全文获取类型
收费全文 | 426篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
化学 | 239篇 |
力学 | 18篇 |
数学 | 70篇 |
物理学 | 111篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 22篇 |
2020年 | 16篇 |
2019年 | 13篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 7篇 |
2014年 | 12篇 |
2013年 | 34篇 |
2012年 | 29篇 |
2011年 | 37篇 |
2010年 | 24篇 |
2009年 | 14篇 |
2008年 | 24篇 |
2007年 | 10篇 |
2006年 | 14篇 |
2005年 | 12篇 |
2004年 | 13篇 |
2003年 | 14篇 |
2002年 | 8篇 |
2001年 | 11篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有438条查询结果,搜索用时 15 毫秒
21.
Mustafa Siti Fatimah Zaharah Arsad Siti Rosilah Mohamad Habsah Abdallah Hassan H. Maarof Hasmerya 《Structural chemistry》2021,32(3):1151-1161
Structural Chemistry - Binding affinity and intermolecular interactions are essential characteristics that could be used to comprehend molecular recognition between molecules in supramolecular... 相似文献
22.
We study the phase probability distribution of a three-level atom interacting with a cavity field in the presence of two-photon detuning and decoherence. Anabiosis of the phase probability distribution is observed due to the presence of the Stark shift. The simulation demonstrates that there is an enhancement of the phase sensitivity as soon as the two-photon detuning is considered. The W-Wigner function is also examined and it is shown that the nonclassical effect is apparent, however, for a small value of the decoherence factor. 相似文献
23.
S. Abdallah T. A. El-Brolossy S. Negm H. Talaat 《The European physical journal. Special topics》2008,153(1):199-202
Photoacoustic absorption spectra of the
porous silicon samples (P-Si) of different thickness and porosity percentage
were measured at different modulation frequency. The absorption edge of the
P-Si layer for all samples shows a blue shift from that of crystalline
silicon (C-Si) at 1.1 eV. At low modulation frequency the estimated energy
gap (1.88 eV) is almost the same for all samples and the PA signal increases
as the porosity percentage increases. At the higher modulation frequency,
the spectra show an increase in the energy gap indicating the effect of
quantum confinement as the porosity increasing. The Raman shifts of the P-Si
samples are correlated with the particle size leading to an estimated
average particle size. The quantum confinement interpretation of the PA
results is in agreement with the Raman measurements that indicate the
presence of such nanostructure in the P-Si layer. 相似文献
24.
Azotobacter vinelandii, a nitrogen-fixing soil bacterium, secretes in iron deficiency azotobactin delta, a highly fluorescent pyoverdin-like chromopeptidic hexadentate siderophore. The chromophore, derived from 2,3-diamino-6,7 dihydroxyquinoline, is bound to a peptide chain of 10 amino acids: (L)-Asp-(D)-Ser-(L)-Hse-Gly-(D)-beta-threo-HOAsp-(L)-Ser-(D)-Cit-(L)-Hse-(L)-Hse lactone-(D)-N(delta)-Acetyl, N(delta)-HOOrn. Azotobactin delta has three different iron(III) binding sites which are one hydroxamate group at the C-terminal end of the peptidic chain (N(delta)-Acetyl, N(delta)-HOOrn), one alpha-hydroxycarboxylic function in the middle of the chain (beta-threo-hydroxyaspartic acid), and one catechol group on the chromophore. The coordination properties of its iron(III) and iron(II) complexes were measured by spectrophotometry, potentiometry, and voltammetry after the determination of the acid-base functions of the uncomplexed free siderophore. Strongly negatively charged ferric species were observed at neutral p[H]'s corresponding to a predominant absolute configuration Lambda of the ferric complex in solution as deduced from CD measurements. The presence of an alpha-hydroxycarboxylic chelating group does not decrease the stability of the iron(III) complex when compared to the main trishydroxamate siderophores or to pyoverdins. The value of the redox potential of ferric azotobactin is highly consistent with a reductive step by physiological reductants for the iron release. Formation and dissociation kinetics of the azotobactin delta ferric complex point out that both ends of this long siderophore chain get coordinated to Fe(III) before the middle. The most striking result provided by fluorescence measurements is the lasting quenching of the fluorophore in the course of the protonation of the ferric azotobactin delta complex. Despite the release of the hydroxyacid and of the catechol, the fluorescence remains indeed quenched, when iron(III) is bound only to the hydroxamic acid, suggesting a folded conformation at this stage, around the metal ion, in contrast to the unfolded species observed for other siderophores such as ferrioxamine or pyoverdin PaA. 相似文献
25.
Abdallah R Meille V Shaw J Wenn D de Bellefon C 《Chemical communications (Cambridge, England)》2004,(4):372-373
A microstructured mesh contactor that can offer residence time of more than minutes is used for gas-liquid-solid hydrogenations and gas-liquid asymmetric hydrogenations. Applications for catalyst/chiral inductor screening and for kinetic data acquisition are demonstrated. 相似文献
26.
27.
Solid solutions of cadmium and lead fluoroapatite [Pb(10−x)Cdx(PO4)6F2 (0?x?5)] were synthesized by a wet process in a basic medium. Replacement of lead by cadmium induces a linear variation of the crystallographic parameters “a” and “c” according to Végard's law. The cadmium content, as obtained from the refinement, is in agreement with the chemical analysis. The distribution of the lead and cadmium ions between two non-equivalent crystallographic sites, M(1) and M(2), was determined by the Rietveld method. The site-occupancy factors of atoms clearly indicate a preference of cadmium for site M(1) in the apatite structure in agreement with its smaller ionic radii. A progressive shift of the F− ion toward the center of the triangles formed by the site M(2) metals has been observed with increasing cadmium content. 相似文献
28.
29.
High-sensitivity moiré interferometry and finite-element analysis are used to analyze the state of deformation and stress in the region of contact between a plane orthotropic rectangular punch bonded to a foundation with dissimilar elastic properties which models a highly loaded region of a composite material rocket motor casing. Stress distributions are presented for the contact region and an estimate of the maximum shear stress in the foundation is given. The displacement components show good qualitative agreement between analysis and experiment. The lack of quantitative agreement between the experimental and the finite-element analysis is attributed to uncertainty of the material properties. 相似文献
30.
Ahmed Abouelaz Enrico Casadio Tarabusi Abdallah Ihsane 《Mediterranean Journal of Mathematics》2009,6(3):303-316
We study the Radon transform R on the discrete Grassmannian of rank-d affine sublattices of Z
n
for 0 < d < n, extending and building on previous work of the first- and third-named authors in codimension 1. By analogy with the integral
geometry on Grassmannians in R
n
, various natural questions are treated, such as definition and properties of R and its dual transform R
*, function space setting, support theorems and inversion formulas. 相似文献