全文获取类型
收费全文 | 45966篇 |
免费 | 3914篇 |
国内免费 | 2015篇 |
专业分类
电工技术 | 2493篇 |
技术理论 | 2篇 |
综合类 | 2502篇 |
化学工业 | 7700篇 |
金属工艺 | 2609篇 |
机械仪表 | 2931篇 |
建筑科学 | 3021篇 |
矿业工程 | 1296篇 |
能源动力 | 1275篇 |
轻工业 | 2860篇 |
水利工程 | 649篇 |
石油天然气 | 2478篇 |
武器工业 | 337篇 |
无线电 | 5397篇 |
一般工业技术 | 5981篇 |
冶金工业 | 4227篇 |
原子能技术 | 492篇 |
自动化技术 | 5645篇 |
出版年
2024年 | 245篇 |
2023年 | 876篇 |
2022年 | 1511篇 |
2021年 | 2172篇 |
2020年 | 1573篇 |
2019年 | 1462篇 |
2018年 | 1513篇 |
2017年 | 1549篇 |
2016年 | 1451篇 |
2015年 | 1899篇 |
2014年 | 2262篇 |
2013年 | 2695篇 |
2012年 | 2777篇 |
2011年 | 3158篇 |
2010年 | 2484篇 |
2009年 | 2443篇 |
2008年 | 2456篇 |
2007年 | 2184篇 |
2006年 | 2290篇 |
2005年 | 1839篇 |
2004年 | 1333篇 |
2003年 | 1204篇 |
2002年 | 1132篇 |
2001年 | 985篇 |
2000年 | 948篇 |
1999年 | 1042篇 |
1998年 | 1430篇 |
1997年 | 1029篇 |
1996年 | 833篇 |
1995年 | 652篇 |
1994年 | 483篇 |
1993年 | 376篇 |
1992年 | 240篇 |
1991年 | 221篇 |
1990年 | 191篇 |
1989年 | 174篇 |
1988年 | 111篇 |
1987年 | 103篇 |
1986年 | 65篇 |
1985年 | 71篇 |
1984年 | 37篇 |
1983年 | 38篇 |
1982年 | 41篇 |
1981年 | 30篇 |
1980年 | 36篇 |
1979年 | 17篇 |
1978年 | 19篇 |
1977年 | 55篇 |
1976年 | 107篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Y.-Y. Won H.-C. Kwon S.-K. Han 《Optoelectronics, IET》2007,1(2):61-64
A new scheme for reducing optical beat interference (OBI) noise in optical network units is proposed for subcarrier multiplexing-based access network applications. The optical spectrum of the transmit lasers is broadened by using a radio frequency (RF) clipping tone with a modulation depth greater than one. This reduces the impact of the OBI noise. The distortions caused by an RF clipping tone are also suppressed by introducing a gain-saturated reflective optical amplifier, which shows the characteristics of high-pass filter. The proposed scheme has been verified by measuring the error vector magnitude of 16QAM signal with 20 Mbps. Error-free transmission has been achieved even when the light of OBI-noise-causing lasers is stronger than that of the signal laser by 7 dB 相似文献
22.
Cu—Zn—Al系合金热弹性马氏体相变的热滞 总被引:3,自引:0,他引:3
韩明 《有色金属材料与工程》1997,18(2):53-55
本文通过热处理工艺及添加第四组元研究了Cu-Zn-Al系记忆合金的相变热滞。结果表明,淬火冷却速度影响合金的相变热滞大小,随着母相时效时间的延长,马氏体相变热滞变大.Mn元素的加入可以减小CU-Zn-Al合金相变热滞. 相似文献
23.
KW Sax SM Strakowski PE Keck SL McElroy SA West SP Stanton 《Canadian Metallurgical Quarterly》1998,44(8):784-786
BACKGROUND: This study examined patients with a first-episode of affective psychosis during acute and compensated states in order to determine whether changes in attentional functioning over time were accompanied by changes in the severity of psychotic or affective symptoms. METHODS: Attentional performance was measured in patients (n = 27) using the degraded-stimulus continuous Performance Test (CPT) and symptoms were assessed at the time of index hospitalization, and 2 months after discharge. A comparison group of normal volunteers (n = 31) also performed the CPT two months apart. RESULTS: Patients performed significantly worse than controls at the initial testing but not at follow-up. The improvement in attentional performance significantly correlated with decreased severity of manic symptoms. CONCLUSIONS: Results suggest attentional dysfunction is a state-dependent characteristic of mania, and may provide an additional measure of clinical improvement following treatment. 相似文献
24.
在一定实验条件下,屏蔽暂堵的反排解堵效率随压差、温度的增大而增大,反排解堵在很短的时间内就可完成。一般的反排解堵率都在60%以上,但反徘不能完全解堵。 相似文献
25.
26.
27.
M. S. Han S. R. Hahn H. C. Kwon Y. Bin T. W. Kang J. H. Leem Y. B. Hou H. C. Jeon J. K. Hyun Y. T. Jeoung H. K. Kim J. M. Kim T. W. Kim 《Journal of Electronic Materials》1998,27(6):680-683
Double-crystal x-ray rocking curve (DCRC) and secondary-ion mass-spectroscopy (SIMS) measurements have been performed to investigate the effect of rapid thermal annealing on the interdiffusion behavior of Hg in HgTe/CdTe superlattices grown on Cd0.96Zn0.04Te (211)B substrates by molecular beam epitaxy. The sharp satellite peaks of the DCRC measurements on a 100-period HgTe/CdTe (100Å/100Å) superlattice show a periodic arrangement of the superlattice with high-quality interfaces. The negative direction of the entropy change obtained from the diffusion coefficients as a function of the reciprocal of the temperature after RTA indicates that the Hg diffusion for the annealed HgTe/CdTe superlattice is caused by an interstitial mechanism. The Cd and the Hg concentration profiles near the annealed HgTe/CdTe superlattice interfaces, as measured by SIMS, show a nonlinear behavior for Hg, originating from the interstitial diffusion mechanism of the Hg composition. These results indicate that a nonlinear interdiffusion behavior is dominant for HgTe/CdTe superlattices annealed at 190°C and that the rectangular shape of HgTe/CdTe superlattices may change to a parabolic shape because of the intermixing of Hg and Cd due to the thermal treatment. 相似文献
28.
蒙特卡罗方法在空间辐射制冷器理论分析及热设计计算中的应用 总被引:1,自引:1,他引:0
介绍了二级抛物面型辐射制冷器的热物理模型及用蒙特卡罗方法数值模拟解决其热流理论和辐射热耦合表面(漫发射、镜反射)辐射热交换的处理方法。 相似文献
29.
The incidence of stress fractures is increasing among competitive and recreational athletes as well as among children and the elderly. By understanding the continuum of bone's response to stress and maintaining an appropriate index of suspicion, the health care provider can diagnose these injuries appropriately. An accurate history and examination is essential and will differentiate stress fractures from other stress reactions. The more common stress fractures are discussed. 相似文献
30.
PC/PET共混物的非等温结晶动力学 总被引:9,自引:0,他引:9
采用等速变温DSC法对PC/PET共混体系的非等温结晶动力学进行了研究,结果表明,从玻璃态结晶时,随着PC含量的增加,PET组分的结晶速率先增加后降低。耐从熔体结晶时,体系的结晶速率随着PC含量的增加而增加,讨论了PC对PET组分结晶过程的影响。 相似文献