全文获取类型
收费全文 | 172903篇 |
免费 | 37981篇 |
国内免费 | 26276篇 |
专业分类
化学 | 114970篇 |
晶体学 | 2061篇 |
力学 | 11378篇 |
综合类 | 670篇 |
数学 | 20681篇 |
物理学 | 87400篇 |
出版年
2024年 | 724篇 |
2023年 | 2757篇 |
2022年 | 4228篇 |
2021年 | 4327篇 |
2020年 | 5107篇 |
2019年 | 5193篇 |
2018年 | 4790篇 |
2017年 | 5018篇 |
2016年 | 7027篇 |
2015年 | 7024篇 |
2014年 | 8000篇 |
2013年 | 11357篇 |
2012年 | 12892篇 |
2011年 | 14467篇 |
2010年 | 14926篇 |
2009年 | 14875篇 |
2008年 | 9477篇 |
2007年 | 8394篇 |
2006年 | 7668篇 |
2005年 | 7027篇 |
2004年 | 6741篇 |
2003年 | 5356篇 |
2002年 | 4966篇 |
2001年 | 5057篇 |
2000年 | 4021篇 |
1999年 | 4392篇 |
1998年 | 3740篇 |
1997年 | 3519篇 |
1996年 | 3802篇 |
1995年 | 3986篇 |
1994年 | 3893篇 |
1993年 | 3752篇 |
1992年 | 3248篇 |
1991年 | 2812篇 |
1990年 | 2382篇 |
1989年 | 2309篇 |
1988年 | 2169篇 |
1987年 | 1434篇 |
1986年 | 1501篇 |
1985年 | 1125篇 |
1984年 | 1136篇 |
1983年 | 472篇 |
1982年 | 995篇 |
1981年 | 795篇 |
1980年 | 812篇 |
1979年 | 548篇 |
1978年 | 541篇 |
1977年 | 641篇 |
1976年 | 1049篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
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
85.
Rong Yin Jihui Zhang Xudong Shang 《Mathematical Methods in the Applied Sciences》2020,43(15):8736-8752
This paper is dedicated to studying the following Schrödinger–Poisson system Under some different assumptions on functions V(x), K(x), a(x) and f(u), by using the variational approach, we establish the existence of positive ground state solutions. 相似文献
86.
Solid‐state 31P NMR investigation on the status of guanine nucleotides in paclitaxel‐stabilized microtubules
下载免费PDF全文
![点击此处可从《Magnetic resonance in chemistry : MRC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ga Hyang Lee Su Young Oh Kwon Joo Yeo Taslima Ferdous Meeyeon Cho Younkee Paik 《Magnetic resonance in chemistry : MRC》2015,53(5):330-336
Microtubule dynamics is a target for many chemotherapeutic drugs. In order to understand the biochemical effects of paclitaxel on the GTPase activity of tubulin, the status of guanine nucleotides in microtubules was investigated by 31P cross‐polarization magic angle spinning (CPMAS) NMR. Microtubules were freshly prepared in vitro in the presence of paclitaxel and then lyophilized in sucrose buffer for solid‐state NMR experiments. A 31P CPMAS NMR spectrum with the SNR of 25 was successfully acquired from the lyophilized microtubule sample. The broadness of the 31P spectral lines in the spectrum indicates that the molecular environments around the guanine nucleotides inside tubulin may not be as crystalline as reported by many diffraction studies. Deconvolution of the spectrum into four spectral components was carried out in comparison with the 31P NMR spectra obtained from five control samples. The spectral analysis suggested that about 13% of the nucleotides were present as GTP and 37% as GDP in the β‐tubulin (E‐site) of the microtubules. It was found that most of the GDPs were present as GDP‐Pi complex in the microtubules, which seems to be one of the effects of paclitaxel binding. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
87.
88.
Recent Progress in the $L_p$ Theory for Elliptic and Parabolic Equations with Discontinuous Coefficients
下载免费PDF全文
![点击此处可从《分析论及其应用》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hongjie Dong 《分析论及其应用》2020,36(2):161-199
In this paper, we review some results over the last 10-15 years on elliptic and parabolic equations with discontinuous coefficients. We begin with an approach given by N. V. Krylov to parabolic equations in the whole space with $\rm{VMO}_x$ coefficients. We then discuss some subsequent development including elliptic and parabolic equations with coefficients which are allowed to be merely measurable in one or two space directions, weighted $L_p$estimates with Muckenhoupt ($A_p$) weights, non-local elliptic and parabolic equations, as well as fully nonlinear elliptic and parabolic equations. 相似文献
89.
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
90.
Naphthalimide‐phthalimide derivative based photoinitiating systems for polymerization reactions under blue lights
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)
Pu Xiao Frédéric Dumur Jing Zhang Bernadette Graff Didier Gigmes Jean Pierre Fouassier Jacques Lalevée 《Journal of polymer science. Part A, Polymer chemistry》2015,53(5):665-674
Naphthalimide‐phthalimide derivatives (NDPDs) have been synthesized and combined with an iodonium salt, N‐vinylcarbazole, amine or 2,4,6‐tris(trichloromethyl)‐1,3,5‐triazine to produce reactive species (i.e., radicals and cations). These generated reactive species are capable of initiating the cationic polymerization of epoxides and/or the radical polymerization of acrylates upon exposure to very soft polychromatic visible lights or blue lights. Compared with the well‐known camphorquinone based systems used as references, the novel NDPD based combinations employed here demonstrate clearly higher efficiencies for the cationic polymerization of epoxides under air as well as the radical polymerization of acrylates. Remarkably, one of the NDPDs (i.e., NDPD2) based systems is characterized by an outstanding reactivity. The structure/reactivity/efficiency relationships of the investigated NDPDs were studied by fluorescence, cyclic voltammetry, laser flash photolysis, electron spin resonance spin trapping, and steady state photolysis techniques. The key parameters for their reactivity are provided. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 665–674 相似文献