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21.
Yan YG Li QX Huo SJ Ma M Cai WB Osawa M 《The journal of physical chemistry. B》2005,109(16):7900-7906
A versatile two-step wet process to fabricate Pt, Pd, Rh, and Ru nanoparticle films (simplified as nanofilms hereafter) for in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) study of electrochemical interfaces is presented, which incorporates an initial chemical deposition of a gold nanofilm on the basal plane of a silicon prism with the subsequent electrodepostion of desired platinum group metal overlayers. Galvanostatic electrodeposition of Pt, Rh, and Pd from phosphate or perchloric acid electrolytes, or potentiostatic electrodeposition of Ru from a sulfuric acid electrolyte, yields sufficiently "pinhole-free" overlayers as evidenced by electrochemical and spectroscopic characterizations. The Pt group metal nanofilms thus obtained exhibit strongly enhanced IR absorption. In contrast to the corresponding metal films electrochemically deposited directly on glassy carbon and bulk metal electrodes, the observed enhanced absorption for the probe molecule CO exhibits normal unipolar band shapes. Scanning tunneling microscopic (STM) images reveal that fine nanoparticles of Pt group metals are deposited around wavy and stepped bunches of Au nanoparticles of relatively large sizes. This ubiquitous strategy is expected to open a wide avenue for extending ATR surface-enhanced IR absorption spectroscopy to explore molecular adsorption and reactions on technologically important transition metals, as exemplified by successful real-time spectroscopic and electrochemical monitoring of the oxidation of CO at Pd and that of methanol at Pt nanofilm electrodes. The spectral features of free water molecules coadsorbed with CO on Pt, Pd, Rh, and Ru are also discussed. 相似文献
22.
Tomoyuki Manaka Shin‐Ichiro Nagayama Wannaporn Desadee Naoki Yajima Takuya Kumamoto Toshiko Watanabe Tsutomu Ishikawa Masatoshi Kawahata Kentaro Yamaguchi 《Helvetica chimica acta》2007,90(1):128-142
Nucleophilic ring‐opening reactions of 3‐aryl‐1‐benzylaziridine‐2‐carboxylates were examined by using O‐nucleophiles and aromatic C‐nucleophiles. The stereospecificity was found to depend on substrates and conditions used. Configuration inversion at C(3) was observed with O‐nucleophiles as a major reaction path in the ring‐opening reactions of aziridines carrying an electron‐poor aromatic moiety, whereas mixtures containing preferentially the syn‐diastereoisomer were generally obtained when electron‐rich aziridines were used (Tables 1–3). In the reactions of electron‐rich aziridines with C‐nucleophiles, SN2 reactions yielding anti‐type products were observed (Table 4). Reductive ring‐opening reaction by catalytic hydrogenation of (+)‐trans‐(2S,3R)‐3‐(1,3‐benzodioxol‐5‐yl)aziridine‐2‐carboxylate (+)‐trans‐ 3c afforded the corresponding α‐amino acid derivative, which was smoothly transformed into (+)‐tert‐butyl [(1R)‐2‐(1,3‐benzodioxol‐5‐yl)‐1‐methylethyl]carbamate((+)‐ 14 ) with high retention of optical purity (Scheme 6). 相似文献
23.
Yoshida T Sakakibara K Asami M Chen KH Lii JH Allinger NL 《Journal of computational chemistry》2003,24(3):319-327
The MM3 force field has been extended to deal with the lithium amide molecules that are widely used as efficient catalysts for stereoselective asymmetric synthesis. The MM3 force field parameters have been determined on the basis of the ab initio MP2/6-31G* and/or DFT (B3LYP/6-31G*, B3-PW91/6-31G*) geometry optimization calculations. To evaluate the electronic interactions specific to the lithium amides derived from the diamine molecules properly, the Lewis bonding potential term for the interaction between the lithium atom and the nonbonded adjacent electronegative atom such as nitrogen was introduced into the MM3 force field. The bond dipoles were evaluated correctly from the electronic charges on the atoms calculated by fitting to the electrostatic potential at points selected. The MM3 results on the molecular structures, conformational energies, and vibrational spectra show good agreement with those from the quantum mechanical calculations. 相似文献
24.
Houjou H Kanesato M Hiratani K Mandon D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(18):4576-4583
Novel diiron complexes with an Fe2(mu-OMe)2 core were studied as models of the active site of nonheme iron-containing enzymes. X-ray crystal structures of the complexes showed the existence of two types of ligand folding-parallel and twisted-both of which have four virtually equivalent phenolato groups sticking out from the Fe2O2 rhombic plane. Cyclic voltammetry measurements revealed two or more distinct redox waves in a region of relatively high potential, in addition to known Fe(II)/Fe(III) redox waves in a region of lower potential. These new peaks were assigned to the high-valence state of iron atoms, that is, Fe(III)Fe(IV) and Fe(IV)Fe(IV), resonating with the phenoxyl radical(s). The split width of the redox waves ranged from 0.14 to 0.20 eV, which may be a measure of the electronic interaction of the phenolate groups through the Fe2(mu-OMe)2 core. 相似文献
25.
