全文获取类型
收费全文 | 75114篇 |
免费 | 6723篇 |
国内免费 | 3603篇 |
专业分类
电工技术 | 4825篇 |
技术理论 | 6篇 |
综合类 | 5496篇 |
化学工业 | 12516篇 |
金属工艺 | 3996篇 |
机械仪表 | 4560篇 |
建筑科学 | 6043篇 |
矿业工程 | 2012篇 |
能源动力 | 2010篇 |
轻工业 | 7127篇 |
水利工程 | 1492篇 |
石油天然气 | 3656篇 |
武器工业 | 670篇 |
无线电 | 8598篇 |
一般工业技术 | 8561篇 |
冶金工业 | 3033篇 |
原子能技术 | 958篇 |
自动化技术 | 9881篇 |
出版年
2024年 | 383篇 |
2023年 | 1313篇 |
2022年 | 2503篇 |
2021年 | 3201篇 |
2020年 | 2461篇 |
2019年 | 1987篇 |
2018年 | 2278篇 |
2017年 | 2518篇 |
2016年 | 2198篇 |
2015年 | 3094篇 |
2014年 | 3900篇 |
2013年 | 4530篇 |
2012年 | 5090篇 |
2011年 | 5436篇 |
2010年 | 4740篇 |
2009年 | 4674篇 |
2008年 | 4679篇 |
2007年 | 4197篇 |
2006年 | 4155篇 |
2005年 | 3483篇 |
2004年 | 2365篇 |
2003年 | 2019篇 |
2002年 | 1937篇 |
2001年 | 1649篇 |
2000年 | 1605篇 |
1999年 | 1679篇 |
1998年 | 1353篇 |
1997年 | 1140篇 |
1996年 | 993篇 |
1995年 | 888篇 |
1994年 | 650篇 |
1993年 | 496篇 |
1992年 | 442篇 |
1991年 | 305篇 |
1990年 | 238篇 |
1989年 | 220篇 |
1988年 | 169篇 |
1987年 | 97篇 |
1986年 | 87篇 |
1985年 | 59篇 |
1984年 | 41篇 |
1983年 | 32篇 |
1982年 | 35篇 |
1981年 | 22篇 |
1980年 | 29篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
Poly(ethylene terephthalate) (PET) was blended with two different poly(oxybenzoate‐p‐trimethylene terephthalate) copolymers, designated T28 and T64, with the level of copolymer varying from 1 to 15 wt %. All samples were prepared by solution blending in a 60/40 (by weight) phenol/tetrachloroethane solvent at 50°C. The crystallization behavior of the samples was studied by DSC. The results indicate that both T28 and T64 accelerated the crystallization rate of PET in a manner similar to that of a nucleating agent. The acceleration of PET crystallization rate was most pronounced in the PET/T64 blends with a maximum level at 5 wt % of T64. The melting temperatures for the blends are comparable to that of pure PET. The observed changes in crystallization behavior are explained by the effect of the physical state of the copolyester during PET crystallization as well as the amount of copolymer in the blends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1599–1606, 2002 相似文献
43.
Donggang Yao Pratapkumar Nagarajan Lei Li Allen Y. Yi 《Polymer Engineering and Science》2007,47(4):530-539
An embossing strategy involving a hot station and a cold station for sequentially heating and cooling the embossing tool was investigated to reduce cycle times in hot embossing polymer microstructures. Experimental studies showed that aluminum stamps with a thickness of 1.4 mm can be rapidly heated from room temperature to 200°C in 3 s using contact heating against a hot station at 250°C. Microchannels and microlenses were successfully embossed onto high‐density polyethylene and acrylonitrile–butadiene–styrene substrates using a heating time less than 3 s and a total cycle time around 10 s. The two‐station embossing process for the microlens was also numerically studied. The simulated filling behavior agreed with the experimental observation and the predicted thermal and deformation history of the polymer offered a good explanation on the experimentally observed process characteristics. POLYM. ENG. SCI., 47:530–539, 2007. © 2007 Society of Plastics Engineers. 相似文献
44.
Photoinitiated crosslinking of EVA in the presence of benzophenone (BP) as photoinitiator and triallyl isocyanurate (TAIC) as crosslinker and characterization of the related properties have been studied by gel determination, heat extension, DSC, DMTA, TGA, and mechanical measurements. The photoinitiated crosslinking efficiency of the EVA‐BP‐TAIC system and various factors affecting the crosslinking process, such as photoinitiator and crosslinker and their concentrations, irradiation temperature, and irradiation atmosphere were studied in detail and optimized by comparison of gel contents. The results show that the EVA samples with a thickness of 1 mm are readily crosslinked to a gel content of above 80% with 5 s UV‐irradiation under optimum conditions. The data from the heat extension and DSC show that the crosslinking density of photocrosslinked EVA increase and their crystallinities decrease with increasing the UV‐irradiation time. At the same time, photocrosslinking of EVA leads to a lowering of the melt temperature and a decrease of heat of fusion. The DMTA results show that photocrosslinking increases the amorphous phase and storage modulus of the crosslinked EVA, but does not change the glass transition temperature. The data from TGA and mechanical tests give evidence that the thermal stability and mechanical properties of photocrosslinked EVA samples are much better than those of the uncrosslinked EVA. POLYM. ENG. SCI., 47:1761–1767, 2007. © 2007 Society of Plastics Engineers 相似文献
45.
