全文获取类型
收费全文 | 823篇 |
免费 | 25篇 |
国内免费 | 4篇 |
专业分类
化学 | 473篇 |
晶体学 | 4篇 |
力学 | 28篇 |
数学 | 162篇 |
物理学 | 185篇 |
出版年
2022年 | 6篇 |
2021年 | 10篇 |
2020年 | 13篇 |
2019年 | 12篇 |
2018年 | 11篇 |
2017年 | 12篇 |
2016年 | 25篇 |
2015年 | 24篇 |
2014年 | 25篇 |
2013年 | 45篇 |
2012年 | 39篇 |
2011年 | 59篇 |
2010年 | 42篇 |
2009年 | 32篇 |
2008年 | 60篇 |
2007年 | 40篇 |
2006年 | 48篇 |
2005年 | 73篇 |
2004年 | 52篇 |
2003年 | 31篇 |
2002年 | 29篇 |
2001年 | 17篇 |
2000年 | 19篇 |
1999年 | 10篇 |
1998年 | 15篇 |
1997年 | 10篇 |
1996年 | 19篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有852条查询结果,搜索用时 0 毫秒
771.
The weak-link approach has been employed to synthesize a series of bimetallic Cu(I) macrocycles in high yield. Addition of phosphinoalkylether or -thioether ligands to [Cu(MeCN)4]PF6 produces "condensed" intermediates, [mu-(1,4-(PPh2CH2CH2X)2Y)2Cu2][PF6]2 (X = S, O; Y = C6H4, C6F4), containing strong P-Cu bonds and weaker O-Cu or S-Cu bonds. The weak bonds of these intermediates can be cleaved through ligand substitution reactions to generate macrocyclic structures, [mu-(1,4-(PPh2CH2CH2X)2Y)2(Z)nCu2][PF6]2 (X = S, O; Y = C6H4, C6F4; Z = pyridine, acetonitrile, diimines, isocyanide) in nearly quantitative yields. The incorporation of tetrahedral Cu(I) metal centers into these macrocycles provides a pathway to complexes that differ from analogous d8 square planar macrocycles generated via this approach in their increased air stability, small molecule reactivity, and ability to form multiple structural isomers. Solid-state structures, as determined by single-crystal X-ray diffraction studies, are presented for condensed intermediates and an open macrocycle 相似文献
772.
We have found that addition of a 2:1 ratio of the bulky ligand Li[N(mesityl)(SiMe(3))] to SnCl(2) yields Sn[N(mesityl)(SiMe(3))](2), which is found by X-ray crystallography to be monomeric in the solid state. Interestingly, the solid state structure of the stannylene exhibits a "minipocket" caused by the parallel arrangement of the phenyl rings. A 1:1 ratio of ligand to SnCl(2) affords the new chlorotin amide [Sn(mu-Cl)[N(mesityl)(SiMe(3))]](3), which adopts a unique trimeric structure in the solid state. The chairlike (Sn-Cl)(3) backbone shown here has not been seen previously in Sn-halide chemistry. 相似文献
773.
The reactions of the ligands N-methyldiethanol amine and N-ethyldiethanol amine (abbreviated H(2)mdea and H(2)edea, respectively) with [Mn(12)O(12)(O(2)CCH(3))(16)(H(2)O)(4)] yield novel dodecanuclear wheel-shaped products. The capability of the ligands H(2)mdea and H(2)edea to support wheel structures in metals other than Mn is demonstrated with the crystal structure of a new hexanuclear ferric wheel. 相似文献
774.
In this study, an inductively coupled plasma mass spectrometer (ICP-MS) was used for the inorganic chemical characterization of biological materials by direct injection. ICP-MS has the advantage of sub-nanogram/gram detection limits for most elements making it a sensitive tool for the detection and characterization of aerosolized biological material. Suspended, microgram-sized samples of Bacillus subtilis spores (BG), Bacillus subtilis vegetative cells (Bg), and Bacillus thuringiensis (Bt) were analyzed via direct injection and they exhibit unique chemical signatures reflecting the processing history of each organism. 相似文献
775.
Karl?SvozilEmail author Lev?B.?Levitin Tommaso?Toffoli Zachary?Walton 《International Journal of Theoretical Physics》2005,44(7):965-970
We consider a quantum gate, driven by a general time-dependent Hamiltonian, that complements the state of a qubit and then
adds to it an arbitrary phase shift. It is shown that the minimum operation time of the gate is
, where h is Planck's constant, E is the average over time of the quantum-mechanical average energy, and θ is the phase shift modulo π. 相似文献
776.
We present a preliminary series of clinical experiments showing that ultrasound modulation of light in tissues allows tissue properties to be determined well inside the tissue. In this series of clinical experiments the optical scattering coefficient determined by the optical technique is compared with the bone density obtained by dual x-ray absorption. A correlation of 0.84 (p = 0.005) was found for a limited number of patients, showing the potential of this technique for the assessment of osteoporosis. 相似文献
777.
Lev Vaidman 《Foundations of Physics》2003,33(3):491-510
Interaction-free measurements introduced by Elitzur and Vaidman [Found. Phys.
23, 987 (1993)] allow finding infinitely fragile objects without destroying them. Many experiments have been successfully performed showing that indeed, the original scheme and its modifications lead to reduction of the disturbance of the observed systems. However, there is a controversy about the validity of the term interaction-free for these experiments. Broad variety of such experiments are reviewed and the meaning of the interaction-free measurements is clarified. 相似文献
778.
Krishnan R Voo JK Riordan CG Zahkarov L Rheingold AL 《Journal of the American Chemical Society》2003,125(15):4422-4423
Reaction of the nickel metalloligands [EtN2S2]Ni (EtN2S2, N,N'-diethyl-3,7-diazanonane-1,9-dithiolate) or K2[Ni(phmi)] (phmi, N,N'-1,2-phenylenebis(2-sulfanyl-2-methylpropionamide)) with [Cu(CH3CN)4]BF4 yields polynuclear complexes in which two copper(I) ions are bridged by the nickel metalloligands. Alternatively, reaction with the Cu(I) source, [(PhTttBu)Cu] (PhTttBu, phenyltris((tert-butylthio)methyl)borate), generates discrete binuclear NiCu complexes that may serve as models of the acetyl coenzyme A synthase active site. The binuclear species react reversibly with CO via rupture of the thiolate bridges. 相似文献
779.
780.
The second author carried this work as part of his Ph.D. thesis research in Tel-Aviv University under the supervision of Professor Marcel Herzog. 相似文献