全文获取类型
收费全文 | 247566篇 |
免费 | 18230篇 |
国内免费 | 9210篇 |
专业分类
电工技术 | 13277篇 |
技术理论 | 13篇 |
综合类 | 14139篇 |
化学工业 | 41016篇 |
金属工艺 | 14888篇 |
机械仪表 | 15212篇 |
建筑科学 | 17147篇 |
矿业工程 | 6304篇 |
能源动力 | 5856篇 |
轻工业 | 14089篇 |
水利工程 | 4622篇 |
石油天然气 | 14368篇 |
武器工业 | 1705篇 |
无线电 | 25877篇 |
一般工业技术 | 36187篇 |
冶金工业 | 14978篇 |
原子能技术 | 5824篇 |
自动化技术 | 29504篇 |
出版年
2024年 | 700篇 |
2023年 | 3375篇 |
2022年 | 6041篇 |
2021年 | 8963篇 |
2020年 | 6886篇 |
2019年 | 5818篇 |
2018年 | 7251篇 |
2017年 | 8035篇 |
2016年 | 7228篇 |
2015年 | 8567篇 |
2014年 | 11006篇 |
2013年 | 13539篇 |
2012年 | 14707篇 |
2011年 | 15795篇 |
2010年 | 13435篇 |
2009年 | 13193篇 |
2008年 | 12929篇 |
2007年 | 12251篇 |
2006年 | 11972篇 |
2005年 | 10408篇 |
2004年 | 7544篇 |
2003年 | 7070篇 |
2002年 | 6914篇 |
2001年 | 6241篇 |
2000年 | 5938篇 |
1999年 | 5840篇 |
1998年 | 4705篇 |
1997年 | 3876篇 |
1996年 | 3690篇 |
1995年 | 3127篇 |
1994年 | 2603篇 |
1993年 | 2054篇 |
1992年 | 1863篇 |
1991年 | 1588篇 |
1990年 | 1451篇 |
1989年 | 1317篇 |
1988年 | 1145篇 |
1987年 | 1000篇 |
1986年 | 857篇 |
1985年 | 787篇 |
1984年 | 746篇 |
1982年 | 703篇 |
1979年 | 742篇 |
1978年 | 779篇 |
1977年 | 739篇 |
1976年 | 755篇 |
1975年 | 713篇 |
1974年 | 719篇 |
1973年 | 723篇 |
1972年 | 705篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
131.
三元复合驱油体系中驱油剂的协同效应,会使油水间的界面张力大幅度下降,原油采收率大幅度提高;但三元复合驱油体系的色谱分离现象也会破坏其协同效应和完整性,揭示色谱分离现象及其影响因素对于改善三元复合驱油效果具有十分重要意义。以油藏工程和分析化学理论为指导,以化学分析和物理模拟为技术途径,并以大庆喇嘛甸油田典型区块地质特征和流体性质为研究对象,开展强碱三元复合驱色谱分离现象及其影响因素研究。结果表明,采用前置高浓度聚合物段塞后,可以有效扩大波及体积,但表面活性剂与碱和聚合物之间无因次等浓距增加,色谱分离现象加剧。大庆油区喇嘛甸油田不同区块油水性质差异对色谱分离现象存在影响,原因在于部分重烷基苯石油磺酸进入油相,影响水相中浓度检测值。强碱三元复合驱油体系中表面活性剂与碱和聚合物之间色谱分离程度比较严重,碱与聚合物之间较弱。 相似文献
132.
133.
134.
135.
Strength of Materials - A metallographic method, dilatometry, and X-ray diffraction were applied to investigate the effects of undercooling and holding time on bainitic transformation,... 相似文献
136.
Sleptsov V. V. Kukushkin D. Yu. Kulikov S. N. Diteleva A. O. 《Russian Engineering Research》2021,41(5):416-418
Russian Engineering Research - Thin-film vacuum technology permits the creation of new electrode materials on the basis of a flexible carbon matrix with a highly developed surface. Supercapacitor... 相似文献
137.
