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81.
Najib Abusalbi David W. Schwenke C. Alden Mead Donald G. Truhlar 《Theoretical chemistry accounts》1987,71(5):333-357
We discuss molecule-frame and laboratory-frame symmetry-adapted formalisms for electron scattering by a spherical top. The molecule-frame formalism is based on the fixed-nuclear-orientation approximation, both for electronically elastic scattering by a vibrationally rigid molecule and also for the more general case where electronic excitation and vibrational degrees of freedom are included. The laboratory-frame formalism is based on the exact symmetries of the problem, which are carefully related to the approximate symmetries of the molecule-frame treatment. We present both the forward and backward transformations between the two representations. 相似文献
82.
We have performed large-scale close coupling calculations of rotational-to-rotational energy transfer in HF? HF collisions for the realistic potential energy surface of Brobjer and Murrell. We employ up to 525 angular terms in the expansion of the potential and up to 440 coupled channels in the rotational-orbital basis set. The results for zero total angular momentum are well converged for relative translational energies up to over 0.6 eV, and they show extensive rotational excitation. 相似文献
83.
The effect of sample volume, tube length, tube diameter, peak height and sampling rate on the determination of phosphorus in acidic plant digests was investigated, and optimal conditions for the flow injection method are described. Sampling rates of 420 samples per hour were achieved without incurring problems from carryover of samples, and evidence was obtained that rates as high as 700 samples per hour are possible. The flow injection method was proved to be suitable for routine analyses and has obvious advantages over other automated or manual methods in sampling rate, simplicity of design and cost. 相似文献
84.
The hydrolysis of chromate ion was studied potentiometrically in a concentration cell fitted with hydrogen electrodes by titrating basic NaCl–Na2CrO4 solutions with standardized HCl against a NaOH reference solution. The temperature was varied from 25 to 175°C at 25° intervals at the following ionic strengths (I): 0.1140, 0.2346, 0.5337, 0.9988, 2.940, and 5.239 (NaCl). Depending on the ionic strength, the molality of total chromium was varied from 0.001 to 0.100. The resulting titration curves could be resolved best in terms of three equilibria involving the formation of HCrO
4
–
(aq), Cr2O3– (aq), and CrO3Cl– (aq). The equilibrium quotients for all three reactions were fitted as a function of temperature and ionic strength, and the molal thermodynamic parameters that were computed from these relationships are tabulated at specific ionic strengths over the experimental temperature range. 相似文献
85.
It has been known for some time that the pre-treatment of platinum electrodes often effects subsequent electrochemical reactions. Part of the effect of pre-treatment is due to the fact that anodized or chemically oxidized platinum electrodes become coated to some degree with a film of platinum oxide. This work was concerned with quantitative measurement of kinetic parameters as a function of the extent of oxide film formation. Whenever possible, variations in reaction mechanisms are proposed.
Most of the experimental evidence has been taken from current-potential curves but the techniques of chronopotentiometry and microscopy were also used.
The reduction of vanadiumV chromiumVI, arsenicV, iodate and oxygen were investigated as well as the oxidation of vanadiumIV, arsenicIII, oxalic acid, and formic acid. The presence of the platinum oxide film effected the reactions studied in a variety of ways but in every case some variation in the kinetic parameters of the reactions studied was recorded. For a number of cases, a modified oxygen bridge theory was found useful. 相似文献
86.
DeClue MS Baldridge KK Künzler DE Kast P Hilvert D 《Journal of the American Chemical Society》2005,127(43):15002-15003
Isochorismate pyruvate lyase (IPL) catalyzes the cleavage of isochorismate to give salicylate and pyruvate, a key step in bacterial siderophore biosynthesis. We investigated the enzyme from Pseudomonas aeruginosa using isochorismate selectively deuterated at C2 as a substrate. Monitoring the reaction by 2H NMR spectroscopy revealed that the label is quantitatively transferred from C2 to C9, producing stoichiometric amounts of [3-2H]pyruvate as product. Moreover, the deuterium kinetic isotope effect of 2.34 +/- 0.08 on kcat indicates that C-H cleavage is significantly rate limiting. Consistent with these data, hybrid density functional theory (HDFT) calculations at the Becke3LYP/DZ+(2d,p) level of theory predict a concerted but highly asynchronous pericyclic transition structure, in which carbon-oxygen bond cleavage is more advanced than hydrogen atom transfer from C2 to C9; the calculated 2H isotope effect of 2.22 at C2 is in excellent accord with the experimental value. Together, these findings indicate that IPL should be added to the small set of proteins that are known to catalyze pericyclic reactions. They also raise the possibility that enzymes, such as chorismate pyruvate lyase, salicylate synthase, 4-amino-4-deoxychorismate lyase, and anthranilate synthase, which accelerate formally similar reaction steps, may also exploit pericyclic mechanisms. 相似文献
87.
John J. Monaghan Michael Barber Robert S. Bordoli R. Donald Sedgwick Andrew N. Tyler 《Journal of mass spectrometry : JMS》1983,18(2):75-82
Fast atom bombardment mass spectra of a range of involatile monophosphonated and mixed sulphonated/monophosphonated azo dyestuffs are presented. Good spectra are obtained and the fragmentations are discussed with special reference to the ions formed by cleavage of the azo linkage. The negative ion spectra are shown to be superior in terms of signal to background and structural information to those obtained in the positive ion mode. The results are compared with those obtained from sulphonated azo dyestuffs. 相似文献
88.
We have calculated the interaction potential for HeI2 in T-shaped geometries using Hartree—Fock and Møller—Plesset third-order perturbation t 相似文献
89.
Donald F. Heller 《Chemical physics letters》1979,61(3):583-587
The apparent simplicity of polyatomic overtone spectra and the conceptual utility of local modes are considered. The form and basis-set-dependence of the dipole moment operator are discussed and a criterion given for overtone spectra to be well described within a local mode picture. Caution is needed in making dynamical inferences based on agreement between overtone and local mode line positions. 相似文献
90.
A kinetic study of the fluoride ion catalyzed isomerization of a series of 2-aryl1-butenes shows the reactions to be pseudo first order in olefin at constant fluoride ion concentration. The resultant Hammett plot is non-linear witb a concave downward break near =0. A two step mechanism involving formation of a carbanionic intermediate is proposed. A change in the rate limiting step causes the break in the Hammett plot. Carbanion trapping experiments are also reported. 相似文献