本文针对地铁车厢内控制设备分散的问题,设计了基于TCNRTP的地铁列车控制网络系统。采用NS2网络模拟软件构建的虚拟网络环境,编写消息数据传输层协议,通过测试列控网络的通信效率,得出了影响通信效率的因素;通过配置列控通信设备的基本功能和设定装置运行参数达到配置网络化通信的目的。 相似文献
46.
建设鄱阳湖生态经济区是国家从战略全局和长远发展出发作出的一项重大决策。如何主动策应鄱阳湖生态经济区建设,推动吉安进位赶超、跨越发展,是摆在我们各级政府和科技部门面前一项亟待解决的问题。为此,一是要提高认识,统一思想,切实增强策应规划的使命感和责任感;二是要结合实际,突出重点,全面对接鄱阳湖生态经济区规划;三是要加强领导,落实措施,确保吉安进位赶超、绿色崛起取得明显成效。 相似文献
47.
Jianfeng Wu Jian Li Xiaohong Xu Lanfang Yang Jufang Wu Fang Zhao Chuanguo Li 《武汉理工大学学报(材料科学英文版)》2009,24(4):651-653
A new type of high temperature energy storage material was obtained through the melt infiltration method, using compounding
SiC ceramic foam as matrix and Na2SO4 as phase change material. The resulting composite material was measured by XRD, SEM, TG-DSC methods. The experimental results
indicate that the composite is composed of silicon carbide, sodium sulfate and square quartz, and no chemical reactions occurs
between Na2SO4 and SiC matrix. Na2SO4 has a good bonding with the SiC ceramic foam matrix. As the composite material is characterized by high thermal energy storage
density and high thermal conductivity, it is suit for energy storage under high temperature.
Funded by the “863” Hi-Tech Research and Development Program of China (2008AA05Z418) 相似文献
48.
Phosphatidylcholine acyltransferase (lecithin:cholesterol acyltransferase or LCAT; EC 2.3.1.43) activity was found to be present
in pig ovarian follicular fluid (POFF), in addition to pig serum (PS). The cholesterol esterification rate in both POFF and
PS is linear with incubation time up to 2 hr. The mean absolute rate of POFF-cholesterol esterification was 8.1±0.4 nmoles
per ml per hr approximately one-fourth of that in PS. However, the fractional rate (percent of labeled cholesterol esterified
per hr) of POFF-cholesterol esterification was similar to that observed in PS. There was little variation of absolute rate
of cholesterol esterification in the fluid obtained from different sizes of follicles. Fatty acid or triacylglycerol did not
participate in the reaction of cholesterol esterification in POFF. No appreciable change in enzymatic activity was found from
storing POFF at 4 C for periods of time up to 24 hr or at −70 C up to 2 months, but activity was lost thereafter. On the other
hand, PS showed a much longer period of stability (5 days at 4 C and 9 months at −70 C). A discrepancy between the fatty acid
composition of cholesteryl esters formed by the LCAT reaction and the fatty acid composition at the C-2 position of phosphatidylcholine
led us to propose a two-step mechanism for the LCAT reaction. It is concluded that the LCAT of POFF, as well as that of plasma,
is specific for individual fatty acids rather than for the fatty acid composition of phosphatidylcholine. The fatty acid concentration
of lysophosphatidylcholine decreased during prolonged incubation times (6 to 21 hr) suggesting that the increased lysophosphatidylcholine
formed as a product of the LCAT reaction may be reused as substrate for the LCAT reaction or for hydrolysis by lysophosphatidylcholine
hydrolase.
Presented at the AOCS Meeting, New York, May 1977. 相似文献
49.
Self-sustained oscillations obtained during the catalytic oxidation of CO and H2 were studied over Rh/SiO2 by an FTIR-mass spectrometric technique. An average oscillatory period of 7.1±0.5 minutes was obtained for the CO/O2 reaction at 348 K. For the H2/O2 oscillatory reaction the period was observed to be 1.3±0.8 minutes. When the oscillations were coupled at the same temperature, the period for both the CO/O2 and the H2/O2 reactions was observed to be 7.9±0.8 minutes. The kinetic coupling of the reaction rates is explained by considering the periodic fluctuations in surface temperature which occur as a result of the more exothermic CO/O2 reaction. 相似文献
50.
Efficient and selective oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones catalyzed by potassium permanganate supported on Kieselguhr reagent under solvent free conditions are reported. 相似文献