全文获取类型
收费全文 | 19753篇 |
免费 | 539篇 |
国内免费 | 113篇 |
专业分类
化学 | 14107篇 |
晶体学 | 189篇 |
力学 | 378篇 |
综合类 | 1篇 |
数学 | 2957篇 |
物理学 | 2773篇 |
出版年
2022年 | 164篇 |
2021年 | 200篇 |
2020年 | 294篇 |
2019年 | 290篇 |
2018年 | 187篇 |
2017年 | 181篇 |
2016年 | 406篇 |
2015年 | 357篇 |
2014年 | 451篇 |
2013年 | 929篇 |
2012年 | 977篇 |
2011年 | 1268篇 |
2010年 | 619篇 |
2009年 | 524篇 |
2008年 | 1014篇 |
2007年 | 1092篇 |
2006年 | 1073篇 |
2005年 | 1038篇 |
2004年 | 881篇 |
2003年 | 745篇 |
2002年 | 732篇 |
2001年 | 250篇 |
2000年 | 254篇 |
1999年 | 230篇 |
1998年 | 223篇 |
1997年 | 259篇 |
1996年 | 284篇 |
1995年 | 227篇 |
1994年 | 212篇 |
1993年 | 244篇 |
1992年 | 203篇 |
1991年 | 185篇 |
1990年 | 164篇 |
1989年 | 141篇 |
1988年 | 140篇 |
1987年 | 158篇 |
1986年 | 135篇 |
1985年 | 203篇 |
1984年 | 249篇 |
1983年 | 179篇 |
1982年 | 220篇 |
1981年 | 241篇 |
1980年 | 180篇 |
1979年 | 181篇 |
1978年 | 214篇 |
1977年 | 159篇 |
1976年 | 157篇 |
1975年 | 150篇 |
1974年 | 165篇 |
1973年 | 140篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Irradiation of in methanoi with λ 254 nm yields and as the main primary products which result from the excited singlet state hy initial cyclopropane bond homolysis, but no primary photosolvolysis products. 相似文献
92.
Wormer PE 《The Journal of chemical physics》2005,122(18):184301
A short self-contained derivation is given for the second virial coefficient B2(T) of a gas consisting of identical interacting asymmetric rigid rotors. The resulting expression is correct through variant Planck's over h2. First, the canonical partition function is derived by means of an variant Planck's over h expansion of exp[-H/(k(B)T)] due to Friedmann [Adv. Chem. Phys. 4, 225 (1962)]. The present work applies angular momentum operators and known facts from angular momentum theory. It is considerably more accessible than Friedmann's exposition, which is not based on angular momentum operators, but instead on explicit derivatives with respect to Euler angles. The partition function obtained from the variant Planck's over h expansion is applied to the derivation of an expression for B2(T) that is identical in appearance to the expression for symmetric rotors of T Pack [J. Chem. Phys. 78, 7217 (1983)]. The final equation in this work is valid for rigid rotors of any symmetry. 相似文献
93.
Hans-Rudolf Waespe Heinz Heimgartner Hans Schmid Hans-Jürgen Hansen Henning Paul Hanns Fischer 《Helvetica chimica acta》1978,61(1):401-429
The photochemical reactions of different allyl aryl ethers (Scheme 3) were investigated in hydrocarbons (Chap. 3.1) and in alcoholic solvents (Chap. 3.2). The composition of the photoproducts depended very much on the nature of the solvent. Irradiation (3–95 h) of different methyl substituted allyl aryl ethers ( 1, 3, 5, 7 and 11 ) with a low pressure mercury lamp (λEmiss. = 254 nm; 6 or 15 Watt) under argon (quartz vessel) resulted in the formation of 2-, 3– and 4-substituted phenols, dienones and products of consecutive reactions (Tables 1–4 and 6). The results suggested that all products were formed by homolytic cleavage of the C? O bond in the singlet state of the ethers to intermediate radical-geminates (Scheme 5) followed by radical recombination of the two fragments. No products were formed by concerted processes (Table 5, Schemes 5 and 6). Upon irradiation of allyl aryl ethers lacking alkyl substituents at position 4 ( 1 and 5 ) in protic solvents, mainly 2- and 4-allylated phenols were obtained (Tables 1 and 4); 3-allylated phenols were formed only in small amounts (0.02%). However, in aromatic hydrocarbons or cyclohexane 3-allylated phenols were obtained from 1 , 5 and 11 in significant amounts (3–11%; Tables 1, 4 and 6). E.g., upon irradiation of allyl-2,6-dimethyl-2,4-cyclohexadien-1-one ( 6 ) besides 3- and 4-allyl-2, 6-dimethyl-phenol ( 23 and 24 ). Irradiation of 5 in methanol afforded 23 and 6 only in traces, whereas 24 was the main product. 相似文献
94.
