全文获取类型
收费全文 | 66750篇 |
免费 | 5947篇 |
国内免费 | 11967篇 |
专业分类
化学 | 47911篇 |
晶体学 | 1894篇 |
力学 | 697篇 |
综合类 | 435篇 |
数学 | 3316篇 |
物理学 | 13347篇 |
综合类 | 17064篇 |
出版年
2024年 | 187篇 |
2023年 | 1047篇 |
2022年 | 1988篇 |
2021年 | 1998篇 |
2020年 | 2059篇 |
2019年 | 1891篇 |
2018年 | 1584篇 |
2017年 | 2045篇 |
2016年 | 2235篇 |
2015年 | 2092篇 |
2014年 | 2856篇 |
2013年 | 5285篇 |
2012年 | 4181篇 |
2011年 | 4489篇 |
2010年 | 3873篇 |
2009年 | 4574篇 |
2008年 | 4411篇 |
2007年 | 4798篇 |
2006年 | 4473篇 |
2005年 | 3888篇 |
2004年 | 3671篇 |
2003年 | 3142篇 |
2002年 | 2572篇 |
2001年 | 2104篇 |
2000年 | 1968篇 |
1999年 | 1694篇 |
1998年 | 1314篇 |
1997年 | 1199篇 |
1996年 | 1023篇 |
1995年 | 1008篇 |
1994年 | 894篇 |
1993年 | 744篇 |
1992年 | 710篇 |
1991年 | 560篇 |
1990年 | 404篇 |
1989年 | 347篇 |
1988年 | 283篇 |
1987年 | 191篇 |
1986年 | 132篇 |
1985年 | 119篇 |
1984年 | 96篇 |
1983年 | 37篇 |
1982年 | 66篇 |
1981年 | 92篇 |
1980年 | 66篇 |
1979年 | 67篇 |
1978年 | 46篇 |
1977年 | 50篇 |
1976年 | 30篇 |
1973年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
A diagnostic study q (energy transfer processes in a He-N2 flowing discharge and afterglow has been performed in a radiofrequency-produced plasma cooled in a liquid nitrogen hath. Optical emission spectroscopy in the visible and infrared spectral range as well as Langrnuir probe diagnostics were used. The vibrational kinetics of CO injected in such an afterglow has been examined. It shows a slow cooling of the electrons in the afterglow regime. The electron kinetics responsible joy CO vibrahonal excitation is turned off when N2 is added to the He discharge, while that for vibrationally excited N2 molecules is turned on. The results are discussed on the basis of previous theorerical calculations and experiments on the He-N2 system. 相似文献
152.
本文证明了d2k =δ2k =d2k ≥b2k,其中d2k ,δ2k , b2k分别表示A(BlMp)在lNq下的Kolmogorov,线性,Bernstein 2k-宽度,d2k 表示AT(BlN相似文献
153.
A model is reported to foresee ,for different mirror choices, the spectral properties of a high pressure, frequency tunable, CO2 laser, operating with a non-Littrow grating mounting. The calculations show a larger frequency selectivity for not collimated plane cavities. The model is experimentally verified in a suitable high pressure laser. In particular narrowed linewidths less than 300MHz ( FWHM) are obtained. 相似文献
154.
Hiroshi Ito Masaki Okazaki Dolores C. Miller 《Journal of polymer science. Part A, Polymer chemistry》2004,42(6):1478-1505
Radical copolymerizations of electron‐deficient 2‐trifluoromethylacrylic (TFMA) monomers, such as 2‐trifluoromethylacrylic acid and t‐butyl 2‐trifluoromethylacrylate (TBTFMA), with electron‐rich norbornene derivatives and vinyl ethers with 2,2′‐azobisisobutyronitrile as the initiator were investigated in detail through the analysis of the kinetics in situ with 1H NMR and through the determination of the monomer reactivity ratios. The norbornene derivatives used in this study included bicyclo[2.2.1]hept‐2‐ene (norbornene) and 5‐(2‐trifluoromethyl‐1,1,1‐trifluoro‐2‐hydroxylpropyl)‐2‐norbornene. The vinyl ether monomers were ethyl vinyl ether, t‐butyl vinyl ether, and 3,4‐dihydro‐2‐H‐pyran. Vinylene carbonate was found to copolymerize with TBTFMA. Although none of the monomers underwent radical homopolymerization under normal conditions, they copolymerized readily, producing a copolymer containing 60–70 mol % TFMA. The copolymerization of the TFMA monomer with norbornenes and vinyl ethers deviated from the terminal model and could be described by the penultimate model. The copolymers of TFMA reported in this article were evaluated as chemical amplification resist polymers for the emerging field of 157‐nm lithography. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1478–1505, 2004 相似文献
155.
Tatiana B. Mikenas Vladimir A. Zakharov Lyudmila G. Echevskaya Mikhail A. Matsko 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5057-5066
The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl2/MgCl2‐Al(i‐Bu)3 (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl2/MgCl2‐Al(i‐Bu)3 has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl2/MgCl2‐Al(i‐Bu)3 has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007 相似文献
156.
157.
Abakumov G. A. Druzhkov N. O. Kurskii Yu. A. Shavyrin A. S. 《Russian Chemical Bulletin》2003,52(3):712-717
Products of thermal transformation of substituted N-aryl-o-quinoneimines were studied using NMR spectroscopy. The formation of 4aH-phenoxazine, which was further dimerized by the Diels—Alder reaction, was established. 相似文献
158.
C2F6是一种人造气体,它在半导体工业中有着非常广泛的应用.由于它的分解率极低,所以很难把它从环境中排除掉,对温室效应的影响比较显著.采用光吸收技术和电子散射方法已对C2F6分子的电子结构进行了研究.然而,迄今为止,尚没有关于该分子的绝对广义振子强度实验测量.Lassettre及其合作者首先采用角分辨的电子能量损失谱技术用于精确的偶极振子强度测量,角分辨的电子能量损失谱仪的原理和实验方法已在其他文中作了详细的介绍[1].通过采用Bethe求和规则可独立地对任意动量转移下的广义阵子强度进行绝对定标,本次实验中谱仪的能量分辨率为0.8e… 相似文献
159.
We introduce new classes of 2-weight cyclic codes which are direct sums of 1-weight irreducible cyclic codes
相似文献
160.
A palladium‐TPPTS catalyst heterogenized on KF/alumina has been shown to be effective and recyclable for the selective formation of monooctadienylxylopyranosides via the telomerization of butadiene with D ‐xylose. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献