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991.
Nathalie Boutonnet Daniel Van Belle Shoshana J. Wodak 《Theoretical chemistry accounts》2001,106(1-2):10-21
With the aim of identifying structural changes in acetylcholinesterase, induced by ligand binding, we use a completely automatic
procedure to analyse the differences between the backbone conformation of the free enzyme and those in eight complexes of
Torpedo californica acetylcholinesterase, with various quaternary ammonium ligands, and with the protein inhibitor fasciculin. In order to discriminate
between structural changes due to ligand binding and those arising from model imprecision, we also examine protein–ligand
and protein–water contacts. Except for the peptide flip in the complex with huperzine A, the backbones of other complexes
with quaternary ammonium ligands display negligible changes relative to the free enzyme. Another exception is the complex
with the bisquaternary ammonium ligand decamethonium, where several loops display above average deformations, but only two,
those spanning residues 334–348 and residues 277–304, seem to move as a result of ligand binding. Movement of the ω loop (residues
61–95) is detected only in the complex with the protein fasciculin.
Received: 21 July 2000 / Accepted: 18 September 2000 / Published online: 28 February 2001 相似文献
992.
Spontaneous pair creation in the field of a large Reissner singularity (a point-like charge e whose mass M is such that ) is here considered. Using as a guide the definition of the positive and negative energy states of a classical particle in this field, a particular basis of quantum states is chosen which contains resonance states — these are interpreted by invoking particle creation. Extremely energetic particles are shown to burst out to infinity whereas the antiparticles dress up and neutralize the singularity. This result is contrasted with the process of pair production by black holes and compared with the isotropization of the early universe by creation of matter. 相似文献
993.
Nathalie Eisenbaum 《Probability Theory and Related Fields》2003,125(3):381-392
We show that fractional Brownian motions with index in (0,1] satisfy a remarkable property: their squares are infinitely
divisible. We also prove that a large class of Gaussian processes are sharing this property. This property then allows the
construction of two-parameters families of processes having the additivity property of the squared Bessel processes.
Received: 1 April 2002 / Revised version: 7 September 2002 / Published online: 19 December 2002
Mathematics Subject Classification (2000): 60E07, 60G15, 60J25, 60J55
Key words or phrases: Gaussian processes – Infinite divisibility – Markov processes 相似文献
994.
Nathalie Charton Achim Feldermann Alexander Theis Martina H. Stenzel Thomas P. Davis Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2004,42(20):5170-5179
An Erratum has been published for this article in J. Polym. Sci. Part A: Polym. Chem. (2004) 42(21) 5559 . The initiator efficiency, f, of 2,2′‐azobis(isobutyronitrile) (AIBN) in dodecyl acrylate (DA) bulk free‐radical polymerizations has been determined over a wide range of monomer conversion in high‐molecular‐weight regimes (Mn ? 106 g mol?1 [? 4160 units of DA)] with time‐dependent conversion data obtained via online Fourier transform near infrared spectroscopy (FTNIR) at 60 °C. In addition, the required initiator decomposition rate coefficient, kd, was determined via online UV spectrometry and was found to be 8.4 · 10?6 s?1 (±0.5 · 10?6 s?1) in dodecane, n‐butyl acetate, and n‐dodecyl acetate at 60 °C. The initiator efficiency at low monomer conversions is relatively low (f = 0.13) and decreases with increasing monomer to polymer conversions. The evolution of f with monomer conversion (in high‐molecular‐weight regimes), x, at 60 °C can be summarized by the following functionality: f60 °C (x) = 0.13–0.22 · x + 0.25 · x2 (for x ≤ 0.45). The reported efficiency data are believed to have an error of >50%. The ratio of the initiator efficiency and the average termination rate coefficient, 〈kt±, (f/〈kt〉) has been determined at various molecular weights for the generated polydodecyl acrylate (Mn = 1900 g mol?1 (? 8 units of DA) up to Mn = 36,500 g mol?1 (? 152 units of DA). The (f/〈kt〉) data may be indicative of a chain length‐dependent termination rate coefficient decreasing with (average) chain length. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5170–5179, 2004 相似文献
995.
Current status of molecularly imprinted polymers as alternatives to antibodies in sorbent assays 总被引:2,自引:0,他引:2
Nathalie Lavignac Christopher J. Allender Keith R. Brain 《Analytica chimica acta》2004,510(2):139-145
The literature on the use of molecularly imprinted polymers (MIPs) in antibody-like sorbent assay using radio, fluoro and enzyme-linked approaches is comprehensively reviewed, and their current status discussed. Although immunoassays are still commonly carried out using antibodies, recent developments have demonstrated that molecularly imprinted polymers can be viable alternatives. It is predicted that both traditional antibody-based and MIP sorbent assays will continue to develop in parallel, with each having superiority in certain areas. 相似文献
996.
