全文获取类型
收费全文 | 7268篇 |
免费 | 1363篇 |
国内免费 | 1102篇 |
专业分类
化学 | 5236篇 |
晶体学 | 197篇 |
力学 | 451篇 |
综合类 | 111篇 |
数学 | 828篇 |
物理学 | 2910篇 |
出版年
2024年 | 14篇 |
2023年 | 124篇 |
2022年 | 296篇 |
2021年 | 291篇 |
2020年 | 346篇 |
2019年 | 384篇 |
2018年 | 303篇 |
2017年 | 333篇 |
2016年 | 416篇 |
2015年 | 460篇 |
2014年 | 520篇 |
2013年 | 664篇 |
2012年 | 764篇 |
2011年 | 720篇 |
2010年 | 560篇 |
2009年 | 561篇 |
2008年 | 534篇 |
2007年 | 441篇 |
2006年 | 347篇 |
2005年 | 317篇 |
2004年 | 248篇 |
2003年 | 182篇 |
2002年 | 162篇 |
2001年 | 119篇 |
2000年 | 82篇 |
1999年 | 109篇 |
1998年 | 59篇 |
1997年 | 63篇 |
1996年 | 69篇 |
1995年 | 69篇 |
1994年 | 31篇 |
1993年 | 30篇 |
1992年 | 20篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有9733条查询结果,搜索用时 15 毫秒
81.
82.
A kind of aziridine crosslinkers was synthesized and used to crosslink acrylate copolymers. The crosslinkingproperties and curing kinetics of the resin were studied. It was found that with the increase of the content of crosslinker in theemulsion, the mechanical properties and solvent resistance of the resin will be apparently improved, but its glass transitiontemperature (T_g) is very low. The lowest amount of crosslinker used in the acrylic resin emulsion is 0.25%. Curing kineticsstudied by DSC show that this curing reaction occurs readily because the apparent activation energy of the reaction is low(65.1 kJ/mol). These results demonstrate that the aziridine crosslinker is indeed a low temperature crosslinking agent and canbe used at room temperature. 相似文献
83.
Jin Hui YANG Jiu Gao YU Xiao Fei MA 《中国化学快报》2006,17(1):133-136
TPS was a biodegradable material based on starch. Starch was an inexpensive and natural renewable polysaccharide, which was widely investigated as the substitute of petroleum-derived plastics. Native starch commonly existed in granule structure with about… 相似文献
84.
New polymeric adsorbents (ZH-02, ZH-03) containing benzoyl group for adsorbing and removing 4-methylaniline from its aqueous solutions were prepared. Studies on the isotherms and the comparison of desorption conditions evidenced through the adsorption of 4-methylaniline in water onto ZH-02 and ZH-03, namely that there are chemisorption‘s transitions at a proper higher temperature. Mini-colunm adsorption studies of 4-methylaniline on XAD-4, ZH-02 and ZH-03 at 288 K show that the breakthrough capacities are 2.39, 2.99 and 3.19 mmol/g and the total capacities are 3.45, 3.92 and 4.35 mmol/g, respectively. 相似文献
85.
Xiu Yang LU Qi JING Zhun LI Lei YUAN Fei GAO Xin LIU 《中国化学快报》2006,17(6):841-844
High temperature liquid water (HTLW), as an environmentally benign medium, has drawn increasing attention for organic chemical reactions and biomass conversion1-3. HTLW has a strong tendency to ionize and can act as an acid and/or base catalyst. In addition, HTLW can dissolve organic compounds to some extent allowing for a homogenous reaction within an aqueous phase. Extensive researches4-10 have been pursued on acid/base-catalysis reactions in HTLW without addition of acid or base. Howe… 相似文献
86.
