全文获取类型
收费全文 | 206843篇 |
免费 | 15525篇 |
国内免费 | 7864篇 |
专业分类
电工技术 | 11317篇 |
技术理论 | 14篇 |
综合类 | 11293篇 |
化学工业 | 35856篇 |
金属工艺 | 10597篇 |
机械仪表 | 12056篇 |
建筑科学 | 16544篇 |
矿业工程 | 4990篇 |
能源动力 | 5891篇 |
轻工业 | 12755篇 |
水利工程 | 3231篇 |
石油天然气 | 11113篇 |
武器工业 | 1354篇 |
无线电 | 25644篇 |
一般工业技术 | 26879篇 |
冶金工业 | 10977篇 |
原子能技术 | 2136篇 |
自动化技术 | 27585篇 |
出版年
2024年 | 890篇 |
2023年 | 3282篇 |
2022年 | 5889篇 |
2021年 | 7999篇 |
2020年 | 5832篇 |
2019年 | 5061篇 |
2018年 | 5458篇 |
2017年 | 6266篇 |
2016年 | 5733篇 |
2015年 | 7356篇 |
2014年 | 9571篇 |
2013年 | 12336篇 |
2012年 | 12303篇 |
2011年 | 13951篇 |
2010年 | 11685篇 |
2009年 | 11516篇 |
2008年 | 10934篇 |
2007年 | 10523篇 |
2006年 | 10919篇 |
2005年 | 9659篇 |
2004年 | 6595篇 |
2003年 | 5807篇 |
2002年 | 5280篇 |
2001年 | 4743篇 |
2000年 | 4888篇 |
1999年 | 5658篇 |
1998年 | 5300篇 |
1997年 | 4369篇 |
1996年 | 3967篇 |
1995年 | 3319篇 |
1994年 | 2773篇 |
1993年 | 2193篇 |
1992年 | 1709篇 |
1991年 | 1280篇 |
1990年 | 1021篇 |
1989年 | 879篇 |
1988年 | 683篇 |
1987年 | 497篇 |
1986年 | 394篇 |
1985年 | 334篇 |
1984年 | 212篇 |
1983年 | 198篇 |
1982年 | 163篇 |
1981年 | 145篇 |
1980年 | 131篇 |
1979年 | 97篇 |
1978年 | 63篇 |
1977年 | 63篇 |
1976年 | 77篇 |
1975年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
This study was undertaken to develop a modified atmosphere package to control microbial growth in ready‐to‐eat (RTE) products stored at ambient temperature. Ethanol and/or limonene associated with modified atmosphere (CO2 : O2 : N2 = 30% : 5% : 65%) was used to inhibit the growth of total air‐borne microorganisms and Escherichia coli in RTE products stored at 25°C. The results indicated that 0.05% ethanol vapour in the headspace was effective to inhibit the growth of air‐borne microorganisms and E. coli at 25°C for 72 h in a model study, and the effectiveness was related to ethanol content. Both 73 ppm limonene and 0.05% ethanol vapour enhanced the bacteriostatic effect of modified atmosphere in RTE sushi roll products, and no off‐flavour was detected using this formulated gas; however, no significant inhibitory effect was observed for RTE cold noodle products. This study concludes that combinations of carbon dioxide, ethanol or limonene vapours are effective to inhibit microbial growth in RTE food at ambient temperature, and the outcome may be due to the hurdle effect. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
2.
Data mining extracts implicit, previously unknown, and potentially useful information from databases. Many approaches have been proposed to extract information, and one of the most important ones is finding association rules. Although a large amount of research has been devoted to this subject, none of it finds association rules from directed acyclic graph (DAG) data. Without such a mining method, the hidden knowledge, if any, cannot be discovered from the databases storing DAG data such as family genealogy profiles, product structures, XML documents, task precedence relations, and course structures. In this article, we define a new kind of association rule in DAG databases called the predecessor–successor rule, where a node x is a predecessor of another node y if we can find a path in DAG where x appears before y. The predecessor–successor rules enable us to observe how the characteristics of the predecessors influence the successors. An approach containing four stages is proposed to discover the predecessor–successor rules. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 621–637, 2006. 相似文献
3.
