全文获取类型
收费全文 | 1832篇 |
免费 | 54篇 |
国内免费 | 6篇 |
专业分类
化学 | 1489篇 |
晶体学 | 32篇 |
力学 | 27篇 |
数学 | 60篇 |
物理学 | 284篇 |
出版年
2023年 | 8篇 |
2022年 | 18篇 |
2021年 | 14篇 |
2020年 | 24篇 |
2019年 | 25篇 |
2018年 | 17篇 |
2016年 | 31篇 |
2015年 | 31篇 |
2014年 | 39篇 |
2013年 | 113篇 |
2012年 | 87篇 |
2011年 | 97篇 |
2010年 | 73篇 |
2009年 | 67篇 |
2008年 | 112篇 |
2007年 | 86篇 |
2006年 | 108篇 |
2005年 | 96篇 |
2004年 | 79篇 |
2003年 | 81篇 |
2002年 | 107篇 |
2001年 | 29篇 |
2000年 | 21篇 |
1999年 | 31篇 |
1998年 | 16篇 |
1997年 | 25篇 |
1996年 | 26篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 35篇 |
1984年 | 25篇 |
1983年 | 14篇 |
1982年 | 28篇 |
1981年 | 20篇 |
1980年 | 31篇 |
1979年 | 23篇 |
1978年 | 17篇 |
1977年 | 17篇 |
1976年 | 17篇 |
1975年 | 15篇 |
1973年 | 12篇 |
1972年 | 8篇 |
排序方式: 共有1892条查询结果,搜索用时 15 毫秒
31.
X-ray analysis of the title complex revealed hydrogen-bonded chains comprising two crystallographically independent types of -9,10-dihydroxy-9,10-diphenyl-9,10-dihydroanthracene molecules, in which the central 1,4-cyclohexadiene rings are respectively flat and very slightly puckered, with the ethanol molecules attached exclusively to the latter type. 相似文献
32.
Israel Goldberg Zafra Stein Koichi Tanaka Fumio Toda 《Journal of inclusion phenomena and macrocyclic chemistry》1991,10(1):97-107
The crystal structures of the 2,2-di(p-hydroxyphenyl)propane host and its 1:1 adducts withm-andp-cresol guests have been studied. The preferential complexation of this host withp-cresol overm-cresol is related to the opposite trend exhibited by 1,1-di(p-hydroxyphenyl)cyclohexane; both hosts can separate effectively the two cresols from their liquid mixture by crystalline inclusion. A plausible explanation of the different inclusion features is provided by examining the intermolecular association in the corresponding solids. The analysed structures are stabilized by strong and continuous H-bonding between the constituent entities along two dimensions, and by weak van der Waals forces along the third axis. The p-cresol complex of the title host reveals a unique arrangement within and a more efficient packing of the layered structure, and thus represents a more stable and less soluble crystal lattice than itsm-cresol analog.
Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82099 (8 pages). 相似文献
33.
Koichi Kikuta Koji Noda Shin Okumura Toshiaki Yamaguchi Shin-ichi Hirano 《Journal of Sol-Gel Science and Technology》2007,42(3):381-387
Orientation control of perovskite compounds was investigated by the application of a seed layer prepared from oxide nanosheets.
An aqueous suspension of oxide nanosheets was prepared by the exfoliation of a layered compound of KCa2Nb3O10 oxide grains. A seed layer composed of (TBA)Ca2Nb3O10 nanosheets (TBA = tetrabutylammonium) was formed on a glass substrate by simply dip coating it in the suspension. Two kinds
of perovskite compounds, LaNiO3 (LNO) and Pb(Zr,Ti)O3 (PZT) with a preferred orientation of (00l) were successfully grown on this seeded glass substrate. In this study, the relation between lattice mismatch and electrical
properties is investigated. A large, oriented PZT film with a size of 5 ×4 cm shows an improved P-E hysteresis behavior by
use of this orientation control. 相似文献
34.
Katsunori Wakabayashi Mitsutaka Fujita Koichi Kusakabe Kyoka Nakada 《Czechoslovak Journal of Physics》1996,46(4):1865-1866
Anoble mechanism of spin polarization is proposed for finite graphite sheet with edge. For graphite ribbon with zigzag edge, there appear peculiar ‘edge states’. These localized states comprise nearly flat band at the Fermi level, which easily causes magnetic instability. Magnetic structure is suggested from Hartree-Fock analysis of the Hubbard model, where huge magnetic moments are induced at around both of edges by weak HubbardU and are coupled antiferromagnetically with each other. 相似文献
35.
[reaction: see text] A three-step route of converting allylsilanes to functionalized allenes was developed. Thermal decomposition of 1,1-dibromo-2-(silylmethyl)cyclopropanes, which were quantitatively prepared by treatment of allylsilane derivatives with CHBr3/KO(t)Bu, afforded substituted 2-bromo-1,3-butadienes with elimination of bromosilanes. The Pd-catalyzed reaction of the bromodienes with soft nucleophiles gave the allene derivatives. Previously inaccessible tri- and tetrasubstituted allenes can be prepared by this method as well. 相似文献
36.
