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921.
Two models, one linear and one non‐linear, were employed for the prediction of flow discharge hydrographs at sites receiving significant lateral inflow. The linear model is based on a rating curve and permits a quick estimation of flow at a downstream site. The non‐linear model is based on a multilayer feed‐forward back propagation (FFBP) artificial neural network (ANN) and uses flow‐stage data measured at the upstream and downstream stations. ANN predicted the real‐time storm hydrographs satisfactorily and better than did the linear model. The results of sensitivity analysis indicated that when the lateral inflow contribution to the channel reach was insignificant, ANN, using only the flow‐stage data at the upstream station, satisfactorily predicted the hydrograph at the downstream station. The prediction error of ANN increases exponentially with the difference between the peak discharge used in training and that used in testing. ANN was also employed for flood forecasting and was compared with the modified Muskingum model (MMM). For a 4‐h lead time, MMM forecasts the floods reliably but could not be applied to reaches for lead times greater than the wave travel time. Although ANN and MMM had comparable performances for an 8‐h lead time, ANN is capable of forecasting floods with lead times longer than the wave travel time. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
922.
Singh H. Bellingham J.G. Hover F. Lemer S. Moran B.A. von der Heydt K. Yoerger D. 《Oceanic Engineering, IEEE Journal of》2001,26(4):498-514
In this paper, we examine the issues associated with docking autonomous underwater vehicles (AUVs) operating within an Autonomous Ocean Sampling Network (AOSN). We present a system based upon an acoustic ultrashort baseline system that allows the AUV to approach the dock from any direction. A passive latch on the AUV and a pole on the dock accomplish the task of mechanically docking the vehicle. We show that our technique for homing is extremely robust in the face of the two dominant sources of error-namely the presence of currents and the presence of magnetic anomalies. Our strategy for homing is independent of the initial bearing of the dock to the AUV, includes a method for detecting when the vehicle has missed the dock, and automatically ensures that the AUV is in a position to retry homing with a greater chance of success. Our approach is seen to be extremely successful in homing the vehicle to the dock, mechanically attaching itself to the dock, aligning inductive cores for data and power transfer, and undocking at the start of a fresh mission. Once the AUV is on the dock, we present a methodology that allows us to achieve the complex tasks with ensuring that the AUV is securely docked, periodically checking vehicle status, reacting to a vehicle that requires charging, tracking it when it is out on a mission, archiving and transmitting via satellite the data that the AUV collects during its missions, as well as providing a mechanism for researchers removed from the site to learn about vehicle status and command high-level missions. The dock is capable of long-term deployments at a remote site while respecting the constraints - low power, small size, low computational energy, low bandwidth, and little or no user input - imposed by the amalgamation of acoustic, electronic and mechanical components that comprise the entire system 相似文献
923.
A time sequence over 80 min of coronal green-line spectra was obtained with a corona- graph at the Norikura Solar Observatory. Doppler velocities, line intensities, and line widths were derived through fitting a single Gaussian to the observed line profiles. Coronal waves have been clearly detected in the Doppler velocity data. The Fourier analysis shows powers in a 1–3 mHz range, and in higher frequencies (5–7 mHz) at localized regions. The propagation speed of the waves was estimated by correlation analysis. The line intensity and line width did not show clear oscillations, but their phase relationship with the Doppler velocity indicates propagating waves rather than standing waves. The existence of Alfvén waves whose speed is 500 km s–1 or faster is possible but inconclusive, while the existence of slower waves (of the order of 100 km s–1, possibly sound waves) is evident. The energy carried by the detected sound waves is far smaller than the required heat input rate to the quiet corona. 相似文献
924.
A. K. Singh 《Astrophysics and Space Science》1985,115(2):387-391
The effect of large suction on laminar hydromagnetic boundary-layer flows is investigated by employing the perturbation method. The resulting equations have been solved by analytical method. It is found that an increase in magnetic parameter leads to an increase in velocity, skin-friction and rate of heat transfer and a fall in temperature. 相似文献
925.
The points raised by Lorenz-Petzold (1985) on our paper (1983) are discussed. It is shown that the conclusions drawn by him are not substantiated. 相似文献
926.
Assuming that the initial state of the Universe can be simulated by a thin large-scale homogeneous ambiplasma described by fluid type equations for charged particles (both matter and antimatter particles), stability calculations have been carried out of the various normal modes which might be supported by such a system. The present simplified analysis does not lead to the formation of matter-antimatter symmetric domains smaller than the size of the proto-metagalaxy (Alfvén, 1981) from the initial state of the Universe. 相似文献
927.
A study of the slowly rotating cosmological universe filled with viscous fluid has been made by assuming the matter angular
velocity Ω is proportional to the metric angular velocity Ω and the Universe is expanding under the Hubble's law. The physical
properties of the solutions obtained are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
928.
In this paper, similarity solutions for the propagation of strong-plane shock waves in optically-thin grey atmospheres are obtained in the presence of a magnetic field. Density and magnetic field are constant in the undisturbed gaseous medium in front of the shock. Planck's diffusion approximation has been taken into account in this problem and a comparative study has been made between the results of ordinary gasdynamics and magnetogasdynamics. 相似文献
929.
J. B. Singh 《Astrophysics and Space Science》1982,87(1-2):347-355
Self-similar flows of self-gravitating gas behind a spherical shock wave which are driven out by a propelling contact surface, propagating in a nonuniform atmosphere at rest, are investigated. The total energy content of the flow between a shock front and contact surface is taken to be time-dependent. In brief, the self-similar homothermal flows of self-gravitating gas behind a shock wave and Roche's model case are also studied in the present paper. 相似文献
930.