全文获取类型
收费全文 | 260800篇 |
免费 | 4731篇 |
国内免费 | 873篇 |
专业分类
化学 | 125690篇 |
晶体学 | 2780篇 |
力学 | 8562篇 |
综合类 | 8篇 |
数学 | 28957篇 |
物理学 | 65381篇 |
无线电 | 35026篇 |
出版年
2021年 | 1772篇 |
2020年 | 2099篇 |
2019年 | 2023篇 |
2018年 | 2512篇 |
2017年 | 2394篇 |
2016年 | 4732篇 |
2015年 | 3757篇 |
2014年 | 4498篇 |
2013年 | 12075篇 |
2012年 | 10163篇 |
2011年 | 11642篇 |
2010年 | 7627篇 |
2009年 | 7934篇 |
2008年 | 11414篇 |
2007年 | 11692篇 |
2006年 | 11149篇 |
2005年 | 10521篇 |
2004年 | 9388篇 |
2003年 | 8184篇 |
2002年 | 7778篇 |
2001年 | 8481篇 |
2000年 | 6859篇 |
1999年 | 5390篇 |
1998年 | 4385篇 |
1997年 | 4261篇 |
1996年 | 4314篇 |
1995年 | 3773篇 |
1994年 | 3794篇 |
1993年 | 3645篇 |
1992年 | 3900篇 |
1991年 | 3767篇 |
1990年 | 3437篇 |
1989年 | 3286篇 |
1988年 | 3152篇 |
1987年 | 2690篇 |
1986年 | 2593篇 |
1985年 | 3612篇 |
1984年 | 3565篇 |
1983年 | 2884篇 |
1982年 | 3064篇 |
1981年 | 2954篇 |
1980年 | 2868篇 |
1979年 | 2703篇 |
1978年 | 2782篇 |
1977年 | 2703篇 |
1976年 | 2663篇 |
1975年 | 2587篇 |
1974年 | 2462篇 |
1973年 | 2599篇 |
1972年 | 1526篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Probing the Catalytic Activity of Reduced Graphene Oxide Decorated with Au Nanoparticles Triggered by Visible Light
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Jiale Wang Dr. Fabiane J. Trindade Caroline B. de Aquino Joana C. Pieretti Prof. Dr. Sergio H. Domingues Prof. Dr. Romulo A. Ando Prof. Dr. Pedro H. C. Camargo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9889-9894
Hybrid materials in which reduced graphene oxide (rGO) is decorated with Au nanoparticles (rGO–Au NPs) were obtained by the in situ reduction of GO and AuCl4?(aq) by ascorbic acid. On laser excitation, rGO could be oxidized as a result of the surface plasmon resonance (SPR) excitation in the Au NPs, which generates activated O2 through the transfer of SPR‐excited hot electrons to O2 molecules adsorbed from air. The SPR‐mediated catalytic oxidation of p‐aminothiophenol (PATP) to p,p′‐dimercaptoazobenzene (DMAB) was then employed as a model reaction to probe the effect of rGO as a support for Au NPs on their SPR‐mediated catalytic activities. The increased conversion of PATP to DMAB relative to individual Au NPs indicated that charge‐transfer processes from rGO to Au took place and contributed to improved SPR‐mediated activity. Since the transfer of electrons from Au to adsorbed O2 molecules is the crucial step for PATP oxidation, in addition to the SPR‐excited hot electrons of Au NPs, the transfer of electrons from rGO to Au contributed to increasing the electron density of Au above the Fermi level and thus the Au‐to‐O2 charge‐transfer process. 相似文献
112.
Highly Selective Copper‐Catalyzed Asymmetric [3+2] Cycloaddition of Azomethine Ylides with Acyclic 1,3‐Dienes
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
María González‐Esguevillas Ana Pascual‐Escudero Dr. Javier Adrio Prof. Dr. Juan C. Carretero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4561-4565
The first examples of the catalytic asymmetric 1,3‐dipolar cycloaddition of azomethine ylides with acyclic activated 1,3‐dienes (and 1,3‐enynes) are described. Under copper catalysis, a selective cycloaddition at the terminal γ,δ‐C?C bond is observed. In addition, depending on the ligand used, either the exo or the endo adduct can be obtained with high selectivity. Under appropriate reaction conditions, the acyclic 1,6‐addition product is detected, suggesting a stepwise mechanism. The resulting C4‐alkenyl‐substituted pyrrolidines are suitable substrates for further access to polycyclic systems, as highlighted by the preparation of hexahydrochromeno[4,3‐b]pyrrole and the tetracyclic core of the alkaloid gracilamine. 相似文献
113.
