全文获取类型
收费全文 | 61119篇 |
免费 | 14335篇 |
国内免费 | 6512篇 |
专业分类
化学 | 60935篇 |
晶体学 | 854篇 |
力学 | 1990篇 |
综合类 | 370篇 |
数学 | 5041篇 |
物理学 | 12776篇 |
出版年
2024年 | 67篇 |
2023年 | 608篇 |
2022年 | 1065篇 |
2021年 | 1362篇 |
2020年 | 2422篇 |
2019年 | 3758篇 |
2018年 | 2090篇 |
2017年 | 1780篇 |
2016年 | 4577篇 |
2015年 | 4917篇 |
2014年 | 5115篇 |
2013年 | 6137篇 |
2012年 | 5484篇 |
2011年 | 4688篇 |
2010年 | 4695篇 |
2009年 | 4644篇 |
2008年 | 4279篇 |
2007年 | 3377篇 |
2006年 | 3001篇 |
2005年 | 2959篇 |
2004年 | 2538篇 |
2003年 | 2165篇 |
2002年 | 2940篇 |
2001年 | 2164篇 |
2000年 | 1892篇 |
1999年 | 842篇 |
1998年 | 430篇 |
1997年 | 305篇 |
1996年 | 281篇 |
1995年 | 203篇 |
1994年 | 210篇 |
1993年 | 182篇 |
1992年 | 142篇 |
1991年 | 133篇 |
1990年 | 108篇 |
1989年 | 78篇 |
1988年 | 70篇 |
1987年 | 50篇 |
1986年 | 57篇 |
1985年 | 45篇 |
1984年 | 23篇 |
1983年 | 20篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1971年 | 4篇 |
1959年 | 5篇 |
1936年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
关新民 《新疆大学学报(理工版)》2002,19(1):95-99
介绍了采用MATLAB V5.2提供的模糊逻辑工具箱来设计研究电孤纺电极调节系统中的模糊--PD控制器,讨论了在SIMULINK环境下模糊-PD控制器的参数自调速原理、结构、建立模糊控制规则库和模糊推论方法,并给出仿真结果与结论。 相似文献
102.
103.
104.
105.
A graph G is N2‐locally connected if for every vertex ν in G, the edges not incident with ν but having at least one end adjacent to ν in G induce a connected graph. In 1990, Ryjá?ek conjectured that every 3‐connected N2‐locally connected claw‐free graph is Hamiltonian. This conjecture is proved in this note. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 142–146, 2005 相似文献
106.
The Iyengar Type Inequalities with Exact Estimations and the Chebyshev Central Algorithms of Integrals 总被引:3,自引:0,他引:3
Xing Hua WANG Shi Jun YANG 《数学学报(英文版)》2005,21(6):1361-1376
In this paper, both low order and high order extensions of the Iyengar type inequality are obtained. Such extensions are the best possible in the same sense as that of the Iyengar inequality. hzrthermore, the Chebyshev central algorithms of integrals for some function classes and some related problems are also considered and investigated. 相似文献
107.
In this paper, the transformation processes of two types of bis(8-hydroxyquinoline)zinc: Znq2 dihydrate and anhydrous (Znq2)4 were investigated by X-ray diffraction (XRD), infrared spectra (IR), scanning electron microscope (SEM), differential scanning calorimetry (DSC) and thermogravimetry (TG). The effects of crystal structure on optical properties of bis(8-hydroxyquinoiline)zinc were analyzed. Znq2 dihydrate can be transformed into anhydrous (Znq2)4 during heating under vacuum. Reversal transformation occurs by the interaction between chloroform and (Znq2)4. But (Znq2)4 was partially transformed into Znq2 dihydrate by the interaction between ethanol and (Znq2)4. The different molecular structure results in different crystal stacking and electronic structure, thereby affect its optical properties. 相似文献
108.
ZENG Hao BAI Xingyu RAO Jun 《核工业西南物理研究院年报(英文版)》2004,(1):65-67
When we carry out lower hybrid wave heating and current driving plasma experiment at tokamak, we need mega-watt order of microwave power. The microwave signal at frequency of 2450 MHz is generated by a microwave exciter. According to the experiment's demands, the microwave exciter must provide output power of 1.5~ 2. 5 W with stabilized frequency and amplitude tobe used as the klystron input. Being amplified by the klystron, the microwave signal is transmitted through the transmitting system to the antenna and is emitted into the HL-2A tokamak. So we can see that the microwave exciter's function is very important to the lower hybrid wave heating and current driving plasma experiment. 相似文献
109.
A Promising MoO_x-based Catalyst for n-Heptane Isomerization 总被引:1,自引:0,他引:1
Song Hai CHAI Xin Ping WANG* Ying Jun WANG Tian Xi CAI State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 《中国化学快报》2003,14(7)
The increasing demand for higher-octane gasoline and the regulations limiting the amount of aromatics in the fuel motivate the interest in catalytic isomerization of n-alkanes. In the last ten years, transition metal oxides or oxycarbides based on molybdenum or tungstate have attracted much attention due to their high activity and isomerization selectivity compared to the conventional bifunctional supported platinum catalyst and high resistance to sulphur and nitrogen catalyst poisons1-5. Ma… 相似文献
110.
Ching‐Yuan Cheng Kuan‐Jiuh Lin 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):m363-m365
In the title compound, catena‐poly[lithium‐μ3‐ethylenediphosphonato], [Li(C2H7O6P2)]n, the supramolecular monoclinic (C2/c) structure consists of one‐dimensional lithium chains [Li⋯Li = 2.7036 (8) Å] that are embedded within ethylenediphosphonate anions linked by strong symmetric hydrogen bonds [O⋯O = 2.473 (3) Å]. The Li atoms and the H atom in the symmetric hydrogen bond reside on twofold rotation axes and there is an inversion center at the mid‐point of the C—C bond of the ethylenediphosphonate ligand. 相似文献