首页 | 官方网站   微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1170篇
  免费   96篇
工业技术   1266篇
  2024年   2篇
  2023年   9篇
  2022年   45篇
  2021年   92篇
  2020年   39篇
  2019年   45篇
  2018年   43篇
  2017年   40篇
  2016年   52篇
  2015年   46篇
  2014年   52篇
  2013年   85篇
  2012年   84篇
  2011年   80篇
  2010年   71篇
  2009年   70篇
  2008年   80篇
  2007年   58篇
  2006年   46篇
  2005年   36篇
  2004年   33篇
  2003年   20篇
  2002年   21篇
  2001年   23篇
  2000年   11篇
  1999年   11篇
  1998年   2篇
  1997年   9篇
  1996年   6篇
  1995年   9篇
  1994年   6篇
  1993年   5篇
  1992年   2篇
  1991年   2篇
  1990年   7篇
  1989年   3篇
  1988年   3篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1984年   2篇
  1983年   2篇
  1982年   1篇
  1980年   2篇
  1979年   2篇
  1975年   1篇
  1974年   2篇
  1972年   2篇
排序方式: 共有1266条查询结果,搜索用时 31 毫秒
91.
92.
Investigated appearance management (AM) as a social–psychological variable in 322 physically disabled university students. The questionnaire included an AM and social interaction scale and measures of acceptance of disability. A tendency to regard AM as a form of compensation was associated with a tendency to view physical disability as a central or salient aspect of personal identity. Data suggest that AM is regarded by some as a means for ameliorating the social impact of a physical disability, but is expected to serve only a secondary role in impression formation. The relationship between disability acceptance and predisposition toward AM is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
93.
Sardine (Sardina pilchardus) is a species that for its abundance assumes great importance in the Portuguese fishing sector. In order to contribute for a better utilisation of this species, the aim of this study was to investigate the effect of the pre‐treatment with soluble gas stabilisation (SGS) (100% CO2 at 2 bar, during 15 and 30 min) on the quality and shelf‐life of sardine fillets, packed in air (AP), vacuum (VP) and modified atmosphere (MAP: 5% O2/35% CO2/60% N2). During the chilled storage, the quality changes were evaluated by sensory evaluation, chemical and microbiological analysis. The total volatile basic nitrogen content remained almost constant, between 16 and 19 mg N/100 g muscle, during the storage period, for all samples. The TBARs values increased with storage time, for all batches and storage conditions. The application of SGS treatment to sardine fillets, resulted in a bacteriostatic effect, contributing to the improvement of the microbiological quality of fillets. Considering a sensory criteria, the shelf‐life of SGS pre‐treated sardine fillets was found to be 5 days in AP and MAP while in VP‐treated fillets a shelf‐life of 8 days was reported. At sensory rejection, sardine fillets presented a K‐value of 30% in AP and MAP batches and 40% in VP batch.  相似文献   
94.
Wide‐angle X‐ray scattering and differential scanning calorimetry measurements have been conducted on seven random copolymers of propylene with ethylene in order to study the γ phase formation as a function of the comonomer content. The lamellar morphology of the samples was also investigated by small‐angle X‐ray scattering. The content of the γ phase was found to go through a maximum with crystallization temperature and to increase with comonomer concentration, up to a point (ethylene ≥6.5 wt%) where the latter parameter became less influential. The multiple melting endotherms behaviour of the samples was studied by DSC and temperature‐controlled diffractometric techniques. The attribution of the DSC peaks to the different isotactic polypropylene polymorphs that form in these conditions was confirmed. The results obtained permitted us to ascertain that, in the experimental conditions chosen, some further formation of crystallites takes place during the quenching to room temperature after the crystallization isotherm. In this phase, the chains organize themselves in stacks with thin lamellae, forming a distinct population with respect to those formed on isothermal crystallization. The melting of the thinner lamellae determines a convergence of the two populations into just one, still retaining an organization in stacks, that gradually disappears until complete melting of the material. Copyright © 2004 Society of Chemical Industry  相似文献   
95.
