全文获取类型
收费全文 | 43740篇 |
免费 | 19631篇 |
国内免费 | 44587篇 |
专业分类
测绘学 | 3813篇 |
大气科学 | 22512篇 |
地球物理 | 14593篇 |
地质学 | 40013篇 |
海洋学 | 16875篇 |
天文学 | 1293篇 |
综合类 | 5314篇 |
自然地理 | 3545篇 |
出版年
2024年 | 219篇 |
2023年 | 527篇 |
2022年 | 1024篇 |
2021年 | 1345篇 |
2020年 | 2425篇 |
2019年 | 5881篇 |
2018年 | 6160篇 |
2017年 | 5800篇 |
2016年 | 5922篇 |
2015年 | 5196篇 |
2014年 | 4852篇 |
2013年 | 5382篇 |
2012年 | 5122篇 |
2011年 | 5009篇 |
2010年 | 4851篇 |
2009年 | 4187篇 |
2008年 | 3467篇 |
2007年 | 3515篇 |
2006年 | 3085篇 |
2005年 | 2846篇 |
2004年 | 3062篇 |
2003年 | 2805篇 |
2002年 | 2616篇 |
2001年 | 2356篇 |
2000年 | 1957篇 |
1999年 | 1974篇 |
1998年 | 1968篇 |
1997年 | 1994篇 |
1996年 | 1592篇 |
1995年 | 1507篇 |
1994年 | 1404篇 |
1993年 | 1342篇 |
1992年 | 1092篇 |
1991年 | 828篇 |
1990年 | 781篇 |
1989年 | 641篇 |
1988年 | 566篇 |
1987年 | 426篇 |
1986年 | 351篇 |
1985年 | 273篇 |
1984年 | 296篇 |
1983年 | 182篇 |
1982年 | 213篇 |
1981年 | 156篇 |
1980年 | 110篇 |
1979年 | 114篇 |
1978年 | 49篇 |
1977年 | 44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 15 毫秒
71.
青藏块体东北缘地壳水平运动状态 总被引:10,自引:6,他引:4
应用青藏块体东北缘1999~2003年多期GPS观测资料,计算了不同时段GPS点水平运动速率。通过分析发现:甘青块体可分为东部块体和西部块体,东、西部块体的运动状态存在明显的差异;受2001年11月14日昆仑Ms8.1地震的影响,震后地壳运动状态发生了明显的改变。 相似文献
72.
This paper considers the problem of estimatingm, the number of components in a finite mixture of distributions from a parametric family. A step-up procedure using the bootstrap method is proposed. Some properties of the procedure are illustrated with simulation studies. An example of the method, applied to orientation of beach clasts, is given. 相似文献
73.
企鹅珍珠贝人工苗生长的初步观察 总被引:3,自引:0,他引:3
为了解企鹅珍珠贝生长规律,观察了壳高2.5~5.0mm的出池幼苗,按月测量其生长参数和成活率,以及环境因子。结果表明,企鹅珍珠贝生长最快的月份为7~11月和次年4~6月,壳长,壳高和壳宽月均增加量分别为3.8~13.0mm、4.7~11.2mm、2.3~3.8mm,月成活率97.8%~98.6%。企鹅珍珠贝生长最慢月份是11月至次年3月。 相似文献
74.
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
75.
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
76.
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
77.
78.
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
79.
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
80.