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91.
Engineered transport of material at the nano/micro scale is essential for the manufacturing platforms of the future. Unlike conventional transport systems, at the nano/micro scale, transport has to be achieved in the presence of fundamental sources of uncertainty such as thermal noise. Remarkably, it is possible to extract useful work by rectifying noise using an asymmetric potential; a principle used by Brownian ratchets. In this article a systematic methodology for designing open-loop Brownian ratchet mechanisms that optimize velocity and efficiency is developed. In the case where the particle position is available as a measured variable, closed loop methodologies are studied. Here, it is shown that methods that strive to optimize velocity of transport may compromise efficiency. A dynamic programming based approach is presented which yields up to three times improvement in efficiency over optimized open loop designs and 35% better efficiency over reported closed loop strategies that focus on optimizing velocities. 相似文献
92.
The correlation between rheological behavior and time evolution of the phase separation patterns was investigated in the epoxy/thermoplastic blends. Before and during the induction period of phase separation, the storage and loss modulus initially increased with epoxy curing reaction and the concentration fluctuation. At the late stage of phase separation, the modulus values also increased and showed a sharp enhancement around the epoxy gel point. However, the time evolution during the reaction induced phase separation process differed a lot at various thermoplastic (TP) concentrations. At the low TP concentrations, the rheological parameters decreased with the coarsening of sea-island structure. At the high TP concentrations, the TP-rich continuous structures initially formed and maintained until the end, resulting in a continuous increase for the rheological characters. At middle TP concentrations, formation and evolution of the three-layered structure displayed a complicated rheological behavior. It was found that the storage modulus quickly increased, reached a vertex, then rapidly decreased, reached a minimum, and increased again afterwards. Although the rheological behaviors were almost phenomenologically similar as that in the normal dynamically symmetric system, driving force for the variation was fundamentally different. Especially for the case of middle TP concentrations, the behavior of the holistic volume shrinking of the slow dynamic TP-rich network and the flowing out of the fast dynamic epoxy-rich phase from the network during this period, as radically transformed the nature of the matrix from an elastic network to a macro-phase separated layer structure and caused the dramatic change of the rheological behaviors. 相似文献
93.
94.
The marine operation of floating liquefied natural gas (FLNG) demands process compactness, flexibility, simplicity of operation, safety, and higher efficiency. The modified single mixed refrigerant (MSMR) process satisfies the FLNG process requirements and is accepted as a suitable technology for FLNG operation. The aim of this study was to develop a plant-wide control structure or strategy that can sustain the economic efficiency of the MSMR process. The NGL recovery and liquefaction units were integrated in the MSMR process to provide a compact plant structure with an efficient operation. Steady-state optimality analysis was intensively conducted in a rigorous dynamic simulation environment to determine the correct variable to sustain the economic efficiency of MSMR process. The results showed that the flow rate ratio of heavy and light mixed refrigerant (HK/LK ratio) is a promising self-optimizing controlled variable. Controlling this variable can sustain the MSMR optimality, even when the process is operated under off-design operating conditions or in the presence of disturbances. Based on the control structure tests, the control configuration with the HK/LK ratio loop showed excellent performance, maintaining the process stability against a range of disturbances. The proposed approach can also be applied to any cryogenic liquefaction technology for determining a possible optimizing controlled variable. 相似文献
95.
A novel class of polyurea-b-polyimide (PUI) block copolymer coating containing environmentally friendly aromatic polyurea has been successfully synthesized for corrosion protection of aluminum alloy 2024-T3 (Al 2024-T3). The PUI copolymer is able to self-assemble into a supramacromolecule by means of intra and inter-hydrogen bonds (H-bonds). The formation of H-bonds and effect of the later on the crystallinity of the copolymer was studied by using Fourier transform infrared spectroscopy (FTIR) and wide angle X-ray diffraction (WAXD). It was shown that increasing polyurea mole fraction up to 50 mol%, enhanced occurrence of H-bonding induced self-assembly, and resulted in remarkable enhancement in the degree of crystallinity, and corrosion resistance. Corrosion resistance and diffusivity of the copolymer coatings were investigated by electrochemical impedance spectroscopy (EIS), in a 3.5 wt% NaCl solution. The coating lifetime determined by using time-based corrosion resistance, was shown to be about 8 years for the optimized PUI copolymer coating. PUI coating synthesized by using 50 mol% of polyurea has a high contact angle (110°) and remarkably low surface energy of about 25.5 mJ/m2. 相似文献
96.
97.
选取肥料级磷酸一铵为原料,采取溶解、除杂、一次蒸干或者浓缩重结晶的方法制得磷酸一铵水溶肥,通过讨论各工艺条件的影响,确定了较优的工艺条件:溶解温度96℃、溶解时间30 min、溶质过量1.1倍、沉降(60 min)+真空过滤。产品w(N+P2O5)≥60%,满足水溶肥料化工行业标准HG/T 4365—2012。此法开辟了粉状磷酸一铵新的用途,为於渣酸料浆法生产磷酸一铵水溶肥提供除杂依据和工艺参考。 相似文献
98.
利用Gleeble-3500热模拟试验机对18CrNiMo7-6齿轮钢进行了等温单道次压缩试验,研究了变形温度为900~1150℃,应变速率为0.01~5 s-1,应变为0.76的条件下材料的热变形行为;并且通过光学显微镜对热变形后的微观组织进行了分析。建立了唯象型Arrhenius本构方程,预测的峰值应力与试验数据具有很好的一致性。高温热变形过程是加工硬化与动态回复以及动态再结晶的竞争过程,在热变形的过程中会形成变形晶粒、再结晶晶粒、等轴晶和晶粒长大等4种类型的微观组织。当应变速率为0.01 s-1时,动态再结晶程度与变形温度成正比,当变形温度超过1050℃时,变形能转变成晶粒长大的驱动能,使得晶粒粗大;当应变温度一定(1050℃)时,随着应变速率的增大,动态再结晶发生不完全,导致晶粒组织出现细化、畸变、不完全再结晶共存的现象。变形程度越大,晶粒越细小。 相似文献
99.
100.
通过热压缩实验研究了ZL270LF铝合金在变形量为70%,温度为300~550 ℃,应变速率为 0.01~10 s-1范围的热变形行为,建立了流变应力本构方程模型,绘制出了二维热加工图,确定了最佳热加工区域,采用电子背散射衍射(EBSD)和透射电子显微镜(TEM)技术研究了该合金的组织演变规律。结果表明:ZL270LF铝合金的流变应力随变形温度的升高和应变速率的降低而降低,热变形激活能为309.05 kJ/mol,最优热加工区为温度470~530 ℃、应变速率为0.01~1 s-1。该合金在热变形过程中存在3种不同的DRX机制,即连续动态再结晶(CDRX)、不连续动态再结晶(DDRX)和几何动态再结晶(GDRX),其中CDRX是ZL270LF铝合金动态再结晶的主要机制。 相似文献