全文获取类型
收费全文 | 680篇 |
免费 | 2篇 |
国内免费 | 2篇 |
专业分类
化学 | 396篇 |
晶体学 | 3篇 |
力学 | 25篇 |
数学 | 119篇 |
物理学 | 141篇 |
出版年
2022年 | 2篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 16篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 25篇 |
2012年 | 45篇 |
2011年 | 58篇 |
2010年 | 25篇 |
2009年 | 22篇 |
2008年 | 47篇 |
2007年 | 40篇 |
2006年 | 47篇 |
2005年 | 43篇 |
2004年 | 42篇 |
2003年 | 30篇 |
2002年 | 29篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 17篇 |
1998年 | 3篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 2篇 |
排序方式: 共有684条查询结果,搜索用时 15 毫秒
101.
Limoges B Marchal D Mavré F Savéant JM Schöllhorn B 《Journal of the American Chemical Society》2008,130(23):7259-7275
The use of enzyme labeling techniques to convert biorecognition events into high sensitivity electrochemical signals may follow two different strategies. One, in which the current is the electrocatalytic response of a redox couple serving as cosubstrate to a redox enzyme label and another that consists in the detection of an electrochemically active product of the enzyme label. The theoretical relationships that link, in the latter case, the electrochemical current response to the amount of recognized labeled target analyte are established for steady-state diffusion-convection chronoamperometric regimes. Two governing parameters thus emerge. One measures the Michaelis-Menten competition in the enzyme kinetics. The other characterizes the competition between the enzymatic kinetics and the diffusion of the substrate. The electrochemical response is finally related to the labeled target analyte concentration in solution through the recognition isotherm. The direct electrochemical product detection thus provides a route to the characteristics of the recognition isotherm, which serves as a calibration curve in analytical applications. The establishment of further theoretical relationships allows one to surmise the increase in sensitivity that may be obtained by using cyclic voltammetry instead of steady-state chronoamperometry in standard electrochemical cells or by accumulation of the enzyme-product in cells of small volume/surface ratios. The theoretical predictions are tested with the example of the avidin-biotin recognition process in a system that involves alkaline phosphatase as enzyme label and 4-amino-2,6-dichlorophenyl phosphate as substrate, generating 4-amino-2,6-dichlorophenol as electrochemically active product. The advantages of the dichloro-substitution are discussed. The theoretical analysis is a requisite for a rational and realistic discussion of the analytical performances of the steady-state chronoamperometric and cyclic voltammetric approaches. These are shown to compare favorably with the best heterogeneous bioaffinity assays so far reported. 相似文献
102.
Shen J El Ojaimi M Chkounda M Gros CP Barbe JM Shao J Guilard R Kadish KM 《Inorganic chemistry》2008,47(17):7717-7727
A series of manganese(III) corroles were investigated as to their electrochemistry and spectroelectrochemistry in nonaqueous solvents. Up to three oxidations and one reduction were obtained for each complex depending on the solvents. The main compound discussed in this paper is the meso-substituted manganese corrole, (Mes 2PhCor)Mn, and the main points are how changes in axially coordinated anion and solvent will affect the redox potentials and UV-vis spectra of each electrogenerated species in oxidation states of Mn(III), Mn(IV), or Mn(II). The anions OAc (-), Cl (-), CN (-), and SCN (-) were found to form five-coordinate complexes with the neutral Mn(III) corrole while two OH (-) or F (-) anions were shown to bind axially in a stepwise addition to give the five- and six-coordinate complexes in nonaqueous media. In each case, complexation with one or two anionic axial ligands led to an easier oxidation and a harder reduction as compared to the uncomplexed four-coordinate species. 相似文献
103.
Henri Berestycki Jean-Michel Roquejoffre Luca Rossi 《Communications in Mathematical Physics》2016,343(1):207-232
We establish a new property of Fisher-KPP type propagation in a plane, in the presence of a line with fast diffusion. We prove that the line enhances the asymptotic speed of propagation in a cone of directions. Past the critical angle given by this cone, the asymptotic speed of propagation coincides with the classical Fisher-KPP invasion speed. Several qualitative properties are further derived, such as the limiting behaviour when the diffusion on the line goes to infinity. 相似文献
104.
105.
106.
The one-electron electrochemical and homogeneous oxidations of two closely similar aminophenols that undergo a concerted proton-electron transfer reaction, in which the phenolic proton is transferred to the nitrogen atom in concert with electron transfer, are taken as examples to test procedures that allow the separate determination of the degree of adiabaticity and the reorganization energy of the reaction. The Marcus (or Marcus-Hush-Levich) formalism is applicable in both cases, but not necessarily in its adiabatic version. Linearization of the activation-driving force laws simplifies the treatment of the kinetic data, notably allowing the use of Arrhenius plots to treat the temperature dependence of the rate constant. A correct estimation of the adiabaticity and reorganization energy requires the determination of the variation of the driving force with temperature. Application of these procedures led to the conclusion that, unlike previous reports, the homogeneous reaction is non-adiabatic, with a transmission coefficient of the order of 0.005, and that the self-exchange reorganization energy is about 1 eV lower than previously estimated. With such systems, the intramolecular reorganization energy, although sizable, is in fact rather modest, being only slightly larger than that for the outer-sphere electron transfer that produced the cation radical. The electrochemical reaction is, in contrast, adiabatic, as revealed by the temperature dependence of its standard rate constant obtained from cyclic voltammetric experiments. This difference in behavior is deemed to derive from the effect of the strong electric field within which the electrochemical reaction takes place, stabilizing a zwitterionic form of the reactant (in which the proton has been transferred from oxygen to nitrogen). Taking this difference in adiabaticity into account, the magnitudes of the reorganization energies of the two reactions appear to be quite compatible with one another, as revealed by an analysis of the solvent and intramolecular contributions in both cases. 相似文献
107.
