全文获取类型
收费全文 | 431071篇 |
免费 | 27280篇 |
国内免费 | 18271篇 |
专业分类
化学 | 232477篇 |
晶体学 | 6711篇 |
力学 | 21788篇 |
综合类 | 28篇 |
数学 | 50453篇 |
物理学 | 165165篇 |
出版年
2021年 | 2927篇 |
2020年 | 3528篇 |
2019年 | 4298篇 |
2018年 | 4979篇 |
2017年 | 5563篇 |
2016年 | 7905篇 |
2015年 | 6231篇 |
2014年 | 8103篇 |
2013年 | 20199篇 |
2012年 | 16546篇 |
2011年 | 21036篇 |
2010年 | 18414篇 |
2009年 | 18603篇 |
2008年 | 17576篇 |
2007年 | 16996篇 |
2006年 | 16148篇 |
2005年 | 15211篇 |
2004年 | 15054篇 |
2003年 | 12879篇 |
2002年 | 12640篇 |
2001年 | 14390篇 |
2000年 | 10938篇 |
1999年 | 9112篇 |
1998年 | 7477篇 |
1997年 | 7230篇 |
1996年 | 7341篇 |
1995年 | 7171篇 |
1994年 | 7114篇 |
1993年 | 7071篇 |
1992年 | 7021篇 |
1991年 | 6871篇 |
1990年 | 6135篇 |
1989年 | 6228篇 |
1988年 | 6216篇 |
1987年 | 5443篇 |
1986年 | 5220篇 |
1985年 | 6720篇 |
1984年 | 6916篇 |
1983年 | 5334篇 |
1982年 | 6077篇 |
1981年 | 5741篇 |
1980年 | 5610篇 |
1979年 | 5511篇 |
1978年 | 5634篇 |
1977年 | 5635篇 |
1976年 | 6009篇 |
1975年 | 5009篇 |
1974年 | 4981篇 |
1973年 | 5266篇 |
1972年 | 3678篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
π-Extended molecules are key components for the development of materials science. In fact, polyaromatic structures are fundamental for the scientific and technological progress of fields such as organic electronics and bio-applications. Beneficial properties of π-extended structures are absorption in the visible region, often luminescence, high electron mobilities and stability. Common approaches to adjust the properties of polyaromatic structures to functional setups involve changes in shape and size at the molecular level. Recently, incorporating hetero-elements emerged as successful approach. In this regard, organophosphorus conjugated molecules are new materials holding great promise for potential applications. In this review, we comprehensively discuss the design/development of polyaromatic phosphorus materials and their applicability. We establish structure/property/applicability relationships to provide key guidelines for the engineering of newer, future applications. This article thus provides a source of information for the further development of this rapidly evolving field of research. 相似文献
132.
Yablokov M. Yu. Shchegolikhin A. N. Lebedev O. V. Goncharuk G. P. Ozerin A. N. 《Russian Chemical Bulletin》2021,70(9):1816-1821
Russian Chemical Bulletin - Gradient polymer composites were prepared by melt-mixing of carbon black and polypropylene in a compounder and subsequent hot pressing of pellets. The thermally treated... 相似文献
133.
134.
Mathematical Notes - 相似文献
135.
Experimental Mechanics - There have been relatively few studies on mechanical properties of nanomaterials under high strain rates, mainly due to the lack of capable nanomechanical testing devices.... 相似文献
136.
Immobilized Catalysts for Iridium‐Catalyzed Allylic Amination: Rate Enhancement by Immobilization
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. Chandi C. Malakar Prof. Dr. Günter Helmchen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(19):7127-7134
The first immobilized catalyst for Ir‐catalyzed asymmetric allylic aminations is described. The catalyst is a cationic (π‐allyl)Ir complex bound by cation exchange to an anionic silica gel support. Preparation of the catalyst is facile, and the supported catalyst displayed considerably enhanced activity compared with the parent homogeneous catalyst. Up to 43 consecutive amination runs were possible in recycling experiments. 相似文献
137.
Gelikonov G. V. Ksenofontov S. Yu. Shilyagin P. A. Gelikonov V. M. 《Radiophysics and Quantum Electronics》2019,62(3):228-236
Radiophysics and Quantum Electronics - We propose and experimentally test a numerical method for correction of the influence of fluctuations in the distance to objects during noncontact probing in... 相似文献
138.
A.G. Rousskikh A.V. Fedyunin A.P. Artyomov A.S. Zhigalin V.I. Oreshkin 《Current Applied Physics》2019,19(6):704-708
The aim of the study presented in this paper was to characterize quantitatively the erosion of aluminum cathodes in high-current vacuum arcs. The experimental setup comprised two current generators. The first one, capable of generating a current of amplitude up to 350 kA, was used to produce a plasma jet, that is, the object to be investigated. The second generator was used to produce a source of probe radiation for imaging the object under investigation in soft x rays of energy ?ν ≈ 0.5–3 keV. The findings of the study are based on experimental data obtained by electrophysical and radiographic methods. It has been shown that the cathode erosion rate in a high-current vacuum arc is a function of the charge passed through the cathode. 相似文献
139.
140.
Savita Verma Deepak M. Maher Samadhan S. Nagane Bhausaheb V. Tawade Prakash P. Wadgaonkar 《Journal of polymer science. Part A, Polymer chemistry》2019,57(5):588-597
New aromatic (co)polyesters containing pendant propargyloxy groups were synthesized by phase transfer‐catalyzed interfacial polycondensation of 5‐(propargyloxy)isophthaloyl chloride (P‐IPC) and various compositions of P‐IPC and isophthaloyl chloride with bisphenol A. FTIR and NMR spectroscopic data, respectively, revealed successful incorporation of pendant propargyloxy groups into (co)polyesters and formation of (co)polyesters with desired compositions. (Co)polyesters exhibited good solubility in common organic solvents such as chloroform, dichloromethane, and tetrahydrofuran and could be cast into transparent, flexible, and tough films from chloroform solution. Inherent viscosities and number average molecular weights of (co)polyesters were in the range 0.77–1.33 dL/g and 43,600–118,000 g/mol, respectively, indicating the achievement of reasonably high‐molecular weights. The 10% weight loss temperatures of (co)polyesters were in the range 390–420 °C, demonstrating their good thermal stability. (Co)polyesters exhibited Tg in the range 146–170 °C and Tg values decreased with increase in mol % incorporation of P‐IPC. The study of non‐isothermal curing by DSC indicated thermal crosslinking of (co)polyesters via propargyloxy groups. The utility of pendant propargyloxy group was demonstrated by post‐modification of the selected copolyester with 1‐(4‐azidobutyl)pyrene, 9‐(azidomethyl)anthracene, and azido‐terminated poly(ethyleneglycol) monomethyl ether via copper(I)‐catalyzed Huisgen 1,3‐dipolar cycloaddition reaction. FTIR and 1H NMR spectra confirmed that click reaction was quantitative. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 588–597 相似文献