The focal point of our discussion is the examination of truncated basis sets used in obtaining an accurate first principles clculation of the effective valence shell Hamiltonian by the canonical transformation-cluster expansion approasch. Subsequent diagonalization of this effecitve valence shell hamiltonian yields the valence shell transition energies. A detailed analysis of numerical results obtained using a number of different basis sets of hydrogen-like orbitals together with rigorous symmetry arguments celarly demonstrates the special role played by d orbitals in computing the 3P → 1D transition energy in carbon. The failure of early attempts to calculate the effective Hamiltonian for ethylene from first principles is examined in the light of recent ab initio calculations on ethylene involving d orbitals and the computations reported in this paper. We conclude that accurate calculations of the effective valence shell Hamiltonian for molecules must consider d orbitals in the excited orbital basis set. 相似文献
95.
Derrouiche S Gravejat P Bianchi D 《Journal of the American Chemical Society》2004,126(40):13010-13015
The heats of adsorption of two linear CO species adsorbed on the Au degrees particles (denoted L(Au degrees)) and on the Ti(+delta) sites (denoted L(Ti+delta)) of a 1% Au/TiO(2) catalyst are determined as the function of their respective coverage by using the AEIR procedure (adsorption equilibrium infrared spectroscopy) previously developed. Mainly, the evolutions of the IR band area of each adsorbed species (2184 cm(-1) for L(Ti+delta) and at 2110 cm(-1) for L(Au degrees)) as a function of the adsorption temperature T(a), at a constant CO adsorption pressure P(CO), provide the evolutions of the coverages theta(LTi+delta) and theta(LAu degrees ) of each adsorbed CO species with T(a) in isobar conditions that give the individual heats of adsorption. It is shown that they linearly vary from 74 to 47 kJ/mol for L(Au degrees ) and from 50 to 40 kJ/mol for L(Ti+delta) at coverages 0 and 1, respectively. These values are consistent with literature data on model Au particles and TiO(2). In particular, it is shown that the mathematical formalism supporting the AEIR procedure can be applied to literature data on Au-containing solids (single crystals and model particles). 相似文献
96.
97.
98.
Klaus Deimling Paul Szilágyi 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1994,45(1):53-60
Dry friction problems lead to discontinuous differential equations, e.g. to
相似文献
99.
100.
Bockhorst M. Burbach G. Burgwinkel R. Empt J. Guse B. Guse B. Haas K. -M. Hannappel J. Heinloth K. Hey T. Hoffmann-Rothe P. Honscheid K. Jahnen T. Jakob H. P. Jöpen N. Jüngst H. Kirch U. Klein F. -J. Kostrewa D. Lindemann L. Link J. Manns J. Menze D. Merkel H. Merkel R. Neuerburg W. Paul E. Plötzke R. Schenk U. Schmidt S. Scholmann J. Schütz P. Schultz-Coulon H. -C. Schweitzer M. Schwille W. J. Tran M. -Q. Umlauf G. Vogl W. Wedemeyer R. Wehnes F. Wißkirchen J. Wolf A. 《Zeitschrift fur Physik C Particles and Fields》1994,63(1):37-47
The reactions pK
+ and pK
+ 0 have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the polarization and, for the first time, the 0 polarization have been determined in a photon induced reaction. All data are presented as functions of the photon energy (from threshold up to 1.47 GeV) and of the kaon production angle (0°–180°). The polarization of both and 0 is substantial at all energies and varies strongly with the production angle.This work is supported by the Bundesminister für Forschung und Technologie (BMFT), FK 06 BN 621 I 相似文献
|