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981.
Ivar Aavatsmark 《Computational Geosciences》2007,11(3):199-206
Control-volume formulations for elliptic equations often use two-point flux stencils, even for skew grids. Any two-point flux
stencil may be interpreted as a multipoint flux stencil. This yields a definition of the permeability (or conductivity) tensor.
Formulas for calculating the permeability tensor, based on the user-specified quantities in the two-point flux stencil, are
given. Numerical test examples demonstrate the validity of the derivation.
相似文献
982.
983.
984.
985.
The spaceborne laser ranging (or lasering) system provides a method of precise positioning of a large number of points on
the earth's surface in a short period of time. That is, a measure of the relative location of geodetic markers from a space
platform can maintain horizontal and vertical control to 2 to 5 cm. At this level of control, small earth surface crustal
motions should be detectable. Development of a model for the strain field can be constructed. Furthermore, the spaceborne
lasering system can survey an area in a very short period of time (one to two weeks) and resurvey the area as required.
System design parameters are now being established by NASA for a possible test flight aboard the Shuttle in 1982. These include
design specifications of economical corner cubes for ground retroreflectors coupled with the evolution of engineering model
to flight model development. If the experiment of the Shuttle proves to be successful, it is hoped to put the laser in a free
flight satellite. This paper presents the results of a simulated analysis for this latter case.
The system is conceived as an orbiting ranging device with a ground base grid of reflectors or transponders (spacing 10 to
30 km), which are projected to be of low cost (maintenance-free and unattended) and which will permit the saturation of a
local area to obtain data useful to monitor crustal movements. The test network includes 75 stations with roughly half of
them on either side of the San Andreas fault zone. Critical study comparatively evaluates various observational schemes and
statistically analyzed crustal motion recovery.
The study considers laser radar as the main ranging system pending final selection from many possible candidates. The satellite
orbit is inclined at 110° and slightly eccentric (e=0.04) with orbital altitudes varying from 370 km to 930 km.
The results indicate that the geometric mode (simultaneous ranging) with a minimum of five grid and three distant (fundamental)
stations and mixed ranging to satellite and airplane seems to be most promising. The fundamental stations are distinguished
from the grid station in their location and this location should be “distant” enough from the area of crustal movement so
that they can be considered stationary over the time span of the motion involved.
Presented at the 1977 I.A.G. International Symposia on Satellite Geodesy, Budapest, Hungary, June 28–July 1, and on Recent
Crustal Movements, Palo Alto, California, USA, July 25–30. 相似文献
986.
In conventional seismic hazard analysis, uniform distribution over area and magnitude range is assumed for the evaluation of source seismicity which is not able to capture peculiar characteristic of near-fault ground motion well. For near-field hazard analysis, two important factors need to be considered: (1) rupture directivity effects and (2) occurrence of scenario characteristic ruptures in the nearby sources. This study proposed a simple framework to consider these two effects by modifying the predictions from the conventional ground motion model based on pulse occurrence probability and adjustment of the magnitude frequency distribution to account for the rupture characteristic of the fault. The results of proposed approach are compared with those of deterministic and probabilistic seismic hazard analyses. The results indicate that characteristic earthquake and directivity consideration both have significant effects on seismic hazard analysis estimates. The implemented approach leads to results close to deterministic seismic hazard analysis in the short period ranges (T < 1.0 s) and follows probabilistic seismic hazard analysis results in the long period ranges (T > 1.0 s). Finally, seismic hazard maps based on the proposed method could be developed and compared with other methods. 相似文献
987.
988.
The cable shovel is widely used in surface mining. High operating and ownership costs necessitate efficient use of the cable
shovel. Operator practices have long been suspected to contribute towards the inefficient use of the shovel. Crowd arm and
hoist rope speeds are key measures of operator practices. The objective of this work is to find the crowd arm and hoist rope
speeds for optimal shovel performance for given initial conditions and material properties. Shovel kinematics and dynamic modeling, using shovel
geometry and the simultaneous constraint method, respectively, have been employed to build models of the excavation process.
Dynamic models of the shovel payload and the material cutting resistance have also been developed using geometric simulation
and passive soil pressures techniques, respectively. These models are solved numerically by combining Runge–Kutta and Gaussian
elimination algorithms to compute the work done and the resistive forces during shovel excavation. The algorithms have been
combined into a shovel simulator. The simulator has been used to simulate the P&H 2100BL shovel. The simulation results indicate
that input energy and digging time increase with increasing crowd arm and decreasing hoist rope speeds. The input energy per
unit loading rate is proposed as an appropriate measure of shovel performance. High energy per unit loading rate occurs for
high crowd speeds and low hoist rope speeds. For the simulated conditions and crowd arm and hoist rope speeds ranging from
0.25 to 0.5 ms−1 and 0.5 to 0.7 ms−1, respectively, the optimal crowd arm and hoist rope speeds were found to be 0.25 ms−1 and 0.7 ms−1, respectively, and the objective function value was 0.21 KJs/kg. This work establishes, theoretically, the fact that operator
practices have an effect on shovel performance and is useful in establishing optimum practices. The results are the initial
steps towards full automation of the excavation process. 相似文献
989.
The extensive volcanic activity of Rajmahal occurred during early Cretaceous (~117 Ma). Potentially perspective Gondawana sediments containing coal seam is partially covered by these basalts. Basalts as well as coal are already known to be of immense economic importance over Rajmahal traps. The present study mainly deals with delineation of basaltic lava flows and associated coal layers using the Audio-magneto-telluric (AMT) study in the south central region of Rajmahal traps near Suri, West Bengal, India. Initially, the field situations have been simulated using forward model with top alluvium cover followed by basaltic lava flows, a wedge shaped inter-trappean sedimentary formation with second basaltic lava flows and basement at the bottom. The model was constrained using available litholog. The model study reveals the presence of moderately resistive basalts, relatively conductive inter-trappeans and the basement, except the top alluvium layer and thin inter-trappeans. Subsequently, threeAMT sounding have been carried out over Cholaguria, Hatgacha and Pachami, Suri, West Bengal. The field AMT study reveals three basaltic lava flows with varying thickness from ~40m to ~350m and composite thickness of ~620m to ~640m, which match well with the published borehole litholog. The inter-trappeans have been identified at 500m to 620m, 310m to 400m and 500m to 640m depths over Cholaguria, Hatgacha and Pachami, respectively. It is interesting to mention that the identified inter-trappeans are inferred to be coal/shaly-coal which are matching very well with the published borehole lithologs. 相似文献
990.
TANGYa XIEJiasui SUNHui 《山地科学学报》2004,1(1):38-45
Dry valleys are a striking geographic landscape in Hengduan Mountains Region and are characterized by low rainfall, desert type of vegetation and fragile environment. Past efforts and resources have been concentrated mainly on rehabilitation of degraded ecosystem and fragile environment, particularly reforestation, while socio-economic development has been largely overlooked. Despite successes in pocket areas, the overall trend of unsustainability and environmental deterioration are continuing. It is important to understand that uplift of the Tibetan Plateau is the root cause of development of dry valleys, and development and formation of dry valleys is a natural process. Human intervention has played a secondary role in development of dry valleys and degradation of dry valleys though human intervention in many cases has speeded up environmental degradation of the dry valleys. It is important to understand that dry valleys are climatic enclaves and an integrated approach that combines rehabilitation of degraded ecosystems and socio-economic development should be adopted if the overall goal of sustainable development of dry valleys is to be achieved. Promotion of niche-based cash crops, rural energy including hydropower, solar energy, biogas and fuelwood plantation is recommended as the priority activities. 相似文献