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261.
Using deformations of singular twistor spaces, a generalisation of the connected sum construction appropriate for quaternionic manifolds is introduced. This is used to construct examples of quaternionic manifolds which have no quaternionic symmetries and leads to examples of quaternionic manifolds whose twistor spaces have arbitrary algebraic dimension.Partially supported by the National Science Foundation grant DMS-9296168. 相似文献
262.
S.J. Poon 《Solid State Communications》1983,45(7):531-534
Systematic occurence of low temperature resistivity anomalies (upturn) in amorphous alloys Zr50Cu50, Zr75Ni25, and Y75A?25 containing up to 4 at .% Gd is observed. Detailed analysis of ‘background’ impurity (other than Gd) effects on the electrical resistivity of the alloy host Zr50Cu50 provides unambiguous evidence that the anomalies are due solely to the Gd ions. The present results are interpreted in terms of conduction electrons with short mean free path scattering from nearest neighboring pairs of Gd spins. Predictions derived from the diffraction type model of magnetic interference, however, fail to describe all the results on metals with high electrical resistivity. Data on Zr50Cu50 containing Fe and Mn are also discussed. 相似文献
263.
264.
The dynamics of the neutrally buoyant inflated viscoelastic cantilevers constituting a submarine detection system is investigated. Thin shell theory is used to account for the stresses arising due to the internal pressure. A significant feature of the analysis is the use of the reduced shell equation which is similar in form to that for a vibrating beam with rotary effects. The forcing function in the form of surface wave excitation consists of a fundamental frequency and its second harmonic. Both the effects of apparent inertia and viscous drag are accounted for. The highly complicated non-linear, coupled equations are analyzed numerically. Use of the reduced form of the shell equations appears to avoid the problems of numerical instability and convergence reported by several investigators. The amount of information generated is rather enormous; however, for conciseness, only a few of the typical data, sufficient to establish trends, are presented. The results suggest that for the case of simple harmonicexcitation, the non-linear hydrodynamic drag introduces no superharmonic components into the response. The analysis provides valuable information concerning the system parameters leading to critical response and hence should prove useful in the design of inflatable structural members. 相似文献
265.
266.
A sensitive procedure for studying the metabolism of the steroidal aromatase inhibitor 4-hydroxy-androst-4-ene-3,17-dione (4OHA) was developed based on enzyme hydrolysis, liquid-liquid extraction and reversed-phase liquid chromatography coupled with a mass spectrometer (LC-MS) using a thermospray interface. Seven metabolites were identified from the hydrolysed urine samples together with the parent drug. The major routes of metabolism were via dehydrogenation, reduction of the ketone functional groups, reduction at the C-4-C-5 double bond and hydroxylation at the C-5 position. Confirmation of the identity of 4OHA and its metabolites isolated from female patients' urine samples was accomplished by comparison of the retention times of their corresponding synthetic standards on LC-MS. We have demonstrated that this technique is particularly suitable for studying the metabolism of steroidal drugs. 相似文献
267.
268.
Peng Han Lam Jacky W. Y. Leung Fennie S. M. Poon Tommy W. H. Wu Andrew X. Yu Nai-Teng Tang Ben Zhong 《Journal of Sol-Gel Science and Technology》2001,22(3):205-218
Macroscopically homogeneous and visually transparent fullerene-containing glasses are fabricated from sol-gel mixtures of aminated C60 derivatives and tetraethyl orthosilicate (TEOS) through physical blending and chemical reaction. The aminated fullerenes are synthesized by the amination reactions of C60 with 6-amino-1-hexanol, cyclohexylamine, 2-(2-aminoethoxy)ethanol, and 3-aminopropyltriethoxysilane at 100°C under nitrogen. The amination products are purified by filtration, precipitation, and column chromatography and are isolated in good to excellent yields (32–82%). Characterization by NMR, MS, and TGA analyses reveals that the aminated fullerenes possess molecular structures H
x
C60[NH(CH2)6OH]
x
, H
x
C60(NH-cyclo-C6H11)
x
, H
x
C60[NH(CH2CH2O)2H]
x
, and H
x
C60[NH(CH2)3Si(OCH2CH3)3]
x
. All the aminated fullerenes except 2 are completely soluble in aqueous alcoholic solutions of TEOS and can be incorporated into silica gel networks by sol-gel process in the absence or presence of drying-control chemical additives, giving crack-free monoliths of large sizes (up to 60 mm). Electronic absorption spectrum of the fullerene glass continuously red shifts with an increase in the C60 content, suggesting the formation of fullerene nanoclusters in the sol-gel process. The fullerene glasses are thermally and optically stable, resisting continuous attack of strong laser pulses of 532 nm for a prolonged period of time without losing their optical limiting power. 相似文献
269.
J. Wosnitza R. van den Berg H. v. Löhneysen S. J. Poon 《Zeitschrift für Physik B Condensed Matter》1988,70(1):31-35
Icosahedral (I) Pd0.588U0.206Si0.206 can be obtained from melt-spun amorphous (A) ribbons by annealing. The specific heatC (measured betweenT=0.1 K and 20 K) shows very similar behavior for both phases. The main features ofC are as follows. (i) The vibrational heat capacityC
ph dominatesC at highT.C
ph is almost identical in both phases, in agreement with recent inelastic neutron scattering data. (ii) Shallow maxima in (C–C
ph)/T vs.T are found at 5.4 and 4.3 K forI andA phases, respectively, associated with magnetic order. These maxima are suppressed by 20% in an applied magnetic field of 6 T. (iii) A large quasi-linear contribution is observed with a low-T coefficient =165 mJ/mole U K2 for theI phase and =120 mJ/mole U K2 for theA phase. In the low-T region,C is hardly affected by a field of 6 T. This hints at the formation of a narrow 5f band with a comparable density of states for bothI andA phases. 相似文献
270.
The unique electronic and structural nature of the alpha-acylphosphonate functional group affords both dimeric and chelated complexes of diethyl crotonyl phosphonate (1; DECP) with stannic chloride (SnCl(4)). The dimeric complex, SnCl(4).(DECP)(2) (5) results from the coordination of two DECP molecules, ligated via the phosphoryl oxygens to the tin atom. The chelated complex, SnCl(4).(DECP) (6), is best represented with both phosphoryl and carbonyl oxygens coordinated to the metal center. Both metal ligated and chelated complexes have unique (13)C (31)P, and (119)Sn NMR spectra. In complex 5, the (13)C NMR resonances attributed to the carbonyl carbons were shifted upfield of free DECP. A monocoordinating Lewis acid, BF(3).OEt(2), produced a similar chemical shift trend in both the (13)C and (31)P NMR spectra of the BF(3).DECP complex. Essentially quantitative yields and moderate diastereomeric excesses favoring anti (or trans) diethyl 6-phenyl-4,5-dimethyl-6-(trimethylsilyloxy)-2-dihydropyranphosphonate (3) and diethyl 5-phenyl-3,4-dimethyl-1,5-dioxopentanephosphonate (4) were obtained from both chelated and dimeric SnCl(4).(DECP)(n) (n = 1, 2) when treated with either diastereomeric (Z)- or (E)-1-phenyl-1-(trimethylsilyloxy)-1-propene 2. Diethyl crotonylphosphonate (1), 3, and 4 were fully characterized. 相似文献