Toubas D Essendoubi M Adt I Pinon JM Manfait M Sockalingum GD 《Analytical and bioanalytical chemistry》2007,387(5):1729-1737
The incidence of fungal infections, in particular candidiasis and aspergillosis, has considerably increased during the last
three decades. This is mainly due to advances in medical treatments and technologies. In high risk patients (e.g. in haematology
or intensive care), the prognosis of invasive candidiasis is relatively poor. Therefore, a rapid and correct identification
of the infectious agent is important for an efficient and prompt therapy. Most clinical laboratories rely on conventional
identification methods that are based on morphological, physiological and nutritional characteristics. However, these have
their limitations because they are time-consuming and not always very accurate. Moreover, molecular methods may be required
to determine the genetic relationship between the infectious strains, for instance in Candida outbreaks. In addition, the latter methods require time, expensive consumables and highly trained staff to be performed adequately.
In this study, we have applied the FTIR spectroscopic approach to different situations encountered in routine mycological
diagnosis. We show the potentials of this phenotypic approach, used in parallel with routine identification methods, for the
differentiation of 3 frequently encountered Candida species (C. albicans, C. glabrata and C. krusei) by using both suspensions and microcolonies. This approach, developed for an early discrimination, may help in the initial
choice of antifungal treatment. Furthermore, we demonstrate the feasibility of the method for intraspecies comparison (typing)
of 3 Candida species (C. albicans, C. glabrata and C. parapsilosis), particularly when an outbreak is suspected. 相似文献
108.
The possibility of internal standardisation in laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES)
of geological materials by added Sc2O3 and Y2O3 has been examined to cover the wide range of concentrations of major and minor constituents both in silicate rocks and limestones.
A Nd : YAG laser (355 nm, 10 Hz, 10 mJ per shot) was used for the ablation of discs obtained by fusion of the mixture of samples
and oxides of Sc and Y with lithium tetraborate. The flux/sample ratio was in the range from 6 to 10. The contents of analytes
were within the concentration range from hundredths to tens of percentage. The trace elements copper and nickel were studied,
too. An ICP emission spectrometer OPTIMA 3000 DV was used for the measurement of Si, Al, Ca, Mg, Sr, Ba, Fe, Ti, Mn, Ni, Cu,
Na and K analyte lines and Y and Sc reference lines in the axial observation mode. The long-term and the short-term repeatability
of measurement were improved by employing scandium or yttrium internal references lines for the above analytes from 6% to
1.5% of RSD and from 2.4% to 1.0% of RSD, respectively. The correlation of signals with concentrations was improved in terms
of the correlation coefficient r from 0.90–0.97 to 0.98–0.998 and the relative uncertainity on the centroid of concentrations was improved 2–3 times. A single
calibration graph covering the concentration range both in silicates and carbonates is possible for each of elements, as the
matrix effects are compensated for by internal standards and the excess of Li2B4O7.
Received: 20 June 1998 / Revised: 20 July 1998 / Accepted: 21 September 1998 相似文献
109.
Laura Marcu Warren S. Grundfest Jean-Michel I. Maarek 《Photochemistry and photobiology》1999,69(6):713-721
To study the photobleaching of the main fluorescent compounds of the arterial wall, we repeatedly measured the time-resolved fluorescence of elastin, collagen and cholesterol during 560 s of excitation with nitrogen laser pulses. Three fluence rate levels were used: 0.72, 7.25 and 21.75 microW/mm2. The irradiation-related changes of the fluorescence intensity and of the time-resolved fluorescence decay constants were characterized for the emission at 390, 430 and 470 nm. The fluorescence intensity at 390 nm decreased by 25-35% when the fluence delivered was 4 mJ/mm2, a common value in fluorescence studies of the arterial wall. Cholesterol fluorescence photobleached the most, and elastin fluorescence photobleached the least. Photobleaching was most intense at 390 nm and least intense at 470 nm such that the emission spectra of the three compounds were markedly distorted by photobleaching. The time-resolved decay constants and the fluorescence lifetime were not altered by irradiation when the fluence was below 4 mJ/mm2. The spectral distortions associated with photobleaching complicate the interpretation of arterial wall fluorescence in terms of tissue content in elastin, collagen and cholesterol. Use of the time-dependent features of the emission that are not altered by photobleaching should increase the accuracy of arterial wall analysis by fluorescence spectroscopy. 相似文献
110.
Gleb S. Pokrovski Jean-Michel Bény Alexandre V. Zotov 《Journal of solution chemistry》1999,28(12):1307-1327
Solubilities of arsenolite (As2O3, cub.) were measured from 22 to 90°C in water–acetone, water–acetic acid, and water—formic acid solutions of compositions ranging from the pure organic compound to pure water. Raman spectra were obtained at ambient temperature on As-containing water–acetic acid and water–acetone solutions. Results show that arsenic solvation by these organic compounds is negligible and hydroxide species dominate As speciation over a wide range of water activity (aH
2
O> 0.01). The solubility data were analyzed using an approach based on stoichiometric hydration reactions. Results show that As2O3 solubility can be described as a function of water activity, independently of the nature of the organic compound, by involving two neutral As hydroxide complexes: As(OH)3 and As(OH)3·4H2O. Stability constants derived for these species indicate that hydration weakens with increasing temperature. Calculations using these constants show that at low temperatures the tetrahydrate As(OH)3·4H2O is dominant in water-rich solutions; by contrast, in high-temperature crustal fluids, As(OH)3 becomes the major As species. The proposed hydration model can be used to analyze solubility of arsenic-bearing minerals and arsenic transport in complex H2O–CO2—electrolyte solutions encountered in natural and industrial environments. 相似文献