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181.
182.
Using a stereospecifically labelled precursor, the peroxide catalysed cyclisation of N--butyldihydrocinnamamide to the corresponding β-lactam was shown to proceed with complete loss of stereochemistry at the benzylic carbon atom. 相似文献
183.
The low temperature (125K) X-ray crystal structures of (TMTSF)2X, X=C104-, PF6-, and AsF6- reveal decreases in the intermolecular interand intrastack Se-Se contact distances upon cooling (298K to 125K) which are highly anisotropic and different from one salt to another. The changes in the interstack distances, which are normal to the stacking direction, are approximately twice those involving intrastack Se-Se interactions. These observations establish that the anisotropic structural changes which accompany decreased temperature are common to numerous (TMTSF)2X radical cation conducting salts. 相似文献
184.
A multiple objective waste-disposal model is developed and analysed. The model is a modification of the single objective waste-disposal model of Alley, Aguado and Remson. The solution structure is obtained using the method of constraints so that dual variables (shadow prices) are available with the solutions. 相似文献
185.
The quantum yields of SO3 formation have been determined in pure SO2 and in SO2 mixtures with NO, CO2, and O2 using both flow and static systems. In separate series of experiments excitation of SO2 was effected within the forbidden band, SO2(3B1) ← \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm SO}_2 (\tilde X,^1 A_1 ) $$\end{document}, and within the first allowed singlet band at 3130 Å. The values of Φ were found to be sensitive to the flow rate of the reactants. These results and the apparently divergent quantum yield results of Cox [10], Allen and coworkers [24, 26, 29], and Okuda and coworkers [11] were rationalized quantitatively in terms of the significant occurrence of the reactions SO + SO3 → 2SO2 (2), and 2SO → SO2 + S [or (SO)2] (3), in experiments of long residence time. From the present rate data, values of the rate constants were estimated, k2=(1.2±0.7) × 106; k3=(5±4) × 105 l˙/mole · sec. Φ values from triplet excitation experiments at high flow rates of NO? SO2 and CO2? SO2 mixtures showed the sole reactant with SO2 leading to SO3 formation in this system to be SO2(3B1); SO2(3B1) + SO2 → SO3 + SO(3Σ?) (la); k=(4.2±0.4) × 107 l./mole · sec. With excitation of SO2 at 3130 Å both singlet and triplet excited states play a role in SO3 formation. If the reactive singlet state is 1B1, the long-lived fluorescent state, SO2(1B1) + SO2 → SO3 + SO (1 Δ or 3Σ?) (lb), then k=(2.2±0.5) × 109 l./mole · sec. From the observed inhibition of SO formation by added nitric oxide, it was found that the SO3-forming triplet state, generated in this singlet excited SO2 system, had a relative reactivity toward SO2 and NO which was equal within the experimental error to that observed here for the SO2(3B1) species. Either SO2(3B1) molecules were created with an unexpectedly high efficiency in 3130 Å excited SO2(1B1) quenching collisions, or another reactive triplet (presumably 3A2 or 3B2) of almost identical reactivity to SO2(3B1) was important here. 相似文献
186.
As part of our continuing studies of pyrone-containing natural products, a series 6-methoxypyran-2-ones were synthesized. These were found to react with molecular oxygen at 20 degrees C, and this novel reaction yielded a series of highly functionalized alpha,beta-butenolides. [reaction: see text] 相似文献
187.
We consider a depinning transition in vortex systems with columnar disorder and tilted applied magnetic fields. From scaling arguments and Monte Carlo simulations, we find that this transverse Meissner transition is governed by a fixed point which is anisotropic in all three directions. This generalization of conventional anisotropic scaling means that the correlation length in different directions diverges with different rates, and we derive exact results for the anisotropy exponents. We make predictions which can be tested in experiments on superconductors with columnar disorder. 相似文献
188.
We discuss the interplay between transport and intrinsic dissipation in quantum Hall bilayers, within the framework of a simple thought experiment. We compute, for the first time, quantum corrections to the semiclassical dynamics of this system. This allows us to reinterpret tunneling measurements on these systems. We find a strong peak in the zero-temperature tunneling current that arises from the decay of Josephson-like oscillations into incoherent charge fluctuations. In the presence of an in-plane field, resonances in the tunneling current develop an asymmetric line shape. 相似文献
189.
Samorì P Donners JJ Severin N Otten MB Rabe JP Nolte RJ Sommerdijk NA 《Langmuir : the ACS journal of surfaces and colloids》2004,20(21):8955-8957
The isolation of single polyelectrolyte chains of water-soluble poly(isocyanodipeptide)s (PICs) bearing carboxylic acid terminated side chains occurring both at surfaces and in solution was accomplished by reducing the intermolecular interactions through complexation with cations or positively charged surfactants.Scanning force microscopy and viscosity analyses revealed that this method allows to tune the conformation of the macromolecule, which is of importance for tailoring the physicochemical properties of the material.This is particularly significant for the use of these polymer chains as seed for biomineralization processes. 相似文献
190.
Bernhardt PV Harrowfield JM Kim Y Koutsantonis GA Lee YH Thuéry P 《Inorganic chemistry》2004,43(5):1681-1688
Reaction between ethane-1,2-diamine and 3,3'-dichloropivalic acid results in different, isomeric tetra-amine derivatives, one a tetraamino carboxylic acid and the other a carboxamidotriamino alcohol, depending upon reaction conditions. Intended conversion of the Cu(II) complex of the former to a cyclam-like macrocycle through reaction with nitroethane and formaldehyde results in isolation of derivatives of both the former and the latter. This can be rationalized by assuming the intermediacy of an azetidinone, a species similar to that seen in simpler reactions of dichloropivalates. A single reaction thereby provides pendent-arm macrocycles where one has an electrophilic and the other a nucleophilic substituent. Parallel chemistry is not seen in the reaction between propane-1,3-diamine and 3,3'-dichloropivalate. 相似文献