全文获取类型
收费全文 | 804篇 |
免费 | 8篇 |
国内免费 | 2篇 |
专业分类
化学 | 664篇 |
晶体学 | 1篇 |
力学 | 15篇 |
数学 | 53篇 |
物理学 | 81篇 |
出版年
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 11篇 |
2014年 | 11篇 |
2013年 | 20篇 |
2012年 | 26篇 |
2011年 | 25篇 |
2010年 | 23篇 |
2009年 | 17篇 |
2008年 | 17篇 |
2007年 | 23篇 |
2006年 | 21篇 |
2005年 | 12篇 |
2004年 | 17篇 |
2003年 | 11篇 |
2002年 | 9篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1996年 | 4篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1989年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1970年 | 2篇 |
1966年 | 2篇 |
1964年 | 25篇 |
1963年 | 52篇 |
1962年 | 74篇 |
1961年 | 42篇 |
1960年 | 45篇 |
1959年 | 31篇 |
1958年 | 59篇 |
1957年 | 57篇 |
1956年 | 47篇 |
1933年 | 3篇 |
1927年 | 2篇 |
1888年 | 2篇 |
排序方式: 共有814条查询结果,搜索用时 296 毫秒
21.
22.
Ag atoms isolated in N2 matrices were studied by simultaneous observation of optical absorption and electron spin resonance (ESR). In matrices with low Ag/N2 ratios two ESR signals were observed, both of which could be correlated to the well known absorption triplet corresponding to the 5s 2S → 5p 2P resonance transition. One of the two ESR signals disappeared irreversably upon annealing up to 20 K. The stable species is attributed to Ag atoms in a nanocrystalline environment whereas the unstable species corresponds to atoms in the non-crystalline regions between the crystallites. In higher doped matrices a new Ag spectrum showed up, both in the optical absorption and in the ESR. It is assigned to Ag atoms with near-by complexes, possibly Ag clusters. 相似文献
23.
Arkke J. Eskola Timo T. Reijonen Timo T. Pekkanen Petri Heinonen Satya P. Joshi Raimo S. Timonen 《Proceedings of the Combustion Institute》2021,38(1):813-821
The kinetics of the i-C4H5 (buta-1,3-dien-2-yl) radical reaction with molecular oxygen has been measured over a wide temperature range (275–852 K) at low pressures (0.8–3 Torr) in direct, time-resolved experiments. The measurements were performed using a laminar flow reactor coupled to photoionization mass spectrometer (PIMS), and laser photolysis of either chloroprene (2-chlorobuta-1,3-diene) or isoprene was used to produce the resonantly stabilized i-C4H5 radical. Under the experimental conditions, the measured bimolecular rate coefficient of i-C4H5 + O2 reaction is independent of bath gas density and exhibits weak, negative temperature dependency, and can be described by the expression k3 = (1.45 ± 0.05) × 10?12 × (T/298 K)?(0.13±0.05) cm3 s?1. The measured bimolecular rate coefficient is surprisingly fast for a resonantly stabilized radical. Under combustion conditions, the reactions of i-C4H5 radical with ethylene and acetylene are believed to play an important role in forming the first aromatic ring. However, the current measurements show that i-C4H5 + O2 reaction is significantly faster under combustion conditions than previous estimations suggest and, consequently, inhibits the soot forming propensity of i-C4H5 radicals. The bimolecular rate coefficient estimates used for the i-C4H5 + O2 reaction in recent combustion simulations show significant variation and are up to two orders of magnitude slower than the current, measured value. All estimates, in contrast to our measurements, predict a positive temperature dependency. The observed products for the i-C4H5 + O2 reaction were formaldehyde and ketene. This is in agreement with the one theoretical study available for i-C4H5 + O2 reaction, which predicts the main bimolecular product channels to be H2CO + C2H3 + CO and H2CCO + CH2CHO. 相似文献
24.
