全文获取类型
收费全文 | 239917篇 |
免费 | 20654篇 |
国内免费 | 14774篇 |
专业分类
电工技术 | 8582篇 |
技术理论 | 8篇 |
综合类 | 15799篇 |
化学工业 | 62226篇 |
金属工艺 | 20752篇 |
机械仪表 | 11425篇 |
建筑科学 | 9586篇 |
矿业工程 | 6308篇 |
能源动力 | 7663篇 |
轻工业 | 18449篇 |
水利工程 | 3200篇 |
石油天然气 | 9754篇 |
武器工业 | 1702篇 |
无线电 | 22853篇 |
一般工业技术 | 29584篇 |
冶金工业 | 12849篇 |
原子能技术 | 2664篇 |
自动化技术 | 31941篇 |
出版年
2024年 | 924篇 |
2023年 | 3887篇 |
2022年 | 7298篇 |
2021年 | 8520篇 |
2020年 | 7437篇 |
2019年 | 6426篇 |
2018年 | 5750篇 |
2017年 | 7140篇 |
2016年 | 8078篇 |
2015年 | 8248篇 |
2014年 | 12731篇 |
2013年 | 14108篇 |
2012年 | 16082篇 |
2011年 | 19180篇 |
2010年 | 14645篇 |
2009年 | 16122篇 |
2008年 | 13983篇 |
2007年 | 16589篇 |
2006年 | 15351篇 |
2005年 | 12456篇 |
2004年 | 10337篇 |
2003年 | 9056篇 |
2002年 | 7413篇 |
2001年 | 5931篇 |
2000年 | 5258篇 |
1999年 | 4261篇 |
1998年 | 3266篇 |
1997年 | 2613篇 |
1996年 | 2405篇 |
1995年 | 1929篇 |
1994年 | 1749篇 |
1993年 | 1287篇 |
1992年 | 1032篇 |
1991年 | 840篇 |
1990年 | 625篇 |
1989年 | 510篇 |
1988年 | 350篇 |
1987年 | 249篇 |
1986年 | 244篇 |
1985年 | 161篇 |
1984年 | 138篇 |
1983年 | 102篇 |
1982年 | 104篇 |
1981年 | 89篇 |
1980年 | 100篇 |
1979年 | 63篇 |
1978年 | 30篇 |
1977年 | 38篇 |
1975年 | 32篇 |
1951年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Diphenylzinc, alone or in combination with water and butanone as coinitiators, was used as a polymerization initiator system for a variety of lactones at varying temperatures. The resulting data indicate that the course of the polymerization is greatly influenced by the lactone structure, as well as by the molar ratio of coinitiator to diphenylzinc. When used alone, diphenylzinc exhibited high activity as an initiator in δ‐valerolactone polymerizations, although it was less efficient when used in the β‐butyrolactone and the β‐propiolactone polymerizations. Activity in the polymerization of β‐lactones was increased by adding small amounts of butanone or water. It was also observed that the diphenylzinc–butanone combination was more effective than the diphenylzinc–water mixture in the polymerizations of β‐butyrolactone and β‐propiolactone. Copyright © 2003 Society of Chemical Industry 相似文献
4.
Mitsuo Miyazawa Hideki Kawazoe Mitsuro Hyakumachi 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(6):620-625
The microbial transformation of l‐menthol ( 1 ) was investigated by using 12 isolates of soil‐borne plant pathogenic fungi, Rhizoctonia solani (AG‐1‐IA Rs24, Joichi‐2, RRG97‐1; AG‐1‐IB TR22, R147, 110.4; AG‐1‐IC F‐1, F‐4, P‐1; AG‐1‐ID RCP‐1, RCP‐3, and RCP‐7) as a biocatalyst. Rhizoctonia solani F‐1, F‐4 and P‐1 showed 89.7–99.9% yields of converted product from 1 , RCP‐1, RCP‐3, and RCP‐7 26.0–26.9% and the other isolates 0.1–12.0%. In the cases of F‐1, F‐4 and P‐1, substrate 1 was converted to (?)‐(1S,3R,4S,6S)‐6‐hydroxymenthol ( 2 ), (?)‐(1S,3R,4S)‐1‐hydroxymenthol ( 3 ) and (+)‐(1S,3R,4R,6S)‐6,8‐dihydroxymenthol ( 4 ), which was a new compound. Substrate 1 was converted to 2 and/or 3 by RRG97‐1, 110.4, RCP‐1, RCP‐3 and RCP‐7. The structures of the metabolic products were elucidated on the basis of their spectral data. In addition, metabolic pathways of the biotransformation of 1 by Rhizoctonia solani are discussed. Finally, from the main component analysis and the differences in the yields of converted product from 1 , the 12 isolates of Rhizoctonia solani were divided into three groups based on an analysis of the metabolites. Copyright © 2003 Society of Chemical Industry 相似文献
5.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
6.
