全文获取类型
收费全文 | 1273篇 |
免费 | 61篇 |
国内免费 | 10篇 |
专业分类
化学 | 868篇 |
晶体学 | 2篇 |
力学 | 21篇 |
数学 | 207篇 |
物理学 | 163篇 |
无线电 | 83篇 |
出版年
2023年 | 13篇 |
2022年 | 19篇 |
2021年 | 29篇 |
2020年 | 33篇 |
2019年 | 22篇 |
2018年 | 30篇 |
2017年 | 19篇 |
2016年 | 57篇 |
2015年 | 39篇 |
2014年 | 41篇 |
2013年 | 69篇 |
2012年 | 101篇 |
2011年 | 96篇 |
2010年 | 60篇 |
2009年 | 56篇 |
2008年 | 106篇 |
2007年 | 90篇 |
2006年 | 94篇 |
2005年 | 76篇 |
2004年 | 64篇 |
2003年 | 40篇 |
2002年 | 40篇 |
2001年 | 18篇 |
2000年 | 10篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 12篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1344条查询结果,搜索用时 15 毫秒
11.
Ignacio Gimeno Ainhoa Urtizberea Juan Romn-Roche David Zueco Agustín Camn Pablo J. Alonso Olivier Roubeau Fernando Luis 《Chemical science》2021,12(15):5621
We explore how to encode more than a qubit in vanadyl porphyrin molecules hosting a S = 1/2 electronic spin coupled to a I = 7/2 nuclear spin. The spin Hamiltonian and its parameters, as well as the spin dynamics, have been determined via a combination of electron paramagnetic resonance, heat capacity, magnetization and on-chip magnetic spectroscopy experiments performed on single crystals. We find low temperature spin coherence times of micro-seconds and spin relaxation times longer than a second. For sufficiently strong magnetic fields (B > 0.1 T, corresponding to resonance frequencies of 9–10 GHz) these properties make vanadyl porphyrin molecules suitable qubit realizations. The presence of multiple equispaced nuclear spin levels then merely provides 8 alternatives to define the ‘1’ and ‘0’ basis states. For lower magnetic fields (B < 0.1 T), and lower frequencies (<2 GHz), we find spectroscopic signatures of a sizeable electronuclear entanglement. This effect generates a larger set of allowed transitions between different electronuclear spin states and removes their degeneracies. Under these conditions, we show that each molecule fulfills the conditions to act as a universal 4-qubit processor or, equivalently, as a d = 16 qudit. These findings widen the catalogue of chemically designed systems able to implement non-trivial quantum functionalities, such as quantum simulations and, especially, quantum error correction at the molecular level.We show that a sizeable electronuclear entanglement of the S = 1/2 and I = 7/2 spins of a vanadyl porphyrin provides the conditions to act as a universal 4-qubit processor, and thus implement quantum error correction at the molecular level. 相似文献
12.
José M. Bartoloméa Jesús AlcázarJ.Ignacio Andrés Marcel De BruynJavier Fernández Encarna MatesanzKristof Van Emelen 《Tetrahedron letters》2003,44(47):8545-8548
The synthesis of a series of novel analogues of the 3-substituted-2,3-dihydro-1,4-dioxino[2,3-b]pyridine core, modified in the non-aromatic ring, is described. Due to the presence of a versatile hydroxymethyl group in their structure, these novel scaffolds are attractive intermediates for the preparation of potential new therapeutic agents. 相似文献
13.
The reactions of [Ru(3)(CO)(12)] with half equivalent of 2-amino-6-methylpyridine (H(2)ampy) or 2-aminopyridine (H(2)apy) in refluxing xylene give the hexanuclear products [Ru(6)(mu(3)-H)(2)(mu(5)-eta(2)-L)(mu-CO)(2)(CO)(14)] (L = ampy, 1; apy, 2). These reactions represent the first high-yield syntheses of hexanuclear complexes with a basal edge-bridged square pyramidal metallic skeleton. Five metal atoms of these complexes are bridged by the N-donor ligand in such a way that the edge-bridging metal atom is attached to the pyridine nitrogen, while the basal atoms of the square pyramid are capped by an imido fragment that arises from the activation of both N-H bonds of the NH(2) group. The reactive sites of these complexes in CO substitution reactions have been determined by studying the reactivity of 1 with triphenylphosphine. Two kinetically controlled monosubstitutions take place on the edge-bridging metal atom in positions cis to the pyridine nitrogen, leading to a mixture of two isomers of formula [Ru(6)(mu(3)-H)(2)(mu(5)-eta(2)-ampy)(mu-CO)(2)(CO)(13)(PPh(3))] (3 and 4). On heating at 80 degrees C, these monosubstituted isomers are transformed, via a dissociative pathway, into the product of thermodynamic control (5), which has the PPh(3) ligand on the apical Ru atom. The di- and trisubstituted derivatives [Ru(6)(mu(3)-H)(2)(mu(5)-eta(2)-ampy)(mu-CO)(2)(CO)(12)(PPh(3))(2)] (6) and [Ru(6)(mu(3)-H)(2)(mu(5)-eta(2)-ampy)(mu-CO)(2)(CO)(11)(PPh(3))(3)] (7) are stepwise formed from 3-5 and PPh(3). Compound 6 has the PPh(3) ligands on the edge-bridging and apical Ru atoms, and compound 7 has an additional PPh(3) ligand on an unbridged basal Ru atom. The compound [Ru(6)(mu(3)-H)(2)(mu(5)-eta(2)-ampy)(mu-CO)(2)(CO)(12)(mu-dppm)] (8), in which a basal and the apical Ru atoms are spanned by the dppm ligand, has been isolated from the reaction of 1 with bis(diphenylphosphino)methane. 相似文献
14.
