全文获取类型
收费全文 | 33516篇 |
免费 | 3452篇 |
国内免费 | 1937篇 |
专业分类
电工技术 | 4014篇 |
技术理论 | 1篇 |
综合类 | 2872篇 |
化学工业 | 3522篇 |
金属工艺 | 1305篇 |
机械仪表 | 2682篇 |
建筑科学 | 2334篇 |
矿业工程 | 1609篇 |
能源动力 | 746篇 |
轻工业 | 3201篇 |
水利工程 | 784篇 |
石油天然气 | 1778篇 |
武器工业 | 999篇 |
无线电 | 4724篇 |
一般工业技术 | 2484篇 |
冶金工业 | 1680篇 |
原子能技术 | 348篇 |
自动化技术 | 3822篇 |
出版年
2024年 | 137篇 |
2023年 | 448篇 |
2022年 | 848篇 |
2021年 | 1103篇 |
2020年 | 1245篇 |
2019年 | 865篇 |
2018年 | 755篇 |
2017年 | 1045篇 |
2016年 | 1243篇 |
2015年 | 1354篇 |
2014年 | 2380篇 |
2013年 | 2002篇 |
2012年 | 2746篇 |
2011年 | 2664篇 |
2010年 | 1953篇 |
2009年 | 1978篇 |
2008年 | 1620篇 |
2007年 | 2223篇 |
2006年 | 1956篇 |
2005年 | 1820篇 |
2004年 | 1393篇 |
2003年 | 1355篇 |
2002年 | 1115篇 |
2001年 | 888篇 |
2000年 | 750篇 |
1999年 | 604篇 |
1998年 | 429篇 |
1997年 | 339篇 |
1996年 | 306篇 |
1995年 | 254篇 |
1994年 | 208篇 |
1993年 | 174篇 |
1992年 | 159篇 |
1991年 | 117篇 |
1990年 | 88篇 |
1989年 | 68篇 |
1988年 | 52篇 |
1987年 | 28篇 |
1986年 | 20篇 |
1985年 | 26篇 |
1984年 | 23篇 |
1983年 | 19篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1975年 | 4篇 |
1964年 | 6篇 |
1959年 | 5篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
101.
钢铁企业的氧气厂要深入了解本企业的用氧情况及周边市场的需要,据此确定拟新增空分装置的设计参数,选定最适宜的空分流程。探讨了空分流程选择时要考虑的几个方面。介绍了一种对空分装置的投资和长期运行费用之间进行经济性分析的定量计算公式,并得出了四点结论。 相似文献
102.
耀江大厦顶层屋面热泵的振动治理 总被引:1,自引:0,他引:1
本文通过耀江大厦27层屋面上六台热泵振动治理前后的振动和噪声测试数据的对比,简要阐述了安装在屋面上热泵的振动影响的程度和范围、产生振动影响和固体噪声传递的原因,并介绍了热泵双层隔振的方法和隔振效果。 相似文献
103.
104.
105.
Evidence is presented that bears on 9 hypotheses about the link between religion or spirituality and mortality, morbidity, disability, or recovery from illness. In healthy participants, there is a strong, consistent, prospective, and often graded reduction in risk of mortality in church/service attenders. This reduction is approximately 25% after adjustment for confounders. Religion or spirituality protects against cardiovascular disease, largely mediated by the healthy lifestyle it encourages. Evidence fails to support a link between depth of religiousness and physical health. In patients, there are consistent failures to support the hypotheses that religion or spirituality slows the progression of cancer or improves recovery from acute illness but some evidence that religion or spirituality impedes recovery from acute illness. The authors conclude that church/service attendance protects healthy people against death. More methodologically sound studies are needed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
106.
Salinger Walter L.; Ladrow Pamela; Wheeler Catherine 《Canadian Metallurgical Quarterly》2003,117(6):1257
Reeler (rl/rl) and reeler/wild-type (+/rl) mice synthesize Reln at subnormal rates, as do patients with schizophrenia, bipolar disorder, and autism, thereby forming the basis for a Reln hypothesis for vulnerability to these psychopathologies and justifying attention to the behavioral phenotypes of Reln-deficient mice. Tests of gait, emotionality, social aggression, spatial working memory, novel-object detection, fear conditioning, and sensorimotor reflex modulation revealed the behavioral phenotype of rl/rl, but not +/rl, mice to be different from that of wild-type (+/+) mice. These results reveal no effect of Reln gene dosage and provide significant challenges to both the Reln and the neurodevelopmental hypotheses of the etiology of major psychopathologies. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
107.
指出了皮带及链传动现有张紧方法的缺点,设计了一种结构简单、工作可靠的用于皮带及链传动的恒张力控制装置,该装置能自动调整压在皮带或链上的力,在很大挠角范围内保持其张力基本恒定。 相似文献
108.
109.
We report improvement of emission efficiency in polymer light-emitting devices (PLEDs) employing phosphorescent polymers. A hole-blocking layer was inserted between the emissive layer and the cathode to enhance recombination efficiency for the injected holes and electrons. Aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolato (BAlq) was used for the hole-blocking layer. The resultant PLEDs exhibited significant improvement of emission efficiency. The respective external quantum efficiencies for red, green and blue PLEDs were 6.6, 11 and 6.9%. These values are very high compared with those based on conventional fluorescent polymers. 相似文献
110.
Claudio Sacchi Gianluca Gera Carlo S. Regazzoni 《International Journal of Satellite Communications and Networking》2004,22(2):193-215
This paper aims at focusing on the aspects concerning the physical layer design for an innovative satellite communication experiment. Such an experiment, denoted by the acronym DAVID–DCE (Data and Video Interactive Distribution—Data Collection Experiment) is based on the exploitation of the W‐band (75–110 GHz) for high‐bit‐rate satellite transmission. The potential advantages of using of the W‐band are mainly related to the great bandwidth availability, and to the absence of interference. Moreover, an expected result of the experiment is a substantive improvement in the communication system's performances in the presence of meteorological phenomena (e.g. rain) as compared with the more conventional Ka‐band satellite transmission. On the other hand, problems to be faced concern the non‐ideal behaviours of hardware devices employed for high‐frequency digital transmission. In particular, carrier recovery and timing recovery are the most crucial signal‐processing tasks to be carefully considered in the design of the physical level of the system, because they considerably suffer from hardware impairments. The purpose of this work is to illustrate the proposed solutions in terms of the most critical modulation, demodulation and synchronization design issues, together with the effects of non‐ideal behaviours of hardware components on BER performances. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献