全文获取类型
收费全文 | 1645篇 |
免费 | 91篇 |
国内免费 | 8篇 |
专业分类
化学 | 1374篇 |
晶体学 | 13篇 |
力学 | 18篇 |
数学 | 121篇 |
物理学 | 218篇 |
出版年
2024年 | 3篇 |
2023年 | 21篇 |
2022年 | 19篇 |
2021年 | 22篇 |
2020年 | 35篇 |
2019年 | 49篇 |
2018年 | 42篇 |
2017年 | 17篇 |
2016年 | 37篇 |
2015年 | 66篇 |
2014年 | 58篇 |
2013年 | 90篇 |
2012年 | 109篇 |
2011年 | 107篇 |
2010年 | 75篇 |
2009年 | 68篇 |
2008年 | 119篇 |
2007年 | 103篇 |
2006年 | 121篇 |
2005年 | 121篇 |
2004年 | 112篇 |
2003年 | 74篇 |
2002年 | 54篇 |
2001年 | 20篇 |
2000年 | 17篇 |
1999年 | 11篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1988年 | 5篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1964年 | 2篇 |
排序方式: 共有1744条查询结果,搜索用时 0 毫秒
991.
Minoru Ozeki Honoka Egawa Toshiki Takano Hideki Mizutani Narumi Yasuda Kenji Arimitsu Tetsuya Kajimoto Shinzo Hosoi Hiroki Iwasaki Naoto Kojima Manabu Node Masayuki Yamashita 《Tetrahedron》2017,73(15):2014-2021
A practical method for the synthesis of chiral β2,3-amino esters having various substituents was developed, which is characterized by an asymmetric Michael addition reaction of a chiral lithium amide with trisubstituted (E)-α,β-unsaturated esters. We found that a highly face-selective protonation occurred by the quick addition of water to the enolate intermediate derived from the Michael addition reaction to afford N-protected β2,3-amino esters in moderate to excellent yields. This finding was made possible by the facile preparation of geometrically pure trisubstituted (E)-α,β-unsaturated esters, which was established recently by our group. The subsequent deprotection of the amino group in the Michael adduct by using N-iodosuccinimide (NIS) efficiently provided β2,3-amino esters having various substituents. 相似文献
992.
Takuya Matsumoto Naoto Kojima Akinobu Akatsuka Takao Yamori Shingo Dan Hiroki Iwasaki Masayuki Yamashita 《Tetrahedron》2017,73(17):2359-2366
The convergent synthesis of thiophene-3-carboxamide analogues of annonaceous acetogenins was accomplished through the asymmetric alkynylation of a 2-formyl THF ring fragment with an alkyne having a thiophene ring as the key step. Eight stereoisomers of the THF ring moiety were synthesized by this convergent route and their antiproliferative activities against 39 human cancer cell lines were evaluated. It was revealed that derivatives having the threo configuration between C17–C18 positions showed more potent activities than the corresponding erythro ones. 相似文献
993.
Magnet Design by Integration of Layer and Chain Magnetic Systems in a π‐Stacked Pillared Layer Framework 下载免费PDF全文
Hiroki Fukunaga Prof. Dr. Hitoshi Miyasaka 《Angewandte Chemie (International ed. in English)》2015,54(2):569-573
The control of inter‐lattice magnetic interactions is a crucial issue when long‐range ordered magnets that are based on low‐dimensional magnetic frameworks are designed. A “pillared layer framework (PLF)” model could be an efficient system for this purpose. In this report, A magnet based on a π‐stacked PLF with a phase transition temperature of 82 K, which can be increased to 107 K by applying a pressure of 12.5 kbar, is rationally constructed. Two types of low‐dimensional magnetic framework systems, an electron donor/acceptor magnetic layer and a charge transfer [FeCp*2]+TCNQ.? columnar magnet ([FeCp*2]+=decamethylferrocenium; TCNQ=7,7,8,8‐tetracyano‐p‐quinodimethane), are integrated to fabricate the magnet. This synthetic strategy employing a combination of layers and chains is widely useful not only for magnet design, but also for the creation of multifunctional materials with pores and anisotropic frameworks. 相似文献
994.
995.