Transarterial vascular embolization and chemoembolization has become common medical procedures, where partially hydrolyzed poly(vinyl alcohol) (PVA) beads remains as one of the most used embolic agent materials. Although synthetic, PVA cannot be synthesized by direct polymerization and must be obtained by chemical modification of another polymer, usually poly(vinyl acetate) (PVAc). The aim of the present work is to synthesize spherical core‐shell PVAc/PVA particles and study the morphological and molecular modifications during shell formation. The polymer particles where produced in two stages, where first the PVAc core was obtained by suspension polymerization of vinyl acetate (VAc) and then the PVA shell synthesized through hydrolysis. Spherical PVAc particles were successfully produced and isolated using an optimized suspension polymerization process. During the shell formation, it was shown that none of the conditions used affected the overall morphology of the particles although changes in the final size distribution could be observed. However, it was possible to identify the process variables and reaction condition that affect the molecular weight averages and polydispersities of the final copolymer. POLYM. ENG. SCI., 55:2237–2244, 2015. © 2015 Society of Plastics Engineers  相似文献   
96.
The purpose of this study was to analyze, by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM), the morphology of sealant/enamel interface after surface treatment with Biosilicate. Before pits and fissures sealing, the occlusal surfaces of 10 sound human molars were sectioned perpendicularly at the fissures in order to obtain three slices for each tooth. Slices were randomly assigned into three groups (n = 10) according to sealing protocol: Group 1‐ Acid etching + Biosilicate + glass ionomer‐based sealant (Clinpro XT Varnish, 3M ESPE); Group 2‐ Acid etching + glass ionomer‐based sealant (Clinpro XT Varnish, 3M ESPE); Group 3‐ No sealing. All slices were subjected to thermal cycling (5,000 cycles; 5–55°C; dwell time: 30s). Half of the slices from each group (n = 5) were analyzed by CLSM and the other half by SEM. Groups 1 and 2 were also submitted to EDS analysis and their data were evaluated by Two‐Way ANOVA e Tukey's test (α=5%). EDS data analysis showed higher amounts of silicon (Si) ions than calcium (Ca) ions in Group 1 (P < 0.05); Group 2 presented higher amounts (P < 0.05) of Ca ions than Si ions. It may be concluded that the use of Biosilicate for surface treatment did not affect the morphology of glass ionomer‐based sealant/enamel interfaces. Microsc. Res. Tech. 78:1062–1068, 2015. © 2015 Wiley Periodicals, Inc.  相似文献   
97.
The application of a rapid, non-destructive, cost-effective technique such as ultrasonic emulsification for the coating of different textiles was explored. The technical benefits for this research were the generation of multifunctional materials and their combinations through environmentally friendly processing technologies. We have shown for the first time that ultrasonic waves can be used to coat proteinaceous micro- and nanospheres (PM) of BSA (Bovine Serum Albumin) protein and casein on the surface of cotton and polyester (PE) fabrics. The creation and the anchoring of the microbubbles to the fabrics were performed by a one-step reaction, and the process is usually stopped after 3 min. The PM of bovine serum albumin (BSA) bonded to cotton and polyester fabrics has shown stability for ∼9 months. The PMs were shown to be attached more strongly to the polyester than to the cotton, and sustained stronger washing conditions on PE. The diameter of the BSA and the casein spheres on cotton was in the range of 0.8–1.0 μm, while on the PE it varied between 60 and 120 nm.  相似文献   
98.
