全文获取类型
收费全文 | 395997篇 |
免费 | 6005篇 |
国内免费 | 2227篇 |
专业分类
电工技术 | 7524篇 |
技术理论 | 5篇 |
综合类 | 3450篇 |
化学工业 | 59073篇 |
金属工艺 | 20449篇 |
机械仪表 | 15682篇 |
建筑科学 | 9704篇 |
矿业工程 | 2824篇 |
能源动力 | 7341篇 |
轻工业 | 29783篇 |
水利工程 | 4800篇 |
石油天然气 | 7488篇 |
武器工业 | 243篇 |
无线电 | 41788篇 |
一般工业技术 | 79648篇 |
冶金工业 | 54992篇 |
原子能技术 | 6792篇 |
自动化技术 | 52643篇 |
出版年
2021年 | 2624篇 |
2019年 | 2252篇 |
2018年 | 22837篇 |
2017年 | 22363篇 |
2016年 | 16138篇 |
2015年 | 3914篇 |
2014年 | 5059篇 |
2013年 | 11887篇 |
2012年 | 12722篇 |
2011年 | 25244篇 |
2010年 | 21746篇 |
2009年 | 19273篇 |
2008年 | 20747篇 |
2007年 | 23237篇 |
2006年 | 8844篇 |
2005年 | 11704篇 |
2004年 | 9379篇 |
2003年 | 8685篇 |
2002年 | 7349篇 |
2001年 | 6556篇 |
2000年 | 6231篇 |
1999年 | 5997篇 |
1998年 | 13067篇 |
1997年 | 9673篇 |
1996年 | 7392篇 |
1995年 | 5609篇 |
1994年 | 5182篇 |
1993年 | 5044篇 |
1992年 | 4016篇 |
1991年 | 3823篇 |
1990年 | 3850篇 |
1989年 | 3802篇 |
1988年 | 3561篇 |
1987年 | 3039篇 |
1986年 | 3073篇 |
1985年 | 3445篇 |
1984年 | 3344篇 |
1983年 | 3100篇 |
1982年 | 2718篇 |
1981年 | 2919篇 |
1980年 | 2658篇 |
1979年 | 2849篇 |
1978年 | 2745篇 |
1977年 | 2868篇 |
1976年 | 3730篇 |
1975年 | 2467篇 |
1974年 | 2308篇 |
1973年 | 2339篇 |
1972年 | 1991篇 |
1971年 | 1794篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
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
113.
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
114.
115.
116.
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
117.
L. Bolzoni 《Metal Powder Report》2019,74(6):308-313
118.
Medel Manuel L. Zulueta Donala Janreddy Shang-Cheng Hung 《Israel journal of chemistry》2015,55(3-4):347-359
In recent years, there has been rapid expansion of glycan synthesis, fueled by the recognition that the structural complexity of sugars translates to a myriad of biological functions. Such chemical syntheses involve many challenges, mostly due to the regio- and stereochemical aspects of glycosidic bond formation. One-pot strategies were developed to assist in attaining faster and more economical access to the glycan constructs. In this front, achievements in protecting group manipulation, glycosylation, and combinations of these have been reported. Protecting group manipulations in one pot take advantage of the reaction compatibility of commonly used transformations, many of which occur in high regioselectivity. Sequential glycosylations, on the other hand, rely on leaving group orthogonalities and reactivity tuning, as well as the preactivation technique. Altogether, these approaches offer attractive means to the much needed glycan structures and, consequently, help usher in advances in glycoscience. 相似文献
119.
120.