全文获取类型
收费全文 | 633篇 |
免费 | 18篇 |
国内免费 | 4篇 |
专业分类
化学 | 481篇 |
晶体学 | 4篇 |
力学 | 12篇 |
数学 | 42篇 |
物理学 | 116篇 |
出版年
2021年 | 6篇 |
2020年 | 3篇 |
2019年 | 10篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 8篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 25篇 |
2012年 | 39篇 |
2011年 | 38篇 |
2010年 | 23篇 |
2009年 | 26篇 |
2008年 | 29篇 |
2007年 | 37篇 |
2006年 | 36篇 |
2005年 | 42篇 |
2004年 | 27篇 |
2003年 | 33篇 |
2002年 | 20篇 |
2001年 | 17篇 |
2000年 | 26篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 12篇 |
1978年 | 2篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 2篇 |
排序方式: 共有655条查询结果,搜索用时 296 毫秒
51.
Ikuma N Tsue H Tsue N Shimono S Uchida Y Masaki K Matsuoka N Tamura R 《Organic letters》2005,7(9):1797-1800
[reaction: see text] Enantiomerically enriched samples of chiral cyclic nitroxides with a 4-hydroxyphenyl group on the stereogenic center bearing the NO radical group undergo unprecedented spontaneous racemization and/or epimerization in aprotic solvents, which can be well accounted for by the multistep equilibrations involving planar quinoid intermediates. 相似文献
52.
Nikitin A Ogasawara H Mann D Denecke R Zhang Z Dai H Cho K Nilsson A 《Physical review letters》2005,95(22):225507
Towards the development of a useful mechanism for hydrogen storage, we have studied the hydrogenation of single-walled carbon nanotubes with atomic hydrogen using core-level photoelectron spectroscopy and x-ray absorption spectroscopy. We find that atomic hydrogen creates C-H bonds with the carbon atoms in the nanotube walls, and such C-H bonds can be completely broken by heating to 600 degrees C. We demonstrate approximately 65 +/- 15 at % hydrogenation of carbon atoms in the single-walled carbon nanotubes, which is equivalent to 5.1 +/- 1.2 wt % hydrogen capacity. We also show that the hydrogenation is a reversible process. 相似文献
53.
Numao N Fujii H Fukazawa Y Hanagata N Tanaka K 《Chemical & pharmaceutical bulletin》2004,52(3):377-379
In the sequence Fourier analysis (SFA) of specific interactions such as those between fibroblast growth factors (FGFs)/FGF receptors (FGFRs), bone morphogenetic proteins (BMPs)/BMP receptors (BMPRs), or tumor repressor protein p53/mouse double minute 2 homolog (MDM2), the characteristic frequency peak(s) could be observed with the hydrophobic scale for 20 amino acids as well as 4 nucleotides as the physicochemical parameter, but not successfully with the absolute electronegativity scale. This result implies that these two independent scales should be appropriately selected in various specific ligand-protein interactions, though the critical difference has to be determined. 相似文献
54.
Brena B Nordlund D Odelius M Ogasawara H Nilsson A Pettersson LG 《Physical review letters》2004,93(14):148302
Using x-ray emission and photoemission spectroscopies to measure the occupied valence levels in a thin crystalline ice film, we resolve the ionization-induced dissociation of water in ice on a femtosecond time scale. Isotope substitution confirms proton transfer during the core-hole lifetime in spite of the nonresonant excitation. Through ab initio molecular dynamics on the core-ionized state, the dissociation and spectrum evolution are followed at femtosecond intervals. The theoretical simulations confirm the experimental analysis and allow for a detailed study of the dissociative reaction path. 相似文献
55.
Itami K Mitsudo K Fujita K Ohashi Y Yoshida J 《Journal of the American Chemical Society》2004,126(35):11058-11066
Some circumstantial evidence for the directing effect of the 2-pyridylsilyl group in the Ru-catalyzed intermolecular Pauson-Khand-type reaction (PKR) of alkenyl(2-pyridyl)silane, alkyne, and carbon monoxide has been provided. Most importantly, we have succeeded in isolating several monometallic Ru complexes relevant to the catalytic reaction: Ru(vinylsilane)(CO)(3) complexes and ruthenacyclopentene. While the stoichimetric reaction of the Ru(vinylsilane)(CO)(3) complex with an alkyne led to the formation of the corresponding cyclopentenone (PKR product) at 100 degrees C, the ruthenacyclopentene intermediate was quantitatively produced at 50 degrees C. This complex was also converted to a cyclopentenone upon heating at 100 degrees C. Moreover, it was also found that the Ru(vinylsilane)(CO)(3) complex and ruthenacyclopentene serve as catalysts in intermolecular PKR. 相似文献
56.
A volume change method for measuring crystal densities is described. It allows the densities of unstable hydrated crystals at room temperature to be determined, by measurements of volume changes during the solidification of aqueous solutions. NaCl x 2H2O, KCl, MgSO4 x 12H2O and K2HPO4 x 6H2O were measured by the method and their densities (SE) are 1.61+/-0.02, 1.99+/-0.05, 1.45+/-0.01 and 1.75+/-0.02 g ml(-1) respectively. Data of NaCl x 2H2O and KCl are in good agreement with the previously reported values. 相似文献
57.
[reaction: see text] The titanium catalyst, which was generated in situ from titanocene dichloride and 2 equiv of butyllithium, was found to catalyze hydrosilation of a variety of alkynes with excellent regio- and syn-selectivity. 相似文献
58.
[reaction in text] A diastereocontrolled route to the eight aldohexoses has been developed starting from a common cyclohexanoid chiral building block. 相似文献
59.
Kise T Ogasawara T Ashida M Tomioka Y Tokura Y Kuwata-Gonokami M 《Physical review letters》2000,84(9):1986-1989
We propose a measurement setup for detecting quantum noise over a wide frequency range using inelastic transitions in a tunable two-level system as a detector. The frequency-resolving detector consists of a double quantum dot which is capacitively coupled to the leads of a nearby mesoscopic conductor. The inelastic current through the double quantum dot is calculated in response to equilibrium and nonequilibrium current fluctuations in the nearby conductor, including zero-point fluctuations at very low temperatures. As a specific example, the fluctuations across a quantum point contact are discussed. 相似文献
60.
描述了如何使用蒙特卡罗方法评估产生在加速器屏蔽混凝土中的感生放射性. 使用EGS4程序模拟了NaI闪烁探测器测量屏蔽混凝土块表面剂量率时, 对于半径和厚度的响应. 结果发现,在屏蔽混凝土块半径和厚度分别达到40cm和30cm时, 表面剂量率达到饱和. 研究了东京大学SF回旋加速器北墙位置8和位置9的表面剂量率, 并和使用NaI闪烁探测器的测量结果进行了对比, 发现模拟和实验结果符合很好. 并且, 获得了表面剂量和表面感生放射性之间的转换系数, 对于60Co转换系数为0.90(Bq·g-1)·(μSv·h-1)-1, 对于152Eu转换系数为1.26(Bq·g-1)·(μSv·h-1)-1. 这样, 就可以通过NaI闪烁探测器表面剂量的测量结果简单评估加速器设备屏蔽混凝土中的感生放射性. 相似文献