全文获取类型
收费全文 | 1414篇 |
免费 | 208篇 |
国内免费 | 273篇 |
专业分类
化学 | 1403篇 |
晶体学 | 32篇 |
力学 | 5篇 |
综合类 | 20篇 |
数学 | 1篇 |
物理学 | 434篇 |
出版年
2024年 | 3篇 |
2023年 | 21篇 |
2022年 | 51篇 |
2021年 | 59篇 |
2020年 | 72篇 |
2019年 | 66篇 |
2018年 | 64篇 |
2017年 | 59篇 |
2016年 | 61篇 |
2015年 | 58篇 |
2014年 | 81篇 |
2013年 | 125篇 |
2012年 | 103篇 |
2011年 | 101篇 |
2010年 | 63篇 |
2009年 | 67篇 |
2008年 | 69篇 |
2007年 | 82篇 |
2006年 | 52篇 |
2005年 | 50篇 |
2004年 | 48篇 |
2003年 | 55篇 |
2002年 | 51篇 |
2001年 | 57篇 |
2000年 | 52篇 |
1999年 | 52篇 |
1998年 | 36篇 |
1997年 | 34篇 |
1996年 | 26篇 |
1995年 | 32篇 |
1994年 | 31篇 |
1993年 | 21篇 |
1992年 | 21篇 |
1991年 | 16篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有1895条查询结果,搜索用时 763 毫秒
51.
The solvatochromic behavior of a penta‐tert‐butyl prydinium N‐phenolate betaine dye was studied using UV‐visible spectrophotometry in several binary mixture solvents. The solvent polarity parameter, ET (1) (kcal. mol?1) was calculated from the position of the longest‐wavelength intramolecular charge transfer absorption band of this penta‐tert‐butyl betaine dye. For binary solvent mixtures, all plots of ET (1) versus the mole fraction of a more polar component are nonlinear owing to preferential solvation of the probe by one component of the binary solvent mixture. In the computation of ET (1) it was assumed that the two solvents mixed interact to form a common structure with an ET (1) value not always intermediate between those of the two solvents mixed. The results obtained are explained by the strong synergism observed for some of the binary mixtures with strong hydrogen bond donors (HBD) solvents such as alcohols. 相似文献
52.
The monomer-dimer equilibrium of an asymmetric cyanine dye has been investigated by means of UV-Vis spectroscopy. The data have been processed by a recently developed chemometric method for quantitative analysis of undefined mixtures, that is based on simultaneous resolution of the overlapping bands in the whole set of absorption. In this work the dimerization constant of 1-carboxydecyl-4-{3-[3-methyl-3H-benzothiazol-2-ylidene]-propenyl}-quinolinium (TO-3) has been determined by studying the dependence of absorption spectrum on temperature in the range 25-72.5 °C at different total concentrations of dye (8.5×10−6 to 2.87×10−5 M). Utilizing the van’t Hoff relation, which describes the dependence of the equilibrium constant on temperature, as constraint we determine the spectral responses of the monomer and dimer species as well as the enthalpy and entropy of the dimerization equilibrium. 相似文献
53.
54.
The capacity for anaerobic decolorization of a sulfonated azo dye, Congo Red, by a strain of a sulfate-reducing bacterium
was evaluated. After optimizing the growth rate of the bacteria on a simple carbon source and terminal electron acceptor pair,
lactate and sulfate, respectively, the effect of the dye concentration on their growth rate was analyzed. The decolorization
rate was affected by the dye concentration in the growth medium. The azo-bond cleavage mechanism of reductive decolorization
with the formation of benzidine was consistent with the results, as this metabolite was identified by high-performance liquid
chromatography. Several fractions of the culture medium, including lysed cell extracts, were examined for the capacity to
reduce the azo dye. This reduction capacity was found in the culture medium in which the cells had previously grown. The results
showed that the mechanism of reductive decolorization of this sulfonated azo dye was extracellular and nonenzymatic, consistent
with the production of sulfide anion by the microorganisms while growing on lactate and sulfate. The sulfide anions were the
cause of the reduction leading to the disappearance of color in the medium. To increase the rate of decolorization, the presence
of ferrous ion was also necessary together with the lactate and sulfate substrates. 相似文献
55.
Christian K. Riener Andreas Ebner Alex A. Gall Yuri L. Lyubchenko Hermann J. Gruber 《Analytica chimica acta》2003,479(1):59-75
We have established an easy-to-use test system for detecting receptor-ligand interactions on the single molecule level using atomic force microscopy (AFM). For this, avidin-biotin, probably the best characterized receptor-ligand pair, was chosen. AFM sensors were prepared containing tethered biotin molecules at sufficiently low surface concentrations appropriate for single molecule studies. A biotin tether, consisting of a 6 nm poly(ethylene glycol) (PEG) chain and a functional succinimide group at the other end, was newly synthesized and covalently coupled to amine-functionalized AFM tips. In particular, PEG800 diamine was glutarylated, the mono-adduct NH2-PEG-COOH was isolated by ion exchange chromatography and reacted with biotin succinimidylester to give biotin-PEG-COOH which was then activated as N-hydroxysuccinimide (NHS) ester to give the biotin-PEG-NHS conjugate which was coupled to the aminofunctionalized AFM tip. The motional freedom provided by PEG allows for free rotation of the biotin molecule on the AFM sensor and for specific binding to avidin which had been adsorbed to mica surfaces via electrostatic interactions. Specific avidin-biotin recognition events were discriminated from nonspecific tip-mica adhesion by their typical unbinding force (∼40 pN at 1.4 nN/s loading rate), unbinding length (<13 nm), the characteristic nonlinear force-distance relation of the PEG linker, and by specific block with excess of free d-biotin. The convenience of the test system allowed to evaluate, and compare, different methods and conditions of tip aminofunctionalization with respect to specific binding and nonspecific adhesion. It is concluded that this system is well suited as calibration or start-up kit for single molecule recognition force microscopy. 相似文献
56.
