全文获取类型
收费全文 | 1720篇 |
免费 | 53篇 |
国内免费 | 13篇 |
专业分类
化学 | 1300篇 |
晶体学 | 10篇 |
力学 | 41篇 |
综合类 | 1篇 |
数学 | 147篇 |
物理学 | 287篇 |
出版年
2022年 | 20篇 |
2021年 | 19篇 |
2020年 | 32篇 |
2019年 | 24篇 |
2018年 | 27篇 |
2017年 | 24篇 |
2016年 | 56篇 |
2015年 | 46篇 |
2014年 | 43篇 |
2013年 | 81篇 |
2012年 | 106篇 |
2011年 | 88篇 |
2010年 | 68篇 |
2009年 | 57篇 |
2008年 | 111篇 |
2007年 | 112篇 |
2006年 | 107篇 |
2005年 | 114篇 |
2004年 | 88篇 |
2003年 | 68篇 |
2002年 | 64篇 |
2001年 | 25篇 |
2000年 | 22篇 |
1999年 | 22篇 |
1998年 | 21篇 |
1997年 | 12篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1993年 | 10篇 |
1991年 | 10篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 18篇 |
1984年 | 19篇 |
1982年 | 21篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 25篇 |
1978年 | 13篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1974年 | 7篇 |
1972年 | 7篇 |
1970年 | 8篇 |
1969年 | 9篇 |
1968年 | 5篇 |
1967年 | 7篇 |
1966年 | 6篇 |
排序方式: 共有1786条查询结果,搜索用时 0 毫秒
91.
Palladium nanoparticles stabilized by a polyion complex composed of poly{4-chloromethylstyrene-co-(4-vinylbenzyl) tributylammonium chloride} and poly(acrylic acid) were easily recovered by filtration after pH treatment. The polyion complex stabilized palladium nanoparticles have high catalytic activity for the Suzuki and Heck reactions in water. 相似文献
92.
Isao Kadota Takayuki Kishi Yuka Fujisawa Yuji Yamagami Hiroyoshi Takamura 《Tetrahedron letters》2010,51(30):3960-5853
A convenient method for the stereoselective construction of angular methyl group of fuzed cyclic ethers is described. Reactions of mixed thioacetals with Me2Zn/Zn(OTf)2 afforded the corresponding methylated products in good yields. Various protective groups such as MOM ether, benzylidene acetal, TBS ether, and pivaloyl group were stable under the reaction conditions. 相似文献
93.
Bis(trifluoromethanesulfonyl)amide (TFSA), hexafluorophosphate (PF(6)(-)), and iodide salts of 1-ferrocenyl-3-alkylimidazolium were prepared and their thermal and physical properties, including the dependence on alkyl chain length (methyl-hexadecyl), were investigated. The TFSA salts were highly viscous ionic liquids with melting points around room temperature. 1-Ferrocenyl-4-methyltriazolium salts were also prepared for comparison. The ferrocenylimidazolium and ferrocenyltriazolium cations showed redox waves for both the ferrocenyl moiety and the azolium moiety and exhibited corresponding charge-transfer bands at around 330 nm, which were analyzed using the Marcus-Hush model. Crystal structure determinations at low temperature revealed that the PF(6) and iodide salts form layerlike structures composed of ionic layers of the charged moieties. The TFSA salt exhibited short hydrogen-bond-like intermolecular contacts between the hydrogen atoms of the cation and oxygen atoms of the anion. 相似文献
94.
Katsumi Katoh Shunsuke Ito Yuji Ogata Jun-ichi Kasamatsu Hiroshi Miya Masaaki Yamamoto Yuji Wada 《Journal of Thermal Analysis and Calorimetry》2010,99(1):159-164
In order to prevent the spontaneous ignition of nitrocellulose (NC), NC is stabilized by washing with industrial water in
its synthesis process. However, there is a possibility that the components in industrial water contribute to the thermal stability
of NC. In this way, the purpose of this study is to clarify the effect of industrial water components on the thermal stability
of NC. In experiments, a heat flux calorimeter was used to observe the thermal behavior of NC with the residue of vaporized
industrial water. The induction period of heat release of NC with 2-mass% residues was approximately 2–5 h shorter than that
of NC alone whose induction period was observed at 7 h. Those results indicate that the residue destabilized NC. On the other
hand, when the additive amount of the residue was increased, the induction period gradually increased as well. Based upon
these results, we assume that inorganic salts contributing to stabilization and destabilization competitively coexist in the
industrial water components. The same thermal analysis was performed on NC with CaCO3, CaSO4, CaCl, ZnSO4, NaCl, and CuCl. Those salts are predicted to exist in the industrial water. In the results, the induction period of NC with
2-mass% CaCO3 was approximately 15-h longer than that of NC alone, while the induction period with the inorganic salts CaSO4, CaCl, ZnSO4, NaCl, and CuCl was 4–5-h shorter. Therefore, when the industrial water components accumulate in NC, the destabilization
by inorganic salts such as CaSO4, CaCl, ZnSO4, NaCl, and CuCl and the stabilization by compounds such as CaCO3 are thought to countervail against each other. 相似文献
95.
