全文获取类型
收费全文 | 131368篇 |
免费 | 26848篇 |
国内免费 | 12064篇 |
专业分类
化学 | 104252篇 |
晶体学 | 1418篇 |
力学 | 6941篇 |
综合类 | 706篇 |
数学 | 13494篇 |
物理学 | 43469篇 |
出版年
2024年 | 370篇 |
2023年 | 2211篇 |
2022年 | 3647篇 |
2021年 | 3840篇 |
2020年 | 5234篇 |
2019年 | 6028篇 |
2018年 | 4423篇 |
2017年 | 3791篇 |
2016年 | 7962篇 |
2015年 | 8014篇 |
2014年 | 8931篇 |
2013年 | 11184篇 |
2012年 | 11757篇 |
2011年 | 11261篇 |
2010年 | 8879篇 |
2009年 | 8665篇 |
2008年 | 8693篇 |
2007年 | 7376篇 |
2006年 | 6686篇 |
2005年 | 5796篇 |
2004年 | 4611篇 |
2003年 | 3845篇 |
2002年 | 4405篇 |
2001年 | 3402篇 |
2000年 | 3097篇 |
1999年 | 2381篇 |
1998年 | 1728篇 |
1997年 | 1696篇 |
1996年 | 1645篇 |
1995年 | 1409篇 |
1994年 | 1213篇 |
1993年 | 1063篇 |
1992年 | 898篇 |
1991年 | 824篇 |
1990年 | 680篇 |
1989年 | 521篇 |
1988年 | 413篇 |
1987年 | 323篇 |
1986年 | 347篇 |
1985年 | 281篇 |
1984年 | 167篇 |
1983年 | 132篇 |
1982年 | 115篇 |
1981年 | 66篇 |
1980年 | 62篇 |
1979年 | 32篇 |
1978年 | 21篇 |
1973年 | 9篇 |
1971年 | 9篇 |
1957年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
161.
A convective flow CO laser composed of polytetrafluoroethylene discharge tubes, nickel–chromium steel components, a cupric heat exchanger and other components is described. Operating in liquid nitrogen condition, output power of 60 W has been obtained from a non-selective cavity. 相似文献
162.
Liyue Liu Yingge Yang Yafei Zhang 《Physica E: Low-dimensional Systems and Nanostructures》2004,24(3-4):343-348
The electrical conductivity was investigated for multi-walled carbon nanotubes (MWNTs) dissolved in chloroform and toluene, respectively. The electrical conductivity remarkably increased with increase in the content of MWNTs, which is in accordance with Archie's equation . Furthermore, a hypothesis of the electronic transport process was proposed to explain the difference between the solution and the solid compound. In addition, the temperature dependence of the electrical conductivity shows that log σ vs. 1/T exist in a good linear relationship. The activation energy of the electrical conductivity decreased with increase in concentration and an inflexion was observed at 60 °C in MWNT/toluene solution. 相似文献
163.
164.
165.
166.
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
167.
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
168.
The inhomogeneous Dirichlet problems concerning divergence form elliptic equations are studied. Optimal regularity requirements on the coefficients and domains for the W1,p theory, 1 < p < ∞, are obtained. The principal coefficients are supposed to be in the John‐Nirenberg space with small BMO seminorms. The domain is a Reifenberg domain. These conditions for the W1,p theory not only weaken the requirements on the coefficients but also lead to a more general geometric condition on the domains. In fact, these domains might have fractal dimensions. © 2004 Wiley Periodicals, Inc. 相似文献
169.
The first α‐diimine nickel(I) complex having a chloro bridge is reported. The centrosymmetric dinuclear structure of {[ArN?C(Me)C(Me)?NAr]NiCl}2[Ar?2,6?C6H3(i‐Pr)2] features two chelating α‐diimine ligands and two bridged chlorine atoms, so that a distorted tetrahedral N2Cl2 coordination geometry for nickel results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
170.
Marcelino Maneiro Manuel R. Bermejo M. Isabel Fernndez Ana M. Gonzlez‐Noya Alexei M. Tyryshkin Robin G. Pritchard 《无机化学与普通化学杂志》2003,629(2):285-290
A new MnIII‐Schiff base complex, [MnL(OH2)](ClO4) ( 1 ) (H2L = N, N′‐bis‐(3‐Br‐5‐Cl‐salicylidene)‐1, 2‐diimino‐2‐methylethane), an inorganic model of the catalytic center (OEC, Oxygen Evolving Complex) in photosystem II (PSII), has been synthesized and characterized by elemental analysis, IR and EPR spectroscopy, mass spectrometry, magnetic susceptibility measurement and the study of its redox properties by cyclic and normal pulse voltammetry. This complex mimics reactivity (showing a relevant photolytic activity), and also some structural characteristics (parallel‐mode MnIII EPR signal from partially assembled OEC cluster) of the natural OEC. The complex 1 was found to rearrange in solution into a crystallographically solved square‐pyramidal complex, [MnLL′] ( 2 ) (HL′ = 6‐bromo‐4‐chloro‐2‐cyanophenol), through a process, which probably liberates radical species (detected by EPR), and provokes a C—N bond cleavage in the ligand. A photo‐radical mechanism is discussed to explain this rearrangement. 相似文献