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51.
Cosper MM Jameson GN Davydov R Eidsness MK Hoffman BM Huynh BH Johnson MK 《Journal of the American Chemical Society》2002,124(47):14006-14007
The combination of resonance Raman, electron paramagnetic resonance and M?ssbauer spectroscopies has been used to investigate the effect of S-adenosyl-l-methionine (SAM) on the spectroscopic properties of the [4Fe-4S]2+ cluster in biotin synthase. The results indicate that SAM interacts directly at a unique iron site of the [4Fe-4S]2+ cluster in BioB and support the hypothesis of a common inner-sphere mechanism for the reductive cleavage of SAM in the radical SAM family of Fe-S enzymes. 相似文献
52.
L.?S.?Roman R.?M.?Q.?Mello F.?Cunha I.?A.?HümmelgenEmail author 《Journal of Solid State Electrochemistry》2004,8(2):118-121
We report the use of sulfonated polyaniline, SPAN, as a positive charge transporting layer in organic electronic devices, demonstrating that it can be used to significantly improve injection into conjugated polymers. The introduction of an intermediate SPAN layer improves device rectification, even when low-work-function anode materials such as tin oxide are used. 相似文献
53.
Roman E. Sioda 《Monatshefte für Chemie / Chemical Monthly》1985,116(1):49-52
The specific dissolution rate, expressed in mol cm–2s–1, and time-variation of the rest potential of copper foil in an aerated aqueous solution ofpH = 2.0 were measured.
Die Auflösbarkeit von Kupfer-Folie in wäriger Lösung von pH 2 (Kurze Mitteilung)
Zusammenfassung Es wurde die spezifische Auflösungsgeschwindigkeit (in mol cm–2s–1) und die zeitliche Veränderung des Restpotentials von Kupfer-Folie in einer belüfteten wäßrigen Lösung von pH 2,0 gemessen.相似文献
54.
Collman JP Kaplun M Sunderland CJ Boulatov R 《Journal of the American Chemical Society》2004,126(36):11166-11167
Electrocatalytic reduction of a series of chemical oxidants of different power (tert-butyl hydroperoxide, potassium peroxomonosulfate, peracetic acid, and m-chloroperbenzoic acid) at iron-porphyrin-modified graphite electrodes is studied in buffered aqueous solutions by rotating disk and ring-disk voltammetry. Both ferric and ferrous porphyrins are catalytically active. Turnover of ferric catalysts is slower than that of the ferrous analogues and involves competing catalytic reduction and disproportionation. The kinetic data are consistent with reactant binding being the rate-determining step in catalysis by Fe(III). In catalysis by Fe(II), the turnover is controlled by the first electron transfer. The covalently linked proximal imidazole ligand is found to be crucial for achieving the Fe(III) catalysis. 相似文献
55.
A procedure for quantitative determination of acetylsalicylic acid and acetaminophen in pharmaceuticals by PLS (partial least squares) and PCR (principal component regression) treatment of FT (Fourier transform)-Raman spectroscopic data is proposed. The proposed method was tested on powdered samples. Three chemometric models were built: the first, for samples consisting of an active substance diluted by lactose, starch and talc; the second, in which a simple inorganic salt was applied as an internal standard and additions were not taken into account; and the third, in which a model was constructed for a commercial pharmaceutical, where all constituents of the tablet were known. By utilising selected spectral ranges and by changing the chemometric conditions it is possible to carry out fast and precise analysis of the active component content in medicines on the basis of the simplified chemometric models. The proposed method was tested on five commercial tablets. The results were compared with data obtained by intensity ratio and pharmacopoeial methods. To appraise the quality of the models, the relative standard error of predictions (RSEPs) were calculated for calibration and prediction data sets. These were 0.7-2.0% and 0.8-2.3%, respectively, for the different PLS models. Application of these models to the Raman spectra of commercial tablets containing acetylsalicylic acid gave RSEP values of 1.3-2.0% and a mean accuracy of 1.2-1.7% with a standard deviation of 0.6-1.2%. 相似文献
56.
