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41.
Dilute 3-component 1-phase solutions in methylene chloride of poly(styrene-acrylonitrile) PSAN and polycarbonate PC are used to cast phase separated thin films. Films of pure PSAN, pure PC and five intermediate compositions are examined. The films are bonded to copper grids and strained at a constant rate of 4.1 × 10–6sec–1. The median tensile strain
v for void formation is determined using an optical microscope and the regions surrounding the voids are examined by TEM. At room temperature and slow strain rates both PSAN and PC plastically deform by shear yielding. For pure PSAN
v was found to be 0.13 whereas for PC
v exceeds 0.23. The addition of the more ductile polymer PC to PSAN at weight fractionsx forx 0.4 decreases
v. In this case voids form in crazes at the boundaries between the PC-rich inclusion and the PSAN-rich matrix. When the PC content is increased tox = 0.8,
v approaches 0.23. The effect of physical ageing (annealing belowT
g the glass transition temperature) on the mode of plastic deformation was also examined over the same compositional range. Physical ageing was found to suppress shear deformation and favour crazing in PSAN and PSAN-rich phases. Because crazes are more susceptible to breakdown than DZ's (shear deformation zones), physical ageing results in a marked decrease in
v. The breakdown statistics of these phase separated partially compatible blends was found to follow a Weibull distribution in strain from which two parameters may be extracted: the Weibull modulus and
w the Weibull scale parameter. is a measure of the breadth of distribution of void initiation and
w is a measure of the median strain to void formation in the films. The behaviour of
w was found to approximately mirror
v. The Weibull modulus appears to be primarily controlled by the matrix phase. 相似文献
42.
Effects of allelochemicals on plant respiration and oxygen isotope fractionation by the alternative oxidase 总被引:8,自引:1,他引:8
The goal of this investigation was to determine the effects of allelochemicals on plant respiration that thereby may be responsible for their role in growth inhibition. We have tested the effects of juglone, quercetin, cinnamic acid, and-pinene on respiration rates, and electron partitioning through the cytochrome and alternative respiratory pathways, by measuring on-line oxygen consumption and oxygen isotope fractionation in soybean cotyledon tissue. Cinnamic acid and-pinene decreased the oxygen consumption rate and increased the relative partitioning of electron transport to the alternative pathway. Possible biochemical mechanisms of these effects are discussed. 相似文献
43.
Rama Subba Reddy Gorla Jorge E. Gatica Bahman Ghorashi Pijarn Ineure Larry W. Byrd 《Chemical Engineering Communications》2004,191(5):718-731
Heat transfer enhancement in an evaporating thin liquid film utilizing a electric field under isothermal interfacial condition is presented. A new mathematical model subjected to van der Waals attractive forces, capillary pressure, and an electric field is developed to describe the heat transfer enhancement in the evaporating thin liquid film. The effect of the electrostatic field on the curvature of the thin film, evaporative flux, pressure gradient distribution, heat flux, and heat transfer coefficient in the thin film is presented. The results show that applying an electric field can enhance heat transfer in a thin liquid film significantly. In addition, utilizing electric fields on the evaporating film will be a way to expand the extended meniscus region to attain high heat transfer coefficients and high rates of heat flux. 相似文献
44.
John A. Byers David L. Wood John Craig Larry B. Hendry 《Journal of chemical ecology》1984,10(6):861-877
Quantities of attractive (exo-brevicomin and frontalin) and inhibitory (trans-verbenol, verbenone, and ipsdienol) pheromones were monitored in both sexes ofDendroctonus brevicomis during their colonization of a ponderosa pine. Verbenone was found in males in the greatest amounts at the time of landing, and it declined more rapidly than the other pheromones in either sex. The amounts of frontalin andexo-brevicomin in males and females, respectively, increased after initial boring within the host but began to decline after mating. The quantity oftrans-verbenol in both sexes (females had significantly more) declined more gradually thanexo-brevicomin, frontalin, and verbenone. Ipsdienol was found only in males during the initial stages of attack when encountering the resin. It is suggested that along with a general decline in all pheromonal components, a sufficient change in the ratio of the attractive pheromones to an inhibitory pheromone,trans-verbenol, may play a role in termination of aggregation.trans-Verbenol may also function along with verbenone and ipsdienol in limiting the density of attack and thus intraspecific competition. These inhibitory pheromones also appear to cause several competing species of bark beetle to avoid landing in areas infested withD. brevicomis, even when their own pheromone is present.Coleoptera:Scolytidae. These studies were supported in part by the Rockefeller Foundation, USDA Forest Service, Regional research project W-110, SEA/ USDA, and the National Science Foundation and Environmental Protection Agency through a grant (NSF GB-34719/BMS 75-04223) to the University of California. 相似文献
45.
