全文获取类型
收费全文 | 10415篇 |
免费 | 342篇 |
国内免费 | 132篇 |
专业分类
测绘学 | 334篇 |
大气科学 | 791篇 |
地球物理 | 2298篇 |
地质学 | 3738篇 |
海洋学 | 763篇 |
天文学 | 2093篇 |
综合类 | 35篇 |
自然地理 | 837篇 |
出版年
2022年 | 60篇 |
2021年 | 103篇 |
2020年 | 113篇 |
2019年 | 161篇 |
2018年 | 304篇 |
2017年 | 287篇 |
2016年 | 402篇 |
2015年 | 252篇 |
2014年 | 368篇 |
2013年 | 623篇 |
2012年 | 410篇 |
2011年 | 525篇 |
2010年 | 478篇 |
2009年 | 601篇 |
2008年 | 511篇 |
2007年 | 460篇 |
2006年 | 466篇 |
2005年 | 389篇 |
2004年 | 387篇 |
2003年 | 313篇 |
2002年 | 294篇 |
2001年 | 189篇 |
2000年 | 217篇 |
1999年 | 181篇 |
1998年 | 191篇 |
1997年 | 168篇 |
1996年 | 160篇 |
1995年 | 129篇 |
1994年 | 121篇 |
1993年 | 124篇 |
1992年 | 117篇 |
1991年 | 107篇 |
1990年 | 81篇 |
1989年 | 82篇 |
1988年 | 90篇 |
1987年 | 92篇 |
1986年 | 103篇 |
1985年 | 108篇 |
1984年 | 109篇 |
1983年 | 117篇 |
1982年 | 101篇 |
1981年 | 99篇 |
1980年 | 86篇 |
1979年 | 100篇 |
1978年 | 68篇 |
1977年 | 53篇 |
1976年 | 48篇 |
1975年 | 49篇 |
1974年 | 46篇 |
1973年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The three-dimensional problem of the dynamics of a moored floating object under the action of regular waves is solved numerically as a boundary value problem by use of the finite-infinite element method. The cross-sectional shape of the floating body and the mooring arrangements may all be arbitrary. The mathematical formulations of the problem and procedures of the numerical method are presented in this paper. A corresponding computer program WALOAD has been developed, which is capable of computing wave forces on fixed and floating structures. Numerical computations using this program could give very accurate results, even though rather coarse meshes were used. The program is easy to use and is readily applicable in many practical situations. 相似文献
102.
This paper addresses an important problem in ship control application—the robust stabilization of underactuated ships on a linear course with comfort. Specifically, we develop a multivariable controller to stabilize ocean surface ships without a sway actuator on a linear course and to reduce roll and pitch simultaneously. The controller adapts to unknown parameters of the ship and constant environmental disturbances induced by wave, ocean current and wind. It is also robust to time-varying environmental disturbances, time-varying change in ship parameters and other motions of the ship such as surge and heave. The roll and pitch can be made arbitrarily small while the heading angle and sway are kept to be in reasonably small bounds. The controller development is based on Lyapunov’s direct method and backstepping technique. A Lipschitz continuous projection algorithm is used to update the estimate of the unknown parameters to avoid the parameters’ drift due to time-varying environmental disturbances. Simulations on a full-scale catamaran illustrate the effectiveness of our proposed controller. 相似文献
103.
Fluxes of particulate carbon, nitrogen, phytoplankton pigments, biogenic silica and dry mass were measured using free-floating and moored sediment trap arrays in the Santa Monica Basin during the period from October 1985 to August 1990 as part of the California Basin Study (CaBS) Program. In field testing for potential sources of sediment trap biases, we found little significant or consistent difference in rate estimates between short-term drifting traps and long-term moored traps, between preserved and unpreserved traps in short-term experiments, between different preservatives (mercury or formalin) in long-term experiments, between different designs of small cylindrical traps, and between deep-moored cylindrical traps and large conical traps. We did, however, find that sediment trap samples collected and analyzed on 0.45 μm silver filters gave estimates of carbon and nitrogen fluxes about 25% higher than samples collected on GF/F glass-fiber filters. Concurrent trap deployments at two stations 18km apart revealed low mesoscale variability in flux estimates. Seasonal patterns in carbon and nitrogen flux were not evident in our data, but strong seasonality, with spring maxima and summer minima, were observed for fluxes of phaeopigments and biogenic silica out of the euphotic zone.Time-averaged rates of particulate flux for long-term trap deployments from January to August 1990, were 121, 18.8, 1.5, 67 and 633mg m−2d−1 at 110–135m for carbon, nitrogen, phaeopigment, biogenic silica and mass, respectively. Flux estimates to the basin floor (835–860m) were 50, 6.5, 0.64, 41.6 and 575mg m−2d−1 for the same parameters. The former estimates are constrained by and in good agreement with independent assessments of new production from nitrate uptake in the euphotic zone. The latter agree with rates previously inferred from the sedimentary record using 210Pb as a tracer. In addition, the difference in carbon estimates in the water column between the euphotic zone and the basin floor is consistent with the requirements for bacterial growth and metabolism at intermediate depths as measured by the thymidine method. 相似文献
104.
105.
The Acid-Producing Potential (APP) and the Acid-Consuming Capacity (ACC) are introduced as basic parameters for long-term
pollution assessment of mud disposal. They can be obtained by a four-step sequential leaching technique. The concentration
of Ca extracted by the first Na-acetate step permits calculating the ACC. Both the Fe- and S-fractions deliberated by subsequent
leaching steps are used to calculate the APP. When the APP of a sample is substacted from its ACC, a negative value indicates
a potential increase of the bioavailability of the toxic metal load upon disposal of this mud in oxic environments. 相似文献
106.
107.
108.
109.
Michael G. Simpson 《Marine environmental research》1992,34(1-4)
As part of a joint workshop organised by the International Council for the Exploration of the Sea (ICES) and the Intergovernmental Oceanographic Commission (IOC) on biological effects monitoring techniques. dad (Limanda limanda) were examined from six spaced stations along a 200 km transect extending from near the mouth of the Elbe River out to the Dogger Bank in the North Sea. Based on historical data, differences in contaminant concentrations in sediments exist along the transect (lipophilic organic xenobiotics at the inshore sites and heavy metals offshore over the Dogger Bank). The most contaminated site sampled was the most inshore, the least contaminated was approximately midway along the transect, with contamination building up again over the farthest point along the transect, over the Dogger Bank. Multiple organs and tissues were examined for full pathology from each fish sampled. Only liver data are presented here (11–20 livers per station). The most significant lesions were considered to be well-developed foci of cellular alteration, high mitotic activity and high neutral lipid accumulation in livers from dab sampled from the most inshore site examined. Livers from the least-contaminated station showed minimal evidence of such changes. Foci of cellular alteration and neutral lipid accumulation were also seen in dab liver sampled from fish from the Dogger Bank site. Thus far, the hepatic changes seen correlate well with the most contaminated sites along the transect. The value of comprehensively examining the histopathology of an organ of toxicological significance, such as the liver in a European species of flatfish, is demonstrated. 相似文献
110.