全文获取类型
收费全文 | 243200篇 |
免费 | 2683篇 |
国内免费 | 428篇 |
专业分类
电工技术 | 4308篇 |
综合类 | 259篇 |
化学工业 | 39688篇 |
金属工艺 | 9405篇 |
机械仪表 | 7430篇 |
建筑科学 | 5615篇 |
矿业工程 | 1394篇 |
能源动力 | 5197篇 |
轻工业 | 24968篇 |
水利工程 | 2511篇 |
石油天然气 | 5100篇 |
武器工业 | 33篇 |
无线电 | 25159篇 |
一般工业技术 | 45137篇 |
冶金工业 | 45712篇 |
原子能技术 | 5959篇 |
自动化技术 | 18436篇 |
出版年
2021年 | 2143篇 |
2019年 | 2052篇 |
2018年 | 3515篇 |
2017年 | 3462篇 |
2016年 | 3737篇 |
2015年 | 2275篇 |
2014年 | 3955篇 |
2013年 | 10326篇 |
2012年 | 6252篇 |
2011年 | 8414篇 |
2010年 | 6645篇 |
2009年 | 7327篇 |
2008年 | 7703篇 |
2007年 | 7812篇 |
2006年 | 6967篇 |
2005年 | 6120篇 |
2004年 | 5867篇 |
2003年 | 5656篇 |
2002年 | 5722篇 |
2001年 | 5589篇 |
2000年 | 5416篇 |
1999年 | 5331篇 |
1998年 | 12615篇 |
1997年 | 8931篇 |
1996年 | 6876篇 |
1995年 | 5359篇 |
1994年 | 4763篇 |
1993年 | 4644篇 |
1992年 | 3678篇 |
1991年 | 3400篇 |
1990年 | 3610篇 |
1989年 | 3489篇 |
1988年 | 3321篇 |
1987年 | 2906篇 |
1986年 | 2944篇 |
1985年 | 3388篇 |
1984年 | 3251篇 |
1983年 | 2911篇 |
1982年 | 2756篇 |
1981年 | 2836篇 |
1980年 | 2736篇 |
1979年 | 2635篇 |
1978年 | 2699篇 |
1977年 | 2961篇 |
1976年 | 3820篇 |
1975年 | 2381篇 |
1974年 | 2256篇 |
1973年 | 2383篇 |
1972年 | 1977篇 |
1971年 | 1859篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
The tensile elastic modulus (E), yield stress (σY) and microhardness (MH) of neat and binary and ternary blends of glassy semicrystalline ethylene–vinyl alcohol copolymer (EVOH), a glassy amorphous polyamide and a semicrystalline nylon‐containing ionomer covering a broad range of properties were examined. The tests were carried out on dry and water‐equilibrated samples to produce stiffer and softer materials, respectively. From the results, more accurate linear correlations were found to describe adequately the microhardness, modulus and yield stress of these strongly self‐associated polymers through hydrogen bonding. Copyright © 2003 Society of Chemical Industry 相似文献
12.
13.
The objective of this study was to compare methane production and characteristics of digested material in anaerobic digestion concepts according to the Animal By-Products Regulation (ABP-Regulation) of the EC (hygienisation of biowaste for 1 hour at 70 degrees C, particle size < 12 mm) and Finnish national regulations (treatment temperature 55 degrees C, feeding interval 24 h, hydraulic retention time (HRT) 20 d, particle size < 40 mm) and with small variations in treatment methods for treating manure and biowaste. Moreover, the survival of three different salmonella bacteria in these processes was studied. Hygienisation of biowaste prior to digestion at 35 degrees C enhanced methane production by 14-18% compared to similar treatment without hygienisation. The differences in treatment temperature, HRT and hygienisation of biowaste prior to digestion did not significantly affect the characteristics of digested material. The concepts according to the ABP-Regulation and Finnish national regulations were effective in destroying salmonella bacteria to an undetectable level. 相似文献
14.
The effects of the cuticle and epicuticular waxes of grapefruit, strawberry and apple on the photodegradation and penetration of chlorpyrifos-methyl were studied. Photodegradation experiments were conducted by exposing the insecticide to the light of a xenon lamp in the presence of a film of wax extracted from the fruit surface. The half-life of chlorpyrifos-methyl irradiated in absence of waxes was 9.6 min. The half-lives of pesticide irradiated in the presence of wax extracts of apple, grapefruit and strawberry were 83, 34 and 26 min, respectively. In penetration studies, fruit with and without wax layers were treated with an aqueous suspension of pesticide. The penetration of the pesticide from the cuticle to the pulp was measured after 24 h. Samples without wax contained a higher total amount of insecticide than those with wax. No pesticide was detected in samples of apple and grapefruit pulp. Residues were detected in all fractions of strawberry. The waxes and cuticle appear to have some effect on the photodegradation and penetration of chlorpyrifos-methyl in fruit samples. 相似文献
15.
16.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture. 相似文献
17.
The characteristics of pulsation processes in dc plasmatrons with the cathode located in the channel center and the anode in the form of a cylindrical or a conical channel wall are investigated in plasmas of argon and nitrogen at atmospheric pressure. The fast Fourier transform of signals and their subsequent computer processing are used to obtain the dependences of the frequency of fluctuations of the arcing voltage on the working parameters of the plasmatron, namely, the electric arc current, the flow rate of plasma-forming gas, and the channel diameter. For plasmatrons with the self-adjusting length of the electric arc, analysis is performed of the mechanism of reclosing of the anode region of the arc, i.e., of the electric arc shunting associated with the stretching of the current filament by a flow of gas and with the electrodynamic interaction of different filament regions. A formula is derived which defines the dependence of the characteristic frequency of fluctuations of the arcing voltage on the external parameters of the problem, namely, the arc current, the flow rate of the working gas, and the characteristic channel diameter. It is demonstrated that the pattern of the dependence of the frequency of voltage fluctuations on the gas flow rate may vary with the values of the parameter of magnetohydrodynamic interaction. The formula generalizes the experimental results of numerous researchers obtained in a wide range of variation of the external parameters. 相似文献
18.
The present work deals with the modelling of damage behaviour for sheet moulding compound (SMC) composite materials using a finite element analysis package. Specifically, a comparison is made between the results obtained experimentally for a three-point bending test, and those obtained from numerical simulation using a material model already implemented. The simulation has been performed for the material models available within the PAM-CRASH software. The simulation results are compared and validated with respect to experimentation. 相似文献
19.
20.
The aim of this study was to evaluate the use of total coliforms (TC) and faecal coliforms (FC) using a membrane filtration method for precise monitoring of faecal pollution in Korean surface water. The samples were collected in Korea from both main rivers and their tributaries. Presumptive TC * FC were enumerated. The ratios of presumptive FC to TC were not constant, but varied widely, and TC were difficult to enumerate because of overgrowth by background colonies. For FC this was not the case. Seven hundred and three purified strains of presumptive TC * FC and their background colonies were biotyped using API 20E. Among 272 presumptive TC, non-faecal related species, Aeromonas hydrophila dominated (34.6%) and E. coli accounted for only 5.1%. In contrast, E. coli made up 89% of the 209 presumptive FC. Furthermore, of 164 background colonies on Endo Agar LES, 54.9% was A. hydrophila, while background colonies on m-FC Agar were few (58 strains), and despite their atypical colony appearance, most of them were biotyped as enteric bacteria. These results reveal that the detection of FC rather than TC using m-FC Agar is more appropriate for faecal pollution monitoring in eutrophicated surface water located in a temperate region. 相似文献