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181.
Yvan Van Rentergem Alexis De Vos Koen De Keyser 《Open Systems & Information Dynamics》2007,14(1):91-116
The (2
w
)! reversible transformations on w wires, i.e. reversible logic circuits with w inputs and w outputs, together with the action of cascading, form a group, isomorphic to the symmetric group S
2
w
. Therefore, we investigate the group S
n
as well as one of its subgroups isomorphic to S
n/2 × S
n/2. We then consider the left cosets, the right cosets, and the double cosets generated by the subgroup. Each element of a coset
can function as the representative of the coset. The coset can then be considered as the set of all group elements that differ
from the representative by merely multiplying (either to the left or to the right or to both sides) by an arbitrary element
of the subgroup. Different choices of the coset space and different choices of the coset representatives lead to six different
syntheses for implementing an arbitrary reversible logic operation into hardware. Evaluation of all six methods, by means
of three different cost functions (gate cost, switch cost, and quantum cost), leads to a best choice. 相似文献
182.
Jose R. Rios Viqueira Nikos A. Lorentzos 《The VLDB Journal The International Journal on Very Large Data Bases》2007,16(2):179-200
An SQL extension is formalized for the management of spatio-temporal data, i.e. of spatial data that evolves with respect
to time. The extension is dedicated to applications such as topography, cartography, and cadastral systems, hence it considers
discrete changes both in space and in time. It is based on the rigid formalization of data types and of SQL constructs. Data types are defined in terms of time and
spatial quanta. The SQL constructs are defined in terms of a kernel of few relational algebra operations, composed of the well-known operations of the 1NF model and of two more, Unfold and Fold. In conjunction with previous work, it enables the uniform management of 1NF structures that may contain not only spatio-temporal
but also either purely temporal or purely spatial or conventional data. The syntax and semantics of the extension is fully
consistent with the {SQL:2003} standard. 相似文献
183.
A necessary and sufficient condition is given for a connected bipartite graph to be the incidence graph of a contact family
of segments and points. We deduce that any four-connected three-colorable plane graph is the contact graph of a family of
segments and that any four-colored planar graph without an induced C4 using four colors is the intersection graph of a family of straight line segments. 相似文献
184.
Fast Recognition of Fibonacci Cubes 总被引:1,自引:0,他引:1
Fibonacci cubes are induced subgraphs of hypercubes based on Fibonacci strings. They were introduced to represent interconnection
networks as an alternative to the hypercube networks. We derive a characterization of Fibonacci cubes founded on the concept
of resonance graphs. The characterization is the basis for an algorithm which recognizes these graphs in O(mlog n) time.
A. Vesel supported by the Ministry of Science of Slovenia under the grant 0101-P-297. 相似文献
185.
Marco Lucamarini Alessandro Ceré Giovanni Di Giuseppe Stefano Mancini David Vitali Paolo Tombesi 《Open Systems & Information Dynamics》2007,14(2):169-178
The security of a deterministic quantum scheme for communication, namely the LM05 [1], is studied in presence of a lossy channel
under the assumption of imperfect generation and detection of single photons. It is shown that the scheme allows for a rate
of distillable secure bits higher than that pertaining to BB84 [2]. We report on a first implementation of LM05 with weak
pulses. 相似文献
186.
Ivan Cimrák 《Archives of Computational Methods in Engineering》2007,15(3):277-309
The Landau-Lifshitz (LL)equation of micromagnetism governs rich variety of the evolution of magnetization patterns in ferromagnetic
media. This is due to the complexity of physical quantities appearing in the LL equation. This complexity causes also an interesting
mathematical properties of the LL equation: nonlocal character for some quantities,nonconvex side-constraints, strongly nonlinear
terms. These effects influence also the numerical approximations. In this work, recent developments on the approximation of
weak solutions, together with the overview of well-known methods for strong solutions,are addressed.
Author is supported by the Fund for Scientific Research - Flanders FWO (Belgium). 相似文献
187.
Xiaodan Zhang Wei Liu Dale Sun Youguo Li 《Metallurgical and Materials Transactions A》2007,38(3):499-505
The transformation of carbides with austenization time of a high speed steel (HSS) roll material, manufactured by a centrifugal
casting method, has been studied. The correlation between wear resistance and the type, morphology, volume fraction, and distribution
of the carbides has also been investigated. Microstructural observations, X-ray diffraction (XRD) analysis, hardness measurements,
and energy dispersive spectroscopy (EDS) have been used to characterize the carbides. The type and volume fraction of carbides
were found to change with austenizing time. During austenization, the transformation of the M3C carbides can be postulated as M3C + γ-Fe → M2C, with much finer nodular and rodlike MC carbides also forming through a solid-state transformation. The M2C carbide decomposes as M2C + γ-Fe → MC + M7C3 + M6C. The decomposed carbide substantially maintains a platelike shape until the end of decomposition. The most important finding
of this study is that austenization results in changes in the type, morphology, volume fraction, and distribution of carbides
and that it can be controlled to produced a homogeneous distribution of hard carbides, resulting in an improvement in the
wear resistance of HSS rolls. This finding may be of great use for the industrial production of HSS rolls. 相似文献
188.
Following the original model for a single cell/dendrite growth by Hunt,[5] systematic numerical simulations are carried out with focus on cell shape evolution and tip radius selection in a directional
solidification process conducted in a capillary tube. Computations indicate that the anisotropy of solid/liquid interfacial
energy and the diameter of a capillary tube have significant influences on the selection of a tip shape. The anisotropy in
dilute SCN-salol alloys has been determined through the equilibrium droplet shape method and its value is 1.09 pct. The calculated
cell/dendrite shapes with this value of anisotropy agree with experimental observations where a single cell/dendrite of SCN-salol
alloys grows in a capillary tube. 相似文献
189.
In the design of algorithms for large-scale applications it is essential to consider the problem of minimizing I/O communication.
Geographical information systems (GIS) are good examples of such large-scale applications as they frequently handle huge amounts
of spatial data. In this paper we develop efficient external-memory algorithms for a number of important problems involving
line segments in the plane, including trapezoid decomposition, batched planar point location, triangulation, red--blue line
segment intersection reporting, and general line segment intersection reporting. In GIS systems the first three problems are
useful for rendering and modeling, and the latter two are frequently used for overlaying maps and extracting information from
them. 相似文献
190.
Confluent graphs capture the connection properties of train tracks, offering a very natural generalization of planar graphs,
and—as the example of railroad maps shows—are an important tool in graph visualization. In this paper we continue the study
of confluent graphs, introducing strongly confluent graphs and tree-confluent graphs. We show that strongly confluent graphs
can be recognized in NP (the complexity of recognizing confluent graphs remains open). We also give a natural elimination
ordering characterization of tree-confluent graphs, and we show that this class coincides with the (6,2)-chordal bipartite
graphs. Finally, we define outerconfluent graphs and identify the bipartite permutation graphs as a natural subclass. 相似文献