全文获取类型
收费全文 | 1066篇 |
免费 | 63篇 |
国内免费 | 7篇 |
专业分类
化学 | 914篇 |
晶体学 | 9篇 |
力学 | 5篇 |
数学 | 38篇 |
物理学 | 170篇 |
出版年
2023年 | 15篇 |
2022年 | 15篇 |
2021年 | 18篇 |
2020年 | 26篇 |
2019年 | 29篇 |
2018年 | 19篇 |
2017年 | 21篇 |
2016年 | 38篇 |
2015年 | 34篇 |
2014年 | 53篇 |
2013年 | 66篇 |
2012年 | 73篇 |
2011年 | 77篇 |
2010年 | 41篇 |
2009年 | 42篇 |
2008年 | 68篇 |
2007年 | 49篇 |
2006年 | 58篇 |
2005年 | 36篇 |
2004年 | 37篇 |
2003年 | 23篇 |
2002年 | 21篇 |
2001年 | 24篇 |
2000年 | 25篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 11篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 4篇 |
1985年 | 13篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1966年 | 4篇 |
排序方式: 共有1136条查询结果,搜索用时 0 毫秒
971.
Katagiri T Tsurugi H Satoh T Miura M 《Chemical communications (Cambridge, England)》2008,(29):3405-3407
Cross-dimerization of various terminal alkynes with different bulky terminal alkynes such as triisopropylsilylacetylene and 1-trimethylsilyloxy-1,1-diphenyl-2-propyne efficiently proceeds in the presence of a rhodium catalyst system to produce the corresponding (E)-enynes with high regio- and stereoselectivity. 相似文献
972.
973.
974.
975.
We have investigated the aggregate structures of a colloidal dispersion composed of ferromagnetic disk-like particles with
a magnetic moment normal to the particle axis at the particle center, by means of 3D Monte Carlo simulations. Such disk-like
particles have been modeled as a circular disk-like particle with the side section shape of spherocylinder. We have attempted
to clarify the influences of the magnetic field strength, magnetic interactions between particles and volumetric fraction
of particles. In order to discuss quantitatively the aggregate structures of clusters, we have focused on the radial distribution
and orientational pair correlation functions, etc. For no applied magnetic field cases, long column-like clusters come to
be formed with increasing magnetic particle–particle interactions. The internal structures of these clusters clearly show
that the particles incline in a certain direction and their magnetic moments alternate in direction between the neighboring
particles in the clusters. For applied magnetic field cases, the magnetic moment of each particle inclines in the magnetic
field direction and therefore the column-like clusters are not formed straightforwardly. If the magnetic field is much stronger
than magnetic particle–particle interactions, the particles do not have a tendency to form the clusters. As the influence
of magnetic particle–particle interactions is significantly strong, thick chain-like clusters or column-like clusters or brick-wall-like
clusters come to be formed along the magnetic field direction. 相似文献
976.
Sawai K Takano Y Izquierdo M Filippone S Martín N Slanina Z Mizorogi N Waelchli M Tsuchiya T Akasaka T Nagase S 《Journal of the American Chemical Society》2011,133(44):17746-17752
Endohedral metallofullerenes are promising materials in biomedical and material sciences. In particular, they are of interest as agents for magnetic resonance imaging (MRI), photovoltaic devices, and semimetallic components. The synthesis of chiral endofullerenes represents one step further in the potential use of these carbon allotropes; however, this step has not been addressed so far. In this regard, enantiopure endofullerenes are expected to open new avenues in fields in which chirality is a key issue. Here, the synthesis and characterization of the first chiral endohedral metallofullerenes, namely, chiral bis-adducts of La@C(72), are reported. Eight optically active isomers were obtained by enantioselective 1,3-dipolar cycloaddition of a N-metalated azomethine ylide onto a non-isolated-pentagon rule metallofullerene derivative, La@C(72)(C(6)H(3)Cl(2)), catalyzed by a copper chiral complex. The chiral bis-adducts of La@C(72), isolated by nonchiral HPLC, showed optical purities as high as 98% as revealed by the remarkable positive or negative Cotton effects observed in the circular dichroic spectra. 相似文献
977.
