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191.
Low Energy Transfer to the Moon 总被引:15,自引:0,他引:15
W. S. Koon M. W. Lo J. E. Marsden S. D. Ross 《Celestial Mechanics and Dynamical Astronomy》2001,81(1-2):63-73
In 1991, the Japanese Hiten mission used a low energy transfer with a ballistic capture at the Moon which required less Vthan a standard Hohmann transfer. In this paper, we apply the dynamical systems techniques developed in our earlier work to reproduce systematically a Hiten-like mission. We approximate the Sun–Earth–Moon-spacecraft 4-body system as two 3-body systems. Using the invariant manifold structures of the Lagrange points of the 3-body systems, we are able to construct low energy transfer trajectories from the Earth which execute ballistic capture at the Moon. The techniques used in the design and construction of this trajectory may be applied in many situations. 相似文献
192.
Unified Approach to Photon-Counting Microlaser Rangers, Transponders, and Altimeters 总被引:1,自引:0,他引:1
John J. Degnan 《Surveys in Geophysics》2001,22(5-6):431-447
Unlike current manned systems, NASA's next generation SLR2000 Satellite Laser Ranging (SLR) station is fully autonomous, eye-safe, relatively compact and inexpensive, and, during daytime tracking, operates at signal-to-noise ratios several orders of magnitude below unity. Tiny, passivelyQ-switched microlasers generate ultra-short pulses with output energies on the order of 100 J at few kHz rates to achieve mm-levelranging precision to satellite altitudesof 20,000 km. Special ranging receivers, combined with Poisson statistical analysis of the received photon distribution, enable the system to rapidly and reliably identify and extract the single photon laser echoes from the solar background. The enhanced rate of return, combined with a uniform signal strength, can actually drive down both systematic and random range errors. The new SLR2000 technology has already spawned exciting new applications. Compact microlaser altimeters, capable of mapping the surface of a planet or other celestial body at multikilohertz rates, is one such application, and a high altitude, airborne version is currently being developed under NASA's Instrument Incubator Program. Interplanetary microlaser transponders would be capable of performing decimeter ranging or subnanosecond time transfer to spacecraft throughout the inner Solar System, resulting in improved knowledge of planetary motions and librations and enhanced General Relativity experiments. 相似文献
193.
Chironomid remains from Big Lake, British Columbia were analysed and paleosalinities were estimated using a pre-existing transfer function and several developed using new regression methods. A two component partial-least-squares model (PLS-2) had the highest coefficient of determination (R2
(Jackknifed) = 0.75) and lowest root-mean-squared error-of-prediction (RMSEP). As compared to the pre-existing model, it was also less sensitive to the influence of rare taxa. Nevertheless, the marginally larger R2
(Jackknifed) and lower RMSEP do not clearly identify a single best model. The models were applied to Big, Mahoney and Kilpoola lakes, revealing the sensitivity of paleosalinity inferences to model selection. A synopsis of chironomid-based paleosalinities in British Columbia and their correspondence with other paleoclimatic data are presented and discussed. 相似文献
194.
Multivariate numerical analyses (DCA, CCA) were used to study the distribution of chironomids from surface sediments of 100 lakes spanning broad ecoclimatic conditions in northern Swedish Lapland. The study sites range from boreal forest to alpine tundra and are located in a region of relatively low human impact. Of the 19 environmental variables measured, ordination by CCA identified mean July air temperature as one of the most significant variables explaining the distribution and the abundance of chironomids. Lossonignition (LOI), maximum lake depth and mean January air temperature also accounted for significant variation in chironomid assemblages. A quantitative transfer function was created to estimate mean July air temperature from sedimentary chironomid assemblages using weightedaveraging partial least squares regression (WAPLS). The coefficient of determination was relatively high (r2 = 0.65) with root mean squared error of prediction (RMSEP, based on jack-knifing) of 1.13 °C and maximum bias of 2.1 °C, indicating that chironomids can provide useful quantitative estimates of past changes in mean July air temperature. The paper focuses mainly on the relationship between chironomid composition and July air temperature, but the relationship to LOI and depth are also discussed. 相似文献
195.
