全文获取类型
收费全文 | 2182篇 |
免费 | 64篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 17篇 |
综合类 | 3篇 |
化学工业 | 289篇 |
金属工艺 | 27篇 |
机械仪表 | 65篇 |
建筑科学 | 39篇 |
矿业工程 | 1篇 |
能源动力 | 51篇 |
轻工业 | 88篇 |
水利工程 | 13篇 |
石油天然气 | 2篇 |
无线电 | 264篇 |
一般工业技术 | 213篇 |
冶金工业 | 939篇 |
原子能技术 | 7篇 |
自动化技术 | 231篇 |
出版年
2023年 | 32篇 |
2022年 | 44篇 |
2021年 | 74篇 |
2020年 | 62篇 |
2019年 | 56篇 |
2018年 | 69篇 |
2017年 | 41篇 |
2016年 | 84篇 |
2015年 | 29篇 |
2014年 | 59篇 |
2013年 | 77篇 |
2012年 | 64篇 |
2011年 | 52篇 |
2010年 | 61篇 |
2009年 | 49篇 |
2008年 | 42篇 |
2007年 | 51篇 |
2006年 | 41篇 |
2005年 | 27篇 |
2004年 | 32篇 |
2003年 | 29篇 |
2002年 | 25篇 |
2001年 | 20篇 |
2000年 | 17篇 |
1999年 | 63篇 |
1998年 | 325篇 |
1997年 | 184篇 |
1996年 | 113篇 |
1995年 | 67篇 |
1994年 | 63篇 |
1993年 | 74篇 |
1992年 | 24篇 |
1991年 | 17篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 12篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 9篇 |
1981年 | 2篇 |
1980年 | 11篇 |
1978年 | 3篇 |
1977年 | 23篇 |
1976年 | 45篇 |
1975年 | 3篇 |
1968年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有2249条查询结果,搜索用时 15 毫秒
161.
Tham Nguyen‐Chung Gábor Jüttner Cindy Löser Tung Pham Michael Gehde 《Polymer Engineering and Science》2010,50(1):165-173
The filling process of a micro‐cavity was analyzed by modeling the compressible filling stage by using pressure‐dependent viscosity and adjusted heat transfer coefficients. Experimental filling studies were carried out at the same time on an accurately controlled microinjection molding machine. On the basis of the relationship between the injection pressure and the filling degree, essential factors for the quality of the simulation can be identified. It can be shown that the flow behavior of the melt in a micro‐cavity with a high aspect ratio is extremely dependent on the melt compressibility in the injection cylinder. This phenomenon needs to be considered in the simulation to predict an accurate flow rate. The heat transfer coefficient between the melt and the mold wall that was determined by the reverse engineering varies significantly even during the filling stage. With increasing injection speed and increasing cavity thickness, the heat transfer coefficient decreases. It is believed that the level of the cavity pressure is responsible for the resulting heat transfer between the polymer and the mold. A pressure‐dependent model for the heat transfer coefficient would be able to significantly improve the quality of the process simulation. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers 相似文献
162.
Hien TT Nam PP Yasuhiro S Takayuki K Norimichi T Hiroshi B 《The Science of the total environment》2007,382(1):70-81
A comparative study of polycyclic aromatic hydrocarbons (PAHs) associated with particulate matter (TSP) in the ambient air in an urban area in Ho Chi Minh City, Vietnam and in Osaka, Japan was carried out from 2005 to 2006. The objective of this study was to investigate the environmental levels, emission sources, seasonal variations and health risk of eleven PAHs in the two cities, especially Ho Chi Minh City where air pollution is becoming a serious concern. The results showed that the concentrations of TSP and total PAHs were significantly higher in Ho Chi Minh City than levels in Osaka. The concentrations of 5- and 6-ring PAHs (BeP, BbF, BkF, BaP, BghiP and InP) were much higher in TSP samples in Ho Chi Minh City than in Osaka, accounting for 82% and 51% of total PAHs, respectively. These PAHs are known to be highly carcinogenic and mutagenic in humans. Vehicular emission is suggested as one of the main pollution sources of PAHs in both cities. Motorcycles and gasoline automobiles are suggested as the main emission sources of PAHs in Ho Chi Minh City, whereas diesel automobiles are the primary source in Osaka. Seasonal variations of PAHs were observed in this study; higher concentrations of PAHs were found in the rainy season (May-December) and lower concentrations corresponded to the dry season (February-April) in Ho Chi Minh City, while higher concentrations of PAHs were observed in the winter (November-January) in Osaka. The number of sunshine hours was an important meteorological factor affecting seasonal variations of PAHs in Ho Chi Minh City, while the temperature was a main factor causing the variations of PAHs in Osaka. The high BaP equivalent concentration of 5- and 6-ring PAHs even in the ambient air is an alarming signal for harmfulness to human health and environmental quality in Ho Chi Minh City. 相似文献
163.
Phuong Pham Thi Thuy Phuong Nguyen Nguyen Kumar P. Senthil Duy Nguyen Phuc Hoang Van Le Quyet Ngoc Le Thi Bao Jalil A. A. Rajendran Saravanan Cheng Chin Kui Nguyen Thanh-Huong Dinh Minh Tuan Nguyen Vo Dai-Viet N. 《Topics in Catalysis》2023,66(1-4):41-52
Topics in Catalysis - CO2 reforming of methanol for producing hydrogen was experimentally carried out in a fixed-bed reactor on 10%Ni/SiO2. The 10%Ni/SiO2 was completely reduced during H2... 相似文献
164.
