全文获取类型
收费全文 | 149774篇 |
免费 | 14110篇 |
国内免费 | 8858篇 |
专业分类
电工技术 | 10629篇 |
技术理论 | 10篇 |
综合类 | 11441篇 |
化学工业 | 22441篇 |
金属工艺 | 9366篇 |
机械仪表 | 10215篇 |
建筑科学 | 11682篇 |
矿业工程 | 4822篇 |
能源动力 | 4583篇 |
轻工业 | 10200篇 |
水利工程 | 3331篇 |
石油天然气 | 7789篇 |
武器工业 | 1738篇 |
无线电 | 17981篇 |
一般工业技术 | 16688篇 |
冶金工业 | 6284篇 |
原子能技术 | 2232篇 |
自动化技术 | 21310篇 |
出版年
2024年 | 690篇 |
2023年 | 2198篇 |
2022年 | 4183篇 |
2021年 | 6015篇 |
2020年 | 4495篇 |
2019年 | 3736篇 |
2018年 | 4116篇 |
2017年 | 4833篇 |
2016年 | 4482篇 |
2015年 | 6265篇 |
2014年 | 8021篇 |
2013年 | 9453篇 |
2012年 | 10750篇 |
2011年 | 11761篇 |
2010年 | 10704篇 |
2009年 | 10250篇 |
2008年 | 10290篇 |
2007年 | 9872篇 |
2006年 | 9303篇 |
2005年 | 7581篇 |
2004年 | 5517篇 |
2003年 | 4565篇 |
2002年 | 4482篇 |
2001年 | 3821篇 |
2000年 | 3236篇 |
1999年 | 2648篇 |
1998年 | 1846篇 |
1997年 | 1551篇 |
1996年 | 1375篇 |
1995年 | 1094篇 |
1994年 | 885篇 |
1993年 | 630篇 |
1992年 | 475篇 |
1991年 | 356篇 |
1990年 | 291篇 |
1989年 | 247篇 |
1988年 | 173篇 |
1987年 | 113篇 |
1986年 | 116篇 |
1985年 | 54篇 |
1984年 | 48篇 |
1983年 | 52篇 |
1982年 | 42篇 |
1981年 | 31篇 |
1980年 | 22篇 |
1979年 | 14篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1959年 | 19篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
71.
Piezoelectric Nanogenerators for Self-Powered Nanodevices 总被引:1,自引:0,他引:1
A novel approach converts nanoscale mechanical energy into electric energy for self-powering nanodevices.In our own work, we've used piezoelectric zinc-oxide nanowire (ZnO NW) arrays to demonstrate a novel approach for converting nanoscale mechanical energy into electric energy. Here, we review the fundamental principle behind the nanogenerator, present an approach for improving its performance, and discuss some of the challenges we face in pushing this technology to reach its potential. 相似文献
72.
73.
Xin Song Xiaoyu Qi Bin Hao Yinbo Qu 《European Journal of Lipid Science and Technology》2008,110(12):1095-1101
Although lipases are widely applied in a wide variety of reactions, available information on the factors that are responsible for the substrate specificities of lipases from different sources is scarce. In this paper, nine lipase‐producing microorganism strains were isolated from oil‐containing samples. The properties of these enzymes, including pH optima, temperature optima, thermal stability, and pH stability, vary significantly with the different sources from which these lipases were isolated. The substrate specificities of the nine lipases, including fatty acid and positional specificities, were also studied. The fatty acid specificities of the nine lipases were observably different toward 15 substrates with different carbon chain lengths, different saturation degrees and different side chains. The lipases from S3 Penicillium citrinum (PCL), MJ1 Aspergillus niger (ANL), MJ2 Aspergillus oryzae (AOL), YM Bacillus coughing (BCL), S9 Geotrichum candidum (GCL), and S11 Candida lypolytica (CLL) showed the strongest specificities to short‐chain esters, and the other lipases showed strong selectivity for medium‐ or long‐chain and branched esters. The positional specificities were examined by analyzing the hydrolytic products of triolein catalyzed by the nine lipases, using TLC. The lipases can be mainly classified into two groups by their specificities for the ester bond at position 2 of triglycerides; one group can selectively hydrolyze the ester bond at position 2 of the triglycerides, the other group cannot. All these nine lipases were divided into four groups by hierarchical clustering analysis on the basis of the results of fatty acid and positional specificities. 相似文献
74.
