全文获取类型
收费全文 | 440篇 |
免费 | 18篇 |
专业分类
化学 | 280篇 |
晶体学 | 16篇 |
力学 | 11篇 |
数学 | 26篇 |
物理学 | 125篇 |
出版年
2023年 | 5篇 |
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 18篇 |
2015年 | 9篇 |
2014年 | 17篇 |
2013年 | 27篇 |
2012年 | 33篇 |
2011年 | 37篇 |
2010年 | 20篇 |
2009年 | 19篇 |
2008年 | 20篇 |
2007年 | 25篇 |
2006年 | 14篇 |
2005年 | 19篇 |
2004年 | 27篇 |
2003年 | 12篇 |
2002年 | 22篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 9篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有458条查询结果,搜索用时 15 毫秒
421.
We show that weak measurements with postselection, proposed in the context of the quantum theory of measurement, naturally appear in the everyday physics of fiber optics telecom networks through polarization-mode dispersion (PMD) and polarization-dependent losses (PDL). Specifically, the PMD leads to a time-resolved discrimination of polarization; the postselection is done in the most natural way: one postselects those photons that have not been lost because of the PDL. The quantum formalism is shown to simplify the calculation of optical networks in the telecom limit of weak PMD. 相似文献
422.
Di Marco VB Bombi GG Tubaro M Traldi P 《Rapid communications in mass spectrometry : RCM》2003,17(18):2039-2046
Electrospray ionization mass spectrometry (ESI-MS) has been applied to the study of solution equilibria between Al(III) and the two ligands 4-hydroxy-3-pyridinecarboxylic acid (4H3P) and 3-hydroxy-4-pyridinecarboxylic acid (3H4P). The results compare well with the speciation data obtained from potentiometric, UV-visible spectroscopy, and NMR measurements. This agreement suggests the applicability of ES-MS to the study of more complicated aluminium-ligand systems. 相似文献
423.
424.
Tetrabutyl-1,3-diacyloxydistannoxanes, (RCOO)Bu2SnOSnBu2(OOCR) (A) and/or tetrabutyl-1-acyloxy-3-hydroxydistannoxanes, (RCOO)Bu2SnOSnBu2(OH) (B), can be prepared from equimolecular amounts of dibutyldiallyltin and carboxylic acid, RCOOH (R = H, CH3, CH2Cl, CHCl2, CCl3, CF3) in moist methanol or acetone/water (50/50, v/v). Isolation of compounds (A) or (B) depends upon the hydrolyzing power of the medium and the nature of R. 相似文献
425.
426.
Valerio Capraro 《Expositiones Mathematicae》2013,31(4):334-349
We define the isoperimetric constant for any locally finite metric space and we study the property of having isoperimetric constant equal to zero. This property, called Small Neighborhood property, clearly extends amenability to any locally finite space. Therefore, we start making a comparison between this property and other notions of amenability for locally finite metric spaces that have been proposed by Gromov, Lafontaine and Pansu, by Ceccherini-Silberstein, Grigorchuk and de la Harpe and by Block and Weinberger. We discuss possible applications of the property SN in the study of embedding a metric space into another one. In particular, we propose three results: we prove that a certain class of metric graphs that are isometrically embeddable into Hilbert spaces must have the property SN. We also show, by a simple example, that this result is not true replacing property SN with amenability. As a second result, we prove that many spaces with uniform bounded geometry having a bi-lipschitz embedding into Euclidean spaces must have the property SN. Finally, we prove a Bourgain-like theorem for metric trees: a metric tree with uniform bounded geometry and without property SN does not have bi-lipschitz embeddings into finite-dimensional Hilbert spaces. 相似文献
427.
Dose Valerio Mercuri Pietro Pal Ankan Stirpe Claudio 《Designs, Codes and Cryptography》2022,90(6):1347-1368
Designs, Codes and Cryptography - We illustrate a general technique to construct towers of fields producing high order elements in $$mathbb {F}_{q^{2^n}}$$ , for odd q, and in $$mathbb {F}_{2^{2... 相似文献
428.
