全文获取类型
收费全文 | 3970篇 |
免费 | 158篇 |
国内免费 | 21篇 |
专业分类
化学 | 2499篇 |
晶体学 | 21篇 |
力学 | 101篇 |
数学 | 820篇 |
物理学 | 708篇 |
出版年
2023年 | 37篇 |
2022年 | 30篇 |
2021年 | 90篇 |
2020年 | 66篇 |
2019年 | 99篇 |
2018年 | 67篇 |
2017年 | 74篇 |
2016年 | 160篇 |
2015年 | 117篇 |
2014年 | 125篇 |
2013年 | 218篇 |
2012年 | 273篇 |
2011年 | 310篇 |
2010年 | 173篇 |
2009年 | 193篇 |
2008年 | 285篇 |
2007年 | 264篇 |
2006年 | 252篇 |
2005年 | 194篇 |
2004年 | 174篇 |
2003年 | 119篇 |
2002年 | 125篇 |
2001年 | 65篇 |
2000年 | 51篇 |
1999年 | 34篇 |
1998年 | 29篇 |
1997年 | 31篇 |
1996年 | 32篇 |
1995年 | 19篇 |
1994年 | 22篇 |
1993年 | 22篇 |
1992年 | 42篇 |
1991年 | 25篇 |
1990年 | 33篇 |
1989年 | 22篇 |
1988年 | 21篇 |
1987年 | 15篇 |
1986年 | 20篇 |
1985年 | 31篇 |
1984年 | 30篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1977年 | 6篇 |
1974年 | 10篇 |
1971年 | 8篇 |
1963年 | 5篇 |
排序方式: 共有4149条查询结果,搜索用时 328 毫秒
991.
Dul MC Ferrando-Soria J Pardo E Lescouëzec R Journaux Y Ruiz-García R Cano J Julve M Lloret F Fabelo O Pasán J Ruiz-Pérez C 《Inorganic chemistry》2010,49(24):11264-11266
Two new heterometallic Ni(II)(n)Cu(II)((9-n)) complexes [n = 1 (2) and 2 (3)] have been synthesized following a multicomponent self-assembly process from a n:(3 - n):2:6 stoichiometric mixture of Ni(2+), Cu(2+), L(6-), and [CuL'](2+), where L and L' are the bridging and blocking ligands 1,3,5-benzenetris(oxamate) and N,N,N',N',N'-pentamethyldiethylenetriamine, respectively. Complexes 2 and 3 possess a unique cyclindrical architecture formed by three oxamato-bridged trinuclear linear units connected through two 1,3,5-substituted benzenetris(amidate) bridges, giving a triangular metallacyclophane core. They behave as a ferromagnetically coupled trimer of two (2)/one (3) S = (1)/(2) Cu(II)(3) plus one (2)/two (3) S = 0 Ni(II)Cu(II)(2) linear units with overall S = 1 Ni(II)Cu(II)(8) (2) and S = (1)/(2) Ni(II)(2)Cu(II)(7) (3) ground states. 相似文献
992.
Jorge Acevedo-Martínez Igor G. Zenkevich Ramón Carrasco-Velar 《Chromatographia》2010,71(9-10):881-889
A simple algorithm is proposed for prediction of linear retention indices, RI, of organic compounds with different structures. The algorithm is based on the hypothesis that any structural moiety of a molecule contributes to gas chromatographic retention to a different extent, depending on its molecular environment. For a given moiety the mean structural increment (MSI) is calculated from the difference between the retention indices of two molecules, one containing it and one not, in different compound families. The mean of these values is the MSI for the corresponding moiety. The correlation between predicted and experimental values affords r 2 = 0.992 and the mean relative error is 1.65% for n = 92 compounds. 相似文献
993.
Roser Sabater i Serra Apostolos Kyritsis Jorge L. Escobar Ivirico Andreu Andrio Balado Jose Luis Gómez Ribelles Polykarpos Pissis Manuel Salmerón-Sánchez 《Colloid and polymer science》2010,288(5):555-565
Poly(L-lactide) networks (PmLA) hydrophilized with different amounts of 2-hydroxyethyl acrylate (HEA) were investigated by
dielectric relaxation spectroscopy, thermally stimulated depolarization currents, and differential scanning calorimetry. The
incorporation of HEA units in the PmLA network, with the aim of modulating the water sorption capacity of the system, results
in a material with a complex behavior. The system consists of phase-separated microdomains richer in one or the other comonomers
that constitute the network. Initially, the addition of smalls amount of HEA units in the network gives rise to a one-phase,
two-component system; however, when the amount of HEA in the system increases, a new phase (HEA-rich one) is formed containing
some mLA chains that modify the main relaxation mode of these domains and the local dynamics of the system. The structure
of the system has been analyzed by comparing the relaxational modes in the PmLA and PHEA homonetworks with those in the copolymer
networks. 相似文献
994.
