全文获取类型
收费全文 | 803篇 |
免费 | 26篇 |
国内免费 | 2篇 |
专业分类
化学 | 660篇 |
晶体学 | 2篇 |
力学 | 11篇 |
数学 | 77篇 |
物理学 | 81篇 |
出版年
2023年 | 13篇 |
2022年 | 46篇 |
2021年 | 45篇 |
2020年 | 18篇 |
2019年 | 19篇 |
2018年 | 13篇 |
2017年 | 14篇 |
2016年 | 30篇 |
2015年 | 24篇 |
2014年 | 24篇 |
2013年 | 56篇 |
2012年 | 72篇 |
2011年 | 86篇 |
2010年 | 49篇 |
2009年 | 32篇 |
2008年 | 60篇 |
2007年 | 39篇 |
2006年 | 30篇 |
2005年 | 32篇 |
2004年 | 31篇 |
2003年 | 16篇 |
2002年 | 17篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有831条查询结果,搜索用时 31 毫秒
811.
Antonio Caldarelli Valeria De Biasio Giovanni B. Giovenzana Gianpiero Mastronardo Roberto Negri 《Molecular diversity》2014,18(4):879-886
Cytotoxicity in the \(\upmu \hbox {M}\) range was observed in cancer cell lines treated with N,N, \(N^{\prime }\!,\!N^{\prime }\) -tetrabenzyl-4,5-diamino-2-cyclopentenone. Cell cycle analysis on HeLa cells showed a clear G1 phase arrest. A preliminary SAR on structural analogs was performed in order to identify the pharmacophores. 相似文献
812.
Alexander Filippov Maria Simonova Tatiana Kirila Gheorghe Fundueanu Valeria Harabagiu 《Journal of Macromolecular Science: Physics》2015,54(9):1105-1121
Poly(N-isopropylacrylamide-co-maleic acid) [poly(NIPAAm-co-MA)] linear copolymer with comonomer molar ratio NIPAAm:MA = 94:6 was synthesized by free-radical copolymerization. The molar mass, MsD = 28,000 Da, of poly(NIPAAm-co-MA) was determined using hydrodynamic methods. The self-assembly of poly(NIPAAm-co-MA) in aqueous solution at a concentration of 0.015 g cm?3 within the pH interval from 1.8 to 10.6 and the temperature interval from 22 to 60°C was investigated by static and dynamic light scattering. The copolymer showed a double temperature and pH responsiveness. Three types of particles, namely, macromolecules (or unimers), micellar-like structures, and loose aggregates existed in the poly(NIPAAm-co-MA) aqueous solutions. The fraction of dissolved entities and the hydrodynamic radii of the micellar-like structures and loose aggregates depended considerably on temperature and pH. The temperature of the phase separation and the width of the phase separation interval increased with pH. An influence of pH on kinetic processes in poly(NIPAAm-co-MA) solutions was observed. 相似文献
813.
Dr. Ananya Sen Dr. Valeria Lepere Dr. Katia Le Barbu‐Debus Prof. Dr. Anne Zehnacker 《Chemphyschem》2013,14(15):3559-3568
The gas‐phase structures of the cinchona alkaloids, hydroquinine and its pseudoenantiomer hydroquinidine, are studied in a supersonic expansion by means of laser‐induced fluorescence and IR/UV double‐resonance spectroscopy. Vibrational spectroscopy combined with density functional calculations show that the conformational properties of the two pseudoenantiomers are identical. In both cases, they exist in two isoenergetic forms, with similar IR spectra. Both conformers are similar to the most stable cis‐γ‐open form of quinine; they differ from each other by the position of the ethyl substituent attached to the quinuclidine ring. Further differences between the two conformers are observed in the laser‐induced fluorescence spectrum. The first electronic transition is characterized by time‐dependent density functional theory and RI‐cc2 calculations, and is of ππ* nature. The results described here emphasize the role of the ethyl substituent in the structural differences between pseudoenantiomers of cinchona alkaloids. 相似文献
814.
Hassan N Verdinelli V Ruso JM Messina PV 《Langmuir : the ACS journal of surfaces and colloids》2011,27(14):8905-8912
Silica-based nanomaterials are of great interest because of their potential applications in constructing electronic and optoelectronic nanodevices. Especially significant are those that combine the properties of photonic crystal with a fibrous semiconductor structure. Here we report the use of microemulsion droplet systems as a simple and controllable route for the synthesis of 3D opals materials with an unusual fibrous microstructure similar to those that exist in nature. By this method, we demonstrate the creation of very long fibrils of 30-50 nm diameter and more than 20 μm length showing simultaneous short and long wavelength light emissions and band gap values (5.50 and 4.41 eV) comparable to those obtained for silicon-based metal oxide semiconductors. 相似文献
815.
Perioli L Ambrogi V Pagano C Massetti E Rossi C 《Colloids and surfaces. B, Biointerfaces》2011,84(2):413-420
The aim of this work was the realization of new formulations for vaginal application to improve the pharmacological effect of benzydamine, displaying both anti-inflammatory and antiseptic activities. For this reasons, this drug was formulated in solid dispersions, by using the mucoadhesive polymers HPMC and/or Carbopol(?), then compressed. Tablets were characterized by studies of friability, hardness, hydration, DSC, mucoadhesion and in vitro release. Kinetics, responsible for drug delivery, was investigated as well. Tablets prepared by using only HPMC showed the best results in terms of swelling and mucoadhesion (time and force) together with prolonged and complete drug release, by diffusive mechanism, through gelled layer. Despite the good mucoadhesive properties, Carbopol(?) does not represent a good excipient because, after the contact with water, it generates a spongy gel layer, not homogeneous, stiff, brittle and with breaking tendency when highly swelled. This kind of gel does not guarantee a linear drug release and could provoke discomfort because of fragment release. HPMC mucoadhesive tablets could be a proper delivery system for benzydamine administration representing a good alternative to traditional dosage forms for vaginal topical therapy. 相似文献
816.
