全文获取类型
收费全文 | 295257篇 |
免费 | 24712篇 |
国内免费 | 15173篇 |
专业分类
电工技术 | 18889篇 |
技术理论 | 51篇 |
综合类 | 40122篇 |
化学工业 | 34165篇 |
金属工艺 | 11951篇 |
机械仪表 | 16054篇 |
建筑科学 | 40206篇 |
矿业工程 | 16276篇 |
能源动力 | 8775篇 |
轻工业 | 16326篇 |
水利工程 | 14995篇 |
石油天然气 | 12243篇 |
武器工业 | 2850篇 |
无线电 | 19710篇 |
一般工业技术 | 21978篇 |
冶金工业 | 17756篇 |
原子能技术 | 3017篇 |
自动化技术 | 39778篇 |
出版年
2024年 | 446篇 |
2023年 | 2705篇 |
2022年 | 5148篇 |
2021年 | 6537篇 |
2020年 | 6951篇 |
2019年 | 5933篇 |
2018年 | 5547篇 |
2017年 | 6720篇 |
2016年 | 8082篇 |
2015年 | 9027篇 |
2014年 | 16514篇 |
2013年 | 15341篇 |
2012年 | 19700篇 |
2011年 | 21087篇 |
2010年 | 16695篇 |
2009年 | 17515篇 |
2008年 | 16410篇 |
2007年 | 21226篇 |
2006年 | 20209篇 |
2005年 | 17635篇 |
2004年 | 15103篇 |
2003年 | 13611篇 |
2002年 | 11340篇 |
2001年 | 9510篇 |
2000年 | 7815篇 |
1999年 | 6433篇 |
1998年 | 4801篇 |
1997年 | 4176篇 |
1996年 | 3878篇 |
1995年 | 3310篇 |
1994年 | 2947篇 |
1993年 | 2245篇 |
1992年 | 1961篇 |
1991年 | 1454篇 |
1990年 | 1292篇 |
1989年 | 1130篇 |
1988年 | 894篇 |
1987年 | 606篇 |
1986年 | 459篇 |
1985年 | 387篇 |
1984年 | 360篇 |
1983年 | 266篇 |
1982年 | 237篇 |
1981年 | 186篇 |
1980年 | 142篇 |
1979年 | 125篇 |
1978年 | 72篇 |
1977年 | 74篇 |
1975年 | 63篇 |
1959年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
The mechanical force to polymeric materials in vacuum at 77 K produces mechano radicals, mechano anions and mechano cations due to homogeneous and heterogeneous scissions of the covalent bonds comprising polymer main chain. The ionic degree of the covalent bond was estimated by calculating the “absolute ΔMulliken atomic charge,” which was defined as the difference between the Mulliken atomic charges of the two adjacent atoms comprising the covalent bond of the polymer main chain. The ionic yield of the covalent bond increased with increasing the absolute ΔMulliken atomic charge. The empirical formula for the ionic yield was obtained with the absolute ΔMulliken atomic charge, and indicates that the ionic yield could be estimated from its chemical structure. 相似文献
992.
Dendrimers are novel three dimensional, hyperbranched globular nanopolymeric architectures. Attractive features like nanoscopic size, narrow polydispersity index, excellent control over molecular structure, availability of multiple functional groups at the periphery and cavities in the interior distinguish them amongst the available polymers. Applications of dendrimers in a large variety of fields have been explored. Drug delivery scientists are especially enthusiastic about possible utility of dendrimers as drug delivery tool. Terminal functionalities provide a platform for conjugation of the drug and targeting moieties. In addition, these peripheral functional groups can be employed to tailor-make the properties of dendrimers, enhancing their versatility. The present review highlights the contribution of dendrimers in the field of nanotechnology with intent to aid the researchers in exploring dendrimers in the field of drug delivery. 相似文献
993.
The progress in atom transfer radical polymerization (ATRP) provides an effective means for the design and preparation of functional membranes. Polymeric membranes with different macromolecular architectures applied in fuel cells, including block and graft copolymers are conveniently prepared via ATRP. Moreover, ATRP has also been widely used to introduce functionality onto the membrane surface to enhance its use in specific applications, such as antifouling, stimuli-responsive, adsorption function and pervaporation. In this review, the recent design and synthesis of advanced functional membranes via the ATRP technique are discussed in detail and their especial advantages are highlighted by selected examples extract the principles for preparation or modification of membranes using the ATRP methodology. 相似文献
994.
995.