Raman and infrared spectroscopy were used to study the nature of hydrogen bonding and the cation inductive effect in solutions of LiCF(3)SO(3) dissolved in hexylamine, a primary amine, and dipropylamine, a secondary amine. Comparison of pure hexylamine and hexylamine dissolved in CCl(4) established that the Raman band maximum of the symmetric stretching mode, nu(s)(NH(2)), in pure hexylamine originates in molecules undergoing no hydrogen bonding interactions. The addition of LiCF(3)SO(3) to hexylamine or dipropylamine shifts the frequencies of the solvent NH stretching modes by two effects: the breaking of hydrogen bonds and the cation inductive effect. Comparison of the infrared and Raman spectra allows (to some degree) the separation of these two effects. During these studies, crystalline compounds of hexylamine:LiCF(3)SO(3) and dipropylamine:LiCF(3)SO(3) were discovered, and their structures were solved by single-crystal X-ray diffraction techniques. Vibrational spectra of these crystals and detailed structural knowledge of the cation-solvent interactions complement analogous spectroscopic studies of the solution phases. The cation-polymer and hydrogen bonding interactions of branched poly(ethylenimine) (BPEI) complexed with LiCF(3)SO(3) were modeled by the solutions of hexylamine and dipropylamine containing dissolved LiCF(3)SO(3). Specifically, lithium ion interactions with the primary and secondary amine groups in BPEI were modeled by the solution studies with hexylamine and dipropylamine, respectively. The analysis of the hexylamine system was particularly useful because the primary amine group of BPEI dominates the NH stretching region of the spectrum. 相似文献
997.
Catala L Le Moigne J Gruber N Novoa JJ Rabu P Belorizky E Turek P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(8):2440-2454
The present work completes and extends our previous reports on the determination of the magnetic ground state and on the strength of the through bond exchange coupling within series of biradicals. This knowledge was subsequently exploited for the analysis of the magnetic interactions in their crystals. We report here the studies of series of triradicals incorporating alpha-nitronyl nitroxides (NN) or alpha-imino nitroxides (IN) as terminal radical fragments connected through a m-phenylene coupling unit in one case and a phenyl acetylene unit in other case. Tetraradical derivatives have also been studied. The studies of isolated molecules (EPR in solution and DFT calculations) allow the assessment of the magnetic interactions through the magnetic coupling unit. All triradical derivatives are found to exhibit a quartet ground state, whereas a singlet ground state is determined for the tetraradical. This last result reinforces previous findings that the singlet ground state is favoured in related biradicals involving similar m-phenylene couplers. Moreover, the through bond magnetic exchange coupling for the ortho-meta connectivity could be demonstrated as being ferromagnetic, thus ascertaining our previous hypotheses. The magnetic properties of the triradicals and tetraradicals in their solid state have been rationalized by using a previously proposed methodology, allowing to identify the most relevant magnetic pathways. 相似文献
998.
Recently, synthetic multifunctional pores have been identified as "universal" detectors of chemical reactions. In this report, we show that with the assistance of enzymes as variable co-sensors, synthetic multifunctional pores can serve as similar universal sensors of variable components in mixed analytes. Sugar sensing in soft drinks is used to exemplify this new concept. This is achieved using invertase and hexokinase as co-sensors and a new synthetic multifunctional pore capable of discriminating between ATP and ADP in an "on-off" manner as sensor. The on-off discrimination between ATP as good and ADP as poor pore blocker is shown to be reasonably tolerant of changing experimental conditions. These results identify universal sensing with synthetic multifunctional pores as a robust, sensitive, and noninvasive method with appreciable promise for practical applications. 相似文献
999.
1000.
Chrétien A Chataigner I L'Hélias N Piettre SR 《The Journal of organic chemistry》2003,68(21):7990-8002
The reaction between indole-3-carboxaldehyde 1a or indole-3-glyoxalate 1b and 2,3-dimethylbutadiene under thermal activation leads exclusively to the Diels-Alder cycloadducts resulting from the participation of the indole 2,3-carbon-carbon double bond. The concomitant use of zinc chloride and high pressure (16 kbar) induces the primary cycloadduct to react further, and biscycloadducts 11 and 12 are now isolated in high yields, the result of two consecutive [4 + 2] processes on, first, the indole 2,3 C=C bond and, second, the 3-carbonyl unit. The possibility of using two different dienes in a tandem, sequential process is demonstrated by the preparation of tetracycle 13. Interactions between the carbonyl dienophile and Danishefsky diene yield exclusively yet another type of product, namely the gamma-dihydropyranones arising from the sequential [4 + 2] heterocycloaddition, hydrolysis of the silyl enol ether, and loss of methanol. Isolation of the Mukaiyama-type adduct 16 indicates that a stepwise mechanism may be involved, at least under zinc chloride catalysis. N,N-Disubstituted indole-3-glyoxamides undergo the expected, usual Diels-Alder process, with the 2,3 C=C bond acting as dienophile, and cycloadducts of the type 3 are obtained in high yields, regardless of the mode of activation. Remarkably, however, N-monosubstituted indole-3-glyoxamides react almost exclusively as heterodienophiles, the 3-carbonyl unit being now the preferred site of reactivity, and gamma-dihydropyranones of the type 6 are isolated in yields ranging from 72 to 92%. Conformational analysis of the Diels-Alder adducts based on both (1)H NMR spectrometry and X-ray diffraction data indicates that the newly created cyclohexene and cyclohexanone rings adopt a pseudoboat conformation. 相似文献