全文获取类型
收费全文 | 1394篇 |
免费 | 44篇 |
国内免费 | 5篇 |
专业分类
化学 | 894篇 |
力学 | 39篇 |
数学 | 328篇 |
物理学 | 182篇 |
出版年
2022年 | 12篇 |
2021年 | 14篇 |
2020年 | 8篇 |
2019年 | 21篇 |
2018年 | 16篇 |
2017年 | 15篇 |
2016年 | 32篇 |
2015年 | 40篇 |
2014年 | 39篇 |
2013年 | 96篇 |
2012年 | 89篇 |
2011年 | 118篇 |
2010年 | 67篇 |
2009年 | 64篇 |
2008年 | 111篇 |
2007年 | 84篇 |
2006年 | 75篇 |
2005年 | 71篇 |
2004年 | 85篇 |
2003年 | 41篇 |
2002年 | 49篇 |
2001年 | 14篇 |
2000年 | 21篇 |
1999年 | 18篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 17篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1971年 | 4篇 |
1936年 | 3篇 |
排序方式: 共有1443条查询结果,搜索用时 15 毫秒
151.
An electrochemical biosensor capable of indirect detection of DNA damage induced by any one of the three endocrine-disrupting compounds (EDCs) – bisphenol A (BPA), 4-nonylphenol (NP) and 4-t-octylphenol (OP), has been researched and developed. The methylene blue (MB) dye was used as the redox indicator. The glassy carbon electrode (GCE) was modified by the assembled dsDNA/graphene oxide-chitosan/gold nano-particles to produce a dsDNA/GO-CS/AuNPs/GCE sensor. It was characterized with the use of electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and scanning electron microscopy (SEM) techniques. The loading/release of the MB dye by the dsDNA/GO-CS/AuNPs film was investigated, and the results showed that the process was reversible. Based on this, the sensor was used to measure the difference between the loading capabilities of intact and damaged dsDNA in the films. The sensor was then successfully applied to detect DNA damage electrochemically. The differential pulse voltammetry (DPV) peak current ratio for MB, observed before and after DNA damage, increased linearly in the presence the BPA, NP or OP compounds; the treatment range was 10–60 min, and the respective damage rates were 0.0069, 0.0044 and 0.0031 min−1, respectively. These results were confirmed by the binding constants: 2.09 × 106 M−1 (BPA-DNA), 1.28 × 106 M−1 (NP-DNA) and 9.33 × 105 M−1 (OP-DNA), all of which were obtained with the use of differential pulse stripping voltammetry (DPSV). 相似文献
152.
Biofunctionalization of Polyoxometalates with DNA Primers,Their Use in the Polymerase Chain Reaction (PCR) and Electrochemical Detection of PCR Products 下载免费PDF全文
Dr. Ahmed M. Debela Dr. Mayreli Ortiz Dr. Valerio Beni Prof. Serge Thorimbert Dr. Denis Lesage Prof. Richard B. Cole Prof. Ciara K. O'Sullivan Prof. Bernold Hasenknopf 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(49):17721-17727
The bioconjugation of polyoxometalates (POMs), which are inorganic metal oxido clusters, to DNA strands to obtain functional labeled DNA primers and their potential use in electrochemical detection have been investigated. Activated monooxoacylated polyoxotungstates [SiW11O39{Sn(CH2)2CO}]8? and [P2W17O61{Sn(CH2)2CO}]6? have been used to link to a 5′‐NH2 terminated 21‐mer DNA forward primer through amide coupling. The functionalized primer was characterized by using a battery of techniques, including electrophoresis, mass spectrometry, as well as IR and Raman spectroscopy. The functionality of the POM‐labeled primers was demonstrated through hybridization with a surface‐immobilized probe. Finally, the labeled primers were successfully used in the polymerase chain reaction (PCR) and the PCR products were characterized by using electrophoresis. 相似文献
153.
A function on an algebra is congruence preserving if for any congruence, it maps congruent elements to congruent elements. We show that on a free monoid generated by at least three letters, a function from the free monoid into itself is congruence preserving if and only if it is of the form \({x \mapsto w_{0}xw_{1} \cdots w_{n-1}xw_n }\) for some finite sequence of words \({w_0,\ldots ,w_n}\). We generalize this result to functions of arbitrary arity. This shows that a free monoid with at least three generators is a (noncommutative) affine complete algebra. As far as we know, it is the first (nontrivial) case of a noncommutative affine complete algebra. 相似文献
154.
The authors show that for any e ∈]0,1[,there exists an analytic outside zero solution to a uniformly elliptic conformal Hessian equation in a ball B C R5 which belongs to C1'ε(B) \ C1'ε+(B). 相似文献
155.
A particle method has been used to simulate the vorticity transport in a two-dimensional flow of an incompressible inviscid fluid. In this method, not only the location and the circulation of the particle are used but also the moments of the internal vorticity. The transport equation for these moments has been derived from the vorticity transport equation. The method has been compared to the usual particle method as well as to Teng's elliptic vortex model. The test case is that of the evolution of two circular patches of vorticity already used by Teng. To cite this article: A. Beaudoin et al., C. R. Mecanique 330 (2002) 51–56 相似文献
156.
