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991.
In this work, we have calculated boron-, aluminum-, titanium-, and nickel-doped La13 clusters by DMOL method based on the density-functional theory. Two doping modes are employed: surface and center doping. The boron, aluminum, and nickel atoms prefer to occupy the surface sites while the titanium atom prefers to occupy the center site. The doped La13 clusters with these four kinds of atoms have lower binding energy than pure La13 clusters. The icosahedral isomers are of lower binding energy than cubotahedral and decahedral isomers for La12B(-1), La12Al(-1), and La12Ni, while doping makes the cubotahedral La12Ti stable with a binding energy a little lower than icosahedral La12Ti. There are electronic shell effects in icosahedral La12B(-1) and La12Al(-1). The icosahedral La12B(-1) is promising to be formed during the doped process experimentally. Furthermore, we have also discussed the distorted structures of center doping by bond lengths, density of states, and charge transfers. 相似文献
992.
Pattarawarapan M Chen J Steffensen M Burgess K 《Journal of combinatorial chemistry》2001,3(1):102-116
Bifunctional linker-scaffolds (compounds 1-3) were designed to meet several criteria for solid-phase syntheses of bivalent ligands. They have two amine-functionalized arms that can be differentially protected. Elaboration of these arms could give ligand-pharmacophore dimers wherein the two active components are held reasonably rigidly at around 10 A separation. Their bifunctional design also enables reactions of libraries with libraries to amplify diversity in a truly combinatorial fashion. Molecules 1-3 are also designed so that cleavage of the linker liberates the scaffold entity into solution under conditions that create only byproducts that should not interfere with biological assays. Thus they contain 2-nitrobenzene sulfonamide components that cleave in the presence of good nucleophiles. In the event, the linker-scaffolds 1-3 were prepared (Schemes 1 and 2). The N-benzyl system 2 was shown to have good stability to the types of conditions that might be used to functionalize the scaffold arms and to be sufficiently labile to the cleavage nucleophile (vide infra). The nucleophiles generally used to cleave nitrobenzene sulfonamides either generate undesirable byproducts (thiophenol or alkane thiols) or proved to be insufficiently reactive for the required solid-phase transformations (n-propylamine). However, sodium sulfide was investigated as a new alternative and shown to be a highly reactive cleavage agent that gives only volatile byproducts and sodium hydroxide. It is suggested that sodium sulfide is a highly desirable nucleophile for cleavage of 2-nitrobenzene sulfonamides, in general. The linker-scaffolds 1-3 were used to prepare a small library of bivalent ligands targeted to a protein receptor having charged cavities separated by approximately 10 A. These systems were made from guanidine, pyridinium, carboxylic acid, and sulfonic acid constituents (Tables 1 and 2). 相似文献
993.
V. N. Panov V. A. Igonin A. V. Goncharov Yu. T. Struchkov A. V. Martinov A. N. Mirskova 《Journal of Structural Chemistry》1993,33(4):615-617
Vladimir State Pedagogical Institute. Institute for Elementorganic Compounds, Russian Academy of Sciences. Irkutsk Institute for Organic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 4, pp. 153–154, July–August, 1992. 相似文献
994.
The phytosteroids 3ß-hydroxy-(24S)-stigmast-5, 22E-dien-7-one and (24S)-stigmasta-5, 22E-diene-3\, 7ß-diol have been synthesized from stigmasterol. 相似文献
995.
T. V. Troepol'skaya G. A. Vagina V. I. Morozov Yu. P. Kitaev 《Russian Chemical Bulletin》1988,37(6):1115-1120
1. | The degree of oxidation of the metal ion in the chelates of Co, Pd, and Cu with -hydroxylamine oximes is 2+ according to electrochemial and EPR data. |
2. | In the first stage of the electroreduction of the investigated chelates of Co with nioxime and of Cu with -hydroxylamine oxime the degree of oxidation of the metal ion in the complex changes, while in the case of the other compounds the first electrons are probably accepted by mixed molecular orbitals, to which the ligand fragment makes the largest contribution. |
3. | The electrode reactions of the Co(II) and Pd(II) chelates with -hydroxylamine oximes are complicated by the catalytic evolution of hydrogen from solutions containing proton donors. |
996.