Ignacio López-García Mateo Sánchez-Merlos Manuel Hernández-Córdoba 《Spectrochimica Acta Part B: Atomic Spectroscopy》1997,52(14):378-2092
A graphite furnace atomic absorption spectrometric procedure for the determination of mercury is presented, in which the samples are suspended in a solution containing hydrofluoric and nitric acids. Silver nitrate (4% m/v) and potassium permanganate (3%) are incorporated, in the order specified, and aliquots are directly introduced into the graphite furnace. A fast heating programme with no conventional pyrolysis step is used. The detection limit for mercury in a 125 mg ml−1 suspension is 0.1 μg g−1. Calibration is performed by using aqueous standards. The reliability of the procedure is proved by analysing certified reference materials. 相似文献
15.
Ignacio Bajo 《Monatshefte für Mathematik》1994,118(1-2):1-6
Let
be a complex Lie algebra,
its underlying real Lie algebra,
a real form of
and ·, · the euclidean product induced by the real part of an hermitian inner product on
. Let aut
be the Lie algebra of skew-symmetric derivations of
. We give necessary and sufficient conditions to ensure that aut
is composed of skew-hermitian derivations. As an application, we study holomorphy in large subgroups of isometries of Lie groups. 相似文献
16.
J. Ignacio Extremiana Aldana L. Javier Herná ndez Paricio M. Teresa Rivas Rodrí guez 《Proceedings of the American Mathematical Society》1996,124(11):3545-3553
For each integer , we give a distinct closed model category structure to the category of pointed spaces such that the corresponding localized category is equivalent to the standard homotopy category of -connected CW-complexes. The structure of closed model category given by Quillen to is based on maps which induce isomorphisms on all homotopy group functors and for any choice of base point. For each , the closed model category structure given here takes as weak equivalences those maps that for the given base point induce isomorphisms on for .
17.
den Brok MW Nuijen B Miranda E Floriano P Munt S Manzanares I Beijnen JH 《Journal of chromatography. A》2003,1020(2):251-258
ES-285 x HCl [(2S,3R)-2-amino-3-octadecanol hydrochloride] is a novel investigational anticancer agent, which has shown in vitro and in vivo cytotoxic activity against various tumor cell lines with selectivity for certain solid tumors. The pharmaceutical development of ES-285 x HCl warranted the availability of an assay for the quantification and purity determination of ES-285 x HCl active pharmaceutical ingredient (API) and its pharmaceutical dosage form. A liquid chromatographic method (LC) comprising of derivatisation of ES-285 x HCl with phenylisothiocyanate and UV-detection was developed. The method was found to be linear, precise and accurate. The assay also proved selectivity as determined by analysing ES-285 x HCl in combination with 15 analogues and in combination with hydroxypropyl-beta-cyclodextrin, the excipient used in the lyophilised pharmaceutical dosage form. Stress testing showed that the degradation products were separated from the parent compound, confirming its stability indicating capacity. The method was found robust as determined with design of experiments (DoE), which made it possible to predict system suitability responses in worst case experimental conditions and to define criteria for system suitability testing. 相似文献
18.
Ignacio Alfonso Covadonga Astorga Vicente Gotor 《Journal of inclusion phenomena and macrocyclic chemistry》2005,53(1-2):131-137
Electrospray ionization mass espectrometry (ESI-MS) has been used for the study of a cyclam derivative noncovalent interactions.
At acidic pH, diprotonated macrocycle bound to different anionic species were observed. The selectivity shown by competitive
experiments is rationalized with the help of semiempirical theoretical calculations. At basic pH, the base peak corresponded
to the macrocycle-alkaline metal complexes, and again competition experiments showed different binding strength. Finally,
experiments carried out in the presence of transition metal salts allowed the detection of the complexes present in the mixture
and revealed their different kinetic behavior. 相似文献
19.
[reaction: see text] A lipase-catalyzed double monoaminolysis of dimethyl malonate by (+/-)-trans-cyclopentane-1,2-diamine allows the sequential resolution of the latter compound, affording an enantiopure bis(amidoester), which is subsequently transformed into an optically active polyamine. As an alternative, both enantiomers of the diamine can be obtained from enantiopure (+)- or (-)-2-aminocyclopentanol, prepared by enzymatic resolution. 相似文献
20.
A. Concheso R. Santamaría R. Menéndez J. M. Jiménez-Mateos R. Alcántara P. Lavela J. L. Tirado 《Journal of Solid State Electrochemistry》2005,9(9):627-633
The effect of oxidative stabilization as a mean to modify the carbon texture was essayed in a group of mesophases previous to carbonization at 900 °C with the aim of evaluating the influence on electrochemical performance when used as electrode materials in lithium test cells. X-ray diffraction, optical microscopy and chemical analysis, Fourier-transform infrared spectroscopy have been used to describe the compositional and textural properties of the as-produced parent mesophases, the samples were further treated under air current to stabilize their microstructures and the corresponding carbonized samples at 900 °C. The electrochemical performance was determined by the galvanostatic method and further correlated to the physical–chemical properties and interface resistance of the materials. In all cases, the stabilization process has demonstrated a beneficial effect on the capacity retention in the measured range. 相似文献