全文获取类型
收费全文 | 434568篇 |
免费 | 39200篇 |
国内免费 | 11060篇 |
专业分类
电工技术 | 23747篇 |
技术理论 | 76篇 |
综合类 | 23719篇 |
化学工业 | 78786篇 |
金属工艺 | 22053篇 |
机械仪表 | 26018篇 |
建筑科学 | 31616篇 |
矿业工程 | 12461篇 |
能源动力 | 12678篇 |
轻工业 | 29818篇 |
水利工程 | 6804篇 |
石油天然气 | 25057篇 |
武器工业 | 3171篇 |
无线电 | 51517篇 |
一般工业技术 | 57779篇 |
冶金工业 | 20835篇 |
原子能技术 | 4246篇 |
自动化技术 | 54447篇 |
出版年
2025年 | 198篇 |
2024年 | 7992篇 |
2023年 | 7438篇 |
2022年 | 10894篇 |
2021年 | 15841篇 |
2020年 | 14931篇 |
2019年 | 14408篇 |
2018年 | 13566篇 |
2017年 | 15240篇 |
2016年 | 14959篇 |
2015年 | 17990篇 |
2014年 | 22081篇 |
2013年 | 26596篇 |
2012年 | 25734篇 |
2011年 | 27955篇 |
2010年 | 24792篇 |
2009年 | 23486篇 |
2008年 | 22653篇 |
2007年 | 21966篇 |
2006年 | 22268篇 |
2005年 | 19457篇 |
2004年 | 13133篇 |
2003年 | 11869篇 |
2002年 | 11076篇 |
2001年 | 10070篇 |
2000年 | 10021篇 |
1999年 | 10799篇 |
1998年 | 8614篇 |
1997年 | 7162篇 |
1996年 | 6664篇 |
1995年 | 5594篇 |
1994年 | 4562篇 |
1993年 | 3261篇 |
1992年 | 2621篇 |
1991年 | 2039篇 |
1990年 | 1567篇 |
1989年 | 1287篇 |
1988年 | 1078篇 |
1987年 | 728篇 |
1986年 | 574篇 |
1985年 | 359篇 |
1984年 | 258篇 |
1983年 | 221篇 |
1982年 | 210篇 |
1981年 | 139篇 |
1980年 | 140篇 |
1979年 | 74篇 |
1978年 | 35篇 |
1977年 | 42篇 |
1976年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Hankun Wang 《Dynamics and Control》1993,3(4):353-369
In this article, we consider stabilization of two wave equations coupled in parallel by viscous damping. Uniform exponential stabilization can be achieved when damping is presented in two equations. In general only strong stabilization can be achieved when damping is present in one equation, while uniform exponential stabilization is still possible for some special cases. 相似文献
142.
Da-Peng Wang Gow-Zaw Liang Yu-Hsing Tu 《Drug development and industrial pharmacy》1994,20(11):1895-1903
A stability-indicating reversed-phase high performance liquid chromatographic method was developed for the detection of mitoxantrone HC1 and its degradation products under accelerated degradation conditions. The degradation kinetics of mitoxantrone HC1 in aqueous solution over a pH range of 1.18 to 7.20 and its stability in propylene glycol-or polyethylene glycol 400-based solutions were investigated. The observed rate constants were shown to follow apparent first-order kinetics in all cases. The pH-rate profile shows that maximum stability of mitoxantrone HC1 was obtained at pH 4.01. No general acid or base catalysis from acetate or phosphate buffer species was observed. The catalysis rate constants on the protonated mitoxantrone imposed by hydrogen ion water and hydroxy ion were determined to be 3.72 × 10 min-1 5.64 × 10-min-1 and 1.108 × 10-2min-1, respectively. The degradation rate constants of mitoxantrone affected by different ionic strength systems. Irradiation with 254 nm UV light at 25±0.5°C was found when canpared with the light-protected controls. Incorporation of nonaqueous propylene glycol or polyethylene glycol in the pH 4.01 mitoxantrone solution shows an increase in its stability at 502±0.5°C. 相似文献
143.
