全文获取类型
收费全文 | 11227篇 |
免费 | 276篇 |
国内免费 | 95篇 |
专业分类
化学 | 7729篇 |
晶体学 | 223篇 |
力学 | 244篇 |
综合类 | 1篇 |
数学 | 2008篇 |
物理学 | 1393篇 |
出版年
2021年 | 93篇 |
2020年 | 122篇 |
2019年 | 118篇 |
2018年 | 92篇 |
2017年 | 94篇 |
2016年 | 226篇 |
2015年 | 189篇 |
2014年 | 201篇 |
2013年 | 563篇 |
2012年 | 532篇 |
2011年 | 608篇 |
2010年 | 316篇 |
2009年 | 276篇 |
2008年 | 578篇 |
2007年 | 610篇 |
2006年 | 584篇 |
2005年 | 552篇 |
2004年 | 488篇 |
2003年 | 389篇 |
2002年 | 455篇 |
2001年 | 122篇 |
2000年 | 87篇 |
1999年 | 83篇 |
1998年 | 81篇 |
1997年 | 130篇 |
1996年 | 168篇 |
1995年 | 110篇 |
1994年 | 112篇 |
1993年 | 122篇 |
1992年 | 115篇 |
1991年 | 99篇 |
1990年 | 122篇 |
1989年 | 111篇 |
1988年 | 110篇 |
1987年 | 88篇 |
1986年 | 96篇 |
1985年 | 179篇 |
1984年 | 191篇 |
1983年 | 135篇 |
1982年 | 223篇 |
1981年 | 190篇 |
1980年 | 167篇 |
1979年 | 154篇 |
1978年 | 148篇 |
1977年 | 134篇 |
1976年 | 143篇 |
1975年 | 126篇 |
1974年 | 146篇 |
1973年 | 127篇 |
1972年 | 79篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Juan D. Gomez William G. P. Mayner Maggie Beheler-Amass Giulio Tononi Larissa Albantakis 《Entropy (Basel, Switzerland)》2021,23(1)
Integrated information theory (IIT) provides a mathematical framework to characterize the cause-effect structure of a physical system and its amount of integrated information (). An accompanying Python software package (“PyPhi”) was recently introduced to implement this framework for the causal analysis of discrete dynamical systems of binary elements. Here, we present an update to PyPhi that extends its applicability to systems constituted of discrete, but multi-valued elements. This allows us to analyze and compare general causal properties of random networks made up of binary, ternary, quaternary, and mixed nodes. Moreover, we apply the developed tools for causal analysis to a simple non-binary regulatory network model (p53-Mdm2) and discuss commonly used binarization methods in light of their capacity to preserve the causal structure of the original system with multi-valued elements. 相似文献
2.
Designs, Codes and Cryptography - Given an integer $$k\ge 3$$ and a group G of odd order, if there exists a 2-(v, k, 1)-design and if v is sufficiently large then there... 相似文献
3.
The Ramanujan Journal - We obtain a combinatorial formula related to the shear transformation for semi-invariants of binary forms, which implies the classical characterization of semi-invariants in... 相似文献
4.
Dr. Zhongyun Liu Dr. Yang Liu Dr. Wulin Qiu Prof. William J. Koros 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(35):14987-14993
Glassy polyimide membranes are attractive for industrial applications in sour natural gas purification. Unfortunately, the lack of fundamental understanding of relationships between polyimide chemical structures and their gas transport properties in the presence of H2S constrains the design and engineering of advanced membranes for such challenging applications. Herein, 6FDA-based polyimide membranes with engineered structures were synthesized to tune their CO2/CH4 and H2S/CH4 separation performances and plasticization properties. Under ternary mixed sour gas feeds, controlling polymer chain packing and plasticization tendency of such polyimide membranes via tuning the chemical structures were found to offer better combined H2S and CO2 removal efficiency compared to conventional polymers. Fundamental insights into structure–property relationships of 6FDA-based polyimide membranes observed in this study offer guidance for next generation membranes for sour natural gas separation. 相似文献
5.
