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21.
The design of a 6 GHz fully monolithic phase-locked loop fabricated in a 1 μm, 20 GHz BiCMOS technology is described. The circuit incorporates a voltage-controlled oscillator that senses and combines the transitions in a ring oscillator to achieve a period equal to two ECL gate delays. A mixer topology is also used that exhibits full symmetry with respect to its inputs and operates with supply voltages as low as 1.5 V. Dissipating 60 mW from a 2 V supply, the circuit has a tracking range of 300 MHz, an rms jitter of 3.1 ps, and phase noise of -75 dBc/Hz at 1 kHz offset 相似文献
22.
Po-An Sung Kwang-Cheng Chen 《Selected Areas in Communications, IEEE Journal on》1996,14(8):1583-1594
We generalize the multiuser (CDMA spread spectrum) communication systems to the fading environments. We first extend Verdu's (1986) conventional optimum receiver to Rayleigh-fading environments and then evaluate its performance. Having no knowledge of the received power at the receiving end, we therefore need an estimator to efficiently estimate the received signal strength of each user in fading environments. A linear minimum mean square error (LMMSE) unbiased estimator is proposed to attain this goal. By using the minimum mean square error (MMSE) Bayesian estimation, we further propose the LMMSE bit estimator for efficient demodulation. Its performance is close to the optimum multiuser receiver but with a much simpler polynomial complexity. To further reduce the complexity, we extend the LMMSE estimator to the sequential LMMSE estimator. In sequential estimation, we do not need to implement the matched filter banks and to perform the matrix inversion when estimating. In addition, it converges after approximately 2k iterations, where k is the number of users. With this fast convergence property and the simple structure, the sequential LMMSE estimator provides an attractive alternative to the implementation of a multiuser system 相似文献
23.
CaO-Al2O3-MgO (CAM) ceramic fibre produced via inviscid melt spinning (IMS) was investigated for phase transformation. Differential thermal analysis (DTA) on the as-spun CAM fibre gave two transformation peaks, one for exothermic peak at around 927°C and the other for endothermic one at around 1100°C. In order to identify each phase transformation x-ray diffraction (XRD) analysis was performed on the CAM fibres heat-treated to each phase transformation completion temperature. The exothermic peak was determined to represent crystallization of remaining amorphous phase in the as-spun CAM fibre. The endothermic peak was determined to correspond to transformation of non-equilibrium CaO · Al2O3 phase to equilibrium 3CaO· 5Al2O3 phase. 相似文献
24.
In 2006, an involutional block cipher using cellular automata was proposed. A self-invertible CA-based structure allows for an efficient hardware implementation. This paper analyzes the insecurity of the cipher due to its conjugate property. The results of this study will make it possible to construct a decryption process without knowledge of the secret key. 相似文献
25.
Aragonite particles dispersed in a bioresorbable polymer matrix are considered to be a good candidate for bone prosthesis
materials. It is important to characterize the microstructure of synthetic aragonite used for biomedical applications, since
the microstructure may influence its integration, resorption and replacement by bone. We studied late stages of aragonite
growth, at an air–liquid interface, from a solution not doped with additives. Comparison was made between the types of synthetic
aragonite microstructure and that of aragonite which is found in nature (mollusc shells, gallstones, Earth's crust). The microstructure
of natural aragonite is unique to certain classes of living organisms and the understanding of its structure/function relationships
may help to select the types of synthetic aragonite for specific biomedical applications. Three types of synthetic aragonite
were observed based on grain size and grain morphology.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
26.
We report a family in which three siblings developed dementia between the ages of 40 and 70 years. Two of the siblings developed symptoms of depression, abnormal behavior, and an inability to function, progressing to severe dementia. The third sibling had a severe dementia, the clinical details of which are not available. In the two deceased siblings neuropathologic examinations demonstrated severe demyelination, axon loss, and gliosis in cerebral white matter. Cerebellar and brainstem white matter were unaffected. Cerebral gray matter was negligibly affected. The disorder, histopathologically classified as a pigmented orthochromatic leukodystrophy, is extremely rare. Its etiology is unknown, but the pathology and familial occurrence imply that it represents a genetic defect in a function localized in the cerebral white matter. 相似文献
27.
Kang Ji-Hoon Hwang Jinyul Sung Hyung Jin Ryu Hoon 《The Journal of supercomputing》2021,77(9):9597-9614
The Journal of Supercomputing - Direct numerical simulations (DNS) of turbulent flows have increasing importance because they not only provide fundamental understanding of turbulent flows but also... 相似文献
28.
H. C. Yang C. H. Nien H. H. Sung C. H. Chen 《Journal of Low Temperature Physics》1989,75(3-4):243-252
The electrical resistivity, ac susceptibility, critical current density, and Josephson tunneling of Pb/Ag multilayers have been measured in wide temperature ranges in order to study the proximity effect. A resistivity drop was found to occur atT
c
of Pb in versusT measurement and, at low temperature, the multilayers show proximity effect. The I-V characteristic of the multilayer shows voltage steps, indicating a resistive state has occurred in the sample. The superconducting properties of the multilayer were analyzed with the bilayer theory of the proximity effect. 相似文献
29.
Sung H. Whang 《Journal of Materials Science》1986,21(7):2224-2238
The application of rapid solidification technology (RST) to titanium alloy systems is relatively new and became the subject of active research since it was demonstrated that novel titanium alloys of higher temperature capability can be synthesized through new alloy design based on rapid solidification processing. The effects of rapid solidification on the occurrence of metastable phases, microstructures and mechanical properties in binary and ternary titanium alloys are reviewed. In particular, earlier results from RS-Ti alloy research have shown that many different novel dispersoids, some of which are coarsening-resistant at elevated temperatures (600 to 800° C), can be created in the matrix through RST. The alloys containing novel dispersoids also exhibit good creep resistance at elevated temperatures. Further studies on/- and-Ti alloys through RST, in conjunction with the development of various processing technologies for bulk alloy manufacturing, are clearly desirable. 相似文献
30.
Kyoung Duck Seo Jang Min Park Hyeonsoo Jeong Dong Sung Kim 《Microsystem Technologies》2014,20(2):243-250
We develop a miniaturized batch-type screw mixer (BSM) for uniform mixing of polymer resin and nanoparticles, based on the stretching of material elements. This stretching is induced by the combination of recirculating cross-sectional flows in deep channels of the screw and high shear stress developed at flight regions. The BSM is used to produce a polymer nano-composite composed of multi-walled carbon nanotubes and polydimethylsiloxane resin. The mixing performance of the BSM is characterized quantitatively by estimating two different types of mixing efficiencies (i.e., dispersive mixing and distributive mixing) via transmitted light microscope images. The developed BSM highly improves the mixing performance rather than that of a conventional ultrasonic mixing device. 相似文献