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41.
[reaction: see text] Three novel domino reaction processes have been discovered and developed that employ the regioselective and stereoselective [Rh(CO)(2)Cl](2)-catalyzed alkylations of allylic trifluoroacetates with alpha-substituted sodiomalonates followed by an intramolecular Pauson-Khand annulation, a [5 + 2] cycloaddition, or a cycloisomerization. A unique aspect of the methodology is that a single catalyst is used to effect sequential transformations simply by increasing the temperature for the second reaction. 相似文献
42.
Proton affinities of a series of triphenyl Group Va compounds have been determined by bracketing using reactant ion monitoring: (C6H5)3N = 904 ± 8 kJ mol?1, (C6H5)3P = 968 ± 5 kJ mol?1, (C6H5)3As = 904 ± 8 kJ mol?1 and (C6H5)3Sb = 846 ± 8 kJ mol?1. The large difference in substituent effect of phenyl for hydrogen between As or P and N may result from overlap of the 2p orbitals of N with the sp2 orbitals on the ring carbons and lack of overlap for P or As. Proton affinities of phenylalkylphosphine oxides are essentially the same, 904 ± 8 kJ mol?1, independent of alkyl group. 相似文献
43.
Nguyen Van Do Tran Duc Thiep Truong Thi An Tran Minh Duc Han Ngoc Cuong 《Journal of Radioanalytical and Nuclear Chemistry》1986,107(1):29-37
Photon activation analysis has been success-fully applied to the fast and non-destructive analysis of tin in cassiterite ores
based on the 159.7 keV gamma line of123mSn produced in the124Sn/γ, n/123mSn reaction. In order to improve the accuracy of analytical results, corrections for self-absorption and pile-up effects were
performed. Under typical conditions /15 μA electron beam current, 15 MeV bremsstrahlung energy, 5 min irradiation time and
10 min measurement/ the sensitivity of the analysis is 10 ppm. The proposed method can be used for routine analysis of tin
in geological samples. 相似文献
44.
Analysis of organotin compounds by grignard derivatization and gas chromatography-ion trap tandem mass spectrometry 总被引:1,自引:0,他引:1
Tsunoi S Matoba T Shioji H Giang le TH Harino H Tanaka M 《Journal of chromatography. A》2002,962(1-2):197-206
The determination of organotin compounds in water using gas chromatography-tandem mass spectrometry (GC-MS-MS) is described. Several organotin derivatives were synthesized by the reaction of organotin chlorides with Grignard reagents such as methyl-, propyl- and pentylmagnesium halides. After the optimization of the GC-MS-MS conditions, several derivatizations with the Grignard reagents were compared by evaluating the molar responses and volatilities of the derivatives and derivatization yields. As a result, the derivatizing reagent of choice is pentylmagnesium bromide. Calibration curves for the mono-, di- and tributyltins and mono-, di- and triphenyltins with pentylmagnesium bromide were linear in the range of 0.5-100 pg of Sn. The instrumental detection limits of six organotins ranged from 0.20 to 0.35 pg of Sn. The recovery tests from water samples (500 ml) were performed by using sodium diethyldithiocarbamate (DDTC) as a complexing reagent. Except for monophenyltin, the absolute recoveries of organotins from pure water at 200 ng of Sn/l were satisfactory. The recoveries calibrated by surrogate compounds (perdeuterated organotin chlorides) ranged from 71 to 109%. The method detection limits ranged from 0.26 to 0.84 pg of Sn (500-ml sample). This method was applied to the recovery of organotins from river water and seawater. The calibrated recoveries were between 90 and 122%. 相似文献
45.
