全文获取类型
收费全文 | 1975篇 |
免费 | 31篇 |
国内免费 | 11篇 |
专业分类
化学 | 1255篇 |
晶体学 | 20篇 |
力学 | 79篇 |
数学 | 277篇 |
物理学 | 386篇 |
出版年
2023年 | 17篇 |
2022年 | 31篇 |
2021年 | 39篇 |
2020年 | 27篇 |
2019年 | 26篇 |
2018年 | 29篇 |
2017年 | 23篇 |
2016年 | 34篇 |
2015年 | 27篇 |
2014年 | 48篇 |
2013年 | 108篇 |
2012年 | 91篇 |
2011年 | 120篇 |
2010年 | 73篇 |
2009年 | 71篇 |
2008年 | 114篇 |
2007年 | 107篇 |
2006年 | 111篇 |
2005年 | 93篇 |
2004年 | 91篇 |
2003年 | 68篇 |
2002年 | 80篇 |
2001年 | 34篇 |
2000年 | 35篇 |
1999年 | 22篇 |
1998年 | 22篇 |
1997年 | 24篇 |
1996年 | 34篇 |
1995年 | 27篇 |
1994年 | 25篇 |
1993年 | 25篇 |
1992年 | 9篇 |
1991年 | 16篇 |
1990年 | 21篇 |
1989年 | 27篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 17篇 |
1985年 | 21篇 |
1984年 | 24篇 |
1983年 | 20篇 |
1982年 | 15篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 15篇 |
1978年 | 19篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1973年 | 7篇 |
排序方式: 共有2017条查询结果,搜索用时 0 毫秒
911.
Letters in Mathematical Physics - We study the quantum open system evolution described by a Gorini–Kossakowski–Sudarshan–Lindblad generator with creation and annihilation... 相似文献
912.
Anna Bertaso Elio Franco De Palo Vito Cirielli Franco Tagliaro 《Electrophoresis》2020,41(12):1039-1044
Forensic inquests, particularly, in assessing time since death currently recognize the importance of the analysis of vitreous humour (VH) biomarkers. Present research, studies, and validates the determination of lactate (La) in VH by CZE with indirect UV detection. The BGE (pH 8.9) consisted of Tris buffer (37 mM) containing 4-methoxybenzoic acid (4 mM) and alkyl-trimethyl-ammonium bromide (1.2 mM). Each VH specimen was diluted with a butyric acid solution (internal standard 0.057 mM) and La and butyrate were separated within 3–5 min (30 kV). The La LOQ and LOD were 4 and 2 mM, respectively. The calibration curve linearity ranged from 4 to 80 mM; intra- and interruns precisions were less than 10% for standard as well as for VH specimen, respectively. To investigate postmortem interval (PMI) and VH lactate level correlation, human VH specimens were collected during autopsy (n = 40) and stored at −20°C until assay. La levels ranged from 16 to 42 mM; PMI values ranged from 10 to 141 h. La (mM) and PMI (h) correlation was statistically significant (r2 = 0.527; p < 0.05). In conclusion, the present CZE analysis is efficacious to determine VH La as a biomarker for PMI investigation. 相似文献
913.
Dattilo AM Decembrini F Bracchini L Focardi S Mazzuoli S Rossi C 《Annali di chimica》2005,95(3-4):177-184
The optical properties of the waters of five different stations, three located in the Messina Strait and two near the Strait (open sea), were analysed. Direct spectral measurements of the downward solar irradiance (290 - 800 nm) at different depths (0.5 m, 7 m, 10 m, 13 m, 20 m) were made using a cosine sensor connected to a spectroradiometer. Water samples were collected in the surface layer and their absorption spectra were analysed. The natural fluorescence profiles, along the water column, were determined using a fluorometer (SBE 911plus - Sea Teach). The spectral attenuation coefficient (K(lambda)), the variation of K(lambda) in different wavelength ranges (deltaK(deltalambda)), the wavelength corresponding to minimum value of K(lambda), the spectral depths of penetration of both 1% and 10% of the sub-surface irradiance values (P(lambda)), the depths of 1% of penetration of UVB, UVA and PAR, the depth ranges of the maxim concentration of Chl a and superficial CDOM were measured at each station. The maximum solar UVB penetration was about 65% of the photic zone and the maximum UVA penetration was nearly 100% (data of the Ionic sea station). Thus, a large part of the photic zone was exposed to UV radiation sufficient to cause a possible reduction in the photosynthetic activity of phytoplankton. The spectral penetration of solar radiation, especially UVB radiation, was significantly different in the three stations of the Strait with respect to the two stations studied in the open sea. This shows that variations in the spectral attenuation along the water column can be used as an indicator of properties of the water body. 相似文献
914.
