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971.
Analysis of Large Flexible Body Deformation in Multibody Systems Using Absolute Coordinates 总被引:5,自引:0,他引:5
To consider large deformation problems in multibody system simulations afinite element approach, called absolute nodal coordinate.formulation,has been proposed. In this formulation absolute nodal coordinates andtheir material derivatives are applied to represent both deformation andrigid body motion. The choice of nodal variables allows a fullynonlinear representation of rigid body motion and can provide the exactrigid body inertia in the case of large rotations. The methodology isespecially suited for but not limited to modeling of beams, cables andshells in multibody dynamics.This paper summarizes the absolute nodal coordinate formulation for a 3D Euler–Bernoulli beam model, in particular the definition of nodal variables, corresponding generalized elastic and inertia forces and equations of motion. The element stiffness matrix is a nonlinear function of the nodal variables even in the case of linearized strain/displacement relations. Nonlinear strain/displacement relations can be calculated from the global displacements using quadrature formulae.Computational examples are given which demonstrate the capabilities of the applied methodology. Consequences of the choice of shape.functions on the representation of internal forces are discussed. Linearized strain/displacement modeling is compared to the nonlinear approach and significant advantages of the latter, when using the absolute nodal coordinate formulation, are outlined. 相似文献
972.
A system for person-independent classification of hand postures against complex backgrounds in video images is presented. The system employs elastic graph matching, which has already been successfully applied for object and face recognition. We use the bunch graph technique to model variance in hand posture appearance between different subjects and variance in backgrounds. Our system does not need a separate segmentation stage but closely integrates finding the object boundaries with posture classification. 相似文献
973.
Matthias Zobel Joachim Denzler Benno Heigl Elmar Nöth Dietrich Paulus Jochen Schmidt Georg Stemmer 《Machine Vision and Applications》2003,14(1):26-34
Abstract. This contribution introduces MOBSY, a fully integrated, autonomous mobile service robot system. It acts as an automatic dialogue-based
receptionist for visitors to our institute. MOBSY incorporates many techniques from different research areas into one working
stand-alone system. The techniques involved range from computer vision over speech understanding to classical robotics.
Along with the two main aspects of vision and speech, we also focus on the integration aspect, both on the methodological
and on the technical level. We describe the task and the techniques involved. Finally, we discuss the experiences that we
gained with MOBSY during a live performance at our institute. 相似文献
974.
Georg Jung John Hatcliff 《International Journal on Software Tools for Technology Transfer (STTT)》2007,9(5-6):417-427
Large distributed systems, including real-time embedded systems, are increasingly being built using sophisticated middleware
frameworks. Communication in such systems is often realized using in terms of asynchronous events whose propagation is implemented
by an underlying publish/subscribe service that hooks components into a generic event communication channel. Event correlation—a mechanism for monitoring and filtering events—has been introduced in some of these systems as an effective technique for
reducing network traffic and computation time. Unfortunately, even though event correlation is used heavily in frameworks
such as ACE/TAO’s real-time event-channel and in mission critical contexts such as Boeing’s Bold Stroke avionics middleware,
the industry standard CORBA Component Model (CCM) does not include a specification of event correlation. While previous proposals
for event correlation usually offer sophisticated facilities to detect combinations in the stream of incoming events, they
have not been constructed to fit within the CCM type system, and they offer relatively little support for transforming and
rearranging filtered events into meaningful output events. In this paper, we present the design rationale, syntax, and semantics
for a new and highly flexible model for event correlation that is designed for integration into the CCM type system. Our model
has been integrated and tested in the Cadena development and analysis framework, which has been designed to support development
of mission-control applications in the Boeing Bold Stroke framework.
This work was supported in part by the US Army Research Office (DAAD190110564), by DARPA/IXO’s PCES program (AFRL Contract
F33615-00-C-3044), by NSF (CCR-0306607) and by Lockheed Martin. 相似文献
975.
As a prerequisite for developing neural control for walking machines that are able to autonomously navigate through rough
terrain, artificial structure evolution is used to generate various single leg controllers. The structure and dynamical properties
of the evolved (recurrent) neural networks are then analysed to identify elementary mechanisms of sensor-driven walking behaviour.
Based on the biological understanding that legged locomotion implies a highly decentralised and modular control, neuromodules
for single, morphological distinct legs of a hexapod walking machine were developed by using a physical simulation. Each of
the legs has three degrees of freedom (DOF). The presented results demonstrate how extremely small reflex-oscillators, which
inherently rely on the sensorimotor loop and e.g. hysteresis effects, generate effective locomotion. Varying the fitness function
by randomly changing the environmental conditions during evolution, neural control mechanisms are identified which allow for
robust and adaptive locomotion. Relations to biological findings are discussed. 相似文献
976.
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979.
Georg Lausen 《Information Systems》1983,8(4):291-301
Formal aspects of optimistic concurrency control in a multiple version database system are discussed. It is distinguished between element-optimistic and set-optimistic methods. In an element-optimistic method the unit of scheduling for the concurrency control is one action/transaction, while in a set-optimistic method a set of transactions is scheduled. The underlying decision problems of serializability are defined and shown to be NP-complete in a model, which is typical for most modern transaction oriented database management systems. Therefore it is most probable, that both optimistic concurrency control types cannot be implemented efficiently in the general case. 相似文献
980.
Gang Luo von Bochmann G. Petrenko A. 《IEEE transactions on pattern analysis and machine intelligence》1994,20(2):149-162
Presents a method of generating test sequences for concurrent programs and communication protocols that are modeled as communicating nondeterministic finite-state machines (CNFSMs). A conformance relation, called trace-equivalence, is defined within this model, serving as a guide to test generation. A test generation method for a single nondeterministic finite-state machine (NFSM) is developed, which is an improved and generalized version of the Wp-method that generates test sequences only for deterministic finite-state machines. It is applicable to both nondeterministic and deterministic finite-state machines. When applied to deterministic finite-state machines, it yields usually smaller test suites with full fault coverage than the existing methods that also provide full fault coverage, provided that the number of states in implementation NFSMs are bounded by a known integer. For a system of CNFSMs, the test sequences are generated in the following manner: a system of CNFSMs is first reduced into a single NFSM by reachability analysis; then the test sequences are generated from the resulting NFSM using the generalized Wp-method 相似文献