The problem of operating freeze drying of pharmaceutical products in vials placed in trays of a freeze dryer to remove free water (in frozen state) at a minimum time was formulated as an optimal control problem. Two different types of freeze dryer designs were considered. In type I freeze dryer design, upper and lower plate temperatures were controlled together, while in type II freeze dryer design, upper and lower plate temperatures were controlled independently. The heat input to the material being dried and the drying chamber pressure were considered as control variables. Constraints were placed on the system state variables by the melting and scorch temperatures during primary drying stage. Necessary conditions of optimality for the primary drying stage of freeze drying process in vials are derived and presented. Furthermore, an approach for constructing the optimal control policies that would minimize the drying time for the primary drying stage was given. In order to analyze optimal control policy for the primary drying stage of the freeze-drying process in vials, a rigorous multi-dimensional unsteady state mathematical model was used. The theoretical approach presented in this work was applied in the freeze drying of skim milk. Significant reductions in the drying times of primary drying stage of freeze drying process in vials were obtained, as compared to the drying times obtained from conventional operational policies. 相似文献
7.
M. Kaiarov E. Rudnayov J. Koval
ík J. Dusza M. Hnatko P. ajgalík A. Merstallinger 《Materialwissenschaft und Werkstofftechnik》2003,34(4):338-342
In the presented work some properties of a recently developed Si3N4/SiC micro/nanocomposite have been investigated. The material was tested using a pin on disc configuration. Under unlubricated sliding conditions using Si3N4 pin at 50 % humidity, the friction coefficient was in the range of 0,6 ‐ 0,7. The reduction of humidity resulted in a lower coefficient of friction, in vacuum the coefficient of friction had a value of about 0,6. The wear resistance in vacuum was significantly lower then that in air. The wear patterns on the Si3N4+SiC disc revealed that mechanical fracture was the wear controlling mechanism. Creep tests were realized in four point bending configuration in the temperature interval 1200‐1400 °C at stresses 50,100 and 150 MPa and the minimal creep deformation rate was established for each stress level. The activation energy, established from the minimal creep deformation had a value of about 360 kJ/mol and the stress exponent values were in the range of 0.8‐1.28. From the achieved stress exponents it can be assumed that under the studied load/temperature conditions the diffusion creep was the most probable creep controlling mechanism. 相似文献
8.
对己二腈工业反应器提出了两釜串联带回流的模型,通过模拟计算得出模型的级间返混系数 f=6的结论。该模型能较好地预测工业反应器中物料组分浓度变化和气、液两相的流动特性;指出了现工业反应器的鼓泡中和段体积偏小是造成己二酸浓度偏高的关键;提出了可以通过增加串连一个鼓泡预反应段的改造方案,能有效地降低己二酸的浓度,从7%降至4%左右,从而能较好地减缓腐蚀和结焦。 相似文献
9.
Dissolved organic carbon (DOC) dynamics were investigated over a two year period in the Upper Rhǒne River to examine the role of side-arms in providing DOC to the main channel in relation to discharge fluctuations, especially floods. Concentrations of DOC are shown to remain low in space and in time (average 1.5 mg ?1) and to be more related to global hydrological events (precipitation) than to any local flushing for backwaters during floods. The results do not support the general assumption that side-arms are the providers of DOC to the main channel. 相似文献
10.
Takeshi Nakajo 《Quality and Reliability Engineering International》1993,9(2):111-119
Work system improvements are implemented in various manufacturing processes to prevent problems caused by human errors. However, they are almost always applied to problems which have already occurred. This paper examines a method of identifying latent human errors existing within the work systems beforehand. A procedure for applying failure mode and effect analysis to this identification problem was defined based on over 1000 empirical errors: a work system decomposition criterion and fundamental error modes for listing latent human errors, and then applied to three practical manufacturing processes in order to evaluate its effectiveness. 相似文献