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141.
BACKGROUND: The aim of this study was to obtain a more precise understanding of the mechanical properties of the periodontal ligament in continuously erupting incisors by comparing the shear stress-strain relations among teeth from four closely related species. METHODS: Four species of experimental animals (mice, hamsters, rats, and rabbits) were used. Transverse sections of the left mandibular incisors were cut from the incisal, middle, and basal regions of each incisor. The tooth was pushed out of the alveolar bone in an extrusive direction at 5 mm/min using a materials testing machine. The maximum shear stress, maximum shear strain, tangent modulus, and failure strain energy density were estimated from the resulting stress-strain curve. Polarized light microscopic observations of collagen fibers were also made. RESULTS: All the biomechanical measures tended to decrease from the incisal toward the basal regions in all species. There were large species differences, especially in the incisal region, with the greatest maximum shear stress and failure strain energy density in hamsters. The greatest tangent modulus and the smallest maximum shear strain were observed in mice. The birefringent fiber architectures of the periodontal ligaments in the four species appeared to be similarly organized; the incisal periodontal ligament appeared to have more organized and thicker collagen fibres than did the middle and basal ligaments in the four species. CONCLUSIONS: These results suggest that the regional differences in the biomechanical properties of the periodontal ligament depend upon the developmental stages of the periodontal collagen fibers that may be related to the general arrangement, diameters, and densities of the collagen fiber bundles and the fiber insertions into the alveolar bone and cementum. The species differences in the biomechanical properties may be due to differences in the width of the periodontal ligament and the waviness as well as the strength and stiffness of the periodontal collagen fibers. 相似文献
142.
143.
A general formula for the capacitance transient response in an MIS system was developed in order to apply the ICTS (isothermal capacitance transient spectroscopy) technique to an MIS diode. A new spectroscopic measurement method for determining the distribution of interface states is proposed and applied to an InAs MIS diode. 相似文献
144.
The asymmetric oxidation of poly(phenylvinyl sulfide) (poly-Ph VS) and poly(t-butylvinyl sulfide) (poly-t-BuVS) was carried out with optically active percamphoric acid, and the optically active polysulfoxides were obtained. The values of the specific rotation for the oxidation products of poly-PhVS and poly-t-BuVS were + 1.0 (having 56% of sulfoxide unit contents) and +9.1 (49%), respectively. The specific rotation of the product increased with increasing the contents of sulfoxide units. The optical rotatory dispersion curves of the oxidation products of poly-PhVS and poly-t-BuVS were positive curves and were found to fit the simple Drude equation. The λc values of the oxidation products (poly-PhVS, 271 mμ; poly-t-BuVS, 212 mμ) suggested that the chromophore which caused optically activity was the sulfoxide group. Similarly, the asymmetric oxidation of t-BuVS–MMA copolymer, t-BuVS–styrene copolymer, and PhVS–MMA copolymer was carried out, and the optically active copolysulfoxides were obtained. Furthermore, the biosynthetic oxidation of poly-PhVS and PhVS–maleic anhydride copolymer treated with aqueous KOH was carried out using Aspergillus niger or Penicillium notatum in Czapeck solution, and the optically active polymers were obtained. 相似文献
145.
Asymmetric addition of thiol to diene polymer in the presence of optically active amines as catalyst
The asymmetric addition reaction of thiolacetic acid or benzylmercaptan to diene polymer (natural rubber, cis- and trans-1,4-polyisoprene, cis-1,4-polybutadiene, various styrenebutadiene copolymers and alternating acrylonitrile-butadiene copolymer) by optically active catalysts such as d-bornylamine ([α]d?45.2°), l-aspartic diethyl ester (?11.2°), l-aspartic dibutyl ester (?5.3°) were carried out in benzene at room temperature to 90°C. The optically active polymers were obtained from natural rubber and cis-1,4- and trans-1,4-polyisoprene, but were not obtained from cis-1,4-polybutadiene, styrene-butadiene copolymers, and butadiene-acrylonitrile copolymer. The [α]25D value of optically active derivatives was ?0.1° ~ ?1.0° (in benzene), and the optical rotatory dispersion curves were found to fit the simple Drude equation. 相似文献
146.
147.
Yamaguchi A Uejo F Yoda T Uchida T Tanamura Y Yamashita T Teramae N 《Nature materials》2004,3(5):337-341
A mesoporous membrane composed of nanochannels with a uniform diameter has a potential use for precise size-exclusive separation of molecules. Here, we report a novel method to form a hybrid membrane composed of silica-surfactant nanocomposite and a porous alumina membrane, by which size-selective transport of molecules across the membrane becomes possible. The nanocomposite formed inside each columnar alumina pore was an assembly of surfactant-templated silica-nanochannels with a channel diameter of 3.4 nm; the channel direction being predominantly oriented along the wall of the columnar alumina pore. Molecules could be transported across the membrane including the silica-surfactant nanocomposite with a capability of nanometre-order size-exclusive separation. Our proposed membrane system has a potential use not only for separation science, but also catalysis and chip technologies. 相似文献
148.
Igarashi S Haraguchi M Aihara J Saito T Yamaguchi K Yamamoto H Hojou K 《Journal of electron microscopy》2004,53(3):223-228
The formation and the phase transitions of iron silicide by solid-phase epitaxy have been investigated by means of plan-view transmission electron microscopy, which enables us to observe a clean interface between Fe and Si. Layers of Fe were deposited on Si (100) at room temperature in an ultrahigh vacuum chamber. The sample was annealed in the electron microscope at a temperature between 673 and 1073 K. After annealing at 673 K, FeSi crystallites were formed with various orientations. When the annealing temperature was increased to 973 K, we found that the crystallites suddenly started to coalesce into grains of several hundreds of nanometers in size and polycrystalline beta-FeSi2 was formed. These phase transitions were also confirmed with electron energy-loss spectroscopy. 相似文献
149.
Nobuhiko Onda Kunio Furusawa Noriko Yamaguchi Masatoshi Tokiwa Yasumasa Hirai 《应用聚合物科学杂志》1980,25(10):2363-2372
In a study of polyacrylamide in solutions we have required the rapid characterization on chromatographies. The application to the aqueous solution of the GPC using controlled-porosity glass has been examined from both the viewpoint of the effect of salt addition and the GPC mechanism. An adequate addition to neutral salt, 0.005M KCI to the eluent, gave rise to the elution behaviors being in accord with the hydrodynamic volume concept of the GPC separation. 相似文献
150.
High-power aging tests on 1.3 ?m double-channel planar buried-heterostructure (DC-PBH) lasers with a reflective coated mirror have been performed. Stable operation for over 6000 h has been demonstrated under constant power conditions of 20 and 30 mW from the front facet at 50°C. 相似文献