Binyuan Liu Yang Li Boo-gyo Shin Li Zhang Weidong Yan 《Polymer Degradation and Stability》2007,92(5):868-875
The thermal properties and degradation behaviors of poly(norbornene-2,3-dicarboxylic acid dialkyl esters) (PNB-dialkyl esters) (alkyl = Me (PNB-Me), Et (PNB-Et), Pr (PNB-Pr), and Bu (PNB-Bu)) were investigated by thermogravimetric analysis (TGA) in dynamic conditions and by infrared (IR) spectroscopy. The PNB-dialkyl esters show good thermal stability up to 350 °C, and the thermal stability decreases in the order Me > Et > Pr > Bu with the increase in size of side chain. The effect of side-chain size on the thermal degradation behaviors of PNB-dialkyl esters is evidenced by one-step thermal degradation profile for PNB-Me while two-step thermal degradation profile for PNB-Et, PNB-Pr, and PNB-Bu. Transformation is deduced to undergo β-hydrogen elimination and formation of anhydride group in the first stage of thermal degradation reaction according to TGA and IR results for PNB-Et, PNB-Pr, and PNB-Bu. The apparent activation energy and thermal degradation model of PNB-dialkyl esters are estimated by means of Ozawa-Flynn-wall method and Phadnis-Deshpande method, respectively. 相似文献
87.
Shidong Fei Jinhua Chen Shouzhuo Yao Guohong Deng Lihua Nie Yafei Kuang 《Journal of Solid State Electrochemistry》2005,9(7):498-503
Electroreduction of -glucose to form sorbitol on Zn/CNTs and Zn alloy/CNTs electrodes has been investigated in this paper. Carbon nanotubes (CNTs) used in this paper are grown directly on graphite disks by chemical vapor deposition. Zn and Zn alloy are electrodeposited on the activated CNTs/graphite electrode by pulse galvanostatic method. The micrographs of Zn/CNTs and Zn alloy/CNTs electrodes are characterized by scanning electron microscopy. The results show that the current efficiency of -glucose reduction on CNTs electrodes is much better than that on flat Zn electrodes. The order of the current efficiency on different electrodes is as follows: Zn/CNT (0.58) Zn–Fe/CNT (0.57)>Zn–Ni/CNT (0.43) Zn/graphite (0.42)>Zn (0.40). It indicates that CNTs have good potential application in electrosynthesis. Additionally, effects of some operating parameters, such as pH, temperature and -glucose concentration, on the current efficiency of -glucose reduction are also discussed. 相似文献
88.
SrO,MsO对异丙醇的分解反应有各自的作用形式,因而产物分布也有明显差别.MgO上异丙醇分解,在较低温度时,主要产物为丙酮和丙烯;随温度升高,生成丙烯的量增加,而丙酮的量减少,直至消失,在SrO上,异丙醇在较高温度时反应,产物几乎为丙酮,丙烯的生成量极少。认为:产物中丙烯来源于异丙醇在催化剂表面强酸中心上的脱水;丙酮在MgO上来源于强碱中心和酸中心协同作用异丙醇的脱氢,而在SrO上则是SrO表面极强的碱中心作用异丙醇而脱氢制得。 相似文献
89.
Eight novel compounds were synthesized by a facile and mild method with high yields, and the structures of all the compounds were characterized by 1H NMR IR mass and high resolution mass spectroscopy. Their inhibitory activity against insect-flight and trehalase in vitro were screened. Some target compounds have moderate inhibitory activity against trehalase, and show inhibition action to insect-flight. 相似文献
90.
YongJIANG PengFeiTU 《中国化学快报》2002,13(4):335-336
Two new xanthone glycosides,polygalaxanthone IV and V were isolated from the roots of Polygala tenuifolia Willd. Their structures were established as 6-O-[α-L-rhamnopyranosyl-(1→2)-β-D-glucopyranosyl]-1-hydroxy-3,7-dimethoxyxanthone(polygalaxanthone IV), and 6-O-[α-L-rhamnopyranosyl-(1→2)-β-D-glucopyranosyl]-1,3-dihydroxyl-7-methoxyxanthone (polyga-laxanthone V),respectively, on the basis of chemical and spectral evidence. 相似文献