Larry N. Lewis Chris A. Sumpter Mark Davis 《Journal of Inorganic and Organometallic Polymers》1995,5(4):377-390
The Command-Cure concept is defined for a curable formulation as one with long work-like at ambient temperature and rapid cure time at elevated temperature. This concept is explored for a curable silicone system, cured via hydrosilylation. CODMCl2 complexes (COD=1.5-cyclo-octadiene:M=Pt. Pd) are reacted with beta-cyclodextrin (-CD) to make 11 inclusion compounds,M=Pd.2;M=Pt.4. Compounds2 and4 were analyzed by1H NMR and X-ray powder diffraction. Their catalytic ability was evaluated in a model system as well as a polymeric system that gels upon cure. Surprisingly, the Pd analog2 was a good command-cure catalyst whereas the guest compound CODPdCl2,1, was not active in the hydrosilylation reaction. The Pt analog,4, was an effective command-cure catalyst while the corresponding guest. CODPtCl2,3, was too active at low temperature in the hydrosilylation reaction. Additional Pt compounds and one Rh inclusion compound were evaluated as command cure catalysts. These inclusion compounds were: 11 -CD:[CODRhCl]2,5: 11 -CD:CpPtMe3,6 (Cp=cyclopentadienyl): 12 -CD:MeCpPtMe3,7; 12 -CO:CODPtMe2,8. The effectiveness of4 8 was evaluated in a number of silicone systems. 相似文献
46.
The kinetics of the extraction of a high-volatile bituminous coal with 1,2,3,4-tetrahydronaphthalene (tetralin) under the influence of ultrasonic energy has been studied at five temperatures: from 47 to 87°C. The effects of intensity of ultrasonic energy, particle size, and hydrogen content of the coal were also recorded. Analysis of the results showed that a second-order reaction followed by a first-order reaction best describes the kinetics of the extraction process. The enthalpies of the second-order and first-order regions were respectively 8.7 and 2.5 kcal/mol, suggesting essentially physical control. The entropies were respectively ?44 and ?70 e.u. Auxiliary experiments and the kinetic data obtained suggest a model for the extraction process. The mechanism of the overall reaction is undoubtedly complex, but the data indicate that van der Waals and hydrogen-bonding forces are most affected by the ultrasonic energy, although stronger bonding is also affected giving much higher yields than would be expected. From the yields obtained in this study it is concluded that ultrasonic energy acts by rupturing bonds that are not affected by the solvent alone; the bonds affected are either strong hydrogen bonds or aliphatic covalent bonds, but not aromatic bonds. 相似文献
47.
The relative viscosity (RV) of polyvinylpyrrolidone (PVP) with different molecular weights was measured with a glass capillary viscometer and with a differential dual‐capillary viscometer in water at different concentrations. For the differential dual‐capillary viscometer, RV increases with a decreasing flow rate, especially for high molecular weight PVP at a 1% concentration. A good agreement in the RV between the two methods can be obtained for PVP with different molecular weights and at various concentrations if an appropriate flow rate is selected for the differential dual‐capillary viscometer. Special precaution is needed when using the differential dual‐capillary viscometer to measure the viscosity of a pure solvent. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1312–1315, 2002 相似文献
48.
49.
Louise M. Canfield Judy M. Hopkinson Anne F. Lima Gail S. Martin Kyoto Sugimoto Jeanne Burr Larry Clark Daniel L. McGee 《Lipids》1990,25(7):406-411
A quantitative method was developed for the assay of vitamin K in human colostrum and milk. The procedure combines preparative
and analytical chromatography on silica gel in a nitrogen atmosphere followed by reversed phase high performance liquid chromatography
(HPLC). Two HPLC steps were used: gradient separation with ultraviolet (UV) detection followed by isocratic separation detected
electrochemically. Due to co-migrating impurities, UV detection alone is insufficient for identification of vitamin K. Exogenous
vitamin K was shown to equilibrate with endogenous vitamin K in the samples. A statistical method was incorporated to control
for experimental variability. Vitamin K1 was analyzed in 16 pooled milk samples from 7 donors and in individual samples from 15 donors at 1 month post-partrum. Vitamin
K1 was present at 2.94±1.94 and 3.15±2.87 ng/mL in pools and in individuals, respectively. Menaquinones, the bacterial form
of the vitamin, were not detected. The significance of experimental variation to studies of vitamin K in individuals is discussed. 相似文献
50.
David Kritchevsky Larry M. Davidson Daniel A. Scott J. J. Van der Watt Dennis Mendelsohn 《Lipids》1988,23(3):164-168
Male Vervet monkeys (7/treatment) were fed a “Western” diet containing 46.2% calories as fat, 39.8% as carbohydrate and 14.0%
as protein. The diet was augmented with 10% cellulose or 10% pectin. A third (control) group of seven monkeys was fed a commercial
ration augmented with fruit and bread. After 34 weeks, serum cholesterol levels were elevated significantly in the two test
groups compared with the controls but there was no difference between the two fiber-fed groups. Serum triglycerides were unaffected.
Liver cholesterol levels were the same in all three groups but liver triglyceride levels were lower in the monkeys fed cellulose.
Biliary lipids were similar in all three groups as were the calculated lithogenic indices. The average aortic sudanophilia
(percent of total area) in the three groups was cellulose, 10.6±2.5; pectin, 8.1±2.5; and control, 1.1±0.4. One animal in
each of the groups fed “Western” diet exhibited an atherosclerotic plaque. The results indicate that there is no difference
between pectin and cellulose with regard to their effects on either lipidemia or aortic sudanophilia in Vervet monkeys fed
a Western-type diet. 相似文献