全文获取类型
收费全文 | 679487篇 |
免费 | 6603篇 |
国内免费 | 1805篇 |
专业分类
化学 | 350691篇 |
晶体学 | 9714篇 |
力学 | 31814篇 |
综合类 | 22篇 |
数学 | 92664篇 |
物理学 | 202990篇 |
出版年
2021年 | 6340篇 |
2020年 | 6916篇 |
2019年 | 7738篇 |
2018年 | 10693篇 |
2017年 | 10638篇 |
2016年 | 15069篇 |
2015年 | 8774篇 |
2014年 | 13658篇 |
2013年 | 31479篇 |
2012年 | 24550篇 |
2011年 | 28742篇 |
2010年 | 21184篇 |
2009年 | 20856篇 |
2008年 | 26870篇 |
2007年 | 26505篇 |
2006年 | 24285篇 |
2005年 | 21817篇 |
2004年 | 20114篇 |
2003年 | 18051篇 |
2002年 | 17681篇 |
2001年 | 18469篇 |
2000年 | 14530篇 |
1999年 | 11172篇 |
1998年 | 9584篇 |
1997年 | 9364篇 |
1996年 | 8961篇 |
1995年 | 8001篇 |
1994年 | 8050篇 |
1993年 | 7697篇 |
1992年 | 8298篇 |
1991年 | 8574篇 |
1990年 | 8294篇 |
1989年 | 8108篇 |
1988年 | 7895篇 |
1987年 | 7705篇 |
1986年 | 7373篇 |
1985年 | 9491篇 |
1984年 | 9838篇 |
1983年 | 8337篇 |
1982年 | 8760篇 |
1981年 | 8139篇 |
1980年 | 7736篇 |
1979年 | 8324篇 |
1978年 | 8605篇 |
1977年 | 8440篇 |
1976年 | 8382篇 |
1975年 | 8062篇 |
1974年 | 7885篇 |
1973年 | 8285篇 |
1972年 | 5882篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Journal of Experimental and Theoretical Physics - We suggest that the principle of holographic duality be extended beyond conformal invariance and AdS isometry. Such an extension is based on a... 相似文献
42.
Functional Carbazole Liquid‐Crystal Block Codendrimers with Optical and Electronic Properties 下载免费PDF全文
Ismael Gracia Beatriz Feringán Prof. José Luis Serrano Dr. Roberto Termine Dr. Attilio Golemme Dr. Ana Omenat Prof. Joaquín Barberá 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(3):1359-1369
The synthesis and characterisation of a family of block codendrimers consisting of highly versatile mesogenic and carbazole‐containing 2,2‐bis(hydroxymethyl)propionic acid (bis‐MPA) dendrons are reported. The liquid‐crystal behaviour was investigated by means of differential scanning calorimetry, polarised‐light optical microscopy and X‐ray diffraction. Depending on the chemical structure of the constituent dendrons, the codendrimers show lamellar or columnar mesophases. On the basis of the experimental results, models both at the molecular level and in the mesophase are proposed. The physical properties of the block codendrimers derived from the presence of the carbazole moiety in their structure were investigated: photoluminescence in solution and in the mesophase, electrochemical behaviour and hole transport. Electrodeposition of carbazole dendrons afforded a globular supramolecular conformation in which the mesogenic molecular side plays a key role. 相似文献
43.
Reactions of Aryl Benzoates with Potassium Aryloxides: Solvent Effects on Reaction Pathway and Kinetics 下载免费PDF全文
Irina A. Khalfina 《国际化学动力学杂志》2015,47(5):302-314
Temperature dependences of the relative reactivity of potassium aryloxides XC6H4O?K+ toward 2,4‐dinitrophenyl benzoate in 50 mol% dimethylformamide (DMF)–50 mol% H2O mixture have been studied using the competitive reactions technique. Correlation analyses of the relative rate constants kX/kH and differences in the activation parameters (ΔΔН≠ and ΔΔS≠) of the competitive reactions have revealed the existence of two isokinetic series of the reactions of 2,4‐dinitrophenyl benzoate with potassium aryloxides with electron‐donating substituent (EDS) and electron‐withdrawing substituent (EWS), respectively. We have investigated the effect of the substituent X on the activation parameters for each isokinetic series and concluded that the mechanism of the reactions of 2,4‐dinitrophenyl benzoate with potassium aryloxides XC6H4O?K+ in 50 mol% DMF–50 mol% H2O mixture is the same as in DMF. Analysis of the obtained data with using the method of two‐dimensional reaction coordinate diagram leads to the conclusion that the variation of the solvent from DMF to 50 mol% DMF–50 mol% H2O mixture affects the reaction pathway. The rate constant kX for the reaction of 3‐nitrophenyl benzoate with potassium 4‐methoxyphenoxide and the relative rate constants kX/kH for the reaction of 3‐nitrophenyl benzoate with potassium aryloxides XC6H4O?K+ with EDS were measured in 50 mol% DMF–50 mol% H2O mixtures at 25°C, and it has been shown that the addition of water to DMF does not change the mechanism but slows down these reactions. 相似文献
44.
45.
46.
Vsevolod Khikhlovskyi Albert J. J. M. van Breemen Jasper J. Michels René A. J. Janssen Gerwin H. Gelinck Martijn Kemerink 《Journal of Polymer Science.Polymer Physics》2015,53(17):1231-1237
In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase‐separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1231–1237 相似文献
47.
48.
Physics of Atomic Nuclei - We have studied the mechanisms influencing production of cumulative pions and protons in the fragmentation of the incident deuterons into cumulative pions and protons... 相似文献
49.
50.
Mechanistic Aspects of a Highly Active Dinuclear Zinc Catalyst for the Co‐polymerization of Epoxides and CO2 下载免费PDF全文
Stefan Kissling Peter T. Altenbuchner Dr. Maximilian W. Lehenmeier Dr. Eberhardt Herdtweck Dr. Peter Deglmann Dr. Uwe B. Seemann Prof. Dr. Bernhard Rieger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8148-8157
The dinuclear zinc complex reported by us is to date the most active zinc catalyst for the co‐polymerization of cyclohexene oxide (CHO) and carbon dioxide. However, co‐polymerization experiments with propylene oxide (PO) and CO2 revealed surprisingly low conversions. Within this work, we focused on clarification of this behavior through experimental results and quantum chemical studies. The combination of both results indicated the formation of an energetically highly stable intermediate in the presence of propylene oxide and carbon dioxide. A similar species in the case of cyclohexene oxide/CO2 co‐polymerization was not stable enough to deactivate the catalyst due to steric repulsion. 相似文献