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991.
ABSTRACT The effects of cake shrinkage on the drying times and energy requirements of the primary and secondary drying stages of the freeze drying process involving the drying of a material in a vial, are estimated through the construction and solution of an extended unsteady state and spatially multidimensional model that accounts for the changes introduced by cake shrinkage on the internal and external mass and heat transfer mechanisms of the freeze drying 相似文献
992.
John P George Jeroen Beeckman Wouter Woestenborghs Philippe F Smet Wim Bogaerts Kristiaan Neyts 《Nanoscale research letters》2013,8(1):62
Barium titanate (BaTiO3) thin films are prepared by conventional 2-methoxy ethanol-based chemical solution deposition. We report highly c-axis-oriented BaTiO3 thin films grown on silicon substrates, coated with a lanthanum oxynitrate buffer layer of 8.9 nm. The influence of the intermediate buffer layer on the crystallization of BaTiO3 film is investigated. The annealing temperature and buffer layer sintering conditions are optimized to obtain good crystal growth. X-ray diffraction measurements show the growth of highly oriented BaTiO3 thin films having a single perovskite phase with tetragonal geometry. The scanning electron microscopy and atomic force microscopy studies indicate the presence of smooth, crack-free, uniform layers, with densely packed crystal grains on the silicon surface. A BaTiO3 film of 150-nm thickness, deposited on a buffer layer of 7.2 nm, shows a dielectric constant of 270, remnant polarization (2Pr) of 5 μC/cm2, and coercive field (Ec) of 60 kV/cm. 相似文献
993.
994.
The accurate calculation of the stresses and torque capacities of adhesively bonded joints is not possible without understanding the failure phenomena of the adhesive joints and the nonlinear behavior of the adhesive.
In this paper, an adhesive failure model of the adhesively bonded tubular single lap joint with steel-steel adherends was proposed to predict the torque capacity accurately.
The model incorporated the nonlinear behavior of the adhesive and the different failure modes in which the adhesive failure mode changed from bulk shear failure, via transient failure, to interfacial failure between the adhesive and the adherend, according to the magnitudes of the residual thermally-induced stresses from fabrication. 相似文献
In this paper, an adhesive failure model of the adhesively bonded tubular single lap joint with steel-steel adherends was proposed to predict the torque capacity accurately.
The model incorporated the nonlinear behavior of the adhesive and the different failure modes in which the adhesive failure mode changed from bulk shear failure, via transient failure, to interfacial failure between the adhesive and the adherend, according to the magnitudes of the residual thermally-induced stresses from fabrication. 相似文献
995.
微孔膜对O/W型乳液破乳的研究 总被引:3,自引:0,他引:3
采用以正丁醇 水为实验体系和十二烷基磺酸钠为表面活性剂制得的乳液为研究对象 ,研究了膜通量随时间的变化规律 ,考察了透过压、乳液中油含量以及膜孔径等因素对破乳效果的影响。结果表明 ,膜破乳技术是一种很有效的破乳技术。乳液通量的稳定在本实验条件下需要 4h以上。增加透过压有利于乳液通量的增加 ,但透过油中油含量会随之增加。在同样操作条件下 ,增加乳液油含量不利于通量增加和透过液中油含量的减少。微孔膜的孔径对膜通量有很大的影响 ,随着孔径增大 ,膜通量迅速增加 ,而透过液的油含量仍可保持较低量 相似文献
996.
997.
Junhyun Cho Hwanyeong Oh Jaeman Park Kyoungdoug Min Eunsook Lee Jy-Young Jyoung 《International Journal of Hydrogen Energy》2014
The mass transport characteristics of a gas diffusion layer (GDL) predominantly affect the performance of a proton exchange membrane (PEM) fuel cell. However, studies examining the transient response related to the GDL are insufficient, although the dynamic behavior of a PEM fuel cell is an important issue. In this study, the effects of the design of a micro porous layer (MPL) on the transient response of a PEM fuel cell are investigated. The MPL slurry density and multiple functional layers are treated as the variable design parameter. The results show that the transient response is determined by the capillary pressure gradient through the GDL. The trade-off relation for the PEM fuel cell performance under low and high humidity conditions due to the hydrophobic GDL is mitigated by designing a reverse capillary pressure gradient in the MPL. 相似文献
998.
