全文获取类型
收费全文 | 64817篇 |
免费 | 23166篇 |
国内免费 | 46953篇 |
专业分类
测绘学 | 5237篇 |
大气科学 | 26003篇 |
地球物理 | 19314篇 |
地质学 | 49168篇 |
海洋学 | 18508篇 |
天文学 | 2369篇 |
综合类 | 7795篇 |
自然地理 | 6542篇 |
出版年
2024年 | 212篇 |
2023年 | 705篇 |
2022年 | 1930篇 |
2021年 | 2406篇 |
2020年 | 3169篇 |
2019年 | 6719篇 |
2018年 | 7097篇 |
2017年 | 6688篇 |
2016年 | 7025篇 |
2015年 | 6072篇 |
2014年 | 5981篇 |
2013年 | 6525篇 |
2012年 | 6151篇 |
2011年 | 6076篇 |
2010年 | 5936篇 |
2009年 | 5281篇 |
2008年 | 4455篇 |
2007年 | 4461篇 |
2006年 | 3809篇 |
2005年 | 3594篇 |
2004年 | 3562篇 |
2003年 | 3282篇 |
2002年 | 3004篇 |
2001年 | 2853篇 |
2000年 | 2659篇 |
1999年 | 3045篇 |
1998年 | 2793篇 |
1997年 | 2773篇 |
1996年 | 2322篇 |
1995年 | 2156篇 |
1994年 | 1972篇 |
1993年 | 1815篇 |
1992年 | 1468篇 |
1991年 | 1158篇 |
1990年 | 999篇 |
1989年 | 847篇 |
1988年 | 753篇 |
1987年 | 526篇 |
1986年 | 453篇 |
1985年 | 332篇 |
1984年 | 359篇 |
1983年 | 231篇 |
1982年 | 248篇 |
1981年 | 185篇 |
1980年 | 129篇 |
1979年 | 126篇 |
1978年 | 55篇 |
1977年 | 51篇 |
1971年 | 53篇 |
1958年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
121.
Chun-sheng Li Qi-jun Fu Yu-hua Yan Shu-ying Jiang Hong-wei Li 《Chinese Astronomy and Astrophysics》1985,9(2):128-133
We propose a model of two acceleration regions, which can explain, on the basis of microwave maser caused by a “hollow-beam” distribution of electrons, the presence of millisecond spikes in the event of 1981 May 16 and their absence in the event of 1981 October 12, and the enhanced continuous emission in the latter. We have also uncovered relations among the features, e.g. the Type IIIG, Type IVDCIM and hard x-ray bursts, that accompany the microwave millisecond spikes during the impulsive phase of a large flare. 相似文献
122.
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
123.
Zhao Yiyang 《中国海洋湖沼学报》1985,3(2):200-211
Geochemical patterns of shelf sediments of China Seas are discussed in the following order: 1) the grain-size control of elements,
2) zonal distribution of elements along the coast, 3) estuarine enrichment of elements, 4) correlation of elements, 5) philo-detrital
property of elements, 6) philo-continental property of elements, 7) rapid accumulation rate of elements. Statistics show that
the abundance of indicator elements in shelf sediments is relatively close to that in terrestrial rocks and continental crust,
and the abundance distribution pattern of elements in shelf sediments is similar to that in continental crust. 相似文献
124.
125.
126.
本矿床是我国金红石矿床重要的成因及工业类型,为具有特定化学成分的岩石在特定变质条件下形成的。本文通过对大量数据的处理,查明了化学成分与成矿的关系:高Al2O3、MgO、Fe2O3+FeO、K2O、P2O5、H2O+、MnO,低SiO2、CaO、Na2O、CO2、S等,利于钛富集;高TiO2、MgO、P2O5、S,低SiO2、CaO、K2O、Al2O3、Fe2O3/FeO,利于金红石形成;高Sc、Zr、Ni、Zn及La/Yb,低Y、Nb、Th、Cd、Ba、Be、ΣREE,利于金红石纯度提高。对研究矿床成因及寻找新的同类矿床等有重要意义 相似文献
127.
128.
通过杂质对导电类型的影响的研究,得出了同种矿物的不同导电类型与矿物形成温度的规律:电子型(n型)导电矿物的形成温度大于电子与空穴混合型导电矿物的形成温度,又大于空穴型(p型)导电矿物的形成温度,绝缘体矿物的形成温度低于上述三种导电类型矿物。应用矿物热电图谱仪,天然金刚石半导体测试仪对闪锌矿、黄铁矿、金刚石等矿物的导电类型进行了测试,并探讨了导电类型成因,证实了上述规律的正确性。 相似文献
129.
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
130.
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