The effect of surface condition on the photoalignment of light-induced methyl red (MR) adsorption phenomena on various substrates based on azo dye-doped liquid crystals is investigated. The results show that the polar surface energy determines the initiation of MR adsorption phenomena. The surface polarity energy of different substrates, which are modulated by oxygen plasma treatment (OPT), is further examined using the sessile drop method. The results also indicate that the uniformity and efficiency of MR adsorption can be enhanced by OPT. Light intensity influences the MR adsorption rate. The uniformity of MR adsorption onto various substrates is analysed via polarised optical microscopy. 相似文献
57.
A novel methodology was implemented in the present study to concurrently control power conversion efficiency (η) and durability (D) of co-sensitized dye solar cells. Applying response surface methodology (RSM) and Desirability Function (DF), the main influential assembling (dye volume ratio and anti-aggregation agent concentration) and operational (performance temperature) parameters were systematically changed to probe their main and interactive effects on the η and D responses. Individual optimization based on RSM elucidated that D can be solely controlled by changing the ratio of vat-based organic photosensitizers, whereas η takes both effects of dye volume ratio and anti-aggregation concentration into account. Among the studied factors, the performance temperature played the most vital role in η and D regulation. In particular, however, multi-objective optimization by DF explored the degree to which one should be careful about manipulation of assembling and operational parameters in the way maximization of performance of a co-sensitized dye solar cell. 相似文献
58.
Four main chain polymeric metal complexes (P1–P4) based on 1,10‐phenanthroline metal complexes via the Heck coupling have been synthesized and characterized by Fourier transform infrared spectroscopy, 1H NMR, UV–Vis absorption, photoluminescence spectroscopy, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, elemental analysis, and cyclic voltammetry. To investigate their photovoltaic properties, the dye‐sensitized solar cells based on these polymers dyes are studied, under the illumination of AM 1.5G, 100 mW/cm2. The study results show the four polymers exhibit good thermally stable and the solar cells based on them have good device performance, and the maximum power conversion efficiency is up to 0.735% for the solar cells based on P3 with a short‐circuit current (Jsc) of 1.68 mA/cm2 and an open‐circuit voltage (Voc) of 0.62 V. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
59.
Lorenzo Milli Dr. Nicola Zanna Andrea Merlettini Matteo Di Giosia Dr. Matteo Calvaresi Prof. Maria Letizia Focarete Prof. Claudia Tomasini 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(34):12106-12112
We present herein the preparation of four different hydrogels based on the pseudopeptide gelator Fmoc‐l ‐Phe‐d ‐Oxd‐OH (Fmoc=fluorenylmethyloxycarbonyl), either by changing the gelator concentration or adding graphene oxide (GO) to the water solution. The hydrogels have been analysed by rheological studies that demonstrated that pure hydrogels are slightly stronger compared to GO‐loaded hydrogels. Then the hydrogels efficiency to trap the cationic methylene blue (MB) and anionic eosin Y (EY) dyes has been analyzed. MB is efficiently trapped by both the pure hydrogel and the GO‐loaded hydrogel through π–π interactions and electrostatic interactions. In contrast, the removal of the anionic EY is achieved in less satisfactory yields, due to the unfavourable electrostatic interactions between the dye, the gelator and GO. 相似文献
60.
Sunny K. S. Freitas Felipe L. Oliveira Thiago C. dos Santos Danilo Hisse Claudia Merlini Célia M. Ronconi Prof. Dr. Pierre M. Esteves 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(7):2342-2347
A thermally stable carbocationic covalent organic network (CON), named RIO-70 was prepared from pararosaniline hydrochloride, an inexpensive dye, and triformylphloroglucinol in solvothermal conditions. This nanoporous organic material has shown a specific surface area of 990 m2 g−1 and pore size of 10.3 Å. The material has CO2 uptake of 2.14 mmol g−1 (0.5 bar), 2.7 mmol g−1 (1 bar), and 6.8 mmol g−1 (20 bar), the latter corresponding to 3 CO2 molecules adsorbed per pore per sheet. It is shown to be a semiconductor, with electrical conductivity (σ) of 3.17×10−7 S cm−1, which increases to 5.26×10−4 S cm−1 upon exposure to I2 vapor. DFT calculations using periodic conditions support the findings. 相似文献