全文获取类型
收费全文 | 50178篇 |
免费 | 6564篇 |
国内免费 | 3887篇 |
专业分类
电工技术 | 2586篇 |
技术理论 | 6篇 |
综合类 | 4151篇 |
化学工业 | 12525篇 |
金属工艺 | 1582篇 |
机械仪表 | 3710篇 |
建筑科学 | 4993篇 |
矿业工程 | 1196篇 |
能源动力 | 6080篇 |
轻工业 | 5105篇 |
水利工程 | 1433篇 |
石油天然气 | 1592篇 |
武器工业 | 356篇 |
无线电 | 2941篇 |
一般工业技术 | 5736篇 |
冶金工业 | 1870篇 |
原子能技术 | 1261篇 |
自动化技术 | 3506篇 |
出版年
2024年 | 183篇 |
2023年 | 905篇 |
2022年 | 1539篇 |
2021年 | 2217篇 |
2020年 | 2017篇 |
2019年 | 1992篇 |
2018年 | 1778篇 |
2017年 | 1819篇 |
2016年 | 1973篇 |
2015年 | 1928篇 |
2014年 | 2860篇 |
2013年 | 3557篇 |
2012年 | 3248篇 |
2011年 | 3718篇 |
2010年 | 2725篇 |
2009年 | 2724篇 |
2008年 | 2590篇 |
2007年 | 3122篇 |
2006年 | 2807篇 |
2005年 | 2638篇 |
2004年 | 2130篇 |
2003年 | 2010篇 |
2002年 | 1636篇 |
2001年 | 1292篇 |
2000年 | 1071篇 |
1999年 | 904篇 |
1998年 | 848篇 |
1997年 | 729篇 |
1996年 | 611篇 |
1995年 | 544篇 |
1994年 | 430篇 |
1993年 | 367篇 |
1992年 | 322篇 |
1991年 | 221篇 |
1990年 | 207篇 |
1989年 | 191篇 |
1988年 | 139篇 |
1987年 | 100篇 |
1986年 | 93篇 |
1985年 | 65篇 |
1984年 | 86篇 |
1983年 | 54篇 |
1982年 | 41篇 |
1981年 | 61篇 |
1980年 | 27篇 |
1979年 | 12篇 |
1966年 | 8篇 |
1959年 | 17篇 |
1956年 | 5篇 |
1951年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Hannerz Harald; Albertsen Karen; Nielsen Martin Lindhardt; Tüchsen Finn; Burr Hermann 《Canadian Metallurgical Quarterly》2004,23(3):283
This study explored whether factors related to the work environment could predict changes in body mass index (BMI) and whether the effect of psychosocial factors was dependent on baseline BMI. The sample consisted of 1,980 male employees from the Danish National Work Environment Cohort Study. Changes in BMI between 1995 and 2000 were analyzed, by multiple regression, as a function of background variables and a series of occupational variables obtained in 1995. Age, baseline BMI, job insecurity, and psychological demands predicted changes in BMI. Job insecurity and high or low psychological demands increased the likelihood of weight gain among obese employees, whereas they increased the likelihood of weight loss among employees with a low BMI. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
102.
从中国石化股份公司济南分公司新上铁路罐车密闭装车计量系统的背景出发,阐述该系统的设计思想和组成;通过分析实际运行过程中仪表比对数据,讨论影响仪表贸易交接准确性的各种因素,提出相应的解决方法;最后通过铁路罐车密闭装车计量系统投用效果。证实该系统可产生明显的经济效益。 相似文献
103.
L. Sheeney‐Haj‐Ichia S. Pogorelova Y. Gofer I. Willner 《Advanced functional materials》2004,14(5):416-424
Three different configurations of Au‐nanoparticle/CdS‐nanoparticle arrays are organized on Au/quartz electrodes for enhanced photocurrent generation. In one configuration, Au‐nanoparticles are covalently linked to the electrode and the CdS‐nanoparticles are covalently linked to the bare Au‐nanoparticle assembly. The resulting photocurrent, φ = 7.5 %, is ca. 9‐fold higher than the photocurrent originating from a CdS‐nanoparticle layer that lacks the Au‐nanoparticles, φ = 0.8 %. The enhanced photocurrent in the Au/CdS nanoparticle array is attributed to effective charge separation of the electron–hole pair by the injection of conduction‐band electrons from the CdS‐ to the Au‐nanoparticles. Two other configurations involving electrostatically stabilized bipyridinium‐crosslinked Au/CdS or CdS/Au nanoparticle arrays were assembled on the Au/quartz crystal. The photocurrent quantum yields in the two systems are φ = 10 % and φ = 5 %, respectively. The photocurrents in control systems that include electrostatically bridged Au/CdS or CdS/Au nanoparticles by oligocationic units that lack electron‐acceptor units are substantially lower than the values observed in the analogous bipyridinium‐bridged systems. The enhanced photocurrents in the bipyridinium‐crosslinked systems is attributed to the stepwise electron transfer of conduction‐band electrons to the Au‐nanoparticles by the bipyridinium relay bridge, a process that stabilizes the electron–hole pair against recombination and leads to effective charge separation. 相似文献
104.
