全文获取类型
收费全文 | 29029篇 |
免费 | 1120篇 |
国内免费 | 2061篇 |
专业分类
测绘学 | 1808篇 |
大气科学 | 2716篇 |
地球物理 | 5549篇 |
地质学 | 14178篇 |
海洋学 | 1586篇 |
天文学 | 1941篇 |
综合类 | 2532篇 |
自然地理 | 1900篇 |
出版年
2024年 | 25篇 |
2023年 | 81篇 |
2022年 | 225篇 |
2021年 | 274篇 |
2020年 | 227篇 |
2019年 | 295篇 |
2018年 | 4975篇 |
2017年 | 4259篇 |
2016年 | 2812篇 |
2015年 | 497篇 |
2014年 | 350篇 |
2013年 | 326篇 |
2012年 | 1246篇 |
2011年 | 2998篇 |
2010年 | 2284篇 |
2009年 | 2576篇 |
2008年 | 2178篇 |
2007年 | 2624篇 |
2006年 | 233篇 |
2005年 | 399篇 |
2004年 | 577篇 |
2003年 | 572篇 |
2002年 | 438篇 |
2001年 | 264篇 |
2000年 | 215篇 |
1999年 | 188篇 |
1998年 | 155篇 |
1997年 | 152篇 |
1996年 | 110篇 |
1995年 | 102篇 |
1994年 | 74篇 |
1993年 | 71篇 |
1992年 | 79篇 |
1991年 | 38篇 |
1990年 | 43篇 |
1989年 | 35篇 |
1988年 | 39篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 28篇 |
1980年 | 24篇 |
1979年 | 4篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 11篇 |
1958年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
351.
The fragile ecological environment of the Gurbantunggut Desert is damaged/disturbed by human activities relating to the development of oil-gas resources and the constructions of desert road and great engineering in the Jungger Basin. It was mainly represented: soil compaction, vegetation cleaning, burial of vegetation, oil polluting, and soil disturbance. With investigation and experiment, we found that when the way and intensity of engineering activities disturbing the eco-environment does not make its ecological stability disintegrated, the desert vegetation has a capacity of natural recovery. To speed and strengthen the process of vegetation recovery efficient assistant measurements, including stabilizing mobile sands promptly and sowing seeds of shrub and herb plants in good time will be needed. 相似文献
352.
Episodic dune formations during the Quaternary are found in many deserts of China. The causes of desert expansions on different time scales are not the same. Desert extension at about 1.1 and 0.9 Ma ago were the response to the active tectonic movements, whereas the desert evolutions on the ten-thousand years time scale were the response to the orbital scale climatic changes. Spatial scale studies on desert evolution indicate that desert margins shifted greatly during the last glacial maximum (LGM) and the Holocene optimum, its changing from 125°E of the LGM to 105°E of the climatic optimum. Historical desertification in the semiarid China is not a response to climate drought but largely associated with the human impacts (mainly over-cultivation) since about 2300 years ago, which leads to the reworking of the underlying LGM sands. 相似文献
353.
Zili Fan Xuncheng Xia Yuling Shen Kurban Alishir Ranghui Wang Shengyu Li Yingjun Ma 《中国科学D辑(英文版)》2002,45(1):102-108
Because of the human exploitation and utilization of water resources in the Tarim Basin, the water resources consumption has changed from mainly natural ecosystem to artificial oasis ecosystem, and the environment has changed correspondingly. The basic changes are: desertification and oasis development coexist, both “the human being advance and the desert retreat” and “the desert advance and the human being retreat” coexist, but the latter is dominant. In the upper reaches, water volume drawing to irrigated agricultural areas has increased, artificial oases have been enlarging and moving from the deltas in the lower reaches of many rivers to the piedmont plains. In the middle and lower reaches of the Tarim River, the stream flow has decreased, old oases have declined, natural vegetations have been degenerating, desertification has been enlarging, and the environment has deteriorated. The transition regions, which consist of forestlands, grasslands and waters between the desert and the oases, have been decreasing continuously, their shelter function to the oases has been weakened, and the desert is threatening the oases seriously. 相似文献
354.
Adrian Williams 《中国科学D辑(英文版)》2002,45(1):109-114
The paper describes Western Australian examples and causes of land degradation. It outlines shortcomings in the methodologies used to rehabilitate these areas. From this a protocol is suggested for an ‘holistic’ approach to land rehabilitation. 相似文献
355.
356.
A general method is developed for optimal application of dampers and actuators by installing them at optimal location on seismic-resistant
structures. The study includes development of a statistical criterion, formulation of a general optimization problem and establishment
of a solution procedure. Numerical analysis of the seismic response in time-history of controlled structures is used to verify
the proposed method for optimal device application and to demonstrate the effectiveness of seismic response control with optimal
device location. This study shows that the proposed method for the optimal device application is simple and general, and that
the optimally applied dampers and actuators are very efficient for seismic response reduction. 相似文献
357.
介绍了近年来华北地区宝龙等 3口井稀有气体的显著异常 ,并据其特征与井孔水位动态的关系 ,对稀有气体异常的成因进行了理论分析与实验研究。结果表明 ,水位下降 10 0mm ,岩层孔隙、裂隙中的气体体积膨胀 0 0 0 90 % (气体体积百分比 ,下同 )左右。由于地下水位大幅度下降 ,岩层孔隙压力减小 ,积聚在岩层孔隙、裂隙中的气体体积膨胀溢出 ,导致井孔地下水中稀有气体含量出现异常变化。这些异常是干扰因素所致 ,不是地震异 相似文献
358.
359.
360.