The activity coefficients at infinite dilution (γ∞) of dimethylsulphide (DMS) in four hydrocarbon solvents were measured using the dilutor technique at temperatures between 288 K and 303 K. The four hydrocarbons were hexane, 1-hexene, 2,2,4-trimethylpentane and 2,4,4-trimethyl-1-pentene. The dilutor technique is based on the stripping of the highly diluted solute, i.e. DMS, by a constant flow of inert gas. The gas composition was analysed by gas chromatography and the rate of solute removal was calculated from the area of the peaks. 相似文献
25.
26.
Petri Myllytie Lennart Salmén Eero Haimi Janne Laine 《Cellulose (London, England)》2010,17(2):375-385
Viscoelastic properties of cellulose microfibril—polymer composites and paper sheets were studied with dynamic mechanical
analysis as a function of relative humidity in order to assess the bonding properties in cellulosic networks. The amount of
associated water in the composites (equilibrium moisture content) was measured by thermogravimetry. Water plasticization was
evidenced by DMA both in composite and paper samples. Polymers with high affinity to water, e.g. carboxymethyl cellulose,
clearly increased the water plasticization in the composites. The plasticization behavior of paper sheet samples was also
influenced by polymers. However, the effect of polymers on the plasticization was different between the composite and the
paper samples. The consideration of fiber bonding domain in paper structure as a gel-like layer consisting of cellulose microfibrils,
polymers, and associated water can help to unveil some of the complex mechanisms behind the strength in fibrous cellulosic
materials. 相似文献
27.
Detection of phase biaxiality in liquid crystals by use of the quadrupole shift in 131Xe NMR spectra
An experimental method to unambiguously distinguish between uniaxial and biaxial liquid crystal phases is introduced. The method is based on the second order quadrupole shift (SOQS) observable in 131Xe NMR spectra of xenon dissolved in liquid crystals. It is shown that besides revealing the biaxiality, the 131Xe SOQS offers a novel method to determine the tilt angle in smectic C phases. As an example, the 131Xe SOQS in a ferroelectric liquid crystal is reported. It yields up a biaxial phase in between isotropic and smectic C phases. 相似文献
28.
Vossen A Seidl R Adachi I Aihara H Aushev T Balagura V Bartel W Bischofberger M Bondar A Bračko M Browder TE Chang MC Chen A Chen P Cheon BG Cho K Choi Y Eidelman S Feindt M Gaur V Gabyshev N Garmash A Golob B Perdekamp MG Haba J Hayasaka K Horii Y Hoshi Y Hou WS Hyun HJ Inami K Ishikawa A Iwabuchi M Iwasaki Y Iwashita T Joshi NJ Kichimi H Kim HO Kim MJ Ko BR Kumita T Lange JS Lee MJ Lee SH Leitgab M Li Y Liu C Liventsev D Louvot R McOnie S Miyata H Miyazaki Y Mizuk R Mohanty GB Nakano E 《Physical review letters》2011,107(7):072004
The interference fragmentation function translates the fragmentation of a quark with a transverse projection of the spin into an azimuthal asymmetry of two final-state hadrons. In e(+)e(-) annihilation the product of two interference fragmentation functions is measured. We report nonzero asymmetries for pairs of charge-ordered π(+)π(-) pairs, which indicate a significant interference fragmentation function in this channel. The results are obtained from a 672 fb(-1) data sample that contains 711 × 10(6) π(+)π(-) pairs and was collected at and near the Υ(4S) resonance, with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. 相似文献
29.
Shape verification aimed for manufacturing process control 总被引:1,自引:0,他引:1
30.
Zoran Petrić 《Journal of Algebraic Combinatorics》2014,39(1):99-125
A family of polytopes introduced by E.M. Feichtner, A. Postnikov, and B. Sturmfels, which were named nestohedra, consists in each dimension of an interval of polytopes starting with a simplex and ending with a permutohedron. This paper investigates a problem of changing and extending the boundaries of these intervals. An iterative application of Feichtner–Kozlov procedure of forming complexes of nested sets is a solution of this problem. By using a simple algebraic presentation of members of nested sets it is possible to avoid the problem of increasing the complexity of the structure of nested curly braces in elements of the produced simplicial complexes. 相似文献