Satoh H Manabe S Ito Y Lüthi HP Laino T Hutter J 《Journal of the American Chemical Society》2011,133(14):5610-5619
An endocyclic pathway is proposed as a reaction mechanism for the anomerization from the β (1,2-trans) to the α (1,2-cis) configuration observed in glycosides carrying 2,3-trans cyclic protecting groups. This reaction occurs in the presence of a weak Lewis or Br?nsted acid, while endocyclic cleavage (endocleavage) in typical glycosides was observed only when mediated by protic media or strong Lewis acids. To rationalize the behavior of this class of compounds, the reaction mechanism and the promoting factors of the endocleavage are investigated using quantum-mechanical (QM) calculations and experimental studies. We examine anomerization reactions of thioglycosides carrying 2,3-trans cyclic protecting groups, employing boron trifluoride etherate (BF(3)·OEt(2)) as a Lewis acid. The estimated theoretical reactivity, based on a simple model to predict transition state (TS) energies from the strain caused by the fused rings, is very close to the TS energies calculated by the TS search along the C1-C2 bond rotation after the endo C-O bond breaking. Excellent agreement is found between the predicted TS energies and the experimental reactivity ranking. The series of calculations and experiments strongly supports the predominance of the endocyclic rather than the exocyclic mechanism. Furthermore, these investigations suggest that the inner strain is the primary factor enhancing the endocleavage reaction. The effect of the cyclic protecting group in restricting the pyranoside ring to a (4)C(1) conformation, extensively discussed in conjunction with the stereoelectronic effect theory, is shown to be a secondary factor. 相似文献
978.
Yu Miura Takeshi Kaneko Kotaro Satoh Dr. Masami Kamigaito Prof. Hiroshi Jinnai Prof. Yoshio Okamoto Prof. 《化学:亚洲杂志》2007,2(5):662-672
Novel copolymers with controlled architectures can function as new building blocks for well‐defined nanostructures on the basis of microphase separation, unlike conventional ABA triblock copolymers. A series of well‐defined AxBAx‐type block–graft copolymers consisting of soft middle segments (dodecyl methacrylate (DMA)) and hard outer graft chains (styrene (St)) were synthesized by ruthenium‐catalyzed living radical block and graft polymerization. NMR spectroscopy and size‐exclusion chromatography combined with multiangle laser light scattering confirmed the well‐defined structure of the AxBAx block–graft copolymers with backbones and graft chains of controlled lengths. Transmission electron microscopy and transmission electron microtomography revealed a series of morphologies for the copolymers. Morphological changes were observed from PSt “honeycomb” cylinders to lamellae and poly(DMA) cylinders with increasing PSt‐graft content, whereby the phase diagram was shifted significantly to lower volume fractions of the larger‐number component (St) relative to those of the corresponding ABA triblock copolymers. More specifically, poly(DMA) cylinders were observed even before the St content reached 50 wt %. The AxBAx and ABA copolymers with 17–30 wt % of St exhibited characteristics of a thermoplastic elastomer with tensile strengths of 1–6 MPa and elongations at break of 70–300 %. These mechanical properties can be related well to the microphase structures of the AxBAx and ABA copolymers. 相似文献
979.
980.
Prof. Dr. Naoki Kanoh Shunya Itoh Kohei Fujita Dr. Kohei Sakanishi Ryosuke Sugiyama Yuta Terajima Prof. Dr. Yoshiharu Iwabuchi Prof. Dr. Shinichi Nishimura Prof. Dr. Hideaki Kakeya 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(25):8586-8595
Heronamides are biosynthetically related metabolites isolated from marine‐derived actinomycetes. Heronamide C shows potent antifungal activity by targeting membrane phospholipids possessing saturated hydrocarbon chains with as‐yet‐unrevealed modes of action. In spite of their curious hypothesized biosynthesis and fascinating biological activities, there have been conflicts in regard to the reported stereochemistries of heronamides. Here, we describe the asymmetric total synthesis of the originally proposed and revised structures of heronamide C, which unambiguously confirmed the chemical structure of this molecule. We also demonstrated nonenzymatic synthesis of heronamides A and B from heronamide C, which not only proved the postulated biosynthesis, but also confirmed the correct structures of heronamides A and B. Investigation of the structure–activity relationship of synthetic and natural heronamides revealed the importance of both long‐range stereochemical communication and the 20‐membered macrolactam ring for the biological activity of these compounds. 相似文献