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951.
952.
Huang Guoliang Liu Tianwei Yan Naichang
Associate Professor Shanghai Jiao Tong University Shanghai
Engineer Shanghai Jiao Tong University Shanghai .
Professor Shanghai Jiao Tong University Shanghai 《中国海洋工程》1997,(4)
In this paper,the maneuvering characteristics of a low speed submersible are investigated.First,the captive model tests are carried out to obtain the hydrodynamic forces acting on the submersibleusing a Planar Motion Mechanism(PMM).For the hydrodynamic forces within a wide range of attack an-gles,the hydrodynamic coefficients which are usually used in the conventional maneuvering motion arequite difficult to be applied.In this case,a Fourier series is adopted to represent the hydrodynamic forcesand it fits the experimental data well.Then,based on the experimental results the simulation calculationsare made to predict some of the maneuvering performance of the low speed submersible. 相似文献
953.
Acoustic volume backscattering strength data were collected and Conductivity Temperature Depth (CTD) measur e m e n t s were
conducted in the southern Yellow Sea in summer 2005 and 2006. The high temporal and vertical resolution acoustic data measured
with a 307 kHz Acoustic Doppler Current Profiler (ADCP) and a 250 kHz acoustic Doppler profile (ADP) had dominant diel variation,
which resulted from vertical migration of sound scatterers. Some scatterers congregating in the bottom layer in the daytime
migrated upward at dusk, and migrated downward into the bottom layer at dawn. The migration speeds were estimated. More than
33 days data show that the diel migration varies with time. The feature of migration measured with ADCP and ADP is consistent
to some extent with what is described in the study on vertical migration of zooplankton in the southern Yellow Sea with conventional
net samples. 相似文献
954.
Predicting the capability-polar-plots for dynamic positioning systems for offshore platforms using artificial neural networks 总被引:1,自引:0,他引:1
As the capability of polar plots becomes better understood, improved dynamic positioning (DP) systems are possible as the control algorithms greatly depend on the accuracy of the aerodynamic and hydrodynamic models. The measurements and estimation of the environmental disturbances have an important role in the optimal design and selection of a DP system for offshore platforms. The main objective of this work is to present a new method of predicting the Capability-Polar-Plots for offshore platforms using the combination of the artificial neural networks (NNs) and the capability polar plots program (CPPP). The estimated results from a case study for a scientific drilling vessel are presented. A trained artificial NN is designed in this work and is able to predict the maximum wind speed at which the DP thrusters are able to maintain the offshore platform in a station-keeping mode in the field site. This prediction for the maximum wind speed will be a helpful tool for DP operators in managing station-keeping for offshore platforms in an emergency situation where the automation of the DP systems is disabled. It is obvious from the obtained results that the developed technique has potential for the estimation of the capability-polar-plots for offshore platforms. This tool would be suitable for DP operators to predict the maximum wind speed and direction in a very short period of time. 相似文献
955.
956.
A version of the WAVEWATCH III wave model featuring a continuously moving spatial grid is presented. The new model option/version is intended for research into wind waves generated by tropical cyclones in deep water away from the coast. The main advantage of such an approach is that the cyclones can be modeled with spatial grids that cover much smaller areas than conventional fixed grids, making model runs with high spatial resolution more economically feasible. The model modifications necessary are fairly trivial. Most complications occur due to the Garden Sprinkler effect (GSE) and methods used to mitigate it. The basic testing of the model is performed using idealized wind fields consisting of a Rankine vortex. The model is also applied to hurricane Lili in the Gulf of Mexico in October 2002. The latter application shows that the moving grid approach provides a natural way to deal with hurricane wind fields that have a high-resolution in space, but a low resolution in time. Although the new model version is originally intended for tropical cyclones, it is suitable for high-resolution modeling of waves due to any moving weather pattern. 相似文献
957.
This article uses a comparison of four different numerical wave prediction models for hindcast wave conditions in Lake Michigan during a 10-day episode in October 1988 to illustrate that typical wave prediction models based on the concept of a wave energy spectrum may have reached a limit in the accuracy with which they can simulate realistic wave generation and growth conditions. In the hindcast study we compared the model results to observed wave height and period measurements from two deep water NOAA/NDBC weather buoys and from a nearshore Waverider buoy. Hourly wind fields interpolated from a large number of coastal and overlake observations were used to drive the models. The same numerical grid was used for all the models. The results show that while the individual model predictions deviate from the measurements by various amounts, they all tend to reflect the general trend and patterns of the wave measurements. The differences between the model results are often similar in magnitude to differences between model results and observations. Although the four models tested represent a wide range of sophistication in their treatment of wave growth dynamics, they are all based on the assumption that the sea state can be represented by a wave energy spectrum. Because there are more similarities among the model results than significant differences, we believe that this assumption may be the limiting factor for substantial improvements in wave modeling. 相似文献
958.
风对福建中部沿岸春、夏季水文结构和上升流的影响 总被引:5,自引:0,他引:5
本文对台湾海峡西侧海坛岛附近海域风情与附近岸站的风情进行了对比分析,结果表明,海上风情和岸站风情变化基本上是一致的;在不同季风的作用下,海域温、盐度呈现不同类型的分布。风情的短期变化对上升流的强弱变化有一定影响。 相似文献
959.
随着航天技术的发展和新型微波载荷的发射(如3维成像高度计),越来越多的小入射角海洋观测雷达将投入运行,如何有效地利用这些小入射角的后向散射数据成为研究的热点课题。利用TRMM(Tropical Rainfall Measuring Mission)的PR(Precipitation Radar)后向散射系数NRCS(Normalized Radar Cross Section)数据对小入射角情况下的海面风速反演方法和风速反演精度进行研究,并对风速反演性能进行统计分析。基于无雨条件下的PR海面后向散射数据,建立小入射角情况下的风速反演算法和经验的GMF模型。风速反演结果分别与浮标、ASCAT进行交叉比对。结果表明:反演风速的偏差小于0.28 m/s,标准差小于1.51 m/s;在中等风速条件下,反演风速的偏差和标准差均小于低风速条件和高风速条件;0°—8°入射角范围内的风速反演精度明显优于8°—12°入射角范围的风速反演精度。 相似文献
960.
Tawanda W. Gara Tiejun Wang Andrew K. Skidmore Shadrack M. Ngene Timothy Dube Mbulisi Sibanda 《国际地球制图》2017,32(11):1243-1253
Understanding factors affecting the behaviour and movement patterns of the African elephant is important for wildlife conservation, especially in increasingly human-dominated savanna landscapes. Currently, knowledge on how landscape fragmentation and vegetation productivity affect elephant speed of movement remains poorly understood. In this study, we tested whether landscape fragmentation and vegetation productivity explains elephant speed of movement in the Amboseli ecosystem in Kenya. We used GPS collar data from five elephants to quantify elephant speed of movement for three seasons (wet, dry and transitional). We then used multiple regression to model the relationship between speed of movement and landscape fragmentation, as well as vegetation productivity for each season. Results of this study demonstrate that landscape fragmentation and vegetation productivity predicted elephant speed of movement poorly (R2 < 0.4) when used as solitary covariates. However, a combination of the covariates significantly (p < 0.05) explained variance in elephant speed of movement with improved R2 values of 0.69, 0.45, 0.47 for wet, transition and dry seasons, respectively. 相似文献