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61.
Sintering characteristics of three kinds of iron and FeCo alloy ultrafine powders (UFPs) in vacuum and a hydrogen atmosphere were examined by continuously measuring their dimensions, and observing their structural changes. The UFPs exposed to air contain mixtures of oxide and hydroxide phases. The oxide phase increased during heating in vacuum. The compacts of the UFPs shrunk slightly at temperatures between 450 and 700 K, where the surface oxides sintered, and then densified rapidly above 700 K. The shrinkage in a stream of hydrogen occurred at much lower temperatures than that in vacuum. The reduction reaction is ratecontrolled by an interface reaction and the reduction rate of the UFPs depends on the oxidation level, where the more highly oxidized UFPs tend to the lower reduction rate. Activation energies of the reduction rate constants of the iron UFPs and FeCo UFPs lie in the range 48–59 kJ mol–1. 相似文献
62.
Jisun Jin Toshinobu Yoko Fumiaki Miyaji Sumio Sakka Toshiharu Fukunaga Masakatsu Misawa 《Journal of the American Ceramic Society》1993,76(3):630-634
The local structure of a Na2 O─SiO2 oxide glass and a Na2 O─iO2 ─Si3 N4 oxynitride glass has been investigated by the pulsed neutron diffraction method. In the oxide glass, the first peak of radial distribution function (RDF) curves appeared at 0.1627 nm corresponding to Si─O boxh length. In the oxynitride glass, the first peak of the RDF curve was shifted to longer distances at 0.1650 nm due to the coexistence of Si─O and Si─N boxhs. The first peak in the RDF curve of the oxynitride glass was deconvoluted into two peaks whose positions are located at 0.1626 and 0.1709 nm. The one at 0.1626 nm is ascribed to Si─O boxhs and the other at 0.1709 nm to Si─N boxhs. The number of silicon atoms around a nitrogen was found to be 2.42, suggesting that not all of the nitrogen atoms are boxhed to three silicon atoms, but 58% twofold (─N─) and 42% threefold (>N─) nitrogens coexist in the present Na-Si-O-N oxynitride glass. The formation of twofold nitrogens may arise from the reaction between ≡Si─O− and ≡Si3 N groups. This model is compatible with the experimental observation that the density and Vickers hardness of oxynitride glasses increase with the nitrogen content. 相似文献
63.
Elastic-plastic analysis of composite beams with incomplete interaction by finite element method 总被引:3,自引:0,他引:3
This paper presents a nonlinear finite element analysis of composite beams with incomplete interaction. A simplified nonlinear model is assumed in this approach. This is applied to the elastic-plastic analysis of reinforced concrete beams and composite beams with incomplete interaction. The numerical results are compared with the test results and existing values based on other numerical methods, and found to be in good agreement. The elastic-plastic behavior of partial composite beams without shear connectors in the negative bending moment region is discussed by the proposed method. 相似文献
64.
Tatsuo Inoue Toshihide Igari Fusahito Yoshida Akihiko Suzuki Sumio Murakami 《Nuclear Engineering and Design》1985,90(3)
Some of the interim results of the Bench Mark Project by the Subcommittee on the Inelastic Analysis and Life Prediction of High Temperature Materials, JSMS, is presented. The purpose of the present bench mark study is to review and evaluate the inelastic constitutive models relevant to material response under the plasticity-creep interaction.By specifying normalized and tempered
steel at 600°C, sixteen bench mark problems of four categories are first established: (I) tensile stress-strain relations and creep curves, (II) material response under mixed modes of plastic and creep loading, (III) ratcheting and deformation under program loads, and (IV) cyclic deformation behaviour under the combination of different strain rates. Then, the outline of seventeen inelastic constitutive models of nine types discussed in this project is presented. Finally, the interim results of these bench mark tests are compared with the corresponding predictions of the constitutive models to evaluate their accuracy in simulating the actual behaviour of the material. 相似文献
65.
An analytical expression for the prompt time response is compared with available data of prompt cures using surface-barrier detectors, yielding a relation for T? = 0.33 ?1/?n = 0.40 ?2 ?n/N where ?1, ?2 rise and decay times of single-electron response, n/N is the optimum value at minimum time resolution. A preliminary method is proposed for computing the plasma time in these detectors. 相似文献
66.
