全文获取类型
收费全文 | 52796篇 |
免费 | 21382篇 |
国内免费 | 45278篇 |
专业分类
测绘学 | 3644篇 |
大气科学 | 24086篇 |
地球物理 | 16990篇 |
地质学 | 43974篇 |
海洋学 | 17657篇 |
天文学 | 1754篇 |
综合类 | 6670篇 |
自然地理 | 4681篇 |
出版年
2024年 | 191篇 |
2023年 | 552篇 |
2022年 | 1370篇 |
2021年 | 1746篇 |
2020年 | 2780篇 |
2019年 | 6137篇 |
2018年 | 6606篇 |
2017年 | 6246篇 |
2016年 | 6511篇 |
2015年 | 5488篇 |
2014年 | 5304篇 |
2013年 | 5878篇 |
2012年 | 5504篇 |
2011年 | 5320篇 |
2010年 | 5133篇 |
2009年 | 4538篇 |
2008年 | 3680篇 |
2007年 | 3715篇 |
2006年 | 3245篇 |
2005年 | 3166篇 |
2004年 | 3227篇 |
2003年 | 2954篇 |
2002年 | 2649篇 |
2001年 | 2480篇 |
2000年 | 2212篇 |
1999年 | 2609篇 |
1998年 | 2504篇 |
1997年 | 2537篇 |
1996年 | 2126篇 |
1995年 | 1985篇 |
1994年 | 1740篇 |
1993年 | 1614篇 |
1992年 | 1346篇 |
1991年 | 998篇 |
1990年 | 930篇 |
1989年 | 736篇 |
1988年 | 654篇 |
1987年 | 504篇 |
1986年 | 399篇 |
1985年 | 319篇 |
1984年 | 333篇 |
1983年 | 204篇 |
1982年 | 239篇 |
1981年 | 166篇 |
1980年 | 140篇 |
1979年 | 133篇 |
1978年 | 62篇 |
1977年 | 53篇 |
1971年 | 55篇 |
1970年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
111.
112.
1 INTRODUCTIONCompact Symmetric Objects (CSOs) are powerful and compact sources (overall size <1 bpc) with lobe emission on both sides of the central engine. The small size of these sourcesis almost certainly to be attributed to the youth of the sources themselves (ages < 104 yr) andnot due to a dense coallning medium (Readhead 1996). The unification scenario assumes thatCSOs evolve into compact steep spectrum (CSS) sotirces and then into Fanaroff-Riley type 11objects (Fanti 1995). … 相似文献
113.
114.
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
115.
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
116.
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
117.
118.
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
119.
位于华南褶皱带南缘的右江盆地,其发展可分为两个不同的阶段。它的轮廓和结构,与NW向及NE向同沉积断裂关系密切。盆地内的沉积物,分别由特征不同的非补偿性和补偿性沉积相组成两个双层结构。盆地内火山活动发育,也明显的分为两个阶段。海西期,古特提斯洋的发展使哀牢山洋盆开裂,导致了右江地区在拉张应力条件下出现若干NW向裂陷带,这时的盆地具有大陆边缘裂谷特点。东吴运动后开始的印支期,区域应力条件发生变化。滨大平洋构造的发生,使盆地轮廓和结构发生明显变化,与此同时开始的哀牢山洋盆向NE方向的俯冲消减作用,使盆地在新的挤压条件下再次发生张裂和拗陷。进入了弧后盆地发展阶段。印支期末,盆地封闭。 相似文献
120.
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