全文获取类型
收费全文 | 4882篇 |
免费 | 82篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 239篇 |
综合类 | 2篇 |
化学工业 | 846篇 |
金属工艺 | 137篇 |
机械仪表 | 99篇 |
建筑科学 | 65篇 |
矿业工程 | 1篇 |
能源动力 | 137篇 |
轻工业 | 359篇 |
水利工程 | 15篇 |
无线电 | 574篇 |
一般工业技术 | 796篇 |
冶金工业 | 1280篇 |
原子能技术 | 104篇 |
自动化技术 | 319篇 |
出版年
2022年 | 33篇 |
2021年 | 58篇 |
2020年 | 26篇 |
2019年 | 24篇 |
2018年 | 48篇 |
2017年 | 50篇 |
2016年 | 86篇 |
2015年 | 58篇 |
2014年 | 77篇 |
2013年 | 184篇 |
2012年 | 158篇 |
2011年 | 180篇 |
2010年 | 127篇 |
2009年 | 171篇 |
2008年 | 169篇 |
2007年 | 128篇 |
2006年 | 122篇 |
2005年 | 133篇 |
2004年 | 99篇 |
2003年 | 115篇 |
2002年 | 113篇 |
2001年 | 117篇 |
2000年 | 108篇 |
1999年 | 152篇 |
1998年 | 506篇 |
1997年 | 293篇 |
1996年 | 253篇 |
1995年 | 152篇 |
1994年 | 139篇 |
1993年 | 129篇 |
1992年 | 64篇 |
1991年 | 70篇 |
1990年 | 59篇 |
1989年 | 47篇 |
1988年 | 59篇 |
1987年 | 49篇 |
1986年 | 46篇 |
1985年 | 50篇 |
1984年 | 60篇 |
1983年 | 53篇 |
1982年 | 46篇 |
1981年 | 49篇 |
1980年 | 54篇 |
1979年 | 35篇 |
1978年 | 31篇 |
1977年 | 29篇 |
1976年 | 48篇 |
1975年 | 15篇 |
1974年 | 24篇 |
1973年 | 13篇 |
排序方式: 共有4973条查询结果,搜索用时 46 毫秒
71.
Summary The ring-opening polymerization of 2-phenyl-1,3,-6,2-trioxaphosphocane (4), an eight-membered cyclic phosphonite, has been investigated. Cationic initiators of PhCH2-Cl and MeOTf gave polymers, whereas anionic and radical initiators did not yield polymer. The structure of polymer was examined by IR, 1H, 31P, and 31C NMR spectroscopy of polymers and elemental analysis as well as the alkaline hydrolysis products. The polymer consisted of two different units, i.e., the major part is the normal phosphinate structure 5 and the minor part is the isomerized unit 6 in 7% with PhCH2Cl initiation and in 34% with MeOTf initiator. The difference in nature of propagating species from these two initiators are discussed in connection with their reactivities.On leave from the Institute of Chemistry, Academia Sinica, Beijing, China 相似文献
72.
Summary The ring-opening polymerization of deoxophostone 5, a five-membered cyclic phosphinite, has been studied. Some cationic initiators gave polymer whereas anionic and radical initiators as well as metal chloride (Lewis acid) catalysts did not yield polymer. The polymer consisted of a phosphine oxide repeating unit 6. The polymerization proceeded via the Arbuzov-type reaction. The reduction of polymer 6 with a HSiCl3/Et3N system gave polyphosphine 7. 相似文献
73.
Fischer–Tropsch synthesis was carried out in slurry phase over uniformly dispersed Co–SiO2 catalysts prepared by the sol–gel method. When 0.01–1 wt.% of noble metals were added to the Co–SiO2 catalysts, a high and stable catalytic activity was obtained over 60 h of the reaction at 503 K and 1 MPa. The addition of noble metals increased the reducibility of surface Co on the catalysts, without changing the particle size of Co metal significantly. High dispersion of metallic Co species stabilized on SiO2 was responsible for stable activity. The uniform pore size of the catalysts was enlarged by varying the preparation conditions and by adding organic compounds such as N,N-dimethylformamide and formamide. Increased pore size resulted in decrease in CO conversion and selectivity for CO2, a byproduct, and an increase in the olefin/paraffin ratio of the products. By modifying the surface of wide pore silica with Co–SiO2 prepared by the sol–gel method, a bimodal pore structured catalyst was prepared. The bimodal catalyst showed high catalytic performance with reducing the amount of the expensive sol–gel Co–SiO2. 相似文献
74.
Hironori Minoshima 《Chemical engineering science》2006,61(6):2101-2102
Previously developed model for spray drying of slurry droplets with high solid content (Liang, 2001) was revised to describe correctly a boundary condition on the outer surface of droplet on basis of the rate of liquid evaporation. 相似文献
75.
