全文获取类型
收费全文 | 1748篇 |
免费 | 82篇 |
国内免费 | 468篇 |
专业分类
测绘学 | 55篇 |
大气科学 | 145篇 |
地球物理 | 773篇 |
地质学 | 639篇 |
海洋学 | 186篇 |
天文学 | 79篇 |
综合类 | 302篇 |
自然地理 | 119篇 |
出版年
2024年 | 5篇 |
2023年 | 13篇 |
2022年 | 11篇 |
2021年 | 10篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 24篇 |
2017年 | 5篇 |
2016年 | 17篇 |
2015年 | 12篇 |
2014年 | 37篇 |
2013年 | 20篇 |
2012年 | 66篇 |
2011年 | 94篇 |
2010年 | 32篇 |
2009年 | 55篇 |
2008年 | 77篇 |
2007年 | 105篇 |
2006年 | 106篇 |
2005年 | 106篇 |
2004年 | 105篇 |
2003年 | 101篇 |
2002年 | 104篇 |
2001年 | 121篇 |
2000年 | 130篇 |
1999年 | 51篇 |
1998年 | 46篇 |
1997年 | 79篇 |
1996年 | 30篇 |
1995年 | 44篇 |
1994年 | 51篇 |
1993年 | 60篇 |
1992年 | 48篇 |
1991年 | 70篇 |
1990年 | 44篇 |
1989年 | 60篇 |
1988年 | 47篇 |
1987年 | 28篇 |
1986年 | 23篇 |
1985年 | 44篇 |
1984年 | 30篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 28篇 |
1979年 | 5篇 |
1947年 | 7篇 |
1939年 | 7篇 |
1926年 | 5篇 |
1924年 | 4篇 |
排序方式: 共有2298条查询结果,搜索用时 15 毫秒
191.
野外证据及显微构造分析证明了Rouergue地区华力西期地体中有三种构造成因的逆变质成带现象,它们与大规模岩片逆冲作用相关,而且变质作用早于岩片向南的构造就位过程。矿物平衡、石榴石—黑云母地质温度计及石榴石—斜长石地质压力计揭示了变质后期、变质同期及变质前期的变形作用导致的三种不同的P-T模式。变质期后的变形作用对逆变质带及相对分带有直接影响,该区变质作用的不连续性是推覆体运移的重要证据。变质周期的逆冲作用导致了与逆冲相关的、剖面上为具有热逆转及正常压力的变质带,明显的压力差异人为地认为是不同的P-T轨迹及不同的抬升速率的产物,在快速上隆(如逆冲层序)时,温度处于峰期而压力最低。变质作用时限可以持续到整个构造事件(除晚期褶皱作用外)结束,此时,同构造期侵入体在推覆接触带内就位,它们对剖面上强烈的温度逆转效应有影响,并且强烈地改变了下伏变质推覆构造单元的等变线分布。 相似文献
192.
刘宝珺 余光明 徐强 G. Einsele W. Frisch 刘光华 J. Wendt A. Wetzel L. Ratschbacher H. P. Luterbacher 《沉积与特提斯地质》1993,(1):32-49
通过对喜马拉雅三叠纪到第三纪区域沉积特征分析,阐明了雅鲁藏布喜马拉雅特提斯造山带从裂谷—被动大陆边缘—前陆盆地的沉积盆地演化史。随着以雅鲁藏布带为代表的喜马拉雅特提斯打开,三叠纪到早侏罗世为特提斯早期裂开的大陆边缘裂谷盆地。早期裂谷中心部位不是现在大陆缝合线的雅鲁藏布一带,而在低分水岭带。晚侏罗世到早白垩世,雅鲁藏布江南测为典型被动大陆边缘,其沉积盆地沉降、海平面变化与沉积作用相吻合。晚白垩世到第三纪为前陆盆地演化阶段,从沉积作用可以识别出晚白垩世晚期为造山第一暮,第三纪初为第二幕。 相似文献
193.
194.
最近在烏克蘭苏維埃社会主义共和國科学院水文研究所的著作中發表了德湼泊河罗茨曼卡明卡已經系统化的歷史水位资料。这些資料表明,現存于年志档案及文学等史料中的德湼泊河最高水位资料属于自十八世紀起直到現在为止这一时期內的资料。1951~1952年烏克蘭社会主义共和國科学院水文研究所在收集歷史水位资料时,發現了罗茨曼卡明卡1818~1927年间最高水位資料及1828~ 相似文献
195.
