全文获取类型
收费全文 | 32643篇 |
免费 | 4066篇 |
国内免费 | 6485篇 |
专业分类
化学 | 35545篇 |
晶体学 | 472篇 |
力学 | 636篇 |
综合类 | 212篇 |
数学 | 1457篇 |
物理学 | 4872篇 |
出版年
2024年 | 37篇 |
2023年 | 480篇 |
2022年 | 707篇 |
2021年 | 1153篇 |
2020年 | 1752篇 |
2019年 | 1449篇 |
2018年 | 1427篇 |
2017年 | 1330篇 |
2016年 | 1634篇 |
2015年 | 1558篇 |
2014年 | 2070篇 |
2013年 | 3356篇 |
2012年 | 1917篇 |
2011年 | 2167篇 |
2010年 | 1750篇 |
2009年 | 1964篇 |
2008年 | 2064篇 |
2007年 | 2239篇 |
2006年 | 2073篇 |
2005年 | 1927篇 |
2004年 | 1867篇 |
2003年 | 1463篇 |
2002年 | 927篇 |
2001年 | 689篇 |
2000年 | 652篇 |
1999年 | 564篇 |
1998年 | 492篇 |
1997年 | 457篇 |
1996年 | 433篇 |
1995年 | 440篇 |
1994年 | 336篇 |
1993年 | 265篇 |
1992年 | 247篇 |
1991年 | 180篇 |
1990年 | 146篇 |
1989年 | 131篇 |
1988年 | 106篇 |
1987年 | 79篇 |
1986年 | 70篇 |
1985年 | 87篇 |
1984年 | 73篇 |
1983年 | 37篇 |
1982年 | 51篇 |
1981年 | 49篇 |
1980年 | 37篇 |
1979年 | 31篇 |
1978年 | 32篇 |
1977年 | 41篇 |
1976年 | 42篇 |
1974年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Mohammad A. Khalilzadeh Soo Young Kim Ho Won Jang Rafael Luque Rajender S. Varma Richard A. Venditti Mohammadreza Shokouhimehr 《Materials Today Chemistry》2022
The requirement of green and sustainable materials to prepare heterogeneous catalysts has intensified for practical reasons over the past few decades. Carbohydrates are possibly the most plentiful and renewable organic materials in nature with inimitable physiochemical properties, plausible low-cost and large-scale production, and sustainability features could be exploited in the generation of nanostructured heterogeneous catalysts. This review article outlines the organic transformations catalyzed by diverse carbohydrate-based nanostructured catalysts in greener and environmentally friendly processes. Selected examples are highlighted for a variety of organic reactions exploiting the proposed catalysts’ reactivity and reusability, and interactions with the intrinsic nature of the applied carbohydrate supports; advantages and speculated challenges of the introduced catalysts are deliberated as well. 相似文献
2.
This review summarizes recent progress in understanding the oxygen reduction and evolution reactions at the lanthanum strontium manganite electrode of a high-temperature solid oxide cell. Information provided here is put into the perspective of the defect chemistry of lanthanum strontium manganite and its impact on the electrode reaction mechanisms itself. After summarizing recent views on the oxygen reduction reaction mechanism, the focus turns to the oxygen evolution reaction, which is significantly less treated in the literature. A combination of the information in the literature on both reactions was the basis for modified reaction mechanism of the oxygen evolution reaction to be proposed under consideration of recent experimental observations and theoretical findings. 相似文献
3.
Two-stage ignition exists in the low-temperature combustion process of n-heptane and the first-stage ignition also shows a negative temperature coefficient(NTC) phenomenon. To study key reactions and understand chemical principles affecting the first-stage ignition of n-heptane, a lumped skeletal mechanism with 62 species is obtained based on the detailed NUIGMech1.0 mechanism using the directed relation graph method assisted by sensitivity analysis and isomer lumping. The lumped mechanism shows good performance on ignition delay time under wide conditions. The study revealed that the temperature after the first-stage ignition is higher and a larger amount of fuel is consumed at lower initial temperatures. The temperature at the first-stage ignition is relatively insensitive to the initial temperature. Further sensitivity analysis and reaction path analysis carried out based on the lumped mechanism show that the decomposition of RO2 to produce alkene and HO2is the most important reaction to inhibit the first-stage ignitions. The chain branching explosion closely related to the first-stage ignition will be terminated when the rate constant for the RO2 decomposition is larger than that of the isomerization of RO2 to produce QOOH. The NTC behavior as well as other characteristics of the first-stage ignition can be rationalized from the competition between these two reactions. 相似文献
4.
5.
氢能的引入能有效提升配电网的供电可靠性,而电解水制氢是实现低碳转型的关键技术,开发高效的电解水催化剂势在必行。过渡金属氧化物储量大、催化活性高,是具有广阔应用前景的析氧反应催化剂。本文通过射频等离子体处理制备石墨烯上负载Co3O4析氧催化剂,XRD、Raman和XPS测试结果显示,二维结构石墨烯的引入加速表面电子迁移,增大了反应面积。等离子体处理促进了纳米粒子在石墨烯上的负载,利用等离子体刻蚀作用在催化剂表面制造出大量碳结构缺陷和氧空位结构,改善了活性位点分布,有效调控Co3O4电子结构,提高析氧催化活性。电化学测试表明,本文中合成的Co3O4@rGO在电流密度为50 mA·cm-2时的过电位为410 mV,动力学反应速率较快,表现出优于商业IrO2的析氧催化活性。 相似文献
6.
