全文获取类型
收费全文 | 57829篇 |
免费 | 10798篇 |
国内免费 | 13607篇 |
专业分类
测绘学 | 4427篇 |
大气科学 | 5404篇 |
地球物理 | 13700篇 |
地质学 | 37247篇 |
海洋学 | 6352篇 |
天文学 | 2180篇 |
综合类 | 4637篇 |
自然地理 | 8287篇 |
出版年
2024年 | 322篇 |
2023年 | 902篇 |
2022年 | 1676篇 |
2021年 | 1979篇 |
2020年 | 2039篇 |
2019年 | 2342篇 |
2018年 | 1920篇 |
2017年 | 2178篇 |
2016年 | 2402篇 |
2015年 | 2549篇 |
2014年 | 3179篇 |
2013年 | 3110篇 |
2012年 | 3444篇 |
2011年 | 3581篇 |
2010年 | 3151篇 |
2009年 | 3717篇 |
2008年 | 3738篇 |
2007年 | 4034篇 |
2006年 | 3914篇 |
2005年 | 3436篇 |
2004年 | 3283篇 |
2003年 | 3063篇 |
2002年 | 2779篇 |
2001年 | 2462篇 |
2000年 | 2347篇 |
1999年 | 2088篇 |
1998年 | 1852篇 |
1997年 | 1690篇 |
1996年 | 1544篇 |
1995年 | 1343篇 |
1994年 | 1346篇 |
1993年 | 1132篇 |
1992年 | 903篇 |
1991年 | 632篇 |
1990年 | 553篇 |
1989年 | 468篇 |
1988年 | 352篇 |
1987年 | 243篇 |
1986年 | 139篇 |
1985年 | 100篇 |
1984年 | 47篇 |
1983年 | 35篇 |
1982年 | 30篇 |
1981年 | 20篇 |
1980年 | 26篇 |
1979年 | 41篇 |
1978年 | 35篇 |
1977年 | 25篇 |
1975年 | 4篇 |
1954年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
以累计频度定量计算方法,分区讨论了河南及邻区1970年以来地震活动非线性度ZL值的时间进程曲线,系统计算了M≥5.0级地震前的ZL值,结果表明:开始出现活跃(平静)异常的时间集中在地震前1—2年,结束异常的时间在地震前一年内,集中于0—4个月。同时提出了异常的定量指标以及发震类型。 相似文献
74.
Recent seismological studies have presented evidence for the existence of a layer with ultra-low seismic velocities at the core-mantle boundary at ca. 2900 km depth. We report high-amplitude, high-frequency, and laterally coherent seismic arrivals from three nuclear explosions in Siberia. With recording station intervals of 15 km, the seismic phases are readily correlated and show the presence of a thin, ultra-low velocity zone in a region where it was not previously reported. The duration and complexity of the arrivals are inconsistent with a simple core-mantle boundary and require a hitherto unidentified, kilometre-scale, fine structure in the ultra-low velocity zone. The observations may be explained by a ca. 7 km thick, two-layer, ultra-low velocity zone with exceptional low velocities, which indicate the presence of high percentages of melt (>15%), in particular in the lower part of the zone. Waveform variation implies lateral change in the thickness and physical properties of the ultra-low velocity zone with a wavelength of less than 100 km. 相似文献
75.
电法在濒海及岛屿地区寻找地下淡水中的应用 总被引:1,自引:0,他引:1
采用电法的基本原理,研究各种不同岩性和成淡水的电性差畀,划分地下成淡水分界面。在严重缺水的濒海及岛屿地区找到了较好的地下淡水,解决了守岛部队吃水难的问题。 相似文献
76.
The Jiaocbang arcuate structure is one of the numerous arcuate structural belts in Sichuan. The present paper gives a further argument about the characteristics of that arcuate structure and the new activity of the Songpinggou fault and affirms that the Songpinggou fault is an active fault in the Holocene epoch. The Diexi M7.5 earthquake took place in 1933 on the west wing of that arcuate structure, near the apex of the arc. Many authors have given quite different opinions about the genetic structure of that earthquake. The authors have made on-the-spot investigations time and again over recent years. Besides this, the authors have also further studied the shape of intensity contour lines, the distribution characteristics of ground surface seismic hazards, the left-lateral dislocation of buildings along the Songpinggou fault, the NWtrending ground fissures that developed on the ground surface after earthquake, and so on. On this basis, it is still considered that the seismogenic fault of the 1933 Diexi M7.5 earthquake was the Songpinggou fault on the west wing of the Jiaochang arcuate structure. 相似文献
77.
Recurrence characteristics of late-quaternary strong earthquakes on the major active faults along the northern border of Ordos block 总被引:1,自引:0,他引:1
Through study on trenches, analysis of recurrence characteristics and recurrence interval cluster/gap of strong earthquakes along the major active faults on the northern border of Ordos block, we found 62 paleoearthquakes that occurred in the late Quaternary, including 33 earthquakes occurring in the Holocene. The recurrence characteristics of the paleoearthquakes are different at three levels, segments, faults, and fault zones. The strong seismic sequence on the independent segments is mostly characterized by long- and short-interval recurrences, while that on the faults and in fault zone is characterized clearly by random and cluster recurrences. Results of the moving window test indicate that the probabilities of "temporal cluster or gap", caused by random coincidence as opposed to intersegment contagion, are 64% and 70% for the Serteng piedmont fault and for the south-border fault of Wula Mountains, respectively, no clear interaction among the segments of each fault; while the probability is 26.8% for the whole fault zone, suggesting a clear interaction among the faults of this fault zone. These recurrence characteristics may imply an effect of the entire block motion on the recurrence of strong earthquakes. Moreover, the elapsed time for the Wujumeng Pass-Dongfeng Village segment of Serteng piedmont fault and the Tuzuo Banner-Wusutu and the Hohhot segments of Daqingshan piedmont fault has exceeded the average recurrence interval, hence these three segments may be the possible places for future strong earthquakes. 相似文献
78.
79.
B. P. Harlamov 《Mathematical Geology》2003,35(4):431-449
Zones of increased concentration formed by a solvent flowing from a source are considered. A matehmatical model for forming such zones is proposed. It takes into account that such a zone is composed of a set of independent particles. Hence the distribution of a substance around the source can be explained by movement of an individual particle. In the model this movement is a continuous semi-Markov process with terminal stopping at some random point in space. Parameters of the process depend on the velocity field of the flow. Forward and backward partial differential equations for the distribution density of a random stopping point of the process are derived. The forward equation is investigated for the centrally symmetric case. Solutions of the equation demonstrate either a maximum or a local minimum at the source location. In the latter case a concentric ring around the source is formed. If different substances vary in their absorption rates, they can form separable concentration zones as a family of concentric rings. 相似文献
80.
Most geostatistical studies consider multiple-related variables. These relationships often show complex features such as nonlinearity, heteroscedasticity, and mineralogical or other constraints. These features are not handled by the well-established Gaussian simulation techniques. Earth science variables are rarely Gaussian. Transformation or anamorphosis techniques make each variable univariate Gaussian, but do not enforce bivariate or higher order Gaussianity. The stepwise conditional transformation technique is proposed to transform multiple variables to be univariate Gaussian and multivariate Gaussian with no cross correlation. This makes it remarkably easy to simulate multiple variables with arbitrarily complex relationships: (1) transform the multiple variables, (2) perform independent Gaussian simulation on the transformed variables, and (3) back transform to the original variables. The back transformation enforces reproduction of the original complex features. The methodology and underlying assumptions are explained. Several petroleum and mining examples are used to show features of the transformation and implementation details. 相似文献