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81.
82.
The kinetics of the gas-phase reaction of the NO3 radical with naphthalene have been investigated at 150 torr O2 + 590 torr N2 and 600 torr O2 + 140 torr N2 at 298 ± 2 K. Relative rate measurements were carried out in reacting NO3? N2O5-naphthalene-propene-O2? N2 mixtures by longpath Fourier transform infrared absorption spectroscopy. A rate constant ratio for the reactions of O2 and NO2 with the NO3-naphthalene adduct of k/k < 4 × 10?7 was obtained from the competition between O2 and NO2 for reaction with the NO3-naphthalene adduct and thermal decomposition of the adduct back to reactants. Atmospheric pressure ionization MS/MS measurements of the nitronaphthalene products of the NO3 radical-initiated reaction of naphthalene are consistent with the proposed reaction mechanism, and the atmospheric implications of the data are discussed. © 1994 John Wiley & Sons, Inc. 相似文献
83.
Reza Dabesrani Robert H. Sik Donald G. Davis George Dubay Colin F. Chignell 《Photochemistry and photobiology》1993,58(3):367-373
Abstract— The photochemistry, photophysics, and photosensitization (Type I and II) of indomethacin (IN) (N-[p-chlorobenzoyl]-5-methoxy-2-methylindole-3-acetic acid) has been studied in a variety of solvents using NMR, high performance liquid chromatography-mass spectroscopy, transient spectroscopy, electron paramagnetic resonance in conjunction with the spin trapping technique, and the direct detection of singlet molecular oxygen (l O2) luminescence. Photodecomposition of IN (λex > 330 nm) in degassed or air-saturated benzene proceeds rapidly to yield a major (2; N-[p-chlorobenzoyl]-5-methoxy-2-methyl-3-methylene-indoline) and a minor (3; N-[p-chlorobenzoyl]-5-methoxy-2, 3-dimethyl-indole) decarboxylated product and a minor indoline (5; 1-en-5-methoxy-2-methyl-3-methylene-in-doline), which is formed by loss of the p-chlorobenzoyl moiety. In air-saturated solvents two minor oxidized products 4 (N-[p-chlorobenzoyl]-5-methoxy-2-methylindol-3-aldehyde) and 6 (5-methoxy-2-methyl-indole-3-aldehyde) are also formed. When photolysis was carried out in 18O2-saturated benzene, the oxidized products 4 and 6 contained 18O, indicating that oxidation was mediated by dissolved oxygen in the solvent. In more polar solvents such as acetonitrile or ethanol, photodecomposition is extremely slow and inefficient. Phosphorescence of IN at 77 K shows strong solvent dependence and its emission is greatly reduced as polarity of solvent is increased. Flash excitation of IN in degassed ethanol or acetonitrile produces no transients. A weak transient is observed at 375 nm in degassed benzene, which is not quenched by oxygen. Irradiation of IN (λex > 325 nm) in N2-gassed C6H6 in the presence of 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) results in the trapping of two carbon-centered radicals by DMPO. One adduct was identified as DMPO/.COC6H4-p-CI, while the other was probably derived from a radical formed during IN decarboxylation. In air-saturated benzene, (hydro) peroxyl and alkoxyl radical adducts of DMPO are observed. A very weak luminescence signal from 1O2 at 1268 nm is observed initially upon irradiation (λex= 325 nm) of IN in air-saturated benzene or chloroform. The intensity of this 1O2 signal increases as irradiation is continued suggesting that the enhancement in 1O2 yield is due to photoproduct(s). Accordingly, when 2 and 3 were tested directly, 2 was found to be a much better sensitizer of 1O2 than IN. In air-saturated ethanol or acetonitrile no IN 1O2 luminescence is detected even on continuous irradiation. The inability of IN to cause phototoxicity may be related to its photo stability in polar solvents, coupled with the low yield of active oxygen species (1O2, O2?-) upon UV irradiation. 相似文献
84.
Two important considerations in the design of an aerobic particulate immobilized cell bioreactor are the provision of sufficient
oxygen to maintain the desired metabolism of the immobilized organism, and the biomass holdup (which is proportional to the
number of immobilized cell particles in the reactor).
The Circulating Bed Reactor, a reactor developed for use with those forms of immobilization that result in particles of essentially
neutral buoyancy, operates with an expanded bed of circulating particles. The particle number density attainable in such a
reactor has been found to be dependent upon the circulation cell aspect ratio, the individual particle properties, the static
bed voidage of the particles, and the superficial gas velocity. The oxygen mass transfer characteristics have been found to
be dependent upon the circulatory nature of the system, the particle (solids) holdup, the particle porosity, and the superficial
gas velocity. 相似文献
85.
Interpretation of the chemical and spectral (IR., UV., 1H- and 13C-NMR.) properties of the antitumor antibiotic hedamycin (C41H50N2O11) suggests that the molecule contains a methyl substituted 1-hydroxyanthraquinone nucleus, an α, β-unsaturated ketone, two sugar-like tetrahydropyran rings ( 4 and 8 ) and an aliphatic chain 2 , presumably with an epoxy group (see the Scheme). 相似文献
86.
The ν1(CN) band of SCN? in acetonitrile solvent has been observed, surface enhanced, at a silver electrode. Adsorption through the S of SCN? is suggested. The changes of frequency and intensity with the change of electrode potential are reported. The υ(CN) band of the solvent is also probably enhanced. 相似文献
87.
