全文获取类型
收费全文 | 2999篇 |
免费 | 242篇 |
国内免费 | 139篇 |
专业分类
电工技术 | 235篇 |
综合类 | 275篇 |
化学工业 | 863篇 |
金属工艺 | 295篇 |
机械仪表 | 121篇 |
建筑科学 | 85篇 |
矿业工程 | 29篇 |
能源动力 | 83篇 |
轻工业 | 246篇 |
水利工程 | 33篇 |
石油天然气 | 132篇 |
武器工业 | 14篇 |
无线电 | 174篇 |
一般工业技术 | 395篇 |
冶金工业 | 95篇 |
原子能技术 | 30篇 |
自动化技术 | 275篇 |
出版年
2024年 | 3篇 |
2023年 | 60篇 |
2022年 | 49篇 |
2021年 | 86篇 |
2020年 | 101篇 |
2019年 | 90篇 |
2018年 | 97篇 |
2017年 | 82篇 |
2016年 | 75篇 |
2015年 | 84篇 |
2014年 | 132篇 |
2013年 | 191篇 |
2012年 | 170篇 |
2011年 | 197篇 |
2010年 | 139篇 |
2009年 | 161篇 |
2008年 | 148篇 |
2007年 | 195篇 |
2006年 | 155篇 |
2005年 | 152篇 |
2004年 | 110篇 |
2003年 | 111篇 |
2002年 | 116篇 |
2001年 | 105篇 |
2000年 | 81篇 |
1999年 | 63篇 |
1998年 | 49篇 |
1997年 | 39篇 |
1996年 | 35篇 |
1995年 | 39篇 |
1994年 | 28篇 |
1993年 | 35篇 |
1992年 | 36篇 |
1991年 | 35篇 |
1990年 | 36篇 |
1989年 | 30篇 |
1988年 | 15篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1969年 | 1篇 |
1965年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有3380条查询结果,搜索用时 31 毫秒
1.
利用蒸馏分离—气相色谱法技术,建立了同时测定煤焦油中苊、氧芴和芴的分析方法。通过对色谱条件的优化,以甲苯为溶剂,正十二烷为内标物,将煤焦油馏分采用DB-5毛细管柱,对煤焦油中苊、氧芴和芴定量分析。分析结果表明:3种主要成分线性关系良好,相关系数均大于0.9995,加标回收率为95.4%~102.4%,相对标准偏差为2.89%~7.14%。该方法分离效果好,检测结果准确、可靠。 相似文献
2.
Ohjin Kwon Xiaoqian Cai Wentao Qu Feng Liu Jadwiga Szydłowska Ewa Gorecka Moon Jong Han Dong Ki Yoon Silvio Poppe Carsten Tschierske 《Advanced functional materials》2021,31(28):2102271
First examples of multichain (polycatenar) compounds, based on the π-conjugated [1]benzothieno[3,2-b]benzothiophene unit are designed, synthesized, and their soft self-assembly and charge carrier mobility are investigated. These compounds, terminated by the new fan-shaped 2-brominated 3,4,5-trialkoxybenzoate moiety, form bicontinuous cubic liquid crystalline (LC) phases with helical network structure over extremely wide temperature ranges (>200 K), including ambient temperature. Compounds with short chains show an achiral cubic phase with the double network, which upon increasing the chain length, is at first replaced by a tetragonal 3D phase and then by a mirror symmetry is broken triple network cubic phase. In the networks, the capability of bypassing defects provides enhanced charge carrier mobility compared to imperfectly aligned columnar phases, and the charge transportation is non-dispersive, as only rarely observed for LC materials. At the transition to a semicrystalline helical network phase, the conductivity is further enhanced by almost one order of magnitude. In addition, a mirror symmetry broken isotropic liquid phase is formed beside the 3D phases, which upon chain elongation is removed and replaced by a hexagonal columnar LC phase. 相似文献
3.
Jinming Wang Meng Yang Guodong Zou Di Liu Qiuming Peng 《Advanced functional materials》2021,31(21):2101180
Lithium (Li) metal, as an appealing candidate for the next-generation of high-energy-density batteries, is plagued by its safety issue mainly caused by uncontrolled dendrite growth and infinite volume expansion. Developing new materials that can improve the performance of Li-metal anode is one of the urgent tasks. Herein, a new MXene derivative containing pure rutile TiO2 and N-doped carbon prepared by heat-treating MXene under a mixing gas, exhibiting high chemical activity in molten Li, is reported. The lithiation MXene derivative with a hybrid of LiTiO2-Li3N-C and Li offers outstanding electrochemical properties. The symmetrical cell assembling lithiation MXene derivative hybrid anode exhibits an ultra-long cycle lifespan of 2000 h with an overpotential of ≈30 mV at 1 mA cm−2, which overwhelms Li-based anodes reported so far. Additionally, long-term operations of 34, 350, and 500 h at 10 mA cm−2 can be achieved in symmetrical cells at temperatures of −10, 25, and 50 °C, respectively. Both experimental tests and density functional theory calculations confirm that the LiTiO2-Li3N-C skeleton serves as a promising host for Li infusion by alleviating volume variation. Simultaneously, the superlithiophilic interphase of Li3N guides Li deposition along the LiTiO2-Li3N-C skeleton to avoid dendrite growth. 相似文献
4.
