首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   79240篇
  免费   1074篇
  国内免费   707篇
测绘学   1911篇
大气科学   5029篇
地球物理   15161篇
地质学   28874篇
海洋学   7299篇
天文学   19070篇
综合类   267篇
自然地理   3410篇
  2022年   669篇
  2021年   1037篇
  2020年   1123篇
  2019年   1220篇
  2018年   2635篇
  2017年   2486篇
  2016年   2902篇
  2015年   1419篇
  2014年   2685篇
  2013年   4192篇
  2012年   2931篇
  2011年   3654篇
  2010年   3304篇
  2009年   4050篇
  2008年   3537篇
  2007年   3701篇
  2006年   3385篇
  2005年   2263篇
  2004年   2235篇
  2003年   2131篇
  2002年   2016篇
  2001年   1864篇
  2000年   1699篇
  1999年   1302篇
  1998年   1345篇
  1997年   1289篇
  1996年   1065篇
  1995年   1067篇
  1994年   939篇
  1993年   811篇
  1992年   806篇
  1991年   815篇
  1990年   882篇
  1989年   689篇
  1988年   712篇
  1987年   733篇
  1986年   640篇
  1985年   845篇
  1984年   910篇
  1983年   807篇
  1982年   773篇
  1981年   684篇
  1980年   685篇
  1979年   633篇
  1978年   649篇
  1977年   532篇
  1976年   494篇
  1975年   502篇
  1974年   443篇
  1973年   507篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
V. Prabhakar  J. Pandurangan   《Ocean Engineering》2006,33(8-9):1044-1055
A polar method for obtaining wave resonating quadruplets {K1, K2, K3, K4} in the computation of nonlinear wave–wave interaction source term of the wave model is presented with results for both deep and finite water depths. The method first determines the end radial points of the locus equation for K2, for each set of input wave vectors (K1, K3) on the symmetry. The locus of K2 (and hence K4) is then traced in the anti-clockwise direction starting with the maximum radial point on the line of symmetry. It is shown that when k3>k1, the number of points on the locus varies when the orientations of the input wave vectors are changed and reduces when the difference in the magnitude of the input wave vectors is increased. A significant advantage in this method is that the angular increment on the locus for K2 can be kept constant.  相似文献   
952.
953.
Abstract. A marine ecosystem in the crater of the Ushishir Volcano (Kraternaya Bight, Yankich Island, the Kuriles) showing gasothcrmal activity was studied for hydrographical, hydrochemical, and biological characteristics. Maximal changes in chemical and biological characteristics were observed in the surface water layer of 0–5 m. This layer had higher water temperature, was saturated with volcanogcnic carbon dioxide (up to 2000 10-6 torr), ovcrsaturatcd with oxygen (up to 200 %), and contained high concentrations of chlorophyll a. Hydrogen sulfide was found in the surface water layer and at a depth of 15 m in the area of maximal effect of volcanic effluents.
The planktonic community is characterized by high rates of production and destruction of organic matter only in the 0–5 m layer. Daily vertical migrations of the ciliatc Mesodinium rubrum were observed, which caused "red tides".
Bacterial, algobacterial, and diatom mats developed on the bottom of the bight in the zone of gasohydrothermal vents and in areas of volcanic water seeping. The rate of organic matter production in algobacterial mats reached 33.4g C-rrr2-d-l, chcmolithotrophy predominating. Bottom settlements had high population density and great animal biomass, which reached 10 kg m-2 in gasohydrothermal fields. They obtain sufficient energy from primary production of microphy-tobenthos, algobacterial, and bacterial mats. Bcnthic species dominant in the bight were not found off the Ushishir Islands.
Some species of macrobenthos inhabiting the Kraternaya Bight differ markedly in size and biomass from the same species found beyond the bight.  相似文献   
954.
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   
955.
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   
956.
957.
958.
One of the most efficient tools of studying meteorological and climatic time series is wavelet analysis, which allows local properties of a nonstationary time series to be examined. New sets of continuous and discrete wavelet-forming functions are proposed. All proposed wavelets are finite (have a bounded carrier), even, and well localized in the spectral space.  相似文献   
959.
Mesoscale eddies are frequently observed in the Greenland and Barents Seas' marginal ice zone (MIZ). The objective of this study was to investigate the hypothesis that acoustic hotspots along the ice-edge region are due to mesoscale eddy currents interacting with the broken-up ice floes in the MIZ. To test this hypothesis, ambient-noise case studies were carried out during the MIZEX 85-87 and SIZEX 89 field experiments. In each experiment, ice-edge eddies were localized visually from aircraft and by use of satellite remote-sensing data obtained in near real time. Sonobuoys were, thereafter, deployed by fix-wing aircraft and helicopters in selected eddy areas. Ambient-noise data, recorded over several hours by aircraft, were analyzed estimating averaged ambient-noise levels at four selected frequencies: 40, 100, 315, and 1000 Hz. The analysis showed high mean levels and large gradients in ambient noise near ice-edge eddies and during strong wind and wave forcing against the ice edge. The conclusion of this study is that mapping of the ice edge and localization of mesoscale ocean processes using remote sensing from space will provide important input to ambient-noise prediction in the MIZ.  相似文献   
960.
This study presents the results of the decoupling of a free-roll decay test by wavelet transforms. A free-roll decay test was performed to determine the coefficients of damping terms in equations of motion. No motion of the model was restricted during the experiment. A slight yaw motion was found while the model was in the free-roll decay motion. It was necessary to extract a pure roll motion from the experimental data. Wavelet transforms were applied to the signals to extract the pure roll motion. The results were compared to those found through the Fourier transform. Discrete wavelet transforms were able to efficiently decouple the test signals, while the continuous wavelet transform and the Fourier transform could not.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号