Syntectonic plutons emplaced in shallow crust often contain intermediate-to low-temperature deformation microstructures but
lack a high-temperature, subsolidus deformation fabric, although the relict magmatic fabric is preserved. The Proterozoic
Vellaturu granite emplaced at the eastern margin of the northern Nallamalai fold belt, south India during the late phase of
regional deformation has a common occurrence of intermediate-to low-temperature deformation fabric, superimposed over magmatic
fabric with an internally complex pattern. But high-T subsolidus deformation microstructure and fabric are absent in this
pluton. The main crystal plastic deformation and fluid enhanced reaction softening was concentrated along the margin of the
granite body. Resulting granite mylonites show Y-maximum c-axis fabric in completely recrystallized quartz ribbonds, dynamic recrystallization of perthites, and myrmekite indicative
of fabric development under intermediate temperature (∼ 500–400°C). The weakly-deformed interior shows myrmekite, feldspar
microfracturing and limited bulging recrystallization of quartz. The abundance of prism subgrain boundaries is indicative
of continuing deformation through low-temperature (∼ 300°C). The relative rates of cooling influenced by advective heat transfer
and deformation of the pluton seem to control the overall subsolidus fabric development. The rapid advective heat transfer
from the interior in the early stages of subsolidus cooling was followed by slow cooling through intermediate temperature
window as a well-developed phyllosilicate rich mylonitic skin around the granite body slowed down conductive heat loss. Low-T
crystal plastic deformation of quartz was effected at a late stage of cooling and deformation of the shallow crustal granite
body emplaced within the greenschist facies Nallamlai rocks. 相似文献
196.
A macroscopic transport model is developed, following the Taylor shear dispersion analysis procedure, for a 2D laminar shear flow between parallel plates possessing a constant specified concentration. This idealized geometry models flow with contaminant dissolution at pore-scale in a contaminant source zone and flow in a rock fracture with dissolving walls. We upscale a macroscopic transient transport model with effective transport coefficients of mean velocity, macroscopic dispersion, and first-order mass transfer rate. To validate the macroscopic model the mean concentration, covariance, and wall concentration gradient are compared to the results of numerical simulations of the advection–diffusion equation and the Graetz solution. Results indicate that in the presence of local-scale variations and constant concentration boundaries, the upscaled mean velocity and macrodispersion coefficient differ from those of the Taylor–Aris dispersion, and the mass transfer flux described by the first-order mass transfer model is larger than the diffusive mass flux from the constant wall. In addition, the upscaled first-order mass transfer coefficient in the macroscopic model depends only on the plate gap and diffusion coefficient. Therefore, the upscaled first-order mass transfer coefficient is independent of the mean velocity and travel distance, leading to a constant pore-scale Sherwood number of 12. By contrast, the effective Sherwood number determined by the diffusive mass flux is a function of the Peclet number for small Peclet number, and approaches a constant of 10.3 for large Peclet number. 相似文献
197.
Accurate modeling of storage of carbon dioxide (CO2) in heterogeneous aquifers requires experiments of the capillary pressure as function of temperature and pressure. We present a method with which static drainage and imbibition capillary pressures can be measured continuously as a function of saturation at various temperature (T) and pressure (P) conditions. The measurements are carried out at (T, P) conditions of practical interest. Static conditions can be assumed as small injection rates are applied. The capillary pressure curves are obtained for the unconsolidated sand–distilled water–CO2 system. The experimental results show a decrease of drainage and imbibition capillary pressure for increasing CO2 pressures and pronounced dissolution rate effects for gaseous CO2. Significant capillary pressure fluctuations and negative values during imbibition are observed at near critical conditions. The measurement procedure is validated by a numerical model that simulates the experiments. 相似文献
198.
山东省飞机增雨天气系统云水资源转化特征分析 总被引:5,自引:1,他引:5
利用水汽辐合法和水汽凝结法,对山东省1997-1999年春秋季18个降水过程的水汽辐合率、凝结率及降水效率等表征云水资源及其转化的特征量进行计算。分析了南方气旋、西北冷锋等主要降水天气系统以上特征量的地域分布和差别。可为人工增雨作业区域选择和航线设计提供气候背景。 相似文献
199.
200.