全文获取类型
收费全文 | 507436篇 |
免费 | 8083篇 |
国内免费 | 3493篇 |
专业分类
电工技术 | 10341篇 |
综合类 | 2558篇 |
化学工业 | 72612篇 |
金属工艺 | 19837篇 |
机械仪表 | 15688篇 |
建筑科学 | 12776篇 |
矿业工程 | 2944篇 |
能源动力 | 13437篇 |
轻工业 | 42477篇 |
水利工程 | 5439篇 |
石油天然气 | 8855篇 |
武器工业 | 279篇 |
无线电 | 63724篇 |
一般工业技术 | 99109篇 |
冶金工业 | 94768篇 |
原子能技术 | 11643篇 |
自动化技术 | 42525篇 |
出版年
2021年 | 4775篇 |
2020年 | 3517篇 |
2019年 | 4055篇 |
2018年 | 6721篇 |
2017年 | 6843篇 |
2016年 | 7201篇 |
2015年 | 5097篇 |
2014年 | 8472篇 |
2013年 | 22631篇 |
2012年 | 13482篇 |
2011年 | 18219篇 |
2010年 | 14537篇 |
2009年 | 16544篇 |
2008年 | 17268篇 |
2007年 | 17241篇 |
2006年 | 15022篇 |
2005年 | 13574篇 |
2004年 | 13101篇 |
2003年 | 12804篇 |
2002年 | 12218篇 |
2001年 | 12691篇 |
2000年 | 11689篇 |
1999年 | 12306篇 |
1998年 | 31067篇 |
1997年 | 21663篇 |
1996年 | 16596篇 |
1995年 | 12556篇 |
1994年 | 11112篇 |
1993年 | 11160篇 |
1992年 | 7922篇 |
1991年 | 7589篇 |
1990年 | 7361篇 |
1989年 | 7168篇 |
1988年 | 6787篇 |
1987年 | 5945篇 |
1986年 | 5863篇 |
1985年 | 6454篇 |
1984年 | 5950篇 |
1983年 | 5608篇 |
1982年 | 5274篇 |
1981年 | 5173篇 |
1980年 | 5110篇 |
1979年 | 4775篇 |
1978年 | 4645篇 |
1977年 | 5398篇 |
1976年 | 7289篇 |
1975年 | 3921篇 |
1974年 | 3846篇 |
1973年 | 3818篇 |
1972年 | 3287篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
We report impedance measurements on PVC matrix membranes which contain KBPh4 with varying proportions of valinomycin. In agreement with our earlier measurements the value of the bulk membrane resistance (Rb) is much larger in the presence of valinomycin, indicating that the mobility of K+ is greatly reduced by the valinomycin. Rb shows a linear variation with valinomycin/K+ ratio between 0 and 1, but it is invariant at higher valinomycin/K+ ratios. Thus there is no evidence for a special transport mechanism for K+ in these membranes. 相似文献
993.
D. N. Mukhiddinov Kh. A. Alimov A. I. Yufa A. V. Ulubabyan V. P. Dudanov 《Fibre Chemistry》1985,16(3):204-206
Conclusions The process of drying cellulose triacetate in a vibrating bed has been studied.For final drying of cellulose triacetate before solution, it is recommended to use an industrial specimen of a unit with a vibrating bed having a capacity of 2700 kg/h.This assembly can be used to dry other fibre-forming disperse polymeric materials containing strongly bound moisture.Translated from Khimicheskie Volokna, No. 3, pp. 49–51, May–June, 1984. 相似文献
994.
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
995.
The short contact time dissolution of vitrinite and inertinite concentrates of an Australian bituminous coal was studied under isothermal conditions with tetralin as solvent. The reactivity of the two maceral types and the yields and nature of the products were determined for a range of reaction temperatures (400, 420 and 440 °C) and reaction times (2–20 min). The dissolution of vitrinite proceeded at a significantly greater rate than for inertinite and was associated with greater selectivity to soluble non-gaseous products. At very short reaction times (2 min), the vitrinite underwent solubilizing reactions to yield products of higher molecular weight and greater oxygen functionality than was the case for inertinite, for which changes in the chemical nature of the products were negligible over the range of conditions studied. At longer reaction times (5 min), the composition of the vitrinite-derived products was similar to that of the inertinite-derived products. 相似文献
996.
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
997.
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
998.
999.
The graft copolymerization of methyl methacrylate onto natural rubber (NR) was carried out varying the concentration of monomer, initiator, thiourea, and silver nitrate over a wide range. The grafting reaction was temperature-dependent. From the Arrhenius plot, the overall energy of activation was computed. A suitable reaction scheme and rate expression for the rate of polymerization was suggested. 相似文献
1000.
Instructional texts rewritten by five expert teams: Revisions and retention improvements. 总被引:1,自引:0,他引:1
Britton Bruce K.; Van Dusen Lani; Gulg?z Sami; Glynn Shawn M. 《Canadian Metallurgical Quarterly》1989,81(2):226
700 undergraduates were tested in 3 experiments on original or rewritten versions of 52 instructional texts about Army job tasks, general science, philosophy, and history. Five experts had rewritten various sets of the texts and stated hypotheses about the efficacious features of their revisions. We tested their hypotheses and several others. Recall and recognition tests were given immediately and after a 24-hr delay. Results showed that revisions made by 3 of the 5 experts improved retention of text information. The kind and number of revisions and improvements varied across the text sets. Most expert hypotheses were not supported, and they made many revisions they were declaratively unaware of. Some of our hypotheses about the revision features were supported, but different features were effective for different sets of texts. It was concluded that some experts have effective knowledge about improving instructional text, but it exists primarily in procedural form. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献