Dr. Yujia Qing Mira D. Liu Denis Hartmann Dr. Linna Zhou Dr. William J. Ramsay Prof. Hagan Bayley 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(36):15841-15846
We report a single-molecule mechanistic investigation into 2-cyanobenzothiazole (CBT) chemistry within a protein nanoreactor. When simple thiols reacted reversibly with CBT, the thioimidate monoadduct was approximately 80-fold longer-lived than the tetrahedral bisadduct, with important implications for the design of molecular walkers. Irreversible condensation between CBT derivatives and N-terminal cysteine residues has been established as a biocompatible reaction for site-selective biomolecular labeling and imaging. During the reaction between CBT and aminothiols, we resolved two transient intermediates, the thioimidate and the cyclic precursor of the thiazoline product, and determined the rate constants associated with the stepwise condensation, thereby providing critical information for a variety of applications, including the covalent inhibition of protein targets and dynamic combinatorial chemistry. 相似文献
6.
The structure and rotational barrier for the mesityl-silicon bond of 2,2-dimesityl-1,1,1,3,3,3-hexamethyltrisilane have been investigated by 1H- and 13C-variable temperature nuclear magnetic resonance (NMR) as well as by density functional theory structural calculations. The calculations show that the lowest energy structure has C2 symmetry with nonequivalent ortho methyl groups, consistent with the crystal structure and solution NMR. The nonequivalent ortho methyl groups exchange through a Cs transition state with a calculated relative free energy of 11.0 kcal mol−1. The barrier for this rotation found by dynamic NMR is 13.4 ± 0.2 kcal mol−1 at 298 K. 相似文献
7.
8.
9.
Physical aging in amorphous poly(ethylene furanoate): Enthalpic recovery,density, and oxygen transport considerations 下载免费PDF全文
Steven K. Burgess Christopher R. Mubarak Robert M. Kriegel William J. Koros 《Journal of Polymer Science.Polymer Physics》2015,53(6):389-399
The current work utilizes three separate techniques to study the physical aging process in amorphous poly(ethylene furanoate) (PEF), which is a recently introduced engineering thermoplastic with enhanced properties compared to petroleum‐sourced poly(ethylene terephthalate). Differential scanning calorimetry aging experiments were conducted at multiple aging temperatures and times, and the resultant enthalpic recovery values compared to the theoretical maximum enthalpy loss evaluated from calculations involving extrapolation of the equilibrium liquid line. Density measurements reveal densification of the matrix for the aged versus unaged samples, and provide an estimate for the reduction in free volume for the aged samples. Complementary oxygen permeation and pressure‐decay sorption experiments provide independent verification of the free volume reduction mechanism for physical aging in glassy polymers. The current work provides the first detailed aging study for PEF. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 389–399 相似文献
10.
Rational Topological Design for Fluorescence Enhancement upon Aggregation of Distyrylfuran Derivatives 下载免费PDF全文
Dr. Charlotte Mallet Dr. Chady Moussallem Alexandre Faurie Magali Allain Dr. Frédéric Gohier Prof. William G. Skene Prof. Pierre Frère 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(21):7944-7953
A series of 2,5‐distyrylfuran derivatives bearing pentafluorophenyl‐ and cyanovinyl units have been synthesized for aggregation‐induced emission (AIE). The effect of the type and extent of the supramolecular connections on the AIE of the furan derivatives were examined and correlated with their X‐ray crystal structures. It was found that the simultaneous presence of cyano and perfluorophenyl units strongly enhances the fluorescence upon aggregation. Single‐crystal X‐ray diffraction analysis confirmed that C?H???F, F???F, C?H???nitrile, Ar???ArF (Ar=aryl, ArF=fluoroaryl), and nitrile???ArF intra‐ and intermolecular interactions drive the topology of the molecule and that solid‐state supramolecular contacts favor AIE of the furan derivatives. 相似文献