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991.
以改善因子损失衡量的测速比和时间效用比为联合指标,评价了CartWheel、Pendulum、SAR-Train等典型编队的性能.采用遗传算法优化编队,以卫星的6个轨道根数为优化变量,仿真证明了性能评价指标和优化算法的正确性.然后根据轨道摄动理论和GMTI(Ground Moving Target Indication)对垂直基线的限制来制定约束条件,优化得到了同时符合紧密编队控制要求和GMTI性能需求的编队构形. 相似文献
992.
研究X波段0.1米分辨率机载SAR系统的超大带宽实现和高准确度成像算法要求的相关问题.深入分析频域合成带宽方法,提出一种适用于去斜率接收信号的类频域合成带宽方法,详细讨论两种方法在实现过程中的具体操作问题,包括频域方法的滤波器设计和解决类频域方法的宽测绘带混叠现象.对Chirp Scaling算法、Chirp z-transform算法和Omega-K算法的聚焦处理进行比较,分析算法的聚焦准确度和计算效率性,给出近似算法对测绘距离和测绘带宽度限制的表达式.讨论合成带宽与成像算法的联合问题,分析两种联合情况的执行过程和特点,给出频域合成带宽直接嵌入成像算法的数据处理流程.最后,通过仿真数据验证了整个分析过程和解决方法. 相似文献
993.
994.
Zhao Yonglin Du Piyi Weng Wenjian Han Gaorong 《Frontiers of Materials Science in China》2007,1(1):59-64
(Pbx,Sr1−x
)0.85Bi0.1TiO3 thin films with the perovskite phase structure were prepared on an ITO glass substrate by sol-gel method. X-ray diffraction
(XRD), scanning electron microscopy (SEM) and an impedance analyzer were respectively used in order to characterize the phase
status, morphology and dielectric properties of the thin films. The results show that during the formation process of (Pbx,Sr1−x
)0.85Bi0.1TiO3 thin films, the nucleus of the perovskite phase are initially formed and then congregated. These aggregated nucleus are then
transformed as the perovskite-phase crystalline in the thin film. Finally, the crystalline phase grows and separates gradually
to form the perfect crystalline-phase structure. The content of the perovskite phase formed in the thin film under rapid thermal
process (RTP) is more than that formed under traditional heat treatment with kinetic equilibrium. This is due to the high
active decomposed ions that form the perovskite phase directly when heat-treated by RTP. The formation of the perovskite phase
therefore overcomes a much lower barrier under RTP than that under traditional calcinations. The structure of the perovskite
phase has a close relation to the ratio of Pb/Sr in the system because of the radius difference between Pb2+ and Sr2+. The transformation temperature between the cubic and the tetragonal structures of the perovskite phase increases with increasing
Pb2+ content because the radius of Pb2+ is larger than that of Sr2+. It appears at room temperature when the content of Pb2+/Sr2+ is about 40/60 in the thin film. Meanwhile, the tetragonality of the perovskite phase is increased when Pb2+ ions increase due to its high polarization. The higher tunability of the (Pbx,Sr1−x
)0.85Bi0.1TiO3 thin film is exhibited when the film composition is close to the transformation point between the paraelectric and ferroelectric
phases. Pb2+ ions show a dominant factor to affect the Curie point of the system and then changing tunability.
Translated from Journal of Inorganic Materials, 2006, 21(2): 466–472 [译自: 无机材料学报] 相似文献
995.
The complex of lanthanum chloride with Glycine and Alanine,La(Gly)2(Ala)3Cl3·2H2O,was synthesized and characterized by IR,elementary analysis,thermogravimetric analysis,and chemical analysis.The dissolution enthalpies of LaCl3 ·7H2O(s),2Gly(s) 3Ala(s)and La(Gly)2(Ala)3Cl3 ·2H2O(s)were determined in 2 mol·L-1 HCl by a solution-reaction isoperibol calorimeter.By designing a thermochemical cycle in terms of Hess' Law and through calculation,the reaction enthalpy of lanthanum chloride seven-hydrate with Glycine and Alanine was obtained:ΔrHθm(298.15 K)=(29.652±0.504)kJ·mol-1,and the standard enthalpy of formation of La(Gly)2(Ala)3Cl3·2H2O(s)ΔfHθm [La(Gly)2(Ala)3Cl3·2H2O,s,298.15 K]=-4467.6±8.3 kJ·mol-1. 相似文献
996.