The solvothermal synthesis of highly luminescent and homogeneous Gd2O3:Eu3+ nanophosphor using diethylene glycol as medium, followed by controlled combustion with citric acid as fuel is reported. The influence of concentrations of carboxylic acid and metal cations on the structure, morphology and luminescence properties are investigated in detail. The microscopic investigations indicate the nanocrystalline nature and the strong influence of cation concentration on the size, shape and agglomeration of the particles. It is found that increase in concentration of metal cations lead to the reduction in agglomeration of nanophosphors. The large value of intensity parameter Ω2, suggested that Eu3+ ions reside in a more asymmetric environment, resulted in intense emission due to 5D0–7F2 electric dipole transition. Emission decay analysis of the samples exhibited one exponential nature. The samples prepared under optimum conditions showed a quantum efficiency of 78.63% and a moderately high life time of 1.217 ms. 相似文献
996.
997.
Sohrab Zendehboudi Ali Shafiei Alireza Bahadori Lesley A. James Ali Elkamel Ali Lohi 《Chemical Engineering Research and Design》2014
Precipitation of asphaltene is considered as an undesired process during oil production via natural depletion and gas injection as it blocks the pore space and reduces the oil flow rate. In addition, it lessens the efficiency of the gas injection into oil reservoirs. This paper presents static and dynamic experiments conducted to investigate the effects of temperature, pressure, pressure drop, dilution ratio, and mixture compositions on asphaltene precipitation and deposition. Important technical aspects of asphaltene precipitation such as equation of state, analysis tools, and predictive methods are also discussed. Different methodologies to analyze asphaltene precipitation are reviewed, as well. Artificial neural networks (ANNs) joined with imperialist competitive algorithm (ICA) and particle swarm optimization (PSO) are employed to approximate asphaltene precipitation and deposition with and without CO2 injection. The connectionist model is built based on experimental data covering wide ranges of process and thermodynamic conditions. A good match was obtained between the real data and the model predictions. Temperature and pressure drop have the highest influence on asphaltene deposition during dynamic tests. ICA-ANN attains more reliable outputs compared with PSO-ANN, the conventional ANN, and scaling models. In addition, high pressure microscopy (HPM) technique leads to more accurate results compared with quantitative methods when studying asphaltene precipitation. 相似文献
998.
Hasan Kouchakzadeh Seyed Abbas Shojaosadati Fazel Shokri 《Chemical Engineering Research and Design》2014
Herein, the poorly water-soluble drug, Tamoxifen (Tmx), was loaded in the amphipathic matrix of human serum albumin (HSA) nanoparticles by a modified desolvation method. In order to enhance the drug loading (DL) and drug entrapment efficiency (DEE) (<2% and 10%, respectively), ultrasonication of Tmx-HSA mixture was performed prior to desolvation process. Tmx loading and entrapment efficiency were optimized by employment of the response surface methodology (RSM)-central composite design (CCD) of experiments. Under the optimum conditions of 1.59 mg Tmx/ml concentration, 7.76 pH and 5 h incubation of HSA-Tmx, the DL of 6.7% and DEE of 74% are achievable. Particles with the average size of 195 nm, zeta potential of −21 mV and polydispersity index of 0.09 were produced under these conditions. A more sustained Tmx release behavior was observed from polyethylene glycol (PEG) conjugated nanoparticles in comparison to the non-PEGylated ones. The short-term stability investigation showed no alteration in physicochemical properties of nanoparticles at 4 and 37 °C, but small increase in nanoparticles size was observed after three months of storage at room temperature. This is the first report for efficient production of a Tmx delivery system based on HSA nanoparticles. 相似文献
999.
In this work we prepared NaBiO3 nanopowders via three synthesis methods (sol-precipitation, dehydration and hydrothermal methods). To evaluate and compare the physical properties of the prepared materials X-ray diffraction analysis, BET measurements, UV–vis spectroscopy and TEM were applied. The results showed changes to the NaBiO3 crystallinity, the specific surface area and the particle shape and size, depending on the method of synthesis. To determine the photocatalytic efficiency of the prepared materials, we evaluated the photocatalytic reduction of CO2. 相似文献
1000.
A series of UV curable hydrophilic acrylate polymers containing sulfonic acid group was prepared via free radical copolymerization using 2-acrylamido-2-methyl propane sulfonic acid (AMPS) as hydrophilic monomer, which were used as prepolymers for anti-fog coatings. The expected structures were confirmed by FT-IR, 1H NMR and gel permeation chromatography (GPC). These UV-curable acrylate polymers were then mixed with reactive diluents and photoinitiator to form coating formulas. Various substrates were coated with these formulas and cured under UV exposure to obtain transparent coatings with good adhesion and hardness. The anti-fog properties of UV-cured coating were measured by contact angle test and anti-fog test. The results showed that the AMPS content in prepolymer had a great influence on the anti-fog properties of UV-cured coating. The formula was optimized and the corresponding UV-curing anti-fog coating was manufactured. The test results indicated that the coatings showed good mechanical properties, great optical transparency and excellent anti-fog performance. 相似文献