The leaching behavior of two different residual oils is investigated with 24 organic solvents including alkanes, aromatics, esters, ethers ketones, alcohols and nitrogen compounds. A 2-g portion of sample oil is shaken with 20 ml of the organic solvent. The leaching of the organic matrix of the oil is determined by weighing the dissolved organic matrix after removal of solvent. The leaching of vanadium, iron and nickel was determined by flame atomic absorption spectrophotometry after ashing of the dissolved fraction. The leaching of those metals depends strongly on the solvent used; for example, vanadine is almost completely leached into toluene, but only slightly into methanol. The leaching of iron is poor compared with that of vanadium or nickel. In most solvents, leaching of those metal-containing species is poorer than that of organic material. Exceptionally, N,N-dimethylformamide is more efficient in leaching vanadium species than organic material. 相似文献
37.
The theory of first-order kinetic collection efficiencies at the double channel electrode is developed for the following two schemes: (I) A±n1e→B (at the generator electrode), B→kP (in solution), B±n2e→Y (at the detector electrode), (II) A±n1e→B, B→kA, B±n2e→Y. The exact expressions for the kinetic collection efficiencies are obtained as ascending and asymptotic series with respect to the kinetic parameter. Further, approximate formulae in exponential forms are given, which hold within an error of about 2% for conventional electrode geometry. Finally, the validity of the approximate procedure, which has been used previously to obtain the kinetic collection efficiencies for fast homogeneous reactions, is discussed in comparison with the present theory. 相似文献
38.
Sato H Tashiro K Shinmori H Osuka A Murata Y Komatsu K Aida T 《Journal of the American Chemical Society》2005,127(38):13086-13087
Upon binding with C60 and diamines, such as 4,4'-bipyridine (bpy) and N,N,N',N'-tetramethylhexane-1,6-diamine (TMHDA), cyclic host 1 possessing two electronically coupled binding sites displays negative homotropic cooperativity and positive heterotropic cooperativity, and their ternary mixtures preferentially form inclusion complexes with hetero-guest pairs 1 supersetC60*bpy and 1 supersetC60*TMHDA under appropriate conditions. Spectroscopic titration profiles in toluene at 20 degrees C demonstrated that the association constants (Kassoc) of C60 with monodiamine complexes 1 supersetbpy (2.8 x 105 M-1) and 1 supersetTMHDA (1.5 x 105 M-1) are 8.5 and 4.5 times greater than that of C60 with guest-free 1 (3.3 x 104 M-1), respectively. On the other hand, mono-C60 complex 1 supersetC60 was 6.1 times more accessible than guest-free 1 toward TMHDA. Absorption spectroscopy in the absence of 1 indicated no direct interaction between C60 and diamines. 相似文献
39.
Nishinaga T Yamazaki D Stahr H Wakamiya A Komatsu K 《Journal of the American Chemical Society》2003,125(24):7324-7335
Novel cyclopentadienyl (Cp)-alkali metal complexes 1-M and 2-M (M = Li, Na, K), in which the Cp ring is annelated with two bicyclo[2.2.2]octene units and substituted with a phenyl group for 1 and a tert-butyl group for 2, were synthesized, and their structures and dynamic behaviors were investigated by means of X-ray crystallography, dynamic (13)C NMR, and DFT calculations. The X-ray crystallography results indicated that 1-Li, 1-Na, and 2-Na form monomeric contact ion pairs (CIP) with three THF molecules coordinated to the metal atom. Also, in THF-d(8), all of the 1-M and 2-M form monomeric CIP in the ground state. However, variable-temperature (13)C NMR measurements of 1-M and 2-M in THF-d(8) demonstrated dynamic behavior in which the metal ion exchanges positions between the upper and lower faces of the Cp ring. From a study of the concentration dependence of the dynamic behavior, the exchange was found to proceed principally as an intramolecular process at concentration ranges lower than 0.2 M. The experimentally observed deltaG values for the intramolecular exchange process for all the 1-M and 2-M (except for 2-Li, whose intramolecular process was too slow to observe) were found to be quite similar in THF-d(8) solution and to fall within the range of 12-14 kcal mol(-)(1). Within this range, a tendency was observed for the deltaG values to increase as the size of the metal decreased. Theoretical calculations (B3LYP/6-31G(d)) afforded considerably large values as the gas-phase dissociation energy for 1-M (162.7 kcal mol(-)(1) for M = Li; 131.6 kcal mol(-)(1) for M = Na; 110.9 kcal mol(-)(1) for M = K) and for 2-M (170.0 kcal mol(-)(1) for M = Li; 137.5 kcal mol(-)(1) for M = Na; 115.4 kcal mol(-)(1) for M = K). These values should be compensated for by a decrease in the solvation energies for the metal ions with increasing size, as exemplified by the calculated solvation energy for M(+)(Me(2)O)(4), which serves as a model for metal ions solvated with four molecules of THF (-122.9 kcal mol(-)(1) for M = Li; -94.7 kcal mol(-)(1) for M = Na; -67.7 kcal mol(-)(1) for M = K). This compensation results in a small difference in the overall energy for dissociation of 1-M or 2-M in ethereal solutions, thus supporting the similar deltaG values observed for the intramolecular metal exchange. 相似文献
40.
Koichi Ohno 《Chemical physics letters》1979,64(3):560-566
Vibrational frequencies in excited and ionized states are calculated for primary aromatic hydrocarbons, on the basis of MO calculations of transition energies and normal coordinate calculations for ground state molecules. Results are in good agreement with experiment. Specific activities of certain types of modes, which exhibit large frequency shifts on excitation, are discussed in terms of vibronic coupling. 相似文献