Todoroki K Hayama T Ijiri S Kazuta A Yoshida H Nohta H Yamaguchi M 《Journal of chromatography. A》2004,1038(1-2):113-120
6-Rhodamine B amine functions as a highly sensitive fluorescence derivatization reagent for mono- and oligosaccharides; it reacts with the reducing end of saccharides under acidic conditions. The fluorescent derivatives of five monosaccharides can be separated within 25 min by reversed-phase liquid chromatography with isocratic elution. The detection limits (S/N = 3) for mono-, di-, and oligosaccharides are 7-51, 13, and 9-35 fmol/20 microl injection, which correspond to analyte concentrations of 35-255, 65, 45-175 nM, respectively. We have applied this derivatization method successfully to the analysis of the components of oligosaccharides in glycoproteins (ribonuclease B and fetuin) following their acidic or enzymatic hydrolysis. The results from these analyses are in good agreements with the reported values established previously. 相似文献
26.
Hideyuki Yoshida Junichiro Sonoda Junichi Ishida Masatoshi Yamaguchi 《Analytica chimica acta》2005,534(2):177-183
A simple screening method of organic aciduria by spectrofluorometric measurement of total dicarboxylic acids in human urine is described. This method is based on an intramolecular excimer-forming fluorescence derivatization with a pyrene reagent, 4-(1-pyrene)butanoic acid hydrazide (PBH). Dicarboxylic acids in urine were converted to the corresponding dipyrene-labeled derivatives by reaction with PBH in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and pyridine, and the derivatives afforded intramolecular excimer fluorescence (420-540 nm) which can clearly be discriminated from the normal fluorescence (360-420 nm) emitted from reagent blanks. The technique is so selective that it permits spectrofluorometric measurement of total amount of dicarboxylic acids by the direct derivatization of diluted urine samples. The same reaction mixture has also served as a liquid chromatographic (LC) sample for the separative determination of individual dicarboxylic acids. The spectrofluorometric data did not contradict with the LC data. These methods were usefully applied to preliminary screening test of glutaric aciduria. In conclusion, the present derivatization method allows rapid and direct determination of total amount of dicarboxylic acids in human urine samples. 相似文献
27.
3,4-Dhydro-6,7-dimethoxy-4-methyl-3-oxo-quinoxaline-2-carbonyl azide is a highly senstive fluorescence derivatization reagent for primary, secondary and tertiary alcohols for high-performance liquid chromatography. Reaction conditions are optimized with benzyl alcohol, n-hexanol, cyclohexanol and 2-methyl-2-butanol. The reagent reacts with the alcohols in benzene to produce the corresponding fluorescent carbamic acid esters, which can be separated on a reversed-phase column YMC Pack C8 with aqueous methanol as eluent. the detection limits for the alchols are 2–5 fmol per 10-μl njection. The reagent also reacts with hydroxysteroids with primary, secondary and/or tertiary alcoholic group(s) to form fluorescent derivatives. Hydroxycarboxylic acids and phenols do not give any chromatographic peaks. 相似文献
28.
Masatoshi Taniguchi Ken-ichi SuzumuraKoji Nagai Tomihisa KawasakiTetsu Saito Jun TakasakiKen-ichi Suzuki Shigeo FujitaShin-ichi Tsukamoto 《Tetrahedron》2003,59(25):4533-4538
The isolation and structure elucidation of YM-254890, a novel Gq/11 inhibitor from Chromobacterium sp. QS3666, is described. The gross structure was determined by one- and two-dimensional NMR studies and mass spectrometry. YM-254890 is a cyclic depsipeptide containing uncommon amino acids; β-hydroxyleucine (two residues), N,O-dimethylthreonine and N-methyldehydroalanine. YM-254890 exists as a mixture of two conformers in a variety of NMR solvents, and the distinction between major and minor conformers appears to lie in the geometry of the amide bond between 3-phenyllactic acid and N-methyldehydroalanine. The absolute stereochemistery was elucidated by Marfey's analysis and chiral HPLC analysis of the acid hydrolysate of YM-254890. 相似文献
29.
Murahashi S Imada Y Kawakami T Harada K Yonemushi Y Tomita N 《Journal of the American Chemical Society》2002,124(12):2888-2889
A chiral titanium complex, Ti(O-i-Pr)(4)/BINOL/tert-butylcatechol, catalyzes enantioselective addition reaction of ketene silyl acetals to nitrones to give optically active beta-amino acid derivatives which are biologically active compounds and useful synthetic intermediates of natural products and pharmaceuticals such as beta-lactam antibiotics. The combined process of catalytic oxidation of secondary amines and enantioselective carbon-carbon bond formation of nitrones thus obtained with ketene silyl acetals provides a useful two-step method for the synthesis of optically active beta-amino acid derivatives and related nitrogen compounds. 相似文献
30.
We show that the mono-N-methylated and -ethylated derivatives of the achiral compound bisguanidinobenzene undergo spontaneous asymmetric crystallization into a chiral form with chiral space group P212121. The absolute configurations of the chiral crystals were determined by X-ray crystallography and correlated with circular dichroism (CD) spectra recorded in the solid state. The corresponding protonated and isopropylated derivatives, by contrast, afforded achiral crystals. 相似文献