全文获取类型
收费全文 | 6010篇 |
免费 | 204篇 |
国内免费 | 32篇 |
专业分类
化学 | 4144篇 |
晶体学 | 19篇 |
力学 | 209篇 |
数学 | 1029篇 |
物理学 | 845篇 |
出版年
2022年 | 33篇 |
2021年 | 59篇 |
2020年 | 65篇 |
2019年 | 80篇 |
2018年 | 85篇 |
2017年 | 79篇 |
2016年 | 152篇 |
2015年 | 141篇 |
2014年 | 169篇 |
2013年 | 257篇 |
2012年 | 326篇 |
2011年 | 367篇 |
2010年 | 233篇 |
2009年 | 231篇 |
2008年 | 330篇 |
2007年 | 324篇 |
2006年 | 332篇 |
2005年 | 302篇 |
2004年 | 262篇 |
2003年 | 241篇 |
2002年 | 285篇 |
2001年 | 106篇 |
2000年 | 102篇 |
1999年 | 56篇 |
1998年 | 58篇 |
1997年 | 65篇 |
1996年 | 76篇 |
1995年 | 53篇 |
1994年 | 64篇 |
1993年 | 52篇 |
1992年 | 49篇 |
1991年 | 57篇 |
1990年 | 47篇 |
1989年 | 44篇 |
1988年 | 39篇 |
1987年 | 44篇 |
1986年 | 39篇 |
1985年 | 84篇 |
1984年 | 83篇 |
1983年 | 51篇 |
1982年 | 86篇 |
1981年 | 56篇 |
1980年 | 77篇 |
1979年 | 56篇 |
1978年 | 74篇 |
1977年 | 56篇 |
1976年 | 56篇 |
1975年 | 42篇 |
1974年 | 44篇 |
1973年 | 33篇 |
排序方式: 共有6246条查询结果,搜索用时 0 毫秒
31.
Pierre Laszlo 《Angewandte Chemie (International ed. in English)》1978,17(4):254-266
With the availability of Fourier transform spectrometers, 23Na-NMR spectroscopy has become an important tool. It affords direct insight into solvation and ion pairing phenomena, both in organic and in bio-inorganic systems. Monitoring the chemical shifts and linewidths of 23Na signals gives access to binding constants, reorientational correlation times and the microdynamics of the sodium coordination shell. The binding of other cations can also be studied by 23Na-NMR spectroscopy, in competition experiments. 相似文献
32.
Claude Balny Jennifer Canva Pierre Douzou Jean Bourdon 《Photochemistry and photobiology》1969,10(6):375-382
Abstract— Chemiluminescence and photochemiluminescence of systems generating excited (singlet) molecular oxygen has been studied at low temperature in fluid media. A possible interpretation is proposed: that dimers of singlet oxygen are directly or indirectly responsible for the observed emission, the species [1 δg +1 σg+ ] predominating. Energy transfer to a fluorescent molecule is possible only when conditions of spectral overlap, required for transfer by inductive resonance, are fulfilled. Evidence is also presented for the formation of a transient complex between oxygen and a sensitiser or acceptor molecule [S…O2 ], which is the precursor of singlet oxygen in these systems. However, other possible mechanisms cannot be excluded. 相似文献
33.
Crystals of Li0.33 MoO3 (blue), Rb0.23MoO3 (blue) and Cs0.31MoO3 (red) were grown by electrolysis from MoO3M2MoO4 melts (M =alkali metal) with composition 70–77 mole% MoO3. Melts richer in M2MoO4 produced MoO2 only. Correlation is made between bronze formation and the coordination of Mo in the melt and in the equilibrium solid phase M2Mo4O13. Li0.33MoO3 and Cs0.31MoO3 are semiconductors with high-temperature-range activation energies 0.16 and 0.12 eV. Rb0.23MoO3 has an electrical behavior similar to that of blue KxMoO3 with a semiconductor-metal transition at (170 ± 5) K. ESR spectra observed in Li0.33MoO3 and Rb0.23MoO3 single crystals at 4.2 K show extensive delocalization of the 4d1 electron associated with Mo(V) centers. Attempts to grow molybdenum bronzes containing Ca or Y were unsuccessful. 相似文献
34.
The face selectivity (endo-face vs. exo-face attack onto the exocyclic s-cis-butadiene moiety) of the [4+2]cycloadditions of 5,6-bis((D)methylidene)-2-bicyclo-[2.2.2]octene ( 11 ) to strong dienophiles has been determined in benzene at 25°. It is ca. 95/5, 75/5, 70/30, 60/40 and 50/50 for N-phenyltriazolinedione (NPTAD), tetracyanoethylene (TCE), dimethyl acetylenedicarboxylate (DMAD), maleic anhydride (MA) and singlet oxygen (1O2), respectively. The endo-face preference is probably due to a participation of the homoconjugated double bond at C(2), C(3) which makes the etheno bridge more polarizable than the ethano bridge in 11. The absence of face selectivity with 1O2 is consistent with an entropy-controlled mechanism involving the intermediacy of an exciplex. 相似文献
35.
Annette Marchand Pierre Gerval Françoise Duboudin M.-H. Gaufryau Marguerite Joanny Pierre Mazerolles 《Journal of organometallic chemistry》1984,267(1):93-106
Intermediates with π-bonded Si or Ge are generated during gas phase pyrolysis of 1,2-disila- or 1,2-digerma-cyclohex-4-enes.Compounds such as R2MMR2 are successfully trapped by addition or [2 + 2] and [4 + 2] cycloadditions. These results were proved by mass spectrometry. 相似文献
36.
André Begouen-Demeaux Gérard Villers Pierre Gibart 《Journal of solid state chemistry》1975,15(2):178-180
The system FeCrTe was investigated around the composition FeCr2Te4. FeCr2Te4 is a metastable compound. Single crystals with Fe0·93Cr1·76Te4 composition were grown by vapor transport or the Bridgman method. These crystals are metallic and anisotropic ferromagnets. 相似文献
37.
Bertrand Pierre Broniatowski Michel Marcotorchino Jean-François 《Advances in Data Analysis and Classification》2022,16(4):1069-1093
Advances in Data Analysis and Classification - This paper aims at comparing two coupling approaches as basic layers for building clustering criteria, suited for modularizing and clustering very... 相似文献
38.
We consider the Hopfield model withM(N)=N patterns, whereN is the number of neurons. We show that if is sufficiently small and the temperature sufficiently low, then there exist disjoint Gibbs states for each of the stored patterns, almost surely with respect to the distribution of the random patterns. This solves a provlem left open in previous work. The key new ingredient is a self-averaging result on the free energy functional. This result has considerable additional interest and some consequences are discussed. A similar result for the free energy of the Sherrington-Kirkpatrick model is also given. 相似文献
39.
40.
We show that, when music pieces are cast in the form of time series of pitch variations, the concepts and tools of dynamical systems theory can be applied to the analysis of temporal dynamics in music. (i) Phase space portraits are constructed from the time series wherefrom the dimensionality is evaluated as a measure of the global dynamics of each piece. (ii) Spectral analysis of the time series yields power spectra ( approximately f(-nu)) close to red noise (nu approximately 2) in the low frequency range. (iii) We define an information entropy which provides a measure of the local dynamics in the musical piece; the entropy can be interpreted as an evaluation of the degree of complexity in the music, but there is no evidence of an analytical relation between local and global dynamics. These findings are based on computations performed on eighty sequences sampled in the music literature from the 18th to the 20th century. (c) 1995 American Institute of Physics. 相似文献