全文获取类型
收费全文 | 242722篇 |
免费 | 2644篇 |
国内免费 | 428篇 |
专业分类
电工技术 | 4319篇 |
综合类 | 257篇 |
化学工业 | 39675篇 |
金属工艺 | 9399篇 |
机械仪表 | 7418篇 |
建筑科学 | 5517篇 |
矿业工程 | 1398篇 |
能源动力 | 5192篇 |
轻工业 | 24893篇 |
水利工程 | 2497篇 |
石油天然气 | 5096篇 |
武器工业 | 32篇 |
无线电 | 25143篇 |
一般工业技术 | 44977篇 |
冶金工业 | 45729篇 |
原子能技术 | 5962篇 |
自动化技术 | 18290篇 |
出版年
2021年 | 2133篇 |
2019年 | 2038篇 |
2018年 | 3509篇 |
2017年 | 3441篇 |
2016年 | 3703篇 |
2015年 | 2250篇 |
2014年 | 3922篇 |
2013年 | 10268篇 |
2012年 | 6185篇 |
2011年 | 8369篇 |
2010年 | 6602篇 |
2009年 | 7273篇 |
2008年 | 7631篇 |
2007年 | 7764篇 |
2006年 | 6924篇 |
2005年 | 6075篇 |
2004年 | 5845篇 |
2003年 | 5634篇 |
2002年 | 5709篇 |
2001年 | 5584篇 |
2000年 | 5405篇 |
1999年 | 5324篇 |
1998年 | 12639篇 |
1997年 | 8942篇 |
1996年 | 6895篇 |
1995年 | 5363篇 |
1994年 | 4769篇 |
1993年 | 4652篇 |
1992年 | 3685篇 |
1991年 | 3400篇 |
1990年 | 3612篇 |
1989年 | 3487篇 |
1988年 | 3324篇 |
1987年 | 2921篇 |
1986年 | 2950篇 |
1985年 | 3402篇 |
1984年 | 3234篇 |
1983年 | 2911篇 |
1982年 | 2760篇 |
1981年 | 2841篇 |
1980年 | 2732篇 |
1979年 | 2650篇 |
1978年 | 2703篇 |
1977年 | 2969篇 |
1976年 | 3823篇 |
1975年 | 2390篇 |
1974年 | 2253篇 |
1973年 | 2391篇 |
1972年 | 1979篇 |
1971年 | 1871篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
F. Cioffi E. M. Cohen Richard Badick 《Drug development and industrial pharmacy》1993,19(14):1741-1746
Carstensen and Rhodes1 have suggested that when, in stability programs, assays cannot be performed immediately after the protocol-designated storage time, then freezing them until such a time when assays can be performed would be a reasonable manner to retain the protocol schedule. They caution, however, that such a procedure may not be valid for dissolution data. The article to follow deals with real-time data showing that such a process is feasible for Nalidixic Acid tablets (and presumably for other tablets as well), and that, furthermore, the dissolution pattern would seem to be “frozen” as well. 相似文献
54.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period 相似文献
55.
E. Smith 《Journal of Materials Science》1993,28(4):880-884
The criterion for crack growth instability in an elastic-softening material that is subjected to displacement control loading conditions is examined. A theoretical analysis of the model of a solid containing two symmetrically situated deep cracks and with tensile loading of the remaining ligament, defines the criterion for crack growth instability. The criterion is expressed in terms of the material's softening characteristics and the solid's geometrical parameters. The analysis covers the complete spectrum of material behaviour from the case where the softening zone is very small to the case where instability does not occur until the softening zone traverses the ligament between the crack tips. 相似文献
56.
57.
We have compared the duration of motor block produced by four local anaesthetics administered into a chronically implanted subarachnoid catheter in rabbits. Each group (n = 6) received four different doses of amethocaine, bupivacaine, lignocaine or procaine, and the duration of the resulting motor block was assessed. Dose-response curves were plotted for each drug. As a measure of activity of the anaesthetics, we used the dose of each drug required to produce block of 60-min duration (D60 min) and the correlation between D60 min and different drug properties was examined. An inverse linear correlation (r = 0.995; P < 0.01) was observed between log D60 min and the log of the partition coefficient of the local anaesthetics. No correlation was found between the effect and degree of protein binding, pKa or molecular weight. These results suggest that, in spinal anaesthesia, the partition coefficient could be used as a predictor of the duration of anaesthetic action. 相似文献
58.
59.
G.D. Wignall R.W. Hendricks W.C. Koehler J.S. Lin M.P. Wai E.L. Thomas R.S. Stein 《Polymer》1981,22(7):886-889
A series of small angle neutron scattering measurements on blends of normal polystyrene (PSH) and labelled (deuterated) polystyrene (PSD) have been made with concentrations of PSD from 5 to 50 mol %. It is shown that the single chain form factor of the polymer in bulk can be obtained from a single concentration measurement for any concentration of labelled molecules, providing the molecular weights of the parent and labelled molecules are the same and the molecular weight distributions are narrow. 相似文献
60.
The properties of a spinel copper cobaltite obtained by thermal decomposition of mixed nitrates of both metals at 350°C and normal pressure are described. It has been shown that the maximum copper content (x) in the spinel CuxCo3?xO4 does not exceed 0.9. When the copper amount in the initial mixture is higher a second phase CuO is formed. The copper ions are distributed over the A- and the B-sites of the spinel lattice, i.e. the spinel is partially inverted. Such a model explains well the data obtained about the lattice parameter, IR-absorption and the magnetic susceptibility of the samples with different x. 相似文献