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991.
Covalent organic frameworks (COFs) are promising solid absorbents for the treatment of gaseous iodine. However, extensive efforts are still focused on empirical optimizations of specific binding sites and pore structures in COFs, and the chemical control of gaseous iodine uptake on COFs remains challenging. In this study, the chemically triggered sorption properties of COF-300 for I2 vapors at the single-particle level with the dark-field microscope (DFM) are explored. The present operando single-particle DFM imaging method enables the direct visualization of an adsorption activity transformation from inactive COF-300 to active solvated COF-300 toward gaseous I2 vapors. Exploiting the useful reaction information from time-lapsed DFM images, the tunable adsorption performance of solvated COF-300 is quantitatively compared by various solvents. The results illustrate that the isopropanol (IPA)-solvated COF-300 achieves the optimum adsorption capacity for I2 among the absorbents. The reaction mechanism is elucidated to be the channel size enlargement and modification of internal surface chemistry in the IPA-solvated COF-300, producing a stable I2/IPA-solvated COF-300 complex after the sorption reaction. The present chemical control of the sorption behavior of COF-300 revealed by DFM opens up a new fundamental paradigm for rationally developing high-performance COF-based absorbents for removing I2 vapors. 相似文献
992.
Shiyong Chen Zhenxin Yi Chongwei Jia Yan Li Houhe Chen Shunguan Zhu Lin Zhang 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(42):2302631
The requirements for high energy and green primary explosives are more and more stringent because of the rising demand in the application of micro initiation explosive devices. Four new energetic compounds with powerful initiation ability are reported and their performances are experimentally proven as designed, including non-perovskites ([H2DABCO](H4IO6)2·2H2O, named TDPI-0) and perovskitoid energetic materials (PEMs) ([H2DABCO][M(IO4)3]; DABCO=1,4-Diazabicyclo[2.2.2]octane, M=Na+, K+, and NH4+ for TDPI-1, -2, and -4, respectively). The tolerance factor is first introduced to guide the design of perovskitoid energetic materials (PEMs). In conjunction with [H2DABCO](ClO4)2·H2O (DAP-0) and [H2DABCO][M(ClO4)3] (M=Na+, K+, and NH4+ for DAP-1, -2, and -4), the physiochemical properties of the two series are investigated between PEMs and non-perovskites (TDPI-0 and DAP-0). The experimental results show that PEMs have great advantages in improving the thermal stability, detonation performance, initiation capability, and regulating sensitivity. The influence of X-site replacement is illustrated by hard–soft-acid–base (HSAB) theory. Especially, TDPIs possess much stronger initiation capability than DAPs, which indicates that periodate salts are in favor of deflagration-to-detonation transition. Therefore, PEMs provide a simple and feasible method for designing advanced high energy materials with adjustable properties. 相似文献
993.
《Journal of the European Ceramic Society》2023,43(8):3684-3693
The microstructural evolution of partially amorphous, atmospheric plasma-sprayed Yb-silicate coatings was investigated after heat treatment (HT, 1300 °C). Open porosity as well as crack area and widths in the coatings were characterized. A correlation was found between the increasing amorphous content of the as-sprayed coatings and the reduction in crack area due to crack healing after HT. Characterization results also suggested larger crack widths in the coatings after HT. The first crack-healing mechanism proposed was the capillarity-driven viscous flow of the amorphous phase in the coatings. It was experimentally shown that viscous flow-driven crack spheroidization (crack width enlargement), and crack healing started in the coatings at 1050 °C. Secondly, metastable to stable phase transformation (> 1100 °C) induced expansion in the constrained coatings was discussed as a crack healing mechanism. Finally, a two-step heat treatment was designed to prevent crack width enlargement during HT resulting in reduced porosity. 相似文献
994.
Siva Kumar Valluri Lawrence Salvati III Edward L. Dreizin Dana D. Dlott 《Propellants, Explosives, Pyrotechnics》2023,48(10):e202300031
Metal/oxidizer composites can potentially release more energy than organic explosives such as HMX (1,3,5,7-Tetranitro-1,3,5,7-tetrazocane), but are generally unsuitable for high-performance explosives due to slow energy release. These composites have physically separated fuel and oxidizer components, and their energetic combustion reactions are usually rate-limited by diffusive mass transfer. Here we describe studies of metal composite microparticles produced by arrested reactive milling (ARM) in an emulsion process fluid, which produces particles with internal pores intended to facilitate rapid shear mixing of fuel and oxidizer under shock compression. The particles were sectioned with a microtome to determine the extent of internal porosity versus particle size. We describe a tabletop high-throughput method for evaluating novel ARM composites, where a small number of composite microparticles are embedded in a transparent polymer and shocked by 4 km/s laser-launched flyer plates. We compared the thermal emission from the composites to an HMX standard to determine whether these particles had potential to release energy fast enough to support a detonation. The thermal emission was analyzed by an optical pyrometer yielding nanosecond time-dependent graybody temperatures and radiances. Thermal images were also obtained with a nanosecond camera in order to determine which particles were ignited by the shock. We found that the larger more porous particles ignited more readily, showing that internal porosity can be engineered to increase chemical reactivity under shock in metal/oxidizer composites. Both the composite and the HMX were ignited by shock on a <20 ns time scale, although the composite temperature of 5000 K was significantly greater than the 3500 K HMX temperature. 相似文献
995.
