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741.
The aim of this study is to estimate the capabilities of forecasting the yield of wheat using an artificial neural network combined with multi-temporal satellite data acquired at high spatial resolution throughout the agricultural season in the optical and/or microwave domains. Reflectance (acquired by Formosat-2, and Spot 4–5 in the green, red, and near infrared wavelength) and multi-configuration backscattering coefficients (acquired by TerraSAR-X and Radarsat-2 in the X- and C-bands, at co- (abbreviated HH and VV) and cross-polarization states (abbreviated HV and VH)) constitute the input variable of the artificial neural networks, which are trained and validated on the successively acquired images, providing yield forecast in near real-time conditions. The study is based on data collected over 32 fields of wheat distributed over a study area located in southwestern France, near Toulouse. Among the tested sensor configurations, several satellite data appear useful for the yield forecasting throughout the agricultural season (showing coefficient of determination (R2) larger than 0.60 and a root mean square error (RMSE) lower than 9.1 quintals by hectare (q ha−1)): CVH, CHV, or the combined used of XHH and CHH, CHH and CHV, or green reflectance and CHH. Nevertheless, the best accurate forecast (R2 = 0.76 and RMSE = 7.0 q ha−1) is obtained longtime before the harvest (on day 98, during the elongation of stems) using the combination of co- and cross-polarized backscattering coefficients acquired in the C-band (CVV and CVH). These results highlight the high interest of using synthetic aperture radar (SAR) data instead of optical ones to early forecast the yield before the harvest of wheat. 相似文献
742.
Xuejie GAO Ying SHI Zhenyu HAN Meili WANG Jia WU Dongfeng ZHANG Ying XU Filippo GIORGI 《大气科学进展》2017,34(4):441-455
A long-term simulation for the period 1990–2010 is conducted with the latest version of the International Centre for Theoretical Physics' Regional Climate Model(RegCM4), driven by ERA-Interim boundary conditions at a grid spacing of 25 km. The Community Land Model(CLM) is used to describe land surface processes, with updates in the surface parameters,including the land cover and surface emissivity. The simulation is compared against observations to evaluate the model performance in reproducing the present day climatology and interannual variability over the 10 main river basins in China,with focus on surface air temperature and precipitation. Temperature and precipitation from the ERA-Interim reanalysis are also considered in the model assessment. Results show that the model reproduces the present day climatology over China and its main river basins, with better performances in June–July–August compared to December–January–February(DJF).In DJF, we find a warm bias at high latitudes, underestimated precipitation in the south, and overestimated precipitation in the north. The model in general captures the observed interannual variability, with greater skill for temperature. We also find an underestimation of heavy precipitation events in eastern China, and an underestimation of consecutive dry days in northern China and the Tibetan Plateau. Similar biases for both mean climatology and extremes are found in the ERA-Interim reanalysis, indicating the difficulties for climate models in simulating extreme monsoon climate events over East Asia. 相似文献
743.
744.
FBS-3A型反馈式宽频带地震计是目前广泛使用的一种地震计.对其传递函数开展相关研究,对仪器的使用、观测数据的分析,以及仪器的设计开发具有十分重要的实际意义.本文运用系统分析方法,从阐明仪器的工作原理入手,详尽地推导了该地震计的传递函数(包括标定过程的传递函数和测量过程的传递函数);在此基础上,分析了其零、极点在复频域的分布情况,从而提供了将该地震计系统从一个高阶系统简化成为一个二阶系统的依据.此外,还以传递函数为基础,对该地震计的频率特性进行了数学仿真计算. 相似文献
745.
IntroductionFBS-3A feedback broadband seismometer is a sensor suitable for digital telemetered seismic network observation, which was developed in a key project among the (Eighth Five-Year Plan( to meet the demand for the development of earthquake and premonitor digital observation experiment system (ZHAO, et al, 1997; ZHUANG, 1995).FBS-3A is quite different from conventional mechanical seismometers because electronic feedback technology is applied to it, as a result the measurement ba… 相似文献
746.
以吉林省长白山地区的天然浮石为原料,成功地合成了13X型分子筛,对其合成路线,反应条件进行了研究,确定了合成13X型分子筛的最佳工艺条件,并通过X射线衍射法及差热分析等手段证明了产物的结构 相似文献
747.
M. Awad 《Environmental Geology》1997,33(1):54-60
Rapid population growth, urbanization expansion of rural settlements, industrial activity, intensively irrigated agriculture,
pesticides consumption, and continuous dumping of hazardous waste in the Amman-Zerqa Basin since 1967 are the major factors
threatening the quality of the environment. Thus, an environmental recommendation is proposed to protect the environment and
water resources in the study area. The chemical analysis of the springs in the study area showed salinity increasing with
time, which indicates water pollution affecting these springs. The laboratory analyses indicated that the quality of the treated
waste water of Khirbet Es-Samra Treatment plant conforms to the World Health Organization (WHO) standards from the chemical,
physical, and the microbiological point of view. Toxic elements such as cadmium identified in the surface water flow of the
basin are in concentrations higher than those recommended by WHO
Received: 30 January 1997 · Accepted: 30 June 1997 相似文献
748.
W. A. Mulder 《Computational Geosciences》1997,1(1):85-108
Simulation of wave propagation for seismic purposes is usually restricted to a small portion of the earth. Artificial boundary
conditions are required where the subsurface model is truncated. Absorbing boundaries should ensure that waves hitting the
artificial boundaries are not reflected. The vast amount of literature on the subject suggests that “good” conditions have
not been found, and only “reasonable” solutions exist. A cursory overview of existing and a few new ideas is presented that
may guide the construction of suitable boundary conditions. Because the intended application of the boundary conditions was
a high-order finite-difference code that runs on a parallel computer, we have restricted our attention to local boundary conditions.
A fundamental problem in the design of accurate local boundary conditions is pointed out: accuracy is required to keep the
amount of reflected energy small, but at the same time allows for growing low-frequency modes. We have settled for Higdon’s
boundary conditions. Higdon proposes to include some damping to suppress the growing low-frequency modes. We show that third-order
conditions provide acceptable results for the simple scalar wave equation and the acoustic equation. In the elastic case,
an additional low-frequency growing mode may occur. This mode can be suppressed by using a dissipative boundary scheme and
by increasing the amount of damping. The increase in damping results in an increase in the amount of reflected energy, which
is larger than in the scalar case. Numerical experiments exhibit a reasonable performance, although some improvement would
be useful, particularly in the anisotropic elastic case.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
749.
750.
赵茂泰 《武汉大学学报(信息科学版)》1991,(3)
本文在论述模块式仪器系统一般总体结构的基础上,着重介绍了模块式DVM的研究和设计,包括硬件构成,软面板和软件系统。 相似文献