全文获取类型
收费全文 | 264篇 |
免费 | 12篇 |
国内免费 | 20篇 |
专业分类
化学 | 178篇 |
晶体学 | 4篇 |
力学 | 14篇 |
综合类 | 4篇 |
数学 | 9篇 |
物理学 | 87篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 2篇 |
2014年 | 9篇 |
2013年 | 19篇 |
2012年 | 16篇 |
2011年 | 19篇 |
2010年 | 10篇 |
2009年 | 12篇 |
2008年 | 23篇 |
2007年 | 27篇 |
2006年 | 18篇 |
2005年 | 8篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1986年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有296条查询结果,搜索用时 187 毫秒
1.
The rotational barriers of the CC bonds of halocarbons are believed to be rather different than those of hydrocarbons. We wish to systematically study the effect of halogen substituents on the conformational flexibility of hydrocarbons. As our initial approach to this problem, we have synthesized the following molecules: Pyrene-(CF2)n-Pyrene (n=3, 4, and 6) and Pyrene-(CF2)n-F (n=4 and 6). We describe here the concentration and temperature dependence of the emissive behavior of these materials. 相似文献
2.
3.
The paper presents an exact analysis of the dispersion of an immiscible solute in a non-Newtonian fluid (known as an incompressible second-order fluid which shows viscoelastic behaviour) flowing slowly in a parallel plate channel in the presence of a periodic pressure gradient. Using a generalized dispersion model which is valid for all times after the solute injection, the diffusion coefficients K i (τ)(i=1,2,3,…) are obtained as functions of time τ in the case when the initial solute distribution is in the form of a slug of finite extent. The analysis leads to the novel result that K 2(τ) (which is a measure of the longitudinal dispersion coefficient of the solute) has a steady part S in addition to a fluctuating part D 2(τ) due to the pulsatility of the flow. It is found that S decreases with increase in the viscoelastic parameter M for given values of the amplitude λ and frequency ω of the pressure pulsation. On the other hand, it is found that at a fixed instant τ, the amplitude of D 2(τ) increases with increase in M for given values of λ and ω. Further it is shown that at a given instant τ, the amplitude of D 2(τ) decreases with increase in ω for given λ and M and the profile for D 2(τ) becomes progressively flatter with increase in ω. Finally the axial distribution of the average concentration θ m of the solute over the channel cross-section is determined at different instants after the solute injection for several values of M, λ and ω. The present study is likely to have important bearing on the problem of dispersion of tracers in blood flow through arteries. 相似文献
4.
5.
6.
7.
Nianchen Zhou Wenjian Xu Yu Zhang Jian Zhu Xiulin Zhu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(4):1522-1528
2,2,6,6‐Tetramethyl‐4‐[d‐(+)‐10‐camphorsulfonyl]‐1‐piperidinyloxy was synthesized and used as a chiral nitroxide for the bulk polymerizations of styrene initiated with benzoyl peroxide (BPO), tetraethylthiuram disulfide (TETD), and thermal initiation. The results showed that the polymerizations proceeded in a controlled/living way; that is, the kinetics presented approximately first‐order plots, and the number‐average molecular weights of the polymers with narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight) increased with the monomer conversion linearly. The molecular weight distributions in the case of thermal initiation were narrower than those in the case of BPO and TETD, whereas the polymerization rate with BPO or TETD as an initiator was obviously faster than that with thermal initiation. In addition, successful chain‐extension reactions were carried out, and the structures of the obtained polymers were characterized by gel permeation chromatography and 1H NMR. The specific rotations of the polymers were also measured by polarimetric analysis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1522–1528, 2006 相似文献
8.
茄子组织生物微电极在儿茶酚测定中表现出了较高的生物催化活性,而对抗坏血酸测定则为稳态响应,这表明该电极能有效地消除抗坏血酸的干扰。该电极的灵敏度高,重现性好,对多巴胺测定的线性范围为5.8×10~(-6)~6.5×10~(-4)mol/L,检出下限为:2.9×10~(-6)mol/L。 相似文献
9.
A new pentacyclic triterpenoid, urs-12-en-29α-oic acid-3β-ol (1), was obtained from the ethanol extract of Chinese herb Oldenlandia cantonensis How. The structure was elucidated by spectroscopy methods, including nuclear magnetic resonance (NMR) (1D and 2D), infrared
spectroscopy (IR), and mass spectrometry (MS). 1 exhibited significant inhibitory activity against the human DNA topoisomerase
I (hTopo I), the cancer cell lines BEL-7402 and MCG-803, with the IC50 values 12.0, 6.5, and 8.0 μg/mL, respectively. The volatile oil, the fraction of petroleum ether: EtOAc = 20:1 (V/V) on Si gel chromatography, was also quantitatively analyzed by gas chromatography mass spectrometry (GC-MS). As a result,
60 compounds were identified. Among them, the long chain aliphatics, terpenes and steroids, as the representative structure
type, were found with percentages of 36.16%, 6.42% and 9.28%, respectively.
Translated from Chinese Journal of Applied Chemistry, 2006, 23(8): 871–874 [译自: 应用化学] 相似文献
10.
Camillo A. Ghiron Maurice R. Eftink David A. Engler Salil K. Niyogi 《Photochemistry and photobiology》1992,55(1):29-34
Steady-state and time-resolved fluorescence studies have been performed with human epidermal growth factor, a small globular protein having two adjacent tryptophan residues near its C-terminus. Based on the relatively red fluorescence and accessibility to solute quenchers, the two tryptophan residues are found to be exposed to solvent. Anisotropy decay measurements show the dominant depolarizing process to have a sub-nanosecond rotational correlation time indicating the existence of rapid segmental motion of the fluorescing tryptophan residues. From an analysis of the low-temperature excitation anisotropy spectrum of the protein (and in comparison with that of tryptophan, the peptide melittin, and the dipeptide trp-trp), it is concluded that homo-energy transfer and/or exciton interaction occurs between the adjacent tryptophan residues. A thermal transition in the structure of the protein, which is observed by circular dichroism measurements, is not sensed by the steady-state fluorescence of the protein. This result, in conjunction with the anisotropy decay results, indicates that the two tryptophan residues are in a highly flexible C-terminus segment, which is not an integral part of the three-dimensional structure of the protein. Fluorescence measurements with three site-directed mutants also show very little variation. 相似文献