996.
Fabian Kraemer Michael Stähler Marcus Klein Matthias Oechsner 《Materialwissenschaft und Werkstofftechnik》2023,54(8):932-944
The fatigue behavior of bolted joints is critical to failure for many applications due to the high notch effect. Among other parameters, the life-time is based on the influence of the surface system, consisting of coating and lubricant. Intended to consider the surface system in the design and dimensioning process of bolted joints systematic experimental investigations are carried out for an exemplary selected basecoat and various lubricant systems. The basis is given by fatigue tests supported by selected methods of material analysis for the fractographic evaluation. A reproducible method to determine the crack initiation as well as the crack propagation has been developed for the evaluation of lubricant systems. 相似文献
997.
《Journal of the European Ceramic Society》2023,43(12):5078-5098
Crack formation is a common problem in ceramic additive manufacturing (CAM) process. In this paper, the forming characteristics of indirect ceramic additive manufacturing (DCAM) and direct ceramic additive manufacturing (IDCAM) technologies are comprehensively compared. The morphology and spatial distribution characteristics of micro and macro cracks in CAM are summarized. The crack formation mechanisms in different process stages of IDCAM, such as forming, sintering and cooling are analyzed and in DCAM are mainly discussed from the perspectives of stress distribution and energy release. The crack inhibition methods, including process parameters, auxiliary energy fields and material components are summarized comprehensively. The challenges and possible future trends of crack research in CAM are proposed. 相似文献
998.
为准确描述焊接结构的疲劳裂纹扩展行为,基于Abaqus、Zencrack及相应子程序建立了考虑材料不连续的疲劳裂纹扩展模拟方法. 对于初始埋藏裂纹位于焊缝区的平板焊接结构,考虑焊缝和母材不同强度匹配,进行疲劳裂纹扩展模拟,研究了不同强度匹配对焊接结构疲劳裂纹扩展寿命和扩展特性的影响. 研究结果表明,当裂纹前缘由焊缝跨越至母材区域时,焊缝和母材区域的应力强度因子计算结果出现明显变化,并随着裂纹尺寸的逐渐加大,两者差异越大. 随着焊缝材料裂纹扩展参数逐渐增大,母材区域的裂纹扩展相对速率逐渐变慢,裂纹形状逐渐由圆形向扁平状椭圆形过渡;相反地,母材区域的裂纹扩展相对速率逐渐变快,裂纹形状逐渐由圆形向椭圆形过渡. 文中的模拟方法有望为准确预测焊接结构的跨材料裂纹扩展行为提供有效途径.
相似文献999.
选区激光熔化的制造过程不可避免地会在构件内部和表面产生缺陷,如何从“合于使用”的角度评价缺陷微观尺度扩展行为对结构寿命周期服役完整性的影响是目前亟需解决的主要问题之一. 为了定量揭示疲劳裂纹萌生行为,借助Tanaka-Mura位错模型描述选区激光熔化成形GH3536合金的疲劳裂纹萌生及短裂纹扩展情况,分析由于缺陷位置、缺陷尺寸和缺陷类型等导致疲劳裂纹的表面和内部萌生的竞争情况. 结果表明,随着缺陷距表面距离的减小或等效缺陷尺寸的增加,疲劳失效模式由表面变为内部失效;选区激光熔化成形GH3536存在对应条件下的损伤容限,当缺陷尺寸较小时,构件的裂纹萌生模式不发生变化,但随着缺陷数量增多,疲劳短裂纹的扩展路径发生多次偏转且萌生寿命明显降低. 相似文献
1000.
《岩石力学与岩土工程学报(英文版)》2023,15(1):255-261
The blast-induced ground vibrations can be significantly controlled by varying the location and orientation of point of interest from blast site. The blast waves generated due to individual holes get superimposed and resultant peak particle velocity (PPV) generates. With the orientation sequence of holes blasts on site, the superimposition angle of wave changes and hence results in significant variation in resultant PPV. The orientation with respect to the initiation of blasts resulting in lowest PPV needs to be identified for any site. By knowing the PPV contour of vibration waves in mine sites, it is possible to reduce the vibration on the structures by changing the initiation sequence. In this paper, experimental blasts were conducted at two different mine sites and the PPV values were recorded at different orientations from the blast site and its initiation sequence. The PPV contours were drawn to identify the orientation with least and highest PPV generation line. It was found that by merely changing the initiation sequence of blasts with respect to the sensitive structure or point of interest, the PPV values can be reduced significantly up to 76.9%. 相似文献