本文介绍了用αβ谱仪系统同时测量αβ谱、实现Rn/Th子体补偿、确定超铀α核素气溶胶体积活度及人工放射性气溶胶总β体积活度的技术途径。利用RaA、RaC′a峰的二段时间计数可确定空气中RaA、RaB、RaC的气溶胶体积活度,相应的,也能给出RaB、RaC对总β计数的贡献。根据一般环境条件下的平衡比,用ThC′的。计数修正Th子体对αβ测量的影响。 ̄[239]pu或/和 ̄[241]Am人工核素的α计数,可通过两段时间分别扣除RaA、RaC′拖尾的方法确定;β计数分别扣除Rn/Th子体β贡献即可确定。在本文规定的测量条件下,对室内天然Rn子体水平在15Bq/m ̄3以下,超铀α核素气溶胶体积活度的测量下限可达到0.1Bq/m ̄3;即使在75Bq/m ̄3环境下,人工核素总β的测量下限也可达lBq/m ̄3以下。 相似文献
144.
An analytical method is presented for calculating the resonant frequency andQ-factor of a superconducting dielectric disk resonator operating in millimeter-wave regime with whispering-gallery mode. Resonant frequency shift due to the optical generation of quasi-particles in superconducting film is investigated as a function of photon flux. An optically tunable resonant frequency of about 500 MHz is estimated, and good agreement is found between numerical results and experimental ones. 相似文献
145.
146.
通过3种不同的碱来制备2,4-二氯-5-氟苯甲酰乙酸甲酯,优选得到了其最佳缩合剂甲醇钠;同时应用正交设计实验,研究了原料配比、反应时间、反应温度对收率的影响,在优选条件下收率为78.5%。 相似文献
147.
In this study, 16 cases of unilateral alveolar cleft with cleft lip and palate were repaired with autografts of cancellous bone (13 cases) or hydroxyapatite (3 cases). The grafts were covered by reflected mucoperiosteal flaps and a mucosal flap from the upper lip. Twelve of the thirteen cases were followed up for 1-5 years. Nine of whom using cancellous bone had bony continuity of the maxilla and 7 cases erupted permanent maxillary canines within the area of autografts. None of the 3 cases using hydroxyapatite erupted a canine tooth. The results showed that autograft was better than hydroxyapatite in terms of maxillary canine eruption. 相似文献
148.
This paper describes a simple and effective way to modify an existing hard-switched flyback power converter into a circuit with zero-voltage switching (ZVS) and zero-current switching (ZCS). The key improvement is to turn the unattractive features of the coupled inductor leakage inductance and snubber capacitor into attractive ones. The coupled inductor leakage inductance and snubber are used to form a quasi-resonant circuit to facilitate ZVS/ZCS of all power devices. The operating principles of the power converter and experimental results are presented 相似文献
149.
The purpose of this study was to analyze the symbolization of colors as cultural codes, based on costume colors. In order to study the significance of colors in cultural changes, we carried out a quantitative analysis and interpreted it from the perspective of cultural semiotics. The range of this study was focused on Korean costume colors, over diverse diachronic stages of Korean culture. For this study 1535 color samples were collected, measured with a spectrophotometer, and analyzed quantitatively according their diachronic stages of origin. As a result, red, blue, and yellow were found to be the most frequently used colors during the Chosun Dynasty, a period based on Confucianism. These colors acted as cultural codes with cultural significance. During the Modern times pink, light blue, and black increased in frequency and represented the reception of western culture, the changing sex role of women in society, and utilitarianism. In these days, neutral colors and grayish tones of all colors are the most significant colors of high frequency. The use of such colors is closely related to industrialization, mechanization, functionalism, and the changes of women's sex roles in the societies. They are used as cultural codes, especially to emphasize a rational and masculine image rather than a feminine image. © 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 71–79, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20290 相似文献
150.
Remote procedure call (RPC) mechanisms over the US Department of Defense transmission control protocol. (TCP) can produce behavior analogous to the silly window syndrome because of a mismatched interface between the socket and the TCP modules. The detection and diagnosis of the problem are addressed. Some pointers to a design approach that could avoid the problems of mismatched communication layers are provided 相似文献