全文获取类型
收费全文 | 32379篇 |
免费 | 17703篇 |
国内免费 | 42158篇 |
专业分类
测绘学 | 2483篇 |
大气科学 | 20987篇 |
地球物理 | 12172篇 |
地质学 | 33533篇 |
海洋学 | 15771篇 |
天文学 | 1271篇 |
综合类 | 3954篇 |
自然地理 | 2069篇 |
出版年
2024年 | 126篇 |
2023年 | 217篇 |
2022年 | 290篇 |
2021年 | 563篇 |
2020年 | 1827篇 |
2019年 | 5291篇 |
2018年 | 5509篇 |
2017年 | 5249篇 |
2016年 | 5294篇 |
2015年 | 4665篇 |
2014年 | 4114篇 |
2013年 | 4719篇 |
2012年 | 4399篇 |
2011年 | 4225篇 |
2010年 | 4166篇 |
2009年 | 3552篇 |
2008年 | 2828篇 |
2007年 | 2849篇 |
2006年 | 2486篇 |
2005年 | 2388篇 |
2004年 | 2762篇 |
2003年 | 2479篇 |
2002年 | 2192篇 |
2001年 | 1946篇 |
2000年 | 1586篇 |
1999年 | 1589篇 |
1998年 | 1694篇 |
1997年 | 1766篇 |
1996年 | 1376篇 |
1995年 | 1326篇 |
1994年 | 1181篇 |
1993年 | 1156篇 |
1992年 | 978篇 |
1991年 | 755篇 |
1990年 | 706篇 |
1989年 | 594篇 |
1988年 | 513篇 |
1987年 | 416篇 |
1986年 | 327篇 |
1985年 | 270篇 |
1984年 | 300篇 |
1983年 | 177篇 |
1982年 | 226篇 |
1981年 | 172篇 |
1980年 | 135篇 |
1979年 | 123篇 |
1978年 | 61篇 |
1977年 | 62篇 |
1971年 | 67篇 |
1970年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Ren Tinawi Marc Sarrazin Andr Filiatrault 《Soil Dynamics and Earthquake Engineering》1993,12(8):469-477
The 1990 edition of the National Building Code of Canada (Associate Committee of the National Building Code, National Research Council, Ottawa, 1990) makes a clear distinction between eastern and western Canada in terms of seismic acceleration and velocity zones. While it is well established that ground motions can be amplified significantly through loose clay deposits, no results are available that take into consideration the typical high frequency content of ground motions in eastern Canada. This paper develops ground amplification curves for clays having depths between 10 and 70 m excited by typical eastern Canadian ground motions scaled to two different values of peak horizontal accelerations. Simplified free-field spectral design curves, which could be used by structural designers, are proposed. The curves show that maximum spectral accelerations occur for structural periods between 0.2 and 0.5 s. In addition, soil depth does not appear to be an important parameter controlling the response of typical clay deposits in eastern Canada. 相似文献
62.
63.
We have analysed short-exposure high-resolution images obtained on the William Herschel Telescope (WHT), Big Telescope Azimuthal (BTA) and CanadaFranceHawaii Telescope (CFHT) in order to investigate mechanical vibrations that are capable of reducing the high angular resolution allowed by speckle-interferometric methods. After filtering the photon noise we have computed power spectra of the image centres of gravity. In these spectra we have found vibration features that differ from one telescope to another and that vary in particular with the zenith angle. In the case of the WHT we discuss these results in terms of possible causes and in terms of degradation of the transfer function. We present some means to improve the data. 相似文献
64.
JiřÍ Polcar Martin Topinka Graziella Pizzichini Eliana Palazzi Nicola Masetti RenÉ Hudec Věra HudcovÁ 《Astrophysics and Space Science》2005,296(1-4):485-488
We report on our statistical research of space–time correlated supernovae and CGRO-BATSE gamma-ray bursts (GRBs). There exists
a significantly higher abundance of core-collapse supernovae among the correlated supernovae, but the subset of all correlated
objects does not seem to be physically different from the whole set. 相似文献
65.
66.
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
67.
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
68.
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
69.
70.