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71.
Polyurethane macroiniferter/poly(methyl methacrylate) block copolymer dispersions with inverse core‐shell morphologies were obtained from 1,1,2,2,‐tetraphenylethane‐1,2‐diol, dimethylol propionic acid, 4,4′‐diphenylmethane diisocyanate, and poly(propylene glycol) via a living radical mechanism. Molecular weight, particle size and dispersion viscosity, and thermal, mechanical, and dynamic mechanical properties of the dispersion cast films are reported as a function of copolymerization time. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1971–1975, 2003 相似文献
72.
Automating fluid delivery in a capillary microfluidic device using low-voltage electrowetting valves
A multilayer capillary polymeric microfluidic device integrated with three normally closed electrowetting valves for timed fluidic delivery was developed. The microfluidic channel consisted two flexible layers of poly (ethylene terephthalate) bonded by a pressure-sensitive adhesive spacer tape. Channels were patterned in the spacer tape using laser ablation. Each valve contained two inkjet-printed silver electrodes in series. Capillary flow within the microchannel was stopped at the second electrode which was modified with a hydrophobic monolayer (valve closed). When a potential was applied across the electrodes, the hydrophobic monolayer became hydrophilic and allowed flow to continue (valve opened). The relationship between the actuation voltage, the actuation time, and the distance between two electrodes was performed using a microfluidic chip containing a single microchannel design. The results showed that a low voltage (4.5 V) was able to open the valve within 1 s when the distance between two electrodes was 1 mm. Increased voltages were needed to open the valves when the distance between two electrodes was increased. Additionally, the actuation time required to open the valve increased when voltage was decreased. A multichannel device was fabricated to demonstrate timed fluid delivery between three solutions. Our electrowetting valve system was fabricated using low-cost materials and techniques, can be actuated by a battery, and can be integrated into portable microfluidic devices suitable for point-of-care analysis in resource-limited settings. 相似文献
73.
Studies have been made of the effect of Cd2+ on the oxidation rate of C3H8 in 80% H3PO4 at 130 C on platinized Pt electrodes.Dissolved Cd2+ discharges, probably as Cd0, and forms a stable sub-monolayer on a Pt electrode at potentials as high as 0·5 V versus RHE. Although this Cd0 layer is apparently substantially desorbed in favor of adsorbed hydrocarbon, C3H8 adsorption is inhibited in its presence. C3H8 oxidation is also inhibited. However, the C3H8 oxidation rate is observed to increase under some circumstances, and this appears to be because Cd isabsorbed into the Pt lattice. Co-plating of Cd and Pt leads to an electrode which, once the excess Cd has been removed, appears to be stable, and which catalyses C3H8 oxidation by about a factor of three at 0·25 V. Above 0·3 V, this absorbed Cd somewhat inhibits C3H8 oxidation. 相似文献
74.
Free acids of the iron substituted heteropoly acids (HPA), H7[(P2W17O61)FeIII(H2O)] (HFe1) and H18[(P2W15O56)2FeIII2(H2O)2] (HFe2) were prepared from the salts K7[(P2W17O61)FeIII(H2O)] (KFe1) and Na12[(P2W15O56)2FeIII4(H2O)2] (NaFe4), respectively. The iron-substituted HPA were adsorbed on to XC-72 carbon based GDLs to form HPA doped GDEs after water washing with HPA loadings of ca. 1 μmol. The HPA was detected throughout the GDL by EDX. Solution electrochemistry of the free acids are reported for the first time in sulfate buffer, pH 1-3. The hydrogen oxidation reaction was catalyzed by KFe1 at 0.33 V, with an exchange current density of 38 mA/cm2. Moderate activity for the oxygen reduction reaction was observed for the iron substituted HPA, which was dramatically improved by selectively removing oxygen atoms from the HPA by cycling the fuel cell cathode under N2 followed by reoxidation to give a restructured oxide catalyst. The nanostructured oxide achieved an OCV of 0.7 V with a Tafel slope of 115 mV/decade. Cycling the same catalysts in oxygen resulted in an improved catalyst/ionomer/carbon configuration with a slightly higher Tafel slope, 128 mV/decade but a respectable current density of 100 mA/cm2 at 0.2 V. 相似文献
75.