N,N-Diethyldithiocarbamate functionnalized 1,4-polyisoprenes were prepared from 1,4-polyisoprenes (natural or synthetic). The syntheses were performed by nucleophilic addition of N,N-diethyldithiocarbamate salts upon oxirane rings of epoxidized units according to a SN2 mechanism with ring opening. Studies on model molecules of epoxidized 1,4-polyisoprene units (1,2-epoxy-1-methylcyclohexane and 4,5-epoxy-4-methyloctane) were previously achieved to develop the procedure. The best yields were obtained at low temperature in polar medium, and more especially in water with sodium N,N-diethyldithiocarbamate (DEDT-Na) as reagent. A diastereospecific addition was noted when reaction was performed in water with DEDT-Na. Afterwards, the developed procedure was successfully generalized to epoxidized synthetic polyisoprenes and epoxidized natural rubber (in THF, then in latex medium). Excellent results were obtained in latex medium with epoxidized natural rubber (ENR) latices. As with the models, a diastereospecific addition of sodium N,N-diethyldithiocarbamate trihydrate onto epoxidized 1,4-polyisoprene units of ENR was observed at the condition to bring the latex medium to pH 8 before introduction of DEDT-Na. Influence of temperature, drc, and DEDT-Na concentration were successively examined to determine the best conditions of the addition on ENR latices. 相似文献
46.
Summary An ,-appended eighteen carbon chains hypercin derivative (2) was synthesized starting from emodin. The overall yield of the seven step synthesis was 12%. The1H and13C NMR, absorption, and emission spectroscopic properties were measured;2 can be dissolved even in apolar solvents and polyethylene.
Synthese und Eigenschaften eines mit C18-Ketten ,-substituierten Hypericinderivats
Zusammenfassung Ein in den Positionen , mit zwei C18-Ketten substituiertes Derivat des Hypericins (2) wurde ausgehend von Emodin synthetisiert. Die Gesamtausbeute der siebenstufigen Synthese betrug 12%. Die1H- und13C-NMR, absorptions- und emissionsspektroskopischen Eigenschaften wurden gemessen;2 kann sogar in apolaren Lösungsmitteln und Polyethylen gelöst werden.相似文献
47.
I. M. Skvortsov I. V. Antipova Yu. A. Pentin Tran Suan Khoan' S. V. Vasil'kovskii 《Chemistry of Heterocyclic Compounds》1975,11(8):949-955
1-(2-Furyl)-3-amino-4,4-dimethylpentane was used to obtain 3-tert-butyl-1,2-dihydropyrrolizine, the catalytic hydrogenation of which over Rh/Al2O3 at room temperature gives a mixture of cis- and trans-3,8-H-3-ter-butylpyrrolizidines with predominance of the cis isomer, whereas hydrogenation at 90–100 °C gives a mixture containing the trans isomer as the principal component. The three-dimensional structures of the isomers follow from data on the catalytic hydrogenation and isomerization and the IR, Raman, and PME spectra. A considerable percentage of the trans-fused form is characteristic for cis-3,8-H-3-tert-butylpyrrolizidine. 相似文献
48.
The self-diffusion coefficient, D, of dibutyltin dilaurate and dibutyltin bismonobutylmaleate have been obtained at 35, 45 and 55° in samples of poly(vinyl chloride) plasticized with 34, 60 and 100 phr of di(2-ethylhexyl)phthalate. D at 2 phr of the laurate is 3–5 times larger than for the smaller maleate molecule. In all cases, D increases with increasing plasticizer concentration, an effect interpreted in terms of the free volume theory of diffusion. D for the laurate increases by a factor of about 2.7 when the laurate diffusant concentration is increased from 0 to 4 phr. The activation energies for diffusion, ED, lie between 50 and 90 kJ mol?1. They increase with increasing plasticizer concentration but become constant at higher plasticizer concentrations (60–100 phr). It is impossible to correlate all the known data on diffusion in plasticized PVC with an equation of the form log D0 = C1 + C2 ED/RT 相似文献
49.
A set S of permutations of k objects is -uniform, t-homogeneous if for every pair A, B of t-subsets of the ground set, there are exactly permutations in S mapping A onto B. Arithmetical conditions and symmetries are discussed. We describe the character-theoretic method which is useful if S is contained in a permutation group. A main result is the construction of a 2-uniform, 2-homogeneous set of permutations on 6 objects and of a 3-uniform, 3-homogeneous set of permutations on 9 objects. These are contained in the simple permutation groups PSL
2(5) and PSL
2(8), respectively. The result is useful in the framework of theoretical secrecy and authentication (see Stinson 1990, Bierbrauer and Tran 1991). 相似文献