全文获取类型
收费全文 | 858篇 |
免费 | 31篇 |
国内免费 | 3篇 |
专业分类
化学 | 620篇 |
晶体学 | 16篇 |
力学 | 14篇 |
数学 | 43篇 |
物理学 | 199篇 |
出版年
2022年 | 9篇 |
2019年 | 8篇 |
2018年 | 15篇 |
2017年 | 6篇 |
2016年 | 20篇 |
2015年 | 16篇 |
2014年 | 8篇 |
2013年 | 40篇 |
2012年 | 50篇 |
2011年 | 46篇 |
2010年 | 25篇 |
2009年 | 31篇 |
2008年 | 54篇 |
2007年 | 32篇 |
2006年 | 38篇 |
2005年 | 46篇 |
2004年 | 37篇 |
2003年 | 45篇 |
2002年 | 29篇 |
2001年 | 15篇 |
2000年 | 25篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 11篇 |
1976年 | 11篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1973年 | 5篇 |
1972年 | 6篇 |
1970年 | 6篇 |
1969年 | 8篇 |
排序方式: 共有892条查询结果,搜索用时 15 毫秒
101.
Imoto M Matsui Y Takeda M Tamaki A Taniguchi H Mizuno K Ikeda H 《The Journal of organic chemistry》2011,76(15):6356-6361
Observations show that nitroanilines exhibit an unusually high S(N)Ar reactivity with OH(-) in aqueous media in reactions that produce nitrophenols. S(N)Ar reaction of 4-nitroaniline (2a) in aqueous NaOH for 16 h yields 4-nitrophenol (4a) quantitatively, whereas a similar reaction of 4-nitrochlorobenzene (1a) gave 4a in 2% yield together with recovered 1a in 97%, suggesting that the leaving ability of the NH(2) group far surpasses that of Cl under these conditions. An essential feature of S(N)Ar reactions of nitroanilines is probably that the NH(2) leaving group participates in a hydrogen-bonding interaction with H(2)O. Density functional theory (DFT) calculations for a set of 4-nitroaniline, OH(-), and H(2)O suggest a possible formation of a Meisenheimer complex stabilized by hydrogen-bonding interactions and a six-membered ring structure. The results obtained here contrast with conventional S(N)Ar reactivity profiles in which nitroanilines are nearly unreactive with nucleophiles in organic solvents. 相似文献
102.
We present a reaction scheme of silver containing 5-substituted uracils (N) bridge formation with two silver ions to a silver-mediated base pair [N-Ag(2)-N] by using the conductor-like polarizable continuum model (CPCM)-B3LYP/aug-cc-pVDZ level of theory. The whole reaction scheme is divided into the following three steps: (1) silver ion binding and deprotonation, (2) silver ion transfer, and (3) dimer formation and structural fluctuation. With a new pK(a) computing scheme proposed in our previous studies, it is found that a silver coordination decreases the pK(a) of N by 2.5-3.0 pK(a) units, which is an important clue for silver-ion selectivity by N. Judging from the calculation, we revealed that the silver ion transfer reaction and the dimerization reaction occur spontaneously. Moreover, both reactions are independent of the C5 ligand in N so that the deprotonation reaction, which is the first step of this scheme, plays a key role in forming the [N-Ag(2)-N] pairing. 相似文献
103.
104.
Kinetically protected 2‐silyl‐1,3‐diphosphapropenes that bear both sp2‐ and sp3‐type phosphorus atoms were employed in the preparation of gold complexes. The structural properties of the 1,3‐diphosphapropene digold(I) complexes were characterized by spectroscopic and crystallographic analyses, which revealed unique aurophilic interactions and conformational properties of the ligand. The 2‐silyl‐1,3‐diphosphapropene‐bis(chlorogold) complexes catalyzed cycloisomerization reactions of 1,6‐enyne derivatives even in the absence of silver co‐catalyst, and were able to be recovered after the reaction. The catalytic activity of the digold complexes primarily depended on the sp2‐type phosphorus atom and the silyl group, and could be tuned by the sp3‐phosphino group. Additionally, results on the catalytic activity of the digold complex in the presence and absence of silver salts showed considerable differences. 相似文献
105.
Journal of Theoretical Probability - We study multivariate stochastic recurrence equations (SREs) with triangular matrices. If coefficient matrices of SREs have strictly positive entries, the... 相似文献
106.
H. Ellinger Siemens Halske A. -G. H. v. Uslar R. Sewig E. Hoffmann M. Matsui Mitarbeiter A. del Campo F. Burriel L. G. Escolar und W. G. Exton 《Fresenius' Journal of Analytical Chemistry》1939,116(3-4):142-143
Ohne Zusammenfassung 相似文献
107.
Yusuke Imai Atsushi Terahara Keitaro Matsui Nobuhiko Ueno 《European Polymer Journal》2009,45(3):630-3519
Transparent organic-inorganic nanocomposites were successfully synthesized from sulfonic acid-modified poly(bisphenol A carbonate) (SPC) and TiO2 or ZrO2 nanoparticles. The dispersibility of nanoparticles was significantly improved by both the surface treatment of nanoparticles with phosphoric acid 2-ethylhexyl esters (PAEH) and the introduction of a sulfonic acid moiety into the PC chain. It was found that in some cases, crystallization of the matrix caused a reduction in transparency. Efficient dispersion of nanoparticles and the absence of crystallization resulted in highly transparent nanocomposites with up to 42 wt% TiO2 and 50 wt% ZrO2 nanoparticles. The refractive indices of the nanocomposites based on SPC increased with the increasing amount of nanoparticles. Theoretical equation based on Maxwell-Garnett effective medium theory provided reasonably close estimation of the refractive indices to the experimentally observed values. The prepared nanocomposites had lower thermal stability than the host matrix polymers. 相似文献
108.
We show how the Landau–Pomeranchuk–Migdal effect on photon production rates in a quark–gluon plasma can be derived via the usual Boltzmann equation. To do this, we first derive the electromagnetic polarization tensor using linear response theory, and then formulate the Boltzmann equation including the collisions mediated by soft gluon exchanges. We then identify the resulting expression for the production rate with that obtained by the field-theoretic formalism recently proposed by Arnold, Moore and Yaffe. To illustrate the LPM effect we solve the Boltzmann equation in the diffusion approximation. 相似文献
109.
Ryosuke Matsui Erina Niijima Tomomi Imai Hiroyuki Kobayashi Akiko Hori Azusa Sato Yuko Nakamura Osamu Kitagawa 《Molecules (Basel, Switzerland)》2022,27(7)
The halogen bond has been widely used as an important supramolecular tool in various research areas. However, there are relatively few studies on halogen bonding related to molecular chirality. 3-(2-Halophenyl)quinazoline-4-thione derivatives have stable atropisomeric structures due to the rotational restriction around an N-C single bond. In X-ray single crystal structures of the racemic and optically pure N-C axially chiral quinazoline-4-thiones, we found that different types of intermolecular halogen bonds (C=S⋯X) are formed. That is, in the racemic crystals, the intermolecular halogen bond between the ortho-halogen atom and sulfur atom was found to be oriented in a periplanar conformation toward the thiocarbonyl plane, leading to a syndiotactic zig-zag array. On the other hand, the halogen bond in the enantiomerically pure crystals was oriented orthogonally toward the thiocarbonyl plane, resulting in the formation of a homochiral dimer. These results indicate that the corresponding racemic and optically pure forms in chiral molecules are expected to display different halogen bonding properties, respectively, and should be separately studied as different chemical entities. 相似文献
110.