Hatano Y Watanabe K Livshits A Busnyuk A Alimov V Nakamura Y Hashizume K 《The Journal of chemical physics》2007,127(20):204707
Nonmetallic impurities segregated onto metal surfaces are able to drastically decrease the chemical reactivity of metals. In the present paper, effects of bulk impurities on the reactivity of metallic surfaces were investigated in a wide temperature range on an example of the sticking of hydrogen molecules and atoms to Nb [polycrystalline, with mainly (100)] containing solute oxygen. At all the investigated surface temperatures, T(S) (300-1400 K), we found the bulk oxygen concentration C(O) to have a strong effect on the integral probability, alpha(H(2) ), of dissociative sticking of H(2) molecules followed by hydrogen solution in the metal lattice: alpha(H(2) ) monotonically decreased by orders of magnitude with increasing C(O) from 0.03 to 1.5 at. %. The sticking coefficient alpha(H(2) ) was found to depend on T(S) but not on the gas temperature. The effect of C(O) on alpha(H(2) ) is explained by the presence of oxygen-free sites (holes in coverage) serving as active centers of the surface reaction in the oxygen monolayer upon Nb. In contrast to H(2) molecules, H atoms were found to stick to, and be dissolved in, oxygen-covered Nb with a probability comparable to 1, depending neither on C(O) nor on T(S). This proves that, unlike H(2) molecules, H atoms do stick to be dissolved mainly through regular surface sites covered by oxygen and not through the holes in coverage. 相似文献
96.
Ishiuchi S Sakai M Tsuchida Y Takeda A Kawashima Y Dopfer O Müller-Dethlefs K Fujii M 《The Journal of chemical physics》2007,127(11):114307
IR spectra of phenol-Arn (PhOH-Arn) clusters with n=1 and 2 were measured in the neutral and cationic electronic ground states in order to determine the preferential intermolecular ligand binding motifs, hydrogen bonding (hydrophilic interaction) versus pi bonding (hydrophobic interaction). Analysis of the vibrational frequencies of the OH stretching motion, nuOH, observed in nanosecond IR spectra demonstrates that neutral PhOH-Ar and PhOH-Ar2 as well as cationic PhOH+-Ar have a pi-bound structure, in which the Ar atoms bind to the aromatic ring. In contrast, the PhOH+-Ar2 cluster cation is concluded to have a H-bound structure, in which one Ar atom is hydrogen-bonded to the OH group. This pi-->H binding site switching induced by ionization was directly monitored in real time by picosecond time-resolved IR spectroscopy. The pi-bound nuOH band is observed just after the ionization and disappears simultaneously with the appearance of the H-bound nuOH band. The analysis of the picosecond IR spectra demonstrates that (i) the pi-->H site switching is an elementary reaction with a time constant of approximately 7 ps, which is roughly independent of the available internal vibrational energy, (ii) the barrier for the isomerization reaction is rather low(<100 cm(-1)), (iii) both the position and the width of the H-bound nuOH band change with the delay time, and the time evolution of these spectral changes can be rationalized by intracluster vibrational energy redistribution occurring after the site switching. The observation of the ionization-induced switch from pi bonding to H bonding in the PhOH+-Ar2 cation corresponds to the first manifestation of an intermolecular isomerization reaction in a charged aggregate. 相似文献
97.
Masato Matsugi Masakazu Hasegawa Sachina Okamoto Yoshimi Ikeya Yuji Mori 《Tetrahedron letters》2007,48(23):4147-4150
A modified light-fluorous Mukaiyama reagent bearing a C8F17 tag was prepared and examined in ester and amide forming condensation reactions. Following the reactions, the desired product was effectively separated from the fluorous pyridone by-product using a simple fluorous solid phase extraction. 相似文献
98.
Cycloheptatrienes were obtained by the reaction of 2-substituted allylic alcohols with alkynes in the presence of catalytic amounts of palladium complexes and p-toluenesulfonic acid. 相似文献
99.
Highly Efficient Access to Both Geometric Isomers of Silyl Enol Ethers: Sequential 1,2‐Brook/Wittig Reactions 下载免费PDF全文
Prof. Dr. Yuji Matsuya Kentaro Wada Dr. Daishiro Minato Dr. Kenji Sugimoto 《Angewandte Chemie (International ed. in English)》2016,55(34):10079-10082
Novel sequential 1,2‐Brook/Wittig reactions were developed for the preparation of silyl enol ethers. This method enables highly selective preparation of both geometric isomers of glyoxylate silyl enol ethers, using aldehydes (E‐selective) and tosylimines (Z‐selective) as a Wittig electrophile. The salt‐free conditions of this reaction system are likely to be advantageous for switching the selectivity. The optimal reaction conditions and generality of the reaction were investigated, and plausible explanations for the observed selectivity were also discussed. 相似文献
100.
Dr. Kuirun Zhang Dr. Soonchul Kang Dr. Zi‐shuo Yao Kazusa Nakamura Dr. Takashi Yamamoto Prof. Dr. Yasuaki Einaga Nobuaki Azuma Dr. Yuji Miyazaki Prof. Dr. Motohiro Nakano Dr. Shinji Kanegawa Prof. Dr. Osamu Sato 《Angewandte Chemie (International ed. in English)》2016,55(20):6047-6050
Heterometallic Prussian blue analogues are known to exhibit thermally induced charge transfer, resulting in switching of optical and magnetic properties. However, charge‐transfer phase transitions have not been reported for the simplest FeFe cyanide‐bridged systems. A mixed‐valence FeII/FeIII cyanide‐bridged coordination polymer, {[Fe(Tp)(CN)3]2Fe(bpe)?5 H2O}n, which demonstrates a thermally induced charge‐transfer phase transition, is described. As a result of the charge transfer during this phase transition, the high‐spin state of the whole system does not change to a low‐spin state. This result is in contrast to FeCo cyanide‐bridged systems that exhibit charge‐transfer‐induced spin transitions. 相似文献