全文获取类型
收费全文 | 27714篇 |
免费 | 1942篇 |
国内免费 | 1213篇 |
专业分类
化学 | 16177篇 |
晶体学 | 222篇 |
力学 | 2158篇 |
综合类 | 82篇 |
数学 | 3824篇 |
物理学 | 8406篇 |
出版年
2022年 | 426篇 |
2021年 | 494篇 |
2020年 | 588篇 |
2019年 | 625篇 |
2018年 | 657篇 |
2017年 | 636篇 |
2016年 | 906篇 |
2015年 | 650篇 |
2014年 | 858篇 |
2013年 | 1210篇 |
2012年 | 1296篇 |
2011年 | 1401篇 |
2010年 | 1126篇 |
2009年 | 1092篇 |
2008年 | 1172篇 |
2007年 | 1059篇 |
2006年 | 978篇 |
2005年 | 776篇 |
2004年 | 705篇 |
2003年 | 683篇 |
2002年 | 726篇 |
2001年 | 651篇 |
2000年 | 521篇 |
1999年 | 451篇 |
1998年 | 418篇 |
1997年 | 403篇 |
1996年 | 390篇 |
1995年 | 347篇 |
1994年 | 312篇 |
1993年 | 348篇 |
1992年 | 330篇 |
1991年 | 314篇 |
1990年 | 340篇 |
1989年 | 320篇 |
1987年 | 269篇 |
1985年 | 294篇 |
1984年 | 301篇 |
1983年 | 272篇 |
1982年 | 288篇 |
1979年 | 302篇 |
1978年 | 329篇 |
1977年 | 320篇 |
1976年 | 404篇 |
1975年 | 360篇 |
1974年 | 388篇 |
1973年 | 396篇 |
1972年 | 369篇 |
1971年 | 331篇 |
1970年 | 314篇 |
1969年 | 298篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
V. A. Mamedov N. A. Zhukova T. N. Beschastnova Ya. A. Levin A. T. Gubaidullin I. A. Litvinov 《Russian Chemical Bulletin》2007,56(11):2308-2314
The condensation of methyl phenylchloropyruvate with 1-phenyl-3-(2-pyridyl)thiourea and its 3-and 4-picolyl homologs affords
the corresponding 4-hydroxythiazolidines, which react with o-phenylenediamine to give one of two possible thiazolo[3,4-a]quinoxalines containing the pyridyl-or picolylimine substituents at position 1. 3a-Hydroxy-3-phenylimino-1-(2-pyridyl)thiazolo[3,4-a]quinoxalin-4-(3H,5H)-one, which is a covalent hydrate of the final product, was isolated as an intermediate in this reaction. 相似文献
992.
The Gemini surfactant 9B-4-9B containing sodium sulfonate as hydrophilic head group was synthesized based on nonylphenol and characterized by FTIR, 1H NMR spectroscopy and the surface tension measurement. The CMC and C20 of the 9B-4-9B were smaller than that of sodium dodecylbenzene sulfonate and sodium dodecylsulfate, respectively, indicating excellent efficiency of micelle formation and reduced surface tension. Conducting polyaniline salts were synthesized by chemical oxidative micellar polymerization of aniline in water firstly using Gemini surfactant 9B-4-9B as the micelle stabilizer and ammonium peroxydisulfate as the oxidant at 0 °C. The stable polyaniline dispersions have been obtained when the molar ratio of the 9B-4-9B to aniline was equal to or above 0.5 used in the polymerization system. The obtained granular polyaniline particles with the size of 1-2 μm were characterized by FTIR, UV-Vis, SEM, WAXD and conductivity measurement. 相似文献
993.
994.
Kuepper K Falub MC Prince KC Galakhov VR Troyanchuk IO Chiuzbaian SG Matteucci M Wett D Szargan R Ovechkina NA Mukovskii YM Neumann M 《The journal of physical chemistry. B》2005,109(19):9354-9361
The electronic properties of a series of colossal magnetoresistance (CMR) compounds, namely LaMnO3, La(1-x)Ba(x)(MnO3 (0.2 < or = x < or = 0.55), La(0.76)Ba(0.24)Mn(0.84)Co(0.16)O3, and La(0.76)Ba(0.24)Mn(0.78)Ni(0.22)O3, have been investigated in a detailed spectroscopic study. A combination of X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), X-ray absorption spectroscopy (XAS), and resonant inelastic X-ray scattering (RIXS) was used to reveal a detailed picture of the electronic structure in the presence of Ba, Co, and Ni doping in different concentrations. The results are compared with available theory. The valence band of La(1-x)()Ba(x)MnO3 (0 < or = x < or = 0.55) is dominated by La 5p, Mn 3d, and O 2p states, and strong hybridization between Mn 3d and O 2p states is present over the whole range of Ba concentrations. Co-doping at the Mn site leads to an increased occupancy of the e(g) states near the Fermi energy and an increase in the XPS valence band intensity between 0.5 and 5 eV, whereas the Ni-doped sample shows a lower density of occupied states near the Fermi energy. The Ni d states are located in a band spanning the energy range of 1.5-5 eV. XAS spectra indicate that the hole doping leads to mixed Mn 3d-O 2p states. Furthermore, RIXS at the Mn L edge has been used to probe d-d transitions and charge-transfer excitations in La(1-x)Ba(x)MnO3. 相似文献
995.
