全文获取类型
收费全文 | 36490篇 |
免费 | 352篇 |
国内免费 | 141篇 |
专业分类
化学 | 17987篇 |
晶体学 | 679篇 |
力学 | 1614篇 |
综合类 | 2篇 |
数学 | 3571篇 |
物理学 | 13130篇 |
出版年
2022年 | 291篇 |
2021年 | 339篇 |
2020年 | 310篇 |
2019年 | 312篇 |
2018年 | 512篇 |
2017年 | 444篇 |
2016年 | 700篇 |
2015年 | 400篇 |
2014年 | 705篇 |
2013年 | 1570篇 |
2012年 | 1485篇 |
2011年 | 1837篇 |
2010年 | 1332篇 |
2009年 | 1331篇 |
2008年 | 1524篇 |
2007年 | 1506篇 |
2006年 | 1386篇 |
2005年 | 1197篇 |
2004年 | 1132篇 |
2003年 | 985篇 |
2002年 | 934篇 |
2001年 | 1346篇 |
2000年 | 966篇 |
1999年 | 801篇 |
1998年 | 607篇 |
1997年 | 581篇 |
1996年 | 508篇 |
1995年 | 470篇 |
1994年 | 441篇 |
1993年 | 389篇 |
1992年 | 463篇 |
1991年 | 468篇 |
1990年 | 458篇 |
1989年 | 421篇 |
1988年 | 444篇 |
1987年 | 429篇 |
1986年 | 374篇 |
1985年 | 440篇 |
1984年 | 470篇 |
1983年 | 343篇 |
1982年 | 386篇 |
1981年 | 375篇 |
1980年 | 318篇 |
1979年 | 400篇 |
1978年 | 378篇 |
1977年 | 394篇 |
1976年 | 391篇 |
1975年 | 342篇 |
1974年 | 322篇 |
1973年 | 339篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Yu. B. Chudinov S. B. Gashev Yu. A. Strelenko Z. A. Starikova M. Yu. Antipin V. V. Semenov 《Russian Chemical Bulletin》2007,56(1):140-147
Model diastereomeric oxazolidinones containing various substituents at positions 3 and 5 were synthesized. Several individual
diastereomers bearing methyl groups at positions 4 and 5 in cis-and trans orientations were isolated. The TLC and 1H NMR spectroscopic data suggest that diastereomers, particularly those containing the aryl substituent at position 5, are
substantially different in the physical and spectral properties. The configurations of some diastereomers were established
by X-ray diffraction and NOESY spectroscopy. For these compounds, the reliable assignment of the characteristic 1H NMR signals of individual groups was made, which provided evidence for the cis or trans orientation of the methyl groups at positions 4 and 5. The scope of the method as applied to the determination of the cis and trans isomers from their 1H NMR spectra is discussed.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 133–139, January, 2007. 相似文献
982.
Laser emission at different wavelengths in the range of 903–914 nm and around 2.5 m has been observed upon excitation of Na2 by uv radiation from an excimer laser at 351 nm and an excimer pumped dye laser in this wavelength range. The emission is attributed to a cascade emission
followed by
. In addition, coupled with the laser emission around 910 nm, broad-band fluorescence peaking around 855.5 nm is observed which, eventually, may be the first observation of the
bound-free transition in Na2. 相似文献
983.
H. Abramowicz F. Dydak J. G. H. de Groot J. Knobloch J. May P. Palazzi F. Ranjard W. D. Schlatter J. Steinberger H. Taureg W. von Rüden H. Wahl J. Wotschack P. Buchholz F. Eisele H. P. Klasen K. Kleinknecht B. Pszola B. Renk H. J. Willutzki T. Flottmann C. Geweniger J. Krolikowski K. Tittel C. Guyot J. P. Merlo A. Para B. Peyaud J. Rander J. Rothberg J. P. Schuller R. Turlay J. T. He T. Z. Ruan W. M. Wu 《Zeitschrift fur Physik C Particles and Fields》1982,12(3):225-227
Right handed weak quark currents coupled to the usual left handed weak lepton current would be seen in inclusive antineutrino scattering on nuclei as a contribution at largey with the quark (not antiquark) structure function. We do not see such a term, and can therefore put an upper limit on the relative strengths of such right handed currents: \(\varrho ^2 = \frac{{\sigma _R }}{{\sigma _L }}< 0.009\) , 90% confidence. This measurement puts limits on the mixing angle of left-right symmetric models. In distinction to similar limits derived from muon decay or β decay, our limits are also valid if the right handed neutrino is heavy. 相似文献
984.