Woo Yong Sung Seung Min Lee Wal Jun Kim Jong Girl Ok Ho Young Lee Yong Hyup Kim 《Diamond and Related Materials》2008,17(6):1003-1007
Complementary electroplating combined with electrophoresis enhanced the field emission characteristics of emitters by improving the adhesions between CNT emitters and substrate. The emitting current of the CNT emitters prepared by our combined method increased nine times higher than that of CNT emitters prepared by electrophoresis only, since electroplating improved the adhesion of CNT emitters. During the life-time measurement for 10 h, the emitting current of CNT emitters fabricated by electrophoresis only was drastically decreased to 13% of the initial current, while that prepared by the combination of electrophoresis and successive electroplating decreased to 64% of the initial current. We suggest that our method is a promising approach for the efficient fabrication of reliable CNT emitters. 相似文献
75.
76.
The rate of filtration and the water content of cake are influenced by the existence of a dense skin in a highly compressible
cake. The phenomenon of the dense skin has been rarely studied, and its existence has not been verified experimentally. In
this study, the porosity variation in a very compressible cake is measured by using a new experimental apparatus, and with
this the existence of dense skin has been established experimentally. ‘Unified theory on solid-liquid separation’, a recently
developed theory, is utilized for calculating the porosity variation in a very compressible cake. 相似文献
77.
Design of the ECRH/ECCD Launcher System for HL-2A Tokamak 总被引:3,自引:0,他引:3
An ECRH/ECCD system with two 68GHz/500kW/1S gyrotrons will be built up in HL-2A tokamak. The location of the Gaussian beam waist is 580 mm away from the center of the plasmas and the beam radius is 37 mm at the center of the plasmas. Compared to the minor plasma radius (420 mm), it is small enough for localized control. The launcher system covers a wide toroidal and poloidal steering range by the two steering plane mirrors. Therefore it is possible to explore the on- and off-axis heating over half of the plasma minor cross section and the co-current drive. 相似文献
78.
化学镀Ni—P镀层的X射线衍射研究 总被引:2,自引:0,他引:2
根据X射线衍射分析结果,对化学镀高P(含P>11wt%或19at%)Ni-P镀层加热时效时,镀层成分和加热温度对结构转变的影响作了研究,结果表明,高P共晶、过共晶(含P>11wt%或19at%)合金的结构转变有如下特征:(1)相同加热时效条件下,Ni-P合金的结构转变与成分有密切关系:(2)对同一成分的过共晶合金,Ni-P合金的结构转变与时效温度密切相关;(3)过共晶合金在290~360℃温度范围内时效处理,出现Ni_xP_y介稳相,X射线衍射分析认为Ni_xP_y为Ni_(12)P_5。 相似文献
79.
An initial Bentall operation was performed on a patient aged 38 years with annuloaortic ectasia and aortic regurgitation. An echocardiogram and RI angiogram revealed a perigraft aortic aneurysm on the same patient aged 45 years. The aneurysm gradually developed and the maximum diameter reached 90 mm in size. The Redo-Bentall operation (Piehler modification) was successfully done once again on the same patient aged 56 years. The anastmosis between the right coronary orifice and the graft was detached on all sides. The anastmosis between the left coronary orifice and the graft was detached two thirds of all sides. 相似文献
80.
Plasmapropertiesoflaser-ablatedSttargetinairWangXiang-Tai(王象泰);ManBao-Yuan(满宝元);WangGong-Tang(王公堂);FanXi-Jun(樊锡君);WangJun(王军)... 相似文献