An experimental technique together with a numerical model is proposed with which the diffusion coefficient and the sorption isotherm of water in paint can be measured. Inside a closed vessel, paint films are on stainless-steel plates. Water is present as water vapour in the air and in the paint. After blowing dry or wet air through the vessel for some time, the situation moves to a new equilibrium. The relative humidity of the air inside the vessel is measured as a function of time. From fitting the theoretical/numerical model against the experimental values, follow the diffusion coefficient and the sorption isotherm of water in the paint. The results show large scattering. When the independently measured sorption isotherm is used as an input parameter in the model, the fitting procedure gives much smaller scattering for the diffusion coefficient. 相似文献
105.
M. Ganschow C. Hellriegel E. Kneuper M. Wark C. Thiel G. Schulz‐Ekloff C. Bruchle D. Whrle 《Advanced functional materials》2004,14(3):269-276
Dye‐loaded AlPO4‐5 single crystals were prepared by microwave‐assisted hydrothermal synthesis from a batch, containing a mixture of three chromophores (Coumarin 40, Rhodamine BE50, and Oxazine 1) differing in their absorption range, molecular dimensions, and solubilities. Confocal fluorescence images reveal a spatial separation effect of the dye molecules, where the slimmer, more‐soluble dye molecule (Coumarin 40) is uniformly distributed in the body of the single crystal, and the bulky and/or less‐soluble ones (Rhodamine BE50, Oxazine 1) are situated in distinct domains. Visible spectra show good panchromatic absorption of visible light. Fluorescence lifetime measurements indicate the presence of an energy transfer cascade of the entirely fixed dye molecules from Coumarin 40 to Oxazine 1. The transfer mechanism is predominantly radiative. 相似文献
106.
三峡三期工程主坝大体积混凝土内部温度控制 总被引:2,自引:2,他引:0
三峡右岸三期工程施工中,为了有效控制坝体大体积混凝土内部温升,采取了高温季节使用预冷混凝土浇筑、控制混凝土出机口温度及浇筑温度、对混凝土内部人工通水进行初冷、中冷和后冷等措施。三峡三期工程大坝混凝土内部温度没有出现超标现象,混凝土温控工作取得了良好的效果。 相似文献
107.
As we approach 100 nm technology the interconnect issues are becoming one of the main concerns in the testing of gigahertz system-on-chips. Voltage distortion (noise) and delay violations (skew) contribute to the signal integrity loss and ultimately functional error, performance degradation and reliability problems. In this paper, we first define a model for integrity faults on the high-speed interconnects. Then, we present a BIST-based test methodology that includes two special cells to detect and measure noise and skew occurring on the interconnects of the gigahertz system-on-chips. Using an inexpensive test architecture the integrity information accumulated by these special cells can be scanned out for final test and reliability analysis. 相似文献
108.
Heat transfer of highly consistent shear-thinning fluids flowing in a horizontal cylindrical channel has been investigated numerically and experimentally when the outer channel wall is subjected to a constant convective heat exchange. The case considered being cooling, a possible ice deposit must be taken into account. The variation of the rheological properties with temperature must be considered as well. 相似文献
109.
倪汉根 《水动力学研究与进展(A辑)》1994,9(1):23-29
本文内容包括:(1)把求解无限小域中孤立悬臂板的振动问题转化为求解水体对板振动的影响,给出了本征值与本征函数摄动量的表达式;(2)利用一个特殊变换求解了规定条件下的附加质量;(3)给出了非淹没板在不计及水面波动时正对称第一、二自振频率的计算结果。 相似文献
110.
本文以系统节能和提高综合经济效益的观点,分析了金属换热器传热系数的影响因素及提高途径;气流阻力与动力消耗;传热面积与投资的定量关系。为正确选用不同结构金属换热器及其性能提供了依据。 相似文献