全文获取类型
收费全文 | 12343篇 |
免费 | 2141篇 |
国内免费 | 3118篇 |
专业分类
测绘学 | 1212篇 |
大气科学 | 2733篇 |
地球物理 | 2757篇 |
地质学 | 5905篇 |
海洋学 | 1861篇 |
天文学 | 542篇 |
综合类 | 1157篇 |
自然地理 | 1435篇 |
出版年
2024年 | 56篇 |
2023年 | 168篇 |
2022年 | 599篇 |
2021年 | 692篇 |
2020年 | 557篇 |
2019年 | 673篇 |
2018年 | 684篇 |
2017年 | 593篇 |
2016年 | 713篇 |
2015年 | 640篇 |
2014年 | 755篇 |
2013年 | 837篇 |
2012年 | 745篇 |
2011年 | 728篇 |
2010年 | 695篇 |
2009年 | 708篇 |
2008年 | 644篇 |
2007年 | 587篇 |
2006年 | 528篇 |
2005年 | 498篇 |
2004年 | 384篇 |
2003年 | 389篇 |
2002年 | 405篇 |
2001年 | 392篇 |
2000年 | 373篇 |
1999年 | 519篇 |
1998年 | 370篇 |
1997年 | 392篇 |
1996年 | 380篇 |
1995年 | 321篇 |
1994年 | 270篇 |
1993年 | 232篇 |
1992年 | 192篇 |
1991年 | 157篇 |
1990年 | 129篇 |
1989年 | 133篇 |
1988年 | 109篇 |
1987年 | 61篇 |
1986年 | 63篇 |
1985年 | 47篇 |
1984年 | 40篇 |
1983年 | 21篇 |
1982年 | 20篇 |
1981年 | 29篇 |
1980年 | 16篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1976年 | 6篇 |
1973年 | 7篇 |
1958年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 810 毫秒
851.
城门山铜、钼矿床的稳定同位素地质 总被引:1,自引:0,他引:1
城门山铜、钼矿床由斑岩型铜、钼矿床,矽卡岩型铜矿床和块状硫化物型铜矿床组成。本文从锶、铅、硫、氢、氧、碳等多种稳定同位素的组成特征,讨论矿床中成矿物质和热液的来源。 相似文献
852.
铌铁锐钛矿是含铌、铁的锐钛矿变种。呈土黄色、褐棕色,板状或土粒状。反射率589nm,15.9%,显微硬度H_v=275.9kg/mm~2。计算比重4.4g/cm~3。主要化学成分Nb_2O_534.92—44.3%,TiO_2 29.38—37.58%,Fe_2O_3 14.94—17.19%。化学式:(Ti_(0.44)Nb_(0.31)Fe_(0.25))_(1.00)O_2X射线分析表明该矿物属四方晶系,α=3.828±0.002,c=9.682±0.009,空间群I4_1/amd,Z=4。 共生矿物钕易解石,深红色者变生现象轻微;浅黄色钕易解石与铌铁锐钛矿可能形成于稍晚、较低温度条件下的矿化过程。 相似文献
853.
A pilot plant study and a full scale plant study were conducted to determine the feasibility of using contact oxidation followed by activated carbon adsorption process in textile wastewater treatment, and to determine the effects of types of packing media in the contact oxidation tank and types of aeration process on the treatment performance. Results indicated that contact oxidation followed by activated carbon adsorption process was effective in removing organics and color from textile wastewaters. Types of packing media and types of aeration processes had little effect on the treatment performance. The pilot plant performance was found to perform slightly better than the performance of the full scale plant. 相似文献
854.
Rui Feng Jun Wang Shuzhen Zheng Guifang Huang Huifen Yan Hainan Zhou Ruoshui Zhang 《地震学报(英文版)》1988,1(4):73-84
Following Airy and Pratt principles, five kinds of local-compensation models are analysed and a rapid 3-D gravity formula
is utilized to calculate isostatic anomalies for 66 models with different parameters. It is noted that isostatic gravity maps
appear nearly identical in their main patterns and features. The optimum compensation model in North China is one of modified
Airy models in which the different density distribution in the surface, upper crust and lower crust is taken into account
and the standard crustal thickness is about 50km. The position of the complete compensation interface is located in the upper
mantle. The North China platform as a whole is under sub-isostatic equilibrium status with an isostatic anomaly of about 18·10−5 m/s2 on an average. The distribution of isostatic gravity anomaly shows an obvious blockwise pattern. Most positive anomaly areas
occur over the eastern part, the Jiao-Liao Block, Mt. Yan block and northern margin of the Hebei-Shandong block, whereas a
negative area occurs in the Shanxi graben. The comparison of models indicates that the Moho discontinuity is not suitable
to be taken as a compensation interface, and the compensation effects in Airy model are better than that in Pratt model, which
is consistent with the feature of dominant layered structure and less lateral inhomogeneity in crust. Some results about composite
compensation, the basic characteristics of isostatic anomaly and deep stucture will be published later in the second part
of this paper.
Wang Bowen took part in some work in this paper. 相似文献
855.
856.
857.
The aim of this paper is to study the REE geochemistry of the Shenzhen Bay (SZB) and Dapeng Bay(DPB) modern sediments, discuss their REE distribution patterns, reveal the REE geochemical difference between the two bays which share the same material source but are deposited in different sedimentary environments, and expound their dynamic changes.It can be concluded that the SZB and DPB sediments are essentially of continental source.Their REE distribution patterns are quite different from those of Pacific pelagic sediments, but are very similar to those of South Chi-na granites.Because of different sedimentary environments prevailing in the SZB and DPB, some REE fractionation would have taken place in the sediments of the two bays. 相似文献
858.
859.
860.
内蒙古中部二叠纪碱性花岗岩及其地球动力学意义 总被引:95,自引:0,他引:95
西伯利亚板块南缘白音乌拉-东乌珠穆沁旗带的碱性花岗岩(Rb-Sr年龄276-286Ma)生成于张性的构造环境,较西伯亚板块同中朝板块之间晚泥盆世-早石炭世的碰撞事件晚约60Ma,属于造山后的A型花岗岩,可作为造山作用结束的标志。但在中朝板块北缘晚石炭世-二叠纪只发育钙碱性的晚造山花岗岩,直到三叠纪才出现碱性正长岩。相邻两大板块边缘之间岩浆活动的非对称性可能是受板块间面积和质量差别的制约。 相似文献