全文获取类型
收费全文 | 1891篇 |
免费 | 97篇 |
国内免费 | 6篇 |
专业分类
化学 | 1548篇 |
晶体学 | 21篇 |
力学 | 13篇 |
数学 | 92篇 |
物理学 | 320篇 |
出版年
2023年 | 11篇 |
2022年 | 13篇 |
2021年 | 28篇 |
2020年 | 33篇 |
2019年 | 43篇 |
2018年 | 28篇 |
2017年 | 27篇 |
2016年 | 63篇 |
2015年 | 55篇 |
2014年 | 87篇 |
2013年 | 95篇 |
2012年 | 140篇 |
2011年 | 148篇 |
2010年 | 69篇 |
2009年 | 69篇 |
2008年 | 154篇 |
2007年 | 144篇 |
2006年 | 128篇 |
2005年 | 104篇 |
2004年 | 98篇 |
2003年 | 76篇 |
2002年 | 66篇 |
2001年 | 20篇 |
2000年 | 8篇 |
1999年 | 17篇 |
1998年 | 15篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 10篇 |
1975年 | 4篇 |
1974年 | 10篇 |
1973年 | 8篇 |
排序方式: 共有1994条查询结果,搜索用时 109 毫秒
141.
Takashi Yoshida Rong Lu Shuqin Han Kazuyuki Hattori Takahiro Katsuta Kei‐Ichi Takeda Kazutoshi Sugimoto Masamitsu Funaoka 《Journal of polymer science. Part A, Polymer chemistry》2009,47(3):824-832
For the synthesis of a new biologically functional polymer from a natural resource by an environment‐friendly method, the laccase‐catalyzed polymerization of a lignin‐based macromonomer, lignocatechol, was carried out for the first time in ethanol–phosphate buffer solvent system to give crosslinked polymers in good yields. Lignocatechol was prepared by the phase separation system of lignin and catechol in aqueous sulfuric acid. The copolymerization was also performed with urushiol to afford the corresponding copolymers in high yields. The polymerization mechanism was estimated by the IR and pyrolysis GC‐MS measurements, suggesting that the polymerization proceeded mainly at the catechol ring through a quinone radical intermediate. The thermal properties were measured by the DSC, TG, and TMA analyses, indicating that the polymers had high thermal stabilities because of the crosslinked structures. In addition, it was found that the resulting polymers had the affinity of bovine serum albumin (BSA) and glucoamylase. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 824–832, 2009 相似文献
142.
We have determined the orientational distribution of cyano-substituted side chains of a rubbed polyimide film, and a liquid crystal monolayer adsorbed on the film, by means of optical second harmonic generation. With the orientational distribution of a main chain that was measured in a previous study by means of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, we have obtained the correlation of all the orientational distributions contributing to the alignment of LC molecules, i.e. pretilt angle. We find that the side chain plays a role in increasing the pretilt angle, but in the case of rubbing strength dependence, the main chain has stronger correlation with the pretilt angle than has the side chain. 相似文献
143.
144.
145.
Takahiro Matsumoto Seikou Nakamura Naoto Kojima Tomohiro Hasei Masayuki Yamashita Tetsushi Watanabe Hisashi Matsuda 《Tetrahedron letters》2017,58(36):3574-3578
From the methanolic extract of the aerial parts of Isodon japonicus, two new ent-kaurane diterpenes, isodonterpenes I and II, were isolated together with 10 known diterpenes. Their chemical structures were elucidated on the basis of chemical and physicochemical evidence. The absolute configuration of isodonterpene I was elucidated by Cu-Kα X-ray crystallographic analysis. Antimutagenic activities of the major diterpenes were evaluated by the Ames test. This study represents the first evaluation of the antimutagenic activities of ent-kaurane diterpenes. 相似文献
146.
Cross-benzoin condensation catalyzed by NHC, prepared from chiral triazolium salts bearing a pyridine ring, afforded α-hydroxy ketones with reasonable chemical yields and enantioselectivities. A wide range of aliphatic and aromatic aldehydes were successfully used in the reaction. 相似文献
147.
Sakaue T 《Physical review letters》2011,106(16):167802
We propose a simple mean-field theory for the structure of ring polymer melts. By combining the notion of topological volume fraction and a classical van der Waals theory of fluids, we take into account many-body effects of topological origin in dense systems. We predict that although the compact statistics with the Flory exponent ν=1/3 is realized for very long chains, most practical cases fall into the crossover regime with the apparent exponent ν?2/5 during which the system evolves toward a topological dense-packed limit. 相似文献
148.
We demonstrate that the spin Hall effect in a thin film with strong spin-orbit scattering can excite magnetic precession in an adjacent ferromagnetic film. The flow of alternating current through a Pt/NiFe bilayer generates an oscillating transverse spin current in the Pt, and the resultant transfer of spin angular momentum to the NiFe induces ferromagnetic resonance dynamics. The Oersted field from the current also generates a ferromagnetic resonance signal but with a different symmetry. The ratio of these two signals allows a quantitative determination of the spin current and the spin Hall angle. 相似文献
149.
In the previous work, it was shown that, in supersymmetric (matrix) discretized quantum mechanics, inclusion of an external field twisting the boundary condition of fermions enables us to discuss spontaneous breaking of supersymmetry (SUSY) in the path-integral formalism in a well-defined way. In the present work, we continue investigating the same systems from the points of view of localization and Nicolai mapping. The localization is studied by changing of integration variables in the path integral, which is applicable whether or not SUSY is explicitly broken. We examine in detail how the integrand of the partition function with respect to the integral over the auxiliary field behaves as the auxiliary field vanishes, which clarifies a mechanism of the localization. In SUSY matrix models, we obtain a matrix-model generalization of the localization formula. In terms of eigenvalues of matrix variables, we observe that eigenvalues' dynamics is governed by balance of attractive force from the localization and repulsive force from the Vandermonde determinant. The approach of the Nicolai mapping works even in the presence of the external field. It enables us to compute the partition function of SUSY matrix models for finite N (N is the rank of matrices) with arbitrary superpotential at least in the leading nontrivial order of an expansion with respect to the small external field. We confirm the restoration of SUSY in the large-N limit of a SUSY matrix model with a double-well scalar potential observed in the previous work. 相似文献
150.
Takahiro Nakae Ryuji Ohnishi Yoshiharu Kitahata Tatsuya Soukawa Hisako Sato Shigeki Mori Tetsuo Okujima Hidemitsu Uno Hiroshi Sakaguchi 《Tetrahedron letters》2012,53(13):1617-1619
6,13-Diiododibenzo[a,h]anthracene and 5,8-diiodopicene were synthesized by AuCl-catalyzed double cyclization. The highly selective reaction yielded a new class of peri-halogenated fused aromatics. 相似文献