 7396篇 |
2015年 | 7677篇 |
2014年 | 7067篇 |
2013年 | 8242篇 |
2012年 | 8750篇 |
2011年 | 8643篇 |
2010年 | 8647篇 |
2009年 | 7739篇 |
2008年 | 7280篇 |
2007年 | 7031篇 |
2006年 | 6454篇 |
2005年 | 5650篇 |
2004年 | 5020篇 |
2003年 | 3989篇 |
2002年 | 3801篇 |
2001年 | 3430篇 |
2000年 | 2882篇 |
1999年 | 2087篇 |
1998年 | 1804篇 |
1997年 | 1825篇 |
1996年 | 1442篇 |
1995年 | 1360篇 |
1994年 | 1210篇 |
1993年 | 1190篇 |
1992年 | 1040篇 |
1991年 | 768篇 |
1990年 | 757篇 |
1989年 | 600篇 |
1988年 | 503篇 |
1987年 | 400篇 |
1986年 | 329篇 |
1985年 | 268篇 |
1984年 | 301篇 |
1983年 | 184篇 |
1982年 | 226篇 |
1981年 | 164篇 |
1980年 | 119篇 |
1979年 | 135篇 |
1978年 | 65篇 |
1977年 | 57篇 |
1976年 | 46篇 |
1971年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Yanjun ZHANG Fenglong ZHANG Full QI Fuquan NI 《东北亚地学研究》2006,9(2):199-203
In view of the situation of excavation of open coal mine for the underground water disaster,we should carry out simulation studies for the numerical value of the water lowering project and improve the accuracy and the level of the water lowering project.On the basis of the hydrological geological conditions of certain open mine digging,a more reasonable seepage numerical model was built according to MODFLOW.It was simulated in advance that the process of the confined water level descending with the time,and combining with the actual observations to test the correctness of the model.The calculation showed that the results coincided well with the results of actual measurement.Based on this,different water lowering numerical simulations were built for the open coal mine digging.It could be simulated and forecast that the changes of the groundwater level in drainage process within and outside the mine pit,and it was quantitatively assessed that the possible water lowering result of the opencast water drainage process,which provide an important basis for the actual water lowering project and the possible project disposal. 相似文献
62.
中国虚拟天文台图像处理分析工具(VO_IMPAT),是由国家天文台虚拟天文台项目组开发的一项服务,它提供了对数字巡天图像数据(Digital Sky Survey,DSS)、天文星表以及其他数据库的交互访问。VO_IMPAT的设计目的是实现多波段天文数据的融合。可以将不同波段的星表叠加到DSS底图上,如光学波段的USNO星表、近红外波段的2MASS星表、射电波段的NVSS星表和X射线波段的RASS星表。同时VO_IMPAT还可以对图像进行放大、缩小、伪彩色、等高线、直方图、尖锐化、平滑化、旋转等处理,不同的星表数据可以采用不同的颜色和图标显示。 相似文献
63.
64.
Axial surveys were performed in the two river tributaries of the Cochin estuary, SW India during November 1988. Surficial sediments were subjected to sequential chemical extractions to delineate five metal fractions, namely, exchangeable, carbonate bound, easily reducible, organic/sulfide bound, and residual. The results indicated selective accumulation of Mn and Ni in carbonate bound and organic/sulfide forms, along with marginal amounts of Co in the exchangeable fraction. Large portions of Fe and Cr occurred in the residual fraction, whereas composite fractionation of Zn species was noticed. The exchangeable fractions of Fe and Cr as well as of easily reducible cobalt were below detection limits. The levels of Cr and Zn indicate anthropogenic inputs in this estuary, whereas Co and Ni show regional contamination exceeding natural levels. The analytical speciation procedure helps to deduce the sedimental diagenetic processes in the estuarine environment. 相似文献
65.
本文在Thorne工作的基础上讨论了吸积盘中黑洞的有关参量的演化,以及由Schwarzschild黑洞吸积盘向Kerr黑洞吸积盘演化过程中对吸积盘辐射通量的影响,最后针对几个典型的辐射过程,分别讨论了黑洞吸积盘在牛顿框架中的温度分布方程与广义相对论的温度分布方程的热不稳定性,并给出此类问题的热不稳定性的判据。 相似文献
66.
67.
Universal cokriging is used to obtain predictions when dealing with multivariate random functions. An important type of nonstationarity is defined in terms of multivariate random functions with increments which are stationary of orderk. The covariance between increments of different variables is modeled by means of the pseudo-cross-covariance function. Criteria are formulated to which the parameters of pseudo-cross-covariance functions must comply so as to ensure positive-definiteness. Cokriging equations and the induced cokriging equations are given. The study is illustrated by an example from soil science. 相似文献
68.
WANG Yachun 《东北亚地学研究》2002,(1)
The paper deals with the methods of formation pressure evaluation for a single well by using the very common ac-cepted parameters, such as drilling exponent , and flowline temperature , etc. which is part of compiling the end well report. 相似文献
69.
70.
The purpose of this work was to reinvestigate the existing hydrogeological conceptual model of the basin of Madrid, Spain. A cumulative chemical isotopic diagram which enabled the distinction between different groups of water as well as calculation of the mode of their blending was used for this investigation. It was found that the groups of discharge were lighter in their isotopic composition than that of recharge. The previous explanation of this fact, backed by carbon-14 dating, was the long residence time due to flow lines going down to depths of more than 1000 m. This flow model assumes homogenous conditions to these depths. This assumption can not be supported by evidence from deep wells. Thus a modified model is suggested which maintains homogenous conditions only to about 300 m and a deep confined aquifer below containing paleowater. The higher degree of depletion of this water has been explained by a colder climate on top of an altitude effect. Another interesting observation was the correlation between the isotopic composition of the rains, the month of the rain event and the composition of the recharge group groundwater. It could be seen that the winter rains resemble the groundwater composition, which shows that practically all the spring and summer rains were evapotranspirated. 相似文献