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排序方式: 共有1014条查询结果,搜索用时 31 毫秒
101.
Jacek Mi?kisz 《Probabilistic Engineering Mechanics》2011,26(1):33-38
We discuss effects of stochasticity and time delays in simple models of population dynamics. In social-type models, where individuals react to the information concerning the state of the population at some earlier time, sufficiently large time delays may cause oscillations. In biological-type models, where some changes already take place in the population at an earlier time, oscillations might not be present for any time delay. We illustrate this idea in models of delayed random walks, gene expression, and population dynamics of evolutionary game theory. 相似文献
102.
Nitrosamines and water 总被引:1,自引:0,他引:1
This paper provides an overview of all current issues that are connected to the presence of nitrosamines in water technology. N-nitrosodimethylamine (NDMA) is the most frequently detected member of this family. Nitrosamines became the hottest topic in drinking water science when they were identified as disinfection by-products (DBPs) in chloraminated waters. The danger that they pose to consumer health seems to be much higher than that from chlorinated DBPs. This review summarizes our contemporary knowledge of these compounds in water, their occurrence, and precursors of nitrosamines in drinking and wastewaters, in addition to attempts to remove nitrosamines from water. The paper also reviews our knowledge of the mechanisms of nitrosamine formation in water technology. The current, commonly accepted mechanism of NDMA formation during chloramination of drinking waters assumes that dichloramine reacts with dimethylamine, forms unsymmetrical dimethylhydrazine and further oxidizes to NDMA. The question to answer is which precursors are responsible for delivering the DMA moiety for the reaction since the presence of DMA in water cannot explain the quantities of NDMA that are formed. There are also reports that other oxidants that are commonly used in water technology may generate NDMA. However, the mechanisms of such transformations are unknown. Methods for the removal of nitrosamines from water are described briefly. However, the research that has been undertaken on such methods seems to be at an early stage of development. It is predicted that photolytic methods may have the greatest potential for technological application. 相似文献
103.
Boron and aluminum doping by diffusion into n-type 4H-SiC Si-face substrates was carried out at the temperatures of 1800-2000 °C. Secondary ion mass spectroscopy (SIMS) was employed to obtain the impurity profiles, which showed that linearly graded boron profile and shallow aluminum profiles have been achieved, which may be a promising application in SiC device fabrication, such as p-n diode or ohmic contact. Characterization of high temperature processing influence on SiC surface morphology has been performed. Elemental boron and aluminum carbide were determined to be the best candidates as an impurity source materials for realizing p-type diffusion. 相似文献
104.
Gisèle Boiteux Pascal Dublineau Michel Feve Christophe Mathieu Gérard Seytre Jacek Ulanski 《Polymer Bulletin》1993,30(4):441-447
Summary The curing of different epoxy-amine model systems which present only gelification and/or vitrification processes has been followed with the evolution of their viscoelastic and electrical behaviours during the network formation. Some attempts are performed to correlate the significant evolution of the mechanical and electrical parameters with the physico-chemical changes of these well defined chemical systems during their hardening and complete curing. 相似文献
105.
This paper describes an algorithm and a computer program which solves numerically (virtually exactly) equations of the restricted open-shell Hartree-Fock and Hartree-Fock-Slater model for diatomic molecules 相似文献
106.
This paper sets out the results of mathematical modeling and numerical simulations of the off-design (part-load) operation of the solid oxide fuel cell hybrid system (SOFC-HS). 相似文献
107.
Metadata requirements for digital museum environments 总被引:1,自引:0,他引:1
Manjula Patel Martin White Nicholaos Mourkoussis Krzysztof Walczak Rafal Wojciechowski Jacek Chmielewski 《International Journal on Digital Libraries》2005,5(3):179-192
We describe a system which addresses all the processes involved in digitally acquiring, modelling, storing, manipulating and creating virtual exhibitions from 3D museum artefacts. More specifically, we examine the significance of metadata in enabling and supporting all of these processes and describe the extensive facilities provided for authoring, maintaining and managing metadata. The development of the system has been heavily influenced by factors relating to interoperability, standards, museum best practice and feedback from two museum pilot sites. Finally, we briefly consider the system in the wider context of applications such as virtual learning environments and distributed repositories of archives. 相似文献
108.
Jacek M. Czaplicki 《Microelectronics Reliability》1985,25(4):695-698
In the paper the model of reliability diagnostic of renewal objects which exploitation process can be described as the interrupting renewal process with the finite time of repair is discussed. The essential relationships between reliability of object and diagnostic parameters are presented. 相似文献
109.
Air-coupled ultrasonic sources are relatively inefficient because the high impedance mismatch at the air/solid boundary means that most of the input energy (in air) is reflected at this boundary. The objective of this research is to increase efficiency—specifically an increase in ultrasonic signal amplitude—by designing and building a focused, 2D-array of electrostatic transducers (individual diameters of 38 mm). The operating frequency of this array is in the range of 50–100 kHz; this range is selected for civil infrastructure applications. Numerical simulations are used to design an array by modeling the pressure field in air, and then optimizing an array consisting of 20 transducers to create a line-source. An array is then built (following this design) and the emitted pressure field (in air) of the as built array is measured with a microphone and compared to the pressure field predicted by the numerical model. Finally, the as built focused array is used as an ultrasonic source, and its robustness is verified by comparing the numerical simulation of a transient line-load on an elastic half-space with (completely non-contact) experimentally measured values. There is excellent agreement between these two representations, which confirms the possibility of developing a completely non-contact, scanning ultrasonic system in the 50–100 kHz range. 相似文献
110.
In this paper we present a computational model of electrical conductivity processes via variable range hopping of electrons between localized states (‘sites’) in quasi one-dimensional disordered systems. For two, slightly different models, the temperature dependence of the conductivity of parallel connected systems of filaments and of quasi-infinite, single filaments are discussed and compared with theoretical and experimental results. 相似文献