全文获取类型
收费全文 | 1265篇 |
免费 | 77篇 |
国内免费 | 3篇 |
专业分类
化学 | 1014篇 |
晶体学 | 16篇 |
力学 | 18篇 |
数学 | 77篇 |
物理学 | 220篇 |
出版年
2023年 | 11篇 |
2022年 | 14篇 |
2021年 | 6篇 |
2020年 | 20篇 |
2019年 | 24篇 |
2018年 | 15篇 |
2017年 | 9篇 |
2016年 | 46篇 |
2015年 | 28篇 |
2014年 | 41篇 |
2013年 | 57篇 |
2012年 | 84篇 |
2011年 | 121篇 |
2010年 | 49篇 |
2009年 | 43篇 |
2008年 | 105篇 |
2007年 | 66篇 |
2006年 | 81篇 |
2005年 | 80篇 |
2004年 | 76篇 |
2003年 | 70篇 |
2002年 | 50篇 |
2001年 | 19篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 12篇 |
1997年 | 16篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 13篇 |
1993年 | 6篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有1345条查询结果,搜索用时 78 毫秒
71.
Direct Synthesis of 1,4‐Diols from Alkenes by Iron‐Catalyzed Aerobic Hydration and C?H Hydroxylation
Takuma Hashimoto Daisuke Hirose Tsuyoshi Taniguchi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(10):2768-2772
Various 1,4‐diols are easily accessible from alkenes through iron‐catalyzed aerobic hydration. The reaction system consists of a user‐friendly iron phthalocyanine complex, sodium borohydride, and molecular oxygen. Furthermore, the effect of additional ligands on the iron complex was examined for a model reaction. The second hydroxy group is installed by direct C(sp3) H oxygenation, which is based on a [1,5] hydrogen shift process of a transient alkoxy radical that is formed by formal hydration of the olefin. 相似文献
72.
Dr. Raphaël Nougué Dr. Shintaro Takahashi Dr. Aymeric Dajnak Dr. Eddy Maerten Dr. Antoine Baceiredo Dr. Nathalie Saffon-Merceron Prof. Vicenç Branchadell Dr. Tsuyoshi Kato 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202202037
Several base-stabilized silyliumylidene ions ( 2 and 3 ) with different ligands were synthesized. Their behaviour appeared strongly dependent on the nature of ligand. Indeed, in contrast to the poorly reactive silyliumylidene ions 3 c,d stabilized by strongly donating ligands (DMAP, NHC), the silylene- and sulfide-supported one ( 2-H and 3 a ) exhibits higher reactivity toward various small molecules. Furthermore, their capability to successively activate multiple small molecules was clearly demonstrated by processes involving successive reactions with silane/formamide, CO2 and H2. Moreover, HBPin adduct of 3 a ( 8-C ) catalyzes the hydroboration of pyridine. Of particular interest, silylene-supported silyliumylidene complex 2-H is one of the rare species able to activate two H2 molecules. 相似文献
73.
The aberration theory applied to co-axial optical systems is extended to off-axial systems, for which third-order aberration coefficients are considered. The derived aberrations are analyzed using three-dimensional ray bundles, spot diagrams, and image charts, and classified in relation to the system symmetry. This theory is very useful for optical designers, allowing them to clarify the relationship between the structures of off-axial optical systems and the corresponding off-axial aberrations. 相似文献
74.
75.
Chiral Phosphoric‐Acid‐Catalyzed Transfer Hydrogenation of Ethyl Ketimine Derivatives by Using Benzothiazoline
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Kodai Saito Kosaku Horiguchi Yukihiro Shibata Prof. Dr. Masahiro Yamanaka Prof. Takahiko Akiyama 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7616-7620
Chiral phosphoric acid catalyzed transfer hydrogenation of ketimines derived from propiophenone derivatives and reductive amination of alkyl ethyl ketone derivatives were extensively examined in the presence of two representative hydrogen donors. The excellent enantioselective transfer hydrogenation was achieved by use of benzothiazoline as a hydrogen donor. The theoretical studies elucidated that the unsymmetrical structure of benzothiazoline plays an important role in high enantioselective hydrogenation. 相似文献
76.
