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991.
A method for estimating and validating the cumulative distribution of a function of random variables (independent or dependent) is presented and examined. The method creates a sequence of bounds that will converge to the distribution function in the limit for functions of independent random variables or of random variables of known dependencies. Moreover, an approximation is constructed from and contained in these bounds. Preliminary numerical experiments indicate that this approximation is close to the actual distribution after a few iterations. Several examples are given to illustrate the method. 相似文献
992.
Puttegowda Kiran Lehn David I. Park Jae H. Athanas Peter Jones Mark 《The Journal of supercomputing》2003,26(3):239-257
A distinguishing feature of reconfigurable computing over rapid prototyping is its ability to configure the computational fabric on-line while an application is running. Conventional reconfigurable computing platforms utilize commodity FPGAs, which typically have relatively long configuration times. Shrinking the configuration time down to the nanosecond region opens possibilities for rapid context switching and virtualizing the computational resources. An experimental context-switching FPGA, called the CSRC, has been created by BAE Systems, and gives researchers the opportunity to explore context-switching applications. This paper presents results obtained from constructing both control-driven and data-driven context switching applications on the CSRC device, along with unique properties of the run-time and compile-time environment. 相似文献
993.
We present a simple simulation of road growing dynamics that can generate global features as belt-ways and star patterns observed in urban transportation infrastructure. The road growing dynamics consist of two steps: Identifying the maximum transportation potential bewteen two locations within the city, followed by the generation of the least expensive road between these two locations. The simulation defines a previously missing component for modeling the co-evolution of urban settlement- and road systems as it can directly be coupled to existing urban settlement simulations. 相似文献
994.
David Corrall 《Requirements Engineering》1997,2(4):217-219
Conclusions It is asserted that current approaches and automated support for requirements engineering are not yet sufficient to build
today’s and tomorrow’s complex systems. Requirements engineering, itself intricately connected to system design and system
solution and not separate from either, needs to be embedded into a total systems engineering approach. This is the route to
systems engineering maturity. Software and systems engineering can and should learn from each other. 相似文献
995.
We address the problem of performing simultaneously reachability analysis and minimization of real-time transition systems represented by timed automata, i.e., automata extended with a finite set of clock variables. The transitions of the automaton may depend on the values of the clocks and may reset some of the clocks. An efficient algorithm is presented for minimizing a system with respect to a given initial partition that respects the enabling conditions of the transitions of the timed automaton. Our algorithm generates the portion of the minimized system that is reachable from a given initial configuration in time polynomial in the input and the size of the minimal reachable system. 相似文献
996.
Perry Fizzano David Karger Clifford Stein Joel Wein 《Journal of Parallel and Distributed Computing》1997,45(2):531
We give a distributed approximation algorithm for job scheduling in a ring architecture. In contrast to many other parallel scheduling models, the model we consider captures the influence of the underlying communications network by specifying that task migration from one processor to another takes time proportional to the distance between those two processors in the network. As a result, our algorithm must balance computational load and communication time. The algorithm is simple, requires no global control, and yields schedules of length at most 4.22 times optimal. We also give a lower bound on the performance of any distributed algorithm and the results of simulation experiments which suggest better performance than does our worst-case analysis. 相似文献
997.
Attila Bérces Ross M. Dickson Liangyou Fan Heiko Jacobsen David Swerhone Tom Ziegler 《Computer Physics Communications》1997,100(3):247-262
The Coupled Perturbed Kohn-Sham equations have been implemented in the Amsterdam Density Functional program package. Our implementation differs from previous ones in many ways. This program uses density fitting to calculate the Coulomb and exchange integrals. Further, all matrix elements of the Fock type matrix and its derivatives are calculated by numerical integration. The frozen core approximation is also implemented. Our implementation is approximately 10 times faster than a finite difference algorithm, and the absolute CPU times also compare favorably with other reported implementations. 相似文献
998.
Our general goal in this paper is to show how to implement in GAMS standard deterministic nonlinear macro models, and stochastic linear macro models with rational expectations. We will also present basic concepts on solution methods and policy analysis for these kinds of models. As a practical illustration, we will use some well known teaching and experimental models in the macroeconomic literature. 相似文献
999.
Saylor David M. Fridy Joseph El-Dasher Bassem S. Jung Kee-Young Rollett Anthony D. 《Metallurgical and Materials Transactions A》2004,35(7):1969-1979
Techniques are described that have been used to create a statistically representative three-dimensional model microstructure
for input into computer simulations using the geometric and crystallographic observations from two orthogonal sections through
an aluminum polycrystal. Orientation maps collected on the observation planes are used to characterize the sizes, shapes,
and orientations of grains. Using a voxel-based tessellation technique, a microstructure is generated with grains whose size
and shape are constructed to conform to those measured experimentally. Orientations are then overlaid on the grain structure
such that distribution of grain orientations and the nearest-neighbor relationships, specified by the distribution of relative
misorientations across grain boundaries, match the experimentally measured distributions. The techniques are applicable to
polycrystalline materials with sufficiently compact grain shapes and can also be used to controllably generate a wide variety
of hypothetical microstructures for initial states in computer simulations.
This article is based on a presentation made at the symposium “Characterization and Representation of Material Microstructures
in 3-D” held October 8–10, 2002, in Columbus, OH, under the auspices of ASM International’s Phase Transformations committee. 相似文献
1000.
Distance labeling schemes are composed of a marker algorithm for
labeling the vertices of a graph with short labels, coupled with a
decoder algorithm allowing one to compute the distance between
any two vertices directly from their labels (without using any additional
information).
As applications for distance labeling schemes
concern mainly large and dynamically changing networks,
it is of interest to study distributed dynamic labeling schemes.
The current paper considers the problem on dynamic trees,
and proposes efficient distributed schemes for it.
The paper first presents a labeling scheme for distances in the dynamic
tree model, with amortized message complexity O(log2
n) per operation,
where n is the size of the tree at the time the operation takes place.
The protocol maintains O(log2
n) bit labels.
This label size is known to be optimal even in the static scenario.
A more general labeling scheme is then introduced for the dynamic tree
model, based on extending an existing static tree labeling
scheme to the dynamic setting. The approach fits a number of
natural tree functions, such as distance, separation level, and flow.
The main resulting scheme incurs an overhead
of an O(log n) multiplicative factor in both the label size and
amortized message complexity in the case of dynamically growing
trees (with no vertex deletions).
If an upper bound on n is known in advance,
this method yields a different tradeoff, with an
O(log2
n/log log n) multiplicative overhead on the label
size but only an O(log n/log log n) overhead on the amortized
message complexity.
In the fully dynamic model the scheme also incurs an increased
additive overhead in amortized communication, of O(log2
n)
messages per operation. 相似文献