全文获取类型
收费全文 | 285篇 |
免费 | 20篇 |
专业分类
化学 | 204篇 |
晶体学 | 12篇 |
力学 | 4篇 |
数学 | 19篇 |
物理学 | 66篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 16篇 |
2021年 | 10篇 |
2020年 | 13篇 |
2019年 | 19篇 |
2018年 | 7篇 |
2017年 | 18篇 |
2016年 | 19篇 |
2015年 | 11篇 |
2014年 | 16篇 |
2013年 | 30篇 |
2012年 | 15篇 |
2011年 | 20篇 |
2010年 | 10篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 15篇 |
2006年 | 10篇 |
2005年 | 8篇 |
2004年 | 11篇 |
2003年 | 1篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1995年 | 2篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有305条查询结果,搜索用时 67 毫秒
71.
S. Naveen Priti Adlakha Chintan Dholakia Anamik Shah M. A. Sridhar J. Shashidhara Prasad 《Structural chemistry》2006,17(6):569-575
A novel dihydropyrimidine (DHPM) derivative bearing a carbamoyl moiety was synthesized by an efficient three-component Biginelli reaction and was characterized spectroscopically and finally confirmed by X-ray diffraction studies. The title compound C20H20N4O4 crystallizes in the monoclinic space group P21/c with cell parameters a=12.8970(12) Å, b=13.6210(11) Å, c=11.8420(13) Å, β=115.860(3)°, Z=4 and V=1872.0(3) Å3. The conformation of the dihydropyrimidine ring is unusual; it is planar instead of the usual boat-like conformation. The 3-nitrophenyl ring is orthogonal to the 3,4-DHPM ring. The carbonyl group is in an anti-clinal conformation. 相似文献
72.
Synthesis and Crystal Structure of [2-(4-chlorobenzoyloxy)-5-methylphenyl]-(4-methylphenyl)methanone
S. Naveen T. D. Venu S. Shashikanth M. A. Sridhar J. Shashidhara Prasad 《Journal of chemical crystallography》2007,37(12):787-791
[2-(4-Chlorobenzoyloxy)-5-methylphenyl]-(4-methylphenyl)methanone was synthesized and characterized by spectroscopic and X-ray diffraction methods. The molecule crystallizes in the monoclinic space group P21/c with cell parameters a = 13.7530(19) Å, b = 10.0560(19) Å, c = 13.469(3) Å, β = 100.630(7)° and Z = 4. There is a large discrepancy between the carbonyl group bond lengths of ketone and the ester. The structure exhibits intermolecular hydrogen bonds of the type C–H···O. 相似文献
73.
Acoustic field assisted demixing was employed to decrease the demixing time in aqueous two-phase systems (polyethylene glycol-maltodextrin and polyethylene glycol-potassium phosphate). Application of acoustic field has decreased the demixing time in polyethylene glycol-maltodextrin by around twofold and up to about 3.2-fold in polyethylene glycol-potassium phosphate systems. Ultrasonication has induced mild circulation currents in the phase dispersion, which has enhanced the rate of droplet coalescence, eventually resulting in decreased demixing time. In the polyethylene glycol-maltodextrin system, phase demixing was found to depend greatly on which of the phases iscontinuous and viscosity of the continuous phase was observed to have a strong influence on the movement of the droplets and hence controlling the phase demixing rate. In case of the polyethylene glycol-potassium phosphate system, droplet coalescence was found to play a critical role in phase demixing. Addition of NaCl increased the demixing time and presence of Escherichia coli cells did not seem to have any influence on phase demixing. 相似文献
74.
J.N. Sharma Naveen Thakur Surinder Singh 《International Journal of Solids and Structures》2009,46(11-12):2309-2319
The present article is devoted to investigate the propagation of elasto-thermodiffusive (ETNP) surface waves in a homogeneous isotropic, thermally conducting semiconductor material of half-space with relaxation of heat and charge carrier fields. The secular equation, a more general functional relation, that governs the propagation of elasto-thermodiffusive (ETNP) surface waves in homogeneous isotropic, thermoelastic semiconductor material halfspace with relaxation of heat and charge carrier fields has been derived by solving a system of coupled partial differential equations. A hybrid numerical technique consisting of Descartes algorithm for solving complex polynomial characteristic equation along with functional iteration scheme has been successfully used to solve the secular equation in order to obtain dispersion curves, attenuation coefficient and specific loss factor of energy dissipation for p-type germanium (Ge) semiconductor. Some particular forms of the general secular equation governing the propagation of elasto-thermodiffusive (ETN/ETP), thermoelastic (ET), elastodiffusive (EP/EN) and thermodiffusive (TP/TN) surface waves have been also deduced and discussed. In order to illustrate the analytical development, the numerical solution of the secular equation and other relevant relations under different situations is also carried out for Ge semiconductor materials to characterize the elasto-thermodiffusive (ETP) and thermodiffusive (TP) surface waves. The computer simulated results have been presented graphically in respect of the dispersion curves, attenuation coefficient and specific loss factor. 相似文献
75.