A. A. Bezrukova V. S. Khandkarova P. V. Petrovskii A. Z. Rubezhov Ya. S. Vygodskii K. P. Butin T. V. Magdesieva G. A. Pirogova 《Russian Chemical Bulletin》1995,44(5):941-945
Binuclear RhIII and RuII complexes of the [M1-CN-M2]+BF
4
–
(M1 and/or M2 are (5-Cp)(3-C3H5)Rh and (6-C6H6)(3-C3H5)Ru) type, heteronuclear organometallic compound (5-Cp)(3-C3H5)RhCNPd(3-C3H5)Cl, and mononuclear RhIII and RuII complexes [(3-C3H5)LM(MeCN)]+
BF4
–
(M = Rh, L = 5-Cp; M = Ru, L = 6-C6H6) were synthesized. An electrochemical study of these compounds in solutions demonstrates that the bond between the bridged CN ligand and the metal atoms is rather strong, and there is no dissociation into mononuclear fragments in solutions. The kinetics of the reaction of [(5-Cp)(3-C3H5)Rh(MeCN)]+
BF4
–
with halide ions was studied by electrochemical methods. The ligand exchange proceeds by a bimolecular dissociative-exchange mechanism.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 968–973, May, 1995. 相似文献
985.
986.
L. M. Khalilov O. V. Shitikova R. I. Khusnutdinov Z. S. Muslimov U. M. Dzhemilev A. A. Panasenko G. A. Tolstikov 《Russian Chemical Bulletin》1990,39(3):484-488
The structures of the dimerization products of spiro(bicyclo[2.2.1]hepta-2,5-diene-7,1-cyclopropane) have been solved using13C NMR spectroscopy and their stereochemical assignments made. The methylene carbon atom signals for the spirocyclopropane fragment can be used as diagnostic signals in making the stereochemical assignments.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 559–564, March, 1990. 相似文献
987.
The complexation reaction between a macrocyclic polyether, 18-crown-6 (18C6), and potassium ion was studied in methanol (MeOH)-acetonitrile (AN), dimethylformamide (DMF)-AN and propylecarbonate (PC)-DMF binary solvent systems at different temperatures using a conductometric method. It was found that the stability of the 1:1 complex formed between K(+) ion and this ligand increases with decreasing temperature. Standard enthalpies and standard entropies of the complex formation were obtained from the temperature dependence of the stability constant. In all cases negative DeltaH(o)(c) and DeltaS(o)(c) values characterize the formation of 18C6-K(+) complex. The results obtained show that the stability of the complex is governed by the solvent medium and the thermodynamic parameters DeltaH(o)(c), DeltaS(o)(c) and DeltaG(o)(c) are sensitive to the composition of the mixed solvents. In addition, it was found that the stability constant of the resulting 1:1 complex among various neat solvents used varies in the order PC > MeOH > AN > DMF. 相似文献
988.
Effect of epitaxial growth on the formation of the cobalt catalysts of the Fischer-Tropsch synthesis
Ya. V. Mikhailova S. A. Sviderskii M. N. Mikhailov I. V. Mishin V. Z. Mordkovich 《Russian Chemical Bulletin》2007,56(9):1922-1926
Mixed oxides CoxAlyO4 with different Al/Co ratios applied as supports for the catalysts of the Fischer-Tropsch synthesis were prepared using the
solid-state chemical reaction. The CoxAlyO4 supports were prepared by modifying gibbsite with various cobalt salts (acetate, nitrate, and basic carbonate). The use of
basic cobalt carbonate gives the Co(20%)/CoxAlyO4 catalyst, which provides an increased yield of hydrocarbons C5+ and a decreased methane content compared to the impregnation catalyst Co(30%)/Al2O3. The introduction of small amounts of rhenium additives makes it possible to enhance the yield of hydrocarbons C5+ (179 g m−3) and also to increase the selectivity with respect to the C5–C18 fraction. The introduction of basic cobalt carbonate into the support, most likely, creates favorable conditions for the
epitaxial growth of the precursor of the active phase.
Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1856–1860, September, 2007. 相似文献
989.
N. S. Vul'fson V. N. Bochkarev G. M. Zolotareva B. V. Unkovskii V. B. Mochalin Z. I. Smolina A. N. Vul'fson 《Russian Chemical Bulletin》1970,19(6):1368-1370
Conclusions The mass spectra ofthree 6-alkoxy-3-dihydropyranes and of three 6-alkoxy-2-dihydropyranes have been studied. As distinct from the previously studied 2-alkoxy-3-dihydropyranes, the dominant fragmentation pattern for the compounds under investigation is by retrodiene degradation. Furthermore, in the case of the 2-isomers the charge is preferentially localized on the olefin fragment while for the 3-isomers, it is located on the diene fragment.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1442–1444, June, 1970. 相似文献
990.
A simple method for the synthesis of N-substituted 5-aminofurfurals based on the reaction of 5-halogenofurfurals with secondary amines has been developed. The reaction takes place through the formation of quaternary salts of N-substituted 5-aminofurfurals. 5-(Diethylamino)-, 5-(N-methyl-N-phenylamino)-, and 5-piperidinofurfurals have been obtained for the first time. 相似文献