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101.
The rate constant of the reaction of OH radicals with butyl acrylate was studied for the first time using an atmospheric simulation chamber at 298 K and ~750 Torr of air or nitrogen. The decay of the organics was followed using a gas chromatograph with a flame ionization detector (GC‐FID), and the rate constant was determined using a relative rate method with different references. The obtained average value of (1.80 ± 0.26) × 10?11 cm3 molecule?1 s?1 is in agreement with previous determinations of the rate constants of OH radicals with acrylates and methacrylates in the literature. Additionally, product identification under atmospheric conditions was performed for the first time by the GC‐MS technique. Butyl glyoxalate was observed as the degradation product in accordance with the addition of OH to the less substituted carbon atom of the double bond, followed by decomposition of the 1,2‐hydroxyalkoxy radicals formed. Room temperature rate coefficient was used to estimate the atmospheric lifetime of the ester studied. Reactivity trends are discussed in terms of the substituent effects and the length of the hydrogenated chain of the ester. The atmospheric persistence of BUAC was calculated taking into account the experimental rate constant obtained. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
102.
A kinetic study on the basic hydrolysis of cephaloridine at pD= 10.5 was carried out by using the 1H? NMR technique. Epimerization at H7, a nucleophilic attack of hydroxyl ion on the β-lactam carbonyl group followed by the release of the pyridine molecule, and isomerization of the double bond at position 3 in the dihydrothiazine ring were the major reactions observed. Based on the results obtained, it should be emphasized that the presence of a pyridine group at 3′ results in a slightly increased formation constant for the exo methylene compound relative to other cephalosporins with different substituents at that position. The activation energy for the epimerization constant and the cleavage of the β-lactam ring at pD 10.5 was 21.2 kcal/mol. © 1993 John Wiley & Sons, Inc. 相似文献
103.
D.?BolléEmail author J.?Busquets Blanco 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,47(2):281-290
The thermodynamic and retrieval properties of the Blume-Emery-Griffiths
neural network with synchronous updating and variable dilution are studied
using replica mean-field theory. Several forms of dilution are allowed
by pruning the different types of couplings present in the Hamiltonian.
The appearance and properties of two-cycles are discussed. Capacity-temperature phase diagrams are derived for several values
of the pattern activity. The results are compared with those for sequential updating. The effect of self-coupling is studied.
Furthermore, the optimal combination of dilution parameters giving the largest critical capacity is obtained. 相似文献
104.
Chazallon B Lebrun N Dhamelincourt P Toubin C Focsa C 《The journal of physical chemistry. B》2005,109(1):432-439
Rapidly frozen aqueous solutions containing variable amounts of dissolved formaldehyde (0.1, 5, 7, 10, 15, and 20 mol %) have been analyzed by micro-Raman spectroscopy at ambient pressure and low temperature. The importance of the formladehyde-ice system has been repeatedly quoted in various contexts, such as atmospheric and snowpack chemistry and interstellar and cometary ices. Understanding and characterizing the effects of freezing and the interactions of formaldehyde with ice are therefore of relevant interest. In this study, the distinct vibrational signatures of the oligomers present in the solution and in the frozen ice mixtures have been identified in the 120-4000 cm(-1) spectral range. From the subtle changes of the bands assigned to the CO and CH group frequencies, at least two distinct crystalline phases (pI and pII) are found to coexist with ice at different temperatures. Depending on the cooling-rewarming protocol, pI is found to crystallize in the 163-213 K temperature range. Above approximately 213 K, pI gets transformed irreversibly into pII which is stable up to approximately 234 K. pII is found to interact more strongly with ice than pI, as revealed, for example, by the drop in frequency of the bands assigned to the O-H stretching as pI transforms into pII. It is suggested that pII consists of a hydrogen-bonded network of oligomers and water molecules. On the other hand, it is suggested that the oligomers mainly present in pI interact through weak forces with the surrounding water molecules. 相似文献
105.
We show the standard two-level continuous-time model of loss-modulated CO2 lasers to display the same regular network of self-similar stability islands known so far to be typically present only in discrete-time models based on mappings. Our results suggest that the two-parameter space of class B laser models and that of a certain class of discrete mappings could be isomorphic. 相似文献
106.
We use Greithers recent results on Brumers Conjecture to prove Rubins integral version of Starks Conjecture, up to a power of 2, for an infinite class of CM extensions of totally real number fields, called nice extensions under the assumption that a certain Iwasawa –invariant vanishes. As a consequence and under the same assumption, we show that the Brumer–Stark Conjecture is true for nice extensions, up to a power of 2.Mathematical Subject Classification (1991): 11R42, 11R58, 11R27Research on this project was partially supported by NSF grants DMS–9801267 and DMS–0196340.in final form: 16 July 2003 相似文献
107.
Structural and spectroscopic study of 5,7-dihydroxy-flavone and its complex with aluminum 总被引:3,自引:0,他引:3
Castro GT Blanco SE 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(10):2235-2241
The structure, stability and molar absorptivity of the complex formed between AlCl(3) and 5,7-dihydroxy-flavone in methanol were investigated using UV-Vis spectroscopy and the AM1 method. The molar ratio method and Job's method of continuous variation were applied to ascertain the stoichiometric composition of the complex in methanol at constant ionic strength. A 1:2 complex was indicated by both methods. The molar absorptivity and stability constant of the complex were determined using a simple and accurate procedure that requires solutions having the ligand and metal ion in the stoichiometric proportion. The high stability constant demonstrates that the complexation reaction is total. The structure of this complex, obtained by the quantum semi-empirical AM1 method, indicates that two classes of metal-ligand interactions are involved in the formation of the metal complex: (a) two simple covalent bonds between the aluminum atom and the oxygen atoms of o-hydroxyl groups of 5,7-dihydroxy-flavone; (b) two stronger Coulombic interactions between the aluminum atom and the carbonyl oxygen atoms of the ligand. 相似文献
108.
On the Norm of Elementary Operators 总被引:3,自引:0,他引:3
The norm problem is considered for elementary operators of theform Ua,b: AA,x axb+bxa (a,bA) in the special case when A isa subalgebra of the algebra of bounded operators on a Banachspace. In particular, the lower estimate || is established when the Banach space is a Hilbertspace and A is the algebra of all bounded linear operators. 相似文献
109.
Spontaneous emission in the presence of complex nanostructures is discussed by use of a calculational scheme that permits us to deal with interfaces of arbitrary shape. Control over the field associated with the emission is shown to be attainable. In particular, decay rates are offered for geometries that lead to focusing and collimation of near- and far-field distributions. Emission from axially symmetric gratings is shown to lead to narrow angular distributions of emission, and focusing at the foci of dielectric ellipsoids is achieved for dimensions comparable with the wavelength. In the latter case the total emission rate for two atoms in an ellipsoidal cavity is shown to be enhanced in a way that deviates from the predictions of the Dicke effect by means of intermediate- and far-field contributions. 相似文献
110.
We elaborate on a recently proposed model of the temporal dependence of polarization mode dispersion in long fiber links. We evaluate the probability that a channel of a wavelength-division multiplexed system never incurs an outage, and the range of frequency over which the parameters that characterize the temporal statistics of the differential group delay are correlated. 相似文献