全文获取类型
收费全文 | 125765篇 |
免费 | 12426篇 |
国内免费 | 7040篇 |
专业分类
电工技术 | 9104篇 |
技术理论 | 6篇 |
综合类 | 9262篇 |
化学工业 | 19258篇 |
金属工艺 | 7304篇 |
机械仪表 | 8348篇 |
建筑科学 | 9952篇 |
矿业工程 | 4398篇 |
能源动力 | 3429篇 |
轻工业 | 8545篇 |
水利工程 | 2655篇 |
石油天然气 | 6950篇 |
武器工业 | 1496篇 |
无线电 | 15238篇 |
一般工业技术 | 13504篇 |
冶金工业 | 5654篇 |
原子能技术 | 1487篇 |
自动化技术 | 18641篇 |
出版年
2024年 | 713篇 |
2023年 | 2204篇 |
2022年 | 4156篇 |
2021年 | 5768篇 |
2020年 | 4282篇 |
2019年 | 3529篇 |
2018年 | 3884篇 |
2017年 | 4337篇 |
2016年 | 3883篇 |
2015年 | 5448篇 |
2014年 | 6616篇 |
2013年 | 7843篇 |
2012年 | 9120篇 |
2011年 | 9695篇 |
2010年 | 8431篇 |
2009年 | 8083篇 |
2008年 | 7830篇 |
2007年 | 7243篇 |
2006年 | 7330篇 |
2005年 | 6126篇 |
2004年 | 4165篇 |
2003年 | 3160篇 |
2002年 | 2867篇 |
2001年 | 2539篇 |
2000年 | 2561篇 |
1999年 | 2507篇 |
1998年 | 1986篇 |
1997年 | 1690篇 |
1996年 | 1538篇 |
1995年 | 1297篇 |
1994年 | 1067篇 |
1993年 | 760篇 |
1992年 | 599篇 |
1991年 | 468篇 |
1990年 | 351篇 |
1989年 | 274篇 |
1988年 | 239篇 |
1987年 | 157篇 |
1986年 | 132篇 |
1985年 | 73篇 |
1984年 | 41篇 |
1983年 | 29篇 |
1982年 | 40篇 |
1981年 | 30篇 |
1980年 | 36篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1976年 | 17篇 |
1975年 | 9篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
81.
Chun Hu Ji Zhao Li G.P. Liu P. Worley E. White J. Kjar R. 《Electron Device Letters, IEEE》1995,16(2):61-63
The effects of the plasma etching process induced gate oxide damages on device's low frequency noise behavior are investigated on MOSFET's fabricated with different field plate perimeter to gate area ratio antennas. Abnormal 1/f noise spectrum with a shoulder centered in the frequency range of 100 and to 1 kHz was frequently observed in small geometry devices, and it is attributable to a nonuniform distribution of oxide traps induced by plasma etching process 相似文献
82.
介绍了用于HT-7托卡马克的的八管弹丸注入器的物理、工程设计原理和结构特点及配置的各种诊断手段。注入器采用气动发射技术,弹丸为1mm×1mm,1.2mm×1.2mm,1.5mm×l.5mm圆柱体氢丸,丸速0.8~1.5km/s工作频率1~8Hz。 相似文献
83.
提出了三维定量储层地质模型及其参数动态预测方法,用该方法可预测储层开采状态,水淹区及剩余油区分布和各剩余油区的可采储量,三维定量储层地质模型的预测图件可为合理开采提供依据。 相似文献
84.