使用聚氯乙烯树脂、增塑剂、敏化剂、稳定剂、抗氧剂、填充剂等添加剂,通过对电线电缆辐照交联聚氯乙烯绝缘料配方体系、工艺性能等方面进行试验研究,获得了性能优良的辐照交联聚氯乙烯绝缘料,可适用于辐照交联聚氯乙烯绝缘料的生产。 相似文献
997.
998.
天然气水合物的生长动力学研究述评 总被引:1,自引:0,他引:1
对天然气水合物进行了介绍,从冰点以上和冰点以下两个温区对国内外水合物生长动力学的研究现状进行了分类与评述。对冰点以上晶体生长的动力学,从Vysniauskas & Bishnoi模型、Lekvam & Ruoff模型、Englezos模型、Englezos简化模型和Chen-Guo模型进行了讨论;对冰点以下的生长动力学,讨论了Sloan&Fleyfel模型和Christiansen & Sloan模型,对各自的优点进行了详细的分析,并指出了所存在的局限性。对水合物生成动力学的进一步研究进行了展望。同时还分析了临界成核半径和表面活性剂之间的关系。 相似文献
999.
Characterization of Hydraulic Fracture with Inflated Dislocation Moving Within a Semi-infinite Medium 总被引:1,自引:0,他引:1
OUYANG Zhi-hua ELSWORTH Derek LI Qiang 《中国矿业大学学报(英文版)》2007,17(2):220-225
Hydraulic fracturing is accompanied by a change in pore fluid pressure. As a result,this may be conveniently represented as inflated dislocation moving within a semi-infinite medium. Theory is developed to describe the pore pressures that build up around an inflated volumetric dislocation migrating within a saturated porous-elastic semi-infinite medium as analog to hydraulic fracturing emplacement. The solution is capable of evaluating the system behavior of both constant fluid pressure and zero flux surface conditions through application of a superposition. Characterization of horizontal moving dislocation processes is conducted as an application of these techniques. Where the mechanical and hydraulic parameters are defined,a priori,type curve matching of responses may be used to evaluate emplacement location uniquely. Pore pressure response elicited at a dilation,subject to pressure control is of interest in representing hydraulic fracturing where leak-off is an important component. The effect of hydraulic fracturing on fracture fluid pressure is evaluated in a poroelastic hydraulic fracture model utilizing dislocation theory. A minimum set of dimensionless parameters are defined that describe the system. Pore fluid pressures recorded during hydraulic fracturing of a well in the San Joaquin Valley of Central California is examined using the proposed model. The estimated geometry of the hydraulic fracture is matched with reasonable fidelity with the measured data. 相似文献
1000.
Differential formation of allophane and imogolite: experimental and molecular orbital study 总被引:1,自引:0,他引:1
Allophane and imogolite are naturally occurring aluminum silicate soil constituents with nano-ball and nano-tube morphology.
Wall of the both materials is composed of Al(OH)3 sheet with orthosilicic acid attached to it. Synthesis of allophane and imogolite can be controlled by addition of alkali
and alkaline-earth metal ions. The main reaction product without or with small amounts addition of the metal ions is imogolite,
while allophane forms when the metal ions were much added. The effect of metal ions on facilitating allophane formation and
inhibition of imogolite formation were greater in the following order of Na, K < Ca, Mg. These metal ions affect the degree
of dissociation of Si–OH group of orthosilicic acid, which may causes differential formation of allophane and imogolite. Structure
optimization of the proto-imogolite model, precursor of allophane and imogolite, showed that when the Si–OH was undissociated,
the shape of proto-imogolite model was transformed to asymmetrical in molecular configuration. This caused curling of the
proto-imogolite model, which lead to formation of imogolite tube. On the other hand, when the Si–OH was dissociated, the shape
of the proto-imogolite model was transformed to symmetrical configuration. This model curved to make a hollow sphere with
placing the orthosilicic acid inside the sphere (allophane). Both of the experimental and molecular orbital calculation results
proved that the dissociation of the Si–OH has an important role during the differential formation of allophane and imogolite. 相似文献