The coordination behavior and reactivity of the phenol-substituted bis(pyrazolyl)methane ligands, (3,5-(t)Bu(2)-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L1-H) and 2-phenol-bis(3,5-Me(2)-pyrazol-1-yl)methane (L2-H) have been investigated in the metal complexes (L1-H)CoCl(2) (1), (L1-H)ZnCl(2) (2), (L3)CuCl(2) (3), (L2)(2)Co(2)Cl(2) (4) (L2-H)ZnCl(2) (5), and (L2-H)CuCl(2)·H(2)O (6). The mononuclear tetrahedral cobalt complex 1 was isolated and fully characterized by X-ray single crystal diffraction and (1)H NMR spectroscopy and relaxometry. The neutral L1-H is κ(2)-coordinated to the metal center whereas the not coordinated hydroxy-phenyl group is involved in extended intermolecular hydrogen bonds. Aerobic oxidation of L1-H was observed in the reaction of this ligand with CuCl(2) to yield the para-quinone derivative L3 (L3 = 2-(t)Bu-6-(bis(3,5-Me(2)-pyrazol-1-yl)methyl)cyclohexa-2,5-diene-1,4-dione). Upon oxidation L3 resulted κ(2)-coordinated to the tetrahedral Cu(II) metal center, affording 3. The reaction of L2-H with CoCl(2)·6H(2)O produced the elimination of 1 equiv of hydrochloric acid and the formation of the binuclear complex 4 in which one cobalt is in an octahedral environment featuring two κ(3)-coordinated deprotonated ligands whereas the second cobalt center is detected in tetrahedral coordination geometry, bound to the octahedral cobalt via two phenoxo bridging moieties. Interestingly L2-H, (3-(t)Bu-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L4-H), or (5-(t)Bu-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L5-H) were not oxidized in the reaction with CuCl(2). The reaction of the ligand L2-H with ZnCl(2) and CuCl(2)·2H(2)O yielded the κ(2)-coordinated tetrahedral complex 5 and the square planar complex 6, respectively. The application of the cobalt complex 1 as molecular dosimeter for H(2)S was explored and compared to that of the zinc analogue 2. Density functional theory (DFT) calculations and NMR experiments to assess the possible mechanisms of H(2)S detection by both 1 and 2 are also described. 相似文献
429.
Stefan Sulmann Dr. Daniele Dell'Orco Valerio Marino Dr. Petra Behnen Prof. Dr. Karl‐Wilhelm Koch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(22):6756-6762
Fundamental components of signaling pathways are switch modes in key proteins that control start, duration, and ending of diverse signal transduction events. A large group of switch proteins are Ca2+ sensors, which undergo conformational changes in response to oscillating intracellular Ca2+ concentrations. Here we use dynamic light scattering and a recently developed approach based on surface plasmon resonance to compare the protein dynamics of a diverse set of prototypical Ca2+‐binding proteins including calmodulin, troponin C, recoverin, and guanylate cyclase‐activating protein. Surface plasmon resonance biosensor technology allows monitoring conformational changes under molecular crowding conditions, yielding for each Ca2+‐sensor protein a fingerprint profile that reflects different hydrodynamic properties under changing Ca2+ conditions and is extremely sensitive to even fine alterations induced by point mutations. We see, for example, a correlation between surface plasmon resonance, dynamic light scattering, and size‐exclusion chromatography data. Thus, changes in protein conformation correlate not only with the hydrodynamic size, but also with a rearrangement of the protein hydration shell and a change of the dielectric constant of water or of the protein–water interface. Our study provides insight into how rather small signaling proteins that have very similar three‐dimensional folding patterns differ in their Ca2+‐occupied functional state under crowding conditions. 相似文献
430.
C.E.A. Grigorescu E. Valerio L. Tortet G. Pavelescu C. Ducu H.J. Trodahl N. Strickland W.R. Branford 《Applied Surface Science》2007,253(19):8102-8106
Thin films of nonstoichiometric Heusler alloys Co2MnSbxSn1−x (x = 0.2; 0.4; 0.6; 0.8) have been grown by pulsed laser deposition (double-target/double beam configuration) on Si (1 0 0) substrates using a KrF excimer laser (λ = 248 nm, τ = 20 ns). The substrate temperature was held at 300 K in all experiments to prevent interface interdiffusion of the species. A comparison between the compositions of films and corresponding targets has been done through energy dispersive X-ray spectroscopy (EDS) analysis showing a very satisfactory match. Scanning electron microscopy (SEM) imaging served to investigate the morphology of the films in order to determine the size and density of droplets which may influence the optical data. Optical conductivity derived from reflectivity measurements shows absorption onsets close to 1 eV, which corresponds to the onset of valence-to-conduction transitions in the minority spin bands theoretically predicted. The values of the saturation magnetisation measured at 300 K on the quaternary alloys are very close to those of ternary ones for which either half-metallic properties or high spin polarisation were theoretically predicted. 相似文献