全文获取类型
收费全文 | 17038篇 |
免费 | 3496篇 |
国内免费 | 4125篇 |
专业分类
测绘学 | 635篇 |
大气科学 | 1038篇 |
地球物理 | 4698篇 |
地质学 | 10876篇 |
海洋学 | 2251篇 |
天文学 | 2058篇 |
综合类 | 812篇 |
自然地理 | 2291篇 |
出版年
2024年 | 106篇 |
2023年 | 330篇 |
2022年 | 580篇 |
2021年 | 619篇 |
2020年 | 680篇 |
2019年 | 782篇 |
2018年 | 670篇 |
2017年 | 711篇 |
2016年 | 737篇 |
2015年 | 824篇 |
2014年 | 923篇 |
2013年 | 878篇 |
2012年 | 1013篇 |
2011年 | 1019篇 |
2010年 | 870篇 |
2009年 | 1187篇 |
2008年 | 1067篇 |
2007年 | 1209篇 |
2006年 | 1146篇 |
2005年 | 970篇 |
2004年 | 1016篇 |
2003年 | 973篇 |
2002年 | 797篇 |
2001年 | 796篇 |
2000年 | 765篇 |
1999年 | 627篇 |
1998年 | 693篇 |
1997年 | 419篇 |
1996年 | 403篇 |
1995年 | 368篇 |
1994年 | 323篇 |
1993年 | 269篇 |
1992年 | 236篇 |
1991年 | 147篇 |
1990年 | 93篇 |
1989年 | 110篇 |
1988年 | 70篇 |
1987年 | 76篇 |
1986年 | 50篇 |
1985年 | 24篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1971年 | 4篇 |
1954年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
171.
172.
173.
河北省峰峰矿区通二井田石炭系—二叠系砂岩显微组构特征分析 总被引:4,自引:0,他引:4
对河北省峰峰矿区通二井田煤系地层砂岩中石英光轴的组构特征进行了显微镜下的观察分析。实测的12个岩组图均呈大圆环带状,表现为多组的极密区和次极密区,并以单斜对称组构为主体,具有一个对称面和垂直对称面的1个二次轴,以该轴两两对称的极密区和次极密区有2对或2对以上,表明研究区发生过不容忽视的旋转或剪切运动,它们的构造变形史可能具有多次活动性,并伴随有地温上升的过程。根据水平相岩组图所做的主应力轨迹图显示F56断层是形成张家庄向斜构造区和集贤村构造区的内部边界条件,并表明通二井田最大主压应力方向在北部以北西—南东向为主,向南逐渐转为东西向;最小主压应力方向在集贤村构造区以北东向为主,在中南部张家庄向斜构造区则以近南北向为主。 相似文献
174.
175.
2-D crustal velocity structure and vp/vs are obtained by processing and interpretation of S-wave data from Maqen-Jingbian deep seismic sounding(DSS)profile.The result shows that there exist obvious differences in 2-D S-wave velocity structure and vp/vs ratio structure along the profile.The S-wave velocities are low and vp/vs ration is high for the westem section of the profile and Haiyuan region,while they are normal for the middle and eastern sections.The changes in lithologic characters of two major anomalous zones are discussed according to lateral variation of S-wave velocity structure and vp/vs ratio structure.It is concluded that the development and occurrence of the Haiyuan strong earthquake is not only related to tectonic activities,but also to lithologic characters of the region. 相似文献
176.
Introduction Greeting the coming of the 21st century, Professor HU Yu-xian and other Chinese scholars briefed the trend of earthquake engineering in China and aboard (HU, 1999; HU, ZHOU, 1999). The experiences and lessons learning from the destructive earthquakes in China and abroad in re-cent years, the damage action of the large velocity impulse in ground motion in near field in seis-mic design, numerous earthquake examples show that there are many weaknesses in aspects of earthquake p… 相似文献
177.
通过对发生于1999~2000年间库玛中东段地区3次5级以上地震前地下流体短临异常的分析对比,得出了该地区地下流体短临异常的时空强演化特征。 相似文献
178.
Fluid mixing as the mechanism of formation of the Dajing Cu-Sn-Ag-Pb-Zn ore deposit,Inner Mongolia ——Fluid inclusion and stable isotope evidence 总被引:2,自引:0,他引:2
Since the 1990s, interest in the magmatic fluids and their relation to mineralization has been re-aroused[1—6]. Studies on stable isotopes of low-sulfidation deposits commonly show the predominance of meteoric water[7]. Paradoxically, the evidence for me… 相似文献
179.
Crustal structure beneath the Songpan—Garze orogenic belt 总被引:2,自引:0,他引:2
The Benzilan-Tangke deepseismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE.Based on the travel times and the related amplitudes of phases in the record sections,the 2-D P-wave crustal structure was ascertained in this paper.The velocity structure has quite strong lateral variation along the profile.The crust is divided into 5layers,where the first,second and third layer belong to the upper crust,the forth and fifth layer belong to the lower crust.The low velocity anomaly zone gener-ally exists in the central part of the upper crust on the profile,and it integrates into the overlying low velocity basement in the area to the north of Ma‘erkang.The crustal structure in the section can be divided into 4parts:in the south of Garze-litang fault,between Garze-Litang fault and Xianshuihe fault,between Xianshuihe fault and Longriba fault and in the north of Longriba fault,which are basically coincided with the regional tectonics division.The crustal thickness decreases from southwest to northeast along the profile,that is ,from62km in the region of the Jinshajiang River to 52km in the region of the Yellow River.The Moho discontinuity does not obviously change across the Xianshuihe fault basesd on the PmP phase analysis.The crustal average velocity along the profile is lower,about 6.30 km/s.The Benzilan-Tangke profile reveals that the crust in the study area is orogenic.The Xianshuihe fault belt is located in the central part of the profile,and the velocity is positive anomaly on the upper crust,and negative anomaly on the lower crust and upper mantle.It is considered as a deep tectonhic setting in favor of strong earthquake‘s accumulation and occurrence. 相似文献
180.
The effect of asymmetry and irregularity of the inputted seismic waves on the earthquake-induced differential settlement of the buildings on natural subsoil is investigated in terms of the earthquake damage phenomena, theoretical analyses, dynamic triaxial tests and shaking table tests. A conclusion can be drawn from the investigation results that, the asymmetrical and irregular character of the inputted seismic waves themselves may have a significant contribution to the differential settlement of subsoil and buildings in some cases, and this is a necessary factor to be considered in reasonable evaluation for the differential settlement and other problems relating to the soil deformation due to earthquakes. 相似文献