全文获取类型
| 收费全文 | 24929篇 |
| 免费 | 5396篇 |
| 国内免费 | 7332篇 |
专业分类
| 测绘学 | 544篇 |
| 大气科学 | 4136篇 |
| 地球物理 | 7552篇 |
| 地质学 | 13692篇 |
| 海洋学 | 4474篇 |
| 天文学 | 124篇 |
| 综合类 | 2065篇 |
| 自然地理 | 5070篇 |
出版年
| 2024年 | 93篇 |
| 2023年 | 316篇 |
| 2022年 | 911篇 |
| 2021年 | 936篇 |
| 2020年 | 1030篇 |
| 2019年 | 1286篇 |
| 2018年 | 1098篇 |
| 2017年 | 1115篇 |
| 2016年 | 1177篇 |
| 2015年 | 1232篇 |
| 2014年 | 1716篇 |
| 2013年 | 1578篇 |
| 2012年 | 1643篇 |
| 2011年 | 1738篇 |
| 2010年 | 1463篇 |
| 2009年 | 1748篇 |
| 2008年 | 1690篇 |
| 2007年 | 1789篇 |
| 2006年 | 1765篇 |
| 2005年 | 1561篇 |
| 2004年 | 1436篇 |
| 2003年 | 1303篇 |
| 2002年 | 1197篇 |
| 2001年 | 1039篇 |
| 2000年 | 995篇 |
| 1999年 | 928篇 |
| 1998年 | 773篇 |
| 1997年 | 736篇 |
| 1996年 | 682篇 |
| 1995年 | 564篇 |
| 1994年 | 498篇 |
| 1993年 | 408篇 |
| 1992年 | 314篇 |
| 1991年 | 229篇 |
| 1990年 | 167篇 |
| 1989年 | 147篇 |
| 1988年 | 102篇 |
| 1987年 | 67篇 |
| 1986年 | 35篇 |
| 1985年 | 29篇 |
| 1984年 | 25篇 |
| 1983年 | 8篇 |
| 1982年 | 12篇 |
| 1981年 | 10篇 |
| 1980年 | 12篇 |
| 1979年 | 12篇 |
| 1978年 | 15篇 |
| 1977年 | 18篇 |
| 1976年 | 1篇 |
| 1954年 | 10篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
31.
There are more than 600 Cenozoic volcanic cones and craters with abeut 50 000 km2of lava flows in northeast China, which formed many volcanic clusters and shown the features of the continental rift - type volcanoes. Most volcanic activities in this area, especially in the east part of Songliao graben, were usually controlled by rifts and faults with the main direction of NE / NNE in parallel and become younger from the central graben towards its both sides, especially to the east continental margin. It is revealed that the volcanism occurred in northeast China was as strong as that occurred in Japan during the Miocene and the Quaternary. The Quaternary basalt that is usually distributed along river valley is called "valley basalt"while Neogene basalt usually distributed in the top of mounts is called "high position basalt". These volcanoes and volcanic rocks are usually composed of alkaline basalts with ultramafic inclusions, except Changbaishan volcano that is built by trachyte and pantellerite. 相似文献
32.
INTRODUCTIONTheSubeiShoalandtheChangjiangRiverestuarineareainthewestoftheHuanghaiandEastChinaSeasisoneofthemarginalseasintheworld ,wheresuspendedmatterisextremelyhigh .Here ,notonlyistheretheTaiwanWarmCurrentoneoftheKuroshio’sbranchesintheEastChinaSea,butalsotheHuanghaiCoastalCurrent,andChangjiangDilutedWater.Sothestrongmixingbetweenthecoastalandoffshorewaterscomplicatessuspendedmatterdistributioninthisarea.HowthesuspendedmatterdischargedfromtheChangjiangRiverandtheabandonedHuan… 相似文献
33.
孙世春 《中国海洋湖沼学报》1995,(2)
Two nemerteans of the Zhoushan Islands, Paranemertes sinensis sp. nov. and P. peregrina, are reportedin this paper. P. sinensis sp. nov. has the body wall longitudinal musculature anteriorly divided,numerous eyes grouped into four clusters, two pairs of cephalic furrows, rhynchocoel 1/3 to 1/2 of fullbody length, cephalic glands well developed and posteriorly extending beyond the cerebral ganglia.precerebral septum absent, cerebral sense organs situated in front of brain, three pairs of nephridiopores,and 17-18 proboscis nerves. 相似文献
34.
周全浩 《云南地理环境研究》1990,2(1):1-9
本文分析了中国石油生产近20年变化的原因,对一些学者认为80年代中国会成为超级产油大国,后又悲观断定80年代中国可能变成石油净进口国作了评述。同时对90年代中国石油生产前景作了初步展望。 相似文献
35.
36.
密度和压缩系数的散射层析成像法 总被引：1，自引：1，他引：0
本文在速度成像的基础上研究了同时对密度和压缩系数成像的散射波层析成像法.对不同散射角度的计算可以得到一系列反演图像,拟合这些图像,从而可以有效地达到对密度和压缩系数（或速度）成像的目的.与单纯的速度成像相比,增加了反演的难度.首先是对资料的方位性要求增加;其次是对资料的利用率下降.即便如此,从对较少量的炮点和检波点资料的数值计算来看,仍取得了满意的成像结果.我们对组成字母“A”的散射体结构进行了成像计算,结果能够同时再现密度和压缩系数,成像清晰,表明了方法的可行性,并能应用于复杂结构的成像问题. 相似文献
37.
Univariate and multivariate stress release models are fitted to historical earthquake data from North China. It is shown that a better fit is obtained by treating separately the Eastern part of the region, including the North China Plain and Bohai Sea, and the Western part of the region, including the Ordos Plateau and its Eastern boundary. Further improvement is obtained by fitting the large events (M7.6) and smaller events in the Western region by different stress release models. The comparisons are made by computing the likelihoods of the fitted models and discounting the number of parameters used by Akaike's AIC criterion. The models are used to develop long-term risk scenarios for the East and West regions. 相似文献
38.
Results of a single group participating in an international experiment are analyzed. The experiment served to verify computational predictions of the ground-motion variations due to near-surface geological effects at a site established for that purpose by the California Department of Conservation. Based on an acceleration record at a rock location, and geotechnical model of medium, records at the other locations of a nearby sedimentary deposit were predicted. A 2-D finite-difference sensitivity analysis suggested that the lateral wave-propagation effects are negligibly small, and locally 1-D computations are sufficient for the present site. Those computations are compared with observations not available to the authors during the blind prediction. Peak accelerations, peak velocities and RMS accelerations were predicted with errors less than 159%, 114% and 62%, respectively. Maxima of the response spectra were fitted within a factor of 2. The predicted and observed Husid's plots (i.e., the normalized cumulative plots of the acceleration squared) have the correlation coefficients 0.98. The detected misfits do not show any simple relation to the instrument location, component, frequency, or time. 相似文献
39.
本文系统描述了中国南部二叠、三叠纪“混生生物群”。根据笔者的统计,目前巳经发现有“二叠纪型”分子36属53种与三叠纪菊石、双壳类、牙形剌共生。 笔者认为中国南部可以以牙形剌Anchignathodus parvus 的出现作为三叠系的底界,双壳类Pteria ussurica variabilis,菊石 Hypophiceras的出现可以作为三叠系开始的辅助标志。文中还将这一界线与世界上其它地区的二叠、三叠系界线进行了对比。 相似文献
40.