114.
Brandão Pedro Francisco Ramos Rui Miguel Rodrigues José António 《Analytical and bioanalytical chemistry》2018,410(26):6873-6880
Analytical and Bioanalytical Chemistry - Formaldehyde is often applied in the industrial production of different products, such as textiles, insulation materials, or cosmetics, due to its... 相似文献
115.
Shaobo Cheng Vidushi Sharma Altug S. Poyraz Lijun Wu Xing Li Amy C. Marschilok Esther S. Takeuchi Kenneth J. Takeuchi Marivi Fernndez-Serra Yimei Zhu 《Chemical science》2020,11(19):4991
Tunneled metal oxides such as α-Mn8O16 (hollandite) have proven to be compelling candidates for charge-storage materials in high-density batteries. In particular, the tunnels can support one-dimensional chains of K+ ions (which act as structure-stabilizing dopants) and H2O molecules, as these chains are favored by strong H-bonds and electrostatic interactions. In this work, we examine the role of water molecules in enhancing the stability of K+-doped α-Mn8O16 (cryptomelane). The combined experimental and theoretical analyses show that for high enough concentrations of water and tunnel-ions, H2O displaces K+ ions from their natural binding sites. This displacement becomes energetically favorable due to the formation of K2+ dimers, thereby modifying the stoichiometric charge of the system. These findings have potentially significant technological implications for the consideration of cryptomelane as a Li+/Na+ battery electrode. Our work establishes the functional role of water in altering the energetics and structural properties of cryptomelane, an observation that has frequently been overlooked in previous studies.Water displaces potassium ions and initiates the formation of a homonuclear dimer ion (K2+) in the tunnels of hollandite. 相似文献
116.
117.
118.
Stievano I.S. Maio I.A. Canavero F.G. Siviero C. 《Advanced Packaging, IEEE Transactions on》2006,29(1):31-38
This paper addresses the impact of device macromodels on the accuracy of signal integrity and performance predictions for critical digital interconnecting systems. It exploits nonlinear parametric models for both single-ended and differential devices, including the effects of power supply fluctuations and receiver bit detection. The analysis demonstrates that the use of well-designed macromodels dramatically speeds up the simulation as well it preserves timing accuracy even for long bit sequences. 相似文献
119.
We present PowerNap, an OS power management scheme, which can significantly improve the battery life of mobile devices. The key feature of PowerNap is the skipping of the periodic system timer ticks associated with the operating system. On an idle device, this modification increases the time between successive timer interrupts and enables us to put the processor/system into a more efficient low power state. This saves the energy consumed by workless timer interrupts and the excess energy consumed by the processor in less efficient low power states. PowerNap is tightly integrated with the kernel and is designed for optimal control of the latency and energy associated with transitioning in and out of the low power states. We describe an implementation of PowerNap and its impact on system software. Experiments with IBM's WatchPad verify the ability of PowerNap to extend battery life. An analytical model that quantifies the ability of the scheme to reduce power is also presented. The model is in good agreement with experimental results. We apply the model to small form-factor devices which use processors that have a PowerDown state. In such devices, PowerNap may extend battery life by more than 42 percent for small processor workloads and for background power levels below 10 mW. 相似文献
120.
Siu-Chung Wong Tse C.K. Orabi M. Ninomiya T. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(2):454-462
This paper describes the modeling of power-factor-correction converters under average-current-mode control, which are widely used in switch-mode power supply applications. The objective is to identify stability boundaries in terms of major circuit parameters for facilitating design of such converters. The approach employs a double averaging procedure, which first applies the usual averaging over the switching period and subsequently applies generalized averaging over the mains period. The resulting model, after two averaging steps and application of a harmonic balance procedure, is nonlinear and capable of describing the low-frequency nonlinear dynamics of the system. The parameter ranges within which stable operation is guaranteed can be accurately and easily found using this model. Experimental measurements are provided for verification of the analytical results. 相似文献