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71.
Hiroaki Takeda Takeshi Shimada Yoshiaki Katsuyama Tadashi Shiosaki 《Journal of Electroceramics》2009,22(1-3):263-269
The electric properties of BaTiO3–(Bi1/2Na1/2)TiO3 (BT–BNT) solid solution ceramics were studied as a lead-free PTCR (positive temperature coefficient of resistivity) thermistor material usable over 130°C. For determining the maximum switching temperature T s, the phase diagram of BT–BNT binary system was clarified. Two semiconductorization processes and their electric properties are described. The lanthanum(La)-doped BBNT ceramics sintered in air still showed dielectric behaviors, but the niobium(Nb)-doped ones had a low resistivity at room temperature, ρ RT, on the order of 103 Ωcm and showed a PTC behavior. Sintering under a low O2 atmosphere produces BT–BNT ceramics with less than 102 Ωcm compared to those prepared in air. Our current research produced the BBNT ceramics with T s values around 210°C by increasing the (Bi1/2Na1/2) content in the ceramics. 相似文献
72.
73.
Yoshiaki Kikuchi Takeshi Nagatome Taka-aki Mizutani Hiroyuki Yoshino 《Soils and Foundations》2011,51(1):151-165
Cement-treated clay with air foam, which is called Super Geo-Material (SGM), was developed to utilize dredged clay in an effective way. As SGM is mainly used at levels below the ground water table, water permeability and absorption properties of SGM will affect the durability of the material. In this research, the changes in SGM permeability and absorption as functions of the air foam fraction were investigated. First, permeability tests with triaxial apparatus and constant rate of consolidation tests were conducted on samples containing less than 10% of air foam by volume. From the results, air foam was found to be an impermeable medium in SGM. Secondly, a series of permeability tests and absorption tests were conducted for the SGM with different fractions of air foam while observing the specimen with a micro focus X-ray Computed Tomography (CT) scanner. The results showed that the permeability of SGM increased dramatically due to the appearance of interior water channels when the air foam fraction exceeded 30% by volume. The density distribution change and water absorbed zones of the specimens during absorption tests were estimated using the X-ray CT data. From these results, the air in the SGM was found to be progressively substituted with water from the surface to the inside of the specimen and the substituted zone expanded as it made its way to the specimen interior. The expansion velocity of the substituted zone was not affected by the coefficient of permeability but by the fraction of the air in the specimen. 相似文献
74.
V.Yu. Osipov A.I. Shames T. Enoki K. Takai M. Endo T. Hayashi Y. Kaburagi A.Ya. Vul' 《Diamond and Related Materials》2009,18(2-3):220-223
Prolonged (up to 2 h) heat treatment at 1600 °C of nanodiamond particles (5 nm) leads to their conversion to the mixture of quasi-spherical carbon onions and multi-shell polyhedral nanographites. Structural and magnetic properties of two (A and B) series of nanographite samples obtained at various annealing intervals were studied. XRD data show that both multi-shell nanographite samples have practically the same crystalline structures. HRTEM evidences that the most of particles obtained by short time (7 min) annealing have a spherical like shape whereas the long time (~ 2 h) annealing leads to the majority of particles having a polyhedral shape with a hollow inside. Electronic and magnetic properties of these nanocarbons were investigated by magnetic susceptibility and EPR. Annealing results in entire transformation of the EPR signal of nanodiamond to new EPR signals of various line shapes and widths. These signals are extremely sensitive to ambient oxygen. Concentrations for all EPR active spins vary from ~ 1 × 1019 spins/g (7 min) to ~ 2 × 1019 spins/g (2 h). Temperature dependences of EPR spectra' parameters were obtained for vacuum-processed samples within the range 4?600 K. Intensity vs. T plots may be well-fitted by the combination of Curie–Weiss and temperature-independent Pauli susceptibility contributions. The latter one increases on heat treatment. Significant extension of electron spin-lattice relaxation time on decreasing temperature was found. 相似文献
75.
76.
