全文获取类型
收费全文 | 1857篇 |
免费 | 78篇 |
国内免费 | 5篇 |
专业分类
化学 | 1322篇 |
晶体学 | 4篇 |
力学 | 10篇 |
数学 | 301篇 |
物理学 | 303篇 |
出版年
2023年 | 9篇 |
2022年 | 17篇 |
2021年 | 24篇 |
2020年 | 32篇 |
2019年 | 40篇 |
2018年 | 17篇 |
2017年 | 20篇 |
2016年 | 46篇 |
2015年 | 66篇 |
2014年 | 57篇 |
2013年 | 83篇 |
2012年 | 107篇 |
2011年 | 112篇 |
2010年 | 80篇 |
2009年 | 67篇 |
2008年 | 94篇 |
2007年 | 114篇 |
2006年 | 90篇 |
2005年 | 110篇 |
2004年 | 67篇 |
2003年 | 67篇 |
2002年 | 74篇 |
2001年 | 50篇 |
2000年 | 33篇 |
1999年 | 25篇 |
1998年 | 32篇 |
1997年 | 26篇 |
1996年 | 29篇 |
1995年 | 21篇 |
1994年 | 31篇 |
1993年 | 15篇 |
1992年 | 17篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 6篇 |
1987年 | 21篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 8篇 |
1982年 | 21篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 13篇 |
1977年 | 6篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1970年 | 7篇 |
1926年 | 4篇 |
排序方式: 共有1940条查询结果,搜索用时 15 毫秒
991.
Münchow F Bruni C Madalinski M Görlitz A 《Physical chemistry chemical physics : PCCP》2011,13(42):18734-18737
We report on the spectroscopic investigation of vibrational levels in the electronic ground state of the heteronuclear molecule (176)Yb(87)Rb. Using two-photon photoassociation spectroscopy in a laser-cooled mixture of (176)Yb and (87)Rb we are able to determine the binding energies of weakly-bound vibrational levels. By applying the LeRoy-Bernstein method we assign the vibrational quantum numbers and deduce a C(6) coefficient for the long-range part of the molecular potential of ~2500 a.u. 相似文献
992.
An operationally simple two-step synthesis of substituted anilides has been developed. The methodology utilizes carboxamides, aldehydes, and olefins (or alkynes) as cheap starting materials and relies upon the sequential combination of condensation, cycloaddition, and oxidation reactions. The intermediate cycloadducts display various functional groups (e.g. Br, OAc, NR(2), COR, Cbz) for further chemical manipulation at the ring periphery or core. Upon oxidation with MnO(2), highly crowded anilides with up to four further substituents (alkyl, aryl, carboxylate, cyano, nitro, bromo) can be prepared in good overall yields. 相似文献
993.
Pfaff A Shinde VS Lu Y Wittemann A Ballauff M Müller AH 《Macromolecular bioscience》2011,11(2):199-210
The synthesis and characterization of spherical sugar-containing polymer brushes consisting of PS cores onto which chains of sugar-containing polymers have been grafted via two different techniques are described. Photopolymerization in aqueous dispersion using the functional monomer MAGlc and crosslinked or non-crosslinked PS particles covered with a thin layer of photo-initiator yielded homogeneous glycopolymer brushes attached to spherical PS cores. As an alternative, ATRP was used to graft poly-(N-acetylglucosamine) arms from crosslinked PS cores. Deprotection of the grafted brushes led to water-soluble particles that act as carriers for catalytically active gold nanoparticles. These glycopolymer chains show a high affinity to adsorb WGA whereas no binding to BSA or PNA could be detected. 相似文献
994.
Deininger SO Cornett DS Paape R Becker M Pineau C Rauser S Walch A Wolski E 《Analytical and bioanalytical chemistry》2011,401(1):167-181
Normalization is critically important for the proper interpretation of matrix-assisted laser desorption/ionization (MALDI)
imaging datasets. The effects of the commonly used normalization techniques based on total ion count (TIC) or vector norm
normalization are significant, and they are frequently beneficial. In certain cases, however, these normalization algorithms
may produce misleading results and possibly lead to wrong conclusions, e.g. regarding to potential biomarker distributions.
This is typical for tissues in which signals of prominent abundance are present in confined areas, such as insulin in the
pancreas or β-amyloid peptides in the brain. In this work, we investigated whether normalization can be improved if dominant
signals are excluded from the calculation. Because manual interaction with the data (e.g., defining the abundant signals)
is not desired for routine analysis, we investigated two alternatives: normalization on the spectra noise level or on the
median of signal intensities in the spectrum. Normalization on the median and the noise level was found to be significantly
more robust against artifact generation compared to normalization on the TIC. Therefore, we propose to include these normalization
methods in the standard “toolbox” of MALDI imaging for reliable results under conditions of automation. 相似文献
995.
