全文获取类型
收费全文 | 114016篇 |
免费 | 6945篇 |
国内免费 | 4686篇 |
专业分类
化学 | 49281篇 |
晶体学 | 1285篇 |
力学 | 9001篇 |
综合类 | 285篇 |
数学 | 35954篇 |
物理学 | 29841篇 |
出版年
2024年 | 143篇 |
2023年 | 778篇 |
2022年 | 1291篇 |
2021年 | 1316篇 |
2020年 | 1489篇 |
2019年 | 1420篇 |
2018年 | 11359篇 |
2017年 | 11129篇 |
2016年 | 7671篇 |
2015年 | 2580篇 |
2014年 | 2424篇 |
2013年 | 2997篇 |
2012年 | 6922篇 |
2011年 | 13683篇 |
2010年 | 7826篇 |
2009年 | 8166篇 |
2008年 | 8925篇 |
2007年 | 10795篇 |
2006年 | 2336篇 |
2005年 | 2929篇 |
2004年 | 2811篇 |
2003年 | 3043篇 |
2002年 | 2023篇 |
2001年 | 1071篇 |
2000年 | 1154篇 |
1999年 | 973篇 |
1998年 | 923篇 |
1997年 | 827篇 |
1996年 | 883篇 |
1995年 | 732篇 |
1994年 | 615篇 |
1993年 | 524篇 |
1992年 | 478篇 |
1991年 | 394篇 |
1990年 | 352篇 |
1989年 | 298篇 |
1988年 | 263篇 |
1987年 | 229篇 |
1986年 | 210篇 |
1985年 | 199篇 |
1984年 | 146篇 |
1983年 | 107篇 |
1982年 | 101篇 |
1981年 | 74篇 |
1980年 | 62篇 |
1979年 | 54篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Dr. Qing Xu Dr. Shanshan Tao Dr. Qiuhong Jiang Prof. Donglin Jiang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(11):4587-4593
A strategy based on covalent organic frameworks for ultrafast ion transport involves designing an ionic interface to mediate ion motion. Electrolyte chains were integrated onto the walls of one-dimensional channels to construct ionic frameworks via pore surface engineering, so that the ionic interface can be systematically tuned at the desired composition and density. This strategy enables a quantitative correlation between interface and ion transport and unveils a full picture of managing ionic interface to achieve high-rate ion transport. Moreover, the effect of interfaces was scaled on ion transport; ion mobility is increased in an exponential mode with the ionic interface. This strategy not only sets a benchmark system but also offers a general guidance for designing ionic interface that is key to systems for energy conversion and storage. 相似文献
22.
23.
The research progress of a novel traffic solution,a submerged floating tunnel(SFT),is reviewed in terms of a study approach and loading scenario.Among existing publications,the buoyancy-weight ratio(BWR) is usually predefined.However,BWR is a critical structural parameter that tremendously affects the dynamic behaviour of not only the tunnel tube itself but also the cable system.In the context of a SFT prototype(SFTP) project in Qiandao Lake(Zhejiang Province,China),the importance of BWR is illustrated by finite element analysis and subsequently,an optimized BWR is proposed within a reasonable range in the present study.In the numerical model,structural damping is identified to be of importance.Rayleigh damping and the corresponding Rayleigh coefficients are attained through a sensitivity study,which shows that the adopted damping ratios are fairly suitable for SFTP.Lastly,the human sense of security is considered by quantifying the comfort index,which helps further optimize BWR in the SFTP structural parameter design. 相似文献
24.
25.
26.
27.
28.
Polypyrrole Shell@3D‐Ni Metal Core Structured Electrodes for High‐Performance Supercapacitors
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)
Gao‐Feng Chen Yu‐Zhi Su Pan‐Yong Kuang Zhao‐Qing Liu Dao‐Yi Chen Xu Wu Nan Li Prof. Shi‐Zhang Qiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4614-4621
Three‐dimensional (3D) nanometal films serving as current collectors have attracted much interest recently owing to their promising application in high‐performance supercapacitors. In the process of the electrochemical reaction, the 3D structure can provide a short diffusion path for fast ion transport, and the highly conductive nanometal may serve as a backbone for facile electron transfer. In this work, a novel polypyrrole (PPy) shell@3D‐Ni‐core composite is developed to enhance the electrochemical performance of conventional PPy. With the introduction of a Ni metal core, the as‐prepared material exhibits a high specific capacitance (726 F g?1 at a charge/discharge rate of 1 A g?1), good rate capability (a decay of 33 % in Csp with charge/discharge rates increasing from 1 to 20 A g?1), and high cycle stability (only a small decrease of 4.2 % in Csp after 1000 cycles at a scan rate of 100 mV s?1). Furthermore, an aqueous symmetric supercapacitor device is fabricated by using the as‐prepared composite as electrodes; the device demonstrates a high energy density (≈21.2 Wh kg?1) and superior long‐term cycle ability (only 4.4 % and 18.6 % loss in Csp after 2000 and 5000 cycles, respectively). 相似文献
29.
30.
The satisfiability (SAT) problem is a core problem in computer science. Existing studies have shown that most industrial SAT instances can be effectively solved by modern SAT solvers while random SAT instances cannot. It is believed that the structural characteristics of different SAT formula classes are the reasons behind this difference. In this paper, we study the structural properties of propositional formulas in conjunctive normal form (CNF) by the principle of structural entropy of formulas. First, we used structural entropy to measure the complex structure of a formula and found that the difficulty solving the formula is related to the structural entropy of the formula. The smaller the compressing information of a formula, the more difficult it is to solve the formula. Secondly, we proposed a -approximation strategy to approximate the structural entropy of large formulas. The experimental results showed that the proposed strategy can effectively approximate the structural entropy of the original formula and that the approximation ratio is more than 92%. Finally, we analyzed the structural properties of a formula in the solution process and found that a local search solver tends to select variables in different communities to perform the next round of searches during a search and that the structural entropy of a variable affects the probability of the variable being flipped. By using these conclusions, we also proposed an initial candidate solution generation strategy for a local search for SAT, and the experimental results showed that this strategy effectively improves the performance of the solvers CCAsat and Sparrow2011 when incorporated into these two solvers. 相似文献