Slags used in steelmaking and continuous casting that contain SiO2, Na2O, and CaF2 tend to be unstable and gaseous. Species, such as NaF and SiF4, evolve simultaneously from these slags at steelmaking temperatures. In addition, the reaction between NaF and SiF4 can occur to produce Na2SiF6 (sodium hexafluorosilicate). In a previous study on the vaporization of NaF into an inert gas stream, the diffusivity of
NaF in argon, nitrogen, and helium was measured. In this study, the rate of NaF vaporization in a SiF4 atmosphere was measured. Ternary diffusion coefficients were then evaluated from the binary diffusion coefficients obtained
in a previous study, and a kinetic analysis was carried out. The rate calculations were found to be in accord with the measured
results, indicating that the experiments were carried out in a regime where diffusion of NaF from the surface of the sample
was rate controlling. 相似文献
77.
Spontaneous fluoride emissions from high-temperature processes can result in an increased atmospheric fluorine content and
environmental contamination. Slags containing SiO2, Na2O, and CaF2 tend to be unstable at high temperatures, and gaseous species such as NaF and SiF4 evolve simultaneously. Furthermore, a reaction between NaF and SiF4 can occur to produce Na2SiF6 (sodium hexafluorosilicate), the behavior and properties of which are not well established. In a previous study, the diffusivity
of NaF in argon, nitrogen, and helium was measured. In this study, the rate of NaF vaporization in a SiF4-Ar atmosphere was investigated and the rates of formation and dissociation of Na2SiF6 were measured.
Kinetic analyses were carried out and the rate constants of the formation and dissociation of Na2SiF6 were obtained. The rate equation for Na2SiF6 formation was expressed as follows:
and the temperature dependences of k
c1 and k
c2 were
相似文献
78.
Thermotropic liquid-crystalline compounds were applied as membrane materials (membrane solvent and neutral carrier) for neutral carrier-type ion sensors to investigate how the ordered arrangement of neutral carriers affects the property of the resulting ion sensors. Nematic, smectic, and cholesteric liquid-crystalline compounds were used as the membrane solvents and crown ether derivatives with a molecular structure similar to the liquid-crystalline solvent as the K+ neutral carriers. Polarized IR spectroscopy and X-ray diffraction experiments confirmed that the highly ordered arrangement of membrane components was retained in the liquid-crystal-based ion-sensing membranes containing a neutral carrier and a lipophilic salt. The ordered arrangement of neutral carriers in the liquid-crystalline membranes enhanced the ion selectivity significantly, probably due to the efficient cooperation of two adjacent crown ether moieties in the highly ordered and aggregated state. 相似文献
79.
Digital watermarking by a holographic technique 总被引:18,自引:0,他引:18
A holographic technique is applied for digital watermarking by a computer. A digital-watermark image to be hidden is phase modulated in a random fashion, and its Fourier-transformed hologram is superposed on a content image. The watermark is reconstructed by means of a holographic-reconstruction technique from the bit-map image that hides it. In the study the processes of constructing and reconstructing a digital hologram are described on the basis of the theory of Fourier optics. The conditions for superposing the hologram onto the content images are investigated in detail. The validity of the present method is verified by changing the weighting of the hologram relative to that of the content image. The effect of image size is also discussed with respect to reconstruction of the watermark, and it is shown that watermark information in a form of a diffuse-type Fourier-transform hologram cannot be removed by cutting it out of the host image. 相似文献
80.
Organosilane self-assembled monolayers (SAMs) have been applied to resist materials for nanolithography based on scanning probe microscopy. An organosilane SAM was prepared on Si substrates from a precursor, that is octadecyltrimethoxysilane. Using an atomic force microscope with a conductive probe, current was injected from the probe into the SAM-covered Si substrate so that the SAM was locally degraded at the probe-contacting point. Nanoscale patterns drawn on the SAM was clearly imaged by lateral force microscopy. The patterning could be conducted in air while, in vacuum at the order of 10(-6) Torr, no detectable patterns were fabricated. The presence of adsorbed water at the probe/sample junction was confirmed to be crucial for the patterning of the SAM/Si. Its mechanism was, thus, ascribed to electrochemical reactions of both the SAM and Si with adsorbed water. 相似文献