Takashi Mitamura Hiroyuki Ogino Hidehiko Kobayashi Toshiyuki Mori Hiroshi Yamamura 《Journal of the American Ceramic Society》1993,76(8):2127-2128
Preparation of BaLa2 O4 , Ba3 ,Y4 O9 , Ba ,In2 O5 , and Ba3 Ga2 O6 powders and their sintering were investigated in Ar or air. These sintered bodies with perovskite-related structure were synthesized by reaction sintering, using mixed powders in the atomic ratios of Ba/La = 1, Ba/Y = 0.75, Ba/In = 1, and Ba/Ga = 1.5. The order-disorder transition temperatures of the BaLa2 O4 , Ba3 Y4 O9 , Ba2 In2 O5 , and Ba3 Ga2 O6 sintered bodies were 270°, 350°, 880°, and 123Oo C, respectively. It was found that the temperatures were influenced by the ionic radius of cations in B sites, and the transition temperatures decreased with increasing ionic radius. 相似文献
76.
Summary Glow discharge polymerizations of allyltrimethylsilane (ATMS) and trimethylvinyloxysilane (TMVOS) were investigated by elemental analysis and infrared spectroscopy. The formed polymers were far different in elemental composition from the starting materials, and possessed high carbon and hydrogen contents. There was less difference in an infrared-spectral sense between the two polymers from ATMS and TMVOS. A polymer-forming process in a discharge state is discussed. 相似文献
77.
78.
Motoi Takahashi Toshiyuki Mori Fei Ye Ajayan Vinu Hidehiko Kobayashi John Drennan 《Journal of the American Ceramic Society》2007,90(4):1291-1294
A Pt on nano-sized CeO2 particles that in turn are supported on carbon black (CB) was synthesized using the co-impregnation method. This potential anode material for fuel cell applications was synthesized in a stepwise process. The pure CeO2 was synthesized using an ammonium carbonate precipitation method, and the Pt particles dispersed on the CeO2 in such a way that a uniform dispersion with the CB was obtained (Pt–CeO2 /CB). The electrochemical activity of the methanol (CH3 OH) oxidation reaction on the Pt–CeO2 /CB was investigated using cyclic voltammetry and chronoamperometry experimentation. The onset potential of CH3 OH oxidation reaction on the Pt–CeO2 /CB anode was shifted to a lower potential as compared with that on commercially available Pt–Ru/carbon (C) alloy anode. In addition, the activation energy of the Pt–CeO2 /CB anode was much lower than that of the Pt–Ru/C alloy anode. Moreover, the current density of the Pt–CeO2 /CB anode was much higher than that of the Pt–Ru/C alloy anode at temperatures between 28° and 60°C. These results suggest that the anode performance of the Pt–CeO2 /CB anode at the operating temperature of typical fuel cells (80°C) is superior to that of the more usual Pt–Ru/C alloy anode. Importantly, the rare metal, Ru, is not required in the present anode material and the amount of Pt required is also significantly reduced. As a consequence, we report a promising candidate Pt–CeO2 /CB composite anode for application in the development of direct methanol fuel cells. 相似文献
79.
Summary Multi-step precipitation separation system was developed by using aqueous mixtures of some thermosensitive polymers. The following
three polymers were used here; poly(N-n-propylacrylamide), poly(N-isopropylacrylamide), and poly(N-isopropylmethacrylamide). A mixture of the three polymers showed three endothermic peaks, and the peak top temperatures were
almost consistent with that of the each polymer solution. The polymers were purified by thermal precipitation to obtain fractions
which can respond in narrow temperature ranges prior to use. In the case of the precipitation separation of two polymers mixtures,
purities of the obtained precipitate and supernatant fractions became high comparing with the case in which the unpurified
polymers were used. Parts of the polymers which were not the precipitation targets were also precipitated by the separation
procedures. This was caused not only by insolubilization of the non-targeted polymers due to their phase transitions but also
by their non-specific entanglement with the targeted polymers. The purities of the fractions also improved when the difference
of the phase transition temperature between two polymers was large enough to avoid the coprecipitation. In the case of the
precipitation separation of mixtures of the three polymers, purities of each fraction also improved when the purified polymers
were used. 相似文献
80.
A Sm(III) exchanged NaY zeolite prepared from aqueous SmCl3 was modified with various amounts of fluorine using NH4F. These fluorinated zeolites exhibit enhanced catalytic activity for the dealkylation of cumene. The evaluation of acid sites by infrared spectroscopy and pyridine adsorption was correlated with fluorine content. 相似文献