V. Senthil Velan G. VelayuthamN. Rajalakshmi K.S. Dhathathreyan 《International Journal of Hydrogen Energy》2014
Gas diffusion layer (GDL) is subjected to compressive stress at high temperature along with polymer electrolyte membrane in the fabrication process and in assembling the fuel cell stacks. Compressive stress decreases the thickness of GDL, electrical conductivity, permeability, and affects the pores. Carbon cloth based GDL withstands higher strain level when compared to carbon paper and the pore structure is also disrupted to a greater extent in cloth based GDL. In the present paper, we have addressed the effects of stress on pore structure of cloth based GDL. An optimum GDL must offer low mass transport resistance in an operating PEM fuel cell. The pore size analysis of pristine GDL and GDLs pressed at different pressure levels (200, 600 & 1000 kg cm−2) and their characteristics are evaluated using capillary flow porometry. The compressive stress affects the three types of pores in GDL called bubble point pore, mean flow pore and smallest pore. The change in electrical resistance, wetting behavior and surface morphology is also examined as a function of compressive stress. The fuel cell performances using these GDLs pressed at different compressive stresses are also evaluated and presented. The highest PEMFC performance is achieved at a compressive stress of 200 kg cm−2, which could be attributed to the combined effect of reduced ohmic resistance and optimized pore structure. The order of increasing performance in terms of current density is observed to be j200 > jPristine > j600 > j1000 at 0.15 V. The thicknesses and pore sizes of custom made GDL for optimum fuel cell performance are recommended. 相似文献
999.
作为钻井液处理剂,反相乳液聚合物与粉状聚合物相比,能够减少聚合物在烘干、粉碎过程中由于降解、交联等反应造成的不利影响,产品可以直接加入钻井液并快速分散,在达到同样效果的前提下,可减少用量,降低钻井液处理费用,且更容易实现绿色环保生产。以丙烯酰胺、2-丙烯酰胺-2-甲基丙磺酸、丙烯酰氧乙基三甲基氯化铵为原料,采用氧化还原引发剂体系,通过反相乳液聚合,制备了两性离子P(AM-AMPS-DAC)反相乳液聚合物。研究了复合乳化剂的HLB、乳化剂用量、引发剂用量、油水体积比、AMPS和DAC用量对共聚物的水溶液表观黏度及所处理钻井液的流变性和滤失量的影响,测定了聚合物的红外光谱和TG曲线。结果表明,当油水体积比为1.0,单体质量分数为30%,复合乳化剂质量分数为5%~6%,复合乳化剂HLB值为7.1,引发剂用量为0.2%,n(AM)∶n(AMPS)∶n(DAC)=0.59∶0.35∶0.06时,能够制得热稳定性好的反相乳液聚合物,且在淡水、盐水、饱和盐水和复合盐水基浆中具有较好的增黏、降滤失能力,抗温、抗盐能力强,同时具有较强的润滑和防塌能力。 相似文献
1000.
建立了包含蓄热层的太阳能烟囱发电系统非稳态传热数学模型,研究了集热系统特性和蓄热层的增温效应,结果表明:蓄热层表面温度、气流温度、集热棚板温度相互影响,随时间有较大波动;气流温升主要发生在气流入口至集热棚半径1/3处,蓄热层表面温度沿径向逐渐升高,在集热棚出口段有明显下降;集热棚板、蓄热层底部及四周是系统热量损失的主要地方;系统运行非稳定期,在没有太阳辐射时,深层蓄热层不参与向气流放热过程,而是继续从浅层蓄热层吸热,浅层蓄热层贮存的热量并不全向气流传递。系统运行平稳期,蓄热层底层的温度趋于定值;理论发电功率的变化趋势与气流温度随时间变化趋势一致。 相似文献