5.
6.
《Ceramics International》2020,46(3):2654-2660
Brown fused alumina is a cost-effective alumina material, and the state of Ti in alumina has a great influence on its high-temperature performance. In this paper, the Ti-containing phases in brown fused alumina particles and Al-brown fused alumina refractory were successfully transformed into Ti(C,N) at 1973 K in flowing N2. The evolution of the Ti-containing phases in brown fused alumina under high temperature and nitrogen conditions was investigated by XRD, SEM and EDS. The results show that the Ti-containing phases in brown fused alumina include Ti2O3, Ti(C,N,O), TiFeSi2, Ca0·95Mg0·9Al10·1(Ti)O17 and a low-melting point Ca3Al2Si3(Mg,Ti)O12 phase. Under high temperature and nitrogen conditions, the TiO2[liquid], MgO[liquid] and SiO2[liquid] in the low-melting point phase are transformed into Ti(C,N), Mg(g) and SiO(g), while they are supplemented from Ti2O3, Ti(C,N,O) and Ca0·95Mg0·9Al10·1(Ti)O17. After heat treatment at 1973 K for 3 h, Ti2O3 and Ti(C,N,O) disappear, Ca0·95Mg0·9Al10·1(Ti)O17 is transformed into plate-like Ca0·55Al11O17.05, and Ti(C,N) is formed on the surface of the corundum particles. The formation of Ti(C,N) reduces the porosity of the brown fused alumina particles and increases their strength. 相似文献
7.
本研究建立了一种液相色谱测定茶皂素含量的方法。色谱柱SUPELCOTM LC-18(4.6 mm×250mm,5μm);流动相为甲醇-0.1%磷酸(体积比40:60);流速0.8 m L/min;检测波长267 nm;柱温30℃。该方法平均加标回收率90.88%~113.13%,精密度达0.19%,定量检出限0.67%,测得水相固形物中茶皂素质量分数为54%,与比色法测定结果相接近,但液相法具有测定简便、快速、准确等特点;与相关液相测定茶皂素方法报道相比,该方法色谱峰分离较好,且避开了溶剂峰干扰等特点,适合作为测定茶皂素含量的分析方法。 相似文献
8.
A. Robina P. Bechthold A. Juan C. Pistonesi M.E. Pronsato 《International Journal of Hydrogen Energy》2018,43(33):16085-16091
Density functional calculations were performed on Zr0.9Ti0.1(Ni0.5Cr0.5-xVx)2 Laves Phase, with x = 0, 0.125, 0.25, 0.375 and 0.5, in order to study its H absorption capacity. Binding energy, electronic structure and bonding were analyzed for the intermetallic compound with different V content and increasing amounts of hydrogen.The optimized geometry was found in good agreement with experimental data of the C14 Laves phase. Hydrogen locates preferentially in A2B2 tetrahedral sites in the AB2 matrix (A = Zr, Ti; B = Ni, Cr, V) but AB3 and B4sites are also stable. The volume of the intermetallic and the H binding energy increases with vanadium content. Theoretically H absorption is possible up to 4.5 H/F.U. but the strongest binding energy is achieved with 3 H/F. U.The main contribution to density of states is due to d states of all components of the structure and an H-metal bonding is observed in the range ?10 to ?4 eV. 相似文献
9.
《Journal of the European Ceramic Society》2020,40(5):1820-1828
In this work, oxidation mechanisms were studied in fine-grained (FG) and coarse-grained (CG) Ti2AlC bulk samples. Results showed that the oxidation kinetics are controlled by the grain size of Ti2AlC. Bigger are the grains, faster is the oxidation. A dense and protective Al2O3 layer forms at the surface of FG-Ti2AlC samples while for the CG-Ti2AlC samples, a thick TiO2 layer forms on top of a discontinuous Al2O3. CG-Ti2AlC was observed to simultaneously transform into Ti3AlC2 and TiC instead of being directly transformed into TiC. This transformation result in the following crystallographically sandwich-like structure: (0001) Ti2AlC // (0001) Ti3AlC2 // (111) TiC. The volume shrinkage associated to this transformation produces elongated holes that are partially filled by α-Al2O3. The stress caused by the volume shrinkage generates cracks at the surface, which makes the oxygen inwards diffusion easier and thus worsens the oxidation resistance the CG-Ti2AlC bulk. 相似文献
10.