全文获取类型
收费全文 | 232279篇 |
免费 | 17784篇 |
国内免费 | 9874篇 |
专业分类
电工技术 | 12682篇 |
技术理论 | 10篇 |
综合类 | 15343篇 |
化学工业 | 37444篇 |
金属工艺 | 13637篇 |
机械仪表 | 14361篇 |
建筑科学 | 14434篇 |
矿业工程 | 5436篇 |
能源动力 | 5442篇 |
轻工业 | 15046篇 |
水利工程 | 4539篇 |
石油天然气 | 12084篇 |
武器工业 | 1585篇 |
无线电 | 25342篇 |
一般工业技术 | 33527篇 |
冶金工业 | 13665篇 |
原子能技术 | 5738篇 |
自动化技术 | 29622篇 |
出版年
2024年 | 724篇 |
2023年 | 2828篇 |
2022年 | 5618篇 |
2021年 | 8030篇 |
2020年 | 6041篇 |
2019年 | 5238篇 |
2018年 | 6443篇 |
2017年 | 7056篇 |
2016年 | 6633篇 |
2015年 | 7858篇 |
2014年 | 10367篇 |
2013年 | 12684篇 |
2012年 | 14146篇 |
2011年 | 15197篇 |
2010年 | 13424篇 |
2009年 | 13189篇 |
2008年 | 13070篇 |
2007年 | 12375篇 |
2006年 | 11721篇 |
2005年 | 9944篇 |
2004年 | 7835篇 |
2003年 | 7420篇 |
2002年 | 7965篇 |
2001年 | 7156篇 |
2000年 | 5667篇 |
1999年 | 4676篇 |
1998年 | 3508篇 |
1997年 | 2946篇 |
1996年 | 2629篇 |
1995年 | 2310篇 |
1994年 | 1877篇 |
1993年 | 1546篇 |
1992年 | 1455篇 |
1991年 | 1262篇 |
1990年 | 1246篇 |
1989年 | 1103篇 |
1988年 | 983篇 |
1987年 | 902篇 |
1986年 | 783篇 |
1985年 | 755篇 |
1984年 | 730篇 |
1981年 | 685篇 |
1979年 | 750篇 |
1978年 | 785篇 |
1977年 | 751篇 |
1976年 | 770篇 |
1975年 | 719篇 |
1974年 | 725篇 |
1973年 | 726篇 |
1972年 | 707篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
941.
器件尺寸按比例缩小是实现超大规模集成电路的有效途径,但寄生和二级效应却将器件限在一定的水平,本文在对比分析常温与低温下小尺寸器件效应的基础上,重点研究了MOS器件亚阈特性对器件性能及按比例缩小的影响,并根据低温工作的特点,提出了MOS器件一种低温按比例缩小规则,该原则对低温器的优化设计,从而更大程度在提高电路与系统性能具有重要的指导意义。 相似文献
942.
943.
文中简要地介绍了一个具有分散采集信号,集中报警的安全报警器的设计,作者利用单片机的优点和功能,成功地设计了复盖地域大,既简单又灵活的报警器。 相似文献
944.
945.
自由电子激光的小型化研究 总被引:2,自引:0,他引:2
本文通过对自由电子激光输出波长的分析,指出了自由电子激光小型化的研究方向─-微型摆动器的研究。在分析了小周期摆动器研究现状的基础上,提出了电流摆动器。它不但具有与静磁摆动器相同的效果,而且它的周期可以任意调节。因而,它便于控制。最后,还指出了有待进一步研究的问题。 相似文献
946.
Neoxanthin, a major carotenoid pigment of spinach, is found in the Chloroplast membrane and has an unknown function in plants. Neoxanthin inhibited the production of superoxide anions in an artificial xanthine and xanthine oxidase system and depressed DNA synthesis in methylcholanthrene (MCA)-initiated C3H10T1/2 fibroblasts. in two-stage carcinogenesis experiments, neoxanthin at 0.2 micrograms/0.2 ml inhibited the formation of tumors that were induced sequentially by 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA) in the buccal pouch of Syrian Golden hamsters. To assess the ongoing process of carcinogenesis, the activity of ornithine decarboxylase (ODC), required for cell proliferation, was analyzed. Neoxanthin inhibited the activity of ODC when animals were treated with neoxanthin one hour before the application of TPA in two-stage carcinogenesis. However, neoxanthin did not inhibit ODC activity when animals were treated with neoxanthin one hour before the application of DMBA in two-stage carcinogenesis, and there was no subsequent tumor formation. In a short-term anti-initiation experiment, neoxanthin inhibited the covalent binding of isotope-labeled DMBA to DNA by 53%. These results indicate that neoxanthin inhibits the initiation stage and the promotion stage in two-stage carcinogenesis. This suggests that neoxanthin may act as a potential chemopreventive agent. 相似文献
947.
