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排序方式: 共有352条查询结果,搜索用时 46 毫秒
1.
Tapasi Chand Laxmikanta Khamari Deepak Chopra Saptarshi Mukherjee Manmohan Kapur 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(43):e202200723
A one-step Rh-catalyzed site-selective ortho-C−H alkynylation of perylene as well as naphthalene mono- and diimides is reported. A single step regioselective access to ortho-C−H alkynylated derivatives of these ryleneimides not only increases the step economy of the ortho-functionalization on these dyes but also provides a quick access route towards highly functionalized dyes that have potential optoelectronic applications. Increased solubility of tetra(triisopropylsilyl)acetylenyl PDIs in organic solvents greatly enhances their utility for further derivatization. 相似文献
2.
Zhongxian Song Yun Xing Tingji Zhang Jinggang Zhao Junkai Wang Yanli Mao Baolin Zhao Xuejun Zhang Min Zhao Ziang Ma 《应用有机金属化学》2020,34(3):e5446
A series of Ce-Fe-Ox catalysts prepared by the different calcination temperatures (marked as CF-X, where X represented calcination temperature) were used to the selectivity catalytic reduction of NOx by NH3. The results explained the relationship between calcination temperature and the sulfate species over Ce-Fe-Ox, and then investigated the surface acidity and catalytic performance. The large amounts of sulfate species were formed over CF-450 and CF-550 while it was decomposed with further the increasing of calcination temperature, which resulted in the loss of surface acidity, causing a decrease in the catalytic activity over Ce-Fe-Ox. Thereby, the CF-450 catalyst showed the best catalytic activity and over 90% NOx conversion was obtained at 244–450 °C. Besides, the favored pore structure, more Fe3+ active species, higher Ce3+ concentration and the abundance of chemical adsorbed oxygen species, as well as the surface acid sites, would together contribute to the excellent catalytic activity of CF-450 catalyst. 相似文献
3.
成分和结构是影响多元过渡金属硒化物电化学活性的关键因素。适当掺杂其他金属元素可以有效提高电极材料的电化学性能。通过简单的一步水热法,在泡沫镍上制备出了一种无黏结剂的Mo掺杂NiMnSe2(记作Ni0.8Mo0.2MnSe2)。Mo的少量掺杂为电极材料提供了丰富的反应活性位点,大大提高了NiMnSe2的电化学性能。在1 A·g-1时,Ni0.8Mo0.2MnSe2的比容量达到1 404.0 F·g-1。掺杂Mo显著降低了NiMnSe2的电荷转移电阻和扩散电阻。组装的混合超级电容器Ni0.8Mo0.2MnSe2//AC (活性炭)比容量达到81.6 F·g-1,且倍率性能优异。在2 A·g-1下连续充放电10 000周,容量保持率为95.8%,表现出超高的循环稳定性。混合超级电容器Ni0.8Mo0.2MnSe2//AC在376.6 W·kg-1的功率密度下,能量密度达25.5 Wh·kg-1,高于NiMnSe2//AC (17.3 Wh·kg-1)。 相似文献
4.
采用并流共沉淀法在不同焙烧温度下制备K改性Ag-Fe/ZnO-ZrO2催化剂,考察不同焙烧温度对催化剂CO加氢合成低碳混合醇醚反应性能的影响。通过N2物理吸附(N2-adsorption)、X射线衍射(XRD)、氢气程序升温还原(H2-TPR)、一氧化碳程序升温脱附(CO-TPD)等手段对催化剂进行表征。结果表明,250 ℃焙烧的催化剂,由于焙烧温度较低,表面尚未形成足够多的活性位,未能达到最佳的催化性能;300 ℃焙烧的催化剂,其CO转化率最高、醇醚选择性较高,醇醚时空产率达到最大值。随着焙烧温度进一步升高,CO转化率逐渐降低,醇选择性先降低后增大,二甲醚(DME)选择性逐渐增大,醇醚时空产率逐渐降低。催化剂性能主要与其比表面积、还原性能、所含银铁复合物分散度及CO吸脱附性能有关,即比表面积较大、易于被还原、银铁复合物分散度较高以及较多的CO吸脱附活性位,有利于催化剂CO加氢转化。催化剂表面活性位对CO的非解离吸附强度降低,有利于醇醚产物的生成;而对CO的解离吸附强度增强,则不利于烃类产物的生成。 相似文献
5.
采用溶胶凝胶法制备LaSrFeMo0.9Co0.1O6,以催化甲烷燃烧为目标反应,研究不同焙烧温度(600、700、800、900℃)对其催化甲烷燃烧性能的影响.通过XRD、BET、H2-TPR及SEM技术对其结构进行表征.结果表明,在不同的焙烧温度下均可形成完整的双钙钛矿晶型,且焙烧温度不同其催化活性不同,随着焙烧温度的升高其催化活性先升高后逐渐降低.当焙烧温度为800℃,样品比表面积为14 m2/g,起燃温度T10%为428℃,T90%为640℃. 相似文献
6.
