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41.
Manuel Tzouros Laurent Bigler Stefan Bienz Manfred Hesse Akira Inada Hiroko Murata Yuka Inatomi Tsutomu Nakanishi Dedy Darnaedi 《Helvetica chimica acta》2004,87(6):1411-1425
The investigation of the MeOH extract of the leaves of Chisocheton weinlandii Harms (Meliaceae) revealed two new open‐chain spermidine alkaloids, chisitine 1 ( 1 ) and chisitine 2 ( 2 ). Their structures were elucidated by NMR spectroscopy, tandem‐mass spectrometry, and independant syntheses (Scheme 3). Detailed MS/MS fragmentation pathways are discussed for both compounds based on H/D exchange and 18O‐labeling experiments (Schemes 1 and 2). 相似文献
42.
Heterocyclic orifices in cage-opened fullerene derivatives are regarded as potential ligands toward metals or ions, being reminiscent of truncated fullerenes as a hypothetical class of macrocycles with spherical π-conjugation. Among a number of cage-opened examples reported thus far, the coordination ability and dynamic behavior in solution still remained unclear due to difficulties in structural determination with multiple coordination sites on the macrocycles. Herein, we present the detailed solution dynamics of a cage-opened C60 derivative bearing a diketo bis(hemiketal) moiety in the presence of alkali metal ions. The NMR spectroscopy disclosed the coordination behavior which is identified as a two-step process with a 1 : 2 stoichiometry. Upon coordination to the Li+ ion, the macrocycle largely varies its properties, i.e., increased absorption coefficients in the visible region due to weakly-allowed charge transfer transitions as well as the inner potential field from neutral to positive by the charge delocalization along with the spherical π-surface. The Li+-complexes formed in situ underwent unprecedented selective dehydroxyhydrogenation under high-pressure conditions. These findings would facilitate further studies on fullerene-based macrocycles as metal sensors, bulky ligands in organic reactions, and ion carriers in batteries and biosystems.A fullerene-based Lewis-basic macrocyclic ligand underwent complexation with alkali-metal ions in 1 : 1 and 1 : 2 fashions, resulting in considerable perturbation to absorption properties as well as the potential surface inside the cage. 相似文献
43.
Yamada K Tanaka M Nakagawa F Yoshida N 《Rapid communications in mass spectrometry : RCM》2002,16(11):1059-1064
Molecular and intramolecular carbon isotope measurements of acetic acid present in natural environments have been performed by off-line procedures. The off-line method is complicated and time-consuming and requires micromolar to millimolar amounts of sample. This limits geochemical isotopic studies, especially at the intramolecular level, on acetic acid present in natural samples. Here, we examine an on-line measurement of intramolecular carbon isotope distribution of acetic acid using continuous-flow isotope ratio mass spectrometry (CF-IRMS) coupled with an on-line pyrolysis system. This is achieved by measurement of the respective carbon isotope ratios of CH4 and CO2 produced by on-line pyrolysis of acetic acid. Results for authentic standards of pure acetic acid demonstrated the practicality of this on-line method, although the carbon isotope ratio of the methyl group could not be determined directly. The precision of the carbon isotope measurements was 0.4 per thousand (1sigma). The carbon isotope distribution determined by the on-line method was identical to that determined by the conventional off-line method within analytical error. The advantages of the on-line method compared with the conventional off-line method are that it is less laborious, requires less analytical time (less than one hour per sample) and, most importantly, uses smaller sample sizes (ca. 10 nanomole). An application of this on-line method to natural geochemical samples will provide an insight into the geochemical cycle of acetic acid. 相似文献
44.
7-Hydroxy-4-methylcoumarin(4-methylumbelliferone, HMC) and Rhodamine 6G(R6G) were encapsulated into silicate polymeric glass prepared by the sol-gel method under acidic, basic, and neutral conditions from tetraethyl orthosilicate. The fluorescence spectra of these molecules encapsulated into the xerogel state depend on the used catalysts. Three types of fluorescence emissions having peak wavelengths of ca. 390 nm, 470 nm, and 550 run, respectively, were observed simultaneously in the xerogel state composed of HMC and R6G which were prepared by acid catalysts. The encapsulated HMC remains stable for more than one year in the prepared xerogel. The results open the way to the development of simultaneous three-band laser emissions. The observation of the fluorescence spectrum of HMC is useful for a molecular level photophysical probe elucidating the structural changes oftetraethyl orthosilicate during sol to gel to xerogel transitions. 相似文献
45.
Specific heparan sulphate-lyases, heparitinases I and II, were used to identify unsaturated disaccharide constituents generated from heterogeneous heparan sulphate isomers. All determinations were made using high-performance liquid chromatography with a column containing a sulphonized styrene-divinylbenzene copolymer. Unsaturated disaccharides generated from variously sulphated heparan sulphate isomers after simultaneous digestion with heparitinases I and II facilitated separation of the individual disaccharides, based on sulphate groups at the specific position of the uronic acid and glucosamine residues. The simultaneous digestion with heparitinases I and II produces unsaturated disaccharides from heparan sulphate isomers with the structure of 4-deoxy-2-O-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-amino-deoxy-D-glucose, 4-deoxy-2-O-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-deoxy-2-sulphamido-D-glucose, 4-deoxy-2-O-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-aminodeoxy-6-O-sulpho-D-glucose, 4-deoxy-2-O-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-deoxy-2-sulphamido-6-O-sulpho-D-glucose, 4-deoxy-2-O-sulpho-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-amino-2-deoxy-6-O-sulpho-D-glucose and 4-deoxy-2-O-sulpho-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-deoxy-2-sulphamido-6-O-sulpho-D-glucose. 相似文献
46.
