全文获取类型
收费全文 | 253716篇 |
免费 | 6383篇 |
国内免费 | 4856篇 |
专业分类
化学 | 132767篇 |
晶体学 | 3591篇 |
力学 | 13948篇 |
综合类 | 329篇 |
数学 | 31317篇 |
物理学 | 83003篇 |
出版年
2021年 | 3390篇 |
2020年 | 3795篇 |
2019年 | 4346篇 |
2018年 | 5572篇 |
2017年 | 5577篇 |
2016年 | 6806篇 |
2015年 | 3900篇 |
2014年 | 6449篇 |
2013年 | 11059篇 |
2012年 | 9794篇 |
2011年 | 11002篇 |
2010年 | 8936篇 |
2009年 | 9043篇 |
2008年 | 9977篇 |
2007年 | 9643篇 |
2006年 | 8652篇 |
2005年 | 7655篇 |
2004年 | 7198篇 |
2003年 | 6504篇 |
2002年 | 6705篇 |
2001年 | 6977篇 |
2000年 | 5243篇 |
1999年 | 4141篇 |
1998年 | 3819篇 |
1997年 | 3501篇 |
1996年 | 3273篇 |
1995年 | 2915篇 |
1994年 | 2914篇 |
1993年 | 2892篇 |
1992年 | 2887篇 |
1991年 | 3204篇 |
1990年 | 3117篇 |
1989年 | 3112篇 |
1988年 | 2891篇 |
1987年 | 2903篇 |
1986年 | 2717篇 |
1985年 | 3252篇 |
1984年 | 3287篇 |
1983年 | 2870篇 |
1982年 | 2905篇 |
1981年 | 2733篇 |
1980年 | 2511篇 |
1979年 | 2913篇 |
1978年 | 3059篇 |
1977年 | 3146篇 |
1976年 | 3325篇 |
1975年 | 3030篇 |
1974年 | 2995篇 |
1973年 | 3173篇 |
1972年 | 2625篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
151.
152.
DFT mechanistic study of the H2‐assisted chain transfer copolymerization of propylene and p‐methylstyrene catalyzed by zirconocene complex
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Cheng‐Gen Zhang Shu‐Yuan Yu Liaoyun Zhang Huayi Li Zhi‐Xiang Wang 《Journal of polymer science. Part A, Polymer chemistry》2015,53(4):576-585
DFT computations have been performed to investigate the mechanism of H2‐assisted chain transfer strategy to functionalize polypropylene via Zr‐catalyzed copolymerization of propylene and p‐methylstyrene (pMS). The study unveils the following: (i) propylene prefers 1,2‐insertion over 2,1‐insertion both kinetically and thermodynamically, explaining the observed 1,2‐insertion regioselectivity for propylene insertion. (ii) The 2,1‐inserion of pMS is kinetically less favorable but thermodynamically more favorable than 1,2‐insertion. The observation of 2,1‐insertion pMS at the end of polymer chain is due to thermodynamic control and that the barrier difference between the two insertion modes become smaller as the chain length becomes longer. (iii) The pMS insertion results in much higher barriers for subsequent either propylene or pMS insertion, which causes deactivation of the catalytic system. (iv) Small H2 can react with the deactivated [Zr]?pMS?PPn facilely, which displace functionalized pMS?PPn chain and regenerate [Zr]? H active catalyst to continue copolymerization. The effects of counterions are also discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 576–585 相似文献
153.
154.
155.
高能重带电粒子能直接穿透靶原子核外电子层,与原子核发生直接碰撞,发生散裂反应,产生一系列具有放射性的剩余产物核.重带电粒子诱发靶材放射性剩余核与辐射防护和人员安全有着密切联系,当前,大部分剩余核产额主要依靠蒙特卡罗粒子输运程序进行模拟计算,其准确程度亟需通过实验测量进行准确评估.本文利用能量为80.5 MeV/u的(12)^C6+粒子对薄铜靶开展了辐照实验与伽玛射线测量,结合伽玛谱学分析方法,得出了辐照产生的18种放射性剩余产物的初始活度和产生截面值,并与PHITS模拟结果进行对比.结果表明,PHITS模拟程序对放射性剩余核种类的估计具有较高可靠性,在其绝对产额方面,与实验测量仍具有较大偏差. 相似文献
156.
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
157.
158.
Following a thermal reduction method, platinum nanoparticles were synthesized and stabilized by polyvinylpyrrolidone. The colloidal platinum nanoparticles were stable for more than 3 months. The micrograph analysis unveiled that the colloidal platinum nanoparticles were well dispersed with an average size of 2.53 nm. The sol–gel‐based inverse micelle strategy was applied to synthesize mesoporous iron oxide material. The colloidal platinum nanoparticles were deposited on mesoporous iron oxide through the capillary inclusion method. The small‐angle X‐ray scattering analysis indicated that the dimension of platinum nanoparticles deposited on mesoporous iron oxide (Pt‐Fe2O3) was 2.64 nm. X‐ray photoelectron spectroscopy (XPS) data showed that the binding energy on Pt‐Fe2O3 surface decreased owing to mesoporous support–nanoparticle interaction. Both colloidal and deposited platinum nanocatalysts improved the degradation of methyl orange under reduction conditions. The activation energy on the deposited platinum nanocatalyst interface (2.66 kJ mol?1) was significantly lowered compared with the one on the colloidal platinum nanocatalyst interface (40.63 ± 0.53 kJ mol?1). 相似文献
159.
Physics of Particles and Nuclei Letters - Resonance structure of the beta decay strength function Sβ(E) for GT β–-decay of halo nuclei 6He and 11Li is analyzed. Compare experimental... 相似文献
160.
Mathematical Notes - 相似文献