全文获取类型
收费全文 | 37579篇 |
免费 | 17884篇 |
国内免费 | 42216篇 |
专业分类
测绘学 | 2562篇 |
大气科学 | 21414篇 |
地球物理 | 13455篇 |
地质学 | 35173篇 |
海洋学 | 16339篇 |
天文学 | 1961篇 |
综合类 | 3979篇 |
自然地理 | 2796篇 |
出版年
2024年 | 126篇 |
2023年 | 222篇 |
2022年 | 310篇 |
2021年 | 643篇 |
2020年 | 1921篇 |
2019年 | 5366篇 |
2018年 | 5613篇 |
2017年 | 5350篇 |
2016年 | 5422篇 |
2015年 | 4767篇 |
2014年 | 4264篇 |
2013年 | 5025篇 |
2012年 | 4574篇 |
2011年 | 4470篇 |
2010年 | 4397篇 |
2009年 | 3840篇 |
2008年 | 3047篇 |
2007年 | 3101篇 |
2006年 | 2679篇 |
2005年 | 2547篇 |
2004年 | 2910篇 |
2003年 | 2675篇 |
2002年 | 2340篇 |
2001年 | 2066篇 |
2000年 | 1734篇 |
1999年 | 1697篇 |
1998年 | 1790篇 |
1997年 | 1842篇 |
1996年 | 1464篇 |
1995年 | 1411篇 |
1994年 | 1274篇 |
1993年 | 1224篇 |
1992年 | 1048篇 |
1991年 | 783篇 |
1990年 | 778篇 |
1989年 | 641篇 |
1988年 | 564篇 |
1987年 | 470篇 |
1986年 | 388篇 |
1985年 | 347篇 |
1984年 | 399篇 |
1983年 | 282篇 |
1982年 | 301篇 |
1981年 | 217篇 |
1980年 | 161篇 |
1979年 | 176篇 |
1978年 | 110篇 |
1977年 | 103篇 |
1976年 | 95篇 |
1973年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
BIAN Jian-min LIN Nian-feng TANG Jie College of Environment Resources Jilin University Changchun Jilin China 《东北亚地学研究》2005,(Z1)
Desertification is an environmental issue in the world. The salt-alkalization desertification land area formed by both primary and secondary salt-alkalization has extended in a large scale, which has become a significant eco-environmental problem. Based on the characteristics of eco-environment and the situation of desertification in western Songnen plain, this paper reports the analyzes of its formation in background and cause. An early warning system on the salt-alkalization desertification is established and the GIS technology is used to abstract the information of desertification evaluation index. Supported by the integrated technology of the GIS and ANN, the orientation and quantitative result of desertification are gained, which is helpful to the eco-environment protection and resource development in western Songnen Plain. 相似文献
82.
Michael E. ZOLENSKY Andrei V. IVANOV S. Vincent YANG David W. MITTLEFEHLDT Kazumasa OHSUMI 《Meteoritics & planetary science》1996,31(4):484-493
Abstract Kaidun is a breccia of disparate enstatite and carbonaceous chondrite clasts that continues to provide real surprises. Many Kaidun clasts have been intensely altered by aqueous fluids, as evidenced by the widespread occurrence of ferromagnesian phyllosilicates and by the presence of carbonate- and phyllo-silicate-filled veins. In this report, we describe an unusual CM lithology containing many mineralogical features not previously reported from any meteorite, including pyrrhotite, with exclusive needlelike morphologies and thick mantles of phyllosilicate, and complex aggregates of phyllosilicate, melanite garnet, crosscut by pentlandite veins. The latter features appear to be due in large part to extensive hydrothermal alteration at temperatures on the order of 450 °C, which is significantly higher than that attained during secondary processing from other known CM material. 相似文献
83.
秦岭凤太矿田层控铅锌(铜)矿床的金属物质、硫和成矿溶液主要来自深部基底的岩石,属海底喷流—沉积成因矿床。从这一理论认识出发可进一步分析控矿地质条件及今后在该区有效地寻找同类矿床。 相似文献
84.
The energy flow ofBranchiura sowerbyi was studied for the first time in China in a shallow macrophytic lake, Biandantang Lake, Hubei Province. The energy flow
was calculated from the measurement of flesh production (12.5241kJ/m2a), egestion (517.7302kJ/m2a), metabolism (38.3273 kJ/m2a), and excretion (4.3798kJ/m2a). The net growth efficiency of the species is about 22.7%, which accords well with the generally reported value for oligochaetes.
In addition, the relationship between starvation respiration (R, mgO2/ind·d), wet weight (Ww, mg) and temperature (T, °C) were also measured, with the regression function beingR=0.008Ww0.736 e0.050T.
Project supported by NSFC (30270278, 3960019), the foundation of the government of Hubei Province (No. 2000J109), and the
foundation of Ecological Station, CAS in the Institute of Hydrobiology. 相似文献
85.
86.
We present a new Very Large Array (VLA) image of Saturn, made from data taken in October 1998 at a wavelength of λ3.6 cm. The moderate ring opening angle (B≈15°) allows us to explore direct transmission of microwave photons through the A and C rings. We find a strong asymmetry of photons transmitted through the A ring, but not in the C ring, a new diagnostic of wake structure in the ring particles. We also find a weak asymmetry between east and west for the far side of the ansae. To facilitate quantitative comparison between dynamic models of the A ring and radio observations, we extend our Monte Carlo radiative transfer code (described in Dunn et al., 2002, Icarus 160, 132-160) to include idealized wakes. We show the idealized model can reproduce the properties of dynamic simulations in directly transmitted light. We examine the model behavior in directly transmitted and scattered light over a range of physical and geometric wake parameters. Finally, we present a wake model with a plausible set of physical parameters that quantitatively reproduces the observed intensity and asymmetry of the A ring both across the planet and in the ansae. 相似文献
87.
青藏块体东北缘地壳水平运动状态 总被引:10,自引:6,他引:4
应用青藏块体东北缘1999~2003年多期GPS观测资料,计算了不同时段GPS点水平运动速率。通过分析发现:甘青块体可分为东部块体和西部块体,东、西部块体的运动状态存在明显的差异;受2001年11月14日昆仑Ms8.1地震的影响,震后地壳运动状态发生了明显的改变。 相似文献
88.
89.
This paper considers the problem of estimatingm, the number of components in a finite mixture of distributions from a parametric family. A step-up procedure using the bootstrap method is proposed. Some properties of the procedure are illustrated with simulation studies. An example of the method, applied to orientation of beach clasts, is given. 相似文献
90.
Andrew J. L. Harris Anna L. Butterworth Richard W. Carlton Ian Downey Peter Miller Pedro Navarro David A. Rothery 《Bulletin of Volcanology》1997,59(1):49-64
Satellite data offer a means of supplementing ground-based monitoring during volcanic eruptions, especially at times or locations
where ground-based monitoring is difficult. Being directly and freely available several times a day, data from the advanced
very high resolution radiometer (AVHRR) offers great potential for near real-time monitoring of all volcanoes across large
(3000×3000 km) areas. Herein we describe techniques to detect and locate activity; estimate lava area, thermal flux, effusion
rates and cumulative volume; and distinguish types of activity. Application is demonstrated using data for active lavas at
Krafla, Etna, Fogo, Cerro Negro and Erebus; a pyroclastic flow at Lascar; and open vent systems at Etna and Stromboli. Automated
near real-time analysis of AVHRR data could be achieved at existing, or cheap to install, receiving stations, offering a supplement
to conventional monitoring methods.
Received: 21 January 1997 / Accepted: 3 April 1997 相似文献