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121.
The critical temperature, T
c, of metals is a fundamental point when vaporization due to high energy exchanges occurs. Although aluminum is a metal often
studied as a benchmark for theories, its critical temperature is not known with a high degree of accuracy. Its determination
by experiment is difficult as a result of its high value. This paper reviews the existing data and proposes new ones resulting
from recent measurements of particular physical properties and recent theoretical approaches. These new estimates lead to
the recommended value of T
c = (6700 ± 800) K. 相似文献
122.
123.
124.
125.
Zorb Ch Weisert A Stapelmann J Smolik G Carter DC Wright BS Brunner-Joos KD Wagner G 《Microgravity science and technology》2002,13(3):22-29
For the purpose of bio-electronics, bacteriorhodopsin was crystallized into two habits through liquid-liquid-diffusion, namely individual needles of up to 1.9 mm in length and needle bunch-like clusters of up to 4.9 mm in total length. In both the reduced gravity experiments performed, the morphology of the individual needles (crystal form A) had improved in terms of sharp needle edges and compact needle packing, compared to the parallel ground controls. For the long duration wide range low gravity condition in the "Diffusion-controlled Crystallization Apparatus for Microgravity (DCAM)" on Mir (STS-89 up), needle bunches on average were longer there than on the ground, while the compactness of the clusters, i.e. the average ratio of clustered length to clustered width was the reverse. Some exceptionally large individual needles were grown in DCAM. For the "Commercial Protein Crystallization Facility (CPCF)" in short duration high definition microgravity condition during a science mission of the Space Shuttle Discovery (STS-95), size and shape of the individual needles were homogeneous and superior to those of both the parallel ground controls and the results in DCAM. In CPCF, the average volume of the individual needles in suspension was increased by 50 % in microgravity compared to those in the ground control. 相似文献
126.
The large-angle convergent beam electron diffraction (LACBED) technique is used for determining the crystal polarity of GaP and GaAs single crystals from < 1 1 0 > cross-sectional samples. The method which is based on an earlier approach using convergent beam electron diffraction (CBED) evaluates the polarity-sensitive contrast of high odd-index Bragg-lines in [0 0 2] dark-field patterns. The polarity is determined by application of a simple contrast rule as well as by direct comparison with dynamical simulations. For the two materials the ranges of applicability are determined by a detailed analysis of the Bragg-line contrast as a function of the sample thickness. The coexistence of the Bragg-line pattern and the of shadow image of the defect in correct rotational relationship to each other makes the analysis straightforward and free from possible sources of errors. As an example, the crystal polarity of GaP is related to the morphology of facetted voids. The LACBED method is shown to be suitable for relating the analysis of extended crystal defects. The advantages and the disadvantages of the LACBED method are discussed in comparison with the corresponding CBED method and with a recent method based on the analysis of bend contours. 相似文献
127.
The systolic processing offers the possibility of solving a large number of standard problems on multicellular computing devices
with autonomous cells (Processing Elements—PEs). The resulting systolic arrays exploit the underlying parallelism of many
computationally intensive problems and offer a vital and effective way of handling them. Advances in technology and especially
in VLSI and FPGA have an ongoing contribution to the evolution of systolic arrays. Herein, a FPGA-based Systolic array prototype
implementing the Factorization stage of the Quadrant Interlocking Factorization—QIF (Butterfly) method is presented and the
corresponding time-complexities achieved are discussed. 相似文献
128.
We address the problem of image similarity in the compressed domain, using a multivariate statistical test for comparing color distributions. Our approach is based on the multivariate Wald-Wolfowitz test, a nonparametric test that assesses the commonality between two different sets of multivariate observations. Using some pre-selected feature attributes, the similarity measure provides a comprehensive estimate of the match between different images based on graph theory and the notion of minimal spanning tree (MST). Feature extraction is directly provided from the JPEG discrete cosine transform (DCT) domain, without involving full decompression or inverse DCT. Based on the zig-zag scheme, a novel selection technique is introduced that guarantees image's enhanced invariance to geometric transformations. To demonstrate the performance of the proposed method, the application on a diverse collection of images has been systematically studied in a query-by-example image retrieval task. Experimental results show that a powerful measure of similarity between compressed images can emerge from the statistical comparison of their pattern representations. 相似文献
129.
Th. Zahner Ch. Stoiber E. Zepezauer H. Lengfellner 《Journal of Infrared, Millimeter and Terahertz Waves》1999,20(6):1103-1111
Thermoelectricity is investigated in a material designed to show anisotropic transport properties: Copper/constantan/copper $ \cdot \cdot \cdot $ multilayer structures were prepared by sintering of a compressed stack of alternating foils of these materials and are described by effective “in-plane” properties $S_\parallel $ and $k_\parallel $ for the Seebeck-coefficient and the thermal conductivity along the layers, and “out-of-plane”-properties $S_ \bot $ and $k_ \bot $ along the stack axis. Samples in form of thin slabs prepared by cutting the stack obliquely to the stack axis showed thermoelectric fields transverse to temperature gradients across the slab due to off-diagonal elements in the Seebeck-tensor, and may be used as devices for detection of laser radiation. 相似文献
130.
J. Reyes-Gasga R. García G O. Alvarez-Fregoso J. A. Chávez-Carvayar L. E. Vargas-Ulloa 《Journal of Materials Science》1999,34(9):2183-2188
When human tooth enamel is heated either in vacuum or air it presents drastic changes in electrical susceptibility, conductivity and structural properties. In this paper we report an insulator-conductive transition which is observed in air around 350°C where enamel conductivity changes drastically and its electrical resistance decreases from 1015 to 105 that is, it goes from an insulator to a super-ionic ceramic behavior. This transition, first evidenced in vacuum by electron microscopy observations, is now completely determined by a.c. impedance spectroscopy technique and its characterization was carried out as a function of the frequency and temperature. X-ray in situ heating diffraction experiments show that there is no structural phase transition during a wide range of temperature including the one where the conductivity transition occurs. 相似文献