全文获取类型
收费全文 | 108075篇 |
免费 | 10725篇 |
国内免费 | 6412篇 |
专业分类
电工技术 | 8284篇 |
技术理论 | 7篇 |
综合类 | 9142篇 |
化学工业 | 16254篇 |
金属工艺 | 6504篇 |
机械仪表 | 7004篇 |
建筑科学 | 8673篇 |
矿业工程 | 3824篇 |
能源动力 | 3240篇 |
轻工业 | 8629篇 |
水利工程 | 2933篇 |
石油天然气 | 5789篇 |
武器工业 | 1209篇 |
无线电 | 11632篇 |
一般工业技术 | 11842篇 |
冶金工业 | 4745篇 |
原子能技术 | 1558篇 |
自动化技术 | 13943篇 |
出版年
2024年 | 427篇 |
2023年 | 1659篇 |
2022年 | 3336篇 |
2021年 | 4568篇 |
2020年 | 3474篇 |
2019年 | 2695篇 |
2018年 | 2980篇 |
2017年 | 3403篇 |
2016年 | 3001篇 |
2015年 | 4261篇 |
2014年 | 5662篇 |
2013年 | 6552篇 |
2012年 | 7808篇 |
2011年 | 8249篇 |
2010年 | 7501篇 |
2009年 | 7367篇 |
2008年 | 7358篇 |
2007年 | 7181篇 |
2006年 | 6761篇 |
2005年 | 5703篇 |
2004年 | 3979篇 |
2003年 | 3059篇 |
2002年 | 2790篇 |
2001年 | 2675篇 |
2000年 | 2550篇 |
1999年 | 2070篇 |
1998年 | 1436篇 |
1997年 | 1220篇 |
1996年 | 1094篇 |
1995年 | 960篇 |
1994年 | 791篇 |
1993年 | 578篇 |
1992年 | 442篇 |
1991年 | 354篇 |
1990年 | 327篇 |
1989年 | 236篇 |
1988年 | 180篇 |
1987年 | 113篇 |
1986年 | 116篇 |
1985年 | 62篇 |
1984年 | 42篇 |
1983年 | 24篇 |
1982年 | 37篇 |
1981年 | 29篇 |
1980年 | 46篇 |
1979年 | 15篇 |
1966年 | 3篇 |
1965年 | 7篇 |
1959年 | 11篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
951.
The investigation of the electrode reactions occurring at metal and vitreous carbon cathodes in the standard chromium electroplating solution, 200 g dm?3 CrO3 and 2 g dm?3 H2SO4, has been continued and this paper considers the mechanism of deposition of metallic chromium and the role of surface films in this process. It is confirmed that chromium deposition occurs at potentials negative to ?1.6 V versus Hg/Hg2SO4 and under galvanostatic or potentiostatic conditions, the current efficiency is 30–45%. Moreover at a vitreous carbon electrode, potential step experiments lead to risingI-t transients characteristic of instantaneous nucleation and three dimensional phase growth. At potentials just prior to metal deposition the potential sweep and step experiments show clear evidence for the formation of a strongly passivating film (this may be in addition to an existing less passivating layer). The important of the film varies with H2SO4 concentration and at intermediate concentrations, potential step experiments lead to unusual oscillatingI-t transients. 相似文献
952.
953.
954.
张掖沙湾水厂的水力循环澄清池是上世纪70年代初建造。由于池深,各部分功能不匹配,动能有效利用率低,排泥不畅,对水量、水质变化适应性差,限制了产水量的提高。经强化絮凝、增设斜管、折板等综合性改造后.单池产水量由原来80m^3/d增加到140m^3/d,药耗降低了15%~20%。改造后仅1年多时间.即可从增产水的效益和节省药耗中收回投资。 相似文献
955.
南极假丝酵母脂肪酶发酵条件优化及酶学性质 总被引:7,自引:0,他引:7
分别用摇瓶和15L发酵罐,对南极假丝酵母产胞外脂肪酶的培养基成分和操作条件进行了实验研究。得到最优的培养基组成为:豆粉40g/L,淀粉15g/L,豆油5mL/L,K2HPO4g/L,MgsO4·7H2O1g/L,Tween-800.1%,酵母膏5g/L;操作条件为:温度24℃,初始pH值为6.0,通气量为10.0L/min。在此培养条件下,发酵周期缩短至54h。由15L发酵罐生产的酶液酶活达到19.2U/mL。酶液在pH值为4.0~6.0和7.5~9.0范围内较稳定,其最适宜pH值范围为6~8.5;70℃时酶的催化活性最大.在40~70℃的温度范围内保持1h后残留酶活为60%。 相似文献
956.
957.
Jiuxin Jiang Bo Zhu Peiling Wang Weiwu Chen Dongsheng Yan Hanrui Zhuang Yibing Cheng 《Journal of the American Ceramic Society》2005,88(4):950-953
The Pr α-sialon powders prepared by self-propagating high-temperature synthesis (SHS), consisting of 55 wt% Pr α-sialon and 45 wt% of β-sialon (abbreviated as α' and β'), were hot-pressed at 1800°C for 1 h. The results showed that Pr α' phase would transfer to β' with the appearance of JEM phase (Pr(Si6− z Al z )(N10− z O z )) after sintering, thus resulting in the increase of β' phase to 86 wt%. The addition of Y2 O3 into SHS-ed Pr α' powders as the starting materials restrains the transformation of α' to β' and prevents the formation of JEM phase as well. The nucleation mechanism of Pr α' grain during hot-pressing was investigated in terms of transmission electron microscope and energy-dispersive spectrometer analysis. Two nucleation modes of Pr α' grains were found, i.e., nucleating on the undissolved Pr α' grains and on the nuclei of (Pr, Y) α' grains precipitated from liquid phase. 相似文献
958.
959.
960.
Microcapsules with phenolic resin (PFR) shell and n‐hexadecane (HD) core were prepared by controlled precipitation of the polymer from droplets of oil‐in‐water emulsion, followed by a heat‐curing process. The droplets of the oil phase are composed of a polymer (PFR), a good solvent (ethyl acetate), and a poor solvent (HD) for the polymer. Removal of the good solvent from the droplets leads to the formation of microcapsules with the poor solvent encapsulated by the polymer. The microstructure, morphology, and phase‐change property as well as thermal stability of the microcapsules were systematically characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimety (DSC), and thermogravimetric analysis (TGA). The phase‐change microcapsules exhibit smooth and perfect structure, and the shell thickness is a constant fraction of the capsule radius. The initial weight loss temperature of the microcapsules was determined to be 330°C in N2 and 255°C in air, respectively, while that of the bulk HD is only about 120°C both in air and N2 atmospheres. The weight loss mechanism of the microcapsules in different atmosphere is not the same, changing from the pyrolysis temperature of the core material in N2 to the evaporation of core material caused by the fracture of shell material in air. The melting point of HD in microcapsules is slightly lower than that of bulk HD, and a supercooling was observed upon crystallization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献