Chun-Tsen Lu Kun-Wei Lin Huey-Ing Chen Hung-Ming Chuang Chun-Yuan Chen Wen-Chau Liu 《Electron Device Letters, IEEE》2003,24(6):390-392
A new and interesting Pd-oxide-Al/sub 0.3/Ga/sub 0.7/As MOS hydrogen sensor has been fabricated and studied. The steady-state and transient responses with different hydrogen concentrations has been measured at various temperatures. Based on the large Schottky barrier height and presence of oxide layer, the studied device exhibits a high hydrogen detection sensitivity and wide temperature operating regime. The studied device exhibits the low-leakage current and obvious current changes when exposed to hydrogen-contained gas. Even at room temperature, a very high hydrogen detection sensitivity of 155.9 is obtained when a 9090 ppm H/sub 2//air gas is introduced. Furthermore, when exposed to hydrogen-contained gas at 95/spl deg/C, both the forward and reverse currents are substantially increased with increased hydrogen concentration. In other words, the studied device can be used as a hydrogen sensor under the applied bidirectional bias. Under the applied voltage of 0.35 V and 9090 ppm H/sub 2//air hydrogen ambient, a fast adsorption response time about 10 s is found. The transient and steady-state characteristics of hydrogen adsorption are also investigated. 相似文献
4.
Chun-Yuan Chen Shiou-Ying Cheng Wen-Hui Chiou Hung-Ming Chuang Wen-Chau Liu 《Electron Device Letters, IEEE》2003,24(3):126-128
A novel InP/InGaAs tunneling emitter bipolar transistor (TEBT) is fabricated and demonstrated. The studied device exhibits a very small collector-emitter offset voltage of 40 mV and an extremely wide operation regime. The operation region is larger than 11 decades in magnitude of collector current (10/sup -12/ to 10/sup -1/A). A current gain of 3 is obtained even if the device is operated at an ultralow collector current of 3.9 /spl times/ 10/sup -12/A (1.56 /spl times/ 10/sup -7/A/cm/sup 2/). Furthermore, the common-emitter breakdown voltage of the studied device is higher than 2 V. Consequently, the studied device shows a promise for low supply voltage, and low-power consumption circuit applications. 相似文献
5.
Polyaryloxydiphenylsilanes were prepared from phosphorus‐containing diols and diphenydichlorolsilane through solution polymerization. With a stoichiometric imbalance in feed monomers, the resulting polymers exhibited moderate melting points and good processing properties. The polymers prepared showed initial decomposition temperatures above 340 °C, excellent thermal stability, high char yields at 850 °C and very high limited oxygen index values of 56–59. The polymers' char yields and their (P + Si) contents showed linear relationships. © 2003 Society of Chemical Industry 相似文献
6.
In this letter, bandpass filters with one or two tunable transmission zeros are proposed. The reconfigurable transmission zeros are implemented through varactors in combination with tapped quarter-wavelength stubs. Based on mixed mode simulations including EM simulation and circuit simulation, the proposed filters were designed and fabricated on low-cost FR4 board. The measurement results verified the design concepts. 相似文献
8.
小剂量辐射对肿瘤细胞K_(562)及肿瘤病人天然杀伤细胞(NK)活性的影响 总被引:2,自引:0,他引:2
已知小剂量辐射可增强机体免疫功能。从对高本底地区的调查发现,该地区居民肿瘤死亡率及某些肿瘤发病率有所降低(1)。NK细胞能直接杀伤肿瘤细胞,在肿瘤免疫中起着重要的作用。本文观察小剂量辐射对肿瘤病人和正常人外周血淋巴细胞NK活性的相对效应以及对人红白血病细胞(K(562)细胞)的影响,以期从体外买验来探索较小剂量辐射对肿瘤治疗的影响 相似文献
9.
用实验方法研究了Al_2O_3陶瓷缺口试件在循环载荷作用下的疲劳寿命。结果表明,缺口导致的应力集中效应显著降低了循环疲劳寿命;若用缺口根部最大应力为应力水平,则不同缺口半径陶瓷试件具有相同疲劳断裂规律,说明陶瓷材料的疲劳集中系数和理论应力集中系数相同。本文还分析讨论了陶瓷材料的循环疲劳寿命表达式和循环疲劳断裂机理。 相似文献
10.
Uses a Markov process to model a real-time expert system architecture characterized by message passing and event-driven scheduling. The model is applied to the performance evaluation of rule grouping for real-time expert systems running on this architecture. An optimizing algorithm based on Kernighan-Lin heuristic graph partitioning for the real-time architecture is developed and a demonstration system based on the model and algorithm has been developed and tested on a portion of the advanced GPS receiver (AGR) and manned manoeuvring unit (MMU) knowledge bases 相似文献