全文获取类型
收费全文 | 41330篇 |
免费 | 19823篇 |
国内免费 | 44297篇 |
专业分类
测绘学 | 4023篇 |
大气科学 | 22470篇 |
地球物理 | 14038篇 |
地质学 | 38415篇 |
海洋学 | 16813篇 |
天文学 | 1021篇 |
综合类 | 5156篇 |
自然地理 | 3514篇 |
出版年
2024年 | 174篇 |
2023年 | 487篇 |
2022年 | 1095篇 |
2021年 | 1485篇 |
2020年 | 2444篇 |
2019年 | 5863篇 |
2018年 | 6027篇 |
2017年 | 5774篇 |
2016年 | 5816篇 |
2015年 | 5213篇 |
2014年 | 4837篇 |
2013年 | 5372篇 |
2012年 | 5144篇 |
2011年 | 4957篇 |
2010年 | 4832篇 |
2009年 | 4099篇 |
2008年 | 3398篇 |
2007年 | 3331篇 |
2006年 | 3000篇 |
2005年 | 2791篇 |
2004年 | 2961篇 |
2003年 | 2670篇 |
2002年 | 2372篇 |
2001年 | 2110篇 |
2000年 | 1770篇 |
1999年 | 1793篇 |
1998年 | 1867篇 |
1997年 | 1904篇 |
1996年 | 1519篇 |
1995年 | 1472篇 |
1994年 | 1297篇 |
1993年 | 1253篇 |
1992年 | 1076篇 |
1991年 | 774篇 |
1990年 | 756篇 |
1989年 | 623篇 |
1988年 | 526篇 |
1987年 | 420篇 |
1986年 | 330篇 |
1985年 | 251篇 |
1984年 | 282篇 |
1983年 | 167篇 |
1982年 | 205篇 |
1981年 | 145篇 |
1980年 | 114篇 |
1979年 | 112篇 |
1978年 | 49篇 |
1977年 | 46篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
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
72.
73.
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
74.
运输系统的区域效应研究 总被引:1,自引:0,他引:1
运输系统改进—运距缩短—产业布局调整这一空间过程对不同的区域可能具有完全不同的意义。本文通过对一个两区域—两部门经济模型的研究得出结论:当较落后的资源产区与经济中心之间的距离由于运输系统的改进而缩短时,资源产区的经济结构向单一化转变,初级产品的生产和输出在经济建设中逐渐占主导地位,加工工业逐渐萎缩,地方经济发展受到阻碍,而且这种变化是在距离的某一特定值处突然出现的,带有跃变的性质。这一研究结果表明,对区域运输系统的任何改进措施都应该慎而行之,以免造成与本来目标相悖的区域效应。 相似文献
75.
Yannick Giraud-Héraud Jean Kaplan François De Volnay Martin Charling Tao Sylvaine Turck-Chièze 《Solar physics》1990,128(1):21-33
The Saclay solar evolution code is used to check the effect of WIMPs on solar evolution. In this paper we study the effects of various types of Cosmion-matter interactions, give constraints on the crosssections compatible with the measured neutrino rate of 2 SNU on chlorine, and relate these constraints to ongoing dark matter detection experiments.Unité associée au CNRS UA 280, F-75251 Paris Cedex 05, France.On leave from LPC, Collège de France. 相似文献
76.
77.
78.
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
79.
80.