Moon Sam Shin Ki-Pung Yoo Chul Soo Lee Hwayong Kim 《Korean Journal of Chemical Engineering》2006,23(3):469-475
A multi-fluid nonrandom lattice fluid model with no temperature dependence of close packed volumes of a mer, segment numbers
and energy parameters of pure systems is presented. The multi-fluid nonrandom lattice fluid (MF-NLF) model with the local
composition concept was capable of describing properties for complex systems. However, the MF-NLF model has strong temperature
dependence of energy parameters and segment numbers of pure systems; thus empirical correlations as functions of temperature
were represented for reliable and convenient use in engineering practices. The MF-NLF model without temperature dependence
of pure parameters could not predict thermodynamic properties accurately. It was found that the present model with three parameters
describes quantitatively the vapor pressure and the saturated density for the pure fluid. 相似文献
76.
Won Seok Lyoo Jeong Hyun Yeum Byung Chul Ji Han Do Ghim Sam Soo Kim Joon Ho Kim Ji Youl Lee Jinwon Lee 《应用聚合物科学杂志》2003,88(6):1482-1487
Water‐soluble high molecular weight (HMW) syndiotactic poly(vinyl alcohol) (s‐PVA) microfibrillar fibers were prepared by the saponification with various conditions such as amount of alkali solution, saponification temperature, and saponification concentration from copoly(vinyl pivalate (VPi)/vinyl acetate (VAc)) copolymerized using various VPi/VAc feed ratios. To produce s‐PVA microbrillar fibers having various water‐soluble temperatures for many industrial applications, the intrinsic viscosities, syndiotactic diad (S‐diad) contents, and degrees of saponification (DS)s of PVAs were finely controlled to 1.2–3.6 dL/g, 56.3–58.3%, and 91.4–98.3%, respectively. Through a series of experiments, it was found that the amount of alkali may alter the structure of the saponified polymers, primarily the DS, and the structural variation changes viscosity. That is, intrinsic viscosity was sharply decreased as the amount of alkali solution was increased. DS was increased with an increase in the amount of alkali solution. S‐diad content was increased with an increase in the VPi content. HMW s‐PVA microfibrillar fibers having S‐diad content of 56.3–58.3% prepared by the saponification of copoly(VPi/VAc) were completely soluble in water at 100°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1482–1487, 2003 相似文献
77.
J. C. Moreland G. L. Wilkes C. G. Moreland S. S. Sankar E. O. Stejskal R. B. Turner 《应用聚合物科学杂志》1994,52(9):1175-1180
High-resolution solid-state 13C-NMR has been used to study the phase separation and molecular motion in two series of polyurethane foams. These two series differ by one possessing the additive of lithium chloride, LiCl. NMR relaxation times can map the motion throughout the polymer molecule and detect changes in that motion arising from either microseparation or phase mixing between the different segments. There are only slight changes in the soft segment T1p(13C) values as well as an increase in the hard segment T1p(1H) values with increase in the hard segment content for the foams studied. The T1p(1H) and T1p(13C) values do indicate that the phase separation of the hard and soft segments is similar for all foams. A decrease in the T1p(1H) and T1p(13C) values with increasing LiCl content indicates that the motion of the soft segments is restricted more by the hard segments. This is explained by more phase mixing in the foams containing the LiCl additive. © 1994 John Wiley & Sons, Inc. 相似文献
78.
Submicrometer epitaxial films of YBa2Cu3O7(YBCO) on (100) LaAlO3 were made by coevaporation and furnace annealing. Samples from more than a dozen runs are used in this study. The zero resistance transition temperature (T
c) is high (89 or 90 K) if the film composition is phase pure (Ba/Y=2, Cu/Y=3) or if it is enriched in Ba and Cu. For these compositions the critical current density (J
c) at 77 K has an average value of 2×105 A cm–2, with a tendency for decreasingJ
c with increasing film thickness (0.2 to 0.8m). Variations inJ
c are not correlated with deviations from ideal stoichiometry. Steeper slopes of the resistance-temperature curves above 100 K and lower values of the room-temperature resistivity are associated with high values ofJ
c. If the film composition is enriched in Y relative to Ba and Cu,T
c decreases by several degrees. 相似文献
79.
Software and Systems Modeling - Advances in model-based system engineering have greatly increased the predictive power of models and the analyses that can be run on them. At the same time, designs... 相似文献
80.