水硬性石灰在欧洲石质文物修复和加固中获得了很大成功。我国的石质文物主要是砂岩,水硬性石灰的修复效果不好。为满足我国石质文物修复和加固的需求,本文以石灰石和黏土为原料,在950℃煅烧不同时间,制备出水硬性石,对试样的成分、微观形貌、收缩率、抗拉强度和拉破坏过程等进行了研究。结果表明:(1)试样中含有水硬性成分2CaO·SiO2(C2S);煅烧8h时,成分与欧洲水硬性石灰NHL5接近;1.5CaO·SiO2·xH2O(C-S-H)和CaCO3的含量随龄期的增加逐渐增加。(2)龄期1~3d,收缩率较小;龄期4~6d,收缩率以线性规律增加;7d以后,收缩率趋于稳定。(3)局部变形区随拉应力的增加而变大,邻近局部变形区逐渐合并,形成面积更大的应变局部化带;载荷超过峰值后,产生微裂隙;随载荷进一步增加,微裂隙扩展,贯穿整个试件,发展成宏观裂隙,使试件破坏。(4)抗拉强度随龄期的增加而增加,水硬性石灰中C-S-H、CaCO3等相互交织,构成空间致密体,使试件力学强度提高。合成的水硬性石灰物理力学性能与欧洲水硬性石灰NHL5相近,并且成分均匀、可控,在石质文物修复和加固工程中具有良好应用前景。 相似文献
7.
Thermogravimetric Analysis of three aquatic materials, i.e. cuttlebone, mussel shell and oyster shell, and other physicochemical characteristics were investigated. The highest decomposition rates of aquatic materials under two surrounding gases, i.e. oxygen and nitrogen, exhibited no significant difference for cuttlebone (3.6×10-5-4.8×10-5 mg s-1 mginitial-1 at heating rate 5 °C/min and 11.8 ×10-5 -12.5×10-5 mg s-1 mginitial-1 at heating rate 15 °C/min) and mussel shell (3.4×10-5- 5.2×10-5 mg s-1 mginitial-1 at heating rate 5 °C/min and 11.9×10-5 – 12.4×10-5 mg s-1 mginitial-1 at heating rate 15 °C/min), while oyster shell provided the higher decomposition rate under nitrogen surrounding gas (7.6×10-4 mg s-1 mginitial-1 at heat rate 5 °C/min and 21.53×10-4 mg s-1 mginitial-1 at heating rate 15 °C/min). This is probably because of the difference in their starting crystalline structures, i.e. aragonite (cuttlebone and mussel shell) and calcite (oyster shell). The cubic calcium oxides were prepared by calcination of three aquatic materials under oxygen and nitrogen surrounding gases at 5 °C/min ramping to 850 °C for 2 hours. All resulting calcium oxides obtained from oxygen atmosphere provided only cubic crystalline phases and the adsorption-desorption isotherms (IUPAC Type III), whereas the calcinations under nitrogen surrounding gas gave a presence of calcium hydroxide crystalline or hydroxyl- contaminate existing with cubic calcium oxide that influences on the strength and the number of carbon dioxide adsorption sites. The specific surface area of all resulting calcium oxides ranged from 0.1 – 1.5 m2/g and the average pore diameter was found in the range of 40-60 nm. The the number of basic sites belonging to CaO derived from Oyster shell or Cuttlebone were improved while firing under oxygen atmosphere. The suitable firing condition is at the low heating rate to develop porous materials. 相似文献
8.
Young-Woon Cho Kyung-Seok Kang Chanhyuk Jee Ji-Hyun Kim Dongju Jang 《Molecular Crystals and Liquid Crystals》2016,634(1):73-81
Polyamic acid (PAA) made from 3,3, 4,4-biphenyltetracarboxylic dianhydride and 4,4-diaminodiphenyl ether was synthesized and used as the backbone of nanoporous polyimide. Thermally labile polyethylene glycol (PEG) at 10, 20 or 30 wt% was introduced to the end group of PAA. Self-assembled PAA-b-PEG micelle-like nanoparticles could be formed as a result of amphiphilic characteristics of hydrophobic PAA and hydrophilic PEG. Thermal imidization and degradation of spin-coated amphiphilic PAA-b-PEG film were performed sequentially through one-step heat treatment to obtain polyimide film with nanopores. Pore sizes decreased with increasing amount of PEG block and their dielectric constants decreased from 2.71 ± 0.13 to 2.38 ± 0.11. 相似文献
9.
Mingjie Wen Xiru Cao Yongqi Zhang Meng Liang Tianlei Zhang Balaganesh Muthiah Ke Zhou Soumendra K. Roy Makroni Lily 《International journal of quantum chemistry》2020,120(23):e26389
A detailed theoretical study on the reaction mechanisms for the formations of H2O2 + 3O2 from the self-reaction of HO2 radicals under the effect of NH3, H3N···H2O, and H2SO4 catalysts was performed using the CCSD(T)/CBS//M06-2X/aug-cc-pVTZ method. The rate constant was computed using canonical variational transition state theory (CVT) with small curvature tunneling (SCT). Our results indicate that NH3-, H3N···H2O-, and H2SO4-catalyzed reactions could proceed through both one-step and stepwise routes. Calculated rate constants show that the catalyzed routes in the presence of the three catalysts all prefer stepwise pathways. Compared to the catalytic efficiency of H2O, the efficiencies of NH3, H3N···H2O, and H2SO4 are much lower due to their smaller relative concentrations. The present results have provided a definitive example of how basic and acidic catalysts influence the atmospheric reaction of HO2 + HO2 → H2O2 + 3O2. These results further encourage one to consider the effects of basic and acidic catalysts on the related atmospheric reactions. Thus, the present investigation should have broad implications in the gas-phase reactions of the atmosphere. 相似文献
10.