全文获取类型
收费全文 | 30835篇 |
免费 | 5515篇 |
国内免费 | 5455篇 |
专业分类
化学 | 14745篇 |
晶体学 | 573篇 |
力学 | 1303篇 |
综合类 | 499篇 |
数学 | 2894篇 |
物理学 | 9056篇 |
无线电 | 12735篇 |
出版年
2024年 | 129篇 |
2023年 | 530篇 |
2022年 | 1007篇 |
2021年 | 1101篇 |
2020年 | 1044篇 |
2019年 | 1008篇 |
2018年 | 997篇 |
2017年 | 1173篇 |
2016年 | 1225篇 |
2015年 | 1567篇 |
2014年 | 1878篇 |
2013年 | 2319篇 |
2012年 | 2456篇 |
2011年 | 2509篇 |
2010年 | 2293篇 |
2009年 | 2283篇 |
2008年 | 2384篇 |
2007年 | 2112篇 |
2006年 | 1948篇 |
2005年 | 1720篇 |
2004年 | 1478篇 |
2003年 | 1424篇 |
2002年 | 1603篇 |
2001年 | 1436篇 |
2000年 | 1087篇 |
1999年 | 647篇 |
1998年 | 406篇 |
1997年 | 287篇 |
1996年 | 284篇 |
1995年 | 221篇 |
1994年 | 216篇 |
1993年 | 172篇 |
1992年 | 142篇 |
1991年 | 135篇 |
1990年 | 96篇 |
1989年 | 82篇 |
1988年 | 71篇 |
1987年 | 47篇 |
1986年 | 40篇 |
1985年 | 31篇 |
1984年 | 38篇 |
1983年 | 31篇 |
1982年 | 21篇 |
1981年 | 32篇 |
1980年 | 20篇 |
1979年 | 18篇 |
1978年 | 11篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Khattari Z Ruschel Y Wen HZ Fischer A Fischer TM 《The journal of physical chemistry. B》2005,109(8):3402-3407
The surface shear viscosity of a myelin mimetic Langmuir monolayer is investigated upon adsorption of myelin basic protein (MBP). We measure an increase of the surface shear viscosity at picomolar concentrations of the protein, suggesting that the globular conformation of MBP changes upon adsorption at the monolayer. The conformational change enables hydrodynamic interactions of the proteins, with a typical separation of hundreds of nanometers. This unfolding is essential for the compactification of the myelin sheath, serving an enhanced saltatory signal transduction in vertebrates. The viscometry used extends the sensitivity of standard surface viscometers toward lower viscosities. 相似文献
52.
Lei He Hui‐Min Liu Xiao‐Lan Luo Wen‐Qin Zhang 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(2):o104-o106
The title compound, 2‐{N‐[2‐(2‐hydroxybenzamido)ethylammonioethyl]aminocarbonyl}phenolate, C18H21N3O4, crystallizes in a zwitterionic form as a result of intermolecular proton transfer and possesses a negatively charged phenolate group and a protonated amino group. The 2‐hydroxybenzamide and 2‐(aminocarbonyl)phenolate moieties attached to the two ends of the C—C—N—C—C backbone adopt a cis conformation in relation to this backbone. All N‐ and O‐bound H atoms are involved in hydrogen‐bond formation; the zwitterions are first linked into head‐to‐tail dimers, which are further organized into a two‐dimensional network parallel to the crystallographic bc plane. 相似文献
53.
54.
Yuehai ShenJianxun Wen 《Journal of fluorine chemistry》2002,113(1):13-15
A new and efficient route has been developed to synthesize 17β-(1-methyl-3-perfluoroalkyl)propyl-3β-androsterol (1) in nine steps from hyodeoxycholic acid via selective addition of 1-perfluoroalkyl iodide to 24-norchola-5,22-dien-3β-ol. From (1), the first series of steroidal liquid crystalline aliphatic esters (smectic A) with fluorocarbon side chains has been prepared. 相似文献
55.
Magnetic beads as interfacial nanoprobes 总被引:1,自引:0,他引:1
Helseth LE Wen HZ Heinig P Fischer TM 《Langmuir : the ACS journal of surfaces and colloids》2004,20(16):6556-6559
We use paramagnetic beads to probe strongly localized magnetic fields from one-dimensional nanomagnets. Using a polarization microscope in reflection mode, we find that light reflected from beads exhibits intensity fluctuations which may help us understand Brownian motion near interfaces. We estimate the height fluctuations and femtonewton forces acting on the beads. 相似文献
56.
High-energy-density batteries are in urgent need to solve the ever-increasing energy storage demand for portable electronic devices, electric vehicles, and renewable solar and wind energy systems. Alkali metals, typically lithium(Li), sodium(Na) and potassium(K), are considered as the promising anode materials owing to their low electrochemical potential, low density, and high theoretical gravimetric capacities. However, the problem of dendrite growth of alkali metals during their plating/stripping process will lead to low Coulombic efficiencies, a short lifespan and huge volume expansion, eventually hindering their practical commercialization. To resolve this issue, a very effective approach is engineering the anodes on structured current collectors. This review summarizes the development of the alkali metal batteries and discusses the recent advances in rational design of anode current collectors. First, the challenges and strategies of suppressing alkali-metal dendrite growth are presented. Then the special attention is paid to the novel current collector design for dendrite-free alkali metal anodes. Finally, we give conclusions and perspective on the current challenges and future research directions toward advanced anode current collectors for alkali metal batteries. 相似文献
57.
Xiao Wen Hu Zhi Min Zheng Cai Hong Xu 《中国化学快报》2007,18(11):1351-1352
Three new 1,3-bis(phenylethynyl)disilazanes were synthesized from the reaction of 1,3-dichlorodisilazanes with (phenylethy- nyl)lithium,and characterized by infrared (IR) spectra,nuclear magnetic resonance (NMR) and mass spectrometry (MS). 相似文献
58.
59.
60.
Propargylic alcohols are versatile precursors to many organic molecules including natural products and pharmaceutical compounds.[1] In our continuing interest in the development of practical methods for synthesis of ferrocene derivatives, we decided to investigate the efficiencies of ferrocenylacetylene addition to aromatic aldehydes under t-BuOKcatalyzed condition.[2] Interestingly, we found that the usually reliable coupling reaction between terminal alkyne of type 1 and aromatic aldehydes of type 2 does not furnish the expected propargylic alcohols, but that the isomeric aryl enones 3are found in high yield and very short reaction time (10~20 min). This provided a promising protocol for preparation of ferrocenyl chalcones in a practical, economical and mild sense compared with the traditional method. To the best of our knowledge, this unusual reaction was first observed for the addition of ferrocenylacetylene to aldehyde in a base-catalyzed manner (Eq. 1). 相似文献