全文获取类型
收费全文 | 21386篇 |
免费 | 4233篇 |
国内免费 | 6049篇 |
专业分类
测绘学 | 2258篇 |
大气科学 | 4127篇 |
地球物理 | 4879篇 |
地质学 | 11847篇 |
海洋学 | 2903篇 |
天文学 | 730篇 |
综合类 | 2222篇 |
自然地理 | 2702篇 |
出版年
2024年 | 115篇 |
2023年 | 395篇 |
2022年 | 1123篇 |
2021年 | 1281篇 |
2020年 | 1045篇 |
2019年 | 1229篇 |
2018年 | 1384篇 |
2017年 | 1158篇 |
2016年 | 1348篇 |
2015年 | 1366篇 |
2014年 | 1456篇 |
2013年 | 1578篇 |
2012年 | 1578篇 |
2011年 | 1606篇 |
2010年 | 1540篇 |
2009年 | 1448篇 |
2008年 | 1271篇 |
2007年 | 1151篇 |
2006年 | 1000篇 |
2005年 | 881篇 |
2004年 | 633篇 |
2003年 | 606篇 |
2002年 | 570篇 |
2001年 | 580篇 |
2000年 | 595篇 |
1999年 | 728篇 |
1998年 | 527篇 |
1997年 | 521篇 |
1996年 | 493篇 |
1995年 | 405篇 |
1994年 | 387篇 |
1993年 | 308篇 |
1992年 | 248篇 |
1991年 | 196篇 |
1990年 | 163篇 |
1989年 | 154篇 |
1988年 | 145篇 |
1987年 | 85篇 |
1986年 | 71篇 |
1985年 | 64篇 |
1984年 | 43篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1981年 | 31篇 |
1980年 | 22篇 |
1979年 | 22篇 |
1978年 | 9篇 |
1976年 | 8篇 |
1958年 | 16篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
41.
断层相关褶皱理论在准噶尔盆地南缘山前带构造研究的应用 总被引:8,自引:4,他引:4
利用断层相关褶皱的构造几何分析方法,对准噶尔盆地南缘山前复杂构造带内基于地震剖面进行了构造解析,搭建了中、东段的构造轮廓和构造组合样式,认为东段阜康断裂带主要表现为至地表的推覆逆掩。由于位移量大部分转移至地表,阜康断裂带的前陆部分无喜山期构造带;西段造山带内的挤压往前陆方向传递过程中以前列式不断释放其位移量,造成在纵向上呈现三排主要的断层相关褶皱带。根据正演平衡地质剖面制作技术对山前复杂构造区地震剖面反射波的构造识别进行了模拟与探讨。 相似文献
42.
STUDY ON GIS FOR YIELD ESTIMATION BY REMOTE SENSING IN JILIN MAIZE BELTSTUDYONGISFORYIELDESTIMATIONBYREMOTESENSINGINJILINMAIZ... 相似文献
43.
The accuracy of the AE index as a measure of the joule heat production rate is examined for a typical substorm event on 18 March 1978 by estimating the global joule heat production rate, as a function of time, using data obtained from the IMS six meridian chains. In spite of the fact that the AE index had had an initial slow growth which was followed by a rapid growth, the joule heat production rate attained a high level during the slow growth and thus their variations were considerably different from those of the AE index. Therefore, although the AE index is statistically linearly related to the global joule heat production rate, one should be cautious in assuming that details of time variations of the AE index during individual events represent those of the joule heat production rate. 相似文献
44.
我们于1989年11月30日晚对PG0027+260进行了时间分辨率为108秒的高速CCD测光,得到了一条完整的光变曲线,从而确认其为激变食变星系统,轨道周期0.146~d 相似文献
45.
46.
A new algorithm of order five is presented for the solution of the initial value problem where the system of ordinary differential equations is of second order and does not contain the first derivative. 相似文献
47.
Afforestation has been suggested as a means of improving soil and water conservation in north‐western China, especially on the Loess Plateau. Understanding of the hydrological responses to afforestation will help us develop sustainable watershed management strategies. A study was conducted during the period of 1956 to 1980 to evaluate runoff responses to afforestation in a watershed on the Loess Plateau with an area of 1·15 km2, using a paired watershed approach. Deciduous trees, including locust (locusta L.), apricot (praecox L.) and elm (ulmus L.), were planted on about 80% of a treated watershed, while a natural grassland watershed remained unchanged. It was estimated that cumulative runoff yield in the treated watershed was reduced by 32% as a result of afforestation. A significant trend was also observed that shows annual runoff reduction increases with the age of the trees planted. Reduction in monthly runoff occurred mainly from June to September, which was ascribed to greater rainfall and utilization by trees during this period. Afforestation also resulted in reduction in the volume and peak flow of storm runoff events in the treated watershed with greater reduction in peak flow. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
48.
Gamma-ray burst remnants become trans-relativistic typically in days to tens of days, and they enter the deep Newtonian phase in tens of days to months, during which the majority of shock-accelerated electrons will no longer be highly relativistic. However, a small portion of electrons are still accelerated to ultra-relativistic speeds and are capable of emitting synchrotron radiation. The distribution function for electrons is re-derived here so that synchrotron emission from these relativistic electrons can be calculated. Based on the revised model, optical afterglows from both isotropic fireballs and highly collimated jets are studied numerically, and compared to analytical results. In the beamed cases, it is found that, in addition to the steepening due to the edge effect and the lateral expansion effect, the light curves are universally characterized by a flattening during the deep Newtonian phase. 相似文献
49.
50.
CORROSION AND ADHERENCE AT SEA OIL-PLATFORM 总被引:1,自引:0,他引:1
Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oilplatforms under different cathodic protection showed corrosion still occurred on these platforms undertheir designed protective potentials. Preliminary conclusions from indoor experiments on the relation betweenadhesive corrosion and cathodic protection showed adhering organisms caused the corrosion onthese platforms. 相似文献