全文获取类型
收费全文 | 3450篇 |
免费 | 685篇 |
国内免费 | 302篇 |
专业分类
化学 | 2453篇 |
晶体学 | 35篇 |
力学 | 190篇 |
综合类 | 14篇 |
数学 | 381篇 |
物理学 | 1364篇 |
出版年
2024年 | 2篇 |
2023年 | 81篇 |
2022年 | 70篇 |
2021年 | 148篇 |
2020年 | 157篇 |
2019年 | 142篇 |
2018年 | 123篇 |
2017年 | 107篇 |
2016年 | 193篇 |
2015年 | 187篇 |
2014年 | 201篇 |
2013年 | 253篇 |
2012年 | 342篇 |
2011年 | 354篇 |
2010年 | 230篇 |
2009年 | 219篇 |
2008年 | 229篇 |
2007年 | 198篇 |
2006年 | 182篇 |
2005年 | 175篇 |
2004年 | 125篇 |
2003年 | 90篇 |
2002年 | 90篇 |
2001年 | 70篇 |
2000年 | 57篇 |
1999年 | 51篇 |
1998年 | 38篇 |
1997年 | 44篇 |
1996年 | 40篇 |
1995年 | 38篇 |
1994年 | 30篇 |
1993年 | 17篇 |
1992年 | 25篇 |
1991年 | 33篇 |
1990年 | 31篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 13篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1959年 | 1篇 |
1947年 | 1篇 |
1946年 | 1篇 |
排序方式: 共有4437条查询结果,搜索用时 187 毫秒
1.
Shilin Jiang Dr. Yalan Liu Dr. Lin Wang Prof. Zhifang Chai Prof. Wei-Qun Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201145
The coordination chemistry of f-block elements (lanthanide and actinide) in molten salts has become a resounding topic in view of its great importance to the research and development (R&D) of molten salt reactors and pyroprocessing. In this Review article, a general overview of the coordination chemistry of f-block elements in molten salts is provided including past achievements and recent advances. Particular emphases are placed on the oxidation state, speciation, and solution structure of f-block metal ions in molten salts, as well as their relationships with the salt composition. Furthermore, this review briefly discusses the spectroscopic and theoretical methods that complement each other in revealing the coordination properties. 相似文献
2.
We propose a conjecture on the relative twist formula of l-adic sheaves, which can be viewed as a generalization of Kato—Saito's conjecture. We verify this conjecture under some transversal assumptions. We also define a relative cohomological characteristic class and prove that its formation is compatible with proper push-forward. A conjectural relation is also given between the relative twist formula and the relative cohomological characteristic class. 相似文献
3.
Weiyi Li Geng Leng Caiqin Li Yajing Lyu 《International journal of quantum chemistry》2020,120(8):e26150
The mechanisms of CO2 coupling with the propargylic alcohol using alkali carbonates M2CO3 (M = Li, Na, K, Cs) have been investigated by means of density functional theory calculations. The calculations reveal that the target product tetronic acid (TA) is yielded through two stages: (a) the formation of the α-alkylidene cyclic carbonate (αACC) intermediate via Cs2CO3-mediated carboxylative cyclization of the propargylic alcohol with CO2, and (b) the conversion of the αACC intermediate with Cs2CO3 to produce the cesium salt of the TA. Since the overall kinetic barriers for the two stages are comparable and affordable, the excellent chemoselectivity to the TA should be primarily originated from the high thermodynamic stability of the cesium salt of the TA. Moreover, relative to the TA, the possibility to yield the by-product acyclic carbonate can be excluded due to the both kinetics and thermodynamic inferiority. This result is different from the organic base-mediated reaction. Alternatively, our calculations predict that CsHCO3 together generated with the cesium salt of the TA might also be an available mediating reagent for the incorporation of CO2 with the propargylic alcohol. Compared to other alkali carbonates M2CO3 (M = Li, Na, K), the stronger basicity of Cs2CO3 and the lower ionic potential of cesium ion can raise the effective concentration of the αACC intermediate, and thus the conversion of the αACC intermediate into the cesium salt of the TA can be achieved with high yield. 相似文献
4.
本文给出了混合型多项式Hammerstein积分方程正解的迭代求法,并将所得结果应用到二阶非线性常微分方程的边值问题 相似文献
5.
运用群论及原子分子反应静力学方法,推导了XY(H,Li,Na)分子基态的电子态及相应的离解极限.并采用密度泛函方法(B3LYP)和二次组态相互作用方法(QCISD)优化计算了XY(H,Li,Na)分子基态的平衡结构、振动频率和离解能.使用QCISD/6-311++G(3df,3pd)方法,对XY(H,Li,Na)分子基态进行了单点能扫描计算,采用最小二乘法拟合Murrell-Sorbie函数得到了相应的势能函数和与该基态相对应的光谱常数(Be,αe,ωe和ωexe),计算结果与实验数据符合得相当好. 相似文献
6.
采用甚高频等离子体增强化学气相沉积技术制备了系列微晶硅薄膜太阳电池,指出了气体总流量和背反射电极的类型对电池性能参数的影响.电池的I-V测试结果表明:随反应气体总流量的增加,对应电池的短路电流密度、开路电压和填充因子都有很大程度的提高,结果使得电池的光电转换效率得以提高.另外,ZnO/Ag/Al背反射电极能明显提高电池的短路电流密度,进而也提高了电池的光电转换效率.对气体总流量和背反射电极类型影响电池效率的原因进行了分析.
关键词:
微晶硅薄膜太阳电池
气体流量
ZnO/Ag/Al背反射电极 相似文献
7.
8.
Geng Sheng WANG 《数学学报(英文版)》2005,21(5):1005-1014
This work is concerned with Pontryagin's maximum principle of optimal control problems governed by some non-well-posed semilinear heat equations. A type of approach to the non-well-posed optimal control problem is given. 相似文献
9.
10.
This paper presents a multiobjective hybrid metaheuristic approach for an intelligent spatial zoning model in order to draw territory line for geographical or spatial zone for the purpose of space control. The model employs a Geographic Information System (GIS) and uses multiobjective combinatorial optimization techniques as its components. The proposed hybrid metaheuristic consists of the symbiosis between tabu search and scatter search method and it is used heuristically to generate non-dominated alternatives. The approach works with a set of current solution, which through manipulation of weights are optimized towards the non-dominated frontier while at the same time, seek to disperse over the frontier by a strategic oscillation concept. The general procedure and its algorithms are given as well as its implementation in the GIS environment. The computation has resulted in tremendous improvements in spatial zoning. 相似文献