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排序方式: 共有531条查询结果,搜索用时 46 毫秒
41.
R. Alexandrescu R. Cireasa B. Dragnea I. Morjan I. Voicu A. Andrei F. Vasiliu C. Popescu 《Advanced functional materials》1995,5(1):19-30
Laser-induced TiCl4 decomposition at vapour pressure was performed and comparative study of the composition and structure of thermally (at 10.6 μm) and photolytically (at 248 nm) deposited Ti-based films is presented. Emphasis was given to the less explored titanium deposition process by CO2 laser pyrolysis of TiCl4. The detailed structure of films deposited on quartz substrates was examined by scanning electron microscopy and X-ray photoelectron spectroscopy. The influence of the incident laser energy on the chemical content of the films as well as on the film growth rate was demonstrated. The results indicate that in the thermal IR decomposition of TiCl4 a multilayer structure is formed with unsaturated TiSix at the interface and oxidized phases at the surface. The photolytic process leads to films with increased purity and a specific growth morphology. 相似文献
42.
In this study, two colloidal dispersions of pure amorphous silicon dioxide particles, acetylated, and heat‐treated samples were tested for a possible application as a wood protection agents. The silicon, acetylated, and heat‐treated samples were exposed to an accelerated weathering experiment, and their dimensional stability was assessed. The weathering experiment comprised cycles of 2 h UV‐light irradiation followed by water spray for 18 min. The surface changes of the weathered samples were characterized by FT‐IR spectroscopy and color measurements. According to results, the silicon treatments showed lower color changes than untreated ones. However, acetylated and heat‐treated samples provided the lowest color changes. The resistance of the silicon, acetylated, and heat‐treated wood to decay was studied by means of brown and white rot fungi in laboratory decay tests. Decay test results revealed that acetylated and heat‐treated wood samples showed better decay resistance against P. placenta and C. versicolor than silicon treatments. Samples modified with silicon were exposed in above ground standard lap‐joint test in Ultuna, Sweden. The dispersions of pure amorphous silicon dioxide impregnated in wood did not significantly influence its hygroscopic and dimensional behavior. However, the silicon treatment reduced the color changes caused by weathering. The silicon impregnated samples showed a weak fungal discoloration similar to that of chromated copper arsenate impregnated controls in above ground standard lap‐joint test. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4506–4513, 2006 相似文献
43.
Dr. Donald R. Griffin Jacob Borrajo Dr. Allyson Soon Giovanny F. Acosta‐Vélez Victor Oshita Nicole Darling Dr. Julia Mack Prof. Thomas Barker Prof. M. Luisa Iruela‐Arispe Prof. Tatiana Segura 《Chembiochem : a European journal of chemical biology》2014,15(2):233-242
The ability to design artificial extracellular matrices as cell‐instructive scaffolds has opened the door to technologies capable of studying the fate of cells in vitro and to guiding tissue repair in vivo. One main component of the design of artificial extracellular matrices is the incorporation of biochemical cues to guide cell phenotype and multicellular organization. The extracellular matrix (ECM) is composed of a heterogeneous mixture of proteins that present a variety of spatially discrete signals to residing cell populations. In contrast, most engineered ECMs do not mimic this heterogeneity. In recent years, photo‐deprotection has been used to spatially immobilize signals. However, this approach has been limited mostly to small peptides. Here we combine photo‐deprotection with enzymatic reaction to achieve spatially controlled immobilization of active bioactive signals that range from small molecules to large proteins. A peptide substrate for transglutaminase factor XIII (FXIIIa) was caged with a photo‐deprotectable group, which was then immobilized to the bulk of a cell‐compatible hydrogel. With focused light, the substrate can be deprotected and used to immobilize patterned bioactive signals. This approach offers an innovative strategy to immobilize delicate bioactive signals, such as growth factors, without loss of activity and enables in situ cell manipulation of encapsulated cells. 相似文献
44.
Minella M Rogora M Vione D Maurino V Minero C 《The Science of the total environment》2011,409(18):3463-3471
A model-based approach is here developed and applied to predict the long-term trends of indirect photochemical processes in the surface layer (5 m water depth) of Lake Maggiore, NW Italy. For this lake, time series of the main parameters of photochemical importance that cover almost two decades are available. As a way to assess the relevant photochemical reactions, the modelled steady-state concentrations of important photogenerated transients (•OH, 3CDOM* and CO3-•) were taken into account. A multivariate analysis approach was adopted to have an overview of the system, to emphasise relationships among chemical, photochemical and seasonal variables, and to highlight annual and long-term trends. Over the considered time period, because of the decrease of the dissolved organic carbon (DOC) content of water and of the increase of alkalinity, a significant increase is predicted for the steady-state concentrations of the radicals •OH and CO3−•. Therefore, the photochemical degradation processes that involve the two radical species would be enhanced. Another issue of potential photochemical importance is related to the winter maxima of nitrate (a photochemical •OH source) and the summer maxima of DOC (•OH sink and 3CDOM* source) in the lake water under consideration. From the combination of sunlight irradiance and chemical composition data, one predicts that the processes involving •OH and CO3−• would be most important in spring, while the reactions involving 3CDOM* would be most important in summer. 相似文献
45.