Though the predictions of the standard model (SM) are in excellent agreement with experiments, there are still several theoretical
problems associated with the Higgs sector of the SM, where it is widely believed that some new physics will take over at the
TeV scale. One beyond the SM theory which resolves these problems is the Little Higgs (LH) model. In this work we have investigated
the effects of the LH model on γγ → γγ scattering [1].
相似文献
76.
Electrokinetic demixing of aqueous two-phase polymer/salt systems is demonstrated, resulting in significant enhancement in demixing rates by about 1-4-fold. The effect of field polarity, field strength, volume ratio, and phase composition on phase demixing has been studied. Further the influence of these parameters on phase demixing could be explained based on the hydrodynamic flow-electroosmotic flow (HEF) model. 相似文献
77.
78.
G.E. Barberis D. Davidov J.P. Donoso F.G. Gandra C. Rettori J.F. Suassuna 《Solid State Communications》1978,28(6):427-433
The resonance properties of the Γ6 ground state of Nd+3 in the type II Superconductors CeRu2, ThRu2 and LaRu2 are reported. A significant change of the g value and lineshape were observed for CeRu2:Nd upon going from the normal state to the superconducting state. The data in the superconducting state is discussed in terms of conduction electron's pairing mechanism and inhomogeneous field distribution mechanism in the superconducting state. A preliminary lineshape analysis is not completely consistent with previous theoretical predictions and experiments. 相似文献
79.
Iqbal K Malik A Mukhtar N Anis I Khan SN Choudhary MI 《Chemical & pharmaceutical bulletin》2004,52(7):785-789
Three C-alkylated flavonoids 7-O-alpha-D-glucopyranosyl-3,5-dihydroxy-3'-(4"-acetoxyl-3"-methylbutyl)-6,4'-dimethoxyflavone (1), 7-O-alpha-D-glucopyranosyl-3,4'-dihydroxy-3'-(4"-acetoxyl-3"-methylbutyl)-5,6-dimethoxyflavone (2), 3,7,4'-trihydroxy-3'-(8"-acetoxy-7"-methyloctyl)-5,6-dimethoxyflavone (3) and a trans-clerodane type diterpenoid (-)-6beta-hydroxy-5beta,8beta,9beta,10alpha-cleroda-3,13-dien-16,15-olid-18-oic acid (4) are reported from Duranta repens along with (+)-hardwickiic acid (5) and (+)-3,13-clerodadien-16,15-olid-18-oic acid (6), isolated for the first time from this species. Their structures were established on the basis of the spectral methods, especially two dimensional (2D) NMR spectroscopy. 相似文献
80.
Rapid control of wound infections by targeted photodynamic therapy monitored by in vivo bioluminescence imaging 总被引:12,自引:0,他引:12
Hamblin MR O'Donnell DA Murthy N Contag CH Hasan T 《Photochemistry and photobiology》2002,75(1):51-57
The worldwide rise in antibiotic resistance necessitates the development of novel antimicrobial strategies. In this study we report on the first use of a photochemical approach to destroy bacteria infecting a wound in an animal model. Following topical application, a targeted polycationic photosensitizer conjugate between poly-L-lysine and chlorin(e6) penetrated the gram (-) outer bacterial membrane, and subsequent activation with 660 nm laser light rapidly killed Escherichia coli infecting excisional wounds in mice. To facilitate real-time monitoring of infection, we used bacteria that expressed the lux operon from Photorhabdus luminescens; these cells emitted a bioluminescent signal that allowed the infection to be rapidly quantified, using a low-light imaging system. There was a light-dose dependent loss of luminescence in the wound treated with conjugate and light, not seen in untreated wounds. Treated wounds healed as well as control wounds, showing that the photodynamic treatment did not damage the host tissue. Our study points to the possible use of this methodology in the rapid control of wounds and other localized infections. 相似文献