全文获取类型
收费全文 | 1254篇 |
免费 | 64篇 |
国内免费 | 4篇 |
专业分类
化学 | 999篇 |
晶体学 | 11篇 |
力学 | 15篇 |
数学 | 61篇 |
物理学 | 236篇 |
出版年
2023年 | 8篇 |
2022年 | 9篇 |
2021年 | 17篇 |
2020年 | 22篇 |
2019年 | 30篇 |
2018年 | 23篇 |
2017年 | 15篇 |
2016年 | 34篇 |
2015年 | 35篇 |
2014年 | 38篇 |
2013年 | 47篇 |
2012年 | 91篇 |
2011年 | 109篇 |
2010年 | 61篇 |
2009年 | 50篇 |
2008年 | 56篇 |
2007年 | 87篇 |
2006年 | 88篇 |
2005年 | 77篇 |
2004年 | 56篇 |
2003年 | 67篇 |
2002年 | 68篇 |
2001年 | 20篇 |
2000年 | 27篇 |
1999年 | 18篇 |
1998年 | 8篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 13篇 |
1994年 | 15篇 |
1993年 | 9篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1968年 | 4篇 |
排序方式: 共有1322条查询结果,搜索用时 78 毫秒
81.
82.
Previously, O-selective phosphorylation on polymer supports in the N-unprotected phosphoramidite method could not be carried out because the amino groups of dA and dC have high reactivity toward tervalent phosphorus(III)-type phosphitylating reagents. In this paper, we developed a new coupling strategy named the "activated phosphite method" in which the phosphitylation is mediated by phosphite triester intermediates 1. Application of 1-hydroxybenzotriazole as the promoter to the solid-phase synthesis resulted in excellent O-selectivity of more than 99.7%. This O-selectivity was explained by the frontier molecular orbital interactions between the reactive intermediates and the nucleophiles such as the amino or hydroxyl groups of nucleosides. Furthermore, longer oligonucleotides were synthesized not only by a manual operation but also by a DNA synthesizer. The utility of our new method was demonstrated by the successful synthesis of a base-labile modified oligodeoxyribonucleotide having 4-N-acetyldeoxycytidine residues. Finally, DNA 20-mers containing dA or dC could be synthesized in good yields by use of a combined reagent of 6-trifluoromethyl-1-hydroxybenzotriazole and benzimidazolium triflate. 相似文献
83.
Hashimoto A Przybyl AK Linders JT Kodato S Tian X Deschamps JR George C Flippen-Anderson JL Jacobson AE Rice KC 《The Journal of organic chemistry》2004,69(16):5322-5327
The synthesis of the ortho- and para-e isomers in the oxide-bridged 5-phenylmorphan series of rigid tetracyclic compounds was accomplished via rac-5-(2-fluoro-5-nitrophenyl)-2-methyl-2-azabicyclo[3.3.1]nonan-9beta-ol ((+/-)-10), an intermediate containing an aromatic nitro-activated fluorine atom. The fluorine atom was used as the leaving group for the formation of the strained tetracyclic trans-fused 5,6-ring system in rac-(1alpha,4aalpha,9aalpha)-1,3,4,9a-tetrahydro-2-methyl-6-nitro-2H-1,4a-propanobenzofuro[2,3-c]pyridine ((+/-)-11), although preference for cis ring fusion during the formation of tricyclic tetra- and hexahydrodibenzofurans has been well-documented. Single-crystal X-ray crystallographic study of the desired para-e isomer ((+/-)-2), as well as of two intermediates in its synthesis, provided assurance of the correct structures. The e-isomers are among the last of the 12 oxide-bridged 5-phenylmorphans to be synthesized. We envisioned the syntheses of these rigid, tetracyclic compounds in order to determine the three-dimensional pattern of a ligand that would enable interaction with opioid receptors as agonists or antagonists. 相似文献
84.
Nakatsuji S Dobrosavljević V Tanasković D Minakata M Fukazawa H Maeno Y 《Physical review letters》2004,93(14):146401
By using a combination of detailed experimental studies and simple theoretical arguments, we identify a novel mechanism characterizing the hopping transport in the Mott insulating phase of Ca2-xSrxRuO4 near the metal-insulator transition. The hopping exponent alpha shows a systematic evolution from a value of alpha=1/2 deeper in the insulator to the conventional Mott value alpha=1/3 closer to the transition. This behavior, which we argue to be a universal feature of disordered Mott systems close to the metal-insulator transition, is shown to reflect the gradual emergence of disorder-induced localized electronic states populating the Mott-Hubbard gap. 相似文献
85.
We report the field-orientation dependent specific heat of the spin-triplet superconductor Sr2RuO4 under the magnetic field aligned parallel to the RuO2 planes with high accuracy. Below about 0.3 K, striking fourfold oscillations of the density of states reflecting the superconducting gap structure have been resolved for the first time. We also obtained strong evidence of multiband superconductivity and concluded that the superconducting gap in the active band, responsible for the superconducting instability, is modulated with a minimum along the [100] direction. 相似文献
86.
Ultraviolet second-harmonic generation in first-order periodically poled MgO:LiNbO3 is presented. Using a high-voltage multipulse application method, we fabricated a first-order nonlinear grating with a period of 1.8 microm and depth of approximately 150 microm over 10-mm interaction length in a 1-mm-thick MgO:LiNbO3 substrate. In a single-pass configuration, continuous-wave 30-mW UV light at 362.5 nm was generated for a fundamental power of 522 mW, corresponding to a normalized conversion efficiency of 11%/W. 相似文献
87.
Nomoto A Mitsuoka H Ozeki H Kobuke Y 《Chemical communications (Cambridge, England)》2003,(9):1074-1075
Introducing a porphyrin bearing electron acceptor onto a self-assembled monolayer (SAM) using a supramolecular method to form a hetero-dimer increased the photocurrent value compared with using porphyrin without an electron acceptor. 相似文献
88.
89.
Kanai M Yasumoto M Kuriyama Y Inomiya K Katsuhara Y Higashiyama K Ishii A 《Organic letters》2003,5(7):1007-1010
[reaction: see text] The highly regioselective hydrogenolysis of bis(alpha-methylbenzyl)amine derivatives proceeded with influence not from the electronic effect but from the steric effect of the trifluoromethyl substituent on the aromatic ring to provide a practical asymmetric synthesis of trifluoromethyl-substituted alpha-phenylethylamines. 相似文献
90.