全文获取类型
收费全文 | 515248篇 |
免费 | 5635篇 |
国内免费 | 1720篇 |
专业分类
化学 | 266292篇 |
晶体学 | 8029篇 |
力学 | 23394篇 |
综合类 | 9篇 |
数学 | 62119篇 |
物理学 | 162760篇 |
出版年
2021年 | 4251篇 |
2020年 | 4582篇 |
2019年 | 5241篇 |
2018年 | 6906篇 |
2017年 | 7069篇 |
2016年 | 10106篇 |
2015年 | 6065篇 |
2014年 | 9760篇 |
2013年 | 24342篇 |
2012年 | 18248篇 |
2011年 | 22132篇 |
2010年 | 15746篇 |
2009年 | 15579篇 |
2008年 | 19819篇 |
2007年 | 19837篇 |
2006年 | 18306篇 |
2005年 | 16316篇 |
2004年 | 15036篇 |
2003年 | 13353篇 |
2002年 | 13259篇 |
2001年 | 15477篇 |
2000年 | 11627篇 |
1999年 | 9124篇 |
1998年 | 7620篇 |
1997年 | 7545篇 |
1996年 | 7042篇 |
1995年 | 6306篇 |
1994年 | 6128篇 |
1993年 | 6138篇 |
1992年 | 6669篇 |
1991年 | 6849篇 |
1990年 | 6565篇 |
1989年 | 6455篇 |
1988年 | 6280篇 |
1987年 | 6313篇 |
1986年 | 5998篇 |
1985年 | 7853篇 |
1984年 | 8032篇 |
1983年 | 6617篇 |
1982年 | 7004篇 |
1981年 | 6670篇 |
1980年 | 6531篇 |
1979年 | 6784篇 |
1978年 | 7029篇 |
1977年 | 6870篇 |
1976年 | 7025篇 |
1975年 | 6440篇 |
1974年 | 6523篇 |
1973年 | 6786篇 |
1972年 | 4574篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Russian Journal of Applied Chemistry - Quenching method was used to obtain glasses in the system xWO3-(100-x)P2O5 (x = 70, 75, 80, 82 mol %). The electrical conductivity of the compositions was... 相似文献
53.
Mohammad Azam Saud I. Al-Resayes Agata Trzesowska-Kruszynska Rafal Kruszynski S.F. Adil N.K. Lokanath 《Journal of Saudi Chemical Society》2019,23(5):636-641
A new derivative of dioxouranium(VI) salen complex, [UO2(L)(pyridine)], where [L = N,N′-Bis(2-hydroxybenzylidene)-2,2-dimethyl-1,3-propanediamine] is synthesized and characterized by elemental analysis (C, H, N), FT-IR, ESI-MS spectrometry, UV/Vis, fluorescence, 1H and 13C NMR spectroscopy and thermal gravimetric (TG) study. Furthermore, the single crystal X-ray diffraction measurements of the complex were carried out at 100 and 273 K. The crystal structure measurements revealed that the complex has distorted pentagonal bipyramidal geometry with uranium atom located at the centre and bonded to two phenoxy oxygen and two azomethine nitrogen in tetradenate fashion and one nitrogen from pyridine making it seven coordinated. In addition, the photoluminescence property of the complex was also recorded. 相似文献
54.
Stolpovskaya N. V. Kruzhilin A. A. Zorina A. V. Shikhaliev Kh. S. Ledeneva I. V. Kosheleva E. A. Vandyshev D. Yu. 《Russian Journal of Organic Chemistry》2019,55(9):1322-1328
Russian Journal of Organic Chemistry - A procedure has been proposed for the synthesis of a series of substituted N-(1,3-thiazol-2-yl)-pyrimidin-2-amines and N-(pyrimidin-2-yl)thioureas by... 相似文献
55.
56.
In the present work, the use of cylindrical turbulators in a double pipe heat exchanger has been investigated. Cylindrical fin type of turbulators has been placed circumferentially separated by 90° on the outer side of an inner pipe at a regular pitch. Experimental studies were undertaken for different air flow rates in a turbulent regime whose Reynolds number range between 2500 and 10000. Heat transfer characteristics like Nu and friction factor have been experimentally determined. Parametric studies were conducted by changing the pitch and also the orientation of the turbulators. Nu and friction factor were found to increase as the pitch is reduced. A model with alternatively changed orientation outperformed others by exhibiting highest Nu and reduced friction factor. 相似文献
57.
Synthesis of partially fluorinated poly(arylene ether sulfone) multiblock copolymers bearing perfluorosulfonic functions 下载免费PDF全文
Luca Assumma Cristina Iojoiu Régis Mercier Sandrine Lyonnard Huu Dat Nguyen Emilie Planes 《Journal of polymer science. Part A, Polymer chemistry》2015,53(16):1941-1956
Partially fluorinated poly(arylene ether sulfone) multiblock copolymers bearing perfluorosulfonic functions (ps‐PES‐FPES), with ionic exchange capacity (IEC) ranging between 0.9 and 1.5 meq H+/g, are synthesized by regioselective bromination of partially fluorinated poly(arylene ether sulfone) multiblock copolymers (PES‐FPES), followed by Ullman coupling reaction with lithium 1,1,2,2‐tetrafluoro‐2‐(1,1,2,2‐tetrafluoro‐2‐iodoethoxy)ethanesulfonate. The PES‐FPES are prepared by aromatic nucleophilic substitution reaction by an original approach, that is, “one pot two reactions synthesis.” The chemical structures of polymers are analyzed by 1H and 19F NMR spectroscopy. The resulted ionomers present two distinct glass transitions and α relaxations revealing phase separation between the hydrophilic and the hydrophobic domains. The phase separation is observed at much lower block lengths of ps‐PES‐FPES as compared with the literature. AFM and SANS observations supported the phase separation, the hydrophilic domains are well dispersed but the connectivity to each other depends on the ps‐PES block lengths. The thermomechanical behavior, the water up‐take, and the conductivity of the ps‐PES‐FPES membranes are compared with those of Nafion 117® and randomly functionalized polysulfone (ps‐PES). Conductivities close or higher to those of Nafion 117® are obtained. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1941–1956 相似文献
58.
Saleh Z. M. Nasser H. Özkol E. Günöven M. Abak K. Canli S. Bek A. Turan R. 《Journal of nanoparticle research》2015,17(10):1-12
Journal of Nanoparticle Research - Plasmonic interfaces consisting of silver nanoparticles of different sizes (50–100&;nbsp;nm) have been processed by the self-assembled dewetting... 相似文献
59.
Mike R. Jeffrey 《Nonlinear dynamics》2015,81(4):1699-1716
60.