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31.
Torsten Barfels Bernd Schmidt Andreas von Czarnowski Hans-Joachim Fitting 《Mikrochimica acta》2002,139(1-4):11-16
For investigation of the luminescent center profile cathodoluminescence measurements are used under variation of the primary
electron energy E
0 = 2…30 keV. Applying a constant incident power regime (E
0·I
0 = const), the depth profiles of luminescent centers are deduced from the range of the electron energy transfer profiles dE/dx.
Thermally grown SiO2 layers of thickness d = 500 nm have been implanted by Ge+-ions of energy 350 keV and doses (0.5–5)1016 ions/cm2. Thus Ge profiles with a concentration maximum of (0.4 – 4) at% at the depth of dm≅240 nm are expected. Afterwards the layers have been partially annealed up to T
a = 1100 °C for one hour in dry nitrogen. After thermal annealing, not only the typical violet luminescence (λ = 400 nm) of
the Ge centers is strongly increased but also the luminescent center profiles are shifted from about 250 nm to 170 nm depth
towards the surface. This process should be described by Ge diffusion processes, precipitation and finally Ge nanocluster
formation. Additionally, a Ge surface layer is piled-up extending to a depth of roughly 25 nm. 相似文献
32.
Molekulare Zusammensetzung von flüssigem Schwefel. Teil: 3 Quantitative Analyse im Bereich 115–350°C
Molecular Composition of Liquid Sulfur. Part 3: Quantitative Analysis in the Temperature Region 115–350°C Relative concentrations of S6, S7, S8, Sx (x > 8) and Sμ (insoluble sulfur) in equilibrium melts of elemental sulfur have been determined from i. r. and Raman spectra. At the freezing point (115°C) the melt consists of 0.6% S6, 2.8% S7, 1.5% Sx, and 95.1% S8. – The solubility of S7 in CS2 has been determined at −77 to −26°C; the solubilities of both S7 and S8 in CS2 are considerably enhanced by the presence of Sx. The thermal decomposition of S8 and Sμ formation from S6, S7, and Sx has been investigated. 相似文献
33.
Enantiomerically pure N-methyl-, N-benzyl-, and N-(methoxyethyl)-S-(phenyl)cinnamylsulfoximines as well as the corresponding crotylsulfoximines have been prepared from N-methyl-, N-benzyl-, and N-(methoxyethyl)-S-(lithiomethyl)sulfoximines and carbonyl compounds by an addition-elimination-isomerization reaction sequence. Under basic conditions, complete isomerization of the vinylic sulfoximines, obtained as intermediates, to the corresponding allylic sulfoximines takes place. Chromatographically separable mixtures of (E) and (Z) allylic sulfoximines were isolated in the case of beta,gamma-disubstituted allylic sulfoximines. The (E/Z) ratio depends on the nature of the substituents in the beta- and gamma-positions, and the equilibrium amount of the (Z) isomer varies from 68% to nil. The allylic N-methylsulfoximines do not racemize thermally, and their rearrangement to the corresponding allylic sulfinamides is negligible. Upon prolonged treatment with boron trifluoride at low temperatures allylic N-methylsulfoximines are recovered unchanged. The crystal structure of S-(3,4-dihydronaphthalen-2-ylmethyl)-N-methyl-S-phenylsulfoximine was determined. Reaction of the allylic sulfoximines with butylcopper in the presence of lithium iodide and boron trifluoride leads with very high gamma-selectivities and moderate to high enantioselectivities to the corresponding chiral alkenes. Their configuration was determined by chemical correlation through ozonolysis to the corresponding carbonyl compounds. The asymmetric induction exerted by the chiral N-methyl-S-phenylsulfoximine group strongly depends on the double bond configuration and the substituents in the beta- and gamma-positions. The (E) allylic sulfoximines are substituted with low to moderate enantioselectivities (2-66%), whereas the (Z) allylic sulfoximines react with much higher enantioselectivities (69-92%). Interestingly, substitution of the beta-methyl-gamma-phenyl-substituted (Z) allylic sulfoximine and its beta-phenyl-gamma-methyl isomer proceeded with almost the same degree of asymmetric induction but with the opposite sense. Replacement of the N-methyl group by a benzyl or a methoxyethyl group has no significant influence on the regio- and enantioselectivity of the substitution. 相似文献
34.
35.
