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991.
The simultaneous incorporation of ferrocene derivatives and glucose oxidase into a carbon-paste matrix results in an effective microelectrode for sensing glucose. The close proximity of the enzymatic, redox mediating and sensing sites offers extremely short response times (t95%=18 s) compared with early ferrocene-based glucose sensors. Several ferrocene derivatives are evaluated, with 1,1′-dimethylferrocene yielding the best results. The influence of the paste composition, operating potential, glucose concentration and other variables is described. The incorporation of stearic acid into the enzyme-containing paste greatly reduces the interference due to ascorbic acid. The microelectrode is easily fabricated, as time-consuming multi-step immobilization schemes are eliminated. Flow-injection measurements at a rate of 90 samples per hour and relative standard deviations of 3% are also reported. 相似文献
992.
Adolfo Sanchez-Flores 《Discrete Mathematics》1995,140(1-3):281-286
The Ramsey number N(3,3,3,3; 2) is the smallest integer n such that each 4-coloring by edges of the complete graph on n vertices contains monochromatic triangles. It is well known that 51 ≤ N(3, 3, 3, 3; 2) ≤ 65. Here we prove that N(3, 3, 3, 3; 2) ≤ 64. 相似文献
993.
Enrique Sanchez Marcos Francisco Sanchez Burgos Alfredo Maestre Alvarez 《Journal of solution chemistry》1982,11(12):889-896
The standard potential of the Zn–Hg (sat)/ZnCl2(M)/AgCl/Ag cell was determined at 25°C using several extrapolation procedures and the value 0.9843 V is proposed for E°. The emf of the Zn–Hg (sat)/ZnCl2(M), salt (M)/AgCl/Ag cell [salt=NaClO4, LiClO4, Mg(ClO4)2, Mg(NO3)2] have been measured at different concentrations of salt. From these data, the mean ionic activity coefficients of ZnCl2 are determined and their variations explained with the aid of Pitzer's treatment. It seems necessary to take into account structure in the ionic cospheres in order to explain the observed variations. 相似文献
994.
995.
A. E. Sanchez Pelaez 《Polyhedron》1982,1(11-12)
The complexes [Zn(BdH)2Cl2] and [Mn(BdH)2Cl2] have been prepared and studied by IR, electronic and ESR spectroscopies and by magnetic measurements. All results agree with a molecular formula for both complexes and a distorted octahedral environment for the metal atoms. 相似文献
996.
997.
2,2-Anhydropyrimidine nucleosides. Novel syntheses and reactions 总被引:3,自引:0,他引:3
998.
Time-resolved investigations of the atomic resonance fluorescence Sr(53P1 → 51S0) and the molecular chemiluminescence from SrCl(A2Π1/2,3/2, B2Σ+ → X2Σ+) are reported following the reaction of the electronically excited strontium atom, Sr(5s5p(3PJ)), 1.807 eV above its 5s2(1S0) electronic ground state, with CH2Cl2. The optically metastable strontium atom was generated by pulsed dye-laser excitation of ground state strontium vapor to the Sr(53P1) state at λ = 689.3 nm (Sr(53P1 ← 51S0)) at elevated temperature (850 K) in the presence of excess helium buffer gas in which rapid Boltzmann equilibration within the 53PJ manifold takes place. Sr(53PJ) was then monitored by time-resolved atomic fluorescence from Sr(53P1) at the resonance wavelength together with chemiluminescence from electronically excited SrCl resulting from reaction of the excited atom with CH2Cl2. The molecular systems recorded in the time-domain were SrCl(A2Π1/2 → X2Σ+) (Δν = 0, λ = 674 nm), SrCl(A2Π3/2 → X2Σ+) (Δν = 0, λ = 660 nm), and SrCl(B2Σ+ → X2Σ+) (Δν = 0, λ = 636 nm). Both the A2Π (179.0 kJ mol?1) and (B2Σ+(188.0) kJ mol?1) states of SrCl are energetically accessible on collision between Sr(3P) and CH2Cl2. Exponential decay profiles for both the atomic and molecular (A,B – X) chemiluminescence emission are observed and the first-order decay coefficients characterized in each case. These are found to be equal under identical conditions and hence SrCl(A2Π, B2Σ+) are shown to arise from direct Cl-atom abstractions on reaction with this halogenated species. The combination of integrated molecular and atomic intensity measurements, coupled with optical sensitivity calibration, yields estimations of the branching ratios into the A1/2,3/2, B, and X states arising from Sr(53 PJ) + CH2Cl2 which are found to be as follows: A1/2, 3.0 × 10?3; A3/2, 1.7 × 10?3; B, 4.4 × 10?4 yielding ΣSrCl(A1/2 + A3/2 + B) = 5.1 × 10?3. As only the X, A and B states of SrCl are accessible on reaction, this indicates an upper limit for the branching ratio into the ground state of 0.995. The present results are compared with previous time-resolved measurements on SrF, Cl, Br(A2Π,B2Σ+ ? X2Σ+) that we have reported on various halogenated species and with analogous chemiluminescence studies on Sr(3P) with other halides obtained from molecular beam measurements. The results are further compared with those from a series of previous analogous investigations in the time-domain we have presented of molecular emissions from CaF, Cl, Br, I (A,B – X) arising from the collisions of Ca(43PJ) with appropriate halides and with branching ratio data for Ca(43PJ) obtained in beam measurements. © 1995 John Wiley & Sons, Inc. 相似文献
999.
Juan M. Antelo Florencio Arce Julia Franco Maria C. Garcia Lopez Maria Sanchez Angel Varela 《国际化学动力学杂志》1988,20(5):397-409
The chlorinations of dimethylamine, diethylamine, methylethanolamine, ethylethanolamine and diethanolamine by N-chlorosuccinimide have been found to be equilibrium reactions of order one with respect to both N-chlorosuccinimide and amine in the forward direction and of order one with respect to succinimide and the resulting N-chloramine in the other. These results are explained by postulating a mechanism in which the rate controlling step consists in direct exchange of positive chlorine between the N-chlorosuccinimide and the amine. 相似文献
1000.