S. A. Osadochnyi Yu. V. Gatilov I. Yu. Bagryanskaya T. V. Rybalova V. G. Shubin 《Russian Chemical Bulletin》1991,40(6):1279-1281
1,2,3,4,5,6,8,9-Octamethyl-C2V-bishomocubane was prepared by the photochemical cyclization of 1R,3S,4,5,6R,8S,9,10-octamethyltricyclo[6.2.0.03,6]deca-4,9-di-ene in benzene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1440–1442, June, 1991.The authors express their gratitude to V. I. Eroshkin for a number of valuable suggestions for carrying out the photochemical experiments. 相似文献
997.
Z. V. Todres G. Ts. Ovsepyan E. A. Ionina A. Yu. Kosnikov S. V. Lindeman Yu. T. Struchkov 《Russian Chemical Bulletin》1988,37(8):1651-1656
1. | o-Dinitrobenzene dianion reacts with p-dimethylaminobenzenediazonium cation to give 2-nitro-4-dimethylaminoazobenzene. |
2. | o-Dinitrobenzene anion-radical reacts with benzenediazonium cations bearing a dimethylamino-or nitro-group in the para-position, to give 3-nitro-4-hydroxy-4-dimethylamino-azobenzene and 3,4-dinitro-4-hydroxyazobenzene respectively. |
3. | In the case of the 4-methoxybenzenediazonium cation, reaction with the o-dinitrobenzene anion-radical affords 4-methoxy-3-(2-nitrophenyl--azoxy)-4-hydroxyazobenzene, the structure of which has been established by x-ray diffraction analysis. |
4. | These azo-compounds are formed in solvents which favor the stability of ion pairs of the dianion or anion-radical of o-dinitrobenzene with potassium cations. Dissociation of the ion pairs results in the occurrence of electron transfer only. |
998.
Yu. B. Vysotsky V. S. Bryantsev O. A. Gorban 《Chemistry of Heterocyclic Compounds》2002,38(12):1451-1468
The effects of benzannellation, phenyl substitution at the nitrogen atom, protonation at the carbene carbon, ionization, and the state of the carbene center (2 or 2) on the electronic structure, diamagnetic susceptibility, induced -electron ring currents, the 1H, 13C, and 14N chemical shifts, and the energies of the lowest electronic transitions of imidazol-2-ylidenes and their oxo and thio analogs were examined in the bound version of -electron perturbation theory. The calculated and experimental data are compared. 相似文献
999.
Akulin Yu. I. Strelets B. Kh. Éfros L. S. 《Chemistry of Heterocyclic Compounds》1977,13(11):1198-1201
The corresponding 6-arylamino derivatives were obtained by reaction of 6-chloro, 6-bromo, and 6-methoxy derivatives of benzo-1,2,3-dithiazolium and their selenium analogs — benzo-1,2,3-thiaselenazolium, benzo-2,1,3-thiaselenazolium, and benzo-1,2,3-diselenazolium salts — with aromatic amines. The 6-methoxy derivatives also react with acetates of secondary aliphatic amines, whereas in the case of the chloro derivatives attack is directed to the heteroring. 6-Aryl(dialkyl)amino derivatives of dithiazolium and 1,2,3-thiaselenazolium salts are protonated in concentrated sulfuric acid at the exocyclic nitrogen atom. The analogous derivatives of 2,1,3-thiaselenazolium and diselenazolium salts under the same conditions form a tautomeric mixture of dications, the position of the equilibrium between which depends on the substituent. The electronic and PMR spectra of the amination products are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1499–1502, November, 1977. 相似文献
1000.
Summary It has been shown by low-temperature photolysis and ESR that mixtures of o-naphthoquinone diazides with phenol-formaldehyde oligomers in solutions and dry films form weak donor-acceptor complexes in which the intramolecular photoreduction of the o-naphthoquinone diazide can take place.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1255–1259, June, 1981. 相似文献