全文获取类型
收费全文 | 107258篇 |
免费 | 9919篇 |
国内免费 | 6148篇 |
专业分类
电工技术 | 7610篇 |
技术理论 | 6篇 |
综合类 | 8274篇 |
化学工业 | 16781篇 |
金属工艺 | 6496篇 |
机械仪表 | 7122篇 |
建筑科学 | 8368篇 |
矿业工程 | 3496篇 |
能源动力 | 3427篇 |
轻工业 | 6507篇 |
水利工程 | 2137篇 |
石油天然气 | 6406篇 |
武器工业 | 1225篇 |
无线电 | 12263篇 |
一般工业技术 | 11863篇 |
冶金工业 | 4845篇 |
原子能技术 | 1398篇 |
自动化技术 | 15101篇 |
出版年
2024年 | 377篇 |
2023年 | 1499篇 |
2022年 | 2853篇 |
2021年 | 4176篇 |
2020年 | 3175篇 |
2019年 | 2716篇 |
2018年 | 3007篇 |
2017年 | 3400篇 |
2016年 | 3067篇 |
2015年 | 4343篇 |
2014年 | 5427篇 |
2013年 | 6510篇 |
2012年 | 7041篇 |
2011年 | 7630篇 |
2010年 | 7203篇 |
2009年 | 6718篇 |
2008年 | 6599篇 |
2007年 | 6365篇 |
2006年 | 6167篇 |
2005年 | 5185篇 |
2004年 | 3911篇 |
2003年 | 3814篇 |
2002年 | 4210篇 |
2001年 | 3624篇 |
2000年 | 2719篇 |
1999年 | 2438篇 |
1998年 | 1689篇 |
1997年 | 1417篇 |
1996年 | 1428篇 |
1995年 | 1103篇 |
1994年 | 826篇 |
1993年 | 652篇 |
1992年 | 512篇 |
1991年 | 359篇 |
1990年 | 291篇 |
1989年 | 221篇 |
1988年 | 199篇 |
1987年 | 109篇 |
1986年 | 97篇 |
1985年 | 58篇 |
1984年 | 36篇 |
1983年 | 32篇 |
1982年 | 37篇 |
1981年 | 23篇 |
1980年 | 25篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1973年 | 4篇 |
1959年 | 5篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
以环氧氯丙烷为交联剂,将聚酰胺胺树状大分子(PAMAM)接枝到稻草基体上,利用FTIR、SEM、XRD、TG等对其结构进行了表征和分析。考察了其对Nd~(3+)、Sm~(3+)、La~(3+)稀土金属离子的吸附性能,探讨了吸附时间、稀土金属离子浓度、吸附温度、溶液pH等因素对吸附性能的影响。同时对吸附过程的动力学、吸附等温线和吸附热力学进行了研究。结果表明,所制备的吸附剂对Nd~(3+)、Sm~(3+)、La~(3+)稀土金属离子的吸附平衡时间约为4 h,平衡吸附量分别为47.14、40.11和50.12 mg/g。吸附过程符合拟二级动力学模型和Freundlich等温线,表明此吸附过程是属于化学吸附过程。吸附热力学研究表明,此吸附过程是自发进行的,同时吸附过程是一个混乱度增加的熵增过程。 相似文献
994.
国内二氯苯生产现状及今后发展之我见 总被引:5,自引:0,他引:5
介绍了国内二氯苯3种不同生产式敢,规模及对二氯苯,邻二氯苯的精帛工艺,并分析了国内二氯苯生产装置中存在的问题,详细分析了对二氯苯,邻二氯苯的市场及应用情况,针对国内二氯苯的生产现状及与国外的差距提出了今后发展的建议。 相似文献
995.
Pramod Kandanarachchi Andrew Guo Dmytro Demydov Zoran Petrovic 《Journal of the American Oil Chemists' Society》2002,79(12):1221-1225
The kinetics and mechanism of the hydroformylation of soybean oil by homogeneous ligand-modified rhodium catalysts were investigated
at 70–130°C and 4000–11,000 kPa. The effects of reaction rates on systematic variations in reaction parameters were evaluated
in order to develop an industrial process to convert vegetable oils to polyaldehydes. The activation energies in the presence
of triphenylphosphine (Ph3P) (61.1±0.8 kJ/mol) (mean±SD) and triphenyl phosphite [(PhO)3P] (77.4±5.0 kJ/mol) were determined. The catalyst was deactivated at temperatures higher than 100°C. An evaluation of the
effects of the reaction parameters on initial rates yielded the rate laws for Ph3P {rate=k [olefin][Rh(CO)2Acac]1.1 [Ph3P]−0.5 (pH2+pCO)1.4, where Rh(CO)2Acac is (acetylacetonato)dicarbonylrhodium (I)} and (PhO)3P {rate=[olefin] [Rh(CO)2Acac]1.2 [(PhO)3P]−0.8 (pH2+pCO)0.9 at total pressures lower than 7000 kPa, and rate =[olefin] [Rh(CO)2Acac]1.2 [(PhO)3P]−0.8(pH2+pCO)1.7 at total pressures higher than 7000 kPa}. 相似文献
996.