Keyes TE Leane D Forster RJ Coates CG McGarvey JJ Nieuwenhuyzen MN Figgemeier E Vos JG 《Inorganic chemistry》2002,41(22):5721-5732
A detailed spectroscopic and electrochemical study of a series of novel phenolate bound complexes, of general formulas [M(L-L)(2)(box)](PF(6)), where M is Os and Ru, L-L is 2,2-bipyridine or 2,2-biquinoline, and box is 2-(2-hydroxyphenyl)benzoxazole, is presented. The objectives of this study were to probe the origin of the LUMOs and HOMOs in these complexes, to elucidate the impact of metal and counter ligand on the electronic properties of the complex, and to identify the extent of orbital mixing in comparison with considerably more frequently studied quinoid complexes. [M(L-L)(2)(box)](PF(6)) complexes exhibit a rich electronic spectroscopy extending into the near infrared region and good photostability, making them potentially useful as solar sensitizers. Electrochemistry and spectroscopy indicate that the first oxidation is metal based and is associated with the M(II)/(III) redox states. A second oxidative wave, which is irreversible at slow scan rates, is associated with the phenolate ligand. The stabilities of the oxidized complexes are assessed using dynamic electrochemistry and discussed from the perspective of metal and counter ligand (LL) identity and follow the order of increasing stability [Ru(biq)(2)(box)](+) < [Ru(bpy)(2)(box)](+) < [Os(bpy)(2)(box)](+). Electronic and resonance Raman spectroscopy indicate that the lowest energy optical transition for the ruthenium complexes is a phenolate (pi) to L-L (pi) interligand charge-transfer transition (ILCT) suggesting the HOMO is phenolate based whereas electrochemical data suggest that the HOMO is metal based. This unusual lack of correlation between redox and spectroscopically assigned orbitals is discussed in terms of metal-ligand orbital mixing which appears to be most significant in the biquinoline based complex. 相似文献
88.
We have developed further a chromatographic model for studying the hydrophobic interactions which characterize the way a ligand binds to its receptor. This model is based on observing the retention behaviour of de novo designed model 18-residue amphipathic alpha-helical peptides (representing the hydrophobic binding domain of a ligand) on reversed-phase packings by varying hydrophobicity (representing a receptor protein with a hydrophobic binding pocket). Mutants of the "native" peptide ligand (which contains seven Leu residues in its non-polar face) were designed by replacing one residue in the center of the extremely non-polar face of the amphipathic alpha-helix. Through reversed-phase liquid chromatography of these peptides at pH 2.0 on cyano and C18 columns, we have demonstrated how an increase in receptor hydrophobicity (represented by an increase in column stationary phase hydrophobicity; cyano --> C18) significantly enhances hydrophilicity of polar amino acid side-chains at the ligand-receptor interface while moderately enhancing the hydrophobicity of non-polar side-chains. The addition of salt (100 mM sodium perchlorate) to the aqueous environment surrounding the binding site of receptor and ligand was also shown to have a profound effect on side-chain hydrophilicity/hydrophobicity in the binding interface. This effect was particularly dramatic for the positively charged side-chains Arg, Lys and His, whose significant enhancement of hydrophobicity in the presence of the cyano column contrasted with their increase in hydrophilicity in the presence of the considerably more hydrophobic C18 stationary phase. Our results have major implications to understanding the influence of hydrophobic and aqueous environment on hydrophilicity/hydrophobicity of amino acid side-chains and the role side-chains play in the folding and stability of proteins. 相似文献
89.
Colin J.H. Morton Richard L. Riggs Nicholas J. Westwood Alexandra M.Z. Slawin 《Tetrahedron》2005,61(3):727-738
Ethyl 2-aryl-4,5-dihydro-5-oxopyrrole-3-carboxylates react with esters or acyl halides in the presence of a strong base to give 4-acyl derivatives, which exist predominantly as either E- or Z-enols. These are cyclised, either in solution at temperatures >200 °C or by microwave irradiation, to 3,6-disubstituted 1H-furo[3,4-c]pyrrolediones which, after N-protection, are convertible by reaction with primary amines into novel N,N′-disubstituted DPP derivatives. 相似文献
90.
Hamlet CG Jayaratne SM Morrison C 《Rapid communications in mass spectrometry : RCM》2005,19(16):2235-2243
A rapid, sensitive and selective method has been developed and validated for the analysis of the contaminant ethyl carbamate (EC) in bread products at the part-per-billion level. The new procedure uses positive ion chemical ionisation (PICI) and tandem mass spectrometry (MS/MS), combined with gas chromatography (GC), on a 'bench-top' triple-quadrupole mass spectrometer. Ammonia was the PICI reagent gas of choice because of its ability to produce abundant [M+H]+ and [M+NH4]+ ions from EC and deuterium-labelled EC (LEC) used as an internal standard. For identification and quantification, selected reaction monitoring (SRM) was used to follow the precursor-to-product ion transitions of m/z 107 --> 90, m/z 107 --> 62 and m/z 90 --> 62 for EC, as well as m/z 112 --> 63 for the LEC internal standard. The limits of detection and quantification were 0.6 and 1.2 microg kg(-1), respectively, and the recovery of the method was 101 +/- 10% at 10 microg kg(-1) and 98 +/- 5% at 100 microg kg(-1). The precision of the method, established under conditions of intermediate reproducibility, did not exceed a relative standard deviation of 7%. The quantitative performance of the new GC/PICI-SRM procedure compared favourably with that of a reference method based on GC/MS and selected ion monitoring (correlation coefficient, r = 0.997). However, the new method had the advantages of reduced sample preparation time, improved sensitivity and unambiguous identification of EC at all concentrations. Application of the new method to the analysis of 50 UK breads showed that levels of EC ranged from 0.6 to 2.3 microg kg(-1) in retail products and from 3.1 to 12.2 microg kg(-1) for breads prepared using domestic breadmaking machines (dry weight basis). Toasting bread in a domestic toaster led to increases of between two- and three-fold in mean EC concentrations. 相似文献