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排序方式: 共有4796条查询结果,搜索用时 46 毫秒
991.
Shi Woong Lee Jang Yeul Shon 《Tunnelling and Underground Space Technology incorporating Trenchless Technology Research》1988,3(4):409-416
A number of Korea's climatological, geographical and social features make earth-sheltered construction an attractive option. This paper compares the thermal performance of an earth-sheltered house (specially designed to accommodate the conditions in Korea) with the thermal performance of a conventional residence. The researchers conclude that, except for the high humidity levels in the earth-sheltered house, the thermal environment of the earth-sheltered house is superior to that of the conventional residence. In light of these findings, the authors recommend that research be aimed at improving waterproofing and condensation control measures in earth-sheltered houses. 相似文献
992.
993.
The authors propose an idle-signal casting multiple access with collision resolution (ICMA/CR) protocol for wireless LAN. This protocol focuses on efficient collision resolution by adopting the binary-tree protocol. By using the collision resolution algorithm, the retransmission process can be controlled so that collisions are resolved more efficiently using nearly immediate feedback information, thereby increasing the throughput-delay performance of the ICMA/CD protocol 相似文献
994.
Hyun M. Jang Jong H. Moon Cheol W. Jang 《Journal of the American Ceramic Society》1992,75(12):3369-3376
Al2 O3 –ZrO2 –SiC whisker composites were prepared by surface-induced coating of the precursor for the ZrO2 phase on the kinetically stable colloid particles of Al2 O3 and SiC whisker. The fabricated composites were characterized by a uniform spatial distribution of ZrO2 and SiC whisker phases throughout the Al2 O3 matrix. The fracture toughness values of the Al2 O3 –15 vol% ZrO2 –20 vol% SiC whisker composites (∼12 MPa.m1/2 ) are substantially greater than those of comparable Al2 O3 –SiC whisker composites, indicating that both the toughening resulting from the process zone mechanism and that caused by the reinforced SiC whiskers work simultaneously in hot-pressed composites. 相似文献
995.
Kim JN Haun MJ Jang SJ Cross LE Xue XR 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1989,36(4):389-392
The dielectric and electromechanical coupling properties of Sm-doped and Mn-doped PbTiO(3) ceramics were investigated from 4.2 to 300 K. The upper and lower limits of the ceramic dielectric and piezoelectric properties were calculated by averaging the single-domain constants that were determined from a phenomenological theory. Comparisons of the measured and calculated properties were then made. The measured dielectric permittivity epsilon(T)(33) and piezoelectric strain coefficient d(33) appear to be mainly due to the averaging of the intrinsic single-domain response. The large piezoelectric and electromechanical anisotropies present in modified PbTiO(3) ceramics also appear to be an intrinsic property of the material. The piezoelectric coefficient d(31), as well as the planar coupling coefficient k(p), was found to have very small values over two temperature regions, from 120 to 170 K and from 240 to 270 K. 相似文献
996.
Zhuang ZQ Haun MJ Jang SJ Cross LE 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1989,36(4):413-416
Pure (undoped) piezoelectric lead zirconate titanate (PZT) ceramic samples at compositions across the ferroelectric region of the phase diagram were prepared from sol-gel-derived fine powders. Excess lead oxide was included in the PZT powders to obtain dense (95-96% of theoretical density) ceramics with large grain size (>7 mum) and to control the lead stoichiometry. The dielectric, piezoelectric, and elastic properties were measured from 4.2 to 300 K. At very low temperatures, the extrinsic domain wall and thermal defect motions freeze out. The low-temperature dielectric data can be used to determine coefficients in a phenomenological theory. The extrinsic contribution to the properties can then be separated from the single-domain properties derived from the theory. 相似文献
997.
998.
Unveiling the Role of Dopant Polarity in the Recombination and Performance of Organic Light‐Emitting Diodes
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The recombination of charges is an important process in organic photonic devices, because the process influences the device characteristics such as the driving voltage, efficiency, and lifetime. Here, by using various homoleptic and heteroleptic Ir complexes as dopants, it is reported that the stationary dipole moment (μ0) of the dopant rather than the trap depth (ΔEt ) is a major factor determining the recombination mechanism in dye‐doped organic light‐emitting diodes (OLEDs). Dopants with large μ0 (e.g., homoleptic Ir(III) dyes) induce large charge trapping on them, resulting in high driving voltage and trap‐assisted recombination‐dominated emission. On the other hand, dyes with small μ0 (e.g., heteroleptic Ir(III) dyes) show Langevin recombination‐dominated emission characteristics with much less charge trapping on them no matter what ΔEt is, leading to lower driving voltage and higher efficiencies. This finding will be useful in any organic photonic devices such as phosphorescent or thermally assisted delayed fluorescent dye sensitized fluorescent OLEDs where trapping and recombination mechanisms play key roles. 相似文献
999.
Air‐Stable Cesium Lead Iodide Perovskite for Ultra‐Low Operating Voltage Resistive Switching
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Ji Su Han Quyet Van Le Jaeho Choi Kootak Hong Cheon Woo Moon Taemin Ludvic Kim Hyojung Kim Soo Young Kim Ho Won Jang 《Advanced functional materials》2018,28(5)
CsPbX3 (X = halide, Cl, Br, or I) all‐inorganic halide perovskites (IHPs) are regarded as promising functional materials because of their tunable optoelectronic characteristics and superior stability to organic–inorganic hybrid halide perovskites. Herein, nonvolatile resistive switching (RS) memory devices based on all‐inorganic CsPbI3 perovskite are reported. An air‐stable CsPbI3 perovskite film with a thickness of only 200 nm is successfully synthesized on a platinum‐coated silicon substrate using low temperature all‐solution process. The RS memory devices of Ag/polymethylmethacrylate (PMMA)/CsPbI3/Pt/Ti/SiO2/Si structure exhibit reproducible and reliable bipolar switching characteristics with an ultralow operating voltage (<+0.2 V), high on/off ratio (>106), reversible RS by pulse voltage operation (pulse duration < 1 ms), and multilevel data storage. The mechanical flexibility of the CsPbI3 perovskite RS memory device on a flexible substrate is also successfully confirmed. With analyzing the influence of phase transition in CsPbI3 on RS characteristics, a mechanism involving conducting filaments formed by metal cation migration is proposed to explain the RS behavior of the memory device. This study will contribute to the understanding of the intrinsic characteristics of IHPs for low‐voltage resistive switching and demonstrate the huge potential of them for use in low‐power consumption nonvolatile memory devices on next‐generation computing systems. 相似文献
1000.
A modeling technique to estimate a NARMAX model is developed to identify nonlinearities which are contained in linear-based nonlinear systems. Considering great contributions by linear parts of the NARMAX model on describing nonlinearities, a linear model, which is estimated from small amplitude input and the corresponding output is taken as the linear part of the NARMAX model. Hence, the capabilities of the model to predict nonlinear behaviors for any input within stable region are fairly improved, and multiplicity problem in selecting a nonlinear regression model is also resolved. As an illustration, one degree of freedom system with cubic stiffness is identified in terms of NARMAX modeling technique using the procedure proposed in this work and conventional one, respectively. By extraction higher order FRFs from the NARMAX models, dominant nonlinearities of the system are predicted, and the results by the two methods are compared with analytic one, which shows the priority of the modeling technique proposed. 相似文献