全文获取类型
收费全文 | 143420篇 |
免费 | 5272篇 |
国内免费 | 1483篇 |
专业分类
电工技术 | 2277篇 |
技术理论 | 3篇 |
综合类 | 3762篇 |
化学工业 | 22156篇 |
金属工艺 | 6758篇 |
机械仪表 | 5261篇 |
建筑科学 | 5051篇 |
矿业工程 | 1555篇 |
能源动力 | 2612篇 |
轻工业 | 10166篇 |
水利工程 | 2047篇 |
石油天然气 | 1984篇 |
武器工业 | 162篇 |
无线电 | 13699篇 |
一般工业技术 | 25592篇 |
冶金工业 | 14225篇 |
原子能技术 | 673篇 |
自动化技术 | 32192篇 |
出版年
2024年 | 170篇 |
2023年 | 790篇 |
2022年 | 1001篇 |
2021年 | 1846篇 |
2020年 | 1470篇 |
2019年 | 1322篇 |
2018年 | 16114篇 |
2017年 | 15120篇 |
2016年 | 11778篇 |
2015年 | 2573篇 |
2014年 | 2778篇 |
2013年 | 4325篇 |
2012年 | 6817篇 |
2011年 | 12695篇 |
2010年 | 11064篇 |
2009年 | 8073篇 |
2008年 | 9525篇 |
2007年 | 10199篇 |
2006年 | 2435篇 |
2005年 | 3172篇 |
2004年 | 2733篇 |
2003年 | 2594篇 |
2002年 | 1915篇 |
2001年 | 1126篇 |
2000年 | 1156篇 |
1999年 | 1248篇 |
1998年 | 3862篇 |
1997年 | 2429篇 |
1996年 | 1708篇 |
1995年 | 1075篇 |
1994年 | 952篇 |
1993年 | 858篇 |
1992年 | 385篇 |
1991年 | 361篇 |
1990年 | 282篇 |
1989年 | 277篇 |
1988年 | 269篇 |
1987年 | 212篇 |
1986年 | 211篇 |
1985年 | 231篇 |
1984年 | 196篇 |
1983年 | 140篇 |
1982年 | 172篇 |
1981年 | 181篇 |
1980年 | 160篇 |
1979年 | 137篇 |
1978年 | 121篇 |
1977年 | 201篇 |
1976年 | 417篇 |
1975年 | 91篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
This paper presents an integrated passive damping approach in hybrid metal-CFRP parts for structural applications. In this concept a viscoelastic material is embedded in the joint zone of the hybrid component. To examine the connection strength single-lap-joint specimens were produced and tested and the influence of the used material combinations, different surface structures, and different process parameters i.e. the moment of cross-linking were evaluated. Afterwards, the metal-CFRP hybrids were tested in quasi-static tests to assess their connection strength and failure behaviour. Dynamic cyclic tensile tests with step-wise increased loading conditions were performed to determine the specimens damping behaviour and to estimate their fatigue performance. Finally, these results are compared to a state of the art metal-CFRP hybrid with rivets connecting both materials. 相似文献
62.
综采工作面在推进过程中经常会受到断层的影响,严重制约了矿井的安全生产及经济效益。以寺河煤矿西井区W2303工作面采用留顶煤、割底矸等手段过逆断层群为工程实例,分析了综采工作面安全、快速过逆断层群技术的应用效果,对于类似矿山也有一定的借鉴价值。 相似文献
63.
64.
László Lőrincz Máté Zsemberi György Bánsághi Tamás Sohajda Edit Székely 《化学工程与技术》2018,41(7):1466-1472
Chiral molecules, especially enantiomers and diastereomers of purity > 99 %, present a significant market share within the chemical, pharmaceutical, and flavor industries. Antisolvent precipitations, both batch and semicontinuous operations to serve the current trends in flow chemistry were demonstrated to be environmentally benign and efficient tools in achieving high optical purities. Although salts are known to be insoluble in supercritical CO2, instabilities of the nascent salts were detected and applied for increasing efficiency. Diastereomeric excess values of the crystalline products exceeded 99 % in maximum of three consecutive steps both by repeated resolution with half molar equivalent of the amine to the acid and by direct recrystallization of the salts. 相似文献
65.
In this paper, we consider the classical finite mixture model, which is an effective tool for modeling lifetime distributions for random samples from heterogeneous populations. We discuss new results on stochastic comparison for two finite mixtures when each of them is drawn from one of the following semiparametric families, i.e., proportional hazards, accelerated lifetime and proportional reversed hazards. 相似文献
66.
Abraham G. Alvarado Rosaura Hernández-Montelongo Martin Rabelero Lourdes A. Pérez-Carrillo Jorge E. Puig Francisco López-Serrano 《Polymer Engineering and Science》2020,60(2):223-232
A simple but comprehensive model considering homogeneous and micellar nucleation, coagulation, entry of radicals to particles and to micelles and radicals' exit from particles, is presented. The model is validated, in a starved semicontinuous heterophase polymerization of ethyl methacrylate, at three monomer addition rates. The model accurately describes the overall and instantaneous conversion, the average particle density and diameter, and the number and weight average molar masses evolutions over time. It is found that even though the average number of radicals is much smaller than 0.5, the system is not 0-1. An empirical function was used to describe the gel effect. The homogeneous nucleation was the prevailing mechanism for particle formation and large exit rates of radicals were observed. POLYM. ENG. SCI., 60: 223–232, 2019. © 2019 Society of Plastics Engineers 相似文献
67.
68.
69.
Variations of Incomplete Open Cubes is the major project by the twentieth-century conceptual artist Sol LeWitt. In this paper we interpret the enumerative component of the project as embeddings of graphs. This formulation permits use of an algorithm to check the completeness of the list of the structures produced by the artist. Our conclusion is that the artist found the correct number of structures (that is, 122), but that his list contains a mistake in the presentation of a pair of incomplete cubes, a discovery that appears not to have been noted before. 相似文献
70.
Qun Ren Haijun Su Jun Zhang Haifang Liu Weidan Ma Guangrao Fan Di Zhao Min Guo Lin Liu Hengzhi Fu 《Ceramics International》2019,45(6):6632-6638
Directionally solidified microstructures of Al2O3-Er3Al5O12 eutectic and off-eutectic in situ composite ceramics were explored under abrupt-change pulling rate conditions. Corresponding temperature distributions and interface locations were studied. In eutectic composition, fluctuation of eutectic spacing occurred when the pulling rate increased abruptly. A gradually increase or abrupt increase in eutectic spacing was observed when the pulling rate decreased abruptly. In hypoeutectic and hypereutectic compositions, formation of the primary phases were suppressed when the pulling rate increased abruptly from 10?µm/s to 100?µm/s, while primary phases precipitated when the pulling rate decreased abruptly from 100?µm/s to 10?µm/s. The interface altitude decreased after the pulling rate increased abruptly, but increased after the pulling rate decreased abruptly. The liquid composition restriction (around the eutectic composition) at the eutectic interface plays an important role in the suppression of the primary dendrite and coupled eutectic oxides can be obtained in off-eutectic compositions even under higher solidification rate conditions. 相似文献