Increased structural complexity leads to higher activity: peptides as efficient and versatile catalysts for asymmetric aldol reactions 总被引:3,自引:0,他引:3
[reaction: see text] Peptides containing a secondary amine and a carboxylic acid in a specific orientation to each other are presented as highly efficient catalysts for asymmetric aldol reactions: (1) their activity is considerably higher compared to that of proline, and (2) the enantioselectivity of the peptidic catalysts can be changed from (R)- to (S)-selectivity by simple modifications of the secondary structure. 相似文献
57.
Roman E. Enrique Castro W. Veronica Camus O. Margarita 《Journal of organometallic chemistry》1985,293(1):93-101
The reactions between the phosphine-organoiron [CpFeII-η6-C6Me5CH2PPh2]+ PF6? (1) and [RhCl(η4-diolefin)(μ-Cl)]2 in CH2Cl2 at reflux give the new heterobinuclear air-stable crystalline complexes [CpFeII-η6-C6Me5CH2)P(Ph)2Rh(η4-diene)Cl]PF6,(D'*-diene=cyclooctadiene (COD): 65%, 2; trimethylfluorobenzobicyclo[2.2.2]octadiene (Me3TFB): 48%, 3). Complexes 2 and 3 have been studied by 1H, 13C and 31P NMR spectroscopy and they are carbonylated (CO, 1 atm). Cyclic voltammetry experiments with addition of MeOH show electron transfer FeIRhI → FeIIRh0, the presence of a catalytic wave FeI/FeII and the possible formation of Rh hydrides. Under normal conditions 2 is a catalyst for hydrogenation of cyclohexene, but it is less efficient than the known mononuclear Rh1 analogues. 相似文献
58.
Consider equations of the form where q is in general a complex vector and the function F depends nontrivially both on q and on qy. We show that a family S of such equations can be investigated by the inverse scattering method. If an equation (*) belongs to S, the function F depends linearly on q and algebraically on qy. We show that the family S contains a subfamily in which each equation can be obtained from the two dimensional Toda lattice equations by a Bäcklund transformation. 相似文献
59.
We generalize the well-known Baker's superstability result for exponential mappings with values in the field of complex numbers to the case of an arbitrary commutative complex semisimple Banach algebra. It was shown by Ger that the superstability phenomenon disappears if we formulate the stability question for exponential complex-valued functions in a more natural way. We improve his result by showing that the maximal possible distance of an -approximately exponential function to the set of all exponential functions tends to zero as tends to zero. In order to get this result we have to prove a stability theorem for real-valued functions additive modulo the set of all integers .
60.
Scientists are constantly looking for better and cheaper separation techniques to replace or complement the current technology. Over the past few decades, and in particular the last 10 years, new separation techniques or modifications of existing techniques have become available for separating compounds from complex sample matrices. There are many areas, however, where the separation technology is not sufficient to achieve high purity and yield while remaining cost effective. In the area of biotechnology, separation techniques are urgently needed to meet demands for ultra-high purity and yield. Thus, a variety of techniques are being developed to address these needs. Generally, biological compounds for the pharmaceutical and biotechnology industries must be obtained at greater than 99.9% purity (sometimes greater than 99.99%) while maintaining high yield. In any area of chemistry this degree of purity would cause problems; in biotechnology it is even more difficult to achieve because of the complex sample matrices. In addition, the compounds of interest may be very similar to impurities or contaminants in the sample matrix, and the compounds could be denatured (or even destroyed) by certain solvents and/or high temperature. In particular, three areas of biotechnology have presented scientists with problems in separations: cell separations, DNA-RNA separations, and protein-peptide separations. The current technology available and possible future trends in these areas are discussed, and also problems to be solved in the future. 相似文献