We report preliminary results from a series of numerical simulations of the reduced magnetohydrodynamic equations used to describe the dynamics of magnetic loops in active regions of the solar corona. A stationary velocity field is applied at the photospheric boundaries to imitate the driving action of granule motions. A turbulent stationary regime is reached, characterized by a broadband power spectrum Ek approximately k-3&solm0;2 and heating rate levels compatible with the energy requirements of active region loops. A dimensional analysis of the equations indicates that their solutions are determined by two dimensionless parameters: the Reynolds number and the ratio between the Alfvén time and the photospheric turnover time. From a series of simulations for different values of this ratio, we determine how the heating rate scales with the physical parameters of the problem, which might be useful for an observational test of this model. 相似文献
196.
This study examined perceptions of the impacts of the antinatalist (OPP) and pronatalist (NPP) policies in Singapore. Data were obtained from a sample of 209 men and 280 women under 45 years old who lived in Ang Mo Kio New Town in the center of the island. Findings indicate that 53.4% of women said that fertility decisions were joint ones. 50% of women and 65% of men said that family size was jointly determined. Over 70% were aware of the OPP "stop at 2" policy. Those who gave accurate, detailed knowledge were mostly over 35 years old. Knowledge of OPP did not vary by education, but did vary by awareness of incentives and disincentives. 45.4% of women believed that OPP was a necessary state policy; 25.4% did not. 36.4% thought that OPP was fair; 28.3% did not. 60.3% of women said that OPP did influence family size in society, but 63.8% said it did not influence their individual family size. Finances, education, and child care were explanatory factors in individual planning. OPP is viewed as a successful policy not because of ideology, but because of the value placed on improved socioeconomic standards. 58.2% of women and 55.5% of men knew the details about the NPP. 51.9% of women said the NPP would encourage larger family size, but 87.8% said it would not affect them personally. Findings suggest that personal freedoms and public ideology are not binary, public-private concepts in fertility decision making. 相似文献
197.
Boyle P Cooke T Halfacree K Smith D 《International journal of population geography : IJPG》1999,5(3):157-178
This paper investigates the problems in integrating different data sets for social science research. A cross-national analysis of the effects of family migration on labor market participation rates for female partners was used as an example to concretize these problems. The data used in the cross national analysis came from the 1991 British Census Sample of Anonymised Records and the 1990 United States Public Use Microdata Sample. The problems addressed were the following: data collection; manipulation and reliability; question type and definition; and measurement of individual and family variables. As part of the analysis, some empirical findings were also presented. Significant overall differences between the US and Great Britain (GB) samples were observed, particularly concerning graduate qualifications, marital and employment status, and ethnic group. There were higher numbers of married partners and full-time workers in the US sample, while female partners undertaking part-time employment were greater in GB. Furthermore, the US sample had more couples with a female graduate as compared with the GB sample who had a higher proportion of nongraduate couples. Finally, this paper recognized the importance of cross- national research in the evaluation of national ideological and institutional structures. 相似文献
198.
A computer program(FEA)is presented for processing historical laboratory data.It performs on a list ofsample entries stored in a laboratory information management system.Using an algorithm which is basedon fuzzy set theory,FEA classifies the entries into a limited number of clusters called sample types.Theclassification is fully user-defined.The program transforms the historical data into a representation whichis more suitable for studying the performance of the laboratory or which can be used as preparation for asimulation project. 相似文献
199.
200.
Transport of three herbicides in ground water at Twin Lake test site,Chalk River,Ontario, Canada 总被引:2,自引:0,他引:2
A field tracer test performed under natural flow conditions at the Twin Lake test site, Chalk River Laboratories of the Atomic Energy of Canada Ltd. in Chalk River, Ontario, Canada, using tritium and three herbicides (Chlortoluron, Terbuthylazine, and Pendimethalin) was interpreted using the dispersion equation with a combined reaction model. The reaction model couples an instantaneous equilibrium reaction governed by a linear adsorption isotherm with a reversible or irreversible kinetic reaction of the first order, and decay. An improved interpretation method consists of a simultaneous fitting of theoretical concentration and mass-recovery curves to the experimental data, which leads to a more reliable determining of reaction models and improves the accuracy of fitting. Tritium served as the reference tracer to determine the flow velocity, dispersivity, and the recovery of the herbicides. Chlortoluron was slightly delayed by equilibrium exchange with strongly reduced concentration due to an irreversible kinetic reaction and/or decay. Terbuthilazine was slightly delayed by equilibrium exchange, with strongly reduced concentration due to a reversible kinetic reaction with some influence of decay. A strong equilibrium reaction and a strong reversible kinetic reaction without degradation governed the transport of Pendimethalin, reducing considerably its concentration. The results obtained show that simulations based only on Kd and decay constant, especially if these parameters are found in the laboratory, may considerably differ from those performed with reaction parameters determined in properly performed field tests. The dominant reaction types, and the values of parameters found in the study, supply useful information on the transport of the investigated herbicides in sandy aquifers under natural flow conditions. 相似文献