全文获取类型
收费全文 | 61771篇 |
免费 | 11028篇 |
国内免费 | 13759篇 |
专业分类
测绘学 | 4775篇 |
大气科学 | 6325篇 |
地球物理 | 14357篇 |
地质学 | 37724篇 |
海洋学 | 6438篇 |
天文学 | 3225篇 |
综合类 | 4152篇 |
自然地理 | 9562篇 |
出版年
2024年 | 232篇 |
2023年 | 628篇 |
2022年 | 1682篇 |
2021年 | 2043篇 |
2020年 | 2075篇 |
2019年 | 2520篇 |
2018年 | 2044篇 |
2017年 | 2244篇 |
2016年 | 2432篇 |
2015年 | 2691篇 |
2014年 | 3302篇 |
2013年 | 3515篇 |
2012年 | 3586篇 |
2011年 | 3913篇 |
2010年 | 3385篇 |
2009年 | 4079篇 |
2008年 | 4071篇 |
2007年 | 4462篇 |
2006年 | 4369篇 |
2005年 | 3748篇 |
2004年 | 3497篇 |
2003年 | 3315篇 |
2002年 | 2933篇 |
2001年 | 2601篇 |
2000年 | 2404篇 |
1999年 | 2291篇 |
1998年 | 1963篇 |
1997年 | 1712篇 |
1996年 | 1575篇 |
1995年 | 1288篇 |
1994年 | 1272篇 |
1993年 | 1110篇 |
1992年 | 882篇 |
1991年 | 617篇 |
1990年 | 544篇 |
1989年 | 423篇 |
1988年 | 328篇 |
1987年 | 202篇 |
1986年 | 140篇 |
1985年 | 106篇 |
1984年 | 46篇 |
1983年 | 35篇 |
1982年 | 39篇 |
1981年 | 26篇 |
1980年 | 33篇 |
1979年 | 31篇 |
1978年 | 46篇 |
1977年 | 32篇 |
1975年 | 5篇 |
1954年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Qin Chengzhi 《中国地震研究》2004,18(2):178-187
The migration of strong earthquakes is an important research topic because the migration phenomena reflect partly the seismic mechanism and involve the prediction of tendency of seismic activity. Research on migration of strong earthquakes has mostly focused on finding the phenomena. Some attempts on getting regularity were comparatively subjective. This paper suggests that there should be indices of migration in earthquake dataset and the indexes should have statistical meaning if there is regularity in the migration of strong earthquakes. In this study, three derivative attributes of migration, i.e., migration orientation, migration distance and migration time interval, were statistically analyzed. Results in the North China region show that the migration of strong earthquakes has statistical meaning. There is a dominant migration orientation (W by S to E by N), a dominant distance (≤100km and on the confines of 300~700km), and a dominant time interval (≤1a and on the confines of 3~4a). The results also show that the migration will differ slightly with different magnitude range or earthquake activity phase. 相似文献
172.
研究油藏内部油水渗流方向时,主要考虑渗透率影响,引入两个水平方向渗透率比、水平与垂向渗透率比参数来分析。前者反映样品所在储层平面上两个水平方向渗流能力的差异,后者反映样品所在储层水平与垂向渗流能力的差异,并经小柱样测试和全岩心测试两种方法确定两个参数。通过对塔中4号油藏CⅠ油组9口井2306个样品两种渗透率比值分布直方图分析,研究了CⅠ油组渗透率的非均质性及其渗流方向:CI油组储层在水平方向的渗流能力有很大差异,具有明显的方向性。储层垂向渗流能力明显小于水平方向的渗流能力。 相似文献
173.
Starting with analysis on the evolving course of oasis and the characteristics and evolution of transitional zone between oasis and desert, in consideration of ecological elements including plant stomata resistance, area covered by vegetation, and physical elements including albedo of vegetation and bare soil, atmosphere temperature, and humidity, under the condition of the balance among net radiation flux, latent heat flux, and sensible heat flux, the following are calculated: temperatures of vegetation and bare soil in different conditions, as well as the evapotranspiration rate of ecosystem. Analysis on evapotranspiration rate indicates that it depends on both the climate of environment and the physiological and ecological conditions of plants. On certain conditions, the evapotranspiration rate of transitional zone between oasis and desert (i.e. area covered by vegetation less than 20%), in some parameter domains, appears in bifurcation or multiequilibrium state. Meanwhile, in such area, ecosystem is extremely unstable. Any minor change to the balance will cause either increase or reduction of area covered by vegetation in ecosystem, on the basis of discussion on the emergency of these phenomena. This paper is attempting to propose an effective way of destruction and rebuilt ecosystem in transitional zone. The way is to control the evaporation of plant through selecting anti-drought country plant with big stomata resistance, and modify the roughness of the underlying surface in ecosystem by establishing rational interspace structure of plant community, so as to put the degenerative ecosystem into the natural succession track. This primary theory is being verified through observation and analysis on historical data. 相似文献
174.
175.
176.
用电测深研究地电断面、寻找隐伏多金属矿体时,以往采用ρ_s(或η_s)等值线断面图进行地质推断解释,因受浅源信号的干扰,效果差。本文提出了采用ρ_s(或η_s)差值法,能排除浅源干扰信号,反映出地电断面的相对变化,突出了深部微弱信息,取得了较好的地质解释效果。 相似文献
177.
古侵蚀沉积间断面型金矿是桂西的主要金矿床类型。文章着重分析该类型金矿成矿地质条件 ,论述矿床成因及成矿机理 ,认为此类型金矿易采易冶 ,经济效益显著 ,建议加大开发力度。 相似文献
178.
179.
Aimed at promoting regional coalitions and expanding the approach to economic links, this paper puts forward some new concepts
such as link intensity and receiving coefficient, expounds the indexes of quantitative analysis of economic links and establishes
the quantitative-analysis model of economic links. With help of the model, this paper calculates the values of the link intensities
between Su-Xi-Chang (Suzhou-Wuxi-Changzhou) region and Shanghai, and analyzes the regional difference of the economic links. 相似文献
180.