Benincori T Pilati T Rizzo S Sannicolò F Burk MJ de Ferra L Ullucci E Piccolo O 《The Journal of organic chemistry》2005,70(14):5436-5441
[reaction: see text] The 2,5-dimethyl-3,4-bis[(2R,5R)-2,5-dimethylphospholano]thiophene (UlluPHOS), a new thiophene-based analogue of (R,R)-1,2-bis(phospholano)benzene (Me-DuPHOS), was synthesized, geometrically and electronically characterized, and employed as ligand of Rh and Ru in some standard hydrogenation reactions of prostereogenic functionalized carbon-carbon and carbon-oxygen double bonds. The synthesis of UlluPHOS is much easier than that provided for Me-DuPHOS. UlluPHOS and Me-DuPHOS display very similar geometries, while the electronic availability of the former is higher than that exhibited by the latter. The Rh and Ru complexes of UlluPHOS produced excellent enantiomeric excesses (98.9-99.5%) in the hydrogenation of N-acetyl-alpha-enamino acids and reaction rates higher than those found when employing the analogous complexes of Me-DuPHOS. 相似文献
915.
Bodo E Sebastianelli F Gianturco FA Pino I 《The journal of physical chemistry. A》2005,109(19):4252-4260
The ab initio calculation of the interaction forces between the LiH+ molecular ion, at its equilibrium geometry, and several He atoms is carried out in order to isolate and assess the importance of many-body contributions in the search for realistic energy and geometry data. The full potential energy surface (PES) with a single helium partner is obtained first by using an aug-cc-pVQZ basis set for He and higher quality ones for Li and H. The calculations were performed at the CAS-SCF plus MRCI level for the lowest potential energy surface over a total of 480 grid points of the two intermolecular Jacobi coordinates, whereas the excited state surface has also been examined in order to exclude the presence of any significant nonadiabatic interaction between the two PESs. A numerical fit of the lower surface is presented and the general physical changes of the ionic interaction when going from the lower to the upper of the two potentials are described and discussed. The fairly limited importance of many-body effects for such systems is seen from further ab initio calculations including several He atoms: our results suggest that, at least in the present case, no strong charge migration occurs after He attachment, and therefore, one could realistically model larger clusters by implementing a sum-of-potentials approach via the presently computed PES. 相似文献
916.
We study the critical depinning current Jc versus the applied magnetic flux Phi, for quasiperiodic (QP) chains and 2D arrays of pinning centers placed on the nodes of a fivefold Penrose lattice. In QP chains, the peaks in Jc(Phi) are determined by a sequence of harmonics of the long and short segments of the chain. The critical current Jc(Phi) has a remarkable self-similarity. In 2D QP pinning arrays, we predict analytically and numerically the main features of Jc(Phi), and demonstrate that the Penrose lattice of pinning sites provides an enormous enhancement of Jc(Phi), even compared to triangular and random pinning site arrays. This huge increase in Jc(Phi) could be useful for applications. 相似文献
917.
We calculate, in the framework of the standard six-quark model and QCD, the corrections due to strong interactions to the transition width for the system, focusing our attention on CP-violating effects. 相似文献
918.
Rhodium oxihydroxide has been synthesized by means of hydrothermal synthesis at 1500 bars and 600°C in acidic media. Powder X-ray diffraction shows small variations in cell parameters which appear to be related to the oxidizing power of the reaction media. On the basis of EPR work such variations can be attributed to the presence of small amounts of either Rh(II) or Rh(IV). This last species had not been fully characterized before by EPR in oxide-like materials. The paramagnetic species seem to be noninteracting and randomly distributed in the Rh(III) sites. These results can be understood on the basis of two different kinds of nonstoichiometry for rhodium oxihydroxide: either proton or hydroxyl ion defects. 相似文献
919.
Meccanica - Il rapporto si propone di delineare gli aspetti specifici degli equilibri per coazione. A tal fine vengono, in primo luogo, raffrontati gli equilibri da forze e quelli da deformazioni... 相似文献
920.