We propose a Cohen-type bond order analysis in terms of orthogonalized atomic basis functions which can be used to analyze NDO wave functions of large organic and metal–organic molecules. It is shown that for small molecules the results gained with this method are in excellent agreement with the same analysis based on ab initio STO -3G wavefunctions. For large planar aromatic systems these all-valence electron bond orders are found to be a consistent generalization of the π-bond order. A simple relation between these bond orders and the corresponding covalent bond energies is established. The method can be easily extended to study excited state multiconfiguration wave functions. We present calculations for C2H2, C2H4, C2H6, and Mn2(CO)10. The results indicate that the method can be used to discuss the photochemistry of organic and metal–organic compounds. 相似文献
36.
Molecular Composition of Liquid Sulfur. Part 2: Qualitative Analysis and Preparation of S7, S12, α-S18, and S20 from S8 Raman spectra of sulfur melts (115–300°C), of quenched melts and of CS2 extracts of quenched melts show besides S8 the presence of S6 and S7. Formation of S7 from S8 at 120°C takes more than 8 h; the S7 equilibrium concentration increases with temperature. Pure crystalline S7, S12, α-S18 and S20 are prepared on a preparative scale by fractional extraction, crystallization, flotation and precipitation of quenched sulfur melts. Also a mixture of larger rings (Sx; x? = 25) has been isolated. Infrared and Raman spectra of α-S18, S20 and Sx are reported. 相似文献
37.
Klaus Burger Gabor Radics Lothar Hennig Christoph B?ttcher Jan Spengler Fernando Albericio 《Monatshefte für Chemie / Chemical Monthly》2005,5(3):763-776
Starting from L-malic, L-citramalic, and rac. thiomalic acids routes to L-homoisoserine, 2-methyl-L-homoisoserine and rac. homoisocysteine have been developed. The new orthogonally protected and carboxy-activated building blocks are GABA as well as -hydroxy and -mercapto acid derivatives, suitable for the construction of peptide and depsipeptide surrogates. 相似文献
38.
A. Breakstone H. B. Crawley A. Firestone M. Gorbics J. W. Lamsa W. T. Meyer D. L. Parker D. Drijard F. Fabbri H. G. Fischer H. Frehse P. Hanke P. G. Innocenti O. Ullaland W. Hofmann M. Panter K. Rauschnabel J. Spengler D. Wegener W. Geist M. Heiden E. E. Kluge T. Nakada A. Putzer K. Doroba R. Gokieli R. Sosnowski 《Zeitschrift fur Physik C Particles and Fields》1981,11(3):203-209
We present an analysis of minimum bias events from proton-proton collisions at \(\sqrt s = 7GeV\) in the CERN ISR. We remove the effects of both the leading protons and compare theB=0 mesonic residue of the events to the hadronic events of similar energy produced ine + e ? collisions. This comparison is presented in terms of the standard jet-type analyses involving quantities such as sphericity and aplanarity. We find significant differences between these data and the data frome + e ? annihilations. The data of this experiment are consistent with the predictions of a longitudinal phase space model. 相似文献
39.
D. Drijard H. G. Fischer W. Geist P. G. Innocenti V. Korbel A. Minten A. Norton S. Stein O. Ullaland H. D. Wahl G. Fontaine C. Ghesquière G. Sajot P. Hanke W. Hofmann M. Panter K. Rauschnabel J. Spengler D. Wegener H. Frehse M. Heiden E. E. Kluge A. Putzer M. Della Negra D. Linglin R. Gokieli R. Sosnowski 《Zeitschrift fur Physik C Particles and Fields》1981,9(4):293-303
Inclusive production of ?0,f, andg 0 mesons and ofK s 0 ,K *0 (892), ? andK *0(1430)mesons has been measured at <y>~2.6 and <p T >~1.1 GeV/c in proton-proton interactions at \(\sqrt s = 52.5\) GeV. The negative particle from the two-body decays of these resonances were identified by a threshold Cerenkov counter and used for triggering. Starting from the measured differential cross section, total inclusive cross sections for the vector and tensor mesons were determined using various parametrizations for they andp T dependence of the differential cross section. The experimental results are discussed in the framework of production models based on the parton picture. The strangeness suppresion factor λ=(0.30±0.10) due toSU(3) symmetry breaking of the quark sea is derived. 相似文献
40.
Let A, B be two matrices of the same order. We write A>B(A>?B) iff A? B is a positive (semi-) definite hermitian matrix. In this paper the well-known result if (cf. Bellman [1, p.59]) is extended to the generalized inverses of certain types of pairs of singular matrices A,B?θ, where θ denotes the zero matrix of appropriate order. 相似文献