全文获取类型
收费全文 | 37520篇 |
免费 | 19018篇 |
国内免费 | 43164篇 |
专业分类
测绘学 | 2864篇 |
大气科学 | 21860篇 |
地球物理 | 13423篇 |
地质学 | 36382篇 |
海洋学 | 16449篇 |
天文学 | 1027篇 |
综合类 | 4876篇 |
自然地理 | 2821篇 |
出版年
2024年 | 121篇 |
2023年 | 330篇 |
2022年 | 721篇 |
2021年 | 984篇 |
2020年 | 2174篇 |
2019年 | 5564篇 |
2018年 | 5834篇 |
2017年 | 5545篇 |
2016年 | 5649篇 |
2015年 | 4916篇 |
2014年 | 4440篇 |
2013年 | 5051篇 |
2012年 | 4726篇 |
2011年 | 4496篇 |
2010年 | 4442篇 |
2009年 | 3788篇 |
2008年 | 3016篇 |
2007年 | 3064篇 |
2006年 | 2697篇 |
2005年 | 2522篇 |
2004年 | 2834篇 |
2003年 | 2590篇 |
2002年 | 2303篇 |
2001年 | 2089篇 |
2000年 | 1752篇 |
1999年 | 1885篇 |
1998年 | 1966篇 |
1997年 | 1969篇 |
1996年 | 1569篇 |
1995年 | 1515篇 |
1994年 | 1358篇 |
1993年 | 1294篇 |
1992年 | 1102篇 |
1991年 | 805篇 |
1990年 | 782篇 |
1989年 | 637篇 |
1988年 | 534篇 |
1987年 | 421篇 |
1986年 | 330篇 |
1985年 | 266篇 |
1984年 | 297篇 |
1983年 | 182篇 |
1982年 | 217篇 |
1981年 | 151篇 |
1980年 | 115篇 |
1979年 | 115篇 |
1978年 | 52篇 |
1977年 | 48篇 |
1971年 | 54篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
81.
The anodic stripping voltammetry with physically-coating mercury film electrode was used to investigate the complexing action
of trace heavy metals in seawater with organic ligands. The apparent copper complexing capacity of seawater was determined
by titrating the organic ligands in natural seawater with standard ionic copper solution. The complexing actions of copper
in seawater with humic acid (HA) or fulvic acid (FA) were investigated by titrating copper in seawater with HA or FA solution.
The equilibrium time, electrodeposition potential, and effect of pH etc. were investigated respectively. The results show
that the interaction of copper in seawater with organic matter is a fast process. At natural pH, HA or FA tend to act with
copper in seawater to form nonlabile complexes. During experimental electrode process, these complexes did not significantly
dissociate. The experimental results were calculated according to 1∶1 complex formation. 相似文献
82.
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
83.
The accuracy of the AE index as a measure of the joule heat production rate is examined for a typical substorm event on 18 March 1978 by estimating the global joule heat production rate, as a function of time, using data obtained from the IMS six meridian chains. In spite of the fact that the AE index had had an initial slow growth which was followed by a rapid growth, the joule heat production rate attained a high level during the slow growth and thus their variations were considerably different from those of the AE index. Therefore, although the AE index is statistically linearly related to the global joule heat production rate, one should be cautious in assuming that details of time variations of the AE index during individual events represent those of the joule heat production rate. 相似文献
84.
85.
严格论证了在对空间或地面目标的定位中,利用伪距测量观测模型的几何因子大于用台站间一次差分观测模型的几何因子.此外,台站间完全差分测量观测的定位精度优于不完全测量情形的定位精度.这些结果给人们在实际工作中采取何种定位方式提供了可靠的理论依据. 相似文献
86.
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
87.
88.
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
89.
90.
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