全文获取类型
收费全文 | 257890篇 |
免费 | 4322篇 |
国内免费 | 3370篇 |
专业分类
测绘学 | 6960篇 |
大气科学 | 19077篇 |
地球物理 | 54194篇 |
地质学 | 88934篇 |
海洋学 | 21323篇 |
天文学 | 56091篇 |
综合类 | 1011篇 |
自然地理 | 17992篇 |
出版年
2021年 | 2255篇 |
2020年 | 2600篇 |
2019年 | 2851篇 |
2018年 | 3286篇 |
2017年 | 2976篇 |
2016年 | 5599篇 |
2015年 | 4223篇 |
2014年 | 6930篇 |
2013年 | 14238篇 |
2012年 | 6433篇 |
2011年 | 7752篇 |
2010年 | 6676篇 |
2009年 | 9386篇 |
2008年 | 8314篇 |
2007年 | 7682篇 |
2006年 | 9698篇 |
2005年 | 7710篇 |
2004年 | 7653篇 |
2003年 | 7153篇 |
2002年 | 6775篇 |
2001年 | 6042篇 |
2000年 | 5968篇 |
1999年 | 5211篇 |
1998年 | 5232篇 |
1997年 | 5048篇 |
1996年 | 4694篇 |
1995年 | 4443篇 |
1994年 | 4120篇 |
1993年 | 3869篇 |
1992年 | 3661篇 |
1991年 | 3597篇 |
1990年 | 3771篇 |
1989年 | 3524篇 |
1988年 | 3307篇 |
1987年 | 3859篇 |
1986年 | 3407篇 |
1985年 | 4241篇 |
1984年 | 4748篇 |
1983年 | 4418篇 |
1982年 | 4331篇 |
1981年 | 3937篇 |
1980年 | 3647篇 |
1979年 | 3513篇 |
1978年 | 3484篇 |
1977年 | 3282篇 |
1976年 | 3046篇 |
1975年 | 2960篇 |
1974年 | 2922篇 |
1973年 | 3078篇 |
1972年 | 2029篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
882.
883.
D. R. Burton 《Ocean Engineering》1983,10(1):33-45
The exothermic reaction which proceeds when small sachets containing particulate mixtures of iron and magnesium are flooded with sea water, has been used for thermal support of free divers. Initial application of such generators to heating of the hands (Burton and Chan, 1981), and later extension to heating of the torso, have been described previously (Chan and Burton, 1981, 1982). Of considerable interest during field trials of the torso heating system was a strong subjective impression among those taking part, that significant increases of dive duration and decreases of perceived discomfort could be obtained with relatively low levels of power generation, for example less than 50% of that required for thermal balance. In this paper, a simple mathematical model of human stored heat loss is used to rationalize this observation. Also it successfully predicts voluntary exposure times of unheated divers who become cold. When used to estimate body heat debt, the model enables documented dives by this laboratory and by others, including recent exposures in Antarctica using low level supplementary heating, to be analysed. 相似文献
884.
885.
M. Arockiasamy H. El-Tahan A.S.J. Swamidas W.E. Russell D.V. Reddy 《Ocean Engineering》1984,11(5):463-490
The paper presents an analytical and experimental study on the transient response of semisubmersibles to bergybit impact and the strength of bergybit ice to high strain-rate loadings. Two approaches have been proposed for the solution of the semisubmersible-bergybit interaction problem, one using the energy approach and the other using the conventional structural dynamics approach with initial velocity conditions. In addition the local behaviour of the impacted regions have been analysed for deformation and failure. Numerical results have been given for local behaviour of an impacted column and global behaviour of semisubmersible-bergybit system. Experimental study has been reported on the impact strength of iceberg ice at strain rates of 10−3, 10−2 and 10−1; the indentation impact strength of ice is found to be 3–4 times the unaixial compressive strength, at the same strain rate. 相似文献
886.
887.
Highly sensitive microstructural probes subjected to noise disturbances are free of these in laboratory tests. This leads necessarily to the working out of methods for complex testsin situ. The paper reports on the successful use for this purpose of a grate (net) suspended from a free-falling probe. The grate sets up turbulence with reproducible structure in the area of sensor location.UDK 551.46.085 相似文献
888.
889.
890.