ABSTRACT: Antioxidant properties of genistein were tested during the low temperature oxidation of linseed oil. Four linseed oil solutions were prepared: linseed oil, linseed oil containing 2 μmol added genistein/g oil, linseed oil containing 4 μmol added genistein/g oil, and linseed oil containing 200 ppm butylated hydroxyanisole (BHA). Dimethyl sulfoxide (DMSO) (1.7%) was added to all solutions to allow for the solubilization of genistein. Antioxidant activities were analyzed using 2 techniques: (i) the oven stability test carried out at 60 °C with periodic determination of peroxide values (PV); and (ii) oxidation on a heated (60 °C) FTIR-ATR crystal with periodic scanning and collection of infrared spectra. Induction points (IP) for each solution were determined. A strong correlation ( r = 0.91) was noted between the 2 analytical methods used. Three significantly ( P < 0.10) different levels of IP were generally observed. The shortest IP (17 h for PV, 36.9 h for FTIR) was found for the linseed oil. Intermediate IP's were obtained for the 2 μmol added genistein/g oil (32.4 h for PV, 43.5 h for FTIR) and 4 μmol added genistein/g oil (33.9 h for PV, 44.2 h for FTIR) samples. The longest IP (39.9 h for PV, 54.2 h for FTIR) was obtained for the 200 ppm BHA containing solution. Although genestein was not as effective as BHT in retarding oxidation, the results clearly demonstrate that it is able to act as an antioxidant in a bulk oil system. 相似文献
165.
Francisco Javier Trujillo Pei Ching Yeow Q. Tuan Pham 《Journal of food engineering》2003,60(4):357-366
The moisture sorption isotherm (MSI) of lean beef and fat beef was experimentally determined. The experimental procedure used was that of the COST 90 project with some modifications to accelerate equilibration. The procedure was validated with the standard reference material microcrystalline cellulose. The MSI of the beef at the highest humidity range was obtained by accelerating equilibration with changes of salts, using a low water activity salt for some time. This procedure was reliable for beef samples but not for the fat samples. No significant changes were found for lean beef in the temperature range 5–40 °C. Three models, GAB, Peleg and Lewicki, were used to fit the experimental data. The best fit was obtained with the GAB equation. The fat MSI was determined at 5, 15 and 25 °C and it was best fitted with the Lewicki model. 相似文献
166.
167.
168.
This paper presents an overview of four algorithms used for training multilayered perceptron (MLP) neural networks and the results of applying those algorithms to teach different MLPs to recognise control chart patterns and classify wood veneer defects. The algorithms studied are Backpropagation (BP), Quickprop (QP), Delta-Bar-Delta (DBD) and Extended-Delta-Bar-Delta (EDBD). The results show that, overall, BP was the best algorithm for the two applications tested. 相似文献
169.
Doan Pham Minh Nathalie Lyczko Haroun Sebei Ange Nzihou Patrick Sharrock 《Materials Science and Engineering: B》2012,177(13):1080-1089
The synthesis of calcium hydroxyapatite (Ca-HA) starting from calcium carbonate and different orthophosphate sources, including orthophosphoric acid, potassium, sodium and ammonium dihydrogen orthophosphates, was investigated under ambient conditions. The reaction started with calcium carbonate dissolution in an acid medium, followed by rapid precipitation of calcium cations with orthophosphate species to form calcium phosphate based particles which were in the size range of 0.4–1 μm. These particles then agglomerated into much larger ones, up to 350 μm in diameter (aggregates). These aggregates possessed an unstable porous structure which was responsible for the porosity of the final products. The highest specific surface area and pore volume were obtained with potassium dihydrogen orthophosphate. On the other hand, orthophosphoric acid led to the highest dissolution of calcium carbonate and the complete precipitation of orthophosphate species. Under ambient conditions, calcium phosphate based solid products of low crystallinity were formed. Different intermediates were identified and a reaction pathway proposed. 相似文献
170.
JA Saidi DT Chang ET Goluboff E Bagiella G Olsen H Fisch 《Canadian Metallurgical Quarterly》1999,161(2):460-462
PURPOSE: Recent reports suggest declining sperm counts in the United States. These reports did not include all available data and did not account for geographic variations noted in prior studies. We examined all available data on U.S. sperm counts and evaluated whether geographic variations account for the decline suggested. MATERIALS AND METHODS: We reviewed all 29 U.S. studies from 1938 to 1996 reporting manually counted semen analyses of 9,612 fertile or presumably fertile men. We determined mean sperm concentrations by geographic location with weighted analysis of variance, and assessed any changes with time by linear regression analysis. RESULTS: Mean sperm concentrations from New York were significantly higher than from all other U.S. cities (98.6 versus 71.6 x 10(6) sperm per cc, respectively, p = 0.006). There has been no statistically significant change with time for mean sperm concentrations reported from New York (p = 0.49) or from U.S. cities other than New York (p = 0.62). Analysis without separating by location revealed a decline (p = 0.047). CONCLUSIONS: Sperm concentrations are highest in New York compared to other U.S. cities. When accounting for this geographic difference and examining all available data, there appears to be no significant change in sperm counts in the U.S. during the last 60 years. Further studies addressing the causes of geographic variations are needed. 相似文献