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901.
The constitutive modeling of cyclic plasticity of soils has made great progress, especially in the area of sands liquefaction modeling. Nowadays, the problem of rutting of flexible pavements linked to permanent deformations occurring in the unbound layers is taken into account only by empirical formulas. This paper presents an elastoplastic model with both isotropic and kinematic hardening. The yield surface, plastic potential, and isotropic hardening are based on a model for sands, which takes into account the influence of the initial void ratio and of the mean stress on the mechanical behavior. A kinematic hardening has been added in order to take into account the mechanical behavior of the material for large cycle numbers. A complete model is then developed, simulations are presented, and comparisons with repeated load triaxial tests carried out on a subgrade soil (clayey sand), have been made. These comparisons underline the capabilities of the model to take into account the monotonic, cyclic, and ratchetting behavior of unbound materials for roads. 相似文献
902.
The optimization of a new or partially existing urban drainage system may be modeled as a subproblems sequence of layout and optimal design within the discrete search space. The design optimization, incorporating the optimal selection of the pumping stations, intermediate manholes, pipe sections, and installation depths, for a general system fixed layout in plan, is a high level sequential decision problem which may be efficiently solved deterministically through a multilevel dynamic programming model. The optimal general layout may be selected in a deterministic way by means of a simple economical comparison of all plan solutions having optimized designs, for small to medium sized systems (if the specific restrictions of the applications are appropriately exploited) in practicable computer time. For larger dimension networks, where it is clearly impossible to achieve plan optimization with full enumeration (which is a NP complete), stochastic search models can be used. For the subproblem layout, an effective enumeration model is presented; the results of a stochastic model proposed previously, using simulated annealing for an application example, are compared and discussed in detail. 相似文献
903.
Modified Kostiakov Infiltration Function: Accounting for Initial and Boundary Conditions 总被引:1,自引:0,他引:1
A. Furman A. W. Warrick D. Zerihun C. A. Sanchez 《Canadian Metallurgical Quarterly》2006,132(6):587-596
The effect of specific initial and boundary conditions is generally not considered when applying the Kostiakov infiltration functions. A methodology is developed to account for changes in water levels and initial soil moisture. First, Richards’ equation is solved numerically to generate a database of one-dimensional infiltration values, with varying initial (water content or pressure head) and boundary (ponding depth) conditions for three contrasting soils. These are then used to calibrate corresponding coefficients for modified Kostiakov models and, by considering linear regressions, to obtain simple correction factors. Results show that the correction factors are not universally valid, and only the correction to the Kostiakov k parameter shows statistically consistent applicability. However, examples demonstrate potentially significant improvement in the accuracy of irrigation models by correcting the Kostiakov equation to account for initial and boundary conditions. 相似文献
904.
Forward directivity effects in the near-fault region produce pulse-type motions that differ significantly from ordinary ground motions that occur at greater distances from the causative fault. Current code site factors are based on empirical observations and analyses involving less intense nonpulse ordinary ground motions. Nonlinear site response analyses with bidirectional shaking are performed using representative site profiles to quantify seismic site response effects for intense near-fault motions resulting from forward directivity. Input rock motions are represented with simplified velocity pulses that characterize the amplitude and period of forward directivity motions. Results indicate that site response affects both the amplitude and period of forward directivity pulses, and hence, local site conditions should be considered when evaluating seismic designs in the near-fault region. Stiff soil sites tend to amplify the peak ground velocity and increase the period of pulse-type motions, particularly, when the period of the rock motion coincides with the degraded period of the site. Amplification is limited at soft soil sites by the dynamic strength of the weak soil, so attenuation occurs for intense input motions. This nonlinearity is not reflected in the site factors in current building codes. Guidance is provided for estimating the amplitude and pulse period for velocity pulses at soil sites. 相似文献
905.
Novel Approach to Integration of Numerical Modeling and Field Observations for Deep Excavations 总被引:1,自引:0,他引:1
Youssef M. A. Hashash Camilo Marulanda Jamshid Ghaboussi Sungmoon Jung 《Canadian Metallurgical Quarterly》2006,132(8):1019-1031
Precedent and observation of performance are an essential part of the design and construction process in geotechnical engineering. For deep urban excavations designers rely on empirical data to estimate potential deformations and impact on surrounding structures. Numerical simulations are also employed to estimate induced ground deformations. Significant resources are dedicated to monitor construction activities and control induced ground deformations. While engineers are able to learn from observations, numerical simulations have been unable to fully benefit from information gained at a given site or prior excavation case histories in the same area. A novel analysis method, self-learning in engineering simulations (SelfSim), is introduced to integrate precedent into numerical simulations. SelfSim is an inverse analysis technique that combines finite element method, biologically inspired material models, and field measurements. SelfSim extracts relevant constitutive soil information from field measurements of excavation response such as lateral wall deformations and surface settlement. The resulting soil model, used in a numerical analysis, provides correct ground deformations and can be used in estimating deformations of similar excavations. The soil model can continuously evolve using additional field information. SelfSim is demonstrated using two excavation case histories in Boston and Chicago. 相似文献
906.