Mami Miyairi Tsuyoshi Taniguchi Tatsuya Nishimura Katsuhiro Maeda 《Angewandte Chemie (International ed. in English)》2020,59(35):14772-14780
An alternative reaction mechanism of the polymerization of diphenylacetylelnes using a catalytic system composed of tungsten(VI) chloride and tetraphenyltin has been proposed through the optimization of reaction conditions and investigation of the effect of the electronic nature of diphenylacetylene monomers on the polymerizability. The detailed structures of the polymers have been suggested by mass spectrometric analysis of the obtained polymers and oligomers, which suggested that a phenyl group of tetraphenyltin has been introduced to an initiating end of the polymer chain. Mass spectrometric analysis also provided information about the termination processes of the polymerization. The experimental results strongly suggested that the polymerization of diphenylacetylenes using tungsten(VI) chloride and tetraphenyltin proceeds through a migratory insertion mechanism rather than the long‐accepted metathesis mechanism. 相似文献
77.
Noboru Oyama Takeo Ohsaka Takeyoshi Okajima Tomoaki Hirokawa Tsuyoshi Maruyama Yukio Ohnuki 《Journal of Electroanalytical Chemistry》1985,187(1):79-96
Liquid crystalline/polymer composite membrane-coated electrodes were prepared by casting a 1,2-dichloroethane solution of N-(4-ethoxybenzylidene)-4′-n-butylaniline (EBBA) and polycarbonate (PC) on an electrode surface. The temperature-dependence of the permeability of the EBBA/PC composite membrane on electrodes to Fe(CN)3?6 ion as a solution-phase redox ion was investigated by means of hydrodynamic voltammetry at a rotating disk electrode. The permeability changed with temperature over the range of the crystalline-nematic-phase transition temperature of EBBA. It is demonstrated that the observed temperature-dependence of the permeability reflects the thermotropic properties of EBBA in the EBBA/PC composite membrane. Furthermore, the dependence of the limiting current of the steady-state current-potential curves for the reduction of Fe(CN)—6 at the EBBA/PC composite membrane-coated electrode upon the membrane thickness, the blend ratio of EBBA and PC and the concentration of Fe(CN)3?6 in a bulk solution was examined in order to understand the transport process of Fe(CN)?36 through the EBBA/PC composite membrane from the membrane/solution interface to the electrode/membrane interface. The transport process of Fe(CN)3?6 within the membrane was found to obey Fick's Law. 相似文献
78.
Murahashi T 《The Analyst》2003,128(6):611-615
A comprehensive two-dimensional HPLC system for the separation of polycyclic aromatic hydrocarbons was developed using a pentabromobenzyl column as the first dimension and two short monolithic C18 columns as the second dimension. The primary column and two secondary columns were coupled by a 10-port 2-position valve. The effluent from the first dimension was repetitively injected into the second dimension every 12 s. Due to its resolution, this technique is a powerful tool for the separation of polycyclic aromatic hydrocarbons in a complex matrix such as environmental samples. 相似文献
79.
Tsuyoshi Satoh Takayuki Kuramoto Shingo Ogata Hiroyuki Watanabe Takahito Saitou Makoto Tadokoro 《Tetrahedron: Asymmetry》2010,21(1):1-5
Treatment of enantiomerically pure 1-chlorovinyl p-tolyl sulfoxides, derived from cyclic ketones and (R)-chloromethyl p-tolyl sulfoxide, with the lithium enolate of tert-butyl carboxylates gave adducts in quantitative yields as single diastereomers. The adducts were treated with i-PrMgCl in toluene to afford optically active bicyclo[n.1.0]alkanes bearing a tert-butyl carboxylate moiety in up to 99% enantiomeric excess through the enantioselective 1,3-CH insertion reaction of the generated chiral magnesium carbenoids. This is the first example of the enantioselective 1,3-CH insertion reaction of magnesium carbenoid. 相似文献