Diego T. Santos Juliana Q. Albarelli Kieran Joyce Michael Oelgemöller 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2009,84(7):1026-1030
BACKGROUND: Green chemistry, also known as sustainable chemistry, refers to environmentally friendly chemicals and processes that result in reduced waste, elimination of costly end‐of‐the‐pipe treatments; safer products, and reduced use of energy and resources. In this context this study aims to evaluate a novel green sensitizer support for photochemistry use. For this propose, Rose Bengal (RB) and juglone production were chosen as a model sensitizer and a model photoreaction, respectively. RESULTS: The results showed that the RB‐alginate beads prepared using a solution of 20% CaCl2 had better stability in the solvent t‐amyl alcohol. Comparing all the immobilized systems a larger reaction yield (57.5%) was obtained when the proportion of the beads in the photoreactor flask was 5% (v/v). Although when using suspended RB the reaction yield was better (62%) the environmental friendly attributes and economical advantages of immobilized systems overcome it. CONCLUSIONS: The potentiality of this new kind of sensitizer immobilization was demonstrated and a mechanism based on immobilization of cells was proposed. Furthermore the use of this novel green support presents a greater efficiency and potentially lower costs than the commercial supported RB Sensitox. Copyright © 2009 Society of Chemical Industry 相似文献
46.
IRÉNA BECK RÉ DEFLANDRE GÉRARD LANG RÉNE ARNAUD JAQUES LEMAIR 《International journal of cosmetic science》1981,3(3):139-152
Benzylidene camphor derivatives have been currently used as ultraviolet filters in sunscreen compositions. When solutions of these compounds are exposed to the light from a solar simulator, a photoinduced cis-trans isomerization is observed. The initial quantum yields of this photochemical isomerization of studied molecules have been determined in several solvents. Their photochemical behaviour depends neither on the concentration nor on the presence or absence of oxygen or other inhibitors such as isopropanol or biacetyl. It means that the lifetime of the precursor states of isomerization is about 10−12 s, that is to say, too short for them to react with neighbouring molecules.
For each compound, the ratio of the respective concentrations of 'E' and 'Z' forms was also determined by photostationary state. A good agreement between theoretical and experimental values of this ratio shows that the studied compounds are only very slightly photodegradable. This was confirmed by the low values of photodegradation quantum yields.
In case of the studied compounds, the isomerization process observed is totally reversible. During irradiation a photostationary state is quickly reached, each isomer may change into the other form after absorption of a photon which leads to a mixture of isomers. In practice, it is this mixture of E and Z forms which acts as UV filters.
It may be said that a very short lifetime of the excited states, a good light stability and a reaction inertia under light irradiation make these compounds excellent sunscreen agents.
Comportement photochimique des antisolaires. Benzylidène camphre et certans de ses dérivés 相似文献
For each compound, the ratio of the respective concentrations of 'E' and 'Z' forms was also determined by photostationary state. A good agreement between theoretical and experimental values of this ratio shows that the studied compounds are only very slightly photodegradable. This was confirmed by the low values of photodegradation quantum yields.
In case of the studied compounds, the isomerization process observed is totally reversible. During irradiation a photostationary state is quickly reached, each isomer may change into the other form after absorption of a photon which leads to a mixture of isomers. In practice, it is this mixture of E and Z forms which acts as UV filters.
It may be said that a very short lifetime of the excited states, a good light stability and a reaction inertia under light irradiation make these compounds excellent sunscreen agents.
Comportement photochimique des antisolaires. Benzylidène camphre et certans de ses dérivés 相似文献
47.
48.
UV‐cured polysiloxane epoxy coatings containing titanium dioxide were prepared by means of a cationic photopolymerization process. A good distribution of the inorganic filler was achieved within the polymeric network with an average size dimension of around 500 nm. UV‐vis analysis performed on organic dye (methylene blue) stained coatings showed a high efficiency of the titania photocatalytic activity: a complete degradation of the dye on the coating surface is reached after 60 min of UV irradiation without affecting the matrix photo‐degradation.
49.
The efficiency of several xanthene dyes as photoinitiators of the free radical polymerization in aqueous medium was evaluated. These results show that dyes with triplet quantum yield higher than 0.1 present similar efficiencies, independently of their different chemical structure. A detailed study of the photophysics of the dyes under the polymerization conditions was carried out using laser time-resolved spectroscopies. These studies show that the active radicals are those which formed in the interaction of excited triplet state of the dye with the amine through an electron transfer process. In spite of this, the photoinitiation efficiency is not correlated with the triplet quantum yield. Also, the photophysics studies show that the quantum yield of the different pathways of the decomposition of the charge transfer intermediate is an important parameter to predict the efficiency of these photoinitiator systems. The experimentally measured active radical formation is well correlated with that calculated from the polymerization rate. The presence of heavy atoms in the xanthene ring increases the triplet quantum yield, but decreases the active radical yield, and then the polymerization rate. 相似文献
50.
通过光化学方法取代传统的金属催化等法合成重要的药物中间体唑烷酮,反应条件温和、操作简便、产率较高且污染少.同时研究了丙酮、甲醇、乙腈3种溶剂与水的不同配比对反应产物的影响.随着溶剂极性增加,立体选择性有一定提高. 相似文献