全文获取类型
收费全文 | 3680篇 |
免费 | 422篇 |
国内免费 | 212篇 |
专业分类
测绘学 | 126篇 |
大气科学 | 298篇 |
地球物理 | 1647篇 |
地质学 | 1168篇 |
海洋学 | 443篇 |
天文学 | 46篇 |
综合类 | 28篇 |
自然地理 | 558篇 |
出版年
2024年 | 18篇 |
2023年 | 31篇 |
2022年 | 37篇 |
2021年 | 84篇 |
2020年 | 163篇 |
2019年 | 126篇 |
2018年 | 118篇 |
2017年 | 169篇 |
2016年 | 165篇 |
2015年 | 133篇 |
2014年 | 155篇 |
2013年 | 376篇 |
2012年 | 76篇 |
2011年 | 124篇 |
2010年 | 105篇 |
2009年 | 188篇 |
2008年 | 247篇 |
2007年 | 223篇 |
2006年 | 213篇 |
2005年 | 199篇 |
2004年 | 158篇 |
2003年 | 131篇 |
2002年 | 108篇 |
2001年 | 97篇 |
2000年 | 121篇 |
1999年 | 115篇 |
1998年 | 110篇 |
1997年 | 99篇 |
1996年 | 73篇 |
1995年 | 71篇 |
1994年 | 58篇 |
1993年 | 55篇 |
1992年 | 36篇 |
1991年 | 27篇 |
1990年 | 26篇 |
1989年 | 23篇 |
1988年 | 21篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1954年 | 2篇 |
排序方式: 共有4314条查询结果,搜索用时 15 毫秒
111.
S. Gamito 《International Journal of Salt Lake Research》1997,6(2):145-173
The Ria Formosa lies in southern Portugal, extending for about 55 km. It is a true barrier island system, comprising mainland,
backbarrier lagoons, inlet deltas, barrier islands, barrier platforms and shoreface. Of the Ria Formosa system, which covers
a total area of 163 km2, 20 km2 are occupied by salinas and aquaculture ponds. The main water reservoir of thesalinas and the extensive aquaculture ponds behave like small lagoons where there are one or more openings to a tidal channel. These
small lagoons have the advantage of being easy to study and to model.
An ecological model was developed to estimate the potential production of the gilthead seabream in the Ria Formosa, in an
extensive aquaculture regime. This model was based on information concerning chemical and physical factors (forcing functions)
and secondary production estimates from four sites in the Ria Formosa with different environmental conditions, where extensive
aquaculture is practised. Published information on optimal growth parameters of the gilthead was used to build the model,
which was based on some assumptions concerning the detrimental effect of an excessive increase of salinity and other environmental
factors both on gilthead growth (one state variable) and on prey production (divided into two state variables), which is essentially
benthic macrofauna.
Reservoirs with low water renewal undergo large environmental fluctuations. The growth of gilthead or other fish can be difficult,
not only because of the adverse environmental conditions but also because of the low secondary production. The maximum yield
of fish is predicted to be less than 6 g m−2. In reservoirs where the water exchanges on almost every tide, the maximum yield of gilthead can be in excess of 22–25 g
m−2. Nevertheless, the high productivity of these sites in terms of secondary production of benthos and fish, as well as primary
production, can lead to oxygen depletion during the night or at day-break. An attempt to further improve fish production by
fertilisation or by adding food could provoke a rapid deterioration of the water quality and endanger all production. 相似文献
112.
G. Umgiesser 《International Journal of Salt Lake Research》1997,6(2):175-199
In this paper, an overview is given on the modelling activities at the National Research Council in Venice (ISDGM-CNR) concerning
the Venice Lagoon. A short history of former modelling efforts is given. A finite element hydrodynamic model is presented
that has been created especially for the Venice Lagoon. This model has been applied to various situations. Residual currents
have been computed for one year. A specific storm surge event has been simulated with spatially varying real winds. A transport
diffusion model has been applied to model the impact of a treatment plant on the central lagoon. And a sub-basin has been
modeled with a high resolution grid. 相似文献
113.
Earthquake magnitude prediction is of vital importance for human safety. The earthquake is a very complicated and non-linear dynamic process. It cannot be described adequately by any deterministic models. In this paper a neural dynamic modelling for earthquake magnitude prediction is reported. Historical records of earthquake magnitude series are used to construct the optimal non-linear dynamic model, and the consequent outcome of the earthquake behaviour is then predicted by this model. In turn, the latest recorded data set can be fed back to improve the accuracy of the neural dynamic model. The modelling of experiments of three earthquake magnitude series in China and Japan and their extrapolated predictions are included in this paper. The values predicted by extrapolation are in good agreement with the historical data. 相似文献
114.
