全文获取类型
收费全文 | 509144篇 |
免费 | 8754篇 |
国内免费 | 2550篇 |
专业分类
电工技术 | 9958篇 |
技术理论 | 5篇 |
综合类 | 1380篇 |
化学工业 | 78932篇 |
金属工艺 | 19776篇 |
机械仪表 | 14736篇 |
建筑科学 | 13702篇 |
矿业工程 | 2523篇 |
能源动力 | 12904篇 |
轻工业 | 45361篇 |
水利工程 | 5036篇 |
石油天然气 | 8684篇 |
武器工业 | 261篇 |
无线电 | 59709篇 |
一般工业技术 | 97795篇 |
冶金工业 | 96035篇 |
原子能技术 | 9933篇 |
自动化技术 | 43718篇 |
出版年
2021年 | 4928篇 |
2020年 | 3483篇 |
2019年 | 4327篇 |
2018年 | 6866篇 |
2017年 | 6853篇 |
2016年 | 7486篇 |
2015年 | 5467篇 |
2014年 | 8894篇 |
2013年 | 23255篇 |
2012年 | 14453篇 |
2011年 | 19385篇 |
2010年 | 15408篇 |
2009年 | 16872篇 |
2008年 | 18202篇 |
2007年 | 18164篇 |
2006年 | 16023篇 |
2005年 | 13998篇 |
2004年 | 12943篇 |
2003年 | 12710篇 |
2002年 | 12226篇 |
2001年 | 12404篇 |
2000年 | 11514篇 |
1999年 | 11985篇 |
1998年 | 28420篇 |
1997年 | 20308篇 |
1996年 | 15614篇 |
1995年 | 11806篇 |
1994年 | 10746篇 |
1993年 | 10577篇 |
1992年 | 7869篇 |
1991年 | 7473篇 |
1990年 | 7440篇 |
1989年 | 7214篇 |
1988年 | 6896篇 |
1987年 | 5948篇 |
1986年 | 5856篇 |
1985年 | 6483篇 |
1984年 | 6138篇 |
1983年 | 5793篇 |
1982年 | 5219篇 |
1981年 | 5296篇 |
1980年 | 4954篇 |
1979年 | 4997篇 |
1978年 | 4680篇 |
1977年 | 5279篇 |
1976年 | 6986篇 |
1975年 | 4062篇 |
1974年 | 3874篇 |
1973年 | 3842篇 |
1972年 | 3277篇 |
排序方式: 共有10000条查询结果,搜索用时 293 毫秒
991.
992.
993.
The Highway Loss Data Institute (HLDI) compiles injury and collision claim information from major insurance companies. These data have indicated that a disproportionately large number of injury claims are made for small cars. As a result, it might be concluded that small cars increase injury risk to their occupants. Recent advertisements by a major automobile manufacturer suggest a similar conclusion should be drawn from these data. In this paper it is shown that the apparent higher injury risk attributed to small cars can reflect the behavior of persons driving small cars. The number of injury claim accidents per collision claim accident is examined as an alternative measure of injury risk. Possible problems in interpretation are discussed. 相似文献
994.
995.
Conclusions The change in some properties of polyvinyl fluoride during the process of fibre spinning has been investigated.It has been found that during the process of converting PVF powder into fibre, the degree of polymer crystallinity plus its resistance to thermal and thermooxidative degradation is increased; depending on the spinning regime, the densities and physicomechanical properties of PVF fibres are different.Translated from Khimicheskie Volokna, No. 4, pp. 34–35, July–August, 1984. 相似文献
996.
Wladek T. Sobol L.John SchreinerLjubis̆a Miljković Maria E. Marcondes-HeleneLeonard W. Reeves M.Mik Pintar 《Fuel》1985
The first results of the analysis of bitumen and oil sands using the recently developed n.m.r. spingrouping technique are presented. The n.m.r. relaxation experiments were carried out on bitumen, and on natural and dried oil sands samples. The results indicate that the spin-grouping can resolve and quantify several components of the samples studied. The bitumen and bitumen fraction of the oil sands are resolved according to their spin-spin relaxation times into three major groups: solid-like (rigid), solid-like (mobile) and semi-liquid. The water in the oil sands exists in two different environments. Tentatively one environment is assigned to be the bridges between the sand grains, while the other is assigned to be the clay surface. One can conclude that with spin grouping of complex mixtures the decomposition (in which components are resolved according to their dynamic state) is possible. The accuracy of such resolution is of the order of a few per cent. 相似文献
997.
In response to an interpretation made by Moore and Akgerman of data taken from a recent publication, previously unexplainable phenomena are accounted for, based on new experimental results. These relate to a thermodynamic equilibrium reaction involving saturation of aromatic hydrocarbons in synthetic crude middle distillates. 相似文献
998.
Erv J. Kuhlmann Dick Y. Jung Richard P. Guptill Charles A. Dyke Hyung K. Zang 《Fuel》1985,64(11):1552-1557
The presence of hydroaromatic, hydrogen donor components in a coal-derived solvent is one of the more important factors in the successful operation of a non-catalytic coal liquefaction process. Various hydrogen donor species present in a hydrogenated creosote oil have been identified. Their rate of disappearance under conditions that are consistent with a short residence time coal liquefaction process has been used to rank the reactivities of the various hydrogen donors. 1,2,3,10b-Tetrahydrofluoranthene was found to be an exceptional donor while 4,5-dihydropyrene, the hexahydropyrenes and 9,10-dihydrophenanthrene were found to be quite active. Sym.-octahydrophenanthrene and 2a,3,4,5-tetrahydroacenaphthene exhibited moderate activity. Tetralin and the four methyltetralin isomers were found to be unreactive under the coal liquefaction conditions employed. 相似文献
999.
Results for various types of polar compounds in SRC-11 coal-derived liquids and other fuels were obtained by one or more of the three analytical methods: non-aqueous titration, i.r. spectroscopy and h.p.l.c. Practical aspects as well as precision, accuracy and assumptions necessary for effective application of each of the methods are discussed. H.p.l.c. is applicable to the widest variety of compound types, is the most rapid, most sensitive and shows the best promise for increased development and improvement. Application and development of these techniques is a logical step toward improving process monitoring, catalyst development, toxicological screening and general fuel analysis. 相似文献
1000.
The benefits of adhesively bonded structures are well known. However, the most significant factor limiting the extensive application of metal bonding in primary aerospace structures is the prevailing lack of confidence in its long term durability under hostile environmental conditions.1,2 相似文献