全文获取类型
收费全文 | 62479篇 |
免费 | 5629篇 |
国内免费 | 3244篇 |
专业分类
电工技术 | 4100篇 |
技术理论 | 4篇 |
综合类 | 4792篇 |
化学工业 | 10138篇 |
金属工艺 | 3507篇 |
机械仪表 | 4091篇 |
建筑科学 | 4788篇 |
矿业工程 | 1390篇 |
能源动力 | 1824篇 |
轻工业 | 4614篇 |
水利工程 | 1269篇 |
石油天然气 | 2705篇 |
武器工业 | 493篇 |
无线电 | 7874篇 |
一般工业技术 | 7960篇 |
冶金工业 | 2555篇 |
原子能技术 | 785篇 |
自动化技术 | 8463篇 |
出版年
2024年 | 243篇 |
2023年 | 885篇 |
2022年 | 1683篇 |
2021年 | 2373篇 |
2020年 | 1718篇 |
2019年 | 1556篇 |
2018年 | 1654篇 |
2017年 | 1851篇 |
2016年 | 1899篇 |
2015年 | 2516篇 |
2014年 | 3019篇 |
2013年 | 3675篇 |
2012年 | 3940篇 |
2011年 | 4333篇 |
2010年 | 3944篇 |
2009年 | 3608篇 |
2008年 | 3651篇 |
2007年 | 3373篇 |
2006年 | 3363篇 |
2005年 | 2875篇 |
2004年 | 2260篇 |
2003年 | 2380篇 |
2002年 | 2989篇 |
2001年 | 2534篇 |
2000年 | 1721篇 |
1999年 | 1428篇 |
1998年 | 1068篇 |
1997年 | 890篇 |
1996年 | 805篇 |
1995年 | 702篇 |
1994年 | 593篇 |
1993年 | 448篇 |
1992年 | 328篇 |
1991年 | 262篇 |
1990年 | 190篇 |
1989年 | 152篇 |
1988年 | 130篇 |
1987年 | 74篇 |
1986年 | 58篇 |
1985年 | 41篇 |
1984年 | 31篇 |
1983年 | 16篇 |
1982年 | 22篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1959年 | 4篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
二过碘酸合银(Ⅲ)钾引发丙类酸甲酯在淀粉上接枝共聚合反应的研究 总被引:2,自引:0,他引:2
研究了由二过碘酸合银(Ⅲ)钾(简称Ag(Ⅲ))与可溶性淀粉组成的氧化还原体系,于碱性介质中引发淀粉的接枝共聚合反应,得到高接枝效率的接枝共聚物,测定了引发剂浓度、单体浓度、pH值和反应温度对接枝参数的影响,并探讨了引发机理。 相似文献
22.
23.
Development of the Chinese Scientometric Indicators (CSI) 总被引:1,自引:0,他引:1
We describe the Chinese Scientometric Indicators (CSI), an indicator database derived from the Chinese Science Citation Database (CSCD). Its design is supported by the Natural Sciences Foundation of China (NSFC). In this indicator database data of a statistical nature are organized and categorized leading to ranked lists and providing bases for comparisons among Chinese institutions and regions. 相似文献
24.
行波热声驱动器的性能分析 总被引:1,自引:0,他引:1
在简单介绍行波热声驱动器的研究历史、工作机理及其与驻波型热声驱动器的区别之后,着重对环路部分的性能进行了预测分析,并给出一些有益的结论。 相似文献
25.
26.
Zhang Li Chun Jin Hai Yan Ye Hong Fei Gao Yu Zhi Ning Bao Jun Mo Bang Xian 《Electron Devices, IEEE Transactions on》2002,49(6):1075-1076
A polysilicon emitter RCA transistor (an ultra-thin interfacial oxide layer exists between polysilicon and silicon emitter) is presented which can operate at 77 K for the first time. An ultra-thin (1.5 nm) interfacial oxide layer is grown deliberately between polysilicon and silicon emitter using RCA oxidation and excellent device stability is obtained after rapid thermal annealing (RTA) treatment in nitrogen atmosphere. The RCA transistor exhibits good electrical performance at very low temperature for an emitter area of 3 × 8 μm2. The maximum toggle frequency of a 1:2 static divider is 1.2 GHz and 732 MHz at 300 K and 77 K, respectively 相似文献
27.
通过试验,分析比较了江西Sb2O3、南宁Sb2O3和大连Sb(Ac)3三种缩聚催化剂对聚酯切片质量的影响。试验结果表明,Sb(Ac)3是优良的缩聚催化剂。 相似文献
28.
Analysis on the effectiveness of the 20-H rule for printed-circuit-board layout to reduce edge-radiated coupling 总被引:1,自引:0,他引:1
Montrose M.I. Er-Ping Li Hong-Fang Jin Wei-Liang Yuan 《Electromagnetic Compatibility, IEEE Transactions on》2005,47(2):227-233
This paper presents the quantified study of the electromagnetic radiation mechanism of the 20-H rule using a numerical approach that has not yet been systematically addressed. The 20-H rule is a rule-of-thumb layout technique recommended to minimize radiated fields propagating from the edges of a printed circuit board (PCB) coupling onto nearby structures. Propagating electromagnetic fields may corrupt adjacent cable assemblies, sheet metal enclosures, and aperture openings. The magnitude of this design rule is investigated using the full-wave finite-difference time-domain (FDTD) method. An analysis on whether benefits exist from use of this rule is examined and under what conditions the rule is valid when correctly implemented. The purpose of this paper is to provide insight into the validity of the 20-H rule, recognizing that every PCB will have different simulation results. FDTD is used to capture a snapshot view of field propagation. This view allows one to determine the validity of the 20-H rule at a single point of time within a dynamic structure and what may be expected when digital components are finally added to a PCB assembly, which generally negates simulated results. 相似文献
29.
The cooling and solidification of melted drops during their movement in an immiscible cooling medium is widely employed for granulation in the chemical industry, and a study of these processes to provides a basis for the design of the granulation tower height and the temperature of the cooling medium is reported. A physical model of the cooling and solidification of the drop is established and the numerical calculation is performed. The influences of the key factors in the solidification, i.e., Bi number, drop diameter, temperature of the cooling medium, etc. are presented. The cooling and solidification during wax granulation in a water‐cooling tower and during urea granulation in an air‐cooling tower (spraying tower) are described in detail. Characteristics of the solidification and temperature distribution within the particle at different times are shown. The model and calculations can be used for structure design of the granulation tower and optimization of the operation parameters. 相似文献
30.
Biodegradable multiblock poloxamers (BMPs) with gel duration of 8 h to several weeks were prepared by varying their molecular weights from 4000 to 40 000 g mol?1. The molecular weight of the BMP was controlled by changing the poloxamer to coupling agent ratio. Assuming a micelle packing model of the BMP gel, as in the case of a poloxamer gel, the micelle properties and critical gel concentration of BMPs were investigated on the basis of the scaling concept. The findings suggest that the control of molecular weight by hydrolyzable groups can be a facile approach to optimize the gel properties for biomedical applications. Copyright © 2005 Society of Chemical Industry 相似文献