Randomized trial of breast self-examination in Shanghai: methodology and preliminary results 总被引:3,自引:0,他引:3
DB Thomas DL Gao SG Self CJ Allison Y Tao J Mahloch R Ray Q Qin R Presley P Porter 《Canadian Metallurgical Quarterly》1997,89(5):355-365
BACKGROUND: The efficacy of breast self-examination in helping to reduce mortality from breast cancer has not been rigorously demonstrated. PURPOSE: To assess efficacy, a large, randomized trial was initiated in Shanghai, China. METHODS: From October 1989 to October 1991, 267040 current and retired female employees associated with 520 factories in the Shanghai Textile Industry Bureau were randomly assigned on the basis of factory to either a self-examination instruction group (133375 women) or a control group (133665 women). The women were born within the period from 1925 through 1958. Women in the instruction group were given intensive training in breast self-examination, including the use of silicone breast models and personalized instruction, plus two subsequent reinforcement sessions and multiple reminders to practice the technique. Women in the control group were asked to attend training sessions on the prevention of low back pain. All women have been followed for the development of breast diseases and for death from breast cancer. RESULTS: A high level of participation during the first 4-5 years of the trial was documented among women in the instruction group. Randomly sampled women in this group demonstrated greater proficiency in detecting lumps in breast models than did randomly sampled women in the control group. Approximately equal numbers of breast cancers were detected in the two groups (331 in the instruction group and 322 in the control group) through 1994, which is the last year for which case-finding efforts have been completed. The breast cancers detected in the instruction group were not diagnosed at an appreciably earlier stage or smaller size than those in the control group. More benign breast lesions were detected in the instruction group than in the control group (1457 versus 623, respectively), suggesting a higher index of suspicion for women who received training. Cumulative breast cancer mortality rates through 5 years from entry into the study were nearly equivalent for the two groups. CONCLUSIONS: Breast self-examination has not led to a reduction in mortality from breast cancer in this study cohort in the first several years since the trial began. A shift toward the diagnosis of disease at a less advanced stage in women given instruction has also not been demonstrated. Longer follow-up of participants in this trial is required before final assessment can be made of the efficacy of breast self-examination. IMPLICATIONS: At this time, there is insufficient evidence to recommend for or against the teaching of breast self-examination. 相似文献
85.
Assaderaghi F. Chen J. Solomon R. Chian T.-Y. Ko P.K. Hu C. 《Electron Device Letters, IEEE》1991,12(10):518-520
It has been found that the subthreshold currents of fully depleted silicon-on-insulator (SOI) MOSFETs show a transient behavior under certain front-gate and back-gate voltage conditions. The cause of this anomaly is explained, and applications for the phenomenon are pointed out. Particularly, a simple way to measure the silicon film thickness is suggested 相似文献
86.
87.
InGaAs/GaAs(100) multiple-quantum-well-based inverted cavity asymmetric Fabry-Perot modulators are vertically integrated with GaAs/AlGaAs heterojunction phototransistors to yield all-optical photonic switches. The photonic switches using `normally on' modulator pixels exhibit an output on-off ratio of 12:1 with internal optical gain of 4 dB. The photonic switches using `normally off' modulator pixels yield similar contrast and gain, but exhibit intrinsic bistable behavior. The inverted cavity modulators employed permit utilizing the transparency of the GaAs substrate at the operating wavelength and offer advantages for fabricating large arrays for optical signal processing 相似文献
88.
89.
In order to investigate the galvanic anodic protection (GAP) of ferrous metals (such as 410, 304 and 316 stainless steels) in acid solutions by doped polyaniline (PANi), separate doped PANi powder-pressed electrodes with different surface areas (the area ratio of the PANi electrode to stainless steel is between 1:1 and 1:2) have been prepared. These were coupled with ferrous metal in the following solutions: 5 M sulphuric acid, 5 M phosphoric acid and industrial phosphoric acid (containing 5 M phosphoric acid and 0.05% chloride ion) to construct a galvanic cell, in which PANi is cathode while ferrous metal is anode. The results indicate that a PANi electrode with sufficient area can provide corrosion protection to stainless steel in these acidic solutions. A pilot scale coupling experiment was carried out. The results indicate that PANi is a promising material as an electrode for the anodic protection of ferrous metals in acidic solutions in industrial situations. 相似文献
90.
Xiaojun Hu Hiroyuki Matsuura Fumitaka Tsukihashi 《Metallurgical and Materials Transactions B》2006,37(3):395-401
The interfacial reaction between CO2-CO gas and molten iron oxide containing P2O5 was investigated by the 13CO2-CO isotope exchange technique at 1773 K with CO2/CO=1.0. The apparent rate constant rapidly decreased with the addition of P2O5 up to 2.86 mol pct PO2.5 and the Fe3+/Fe2+ ratio kept constant at approximately 0.2. By the classic site blockage model, in which the reaction only occurs on the vacant
sites, and the modified site blockage model, in which the reaction occurs on the vacant sites and the sites occupied by phosphorus
simultaneously, the effect of the addition of P2O5 was analyzed and the reaction mechanism of CO2 dissociation was discussed. It may be concluded that the dissociation of the adsorbed CO2 molecule is reasonable as a rate-determining step and that the effect of phosphorus on the interfacial reaction is caused
by the decrease in the number of active sites with the increase of phosphorus content as a surface active element in molten
iron oxide. 相似文献