In this study, 30 subjects were exposed to different combinations of air temperature (Ta: 24, 27, and 30°C) and CO2 level (8000, 10 000, and 12 000 ppm) in a high-humidity (RH: 85%) underground climate chamber. Subjective assessments, physiological responses, and cognitive performance were investigated. The results showed that as compared with exposure to Ta = 24°C, exposure to 30°C at all CO2 levels caused subjects to feel uncomfortably warm and experience stronger odor intensity, while increased mental effort and greater intensity of acute health symptoms were reported. However, no significant effects of Ta on task performance or physiological responses were found. This indicated that subjects had to exert more effort to maintain their performance in an uncomfortably warm environment. Increasing CO2 from 8000 to 12 000 ppm at all Ta caused subjects to report higher rates of headache, fatigue, agitation, and feeling depressed, although the results were statistically significant only at 24 and 27°C. The text typing performance and systolic blood pressure (SBP) decreased significantly at this exposure, whereas diastolic blood pressure (DBP) and thermal discomfort increased significantly. These effects suggest higher arousal/stress. No significant interaction effect of Ta and CO2 concentration on human responses was identified. 相似文献
138.
Anti-washout and tissue adhesion properties are essential for the clinical application of injectable bone materials. In this study, we prepared calcium phosphate cement (CPC) with anti-washout and tissue adhesion properties and attempted to build covalent bonds between CPC and the amino groups in bone tissue under a self-regulating pH system in the CPC (acidic to basic). The results of push-out tests demonstrated that a significant enhancement (from 6.42 ± 0.76 N to 61.5 ± 4.09 N) in tissue adhesion was obtained with the addition of 6% (w/w) oxidized sodium alginate (OSA) in CPC. The FTIR, XRD, anti-washout test, XPS, pH test, and SEM results suggested that the synergistic effect of OSA-citric acid (CA) led to the formation of a three-dimensional gel network structure in the CPC, and the Schiff base reaction between aldehyde and amino groups induced adhesion between CPC and the bone tissue. Further, the addition of less OSA had no significant negative effect on the hydration properties of CPC. Our work aims to promote the development of injectable bone material in clinical applications. 相似文献
139.
Gavshina O. V. Doroganov V. A. Doroganov E. A. Onishchuk V. I. Trepalina Yu. N. 《Refractories and Industrial Ceramics》2019,60(4):350-354
Refractories and Industrial Ceramics - Results of studying the rheotechnological properties of moldable refractory mixes based on bauxite suspensions plasticized with refractory clay are presented.... 相似文献
140.
How to improve the sensitivity of the temperature-sensing luminescent materials is one of the most important objects currently. In this work, to obtain high sensitivity and learn the corresponding mechanism, the rare earth (RE) ions doped Y4.67Si3O13 (YS) phosphors were developed by solid-state reaction. The phase purity, structure, morphology and luminescence characteristics were evaluated by XRD, TEM, emission spectra, etc. The change of the optical bandgaps between the host and RE-doped phosphors was found, agreeing with the calculation results based on density-functional theory. The temperature-dependence of the upconversion (UC) luminescence revealed that a linear relationship exists between the fluorescence intensity ratio of Ho3+ and temperature. The theoretical resolution was evaluated. High absolute (0.083 K−1) and relative (3.53% K−1 at 293 K) sensitivities have been gained in the YS:1%Ho3+, 10%Yb3+. The effect of the Yb3+ doping concentration and pump power on the sensitivities was discussed. The pump-power–dependence of the UC luminescence indicated the main mechanism for high sensitivities in the YS:1%Ho3+, 10%Yb3+. Moreover, the decay-lifetime based temperature sensing was also evaluated. The above results imply that the present phosphors could be promising candidates for temperature sensors, and the proposed strategies are instructive in exploring other new temperature sensing luminescent materials. 相似文献