Ibad MF Langer P Schulz A Villinger A 《Journal of the American Chemical Society》2011,133(51):21016-21027
The solvent-coordinated [Me(3)Si·arene][B(C(6)F(5))(4)] salts (arene = benzene, toluene, ethylbenzene, n-propylbenzene, isopropylbenzene, o-xylene, m-xylene, p-xylene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene) are prepared and fully characterized. As an interesting decomposition product the formation of bissilylated fluoronium ion [Me(3)Si-F-SiMe(3)](+) was observed and even cocrystallized with [Me(3)Si·arene][B(C(6)F(5))(4)] (arene = benzene and toluene). Investigation of the degradation of [Me(3)Si·arene][B(C(6)F(5))(4)] reveals the formation of fluoronium salt [Me(3)Si-F-SiMe(3)][B(C(6)F(5))(4)], B(C(6)F(5))(3), and a reactive "C(6)F(4)" species which could be trapped with CS(2). Upon addition of CS(2), the formation of a formal S-heterocyclic carbene adduct, C(6)F(4)CS(2)-B(C(6)F(5))(3), was observed. The structure and bonding of substituted [Me(3)Si·arene][B(C(6)F(5))(4)] with arene = R(n)C(6)H(6-n) (R = H, Me, Et, Pr, and Bu; n = 0-6) is discussed on the basis of experimental and theoretical data. X-ray data of [Me(3)Si·arene][B(C(6)F(5))(4)] salts reveal nonplanar arene species with significant cation···anion interactions. As shown by different theoretical approaches (charge transfer, partial charges, trimethylsilyl affinity values) stabilizing inductive effects occur; however, the magnitude of such effects differs depending on the degree of substitution and the substitution pattern. 相似文献
996.
Roos M Künzel D Uhl B Huang HH Brandao Alves O Hoster HE Gross A Behm RJ 《Journal of the American Chemical Society》2011,133(24):9208-9211
The competition between intermolecular interactions and lateral variations in the molecule-substrate interactions has been studied by scanning tunneling microscopy (STM), comparing the phase formation of (sub)monolayers of the organic molecule 2,4'-BTP on buckled graphene/Ru(0001) and Ag(111) oriented thin films on Ru(0001). On the Ag films, the molecules form a densely packed 2D structure, while on graphene/Ru(0001), only the areas between the maxima are populated. The findings are rationalized by a high corrugation in the adsorption potential for 2,4'-BTP molecules on graphene/Ru(0001). These findings are supported by temperature programmed desorption (TPD) experiments and theoretical results. 相似文献
997.
We report on a computer simulation study of a Lennard-Jones liquid confined in a narrow slit pore with tunable attractive walls. In order to investigate how freezing in this system occurs, we perform an analysis using different order parameters. Although some of the parameters indicate that the system goes through a hexatic phase, other parameters do not. This shows that to be certain whether a system of a finite particle number has a hexatic phase, one needs to study not only a large system, but also several order parameters to check all necessary properties. We find that the Binder cumulant is the most reliable one to prove the existence of a hexatic phase. We observe an intermediate hexatic phase only in a monolayer of particles confined such that the fluctuations in the positions perpendicular to the walls are less than 0.15 particle diameters, i.e., if the system is practically perfectly 2D. 相似文献
998.
The synthesis of the monoclinic polymorph of {Cu[Hg(SCN)4]}n is reported. The compound, as determined by X-ray diffraction of a twinned crystal, consists of mercury and copper atoms linked by μ1,3-SCN bridges. The crystal packing shows a highly porous infinite 3D structure. Diagnostic resonances for the SCN- ligand and metal-ligand bonds in the IR, far-IR and Raman spectra are assigned and discussed. The electronic band structure along with density of states (DOS) calculated by the DFT method indicates that the compound is an indirect band gap semiconductor. The DFT calculations show that the observed luminescence of the compound arises mainly from an excited LLCT state with small MLCT contributions (from the copper to unoccupied π? orbital of the thiocyanate groups). The X-band EPR spectrum of the powdered sample at room temperature reveals an axial signal with anisotropic g factors consistent with the unpaired electron of Cu(II) ion in the dx2−y2 orbital. 相似文献
999.
We presented a systematic study of surface enhanced Raman scattering (SERS) fiber sensor with a grid nanostructure. The plasmonic resonance peak is stable when measuring gas and double-resonance plasmon can be effectively excited; meanwhile local electric field can be strongly enhanced with the metal coated nanostructured fiber facet. Studies on the influence of polarization effects, the plasmon resonance wavelength shift is relatively small in our structure. 相似文献
1000.
Many quantum mechanical problems (such as dissipative phase fluctuations in metallic and superconducting nanocircuits or impurity scattering in Luttinger liquids) involve a continuum of bosonic modes with a marginal spectral density diverging as the inverse of energy. We construct a numerical renormalization group in this singular case, with a manageable violation of scale separation at high energy, capturing reliably the low energy physics. The method is demonstrated by a nonperturbative solution over several energy decades for the dynamical conductance of a Luttinger liquid with a single static defect. 相似文献