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61.
One of the basic parameters characterizing the bond between a chemisorbed atom (or molecule) and the surface is its dissociation energy. It is difficult, however, to determine the bond energy and therefore it becomes necessary to turn to some other quantity, which is sufficiently close to the bond energy and which can be determined without much difficulty. Such a quantity is the heat of adsorption. Heat of adsorption is defined as the difference between the total energy of the adsorption system prior to and after the adsorption process, i.e., it equals the sum of all energy changes connected with adsorption. Thus the experimentally determined value for the heat of adsorption is obviously closely related to the bond energy of the chemisorbed particle, though this relation is not quite simple [1,2]. 相似文献
62.
Zero-field cooled-field-cooled (ZFC-FC) technique was used to investigate the effect of low temperature (4.6 K) on the interactions of polarons in weakly FeCl3-doped poly(3-dodecylthiophene (PDDT). It was found that the magnetic properties of the system changed with the length of time system spent at low temperature: the Currie–Weiss paramagnetism gradually changed over to “antiferromagnetism” and ultimately to diamagnetism. This effect is connected with the thermochromic properties of self-organized PDDT in primary (10–15 nm) or secondary (30–50 nm) induced aggregates, in which cooling under the glass transition temperature Tg (~240 K) causes extension of the effective conjugation length of coplanar polymer chains. Changes in magnetic properties are related to the inter- and intra-chain interactions of polaron states within both the primary and secondary induced aggregates. 相似文献
63.
J. Čížek O. Melikhova M. Vlček F. Lukáč M. Vlach I. Procházka W. Anwand G. Brauer A. Mücklich S. Wagner H. Uchida A. Pundt 《International Journal of Hydrogen Energy》2013
The development of the microstructure in nanocrystalline, polycrystalline and epitaxial Pd films loaded with hydrogen is investigated. Structural changes in Pd films loaded with hydrogen were characterized by positron annihilation spectroscopy combined with electron microscopy and X-ray diffraction. It was found that hydrogen charging causes plastic deformation which leads to an increase of the defect density in all Pd films studied. Moreover, the formation of buckles was observed in nanocrystalline and polycrystalline Pd films loaded above a certain critical hydrogen concentration. Buckling leads to detachment of the film from the substrate and this is accompanied with in-plane stress relaxation and plastic deformation of the film. 相似文献
64.
Časlav Brukner 《Natural computing》2009,8(3):449-453
Whenever a mathematical proposition to be proved requires more information than it is contained in an axiomatic system, it
can neither be proved nor disproved, i.e. it is undecidable, or logically undetermined, within this axiomatic system. I will
show that certain mathematical propositions on a d-valent function of a binary argument can be encoded in d-dimensional quantum states of mutually unbiased basis (MUB) sets, and truth values of the propositions can be tested in MUB
measurements. I will then show that a proposition is undecidable within the system of axioms encoded in the state, if and
only if the measurement associated with the proposition gives completely random outcomes. 相似文献
65.
Poly{1-[p-(mercaptomethyl)phenyl]ethylene} with a low content of divinylbenzene units as the crosslinking component was prepared from chloromethylated poly(styrene-co-divinylbenzene), and the activity of the thiolate form in the debromination reactions of 1,2-dibromocyclohexane was investigated with respect to the analytical content of the -SH groups. The extent of transformation of the -SH groups into the thiolate form, and the degree of crosslinking of the polymeric carrier were investigated. An almost complete conversion of 1,2-dibromocyclohexane and high yields of cyclohexene were obtained by using polymeric thiols with the initial DVB contents of 1 or 2%; the degree of functionalization of the carrier 100% or 30–60%; and the reaction times of polymeric thiols with sodium methoxide in methanol (1–2h). The debromination reaction required 5h for completion. Under optimum conditions, debromination of 1,2,5,6-tetrabromocyclooctane, α,β-dibromoethylbenzene, α,β,3,4-tetrabromoethylcyclohexane, diethyl2,3-dibromosuccinate and stilbene dibromide gave olefins in yields of 60–100% 相似文献
66.