Using the recorded response at two vertical array sites, the SimSoil model presented in the companion paper is evaluated. The SimSoil model, which describes the small strain nonlinear behavior of granular materials, is implemented as a material model in AMPLE2000, a nonlinear, one-dimensional site response analysis code. Shear wave velocity profiles and laboratory test data available for both the La Cienega site, which was instrumented over 250?m, and the Lotung site, which was instrumented over 47?m, were used to determine SimSoil model parameters. Predictions from AMPLE2000 are compared with the measured response at several elevations for earthquakes that resulted in both nonlinear and nearly linear soil behavior. Using the available laboratory data and known input motions, the predictions of the response at these sites matched the recorded response well for varied magnitudes of shaking with a single set of parameters for each site. 相似文献
907.
This paper describes the proportional demand method and the target demand method, two techniques for adjusting estimated demands in hydraulic models of water distribution networks to produce solutions that are consistent with available supervisory control and data acquisition (SCADA) data. The two techniques assume that pipe resistances and SCADA data are accurate and that the combination of SCADA data and demand estimates produce overdetermined problems. Nodal demands are regarded as stochastic variables which fluctuate about an estimated mean value. The method of weighted least squares is used to obtain solutions that satisfy all of the constraints imposed by SCADA data with adjusted nodal demands that most closely resemble the estimates. The methods are intended for use in real-time modeling but are limited to quasi-steady state flow. The paper demonstrates the methods on two example problems. 相似文献
908.
Christian Licoppe 《Computer Supported Cooperative Work (CSCW)》2006,15(2-3):123-148
Our case study explores the extent to which a “Distributed Cognition”-like ethnographic approach can be used to analyze situations which are not at first sight compatible with the precepts of computational cognition. In the first part of the paper, we analyze the collective listening of phone calls in a helpline. We show why collective listening can be considered a “distributed collective practice”, with a mode of coordination based on repeated verbal re-enactments of difficult phone calls, rather than upon the discrete computational steps normally assumed in the standard model. In the second part of the paper, we analyse the organizational and interactional learning which takes place when collective listening is re-mediated by using e-mail exchanges rather than telephone conversations to communicate distress. Our conclusion discusses critically the viability of the distribution model in a context of collective listening. 相似文献
909.
We develop a method for the estimation of articulated pose, such as that of the human body or the human hand, from a single
(monocular) image. Pose estimation is formulated as a statistical inference problem, where the goal is to find a posterior
probability distribution over poses as well as a maximum a posteriori (MAP) estimate. The method combines two modeling approaches,
one discriminative and the other generative. The discriminative model consists of a set of mapping functions that are constructed
automatically from a labeled training set of body poses and their respective image features. The discriminative formulation
allows for modeling ambiguous, one-to-many mappings (through the use of multi-modal distributions) that may yield multiple
valid articulated pose hypotheses from a single image. The generative model is defined in terms of a computer graphics rendering
of poses. While the generative model offers an accurate way to relate observed (image features) and hidden (body pose) random
variables, it is difficult to use it directly in pose estimation, since inference is computationally intractable. In contrast,
inference with the discriminative model is tractable, but considerably less accurate for the problem of interest. A combined
discriminative/generative formulation is derived that leverages the complimentary strengths of both models in a principled
framework for articulated pose inference. Two efficient MAP pose estimation algorithms are derived from this formulation;
the first is deterministic and the second non-deterministic. Performance of the framework is quantitatively evaluated in estimating
articulated pose of both the human hand and human body.
Most of this work was done while the first author was with Boston University. 相似文献
910.
Plamen Angelov Costas Xydeas 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2006,10(9):836-849
A systematic classification of the data-driven approaches for design of fuzzy systems is given in the paper. The possible ways to solve this modelling and identification problem are classified on the basis of the optimisation techniques used for this purpose. One algorithm for each of the two basic categories of design methods is presented and its advantages and disadvantages are discussed. Both types of algorithms are self-learning and do not require interaction during the process of fuzzy model design. They perform adaptation of both the fuzzy model structure (rule-base) and the parameters. The indirect approach exploits the dual nature of Takagi-Sugeno (TS) models and is based on recently introduced recursive clustering combined with Kalman filtering-based procedure for recursive estimation of the parameter of the local sub-models. Both algorithms result in finding compact and transparent fuzzy models. The direct approach solves the optimisation problem directly, while the indirect one decomposes the original problem into on-line clustering and recursive estimation problems and finds a sub-optimal solution in real-time. The later one is computationally very efficient and has a range of potential applications in real-time process control, moving images recognition, autonomous systems design etc. It is extended in this paper for the case of multi-input–multi-output (MIMO systems). Both approaches have been tested with real data from an engineering process. 相似文献