全文获取类型
收费全文 | 19866篇 |
免费 | 2330篇 |
国内免费 | 1008篇 |
专业分类
电工技术 | 1324篇 |
技术理论 | 3篇 |
综合类 | 1317篇 |
化学工业 | 3563篇 |
金属工艺 | 1010篇 |
机械仪表 | 1254篇 |
建筑科学 | 1216篇 |
矿业工程 | 487篇 |
能源动力 | 676篇 |
轻工业 | 1997篇 |
水利工程 | 326篇 |
石油天然气 | 736篇 |
武器工业 | 177篇 |
无线电 | 2616篇 |
一般工业技术 | 2761篇 |
冶金工业 | 620篇 |
原子能技术 | 211篇 |
自动化技术 | 2910篇 |
出版年
2024年 | 95篇 |
2023年 | 430篇 |
2022年 | 773篇 |
2021年 | 1120篇 |
2020年 | 853篇 |
2019年 | 709篇 |
2018年 | 768篇 |
2017年 | 818篇 |
2016年 | 805篇 |
2015年 | 965篇 |
2014年 | 1184篇 |
2013年 | 1445篇 |
2012年 | 1672篇 |
2011年 | 1596篇 |
2010年 | 1453篇 |
2009年 | 1263篇 |
2008年 | 1257篇 |
2007年 | 1097篇 |
2006年 | 904篇 |
2005年 | 736篇 |
2004年 | 566篇 |
2003年 | 441篇 |
2002年 | 367篇 |
2001年 | 357篇 |
2000年 | 282篇 |
1999年 | 260篇 |
1998年 | 186篇 |
1997年 | 151篇 |
1996年 | 141篇 |
1995年 | 92篇 |
1994年 | 99篇 |
1993年 | 54篇 |
1992年 | 44篇 |
1991年 | 33篇 |
1990年 | 29篇 |
1989年 | 32篇 |
1988年 | 12篇 |
1987年 | 19篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1973年 | 3篇 |
1959年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
A new method to predict the critical heat flux (CHF) is proposed, based on the fuzzy clustering and artificial neural network. The fuzzy clustering classifies the experimental CHF data into a few data clusters (data groups) according to the data characteristics. After classification of the experimental data, the characteristics of the resulting clusters are discussed with emphasis on the distribution of the experimental conditions and physical mechanism. The CHF data in each group are trained in an artificial neural network to predict the CHF. The artificial neural network adjusts the weight so as to minimize the prediction error within the corresponding cluster. Application of the proposed method to the KAIST CHF data bank shows good prediction capability of the CHF, better than other existing methods. 相似文献
62.
63.
YAG:Ce Phosphors for WLED via Nano-Pesudoboehmite Sol-Gel Route 总被引:5,自引:0,他引:5
The sub-micron sized YAG : Ce phosphors were synthesized via a modified sol-gel method by peptizing nano-pesudoboehmite particulate. It is found that YAG phase from the dried gel powders appears at 1000 ℃ then the pure YAG phase exists at a relatively lower sintering temperature of 1400 ℃. The smaller sizes of phosphors in the ranges of 1 - 3 μm are obtained due to the contribution of seeding effects of nano-sized alumina particles to strengthen each step of the processes. Both the excitation and emission spectra of photoluminescence of the phosphor obtained at 1400 ℃ meet well with the spectroscopic requirements of the WLED phosphors. 相似文献
64.
The photonic quantum ring (PQR) laser is a three dimensional whispering gallery (WG) mode laser and has anomalous quantum wire properties, such as microampere to nanoampere range threshold currents and √T‐dependent thermal red shifts. We observed uniform bottom emissions from a 1‐kb smart pixel chip of a 32×32 InGaAs PQR laser array flip‐chip bonded to a 0.35 µm CMOS‐based PQR laser driver. The PQR‐CMOS smart pixel array, now operating at 30 MHz, will be improved to the GHz frequency range through device and circuit optimization. 相似文献
65.