环加成反应、环合反应、电环化反应与环化反应都是合成有机环状化合物的成环反应,它们描述的反应类型完全不同。但是,它们却经常被误用或者混用。阐述了这4类反应的区别,希望能够从教学上明确这4类反应,从源头为将来的有机化学工作者建立起准确的概念。 相似文献
7.
《Acta Crystallographica. Section C, Structural Chemistry》2018,74(2):212-217
A polydentate ligand bridged by a fluorene group, namely 9,9‐bis(2‐hydroxyethyl)‐2,7‐bis(pyridin‐4‐yl)fluorene (L), has been prepared under solvothermal conditions in acetonitrile. Crystals of the three‐dimensional metal–organic framework (MOF) poly[[[μ3‐9,9‐bis(2‐hydroxyethyl)‐2,7‐bis(pyridin‐4‐yl)fluorene‐κ3N:N′:O]bis(methanol‐κO)(μ‐sulfato‐κ2O:O′)nickel(II)] methanol disolvate], {[Ni(SO4)(C27H24N2O2)(CH3OH)]·2CH3OH}n, (I), were obtained by the solvothermal reaction of L and NiSO4 in methanol. The ligand L forms a two‐dimensional network in the crystallographic bc plane via two groups of O—H…N hydrogen bonds and neighbouring two‐dimensional planes are completely parallel and stack to form a three‐dimensional structure. In (I), the NiII ions are linked by sulfate ions through Ni—O bonds to form inorganic chains and these Ni‐containing chains are linked into a three‐dimensional framework via Ni—O and Ni—N bonds involving the polydentate ligand L. With one of the hydroxy groups of L coordinating to the NiII atom, the torsion angle of the hydroxyethyl group changes from that of the uncoordinated molecule. In addition, the adsorption properties of (I) with carbon dioxide were investigated. 相似文献
8.
对硫化镉反蛋白石结构光子晶体薄膜进行了可控合成,用巯基乙酸修饰的纳米晶和P(St-MMA-SPMAP)高分子小球共组装,成功地构筑了反蛋白石结构并用于可见光光解水产氢。结果表明,在可见光(λ≥420 nm)照射下,Cd S-310反蛋白石结构薄膜的光解水产氢性能比硫化镉纳米颗粒提高了一倍。这主要是因为等级孔结构反蛋白石光子晶体特性对催化剂的光催化性能的提升:首先,反蛋白石的周期性结构增加了光子在材料中的传播,提高了催化剂对太阳光的利用率;同时,大孔孔壁是由纳米颗粒堆积而成的,在反应中提供了更多的反应活性位点;此外,孔结构有利于物质的传输和分子的吸附。 相似文献
9.
Qi-Jun Li Ya-Jie Ren Qin Xie Min Wu Hua-Xing Feng Li-Mei Zheng Hua-Xin Zhang Jin-Qiao Long Tian-Shun Wang 《应用有机金属化学》2020,34(10):e5813
Two nickel complexes, [Ni(tpen)](ClO4)2.0.5CH3COCH3 ( 1 ) and [Ni(tpbn)](ClO4)2 ( 2 ), of tetrapyridyl ligands N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,2-ethanediamine (tpen) and N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,4-butanediamine (tpbn) were prepared and their catalysis for water oxidation reaction (WOR) studied. In 0.1 M phosphate buffer solution (PBS) of pH 8.0, complex 1 is a homogeneous molecular catalyst with an overpotential of ~440 mV and a Faradaic efficiency of 89%. At pH ≥ 9.0, complex 1 degraded gradually during the catalytic process and formed NiOx composite (nickel oxide with general formula NixOyHz) active for WOR. In contrast, complex 2 deteriorated under measured conditions (pH 8.0–12.0) and formed NiOx composite active for WOR. The NiOx composite derived from 1 in 0.1 M PBS at pH 11.0 showed an activity with an overpotential of ~500 mV, a Tafel slope of ~90 mV/decade and a Faradaic efficiency of 97%. Mechanisms were proposed for water oxidation catalyzed by 1 and 2 . This work revealed that the catalytic activity of the nickel complexes was related to the flexibility of the tetrapyridyl ligands and the adaptability of the coordination sphere of the nickel(II) center. 相似文献
10.
Mandana Amiri Zahra Tofighi Ali Khodayari Abolfazl Bezaatpour Shabnam Sohrabnezhad Vladyslav Mishyn Rabah Boukherroub Sabine Szunerits 《应用有机金属化学》2020,34(10):e5871
We report a Cu-based metal–organic framework (MOF) decorated by CuO nanostructures as an efficient catalyst for the oxygen evolution reaction (OER). MIL-53(Cu) was synthesized by a hydrothermal approach using 1,4-bezenedicarboxylic acid as organic precursor and further annealed at 300°C to form CuO nanostructures on its surface. The produced electrocatalyst, CuO@MIL-53(Cu), was characterized using various techniques. Under alkaline conditions, the developed electrocatalyst exhibited an overpotential of 801 and 336 mV versus RHE at 10 and 1 mA cm−2, respectively. The reproducibility of the catalytic performance was validated using several electrodes. It was confirmed that the CuO hair-like nanostructures grown on MIL-53(Cu) using thermal treatment exhibit high OER activity, good kinetics and durability. CuO@MIL-53(Cu) is an economic noble-metal-free OER electrocatalyst. It has potential for application as anode material for sustainable energy technologies like batteries, fuel cells and water electrolysis. 相似文献