Herein we demonstrate a unique processing technique for engineering multicomponent ceramic nanopowders with precise morphologies by "nanoblast" calcination/deagglomeration. Multiple "nanoexplosions" of C(3)H(6)N(6)O(6) nanoparticles embedded in preliminary engineered nanoreactors break apart the agglomerates because of the highly energetic impacts of the blast waves. Also, the solid-solubility of one component into the other is enhanced by the extremely high local temperature generated during the nanoexplosions. We applied this technique to produce nanosized agglomerate-free ceria-gadolinia solid solution powder with an average aggregate size of 42 nm. The described method opens the door to the synthesis of a wide range of multimetal oxide ceramic and metal-ceramic composite nanopowders, with precise stoichiometries and uniform morphologies. 相似文献
67.
The internal friction of artificial single crystals of ice is studied by the flexural vibration method, changing temperature, frequency and angle θ between the crystal c-axis and the long axis of the specimen. The height of the main peak in the curve of the internal friction (tan δ) versus temperature depends strongly on the angle θ. The maximum damping (tan δmax) increased with increase in the angle θ up to nearly 60° and decreased a little for values of θ greater than 60°. The results of the experiments except for θ = 0° show that the internal friction peak is caused by a single relaxation phenomenon, the relaxation time of which is τ = τ0exp (H/kT). Values of τ0 and H are 1.66 × 10?16 s and 0.60 eV, respectively.The data are compared with the other experiments and are discussed with special reference to the theoretical treatments by Bass. The orientation dependence of tan δmax is found to be consistent with the theoretical prediction. 相似文献
68.
Ludi Xu Degui Zhu Yunlong Liu Tohru S. Suzuki Byung-nam Kim Yoshio Sakka Salvatore Grasso Chunfeng Hu 《Journal of the European Ceramic Society》2018,38(10):3417-3423
Oxidation resistance of textured Ti3AlC2 ceramics was measured in the temperature range 1273–1573?K. It was found that the oxidation was markedly anisotropic and the samples exhibited a better oxidation resistance when tested along a direction transverse to the c-axis. This behavior was attributed to the rapid diffusion of Al within its basal planes to form a passivating Al2O3 scale and it respected Ellingham diagrams. The scales formed had different compositions depending on the testing direction; this response was clearly resulting from the crystallographic orientation. Even at 1473?K after 20?h exposure, the samples tested in a direction transverse to the c-axis showed a reduced weight gain which was 45 times lower than one seen on a basal plane. 相似文献
69.
Hiromichi Akahori Stéphane Guindon Sumio Yoshizaki Yoshinori Muto 《International journal of molecular sciences》2015,16(12):28472-28485
Ten-eleven translocation (TET) proteins, a family of Fe2+- and 2-oxoglutarate-dependent dioxygenases, are involved in DNA demethylation. They also help regulate various cellular functions. Three TET paralogs have been identified (TET1, TET2, and TET3) in humans. This study focuses on the evolution of mammalian TET genes. Distinct patterns in TET1 and TET2 vs. TET3 were revealed by codon-based tests of positive selection. Results indicate that TET1 and TET2 genes have experienced positive selection more frequently than TET3 gene, and that the majority of codon sites evolved under strong negative selection. These findings imply that the selective pressure on TET3 may have been relaxed in several lineages during the course of evolution. Our analysis of convergent amino acid substitutions also supports the different evolutionary dynamics among TET gene subfamily members. All of the five amino acid sites that are inferred to have evolved under positive selection in the catalytic domain of TET2 are localized at the protein’s outer surface. The adaptive changes of these positively selected amino acid sites could be associated with dynamic interactions between other TET-interacting proteins, and positive selection thus appears to shift the regulatory scheme of TET enzyme function. 相似文献
70.
Kitaoka Haru Amano Ken-ichi Nishi Naoya Sakka Tetsuo 《Optimization and Engineering》2022,23(2):1033-1055
Optimization and Engineering - The Nelder-Mead (NM) method is a popular derivative-free optimization algorithm owing to its fast convergence and robustness. However, it is known that the method... 相似文献