Reactions of KPPh2 with the dimeric cyclopalladated complex {Pd(N∩C)(μ-Cl)}21 derived from N,N-dimethylbenzylamine were studied using different reagent ratios, temperature, reaction time, concentrations and solvents. Complex 3, the μ-Cl-μ-PPh2 analog of 1, was obtained in 76% yield in the one-hour reaction using the 1:1 ratio of dimer 1 and KPPh2 in THF at rt. ortho-(Diphenylphosphino)benzylamine 4 was synthesized in 58% yield by reacting complex 1 with 4.5 equiv. of KPPh2 in THF at rt. A possible mechanism of the aminophosphine formation is proposed on the basis of the experimental data including 31P{1H} NMR spectra of reaction mixtures. 相似文献
817.
Albahily K Fomitcheva V Gambarotta S Korobkov I Murugesu M Gorelsky SI 《Journal of the American Chemical Society》2011,133(16):6380-6387
Reaction of the divalent [(t-Bu)NP(Ph)(2)N(t-Bu)]CrCl(2)Li(THF)(2) (1) with 1 equiv of vinyl Grignard (CH(2)=CH)MgCl reproducibly afforded the triangulo {π-[(t-Bu)N-P(Ph)(2)-N(t-Bu)]Cr}(2)(μ,μ',η(4),η(4)'-C(4)H(4)){σ-[(t-Bu)N-P(Ph)(2)-N(t-Bu)]Cr} (2) containing a σ-/π-bonded butadiene-diyl unit. The diene-diyl moiety was generated by an oxidative coupling and deprotonation of two vinyl anions. The crystal structure revealed that of the three chromium atoms, each bearing one NPN ligand, two are perpendicularly bonded to the two sides of the π-system of the butadiene-diyl residue in a sort of inverted sandwich type of structure. The third is instead coplanar with the doubly deprotonated C(4) unit and σ-bonded to the two terminal carbon atoms. Despite the appearance as a Cr(II)/Cr(I) mixed valence species, DFT calculations have revealed that the structure of 2 consists of three divalent chromium atoms, while the additional electron resides on the π-system of the bridging organic residue. Complex 2 behaves as a single component selective catalyst for ethylene trimerization. 相似文献
818.
Cucurbit[6]uril nanocavity as an enhanced spectrofluorimetric method for the determination of pyrene
The effect of the addition of macrocyclic host cucurbit[6]uril (CB6) on the photophysical properties of polycyclic aromatic hydrocarbon pyrene (PYR) was analyzed. The fluorescence emission spectra of the aromatic compound were determined at 25.0 °C in different acidic media (HCl 18%, w/v, or HCOOH 55%, w/v) with and without CB6. A significant enhancement in the fluorescence signals in the presence of CB6 was observed. The average values of the association constant (KA) for the 1:1 stoichiometry complex and the relative fluorescence quantum yield ratio between the complexed and free PYR (?PYR–CB6/?PYR) in acidic media were (4.0 ± 0.5) × 102 M−1 and (5.7 ± 0.2), respectively.The analytical parameters improved in the presence of CB6. The relative decrease in the limit of detection was 92%. The matrix effect was evaluated in fortified samples of tap water and tea extracts. Apparent recoveries obtained by the proposed method in tap water and tea extracts were (82–103)% and (89–99)%, respectively. Selectivity studies with inorganic and organic species were performed. The method is rapid, direct, selective and simple. 相似文献
819.
Laurent Desvillettes François Golse Valeria Ricci 《Journal of statistical physics》2008,131(5):941-967
We propose a mathematical derivation of Brinkman’s force for a cloud of particles immersed in an incompressible viscous fluid.
Specifically, we consider the Stokes or steady Navier-Stokes equations in a bounded domain Ω⊂ℝ3 for the velocity field u of an incompressible fluid with kinematic viscosity ν and density 1. Brinkman’s force consists of a source term 6π
ν
j where j is the current density of the particles, and of a friction term 6π
ν
ρ
u where ρ is the number density of particles. These additional terms in the motion equation for the fluid are obtained from the Stokes
or steady Navier-Stokes equations set in Ω minus the disjoint union of N balls of radius ε=1/N in the large N limit with no-slip boundary condition. The number density ρ and current density j are obtained from the limiting phase space empirical measure
, where x
k
is the center of the k-th ball and v
k
its instantaneous velocity. This can be seen as a generalization of Allaire’s result in [Arch. Ration. Mech. Anal. 113:209–259,
[1991]] who considered the case of periodically distributed x
k
s with v
k
=0, and our proof is based on slightly simpler though similar homogenization arguments. Similar equations are used for describing
the fluid phase in various models for sprays. 相似文献
820.
Abdulkarim A. Amirov Yogesh A. Chaudhari Subhash T. Bendre Ksenia A. Chichay Valeria V. Rodionova Dibir M. Yusupov Zairbek M. Omarov 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(4):63
Multiferroic BiFe1?xZn x O3 ceramics were prepared by solution combustion method. Their structure, magnetoelectric, dielectric, magnetic, thermal characteristics were studied. The magnetic M(T) and heat capacity C p (T) measurements demonstrate an antiferromagnetic to paramagnetic phase transition (T N ) around 635 K. The anomaly on the temperature dependence of the dielectric constant near T N was observed, which could be induced by the magnetoelectric coupling between electric and magnetic ordering. The magnetoelectric behavior was also confirmed by the linear relation between Δε and M2, which is in the agreement of the Ginzburg-Landau theory for the second-order phase transition. 相似文献