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131.
132.
A rough-interface reverberation model is developed for range-dependent environments. First-order perturbation theory is employed, and the unperturbed background medium can be layered and heterogeneous with arbitrary range dependence. To calculate the reverberation field, two-way forward scatter due to the slowly changing unperturbed environment is handled by fast numerical methods. Backscatter due to small roughness superimposed on any of the slowly varying interfaces is handled efficiently using a Monte Carlo approach. Numerical examples are presented to demonstrate the application of the model. The primary purpose of the model is to incorporate relevant physics while improving computational speed. 相似文献
133.
Keitaro Senga Joze Kobe Roland K. Robins Darrell E. O'Brien 《Journal of heterocyclic chemistry》1975,12(5):893-898
The synthesis of a new series of alkylxanthine analogs containing a bridgehead nitrogen atom is reported. 1,3-Dialkylpyrazolo[1,5-a]-1,3,5-triazine-2,4-diones, were prepared by the treatment of 3-methylpyrazolo[1,5-a]-1,3,5-triazine-2,4-dione (3) with the corresponding alkyl iodide. Similarly, the reaction of 3-methyl-7-phenylpyrazolo[1,5-a]-1,3,5-dialkyl-7-phenylpyrazolo[1,5-a]-1,3,5-triazine-2,4-diones. The starting materials, 3 and 17 , were prepared via the reaction of an appropriate 3-aminopyrazole with ethoxycarbonyl isothiocyanate. Several 8-bromo derivatives were prepared by direct bromination of the 1,3-dialkylpyrazolo[1,5-a]-1,3,5-triazine-2,4-diones. 相似文献
134.
K. Darrell Berlin S. Rengaraju Peter E. Clark 《Journal of heterocyclic chemistry》1970,7(5):1095-1099
Several new phosphorylated aziridines of related structure were prepared. P.m.r. analysis via decoupling experiments provided cis H-H, trans H-H, gem H-H and PNCH coupling values. Similar to simple aziridines, the cis H-H coupling is larger than trans H-H coupling (on vicinal ring carbons) which in turn is larger than gem H-H coupling. In one example operating at 100 MHz and 0° it was possible to detect the presence of two invertomers. 相似文献
135.
The homo-interaction between urea moieties residing in close proximity to each other generally results in very strong intermolecular hydrogen bonding. The bifurcated hydrogen bonding exhibited by n-alkyl substituted ureas means that for those urea surfactants possessing medium and long hydrocarbon chain substituents the crystal to isotropic liquid melting point is high and the solubility in water is very low, compared to other similar chain length nonionic surfactants. In addition, saturated n-alkyl urea surfactants do not form lyotropic liquid crystalline phases in water. In this work the strong intermolecular hydrogen bonding of the urea headgroup has been ameliorated through the introduction of unsaturated hydrocarbon chains, viz., oleyl (cis-octadec-9-enyl), linoleyl (cis, cis-octadec-9,12-dienyl), and linolenyl (cis, cis, cis-octadec-9,12,15-trienyl) with one, two, and three carbon double bonds, respectively. Unsaturation in the C18 urea surfactants lowers the melting point and promotes an inverse hexagonal phase, in oleyl urea-water and linoleyl urea-water systems, which is thermodynamically stable in excess water. As the degree of unsaturation is increased to three in linolenyl urea, there is a tendency for autoxidation/polymerization. The occurrence of an inverse hexagonal phase in the nonionic urea surfactant-water systems has been rationalized in terms of both local molecular and global self-assembled aggregate packing constraints. 相似文献
136.
Amination of 5-bromo-2-thiophenecarboxaldehyde with an acyclic secondary amine - bis(2-methoxyethyl)amine was effected by using weak base sodium bicarbonate. The resulting 5-N,N-bis(2-methoxyethyl)amino-2-thiophenecarboxaldehyde was treated with boron tribromide to give 5-N,N-bis(2-hydroxyethyl)amino-2-thiophenecarbox- aldehyde. 相似文献
137.
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139.
Darrell E. Allgaier 《Wave Motion》1990,12(6):569-581
The leading tail for slowly varying solitary waves for the perturbed Korteweg-de Vries (KdV) equation is analyzed. The path of the core of the solitary wave is obtained and shown to provide a moving boundary for the leading tail. The leading tail is predicted to be triple valued within a penumbral caustic (envelope of characteristics) caused by the initial acceleration of the core. A rescaling in the neighborhood of the singularity shows that the solution there satisfies the diffusion equation. The solution involves an incomplete Airy-type exponential integral, where critical points (significant for Laplace's asymptotic method) satisfy the structure of the penumbral caustic. A wave number shock develops, which separates two different solitary wave tails, one due to the moving core and the other due to the initial condition. The shock velocity is that predicted from conservation of waves. 相似文献
140.
The chemical species created in a low-pressure electrical discharge in oxygen attack the polymer at the surface, converting it to gaseous products. This process is interesting because: 1) the chemical changes on the resulting surface facilitate the formation of strong adhesive bonds and provide sites for the chemical attachment of other molecules, 2) significant morphological features lying below the surface may be revealed, 3) polymer can be cleanly removed from surfaces which are resistant to oxidation, and 4) dielectric breakdown frequently is preceded by the attack on the polymer of chemical species created in a corona discharge. Atomic oxygen is an important chemical species created in such a discharge. It reacts with organic substances rapidly at room temperature, but lives long enough in the low-pressure gas that it can be separated from many other reactive species created in the discharge. “Titration” with NO2 provides a straightforward chemiluminescent means for determining the concentration of atomic oxygen to which the sample is exposed. This paper characterizes the attack of atomic oxygen, perhaps in the presence of long lived but less reactive species such as excited O2molecules, on polymer surfaces, using electron microscopic observations of known morphological features of polyethylene to observe the changes produced by atomic oxygen. Lamellar polyethylene crystals were attacked both at the edges and the fold surfaces. Layers many microns thick were removed from spherulitic samples and replicas obtained from the surfaces thus exposed. Thick samples were thinned to the point at which they were transparent to an electron beam and interior morphological features were directly observed. 相似文献