A. I. Yanovsky N. Ya. Turova A. V. Korolev D. E. Chebukov A. P. Pisarevsky Yu. T. Struchkova 《Russian Chemical Bulletin》1996,45(1):115-121
Anodic oxidation of tantalum in isopropyl alcohol or prolonged reflux of an alcohol solution of Ta(OPri)5 afford crystalline oxoisopropoxide Ta2O(OPri)8 · PriOH (1). In its molecule, two octahedra about Ta atoms are linkedvia the shared edge [(OPri)O]. Compound1 is the first example of oxoalkoxide containing such a small number of metal atoms. Unlike the known polynuclear molecules M
n
O
m
(OR)
p
, oxoalkoxide1 is stable in solutions; on transition to the gas phase, this compound is desolvated to form a very stable molecule Ta2O(OPri)8 (apparently, consisting of two octahedra with a shared edge). According to the data of mass spectrometry, analogous molecules exist in the gas phase over Ta(OAlk)5 (Alk = Me, Et, Pri, or Bu11). When compound1 is heated invacuo (10–2–10–3 Torr), Ta(OPri)5 is sublimated. Crystals of Ta7O9(OPri)17 (2) were formed upon prolonged storage of solutions of1 in PriOH. Heptanuclear molecule2 consists of two [Ta4] tetrahedra with a shared vertex. These tetrahedra are additionally linked togethervia one 3-oxo and two 2-OPri groups. Complex2 is a representative of heptameric oxoalkoxides of a new structural type.Deceased in I995.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 125–131, January, 1996. 相似文献
996.
Wenjie Zhang Xiling Ding Zijie Li Xiaolan Chen Yufen Zhao 《Phosphorus, sulfur, and silicon and the related elements》2020,195(5):359-366
AbstractA one-pot synthetic strategy was developed for the synthesis of heterocyclic 1,4,2-oxazaphosphinanes via a three component Kabachnik-Fields reaction of 2-aminophenol, diphenyl H-phosphonate and carbonyl compounds. Through this newly developed method, 12 organophosphorus heterocycles and 2 related chrysin derivatives were synthesized with high yields. The target compounds were characterized by 1H, 31P and 13C NMR and MS. 相似文献
997.
V. M. Vlasenko V. Ya. Volfson S. A. Soloviev G. F. Kalapusha 《Reaction Kinetics and Catalysis Letters》1979,11(2):179-182
1,1- (AH) ([AH]=6,9 /, 50°C). AH Wi/WO
3=0,40±0,16.
The kinetics and oxidation products of 1,1-diethoxyethane (AH) ozonolysis have been investigated at [AH]=6.9 mol/l and 50 °C. The initiation efficiency of radical oxidation by ozone is Wi/WO 3=0.40±0.16.相似文献
998.
Zhanguang Chen Weifeng Ding Fenglian Ren Jinbin Liu Yizeng Liang 《Analytica chimica acta》2005,550(1-2):204-209
A new assay of nucleic acids at nanogram level was established based on the enhanced resonance light scattering (RLS) signals of two zwitterionics cocamidopropyl hydroxysultaine (HSB) and lauryl betaine (BS-12). Under optimum conditions, the weak RLS signal of HSB is enhanced by nucleic acids, and the enhanced RLS intensity is proportional to the concentration of nucleic acids in the range of 0.02–7.3 mg l−1 for calf thymus DNA and 0.01–8.6 mg l−1 for fish sperm DNA. The detection limits were 1.5 ng ml−1 for calf thymus DNA and 1.9 ng ml−1 for fish sperm DNA. Plasmid DNA extracted from K-12-HB101 colt was determined with satisfactory results. 相似文献
999.
The complex stability constants (K(S)), standard molar enthalpy (DeltaH degrees), and entropy changes (DeltaS degrees) for the inclusion complexation of two families of beta-cyclodextrin (beta-CD) dimers, i.e. beta-CD dimers Se1-Se4 bearing 2,2'-diselenobis(benzoyl) tether (Se-dimers) and beta-CD dimers Py1-Py4 bearing 2,2'-bipyridine-4,4'-dicarboxy tether (Py-dimers), with four bile salt guests, i.e. sodium cholate (CA), sodium deoxycholate (DCA), sodium glycocholate (GCA), and sodium taurocholate (TCA), were determined at 25 degrees C in Tris buffer solution (pH 7.4) at 298.15 K by means of isothermal titration microcalorimetry. The thermodynamic parameters obtained, together with the ROESY spectra of interactions between beta-CD dimers and bile salts, consistently suggest that the length, flexibility, and structure of spacers linking the two beta-CD cavities not only determine the binding modes but also significantly alter the molecular selectivity of beta-CD dimers. 相似文献
1000.
O. Ya. Neiland V. Zh. Tilika A. A. Supe A. S. Édzhinya 《Chemistry of Heterocyclic Compounds》1996,32(1):112-118
The reaction of dimethyl[2,4-dioxo(1H,3H) pynmido]tetrathiafulvalene and its N-alkyl derivatives with iodine leads to the formation of complexes with various numbers of iodine atoms. Depending on the conditions, the betaine of the cation-radical of dimethyl[2, 4-dioxo(1 H, 3H)pyrimidojtetrathiafulvalene or a complex of the latter with dimethy1[2,4-dioxo(1H,3H)pyrimidoltetrathiafulvalene is formed by the oxidation of the pyrimidotetrathiafulvalene. The cation-radical perchlorates are formed on carrying out the oxidation of dimethyl[2,4-dioxo(1H,3H)pyrimidojtetrathiafulvalene and its N-methyl derivatives in the presence of perchloric acid. The preparation of the cation-radical salts is usually linked with the reaction of the cation-radical betaine with acids.For part 2 see [1]. 相似文献