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31.
Rainer Wolf Anne-Marie Dommrse Hans-Fr. Grützmacher 《Journal of mass spectrometry : JMS》1988,23(1):26-32
The secondary α-carbomethoxybenzyl cations a and the tertiary α-carbomethoxybenzyl cations d have been generated by electron impact-induced fragmentation from appropriately α-substituted methyl phenylacetate and 2-phenylpropionates 1–4. The ions a and d are further examples of destabilized carbenium ions with a push–pull substitution at the carbenium ion centre. The characteristic reaction of these ions is a rearrangement by a 1,2-shift of the methoxy group concomitant to the elimination of CO. This rearrangement reaction is associated with a very large and non-statistical kinetic energy release (a : T 50 = 570 meV; d : T 50 = 760 meV), which is attributed to tight transition states along the reaction coordinates corresponding to the three-membered cyclic oxonium ions b and h, respectively. The tertiary ion d can be distinguished from its more stable isomers f and g by the mass-analysed ion kinetic energy and collisional activation spectra. The investigation of specifically deuterated analogues of ions d and g reveals an isomerization of d to g via a species protonated at the phenyl group but no equilibration between d and g. This isomerization exhibits a large isotope effect for the hydrogen transfer, indicating similar energy barriers for the isomerization and for the CO elimination of d. 相似文献
32.
Computer applications in chemical industry are outlined and the CARSA system (computer-assisted research in synthesis and application) is described. This modular system consists of the three main parts: WIFODATA (data base; substance and finding documentation), QSAR (programs for quantitative structure/activity relationships) and RDSS (reaction design by synthon substitution; program package for planning of syntheses). The vital RDSS component is discussed in more detail; the underlying philosophy is explained, and examples are given from practical work. Some future steps towards a real molecular-design system are outlined. 相似文献
33.
A. v. Richthofen Rainer Cremer Ralph Domnick Dieter Neuschütz 《Analytical and bioanalytical chemistry》1997,358(1-2):308-311
Ti-Al-O layers were deposited on Si-<100> wafers at 500 °C by means of reactive magnetron sputtering ion plating (R-MSIP).
An Al-target was sputtered in rf-mode and a Ti-target in dc-mode simultaneously by an oxygen/argon plasma. The influence of
the Al- and Ti-sputter powers on composition, structure, and morphology of the Ti-Al-O layers and the binding states of the
components were investigated. The analysis with EPMA, XPS, AES and TEM yielded the following results: Ti-Al-O coatings with
different Ti, Al, and O contents in the range of TiO2 to Al2O3 were grown. TEM structure analysis revealed: the pure TiO2 film consisted of the tetragonal phases rutile and anatase; the two structures were found in the titanium-rich Ti-Al-O film,
too, but with significant smaller lattice constants. The aluminium-rich Ti-Al-O film displayed the same cubic structure of
γ-Al2O3 as determined for the pure Al2O3 film, but the lattice constant is significant lower. Evaluation of the TEM pattern of the film with a Ti/Al ratio of 0.8
indicates a hexagonal structure with lattice constants similar to those of κ′-Al2O3. All films are nanocrystalline and not textured.
Received: 24 June 1996 / Revised: 27 December 1996 / Accepted: 4 January 1997 相似文献
34.
Sandip Halder Theodor Schneller Rainer Waser Florian Thomas 《Journal of Sol-Gel Science and Technology》2007,41(3):203-207
Nickel thin films have been sputtered on standard Si/SiO2 substrates with TiO2 as an adhesive layer. The thermal stability of these substrates was analyzed. SEM images show an increase in grain size with
annealing temperature. They were found to be stable till 800°C, beyond which the nickel layer disintegrated. These substrates
were used for deposition of BaTiO3 and (Ba,Sr)TiO3 dielectric thin films under a reducing atmosphere. The dielectric thin films were processed with various pyrolysis and annealing
temperatures in order to optimize the dielectric properties. Increased pyrolysis temperatures showed an increase in the grain
size. Results on these nickelised substrates were finally compared with dielectric films deposited on platinized silicon substrates
under identical conditions but crystallized in an oxygen atmosphere. 相似文献
35.
The differential equations and the boundary conditions for the nonequilibrium binary distribution function of an unsymmetrical binary electrolyte are derived from the Ebeling-Falkenhagen continuity equation. The connection between the Onsager reciprocal relation and the binary distribution functions is shown. Further, Feistel's result for thec logc contribution to the conductance is extended to unsymmetrical binary electrolytes. The reason for the difference between Feistel's and Chen'sc logc term is explained, and the significance of Onsager's reciprocal relation for the calculation ofc logc and higher-concentration contributions of the conductance is discussed. 相似文献
36.
