全文获取类型
收费全文 | 2575篇 |
免费 | 50篇 |
国内免费 | 32篇 |
专业分类
电工技术 | 48篇 |
综合类 | 43篇 |
化学工业 | 329篇 |
金属工艺 | 107篇 |
机械仪表 | 58篇 |
建筑科学 | 131篇 |
矿业工程 | 3篇 |
能源动力 | 51篇 |
轻工业 | 190篇 |
水利工程 | 19篇 |
石油天然气 | 19篇 |
武器工业 | 2篇 |
无线电 | 178篇 |
一般工业技术 | 249篇 |
冶金工业 | 1036篇 |
原子能技术 | 6篇 |
自动化技术 | 188篇 |
出版年
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 24篇 |
2020年 | 12篇 |
2019年 | 15篇 |
2018年 | 20篇 |
2017年 | 29篇 |
2016年 | 21篇 |
2015年 | 53篇 |
2014年 | 98篇 |
2013年 | 103篇 |
2012年 | 72篇 |
2011年 | 161篇 |
2010年 | 76篇 |
2009年 | 105篇 |
2008年 | 85篇 |
2007年 | 95篇 |
2006年 | 68篇 |
2005年 | 57篇 |
2004年 | 55篇 |
2003年 | 53篇 |
2002年 | 49篇 |
2001年 | 38篇 |
2000年 | 30篇 |
1999年 | 62篇 |
1998年 | 305篇 |
1997年 | 180篇 |
1996年 | 138篇 |
1995年 | 108篇 |
1994年 | 93篇 |
1993年 | 78篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 37篇 |
1989年 | 30篇 |
1988年 | 18篇 |
1987年 | 19篇 |
1986年 | 7篇 |
1985年 | 16篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1977年 | 30篇 |
1976年 | 59篇 |
1975年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有2657条查询结果,搜索用时 15 毫秒
71.
Liang Li Anders Rasmuson Andy Ingram Mats Johansson Johan Remmelgas Christian von Corswant Staffan Folestad 《American Institute of Chemical Engineers》2015,61(3):756-768
Particle cycle and residence time distributions are critical factors in determining the coating quality in the Wurster process. Positron emission particle tracking experiments are performed to determine the cycle and residence times of particles in different regions of a Wurster fluid bed. The results show that particles tend to recirculate in and sneak out below from the Wurster tube. The experiments also show that a larger batch size leads to a shorter cycle time and a narrower cycle time distribution (CTD). It is possible to avoid recirculations and obtain a shorter cycle time and a narrower CTD by selecting the operating conditions appropriately or via equipment design. Experiments using binary mixtures of particles with a diameter ratio of 1.5 show that large particles have a longer cycle time than small particles and that the cycle time is shorter for mixtures with approximately equal amounts of small and large particles. © 2014 American Institute of Chemical Engineers AIChE J, 61: 756–768, 2015 相似文献
72.
Effect of additives on the melt rheology and thermal degradation of poly[(R)‐3‐hydroxybutyric acid] 下载免费PDF全文
Carlos R. Arza Patric Jannasch Peter Johansson Per Magnusson Alan Werker Frans H. J. Maurer 《应用聚合物科学杂志》2015,132(15)
Thermal degradation of poly[(R)−3‐hydroxybutyric acid] (PHB) during melt mixing results in random chain scission that produces shorter polymer chains containing crotonic and carboxyl end groups. One way of preventing this serious reduction of molar mass is to add agents that react with at least two of the newly generated end groups. Different types of commercially available additives known to react with carboxyl group, namely bis(3,4‐epoxycyclohexylmethyl) adipate (BECMA), 2,2'‐bis(2‐oxazoline) (BOX), trimethylolpropane tris(2‐methyl‐1‐aziridinepropionate) (PETAP), triphenyl phosphate (TPP), tris(nonylphenyl) phosphate (TNPP), polycarbodiimide (PCDI), and poly(methyl metharylate‐co‐glycidyl methacrylate) (GMA.MMA) were mixed with PHB by cocasting from solution in chloroform. Dynamic rheology as well as measurements of molar masses before and after dynamic analysis was used to evaluate the effect of the additives on the melt stability of PHB. Measurements of the dynamic shear modulus and the molar mass of molten PHB with the additives PCDI and GMA.MMA showed a minor improvement on the thermal stability. Furthermore, TPP and TNPP did not affect the thermal stability of PHB, whereas the presence of BECMA, BOX, and PETAP gave a strong decrease of the dynamic modulus compared with neat PHB. © 2014 The Authors Journal of Applied Polymer Science Published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41836. 相似文献
73.
74.
Kimmo Lahtinen Petri Johansson Tommi Kääriäinen David C. Cameron 《Polymer Engineering and Science》2012,52(9):1985-1990
Adhesion of extrusion‐coated polymer sealing layers on an atomic layer deposited (ALD) aluminum oxide (Al2O3) surface coating was investigated with a view to gain information on the applicability of ALD deposited barrier layers in fiber‐based packaging materials. The polymers used for the sealing layer were low density polyethylene (LDPE), polyethylene terephthalate (PET), and polylactide (PLA). They were extrusion‐coated onto the ceramic side of paper/PET/Al2O3 substrates, where the Al2O3 layer was a few tens of nanometers thick. According to the results, good adhesion was obtained for LDPE coating, whereas the other coatings showed a considerable lack of adhesion. Presumably, the oxidation faced by LDPE in the air gap of the extrusion‐coating process was able to create an extensive number of reactive sites that strongly bonded with the hydroxyl groups on the oxide surface of the substrate. With the PET and PLA coatings, such oxidation did not occur and the adhesion obtained remained at a relatively poor level. With all of the coatings, the adhesion levels were improved using corona discharge equipment as a pretreatment prior to the extrusion‐coating process. POLYM. ENG. SCI., 52:1985–1990, 2012. © 2012 Society of Plastics Engineers 相似文献
75.
