全文获取类型
收费全文 | 75959篇 |
免费 | 6564篇 |
国内免费 | 2017篇 |
专业分类
电工技术 | 1144篇 |
综合类 | 4125篇 |
化学工业 | 30516篇 |
金属工艺 | 1712篇 |
机械仪表 | 1022篇 |
建筑科学 | 1587篇 |
矿业工程 | 1459篇 |
能源动力 | 2335篇 |
轻工业 | 26569篇 |
水利工程 | 274篇 |
石油天然气 | 3874篇 |
武器工业 | 129篇 |
无线电 | 1023篇 |
一般工业技术 | 3975篇 |
冶金工业 | 2522篇 |
原子能技术 | 594篇 |
自动化技术 | 1680篇 |
出版年
2024年 | 343篇 |
2023年 | 1067篇 |
2022年 | 2129篇 |
2021年 | 2779篇 |
2020年 | 2444篇 |
2019年 | 2470篇 |
2018年 | 2104篇 |
2017年 | 2552篇 |
2016年 | 2611篇 |
2015年 | 2680篇 |
2014年 | 3921篇 |
2013年 | 4676篇 |
2012年 | 5574篇 |
2011年 | 5653篇 |
2010年 | 3962篇 |
2009年 | 3983篇 |
2008年 | 3524篇 |
2007年 | 4607篇 |
2006年 | 4315篇 |
2005年 | 3607篇 |
2004年 | 3021篇 |
2003年 | 2619篇 |
2002年 | 2319篇 |
2001年 | 1901篇 |
2000年 | 1763篇 |
1999年 | 1504篇 |
1998年 | 1183篇 |
1997年 | 954篇 |
1996年 | 787篇 |
1995年 | 643篇 |
1994年 | 569篇 |
1993年 | 483篇 |
1992年 | 383篇 |
1991年 | 279篇 |
1990年 | 233篇 |
1989年 | 150篇 |
1988年 | 108篇 |
1987年 | 124篇 |
1986年 | 80篇 |
1985年 | 87篇 |
1984年 | 88篇 |
1983年 | 41篇 |
1982年 | 28篇 |
1981年 | 26篇 |
1980年 | 48篇 |
1979年 | 19篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1975年 | 17篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
高镁边缘磷矿制取阻燃剂氢氧化镁的工艺 总被引:1,自引:0,他引:1
为解决大量的高镁低磷边缘磷矿废渣堆存对环境的影响,开发了以其为原料制取阻燃剂氢氧化镁工艺.该工艺主要包括酸解磷矿和镁沉淀过程,重点讨论了沉淀氢氧化镁过程中时间、温度、氨镁摩尔比n(NH3/MgO)等多种因素的影响,得到的最佳工艺条件是:反应温度65℃,反应时间80min,n(NH3/MgO)为5∶ 1,镁的沉淀效率为80%. 相似文献
152.
Fernanda R C Damasceno Denise M G Freire Magali C Cammarota 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):730-738
BACKGROUND: The application of lipase‐rich enzyme pools (such as the crude solid enzymatic preparation (SEP) obtained from Penicillium restrictum solid‐state fermentation of agro‐industrial wastes) to activated sludge systems may be an effective strategy for preventing various operational problems. The continuous addition of SEP to the treatment system can become cost‐prohibitive when in situ production and/or storage are factored in. The application of SEP to high‐fat wastewater treatment would only be justified as an emergency measure, such as a sudden increase in the fat content of the bioreactor influent. Therefore, the primary objective of this work was to investigate the efficiency of a crude SEP during fat shock loads, simulated through the periodic addition of dairy industry waste containing high fat concentrations to the feed stock of an activated sludge system, operated in continuous mode. RESULTS: The test bioreactor exhibited a higher average chemical oxygen demand (COD) removal efficiency than the control bioreactor (83% for control and 90% for test) and the fat accumulation in the biological flocs of the test bioreactor was 3.2 times lower than that in the control bioreactor. Turbidity was also lower in the effluent of the test bioreactor (123 and 66 FTU in control and test, respectively) and it had a shorter recovery time between shock loads, especially when the interval between loads was shorter than one month (biweekly and weekly shock loads). CONCLUSION: The addition of SEP during fat overloads in the reactor feed maintained efficient COD removal in the test bioreactor for 270 days without any operational problems. Copyright © 2008 Society of Chemical Industry 相似文献
153.
154.
Anumberoflanthanideternarycomplexescon tainingheterocyclicamineshavebeenreportedsince1960 [1] .Inrecentyearsmuchattentionhasbeenpaidtoquaternarycomplexesoflanthanidesbecauseofin terestingstructure ,coordinationmode ,competitionre actionandproperty[2~ 9] .ESRcane… 相似文献
155.
156.
157.
158.
159.
Ignacio Rintoul 《Polymer》2005,46(13):4525-4532
A precise data set describing the kinetics of the free radical copolymerization of acrylamide/acrylic acid (AM/AA) in the range of low total monomer concentration as a function of the pH, total monomer concentration, initiator concentration, and comonomer ratio is presented. Strong impact on the reactivity ratios has been identified for the pH and total monomer concentration. Specifically, at constant total monomer concentration of 0.4 mol/l and T=313 K the reactivity ratio of AM increases from 0.54 at pH 1.8 to 3.04 at pH 12. Contrarily, the reactivity ratio of AA decreases from 1.48 to 0.32. The crossover occurs at pH≈4.2. Electrostatic effects due to the variation of the degree of ionization of AA are primarily suggested to influence the kinetics. When the total monomer concentration increases from 0.2 to 0.6 mol/l at constant pH=12, the reactivity ratios of AM and AA decrease from 4.01 to 2.13 and increase from 0.25 to 0.47, respectively. Reduction of electrostatic repulsion between the ionized monomer AA and partially charged growing polymer chain ends due to higher ionic strength at higher total monomer concentration serves as explanation of the effect. The precise data set is the prerequisite for a novel approach to calculate copolymer compositions in case of variable monomer reactivity. 相似文献
160.
报道了硝酸老化处理方法对MgCr_2O_4—Bi_2O_3陶瓷湿敏元件的结构和性能的影响。实验结果表明,硝酸老化处理不仅是一种可行的造孔方法,而且对元件的力学和电学性能有重要影响。用浓度适宜的硝酸处理后,会得到性能较好的元件。 相似文献