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441.
Data from a large number of Russian, American and German sources are examined and found to be correlated in general by
α1?α)12 = K[FDPm]n
where α is voidage or fractional vapour content, K is a constant, FD is a Froude number and P is a physical properties group. However, the exponent m is found to vary from 0 to 0.3 and the exponent n from 23 to 0.79, depending upon the sources of the data. The most probable value for n is 23 but a firm choice cannot be made for m, which is either 0.16 or 0.3. The different values of m depend chiefly upon the method of measurement of the voidage.  相似文献   
442.
A theory of large lossless waves with two fluids in horizontal closed channels of arbitrary cross-section is developed. The dynamic conditions for infinitesimally small disturbances is derived from this theory and it is shown that the dynamic condition for waves of finite magnitude is in agreement with Long's (1956) first order estimate for small waves in channels of rectangular cross-section. It therefore appears probable that an adequately accurate dynamic condition is available for such waves of all sizes. Results from the theory are used to quantitatively explain experimental results by Wallis & Dobson (1973) for the onset of slugging in horizontal channels and by Leach & Thompson (1975) for the counter-current discharge of fluids along a horizontal pipes between closed tanks. In both cases an influence of the ratio of the densities of the phases upon the usually accepted Froude number, which already contains density correction factors, is found. Transfer of miscible unstably stratified fluids through each other in vertical ducts is found to be described by a turbulent diffusion process which is controlled by the rate of energy dissipation and the duct diameter. The process is therefore quite different to that in horizontal ducts.  相似文献   
443.
Symmetrals and X-rays of planar convex bodies   总被引:1,自引:0,他引:1  
  相似文献   
444.
By exploiting recent advances in the understanding of both pheromone biosynthesis pathways and the detection of molecules in the insect nervous system, we are developing a new class of technology for biosynthetic infochemical communication. Here we present a prototype instrument that comprises an integrated chemotransmitter, an odour pathway and a chemoreceiver controlled by a laptop computer. Our initial studies show that the system can transmit, receive and decode a set of volatiles commonly found in fruits. The system is capable of ratiometrically encoding information by releasing complex blends of compounds in specific ratios, detecting the transmitted blends with a sensor array and decoding the infochemical information using neuromorphic algorithms representing ratio processing in the macroglomerular complex (MGC) of the antennal lobe of the moth (e.g. Manduca sexta).  相似文献   
445.
Directoid groups     
We continue the study of directoid groups, directed abelian groups equipped with an extra binary operation which assigns an upper bound to each ordered pair subject to some natural restrictions. The class of all such structures can to some extent be viewed as an equationally defined substitute for the class of (2-torsion-free) directed abelian groups. We explore the relationship between the two associated categories, and some aspects of ideals of directoid groups.  相似文献   
446.
Fully cyclized, organo soluble, phenylethynyl-terminated, ether-imide oligomers of 2–10,000 g/mol (Mn) were prepared by the reaction of 2,2′-bis[4-(3,4-dicarboxyphenoxy)phenyl]-propane dianhydride (bisphenol-A dianhydride, BPADA) with a stoichiometric excess of either para, meta, or isomeric mixtures of phenylene diamine and phenylethynylphthalic anhydride (4-PEPA) endcapper. High para-containing oligomers produced semicrystalline powders, but the all meta isomer was completely amorphous. The lower molecular weight oligomers displayed an attractive low viscosity melt and were cured to very high gel content networks at 350–380°C for 30–90 min. The cured 3000 g/mol oligomers showed a (DSC) glass transition temperature (Tg) of 267°C and produced tough, solvent-resistant films. Excellent adhesion to surface-treated titanium alloys was achieved, as judged by single-lap shear measurements. Resin infusion molding was conducted, which permitted low-void, graphite-fabric composite panels to be prepared. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2943–2954, 1997  相似文献   
447.
The CEARXRF GUI‐Based Monte Carlo–Library Least‐Squares (MCLLS) Code is demonstrated with results from a micro‐focused EDXRF analyzer, which can be used to calculate elemental weight fractions in metal alloys or rock samples accurately by library least‐squares regression of the measured X‐ray spectrum with computer‐generated elemental library spectra. An elemental stratified sampling variance reduction technique has been implemented in the CEARXRF5 code, which equalizes the statistical precision of the elemental libraries within the measured sample independent of the relative elemental amounts that are present. Also, an improved Si(Li) detector response function (DRF) has been obtained for micro‐focused X‐ray fluorescence (XRF) analyzers, and the DRF parameters are obtained based on regression from pure elemental experimental spectra. It is demonstrated that the resulting MCLLS approach can greatly improve the accuracy of elemental XRF analysis results. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
448.
Dirac-like surface states on surfaces of topological insulators have a chiral spin structure that suppresses backscattering and protects the coherence of these states in the presence of nonmagnetic scatterers. In contrast, magnetic scatterers should open the backscattering channel via the spin-flip processes and degrade the state's coherence. We present angle-resolved photoemission spectroscopy studies of the electronic structure and the scattering rates upon the adsorption of various magnetic and nonmagnetic impurities on the surface of Bi2Se3, a model topological insulator. We reveal a remarkable insensitivity of the topological surface state to both nonmagnetic and magnetic impurities in the low impurity concentration regime. Scattering channels open up with the emergence of hexagonal warping in the high-doping regime, irrespective of the impurity's magnetic moment.  相似文献   
449.
Gapless surface states on topological insulators are protected from elastic scattering on nonmagnetic impurities which makes them promising candidates for low-power electronic applications. However, for widespread applications, these states should have to remain coherent at ambient temperatures. Here, we studied temperature dependence of the electronic structure and the scattering rates on the surface of a model topological insulator, Bi2Se3, by high-resolution angle-resolved photoemission spectroscopy. We found an extremely weak broadening of the topological surface state with temperature and no anomalies in the state's dispersion, indicating exceptionally weak electron-phonon coupling. Our results demonstrate that the topological surface state is protected not only from elastic scattering on impurities, but also from scattering on low-energy phonons, suggesting that topological insulators could serve as a basis for room-temperature electronic devices.  相似文献   
450.
A carbon disulfide cell and fiber-optic diffuser have been used in the beam from a pulsed ruby laser to reduce the spatial coherence of the beam and enable nearly speckle-free photographs of transient phenomena to be obtained.  相似文献   
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