全文获取类型
收费全文 | 968篇 |
免费 | 28篇 |
国内免费 | 7篇 |
专业分类
化学 | 681篇 |
晶体学 | 3篇 |
力学 | 21篇 |
数学 | 154篇 |
物理学 | 144篇 |
出版年
2023年 | 7篇 |
2022年 | 33篇 |
2021年 | 42篇 |
2020年 | 29篇 |
2019年 | 27篇 |
2018年 | 13篇 |
2017年 | 14篇 |
2016年 | 43篇 |
2015年 | 20篇 |
2014年 | 45篇 |
2013年 | 67篇 |
2012年 | 60篇 |
2011年 | 87篇 |
2010年 | 50篇 |
2009年 | 37篇 |
2008年 | 48篇 |
2007年 | 55篇 |
2006年 | 47篇 |
2005年 | 43篇 |
2004年 | 41篇 |
2003年 | 23篇 |
2002年 | 26篇 |
2001年 | 13篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1991年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1977年 | 5篇 |
1939年 | 2篇 |
1937年 | 5篇 |
1936年 | 4篇 |
1935年 | 2篇 |
1934年 | 9篇 |
1933年 | 6篇 |
1932年 | 4篇 |
1931年 | 4篇 |
1930年 | 2篇 |
1929年 | 5篇 |
1912年 | 3篇 |
1911年 | 2篇 |
1906年 | 3篇 |
1905年 | 2篇 |
排序方式: 共有1003条查询结果,搜索用时 0 毫秒
91.
Artur Czerwinski 《理论物理通讯》2021,73(8):85101
In this article, we introduce a framework for entanglement quantification of photon pairs represented by two-qubit Werner states. The measurement scheme is based on the symmetric informationally complete POVM. To make the framework realistic, we impose the Poisson noise on the measured two-photon coincidences. For various settings, numerical simulations were performed to evaluate the efficiency of the framework. 相似文献
92.
Magda Carvalho Henriques Maria Amparo F. Faustino Artur M. S. Silva Juliana Felgueiras Margarida Fardilha 《Journal of Coordination Chemistry》2017,70(14):2393-2408
The coordination of ruthenium(II) complexes to anionic oxygen-based donors are very rare. This study describes a simple, one-pot method for obtaining [ruthenium(II)(trithiacyclononane)(curcumin)(S-DMSO)]Cl (1) in 37% yield. The structural characterization of complex 1 by elemental analysis, FT-IR, 1-D and 2-D NMR, ESI+-MS as well as UV–vis and fluorescence spectroscopies are presented. The DNA-melting temperature (Tm) assay shows that salmon sperm DNA (smDNA) in the presence of complex 1 has a higher melting temperature, with ΔTm = 7.4 °C, while in the presence of curcumin the melting temperature remains unaltered. The in vitro cytotoxic activities of curcumin and complex 1 were investigated using the tumor human prostate cell line, PC-3, and the healthy cell line, PNT-2. Complex 1 is innocuous toward normal prostate epithelial cells and, whereas curcumin is toxic, with inhibition rates of ca. 35 and 65% at 50 and 80 μM, respectively. On the tumor cell line PC-3, complex 1 did not cause viability changes, whereas curcumin exhibited dose-dependent inhibition, with ca. 73% inhibition at the highest concentration tested, i.e. 80 μM. This study suggests that coordination with the trithiacyclononane ruthenium(II) scaffold stabilizes the photochemical properties of curcumin and strongly changes its biologic activity. 相似文献
93.
Ana R. Almeida Rui M.B. Carrilho Andreia F. Peixoto Artur R. Abreu Artur Silva Mariette M. Pereira 《Tetrahedron》2017,73(17):2389-2395
Different families of new amino compounds were efficiently synthesized, through optimized sequential processes, involving rhodium catalyzed hydroformylation as the key step. The selection of appropriate hydroformylation catalytic systems and reaction conditions allowed obtaining aldehydes derived from several n-alkyl olefins, cholest-4-ene and 3-vinyl-1H-indole, which were subsequently transformed, in one-pot, in to α-amino acids via hydroformylation/Strecker reaction, and in to tertiary amines via hydroaminomethylation, with excellent yields. 相似文献
94.
Pedersen CM Figueroa-Perez I Boruwa J Lindner B Ulmer AJ Zähringer U Schmidt RR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(42):12627-12641
Streptococcus pneumoniae LTA is a highly complex glycophospholipid that consists of nine carbohydrate residues: three glucose, two galactosamine and two 2‐acetamino‐4‐amino‐2,4,6‐trideoxygalactose (AATDgal) residues that are each differently linked, one ribitol and one diacylated glycerol (DAG) residue. Suitable building blocks for the glucose and the AATDgal residues were designed and their synthesis is described in this paper. These building blocks permitted the successful synthesis of the core structure Glcβ(1‐3)AATDgalβ(1‐3)Glcα(1‐O)DAG in a suitably protected form for further chain extension ( 1 b , 1 c ) and as unprotected glycolipid ( 1 a ) that was employed in biological studies. These studies revealed that 1 a as well as 1 lead to interleukin‐8 release, however not via TLR2 or TLR4 as receptor. 相似文献
95.