66.
本文描述一种采用BP神经网络对雷达辐射源体制和用途进行智能识别的方法 ,包括理论分析、神经网络结构设计、推理和学习算法设计、编程算法设计、实验结果比较与分析等。实验表明 ,该方法有着良好的识别效果 相似文献
67.
利用飞秒激光脉冲分别在水平和竖直方向上进行了推进微型小球的实验.实验中首次利用毫焦量级的飞秒激光脉冲(重复频率1 kHz)推进质量在毫克量级的小球,将直径0.7 mm的铁球水平推进了65 mm,直径接近1 mm的聚苯乙烯小球竖直推进了72 mm.实验研究发现:无论是在水平还是在竖直方向上的推进,小球离开飞秒激光聚焦区域之前与小球发生作用的脉冲个数是决定推进效果的决定性因素.通过增大脉宽、换用较长焦距的聚焦透镜增加与小球作用的脉冲个数,可以将小球推进到更远的距离或更高的高度. 相似文献
68.
Sang Cheol Lee Won Kook Lee 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,55(3):251-261
The extraction of penicillin G from simulated media was performed by water/oil/water (w/o/w) emulsion liquid membranes (ELMs) and studied under various operational conditions in a batch system. The degree of extraction achieved was between 80% and 95% under specific conditions. A concentration of greater than nine times the initial concentration of penicillin G in the external phase was obtained in the internal phase. The pH of the internal aqueous solution, containing a basic salt, was theoretically calculated on the basis of the amount of penicillin G transported into the internal phase. The calculated results agreed with the experimental data well and were used to select a suitable type and concentration of a basic salt in the internal phase to give a pH within the range 5 to 8 where penicillin G was stable after the termination of extraction. The extraction of penicillin G was successfully performed by the ELM process with sodium carbonate in the internal phase. 相似文献
69.
Sang‐Heung Lee Seung‐Yun Lee Hyun‐Cheol Bae Ja‐Yol Lee Sang‐Hoon Kim Bo Woo Kim Jin‐Yeong Kang 《ETRI Journal》2005,27(5):569-578
The purpose of this paper is to describe the implementation of monolithically matching circuits, interface circuits, and RF core circuits to the same substrate. We designed and fabricated on‐chip 1 to 6 GHz up‐conversion and 1 to 8 GHz down‐conversion mixers using a 0.8 µm SiGe hetero‐junction bipolar transistor (HBT) process technology. To fabricate a SiGe HBT, we used a reduced pressure chemical vapor deposition (RPCVD) system to grow a base epitaxial layer, and we adopted local oxidation of silicon (LOCOS) isolation to separate the device terminals. An up‐conversion mixer was implemented on‐chip using an intermediate frequency (IF) matching circuit, local oscillator (LO)/radio frequency (RF) wideband matching circuits, LO/IF input balun circuits, and an RF output balun circuit. The measured results of the fabricated up‐conversion mixer show a positive power conversion gain from 1 to 6 GHz and a bandwidth of about 4.5 GHz. Also, the down‐conversion mixer was implemented on‐chip using LO/RF wideband matching circuits, LO/RF input balun circuits, and an IF output balun circuit. The measured results of the fabricated down‐conversion mixer show a positive power conversion gain from 1 to 8 GHz and a bandwidth of about 4.5 GHz. 相似文献
70.
柴胡皂苷的提取与鉴定 总被引:2,自引:1,他引:1
报道了大孔吸附层析分离提取柴胡皂苷的实验研究。结果表明。提取分离柴胡皂苷的最佳工艺是:30%乙醇洗杂质、70%的乙醇洗脱2个糖基或3个糖基的柴胡皂苷。柴胡总皂苷的提取率为1.96%。TLC、HPLC检测2个糖基的皂苷是柴胡皂苷b2,属于结构类型Ⅱ。 相似文献