Steroid bioconversion: Towards green processes   总被引:1,自引:0,他引:1  
There is an increasing trend towards reducing the use of organic solvents in industry due to environmental constraints and the adoption of green chemistry guidelines. To overcome the low volumetric productivity of aqueous bioconversion systems involving sparingly water soluble hydrophobic compounds, processes are being developed and designed to incorporate green solvent such as supercritical fluids, ionic liquids and natural oils, and liquid polymers, among others as an alternative to organic solvents. Moreover, processes are developed and redesigned to use/reuse chemicals and reagents derived from waste or renewable feed stocks in order to diminish E-factors.In this work, the use of green solvents as key components in the bioconversion media for a multi-step microbial bioconversion was assessed in a suspended whole cell system, combined with the use of by-products as raw materials, ultimately used as carbon source for cell growth and as sterol substrate for bioconversion. The model system is the selective cleavage of the side-chain of β-sitosterol performed by free resting cells of Mycobacterium sp. NRRL B-3805, a well-established industrial multi-enzymatic process involving the use of nine catabolic enzymes in a 14-step metabolic pathway.Bioconversion yields in silicone media were higher than the ones obtained in polyethylene glycol (PEG), polypropylene glycol (PPG) and ionic liquids, as well as in dioctyl phthalate (DOP), an organic solvent that has previously been shown to allow high conversion yields. Total conversion of 12 mM substrate in silicone media was consistently obtained at the end of 120-h bioconversion runs. Similar bioconversion profiles were attained during a 50-fold scale-up, maintaining constant the power consumption per unit of volume.  相似文献   
99.
Measurements of degradation in frying oils are mainly based on physico-chemical properties. Total polar compounds (TPC) and free fatty acids (FFA) content in frying oils are used as a guide for discarding used oils. The purpose of this study was to evaluate the efficacy of a sensory method in detecting degradation in soybean oils used in potato chips deep frying. The sensory evaluation of oil samples was determined by a trained panel; after rigorous selection and training steps. Free fatty acid, TPC and Rancimat induction period (IP) were quantified in the same samples. The proposed sensory method was sensitive to small differences in rancidity. The selected and trained sensory panel discarded oil samples with 0.175% FFA as oleic acid, 18.92% TPC, and 0.20 h IP. According to the results achieved in this research sensorial trained panel response is sensitive and accurate in refusing deteriorated frying oils. Besides this, soybean oil can be used for deep frying procedures and safely discarded according to the panel response, although presenting up to 7% linolenic acid.  相似文献   
100.
Three novel 2,7-substituted acridine derivatives were designed and synthesized to investigate the effect of this functionalization on their interaction with double-stranded and G-quadruplex DNA. Detailed investigations of their ability to bind both forms of DNA were carried out by using spectrophotometric, electrophoretic, and computational approaches. The ligands in this study are characterized by an open-chain (L1) or a macrocyclic (L2, L3) framework. The aliphatic amine groups in the macrocycles are joined by ethylene (L2) or propylene chains (L3). L1 behaved similarly to the lead compound m-AMSA, efficiently intercalating into dsDNA, but stabilizing G-quadruplex structures poorly, probably due to the modest stabilization effect exerted by its protonated polyamine chains. L2 and L3, containing small polyamine macrocyclic frameworks, are known to adopt a rather bent and rigid conformation; thus they are generally expected to be sterically impeded from recognizing dsDNA according to an intercalative binding mode. This was confirmed to be true for L3. Nevertheless, we show that L2 can give rise to efficient π-π and H-bonding interactions with dsDNA. Additionally, stacking interactions allowed L2 to stabilize the G-quadruplex structure: using the human telomeric sequence, we observed the preferential induction of tetrameric G-quadruplex forms. Thus, the presence of short ethylene spacers seems to be essential for obtaining a correct match between the binding sites of L2 and the nucleobases on both DNA forms investigated. Furthermore, current modeling methodologies, including docking and MD simulations and free energy calculations, provide structural evidence of an interaction mode for L2 that is different from that of L3; this could explain the unusual stabilizing ability of the ligands (L2>L3>L1) toward G-quadruplex that was observed in this study.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司    京ICP备09084417号-23

京公网安备 11010802026262号