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21.
Hemicyanine dyes are an extensively investigated group of materials which show promise for second-order non-linear optical properties; they have also proved to be good materials for deposition by the Langmuir-Blodgett technique. This work concerns a closely related group of materials which contain a thiophene moiety in place of the nitrogen heterocycle of the hemicyanine material. The synthesis of several groups of novel amphiphiles containing the thiophene moiety, and their subsequent screening as materials for deposition by the Langmuir Blodgett technique is described. General trends in the behaviour of the simplest materials are noted, whilst the report of the characterization of the more complex D--A thiophenes is extended to include data relating to the production of heterogeneous monolayer and alternate layer structures. 相似文献
22.
C. Birley J. Briddon K. E. Sykes P. A. Barker S. J. Organ P. J. Barham 《Journal of Materials Science》1995,30(3):633-638
Single crystals of poly(hydroxybutyrate), and copolymers of hydroxybutyrate and hydroxyvalerate, have been grown from a variety of solvents and their morphology studied. In all cases the crystals appear elongated, with the crystallographic a axis along the long axis of the crystals. Screw dislocations (which act as branch points and can lead to large crystal aggregates) have been observed, and solvents, e.g. octanol in which more of these dislocations occur, have been identified. Decoration of the crystals with polyethylene shows that the fold plane is the (0 1 0) plane, while crystallographic and crystallinity arguments require successive adjacent folds to be along 1 1 0 directions. It is argued that folding is along [1 1 0] on the top, and [1 ¯1 0] on the bottom surface of a crystal. 相似文献
23.
Replica Placement Strategies in Data Grid 总被引:1,自引:0,他引:1
Replication is a technique used in Data Grid environments that helps to reduce access latency and network bandwidth utilization.
Replication also increases data availability thereby enhancing system reliability. The research addresses the problem of replication
in Data Grid environment by investigating a set of highly decentralized dynamic replica placement algorithms. Replica placement
algorithms are based on heuristics that consider both network latency and user requests to select the best candidate sites
to place replicas. Due to dynamic nature of Grid, the candidate site holds replicas currently may not be the best sites to
fetch replicas in subsequent periods. Therefore, a replica maintenance algorithm is proposed to relocate replicas to different
sites if the performance metric degrades significantly. The study of our replica placement algorithms is carried out using
a model of the EU Data Grid Testbed 1 [Bell et al. Comput. Appl., 17(4), 2003] sites and their associated network geometry. We validate our replica placement
algorithms with total file transfer times, the number of local file accesses, and the number of remote file accesses. 相似文献
24.
25.
C. C. Zammit R. E. Hill R. W. Barker 《Journal of Infrared, Millimeter and Terahertz Waves》1982,3(2):189-203
Further measurements of atmospheric emission from a site in the Canary Islands (Izana, âltitude 2.4 km) have been made during the month of August 1980. The measurements were made with a polarising Interferometer and a composite Ge bolometer. An independent measurement of the precipitable water vapour was made using Infrared Hygrometers. The experimental details are described and the spectra obtained are compared with model spectra using the measured precipitable water vapour. 相似文献
26.
Commercially available lots of plasma derivatives prepared between 1957 and 1975 were tested for hepatitis B surface antigen (HBsAg) by radioimmunoassay. In all, 69 per cent of lots of plasma protein fraction, 40 per cent of factor IX concentrate, 20 per cent of normal serum albumin, 13 per cent of antihemophilic factor, 3 per cent of fibrinogen, and 0.7 per cent of immune serum globulin lots tested were HBsAg-positive. There was great variation in the prevalence of HBsAg-positive lots of each product among the different manufacturers, reflecting not only differences in methods of processing plasma, but also differences in donor populations. Those manufacturers relying upon volunteer donor plasma or placental source material demonstrated lower rates of HBsAg-positive lots of final products than those relying upon commercial donor plasma. There was a marked decrease in the prevalence of positive lots during the period 1971 to 1973, coincident with the onset of routine plasma donor screening for HBsAg. However, current requirements for plasma screening have not resulted in totally HBsAg-free plasma products. Use of more sensitive and more reliable tests for HBsAg will probably reduce contamination of plasma pools with HBsAg to undetectable levels. Despite HBsAg-status, however, the "high-risk" plasma products (fibrinogen, antihemophilic factor, factor IX concentrate) must still be considered capable of transmitting hepatitis and used only with the strictest indications. 相似文献
27.
We have developed an accurate Padé approximant for the plasma dispersion function that is valid for degenerate semiconductors
that occur in ultra-small MOSFETs. The new approximant is based on a two pole model that enables a simple evaluation of the
Lindhard dielectric function for the full dynamic response of electrons of any degeneracy. The importance of this result is
that it enables a fast numerical algorithm for determining the energies and scattering strengths of coupled plasmon-phonon
modes in silicon MOSFET devices with high-κ gate stacks. Moreover, the formalism allows the systematic inclusion of Landau
damping and other processes such as collisional damping that damp out some of the modes at particular ranges of wave vector.
The new model is a non-trivially scaled model of a previous approximant derived for Boltzmann statistics. The new model reduces
to the classical result in the appropriate limit. Results are presented that compare the exact numerically computed complex
plasma dispersion function with the new Padé approximant model. Comparison is also made between exact numerical calculations
and the Padé approximant model for static screening. A brief outline is made of the potential application to high-κ gate stack
devices where the formalism should provide a significantly large reduction in complexity that will enable efficient Monte
Carlo simulation of SO phonon and plasmon scattering. 相似文献
28.
The piled raft is a geotechnical composite construction, consisting of the three elements piles, raft, and soil, which is applied for the foundation of tall buildings in an increasing number. In a parametric study, 259 different piled raft configurations have been analyzed by means of three-dimensional elastoplastic finite element analyses. In the study, the pile positions, the pile number, the pile length, and the raft-soil stiffness ratio as well as the load distribution on the raft has been varied. In the scope of this paper, the results of the parametric study are presented and design strategies for an optimized design of piled rafts subjected to nonuniform vertical loading are discussed. 相似文献
29.
Properties and methods of generation of pseudo-random binary signals are discussed. A theory of linear modelling is developed for multivariable systems in which these signals form the inputs. Modelling with delay operators and exponential weighting function operators is considered. Experimental results are presented to illustrate the theory. 相似文献
30.