全文获取类型
收费全文 | 3256篇 |
免费 | 563篇 |
国内免费 | 757篇 |
专业分类
测绘学 | 146篇 |
大气科学 | 651篇 |
地球物理 | 914篇 |
地质学 | 1657篇 |
海洋学 | 350篇 |
天文学 | 187篇 |
综合类 | 294篇 |
自然地理 | 377篇 |
出版年
2024年 | 22篇 |
2023年 | 73篇 |
2022年 | 129篇 |
2021年 | 171篇 |
2020年 | 123篇 |
2019年 | 140篇 |
2018年 | 159篇 |
2017年 | 134篇 |
2016年 | 153篇 |
2015年 | 165篇 |
2014年 | 179篇 |
2013年 | 179篇 |
2012年 | 176篇 |
2011年 | 177篇 |
2010年 | 149篇 |
2009年 | 210篇 |
2008年 | 177篇 |
2007年 | 147篇 |
2006年 | 142篇 |
2005年 | 136篇 |
2004年 | 99篇 |
2003年 | 86篇 |
2002年 | 74篇 |
2001年 | 94篇 |
2000年 | 118篇 |
1999年 | 171篇 |
1998年 | 133篇 |
1997年 | 153篇 |
1996年 | 122篇 |
1995年 | 81篇 |
1994年 | 109篇 |
1993年 | 84篇 |
1992年 | 61篇 |
1991年 | 39篇 |
1990年 | 53篇 |
1989年 | 31篇 |
1988年 | 31篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1976年 | 1篇 |
1965年 | 1篇 |
1958年 | 5篇 |
1957年 | 1篇 |
排序方式: 共有4576条查询结果,搜索用时 9 毫秒
941.
David W. Ostendorf Lowell E. Leach Erich S. Hinlein Yuefeng Xie 《Ground Water Monitoring & Remediation》1991,11(2):107-120
Two complementary field sampling methods for the determination of residual aviation gasoline content in the contaminated capillary fringe of a fine, uniform, sandy soil were investigated. The first method featured field extrusion of core barrels into pint-size Mason jars, while the second consisted of laboratory partitioning of intact stainless steel core sleeves. The barrel extrusion procedure involved jar headspace sampling in a nitrogen-filled glove box, which delineated the 0.7m thick residually contaminated interval for subsequent core sleeve withdrawal from adjacent boreholes. Soil samples removed from the Mason jars (in the field) and sleeve segments (in the laboratory) were subjected to methylene chloride extraction and gas chromatographic analysis to compare their aviation gasoline content. The barrel extrusion sampling method yielded a vertical profile with 0.10m resolution over an essentially continuous 5.0m interval from the ground surface to the water table. The sleeve segment alternative yielded a more resolved 0.03m vertical profile over a shorter 0.8m interval through the capillary fringe. The two methods delivered precise estimates of the vertically integrated mass of aviation gasoline at a given horizontal location, and a consistent view of the vertical profile as well. In the latter regard, a 0.2m thick lens of maximum contamination was found in the center of the capillary fringe, where moisture filled all voids smaller than the mean pore size. The maximum peak was resolved by the core sleeve data, but was partially obscured by the barrel extrusion observations, so that replicate barrels or a half-pint Mason jar size should be considered for data supporting vertical transport analyses in the absence of sleeve partitions. 相似文献
942.
谢新民 《吉林大学学报(地球科学版)》1991,(2)
阐述了在地下水系统规划研究中引进工程经济分析观点的重要性和迫切性;系统地介绍了工程经济分析的理论和方法,以喀什市地下水系统规划为例,探讨了工程经济分析在地下水系统规划中的应用。 相似文献
943.
A series of melting-crystallization experiments on alkali basalt samples from Minqing, Fujian Province was carried out in
dry and waterbearing systems at high pressures. A high-pressure melting curve was obtained. The results indicate that clinopyroxene
crystallized from basalt melt at 13.5–23.7 kbar. spinel at 23.7–28.6 kbar and garnet at > 28.6 kbar. With increasing pressure,
the CaSiO3 contents of clinopyroxenes increase; and the FeSiO3 decreases, but the chemical composition of garnet does not show any significant difference. The minerals are larger and euhedral
in the water-bearing system. Therefore, we consider that natural megacrysts of the basalt can crystallize from the water-bearing
basalt magma at high pressure. So the megacrysts may be derived from the upper mantle as a result of magmatic crystallization-fractionation
under high pressure.
This project was financially supported by the National Natural Science Foundation of China. 相似文献
944.
湘西汞矿床的地质特征与成因 总被引:2,自引:0,他引:2
湘西汞矿床是湘黔汞矿带的重要组成部分.湘西汞矿受层位和构造双重控制,与岩浆活动没有直接联系,具有层带式整合矿体,矿物成分简单,汞锌矿化分带及后生成矿等地质特征.矿石硫来源于古海水硫酸盐的沉积硫;而汞的来源.则以上地幔去气作用产生的汞为主,寒武系等富汞建造的汞次之.燕山期地台活化时,以硫络合物或硫氢络合物的形式,在碱性溶液中沿深大断裂向上运转,当其与富含膏盐的客矿层相遇时,便与还原硫结合沉淀成矿.形成湘西层控后生汞矿床. 相似文献
945.
河南祁雨沟爆破角砾岩型金矿床包裹体研究 总被引:10,自引:1,他引:10
本文通过包裹体研究了祁雨沟爆破角砾岩型金矿床成矿流体来源、性质和成矿物理化学条件,为该类型金矿找矿与评价提供依据。 相似文献
946.
947.
In this paper, on the basis of intensity data from 85 earthquakes occurred in China, the method of resolving overdetermined equations by using the damped least squares method is applied to inversing for the mean value of 1 s. S wave quality factor, the spreading factor and the S-wave acceleration at the foci of earthquakes in 7 regions of China. The relation between S-wave acceleration at the foci of earthquakes and magnitude is discussed. As an example, 2-DQ S distribution in Taiwan Province is obtained by inversion. It is found that there exists some corresponding relation between this distribution and Bouguer gravitational anomaly and seismicity. Preliminary analysis and discussion on results of the inversion, and estimation of error inQ S are made. 相似文献
948.
949.
950.
Abstract Based on the Rb-Sr isotopic study of the granitoids in the Hengduan Mountains, the classification and geologic significance of whole- rock Rb- Sr isochrons as well as the factors influencing homogenization of the isotopic systems are discussed. Usually, there is no good linear correlation of isochrons for diorites and alkali-rich intrusive rocks (including alkaline rock and alkalic granite). But by means of the external isochron of monominerals from the rocks, isochrons with good linear correlation as well as ages and Sr initial ratios with a high confidence can be obtained. In order to obtain a satisfactory isochron, the discriminant parameters should be calculated from the Rb / Sr ratios and estimated ages of samples. Only those that meet the requirements can be used as the Rb-Sr isochrons. The quality of an isochron should be judged from three factors, i.e. correlation coefficient, MSWD and homogenization degree. 相似文献