本文着重将目前国外比较活跃的几种新型反垣克武器;软杀伤反坦克弹药,末敏弹,反坦克地雷以及智能反坦克子弹药的基本原理,作战效能,装备情况作一介绍,并对其发展方向进行了预测。 相似文献
948.
Shane Y. Hong 《Journal of Intelligent Manufacturing》1993,4(3):233-241
One major bottleneck in the automation of the drilling process by robots in the aerospace industry is drill condition monitoring. This paper describes a system approach to solve this problem through the advancement of new machine design, sensor instrumentation, metal-cutting research, and intelligent software development. All drill failures can be detected and distinguished: chisel edge wear, flank wear, crater wear, margin wear, corner wear, breakage, asymmetry, lip height difference, and chipping at lips. However, in the real manufacturing environment, different workpiece materials, drill size, drill geometry, drill material, cutting speed, feed rate, etc. will change the criteria for judging the drill condition. The knowledge base used for diagnosing the drill failures requires a huge data bank and prior exhaustive testing. A self-learning scheme is therefore introduced to the machine in order to acquire the threshold history needed for automatic diagnosis by using the same new tool under the same drilling conditions. 相似文献
949.
RV Farese M Standaert B Yu H Hernandez DR Cooper 《Canadian Metallurgical Quarterly》1993,268(27):19949-19955
In rat adipocytes and soleus muscles, 2-hydroxypropyl-beta-cyclodextrin (CD) was found to have a relatively small or no effect on basal or insulin-stimulated hexose uptake, but markedly enhanced hexose uptake effects of phorbol esters and/or diacylglycerol. In rat adipocytes, the CD-induced enhancement of hexose uptake during concurrent phorbol ester treatment was not associated with an increase in GLUT4 glucose transporter translocation to the plasma membrane, which was stimulated comparably by insulin and phorbol esters. Moreover, CD appeared to activate or facilitate the activation of glucose transporters subsequent to their translocation to the plasma membrane during ongoing phorbol ester treatment. In rat adipocytes, CD also enhanced the translocation of protein kinase C (PKC)-beta to the plasma membrane during the action of phorbol esters, which alone had little or no effect on this specific PKC translocation. Although it is uncertain how CD alters the function of plasma membranes to enhance the translocation of PKC-beta to, and the activation of glucose transporters within, this subcellular fraction during phorbol ester treatment, our findings provide direct support for a two-step model in the activation of glucose transport. In addition, it seems clear that, at least in some cell types, simple phorbol ester treatment does not necessarily serve as a ubiquitous activator of all activable PKC pools and all potential PKC-mediated responses. 相似文献
950.
Jeong-Woo Choi Jun Hyo Park Shin Chul Lee Dong-Il Kim Won Hong Lee 《Korean Journal of Chemical Engineering》1995,12(5):528-534
The on-line sensing of viable cell weight in plant cell culture process is applied to analysis and control of process. The
fiber-optic fluorescence sensor was constructed to measure the NADH-dependent fluorescence inNicotiana tabacum plant cell culture and the analysis of fluorescence signal was done to be correlated with the viable cell weight. The structured
kinetic model for cell growth was proposed to estimate the theoretical viable cell weight. The dimensional analysis was proposed
for the interpretation of fluorescence signal, in which the path length, the inner filter effect and the hydrodynamic conditions
were considered as the key factors on fluorescence signal. The dimensional analysis and empirical correlation of fluorescence
signal to viable cell weight was applied to the interpretation of the detected fluorescence signal during cultivation. The
proposed interpretation of fluorescence signal using dimensional analysis was well correlated with the viable cell weight
estimated by the structured kinetic model as well as by empirical correlation. 相似文献