全文获取类型
收费全文 | 15889篇 |
免费 | 1418篇 |
国内免费 | 1118篇 |
专业分类
电工技术 | 249篇 |
综合类 | 1212篇 |
化学工业 | 2851篇 |
金属工艺 | 1293篇 |
机械仪表 | 446篇 |
建筑科学 | 1132篇 |
矿业工程 | 1060篇 |
能源动力 | 512篇 |
轻工业 | 809篇 |
水利工程 | 343篇 |
石油天然气 | 4648篇 |
武器工业 | 194篇 |
无线电 | 529篇 |
一般工业技术 | 1396篇 |
冶金工业 | 725篇 |
原子能技术 | 154篇 |
自动化技术 | 872篇 |
出版年
2024年 | 77篇 |
2023年 | 224篇 |
2022年 | 478篇 |
2021年 | 537篇 |
2020年 | 576篇 |
2019年 | 446篇 |
2018年 | 401篇 |
2017年 | 511篇 |
2016年 | 551篇 |
2015年 | 507篇 |
2014年 | 756篇 |
2013年 | 1055篇 |
2012年 | 1000篇 |
2011年 | 1094篇 |
2010年 | 832篇 |
2009年 | 887篇 |
2008年 | 775篇 |
2007年 | 977篇 |
2006年 | 1008篇 |
2005年 | 890篇 |
2004年 | 757篇 |
2003年 | 654篇 |
2002年 | 553篇 |
2001年 | 493篇 |
2000年 | 388篇 |
1999年 | 348篇 |
1998年 | 288篇 |
1997年 | 243篇 |
1996年 | 219篇 |
1995年 | 198篇 |
1994年 | 139篇 |
1993年 | 98篇 |
1992年 | 71篇 |
1991年 | 64篇 |
1990年 | 84篇 |
1989年 | 53篇 |
1988年 | 27篇 |
1987年 | 26篇 |
1986年 | 25篇 |
1985年 | 17篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 4篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1964年 | 5篇 |
1957年 | 3篇 |
1956年 | 3篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Oligomerization of glycine (gly) and diglycine (gly2) on montmorillonite was performed as cyclic, drying-wetting process at temperatures below 100°C, under varying reaction conditions. The influence of substrate/clay ratio, temperature and pH was found to be different for amino acid (AA) dimerization, cyclic anhydride (CA) formation and peptide chain elongation. High temperatures and neutral pH favour CA formation over diglycine production. An AA/catalyst ratio of 0.2 mmol/g leads to optimal yields. This supports the assumption that amino acid dimerization and CA formation take place at the edges of clay particles. Peptide chain elongation, starting from gly2, produces higher yields at higher temperatures and neutral pH. 相似文献
102.
103.
104.
105.
106.
In the present paper, nonlinear features and analytical results for the chaotic bubbling from a submerged orifice are described. A chain of air bubbles was produced from the single orifice of in diameter and micro-convection induced by the bubble generation was recorded using hot-probe anemometer located close to the orifice. The air flow rate was varied widely from q=100 to and the aspects of bubbling were observed by high-speed video. The nonlinear analysis is performed for the time series data of hot-probe anemometer especially in the range of q=435-. The calculated largest Lyapunov exponent shows that with increase of air volume flow rate, the time period for the process of liquid flow to lose stability becomes shorter and at high air flow rate such as , it is shorter than the time period between subsequent bubbles. To explain such chaotic behaviors of bubbling, a simple model has been proposed. The model simulates the process of interaction between the elastic bubble wall and liquid. Simulation results compared well with the analytical results of experimental data. Summarizing, it is concluded that one of the reasons for chaos appearance is the nonlinear character of interaction between an elastic bubble wall and the liquid stream. 相似文献
107.
108.
109.
110.
Jiang Ruixia Xie Zaiku Zhang Chengfang Chen Qingling 《Applied Catalysis A: General》2003,250(2):209-220
The Pd-La/spinel catalyst for the preparation of 2,6-diisopropylaniline (2,6-DIPA) by gas-phase amination of 2,6-diisopropylphenol (2,6-DIPP) has been studied. The catalysts before and after reaction were characterized by BET, XRD, differential thermal analysis (DTA)-thermo gravimetric analysis (TGA), FTIR, and NH3-TPD techniques. The DTA study results show two kinds of coke deposited on the metal and support of Pd-La/spinel catalyst, and they are combusted at about 242 and 324 °C, respectively. The XRD and FTIR spectra of the Pd-La/spinel catalyst show that the coke contains the aromatic and aliphatic rings, alkyl groups, polynuclear aromatic system, hydroxyl groups, and amine groups. The reason for catalyst deactivation can be expressed as follows: coke formed on palladium metals may move from metal to the interface or boundaries of metal-support and acid sites of the support where further dehydrogenation and polymerization are occurring. The H2 plays a key role in retarding coke formation, but must be in suitable amount to get relatively high selectivity. The rare earth promoter La not only promotes the activity and selectivity by retaining Pd species in the metallic state, but also decreases the formation of carbon by neutralizing the strong acid sites on the catalyst. 相似文献