全文获取类型
收费全文 | 10931篇 |
免费 | 1167篇 |
国内免费 | 1356篇 |
专业分类
化学 | 6117篇 |
晶体学 | 199篇 |
力学 | 134篇 |
综合类 | 75篇 |
数学 | 497篇 |
物理学 | 6432篇 |
出版年
2023年 | 42篇 |
2022年 | 108篇 |
2021年 | 141篇 |
2020年 | 145篇 |
2019年 | 190篇 |
2018年 | 219篇 |
2017年 | 230篇 |
2016年 | 274篇 |
2015年 | 237篇 |
2014年 | 397篇 |
2013年 | 945篇 |
2012年 | 514篇 |
2011年 | 552篇 |
2010年 | 499篇 |
2009年 | 697篇 |
2008年 | 684篇 |
2007年 | 763篇 |
2006年 | 728篇 |
2005年 | 604篇 |
2004年 | 569篇 |
2003年 | 540篇 |
2002年 | 479篇 |
2001年 | 413篇 |
2000年 | 429篇 |
1999年 | 387篇 |
1998年 | 345篇 |
1997年 | 289篇 |
1996年 | 293篇 |
1995年 | 282篇 |
1994年 | 242篇 |
1993年 | 195篇 |
1992年 | 249篇 |
1991年 | 148篇 |
1990年 | 95篇 |
1989年 | 92篇 |
1988年 | 92篇 |
1987年 | 59篇 |
1986年 | 44篇 |
1985年 | 44篇 |
1984年 | 43篇 |
1983年 | 22篇 |
1982年 | 25篇 |
1981年 | 17篇 |
1980年 | 19篇 |
1979年 | 18篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1974年 | 10篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
71.
V. B. Sokolov A. N. Chekhlov T. A. Epishina I. V. Martynov 《Russian Chemical Bulletin》1992,41(2):236-240
The O-(arylcarbamoyl)butyrhydroximoyl chlorides were synthesized, and the x-ray structural analysis (XSA) of one of them — O-(o-tolylcarbamoyl)butyrhydroximoyl chloride — was performed. It was established from the data of the XSA and the PMR spectra that all synthesized compounds are the Z isomers.Institute of Physiologically Active Substances, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 315–319, February, 1992. 相似文献
72.
Summary The modifications induced by a magnetic field of arbitrary direction and intermediate strength (i.e not larger than 2.35·105 tesla, the ?atomic tesla?) on the lowest singlet and triplet energy states of the hydrogen molecule are studied. Using a
linear combination of products of field-modified atomic orbitals, it is found that increasing the field strength the depth
of the singlet energy well increases and the equilibrium internuclear distance decreases, yielding more rigid and localized
nuclear vibrations. For sufficiently strong fields perpendicular to the internuclear axis, the triplet state exhibits a bonding
behaviour. An explanation of the above results is given in terms of the field-modified electronic-charge distributions in
the internuclear region.
Based on the thesis submitted by S. Basile to the University of Palermo for graduation in Physics. 相似文献
73.
In this article,the Hausdorff dimension and exact Hausdorff measure function of any random sub-self-similar set are obtained under some reasonable conditions.Several examples are given at the end. 相似文献
74.
Orotic acid (vitamin B13) is a key intermediate in biosynthesis of the pyrimidine nucleotides in living organisms, moreover, it may serve as the biological carrier for some metal ions. cis-Diammine(orotato)platinum(II), cis-[Pt(C5H2N2O4)(NH3)2] can be considered as a new potential cisplatin analogue. The FT-Raman and FT-IR spectra of the title complex are reported, for the first time. The molecular structure, vibrational frequencies, and the theoretical infrared and Raman intensities have been calculated by the density functional mPW1PW91 method. The detailed vibrational assignment has been made on the basis of the calculated potential energy distribution. The theoretically predicted IR and Raman spectra show very good agreement with experiment. Natural bond orbital (NBO) analyses were performed for cisplatin, carboplatin and the title complex. The results provided new data on the nature of platinum–ligand bonding in these compounds. Strong intramolecular hydrogen bond between the orotate ligand and the coordinated ammonia group stabilizes the structure of the platinum(II) complex. Thus, it is suggested that the orotate ligand in the title complex is more inert to the substitution reactions than the chloride ligands in cisplatin. 相似文献
75.
The 57Fe Mössbauer technique has been used to investigate the effect of zinc oxide substitution in (25???x)MnO–xZnO–15Fe2O3–60B2O3 glass system (x?=?0, 5, 10, 15 and 20 mol% of ZnO ). Mössbauer absorption spectra for all the samples recorded at room temperature suggest the existence of the two paramagnetic quadrupole doublets. The observed variations in hyperfine parameters have been explained on the basis of cations distribution and exchange interaction at the lattice sites and it is concluded that B–B interaction increases while the metal–metal interaction decreases due to replacement of manganese oxide by zinc oxide. These results suggest that the present glass system exhibits a paramagnetic behaviour that changes towards the weak paramagnetic when manganese oxide was replaced with zinc oxide. 相似文献
76.
77.
Raman spectra of ceramic Sr2Bi4Ti5O18 (SBTi5) are reported to consist of four different Raman bands. Temperature-dependent spectra reveal the relationship between the lattice vibration and the material's structure. There appears a relatively large change in structure of the material at about 273K, The anharmonic potential of the material has a great influence on its phonon mode full width at half maximum (FWHM), which can be expressed by a function of temperature. Theoretical fittings of the FWHMs for the two modes at around 312 cm^-1 and 464cm^-1 indicate that the latter phonon mode is more anharmonic than the former one. 相似文献
78.
Arabinda Mallick 《Journal of luminescence》2006,118(2):165-172
Solvatochromic effects on the fluorescence behavior of 7-hydroxy-4-methyl-8-(4′-methyl-piperazine-1′ yl)methylcoumarin (HMMC) was studied in different solvents. The fluorescence of HMMC was found to be highly sensitive to both the polarity and the protic character of the solvent. Exploiting the polarity-sensitive fluorescence property of HMMC, its excited-state dipole moment has been determined. Fluorescence (Förster) resonance energy transfer (FRET) process from HMMC to a potent bioactive molecule 3-acetyl-4-oxo-6,7-dihydro-12 H indolo-[2,3-a] quinolizine (AODIQ) was studied. From the determined KSV and R0 values, it is argued that a long-range dipole-dipole interaction is operating for the energy transfer mechanism. The energy transfer efficiency (E) and the distance between the acceptor and the donor (r0) have been determined. 相似文献
79.
80.
Some Results behind Dividend Problems 总被引:1,自引:0,他引:1
Ming Zhou Li Wei Jun-yi Guo 《应用数学学报(英文版)》2006,22(4):681-686
We consider the basic dividend problem of the compound Poisson model with constant barrierstrategy.Some results concealed behind the dividend problem are made explicit in the present work.Differentmethods and some of which are firstly given in this paper.All these results presented certain direct relationshipbetween some important actuary variables in classical risk theory is also revealed. 相似文献