A rapid kinetic method for the simultaneous determination of levodopa, dopamine, and dobutamine was examined and developed.
It was based on a consecutive reaction of a reduction of Cu(II) to Cu(I) by catecholamines, followed by the complexation of
Cu(I) with neocuproine to form a yellow product in an acetic acid-acetate buffer. Spectrophotometric data were recorded at
453 nm (wavelength at the yellow complex absorption maximum) for 300 s. Linear calibrations were obtained in the concentration
ranges of (0.08–1.44) × 10−5 mol L−1, (0.08–1.44) × 10−5 mol L−1, and (0.16–1.44) × 10−5 mol L−1 for levodopa, dopamine, and dobutamine, respectively. A variety of multivariate calibration models was developed for simultaneous
analysis of the three analytes; while most models produced satisfactory prediction results for synthetic samples, the hybrid
linear analysis method was arguably the best-performing (relative prediction error, RPET = 6.6 %). The proposed method was
applied to an analysis of spiked rabbit serum samples and the results showed good agreement with the high performance liquid
chromatography measurements. 相似文献
157.
This tutorial review briefly surveys the chronological evolution of biosensor concepts based on electrogenerated polymers. The most common procedures of biomolecule immobilization are classified as direct electropolymerization, physical entrapment, covalent linkage, and anchoring by affinity interactions via electropolymerized films. These are discussed, and recent bioanalytical applications are described. The discussion emphasizes the use of templates for controlling the formation of nanowires and composite polymers. Recent advances in the design of three-dimensional biological architectures are also highlighted. 相似文献
158.
The concept of colloidal molecules was first evoked by van Blaaderen in 2003 for describing small non-spherical colloids made of the aggregation of a small number of particles. He predicted original properties to the complex assemblies of such colloids, in particular in optics. This critical review deals with the different strategies reported for creating robust clusters of spherical particles which could mimic the space-filling models of simple conventional molecules. These routes concern either the controlled clustering of preformed colloids directed by coalescence, physical routes, chemical routes, or 2-D/3-D geometrical confinement, or strategies starting from a single colloid which is decorated by satellite colloids by taking advantage of controlled phase separation or nucleation and growth phenomena. These routes are compared from the viewpoint of the accessible shapes, their tunability and scalability (146 references). 相似文献
159.
Bojan Šarac Janez Cerkovnik Bernard Ancian Guillaume Mériguet Gaëlle M. Roger Serge Durand-Vidal Marija Bešter-Rogač 《Colloid and polymer science》2011,289(14):1597-1607
The complex aggregation processes of dodecyltrimethylammonium chloride (DTAC) have been studied in dilute solutions of sodium
salicylate (NaSal) by isothermal titration calorimetry and electrical conductivity at temperatures between 278.15 K and 318.15 K.
A structural transformation that was dependent on the concentrations of DTAC and NaSal was observed. The micellization process
in dilute solutions of DTAC has been subjected to a detailed thermodynamic analysis and shown to occur at considerably lower
critical micelle concentrations than reported for DTAC in water and NaCl solutions. Gibbs free energy, Δ
mic
G
o, and entropy, Δ
mic
S
o, were deduced by taking into account the degree of micelle ionization, β, estimated from conductivity measurements. From the temperature dependence of the enthalpy of micellization, Δ
mic
H
o, the heat capacities of micellization, Dmic cpo {\Delta_{{{\rm mic} }}}c_p^o were determined and discussed in terms of the removal of large areas of non-polar surface from contact with water upon micellization.
The process is exothermic at all temperatures, indicating, in addition to the hydrophobic effect, the presence of strong interactions
between surfactant and salicylate ions. These were confirmed by 1H NMR spectroscopy and diffusion NMR experiments. Salicylate ions not only interact with the headgroups but also insert further
into the micelle core. At c
NaSal/c
DTAC > 2.5, the structural rearrangements occur even at relatively low concentrations of NaSal. 相似文献
160.
Quantitative Ultrafast (UF) 2D NMR is a very promising methodology enabling the acquisition of 2D spectra in a single scan. The analytical performances of UF 2D NMR have been highly increased in the last few years, however little is known about the sensitivity of ultrafast experiments versus conventional 2D NMR. A fair and relevant comparison has to consider the Signal-to-Noise Ratio (SNR) per unit of time, in order to answer the following question: for a given experiment time, should we run a conventional 2D experiment or is it preferable to accumulate ultrafast acquisitions? To answer this question, we perform here a systematic comparison between accumulated ultrafast experiments and conventional ones, for different experiment durations. Sensitivity issues and other analytical aspects are discussed for the COSY experiment in the context of quantitative analysis. The comparison is first carried out on a model sample, and then extended to model metabolic mixtures. The results highlight the high analytical performance of the "multi-scan single shot" approach versus conventional 2D NMR acquisitions. This result is attributed to the absence of t(1) noise in spatially encoded experiments. The multi-scan single shot approach is particularly interesting for quantitative applications of 2D NMR, whose occurrence in the literature has been greatly increasing in the last few years. 相似文献