Lenka Monincová Dr. Milos Buděšínský Sabina Čujová Dr. Václav Čeřovský Dr. Václav Veverka 《Chembiochem : a European journal of chemical biology》2014,15(2):301-308
Lasiocepsin is a unique 27‐residue antimicrobial peptide, isolated from Lasioglossum laticeps (wild bee) venom, with substantial antibacterial and antifungal activity. It adopts a welldefined structure consisting of two α‐helices linked by a structured loop. Its basic residues form two distinct positively charged regions on the surface whereas aliphatic side chains contribute to solvent‐accessible hydrophobic areas, thus emphasising the amphipathic character of the molecule. Lasiocepsin structurally belongs to the ShK family and shows a strong preference for anionic phospholipids; this is further augmented by increasing concentrations of cardiolipin, such as those found at the poles of bacterial cells. The membrane‐permeabilising activity of the peptide is not limited to outer membranes of Gram‐negative bacteria. The peptide interacts with phospholipids initially through its N terminus, and its degree of penetration is strongly dependent on the presence of cardiolipin. 相似文献
67.
Zbyšek Pavlík Lukáš Fiala Miloš Jerman Eva Vejmelková Milena Pavlíková Martin Keppert Robert Černý 《International Journal of Thermophysics》2014,35(9-10):1912-1921
The moisture-dependent thermal conductivity of two types of lightweight ceramic brick body is analyzed using both theoretical and experimental approaches. The basic physical properties are determined at first. Then, an impulse method is applied for the thermal-conductivity measurement. Initially, the material samples are dried, after that, they are exposed to liquid water for specific time intervals, and finally the moisture content is allowed to homogenize within the whole volume. The thermal-conductivity measurement is performed for different moisture contents achieved in this way. In the theoretical part, the homogenization principles are used for the calculation of the moisture-dependent thermal conductivity, utilizing the distribution functions based on the pore-size distribution measurement. Finally, a comparison of the measured and calculated data is done, and the validity of the applied effective media treatment is assessed. 相似文献
68.
69.
This paper indicates that changes in chain mobility, heat capacity, WAXS crystallinity, SAXS long period, SAXS peak intensity, specific volume and morphology as a function of increasing temperature, occur in three fairly distinct annealing ranges (I, II and III) that are more or less the same for all crystallized polymers with a lamellar morphology. It is shown that none of the proposed molecular models to date, including the well-known fold surface premelting model, can satisfactorily account for all the experimental data. However, a new molecular interpretation, based primarily on electron microscopy and SAXS studies of changes such as lateral ‘melting’ from edges of microparacrystallites (mPC) within the lamellae seen at the annealing temperatures can account for the data. With our new molecular interpretation, the effect of temperature increase is established to result in a slight breakup of the laterally aligned mPC within the lamellae at low annealing temperatures in range I, and selective lateral ‘melting’ of the exposed mPC and recrystallization at higher annealing temperatures in ranges II and III, with the recrystallization being very limited in range III. Annealing effects seen in cold- or hot-drawn polymers with a fibrillar morphology can also be readily accounted for by this very general molecular mechanism occurring in the same annealing temperature ranges. 相似文献
70.
Creep of two Ni-AI alloys containing 4.8 and 7.0 wt pct Al was studied in the temperature range 873 to 1073 K and stress range
30 to 400 MPa. The former alloy represents the solid solution of aluminum in nickel, the latter a solid solution strengthened
by NI3AI particles.
As to its creep behavior the solid solution alloy belongs to the Class n of solid solu-tions,i.e. the creep controlling mechanism is the same as in pure nickel. From the analy-sis of an effective stress dependence of steady
state creep rate it follows that the mo-tion of jogged screw dislocations can be considered as the most probable creep control-ling
mechanism.
The apparent activation energy of creep in the two phase alloy increases with tempera-ture. This effect is caused by changes
in the volume fraction of second phase particles and by the onset of climb around particles at high temperatures. At lower
temperatures particles are cut by dislocation pairs. 相似文献