Emilia Styczeń Zygmunt Warnke Dariusz Wyrzykowski Julia K?ak Jerzy Mroziński Artur Sikorski 《Structural chemistry》2010,21(1):269-276
The crystal structures of tetrabromocobaltate(II) and tetrabromomanganate(II) salts of general formula [(C2H5)4N]2[CoBr4] (1) and [(C4H9)4N]2[MnBr4] (2) were determined. The manganese and cobalt cations are four-coordinated by bromide anions and they adopt a slightly distorted
tetrahedral coordination. In the structure of both compounds there are neither hydrogen bonds nor any unusual short-range intermolecular interactions. Magnetic measurements of the powdered samples gave negative values of the Weiss constants
equal to −4.9 and −1.1 K for (1) and (2), respectively, which suggest antiferromagnetic interactions to be transferred within the crystal lattice. 相似文献
96.
Fic E Kedracka-Krok S Jankowska U Pirog A Dziedzicka-Wasylewska M 《Electrophoresis》2010,31(21):3573-3579
Sample preparation is a fundamental step in proteomic methodologies. The quality of the results from a proteomic experiment is dependent on the nature of the sample and the properties of the proteins. In this study, various pre-treatment methods were compared by proteomic analysis; we analysed various rat brain structures after chloroform/methanol, acetone, TCA/acetone and TCA protein precipitation procedures. The protein content of the supernatant was also examined by 2-DE. We found that for four of the rat brain structures, precipitation with chloroform/methanol and acetone delivered the highest protein recovery for top-down proteomic analysis; however, TCA precipitation resulted in good protein separation and the highest number of protein spots in 2-DE. Moreover, TCA precipitation also gave high efficiency of protein recovery if prior sonication procedure was performed. 相似文献
97.
In this paper we introduce a kind of “noncommutative neighbourhood” of a semiclassical parameter corresponding to the Planck
constant. This construction is defined as a certain filtered and graded algebra with an infinite number of generators indexed
by planar binary leaf-labelled trees. The associated graded algebra (the classical shadow) is interpreted as a “distortion”
of the algebra of classical observables of a physical system. It is proven that there exists a q-analogue of the Weyl quantization, where q is a matrix of formal variables, which induces a nontrivial noncommutative analogue of a Poisson bracket on the classical
shadow. 相似文献
98.
Sławomir Prucnal Marcin Turek Andrzej Drozdziel Krzysztof Pyszniak Artur Wójtowicz Sheng-Qiang Zhou Alohe Kanjilal Artem Shalimov Wolfgang Skorupa Jerzy Zuk 《Central European Journal of Physics》2011,9(2):338-343
The InAs quantum structures were formed in silicon by sequential ion implantation and subsequent thermal annealing. Two kinds of crystalline InAs nanostructures were successfully synthesized: nanodots (NDs) and nanopyramids (NPs). The peaks at 215 and 235 cm?1, corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs single-phonon modes, respectively, are clearly visible in the Raman spectra. Moreover, the PL band at around 1.3 µm, due to light emission from InAs NDs with an average diameter 7±2 nm, was observed. The InAs NPs were found only in samples annealed for 20 ms at temperatures ranging from 1000 up to 1200°C. The crystallinity and pyramidal shape of InAs quantum structures were confirmed by HRTEM and XRD techniques. The average size of the NPs is 50 nm base and 50 nm height, and they are oriented parallel to the Si (001) planes. The lattice parameter of the NPs increases from 6.051 to 6.055 Å with the annealing temperature increasing from 1100 to 1200°C, due to lattice relaxation. Energy dispersive spectroscopy (EDS) shows almost stoichiometric composition of the InAs NPs. 相似文献
99.
Maria Hoffmann Antoni Konitz Artur Sikorski Urszula Lesińska Maria Bocheńska 《Journal of inclusion phenomena and macrocyclic chemistry》2003,47(3-4):137-142
The synthesis and characterization of the lower rim bis-phosphorylatedtetrakis-p-tert-butyl-25,27-bis(methoxy)calix[4]arenas(compounds 2–4) is presented. The studied compounds were examined as ionophores in ion-selective membrane electrodes, showing selectivity for rubidium, potassium, and for the large and flat guanidinium cations (G+). The correlation wasstudied between the stereochemical structure of the ligands andpotentiometrically determined ion-selectivity. Complex formationconstants in the PVC/BEHS (bis(ethyl)hexyl sebacate) membranes weredetermined. The crystal and molecular structures of compound 4 have been determined by single crystal X-ray diffraction study. 相似文献
100.
João P.C. Tomé Dong-Gyu Cho Maria G.P.M.S. Neves Artur M.S. Silva 《Tetrahedron letters》2006,47(18):3131-3134
Sapphyrins participate in Diels-Alder reactions with pentacene affording novel barrelene-fused sapphyrins. The new compounds were synthesized using traditional heating and microwave irradiation conditions. The experiments carried out under microwave irradiation proved cleaner, affording only the monoadduct and in higher yields. 相似文献