Taisei Ueda Tsuneyasu Adachi Shin-Ichi Nagai Jinsaku Sakakibara Mitsuo Murata 《Journal of heterocyclic chemistry》1988,25(3):791-794
[1,2,4]Triazino[3,2-f]purines 3a-e and [1,2,4]triazepino[3,2-f]purine 5 were synthesized by the reaction of 7,8-diamino-1,3-dimethylxanthine 1 with diketones such as glyoxal, diacetyl, dibenzoyl, pyruvic aldehyde dimethyl acetal, phenylglyoxal or acetylacetone in acetic acid in the presence of boric acid or polyphosphoric acid. 相似文献
47.
Fumiko Ohtsuka 《Geometriae Dedicata》1991,38(2):151-157
The theory of the ideal boundary has arisen as a method of a study of noncompact manifolds. In this paper we shall investigate properties of manifolds whose ideal boundaries satisfy some conditions related to the Tits metric. In Section 2 we shall consider in what conditions the Tits topology is equivalent to the sphere topology and in Section 3 the property of points at infinity which characterize the R-factor. Furthermore, in Section 4 we shall give a sufficient condition for a projective map to be isometríc.Partially supported by Grant-in-Aid for Encouragement of Young Scientists (No. 01740011), The Ministry of Education, Science and Culture, Japan. 相似文献
48.
The INDO calculations were performed on bicyclo[2.1.1]hex-5-yl radical. From these calculations, it was confirmed that the hyperfine coupling constants depend largely on the geometry of the α hydrogen. The localized MO's were obtained from the canonical MO's calculated by using the INDO method. With the use of the localized MO's thus obtained, the variation in the hyperfine coupling constants at the 6exo- and 6endo-protons in this radical was explained in terms of the through-bond and/or the through-space interactions according to the procedure which we proposed previously. That is by the procedure we can selectively pick up a particular interaction between the specified localized MO's. The hyperfine coupling constant in this radical can be expressed by the summation of several interaction terms. The difference in the hyperfine spin coupling constants of the H6exo and H6endo in the radical now concerned has been attempted to explain using MO coefficients of the occupied orbitals. 相似文献
49.
Michiya Itoh Kenji Murata Kunihiro Tokumura Koichi Shudo Naoki Miyata Toshihiko Okamoto 《Tetrahedron》1979,35(9):1059-1063
Photorearrangement reactions of K-region arene oxides, 9,10-epoxy-9,10-dihydrophenanthrene (1a), 3-acetyl-9,10-epoxy-9,10-dihydrophenanthrene (1b), and 3,4-epoxy-3,4-dihydropyrene (1c) in dichloroethane (DCE) solution were investigated by steady irradiation and nanosecond transient spectroscopy. Photorearrangements producing substituted oxepins, 2 occur via the singlet excited state of these compounds, while the phenolic products, 9-hydroxyphenanthrene (3a), 3-acetyl-9-hydroxyphenanthrene (3b), and 4-hydroxypyrene (3c) are formed via the triplet state. Phenol 3 formation from the triplet 1 sensitized by the triplet 3 (i.e. product sensitization) is proposed for the photorearrangement reactions of 1a and 1c, and this process is the only way phenol (3a) is formed because of the negligible intersystem crossing probability of 1a. No product sensitization occurs in the photorearrangement reaction of 1b. 相似文献
50.
Matsuo T Dejima H Hirota S Murata D Sato H Ikegami T Hori H Hisaeda Y Hayashi T 《Journal of the American Chemical Society》2004,126(49):16007-16017
Sperm whale myoglobin, an oxygen storage hemoprotein, was successfully reconstituted with the iron porphycene having two propionates, 2,7-diethyl-3,6,12,17-tetramethyl-13,16-bis(carboxyethyl)porphycenatoiron. The physicochemical properties and ligand bindings of the reconstituted myoglobin were investigated. The ferric reconstituted myoglobin shows the remarkable stability against acid denaturation and only a low-spin characteristic in its EPR spectrum. The Fe(III)/Fe(II) redox potential (-190 mV vs NHE) determined by the spectroelectrochemical measurements was much lower than that of the wild-type. These results can be attributed to the strong coordination of His93 to the porphycene iron, which is induced by the nature of the porphycene ring symmetry. The O2 affinity of the ferrous reconstituted myoglobin is 2600-fold higher than that of the wild-type, mainly due to the decrease in the O2 dissociation rate, whereas the CO affinity is not so significantly enhanced. As a result, the O2 affinity of the reconstituted myoglobin exceeds its CO affinity (M' = K(CO)/K(O2) < 1). The ligand binding studies on H64A mutants support the fact that the slow O2 dissociation of the reconstituted myoglobin is primarily caused by the stabilization of the Fe-O2 sigma-bonding. The IR spectra for the carbon monoxide (CO) complex of the reconstituted myoglobin suggest several structural and/or electrostatic conformations of the Fe-C-O bond, but this is not directly correlated with the CO dissociation rate. The high O2 affinity and the unique characteristics of the myoglobin with the iron porphycene indicate that reconstitution with a synthesized heme is a useful method not only to understand the physiological function of myoglobin but also to create a tailor-made function on the protein. 相似文献