Tungsten(0) carbene complexes of the type (OC)5WC(NMeCH2CHCHCH2OH)R 2 (R=Me: 2a; R=Ph: 2b) were generated by aminolysis of (OC)5WC(OMe)R with cis-NHMeCH2CHCHCH2OH. Like their Cr-congeners 1, complexes 2 exist at room temperature as mixtures of Z- and E-isomers with regard to the C-N bond. The metallacyclic complexes (OC)4WC(η2-NMeCH2CHCHCH2OH)R (4) were obtained in good yields upon photo-decarbonylation of 2. Deprotonation/silylation of the complexes (OC)4MC(η2-NMeCH2CHCHCH2OH)Me (M=Cr: 3a; M=W: 4a) with one equivalent of nBuLi/Me3SiCl gave (OC)4MC(η2-NMeCH2CHCHCH2OSiMe3)CH3 (M=Cr: 5; M=W: 6), whereas with two equivalents of nBuLi/Me3SiCl complexes (OC)4MC(η2-NMeCH2CHCHCH2OSiMe3)CH2SiMe3 (M=Cr: 7; M=W: 8) were formed. Hydrolysis of the latter yielded selectively (OC)4MC(η2-NMeCH2CHCHCH2OH)CH2SiMe3 (M=Cr: 9; M=W: 10). The complexes 1-10 were analyzed in solution by one- and two-dimensional NMR spectroscopy (1H, 13C, 29Si, 1H/1H COSY, 1H/1H NOESY, 13C/1H HETCOR). 相似文献
37.
Wilfredo Hernndez Evgenia Spodine Andres Vega Rainer Richter Jan Griebel Reinhard Kirmse Uwe Schrder Lothar Beyer 《无机化学与普通化学杂志》2004,630(10):1381-1386
The N‐acyl thiourea complexes bis[N,N‐diethyl‐N′‐(p‐nitrobenzoyl)‐thioureato]copper(II) ( 1a,1b ) and bis(N,N‐diphenyl‐N′‐benzoylthioureato)copper(II) ( 2a,2b ) crystallize in each case in two modifications. X‐ray structural analysis shows that 1a and 1b are cis‐trans isomers. This is very unusual for N‐acyl thioureato complexes because with exception of one platinum(II) complex up to now only cis complexes have been found. In contrast X‐ray structural analysis of both forms 2a and 2b of the other complex shows no cis‐trans pair. Both modifications are cis complexes. In solution both isomers of the copper(II) complexes are observable by EPR spectroscopy. 相似文献
38.
Majumdar A Behnke JF Hippler R Matyash K Schneider R 《The journal of physical chemistry. A》2005,109(41):9371-9377
Chemical reactions in a dielectric barrier discharge at medium pressure of 250-300 mbar have been studied in CH(4)/Ar and CH(4)/N(2) gas mixtures by means of mass spectrometry. The main reaction scheme is production of H(2) by fragmentation of CH(4), but also production of higher order hydrocarbon molecules such as C(n)H(m) with n up to 9 including formation of different functional CN groups is observed. Formation of C(2)H(2), C(2)H(4), and C(2)H(6) molecules has been investigated in some detail. Significant differences are noted in comparison to a theoretical estimate. 相似文献
39.
A few 2-substituted 1-(1-ethoxyethyl)benzimidazoles have been prepared and the rate constants for their hydrolysis measured at various temperatures and oxonium ion concentrations. The formal kinetics followed and the effect of varying the 2-substitution on the hydrolysis rate suggest that the acid-catalyzed cleavage of these compounds involves a rapid initial protonation of the benzimidazole ring and a subsequent rate-limiting heterolysis of the protonated substrate to form a free nitrogen base and an ocarbenium ion derived from the ethoxyethyl group. The values obtained for the entropy of activation are consistent with the assumed unimolecular nature of the rate-limiting step. The effects of 2-substituents on the acidities of the protonated substrates and their heterolysis rates have been compared. The latter partial reaction has been suggested to be the subject of steric acceleration. 相似文献
40.
Günter Ehrlich Thomas Nestler Rainer Voigtmann Willi Moldenhauer 《Mikrochimica acta》1989,98(4-6):249-258
To compare concentration profiles in solids in an objective manner, a multi-dimensional generalization of the comparison of two means by Student'st-test is proposed. The approach is based on piecewise modelling the profiles using rougha priori information, estimating the model parameters and their covariance matrix and comparing the estimated parameters by use of multidimensional test variables. The piecewise modelling is treated in the most important cases in such a way that the partial functions are straight lines or cubic polynoms (splines) with continuity at all knots in each case. It enables us to compare whole profiles as well as the most relevant parts of them. Two ways of estimating the covariance matrix as a generalization of the variance estimation are discussed. The approach is useful for any kind of line profiles if rough information on the profile type is available. As an example SIMS depth-profiles of aluminum obtained from thin-layer systems after different technological heat treatments are considered. These profiles are modeled by three straight lines. 相似文献