收费全文 | 566271篇 |
免费 | 6702篇 |
国内免费 | 1003篇 |
电工技术 | 10508篇 |
综合类 | 466篇 |
化学工业 | 90044篇 |
金属工艺 | 23335篇 |
机械仪表 | 18497篇 |
建筑科学 | 12532篇 |
矿业工程 | 4312篇 |
能源动力 | 14429篇 |
轻工业 | 45756篇 |
水利工程 | 6941篇 |
石油天然气 | 14961篇 |
武器工业 | 39篇 |
无线电 | 60279篇 |
一般工业技术 | 116218篇 |
冶金工业 | 95555篇 |
原子能技术 | 14681篇 |
自动化技术 | 45423篇 |
2021年 | 5482篇 |
2019年 | 5269篇 |
2018年 | 9201篇 |
2017年 | 9408篇 |
2016年 | 9832篇 |
2015年 | 6025篇 |
2014年 | 10243篇 |
2013年 | 26102篇 |
2012年 | 15771篇 |
2011年 | 21087篇 |
2010年 | 16970篇 |
2009年 | 18822篇 |
2008年 | 19067篇 |
2007年 | 18765篇 |
2006年 | 16285篇 |
2005年 | 14742篇 |
2004年 | 14007篇 |
2003年 | 13690篇 |
2002年 | 13246篇 |
2001年 | 12850篇 |
2000年 | 12329篇 |
1999年 | 12011篇 |
1998年 | 27649篇 |
1997年 | 20039篇 |
1996年 | 15627篇 |
1995年 | 12005篇 |
1994年 | 10858篇 |
1993年 | 10612篇 |
1992年 | 8332篇 |
1991年 | 8102篇 |
1990年 | 7990篇 |
1989年 | 7763篇 |
1988年 | 7478篇 |
1987年 | 6747篇 |
1986年 | 6533篇 |
1985年 | 7390篇 |
1984年 | 6700篇 |
1983年 | 6437篇 |
1982年 | 5776篇 |
1981年 | 5896篇 |
1980年 | 5630篇 |
1979年 | 5733篇 |
1978年 | 5663篇 |
1977年 | 6178篇 |
1976年 | 7685篇 |
1975年 | 5108篇 |
1974年 | 4903篇 |
1973年 | 4980篇 |
1972年 | 4279篇 |
1971年 | 4038篇 |
The efficiency of any electric cell or battery is very important. To keep it in mind it has been studied the columbic efficiency, voltaic efficiency and energy efficiency of a PKL (Pathor Kuchi Leaf) Quasi Voltaic Cell or Modified Voltaic Cell. It was found that the columbic efficiency data illustrated that this efficiency was lower comparing to other efficiencies may be the absence of salt bridge or separator between the electrodes. Because, our designed and fabricated PKL cell does not have any salt bridge. So that the internal resistance is lower than the traditional voltaic cell and as a result more current was found. The voltage and current changes with time and I–V characteristics for PKL unit cell, module, panel and array have also been studied. It is shown that the voltaic and energy efficiency have been studied. However, the highest efficiency was obtained for 40% PKL sap with 5% secondary salt in 55% aqueous solution, which implies that the concentration of PKL juice can play an important role regarding efficiency. It was also found that the average energy efficiency was 97.43% and it was also found that the average voltaic efficiency was 57.29%. Finally, morphological study FESEM (Field Emission Scanning Electron Microscopy) has also been performed. It is seen that the results confirmed that Zn was deposited on the Cu surface during the electro deposition process in PKL solution. Using AAS, it has been measured the concentration of [Cu2+] as a reactant ion and the concentration of [Zn2+] as a product ion those have been tabulated and graphically discussed. The variation of pH has also been studied with time and which was also tabulated and graphically discussed.
相似文献Stability constants and formation enthalpies of supramolecular complexes of crown ethers and their cyclic and acyclic analogues are determined on the basis of experimental data obtained by different physicochemical methods in the terms of a general approach developed and implemented in the ChemEqui software package. The established regularities of variation of stability of complexes are discussed as dependent on the ligand structure, nature of the cation, solvent, and anion. The applicability of the suggested method of determining complexation selectivity is shown for multicomponent equilibria in solutions.
相似文献