P-SH conversion is commonly observed in teleseismic P waves, and is often attributed to dipping interfaces beneath the receiver. Our modelling suggests an alternative explanation in terms of flat-layered anisotropy. We use reflectivity techniques to compute three-component synthetic seismograms in a 1-D anisotropic layered medium. For each layer of the medium, we prescribe values of seismic velocities and hexagonally symmetric anisotropy about a common symmetry axis of arbitrary orientation. A compressional wave in an anisotropic velocity structure suffers conversion to both SV -and SH -polarized shear waves, unless the axis of symmetry is everywhere vertical or the wave travels parallel to all symmetry axes. The P-SV conversion forms the basis of the widely used 'receiver function' technique. The P-SH conversion occurs at interfaces where one or both layers are anisotropic. A tilted axis of symmetry and a dipping interface in isotropic media produce similar amplitudes of both direct ( P ) and converted ( Ps ) phases, leaving the backazimuth variation of the P-Ps delay as the main discriminant. Seismic anisotropy with a tilted symmetry axis leads to complex synthetic seismograms in velocity models composed of just a few flat homogeneous layers. It is possible therefore to model observations of P coda with prominent transverse components with relatively simple 1-D velocity structures. Successful retrieval of salient model characteristics appears possible using multiple realizations of a genetic-algorithm (GA) inversion of P coda from several backazimuths. Using GA inversion, we determine that six P coda recorded at station ARU in central Russia are consistent with models that possess strong (> 10 per cent) anisotropy in the top 5 km and between 30 and 43 km depth. The symmetry axes are tilted, and appear aligned with the seismic anisotropy orientation in the mantle under ARU suggested by SKS splitting. 相似文献
115.
116.
117.
118.
119.
The Uplift of the Longmenshan Thrust Belt and Subsidence of the West Sichuan Foreland Basin 总被引:8,自引:0,他引:8
Liu Shugen Luo Zhili Dai Sulan Changlu Institute of Technology Chengdu Sichuan ChinaDennis Arne Dalhousie U niversity Canadaand C.J.L. Wilson Melbourne U niversity Australia Jiang M inxi 《《地质学报》英文版》1996,70(1):16-26
Based on fission track dating of apatite, and measurement of vitrinite reflectance of rock samples from the Longmenshan (Longmen Mountain)area and the West Sichuan foreland basin and computer modelling it is concluded that (l)the Songpan-Garze fold belt has uplifted at least by 3-4 km with an uplift rate of no less than 0.3-0.4 mm/a since 10 Ma B.P.; (2) the Longmenshan thrust nappe belt has uplifted at least by 5-6 km with an uplift rate of more than 0.5- 0.6 mm /a since 10 Ma B.P.; (3) the Longmenshan detachment belt has uplifted by 1 - 2 km at a rate of 0.016-0.032 mm/a since 60 Ma B.P.; (4) the West Sichuan foreland basin has uplifted by 1.7-3 km at a rate of 0.028-0.05 mm/a since 60 Ma B.P.; (5) the uplift rate of the area on the west side of the Beichuan-Yingxiu-Xiaoguanzi fault for the last 10 Ma is 40 times as much as that on its east side; (6) the uplifting of the the Songpan - Garze fold belt and the subsidence of the West Sichuan foreland basin 60 Ma ago exhibit a mirro-image correlation, i.e 相似文献
120.
Summary This paper explores an approach to estimation of the viscoelastic parameters of weak floor strata using plate-loading tests. Mathematical equations are derived to describe deformation-time history for the standard Burgers model under three-dimensional stress-strain conditions, which are verified with a finite element model. A number of time-dependent in-mine plate-loading tests were conducted and the values of the viscoelastic parameters were estimated based on the derived equation. It is shown that large discrepancies between the parameter values estimated from the plate-loading tests and those acquired from the in-mine convergence data are the results of neglecting adjacent pillar interaction. Finite element modelling was conducted to investigate the effects of adjacent pillar interactions upon the pillar settlement. Based on the finite element analyses, a correction curve was developed to adjust the viscoelastic parameter values to take into account the interaction between adjacent pillars. With the correction, the parameter values estimated from the plate-loading tests compared favourably with those acquired from the in-mine convergence results. 相似文献