Geoff E. Fair Ming Y. He Robert M. McMeeking F. F. Lange 《Journal of the American Ceramic Society》2005,88(7):1879-1885
Finite element modeling and linear elastic fracture mechanics are used to model the residual stresses and failure stress of ceramic composites consisting of polyhedral alumina cores surrounded by thin alumina/mullite layers in residual compression. This type of composite architecture is expected to exhibit isotropic threshold strength behavior, in which the strength of the composite for a particular assumed flaw will be constant and independent of the orientation of tensile loading. The results of the modeling indicate that the strengths of such architectures will be higher than those of laminates of similar architectural dimensions that were previously found to exhibit threshold strength behavior for a particular flaw type. Flexural testing of the polyhedral architectures reveals that failure is dominated by processing defects found at junctions between the polyhedra. Fractography revealed the interaction of these defects with the residual stresses in the compressive layers that separate the polyhedra. 相似文献
997.
Yun‐He Zhang Qin‐Hua Liu Ya‐Ming Niu Shu‐Ling Zhang Dong Wang Zhen‐Hua Jiang 《应用聚合物科学杂志》2005,97(4):1652-1658
A series of block copolymers composed of poly(ether ether ketone) (PEEK) and poly(ether ether ketone ketone) (PEEKK) components were prepared from their corresponding oligomers via a nucleophlilic aromatic substitution reaction. Various properties of the copolymers were investigated with differential scanning calorimetry (DSC) and a tensile testing machine. The results show that the copolymers exhibited no phase separation and that the relationship between the glass‐transition temperature (Tg) and the compositions of the copolymers approximately followed the formula Tg = Tg1X1 + Tg2X2, where Tg1 and Tg2 are the glass‐transition‐temperature values of PEEK and PEEKK, respectively, and X1 and X2 are the corresponding molar fractions of the PEEK and PEEKK segments in the copolymers, respectively. These copolymers showed good tensile properties. The crystallization kinetics of the copolymers were studied. The Avrami equation was used to describe the isothermal crystallization process. The nonisothermal crystallization was described by modified Avrami analysis by Jeziorny and by a combination of the Avrami and Ozawa equations. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1652–1658, 2005 相似文献
998.
This work was undertaken to discuss in depth the vital differences in the morphological development during synthesis, and properties of starch‐g‐poly‐(vinyl acetate) copolymers using two different initiators, potassium persulfate (KPS) and ceric ammonium nitrate (CAN). KPS‐initiated system gave relatively low values of grafting ratio and grafting efficiency, indicating a great tendency for the formation of poly(vinyl acetate) homopolymer (PVAc). Yet, higher values were seen for the CAN‐initiated system. Transmission electron microscope observations indicated a relatively broad distribution of latex particles for the KPS‐initiated system. The surface potential of latex particles was about ?3.5 mV, which turned out to be insufficient to maintain stability of latex particles. On the other hand, a uniform particle size distribution was found for the CAN‐initiated system, as the surface potential of latex particles was 21.5 mV. Moreover, radicals on starch molecules were generated directly through a redox reaction with positively charged ceric ion. The hydrophobic PVAc chains were thus grafted on starch, resulting in an amphiphilic graft copolymer, which provides a sufficient stabilization degree as a role of surfactant to render a relatively uniform distribution of latex particles. The synthesized starch‐g‐poly(vinyl acetate) copolymers were further converted to starch‐g‐poly(vinyl alcohol) through saponification, which were subjected to evaluations regarding the biodegradation and cell culture capability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3017–3027, 2006 相似文献
999.
基于无线传感器网络的土壤墒情监测系统 总被引:2,自引:0,他引:2
目前农田监测智能化水平低,管理实时性差,远距离信息传输能力弱、可扩展性不强,且市场上普遍的土壤墒情机一般基于有线连接方式,对于农田监测有一定的局限性,价格昂贵,不适合一般农田的智能化管理。设计了一种土壤监测无线传感网络节点及其远程传输装置,该系统通过PICl8F4520单片机将ARN-100土壤水分传感器、ARN—Tw土壤温度传感器及H311-AS002-T土壤酸碱度传感器采集到的土壤参数处理后,通过ZigBee近距离无线通讯网络以及3G远程无线网络,将数据实时传输给监测终端。测试结果验证了该系统的合理性与实用性,符合现代农业发展方向。 相似文献
1000.