全文获取类型
收费全文 | 95645篇 |
免费 | 7644篇 |
国内免费 | 4043篇 |
学科分类
工业技术 | 107332篇 |
出版年
2024年 | 171篇 |
2023年 | 1003篇 |
2022年 | 1592篇 |
2021年 | 2770篇 |
2020年 | 2121篇 |
2019年 | 1997篇 |
2018年 | 2334篇 |
2017年 | 2486篇 |
2016年 | 2571篇 |
2015年 | 3127篇 |
2014年 | 4407篇 |
2013年 | 5599篇 |
2012年 | 6460篇 |
2011年 | 7176篇 |
2010年 | 6407篇 |
2009年 | 6401篇 |
2008年 | 6237篇 |
2007年 | 5768篇 |
2006年 | 5512篇 |
2005年 | 4634篇 |
2004年 | 3921篇 |
2003年 | 3526篇 |
2002年 | 4058篇 |
2001年 | 3563篇 |
2000年 | 2540篇 |
1999年 | 1937篇 |
1998年 | 1836篇 |
1997年 | 1350篇 |
1996年 | 1190篇 |
1995年 | 945篇 |
1994年 | 684篇 |
1993年 | 552篇 |
1992年 | 424篇 |
1991年 | 354篇 |
1990年 | 280篇 |
1989年 | 234篇 |
1988年 | 206篇 |
1987年 | 151篇 |
1986年 | 99篇 |
1985年 | 104篇 |
1984年 | 84篇 |
1983年 | 72篇 |
1982年 | 60篇 |
1981年 | 57篇 |
1980年 | 57篇 |
1979年 | 32篇 |
1977年 | 45篇 |
1976年 | 61篇 |
1975年 | 25篇 |
1974年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
91.
磷酸酯类离子液体在燃油深度脱硫中的应用 总被引:16,自引:6,他引:10
研究了3种磷酸酯类离子液体,即1,3-二甲基咪唑磷酸二甲酯盐([MM im]DM P)、1-乙基-3-甲基咪唑磷酸二乙酯盐([EM im]DEP)和1-丁基-3-甲基咪唑磷酸二丁酯盐([BM im]DBP)的制备过程,考察了这3种磷酸酯类离子液体对模型油中3-甲基噻吩、苯并噻吩和二苯并噻吩的脱除效果及磷酸酯类离子液体的电化学再生方法。实验结果表明,这3种磷酸酯类离子液体的脱硫能力强弱顺序为:[EM im]DEP>[BM im]DBP[MM im]DM P;且对二苯并噻吩的脱除效果最好,对苯并噻吩的脱除效果次之,对3-甲基噻吩的脱除效果较差。以[EM im]DEP为萃取剂,油剂质量比为1∶1时,经5次萃取后,二苯并噻吩的脱除率可达到99.5%。利用电解法对[EM im]DEP进行了再生,在5~10V电压下电解10h,[EM im]DEP的脱硫率可以达到新鲜[EM im]DEP的90%以上。 相似文献
92.
叙述了石油库在发油过程中的HSE管理;发油过程中的危害识别,包括识别范围和内容;发油过程中风险评价的常用基本方法和常见问题;发油过程中危险源的管理控制,包括建立危险源网络图、加强现场监控和制定应急预案。 相似文献
93.
The aim of this study was to evaluate the use of total coliforms (TC) and faecal coliforms (FC) using a membrane filtration method for precise monitoring of faecal pollution in Korean surface water. The samples were collected in Korea from both main rivers and their tributaries. Presumptive TC * FC were enumerated. The ratios of presumptive FC to TC were not constant, but varied widely, and TC were difficult to enumerate because of overgrowth by background colonies. For FC this was not the case. Seven hundred and three purified strains of presumptive TC * FC and their background colonies were biotyped using API 20E. Among 272 presumptive TC, non-faecal related species, Aeromonas hydrophila dominated (34.6%) and E. coli accounted for only 5.1%. In contrast, E. coli made up 89% of the 209 presumptive FC. Furthermore, of 164 background colonies on Endo Agar LES, 54.9% was A. hydrophila, while background colonies on m-FC Agar were few (58 strains), and despite their atypical colony appearance, most of them were biotyped as enteric bacteria. These results reveal that the detection of FC rather than TC using m-FC Agar is more appropriate for faecal pollution monitoring in eutrophicated surface water located in a temperate region. 相似文献
94.
95.
Kee S. Moon M. Levy Yong K. Hong H. Bakhru S. Bakhru 《Ferroelectrics Letters Section》2003,30(3):47-57
Advances in the fabrication of solid-solution single crystal relaxor ferroelectrics have made it possible to produce highly efficient piezoelectric crystals, and have attracted renewed interest in the use of these crystals for a new generation of piezoelectric transducers, actuators and sensors. Of particular interest is their incorporation into micro-electromechanical systems (MEMS). In this paper we report on the laser-induced wet chemical etching of lead zinc niobate-lead titanate (PZN-PT) in hydrochloric acid (HCl). Argon-ion laser radiation at power levels up to 4 W is focused to a spot diameter of about 15μm and results in the chemical etching of grooves at patterning speeds up to 5μm/sec. Crystal ion slicing, an ion-implant-based film separation technique, is used in combination with laser etching to form 5 to 10μm-thick patterned and freestanding films for incorporation into micro-electromechanical devices. 相似文献
96.
Soo Jin Kim Wha Young Lee Yeungho Park Wansoo Huh Young Gwan Ko 《Polymer Engineering and Science》2003,43(5):1011-1017
Supported zirconcene catalysts on a new support, MgO, were prepared and tested in ethylene polymerization. Three types of impregnation methods were employed to find an optimum supporting method for MgO. The direct impregnation of Cp2ZrCl2 on MgO showed low metal loading and polymerization activity, while the catalyst had a higher metal loading and polymerization activity when MgO was treated with methylaluminoxane (MAO) before supporting. Treatment of MgO with MAO during the supporting step invoked two types of catalytic sites, which was evidenced by the bimodal molecular weight distribution of the polymer products. MgO is considered to have potential as a support for metallocenes. 相似文献
97.
在cdma20001x前向信道中,要对一段信号进行传送,一般选用QPSK调制,因为QPSK调制比QAM更适合噪音环境。采用TI6000系列的TMS320C6711芯片处理前向信道信号,可以对复杂性和实时性较高的信号做采集、量化、编码、调制等实时处理,主要功能通过软件编程实现,从而使系统具有结构灵活、可靠性高、可扩展等优点。 相似文献
98.
随机激光器的最新进展 总被引:5,自引:2,他引:3
综述了近年来随机激光器的最新研究结果,包括随机激光产生的机制,随机增益介质的制备方法,随机激光器的激励与发光特性和随机激光理论。最后,介绍了随机激光器的应用前景。 相似文献
99.
100.