全文获取类型
收费全文 | 1056篇 |
免费 | 16篇 |
国内免费 | 11篇 |
专业分类
化学 | 822篇 |
晶体学 | 12篇 |
力学 | 10篇 |
数学 | 62篇 |
物理学 | 177篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 9篇 |
2016年 | 19篇 |
2015年 | 9篇 |
2014年 | 20篇 |
2013年 | 43篇 |
2012年 | 71篇 |
2011年 | 51篇 |
2010年 | 36篇 |
2009年 | 22篇 |
2008年 | 53篇 |
2007年 | 49篇 |
2006年 | 66篇 |
2005年 | 77篇 |
2004年 | 49篇 |
2003年 | 57篇 |
2002年 | 52篇 |
2001年 | 21篇 |
2000年 | 18篇 |
1999年 | 11篇 |
1998年 | 12篇 |
1997年 | 17篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 15篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 18篇 |
1983年 | 21篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1975年 | 13篇 |
1974年 | 8篇 |
1973年 | 4篇 |
1966年 | 3篇 |
排序方式: 共有1083条查询结果,搜索用时 0 毫秒
81.
82.
Ihara T Fujii T Mukae M Kitamura Y Jyo A 《Journal of the American Chemical Society》2004,126(29):8880-8881
Anthracene readily forms photoadducts, anthracene dimers, and this photodimerization reaction has been well characterized. In general, however, the reaction requires close proximity and certain spatial alignment of both reaction partners. DNA could provide an ideal scaffold for accelerating the photocyclic addition. We synthesized a number of anthracene-DNA conjugates. The sequences of the conjugates, 5'AntODNn and 3'AntODNn (the length of methylene linkers: n = 3 or 6), were designed to bind adjacent sequences of the template with the anthracene units directed such that they stacked with each other. The conjugates were only dimerized in the presence of the template by light irradiation. The efficiency was affected by one-base displacement in the template sequence. 相似文献
83.
Two new tetranor-cycloartane glycosides (1, 2) were isolated from Cimicifuga Rhizome. Their structures were determined by spectroscopic analysis. These compounds suggested the existence of a biogenetic pathway into C-23 lactone-type cycloartane glycosides. 相似文献
84.
[reaction: see text] Treatment of allenes with tetraallylmanganate provides allylated products with high regioselectivity. A catalytic amount of MnCl(2) combined with allylmagnesium chloride also achieves efficient allylmetalation of allenes. The resulting alkenylmagnesium species react with various electrophiles. In the presence of molecular oxygen, the alkenylmagnesium undergoes diallylation reaction. A cyclization reaction of 1,2,6-heptatriene with tetraallylmanganate is also described. 相似文献
85.
We derive Sobolev inequalities for Besov spaces B
p,p
(F), 0<<1, 1p< on d-sets F in R
n
, dn, from a metric property of the Bessel capacity on R
n
. We first extend Kaimanovitch's result on the equivalence of Sobolev and capacitary inequalites for contractive p-norms in a general setting allowing unbounded Lévy kernels. A simple part of the Jonsson–Wallin trace theorem for Besov spaces and some basic properties of Bessel and Besov capacities on R
n
are then utilized in getting the desired inequalities. When p=2, the Besov space being considered is a non-local regular Dirichlet space and gives rise to a jump type symmetric Markov process M
over the d-set. The upper bound of the transition function of M
and metric properties of M
-polar sets are then exhibited. 相似文献
86.
STF是KEK为国际直线对撞机(ILC)建立的试验装置. 在STF中, 数字微波低电平系统用于控制超导腔的RF相位和幅度. 在没有实际腔运行的情况下, 设计了一个基于FPGA技术的实时超导腔模拟器, 用于测试微波低电平系统的硬件和算法. 超导腔的数字控制器用FPGA实现, 其中采用了PI反馈控制和前馈控制算法. 测试表明, 超导腔模拟器和控制器都工作良好, 可用于STF微波低电平系统的进一步开发. 相似文献
87.
88.
Kenjiro Onimura Mieko Matsushima Munetoshi Nakamura Tatsuya Tominaga Kazuhiro Yamabuki Tsutomu Oishi 《Journal of polymer science. Part A, Polymer chemistry》2011,49(16):3550-3558
2,3‐Diaryl substituted maleimides as model compounds of conjugated maleimide polymers [poly(RMI‐alt‐Ar) and poly(RMI‐co‐Ar)] were synthesized from 2,3‐dibromo‐N‐substituted maleimide (DBrRMI) [R= cyclohexyl (DBrCHMI) and n‐hexyl (DBrHMI)] and aryl boronic acid using palladium catalysts. To clarify structures of conjugated polymer containing maleimide units at the main chain, 13C NMR spectra of 2‐aryl or 2,3‐diaryl substituted maleimides were compared with those of N‐substituted maleimide polymers. Copolymers obtained with DBrRMI via Suzuki‐Miyaura cross‐coupling polymerizations or Yamamoto coupling polymerizations were dehalogenated structures at the terminal end. This dehalogenation may contribute to the low polymerizability of DBrRMIs. On the other hand, the π‐conjugated compounds showed high solubility in common organic solvents. The N‐substituents of maleimide cannot significantly affect the photoluminescence spectra of 2,3‐diaryl substituted maleimides derivatives. The fluorescence spectra of poly(RMI‐alt‐Ar) and poly(RMI‐co‐Ar) varied with N‐substituents of the maleimide ring. When exposed to ultraviolet light of wavelength 352 nm, a series of 1,4‐phenylene‐ and/or 2,5‐thienylene‐based copolymers containing N‐substituted maleimide derivatives fluoresced in a yellow to blue color. It was found that photoluminescence emissions and electronic state of π‐conjugated maleimide derivatives were controlled by aryl‐ and N‐substituents, and maleimide sequences of copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
89.
Glass bead/x‐ray fluorescence spectrometry of the sludge incineration ashes generated in sewage processing was developed for the determination of ten major components (Na2O, MgO, Al2O3, SiO2, P2O5, K2O, CaO, TiO2, MnO, Fe2O3) and five minor elements (Zn, Cu, Cr, As, Pb). Sewage sludge ashes consisted of rock‐forming minerals and phosphate crystals that had been used for phosphorus removal. Ash samples were melted and molded with lithium tetraborate to 35 mm diameter glass disks in a Pt–Au crucible. Analytical results of ten major components and five minor elements agreed well with the recommended values of a phosphate rock standard reference material (NIST SRM 694). Elemental compositions of sewage sludge ash from seven sewage‐processing plants in Japan were determined using this method. Concentrations of Fe2O3, SiO2, and CaO, along with loss of ignition in sewage sludge ash mutually differed among the sewage‐processing plant products. Seasonal variations in concentrations of ten major components and five minor components of ash samples produced from October 2001 to September 2002 were determined using the proposed method. Concentrations of SiO2increased with the inflow of gravel by rainfall, thereby decreasing concentrations of P2O5 originating from excreta and microorganisms. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
90.