Catalytic Asymmetric Diels–Alder Reaction of Quinone Imine Ketals: A Site‐Divergent Approach 下载免费PDF全文
Dr. Takuya Hashimoto Hiroki Nakatsu Prof.Dr. Keiji Maruoka 《Angewandte Chemie (International ed. in English)》2015,54(15):4617-4621
The catalytic asymmetric Diels–Alder reaction of quinone imine ketals with diene carbamates catalyzed by axially chiral dicarboxylic acids is reported herein. A variety of primary and secondary alkyl‐substituted quinone derivatives which have not been applied in previous asymmetric quinone Diels–Alder reactions could be employed using this method. More importantly, we succeeded in developing a strategy to divert the reaction site in unsymmetrical 3‐alkyl quinone imine ketals from the inherently favored unsubstituted C?C bond to the disfavored alkyl‐substituted C?C bond. 相似文献
996.
Recyclable Ligands for the Non‐Enzymatic Dynamic Kinetic Resolution of Challenging α‐Amino Acids 下载免费PDF全文
Yong Nian Dr. Jiang Wang Dr. Shengbin Zhou Shuni Wang Dr. Hiroki Moriwaki Dr. Aki Kawashima Prof. Dr. Vadim A. Soloshonok Prof. Dr. Hong Liu 《Angewandte Chemie (International ed. in English)》2015,54(44):12918-12922
Structurally simple and inexpensive chiral tridentate ligands were employed for substantially advancing the purely chemical dynamic kinetic resolution (DKR) of unprotected racemic tailor‐made α‐amino acids (TM‐α‐AAs), enabling the first DKR of TM‐α‐AAs bearing tertiary alkyl chains as well as multiple unprotected functional groups. Owing to the operationally convenient conditions, virtually complete stereoselectivity, and full recyclability of the source of chirality, this method should find wide applications for the preparation of TM‐α‐AAs, especially on large scale. 相似文献
997.
Thermal convection and thermophoresis induced by mum-scale local heating are shown to elongate a single DNA molecule. An infrared laser used as a point heat source is converged into a dispersion solution of DNA molecules, which is observed under a fluorescent microscope. The thermal convection around the laser focus manifests as extensional flow for the long DNA chain. A simulation of thermal convection that reproduces the experimental condition provides numerical support for the stretching caused by thermal convection. This DNA elongation technique is a novel method for manipulating the intact single DNA molecules, and it can be applied to a "lab on a chip". 相似文献
998.
Toda R Hieda M Matsushita T Wada N Taniguchi J Ikegami H Inagaki S Fukushima Y 《Physical review letters》2007,99(25):255301
Superfluidity in one and three dimensions has been studied for 4He fluid films adsorbed in nanopores which are straight channels and three-dimensionally connected pores, respectively. We observed the superfluid in one and three dimensions where thermal phonon wavelengths are much longer than the channel diameter and the period of the pore connection, respectively, and found that the superfluid onset depends on the pore connection. In the straight channels, the observed superfluid density disappears at a temperature far below the heat capacity anomaly of the Ginzburg-Landau transition, while in the pores connected in three dimension, the adsorbed 4He films show an evident three-dimensional transition where the superfluid onset occurs at the heat capacity peak. 相似文献
999.
The quantum ferroelectric phase transition of 18O-exchanged SrTiO3 (x% exchanged SrTiO3 is abbreviated as STO18-x) was investigated by Raman scattering as a function of x. The result indicates the ideal soft mode-type quantum ferroelectric phase transition of STO18-x, where the 18O exchange enhances the softening of the soft mode by the suppression of quantum fluctuation. In the vicinity of the quantum critical point (x approximately xc=33%), the system results in the ferroelectric-paraelectric phase coexistence state, in clear contrast to the homogeneous ferroelectric phase in STO18-x, whose x is sufficiently larger than xc. Simultaneously, the softening of the soft mode becomes strongly rounded with the underdamped oscillation. The present result indicates that the sensitivity of the soft phonon vibration to the mass disorder is dramatically enhanced in the vicinity of the quantum critical point. 相似文献
1000.
Using the simple point charge/extended water model, we performed molecular dynamics simulations of homogeneous vapor-liquid nucleation at various values of temperature T and supersaturation S, from which the nucleation rate J, critical nucleus size n(*), and the cluster formation free energy DeltaG were derived. As well as providing lots of simulation data, the results were compared with theories on homogeneous nucleation, including the classical, semi-phenomenological, and scaled models, but none of these gave a satisfactory explanation for our results. It was found that two main factors made the theories fail: (1) The average cluster structure including the nonspherical shape and the core structure that is not like the bulk liquid and (2) the forward rate which is larger than assumed by the theories by about one order of magnitude. The quantitative evaluation of these factors is left for future investigations. 相似文献