Palle Breistein Jonas Johansson Ismail Ibrahem Shuangzheng Lin Luca Deiana Junliang Sun Armando Cordova 《Advanced Synthesis \u0026amp; Catalysis》2012,354(6):1156-1162
The highly enantioselective cascade reaction between N‐protected α‐cyanoglycine esters and α,β‐unsaturated aldehydes is disclosed. The reaction represents a one‐step entry to polysubstituted 5‐hydroxyproline derivatives having a quaternary α‐stereocenter generally in high yields with up to >95:5 dr and 99:1 er. It is also a direct catalytic two‐step entry to functionalized α‐quaternary proline derivatives. 相似文献
76.
ABSTRACT: BACKGROUND: In the 1970s, men in northern Sweden had among the highest prevalences of cardiovascular diseases (CVD) worldwide. An intervention program combining population- and individual-oriented activities was initiated in 1985. Concurrently, collection of information on medical risk factors, lifestyle and anthropometry started. Today, these data make up one of the largest databases in the world on diet intake in a population-based sample, both in terms of sample size and follow-up period. The study examines trends in food and nutrient intake, serum cholesterol and body mass index (BMI) from 1986 to 2010 in northern Sweden. METHODS: Cross-sectional information on self-reported food and nutrient intake and measured body weight, height, and serum cholesterol were compiled for over 140,000 observations. Trends and trend breaks over the 25-year period were evaluated for energy- providing nutrients, foods contributing to fat intake, serum cholesterol and BMI. RESULTS: Reported intake of fat exhibited two significant trend breaks in both sexes: a decrease between 1986 and 1992 and an increase from 2002 (women) or 2004 (men). A reverse trend was noted for carbohydrates, whereas protein intake remained unchanged during the 25-year period. Significant trend breaks in intake of foods contributing to total fat intake were seen. Reported intake of wine increased sharply for both sexes (more so for women) and export beer increased for men. BMI increased continuously for both sexes, whereas serum cholesterol levels decreased during 1986 - 2004, remained unchanged until 2007 and then began to rise. The increase in serum cholesterol coincided with the increase in fat intake, especially with intake of saturated fat and fats for spreading on bread and cooking. CONCLUSIONS: Men and women in northern Sweden decreased their reported fat intake in the first 7 years (1986-1992) of an intervention program. After 2004 fat intake increased sharply for both genders, which coincided with introduction of a positive media support for low carbohydrate-high-fat (LCHF) diet. The decrease and following increase in cholesterol levels occurred simultaneously with the time trends in food selection, whereas a constant increase in BMI remained unaltered. These changes in risk factors may have important effects on primary and secondary prevention of cardiovascular disease (CVD). 相似文献
77.
78.
79.
Dorota Johansson Björn Bergenståhl 《Journal of the American Oil Chemists' Society》1992,69(8):728-733
The influence of water on the interactions between fat and sugar crystals dispersed in triglyceride (vegetable) oils was qualitatively
estimated from sedimentation and rheological experiments. The experiments were performed both with and without food emulsifiers
(monoglycerides and lecithins) present in the oil. The effects of minor natural oil components (nontriglycerides) on the interactions
and on emulsifier adsorption to the crystals were examined by comparing a commercial refined oil and a chromatographically
purified oil. The results show that water generally increases the adhesion between fat and sugar crystals in oils and also
increases the surface activity of the oil-soluble food emulsifiers. Minor oil components give a small increase in the adhesion
between fat and sugar crystals in oils, but do not influence the adsorption of food emulsifiers in any systematic way. 相似文献
80.
Hydrodynamic measurements were made in a bubbling fluidized bed operated at 550°C at three different excess gas velocities (0.15, 0.40 and ). The bed has a cross-sectional area of with an immersed tube bank consisting of 59 horizontal stainless steel tubes (AISI 304L), 21 of which are exchangeable, thus allowing erosion studies. Capacitance probe analysis was used to determine the mean bubble rise velocity, the mean bubble frequency, the mean pierced bubble length, the mean bubble volume fraction and the mean visible bubble flow rate. Tube wastage was calculated from roundness profiles obtained by stylus profilometry.A redistribution of the bubble flow towards the center of the bed occurs when the excess gas velocity is increased. Measurements along a target tube, situated next to the capacitance probe, usually show greater material wastage at the central part of the tube, since the mean bubble rise velocity and the mean visible bubble flow rate are higher there. It is suggested that the greater material degradation is also an effect of the through-flow of a particle-transporting gas stream in the bubbles. With increasing height above the distributor plate the circumferential wastage profiles for the lowest excess gas velocity show a gradual change from an erosion pattern with one maximum (Type B behavior) to a pattern with two maxima (Type A behavior). Power spectral density distributions of the fluctuating pressure signals show that this is a result of the formation of larger bubbles, when the fluidization regime is changed in the upper part of the bed. At the highest excess gas velocity the bubble flow becomes more constrained due to a more rapid coalescence of the bubbles and the tubes show Type A wastage profiles throughout the bed. 相似文献