R.W. Deitcher J.E. RomeP.A. Gildea J.P. O’ConnellE.J. Fernandez 《Journal of chromatography. A》2010,1217(2):199-208
A new thermodynamic model is derived that describes both loading and pulse-response behavior of proteins in hydrophobic interaction chromatography (HIC). The model describes adsorption in terms of protein and solvent activities, and water displacement from hydrophobic interfaces, and distinguishes contributions from ligand density, ligand type and protein species. Experimental isocratic response and loading data for a set of globular proteins on Sepharose™ resins of various ligand types and densities are described by the model with a limited number of parameters. The model is explicit in ligand density and may provide insight into the sensitivity of protein retention to ligand density in HIC as well as the limited reproducibility of HIC data. 相似文献
995.
Dayene M. Carvalho Jorge L. B. MacielJr. Leandro P. Ravaro Rogério E. Garcia Valdemir G. Ferreira Luis V. A. Scalvi 《Journal of Sol-Gel Science and Technology》2010,55(3):385-393
The fluid flow of the liquid phase in the sol-gel-dip-coating process for SnO2 thin film deposition is numerically simulated. This calculation yields useful information on the velocity distribution close
to the substrate, where the film is deposited. The fluid modeling is done by assuming Newtonian behavior, since the linear
relation between shear stress and velocity gradient is observed. Besides, very low viscosities are used. The fluid governing
equations are the Navier–Stokes in the two dimensional form, discretized by the finite difference technique. Results of optical
transmittance and X-ray diffraction on films obtained from colloidal suspensions with regular viscosity, confirm the substrate
base as the thickest part of the film, as inferred from the numerical simulation. In addition, as the viscosity increases,
the fluid acquires more uniform velocity distribution close to the substrate, leading to more homogenous and uniform films. 相似文献
996.
Jorge P. López‐Alonso Dr. Miguel A. Pardo‐Cea Irene Gómez‐Pinto Dr. Irene Fernández Dr. Avijit Chakrabartty Prof. Enrique Pedroso Prof. Carlos González Prof. Douglas V. Laurents Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(18):5314-5323
KIA7, a peptide with a highly restricted set of amino acids (Lys, Ile, Ala, Gly and Tyr), adopts a specifically folded structure. Some amino acids, including Lys, Ile, Ala, Gly and His, form under the same putative prebiotic conditions, whereas different conditions are needed for producing Tyr, Phe and Trp. Herein, we report the 3D structure and conformational stability of the peptide KIA7H, which is composed of only Lys, Ile, Ala, Gly and His. When the imidazole group is neutral, this 20‐mer peptide adopts a four‐helix bundle with a specifically packed hydrophobic core. Therefore, one‐pot prebiotic proteins with well‐defined structures might have arisen early in chemical evolution. The Trp variant, KIA7W, was also studied. It adopts a 3D structure similar to that of KIA7H and its previously studied Tyr and Phe variants, but is remarkably more stable. When tested for ribonucleolytic activity, KIA7H, KIA7W and even short, unstructured peptides rich in His and Lys, in combination with Mg++, Mn++ or Ni++ (but not Cu++, Zn++ or EDTA) specifically cleave the single‐stranded region in an RNA stem–loop. This suggests that prebiotic peptide–divalent cation complexes with ribonucleolytic activity might have co‐inhabited the RNA world. 相似文献
997.
Bañuelos-Prieto J Agarrabeitia AR Garcia-Moreno I Lopez-Arbeloa I Costela A Infantes L Perez-Ojeda ME Palacios-Cuesta M Ortiz MJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(47):14094-14105
Asymmetrically substituted BODIPY analogues of the dye PM567 have been synthesised from 2-acylpyrroles and pyrroles that bear indene, fluorene or difluorene units. The type of linkage between the fluorene and the BODIPY core plays an important role in the photophysics of the BODIPY chromophore. Indeed, an aliphatic bridge gives rise to an energy-transfer process between the chromophores, whereas a vinyl spacer allows an electronic interaction between them, leading to a large red shift of the spectral bands. The laser action of the new dyes has been analysed under transversal pumping at 10 Hz repetition rate, in both liquid phase and incorporated into solid polymeric matrices. Lasing efficiencies of up to 40% were reached with high photostabilities with the laser output remaining at the initial level after 1×10(5) pump pulses in the same position of the sample. The laser action of the new dyes outperforms the laser behaviour of commercial dyes that emit in the same spectral region. The replacement of fluorene by indene quenches the fluorescence and laser emission, but allows the development of an iron cation fluorescent sensor. 相似文献
998.
Franck Denat Prof. Dr. Yuri Antonio Diaz‐Fernandez Dr. Luca Pasotti Dr. Nicolas Sok Dr. Piersandro Pallavicini Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(4):1289-1295
A multitasking fluorescent device can be obtained by forming micelles of Triton X‐100, containing a lipophilic macrocyclic Cu2+ complex and the coordinating fluorophore Coumarin 343 (C343), which features a COOH moiety. At low pH the two micellised components do not interact, and the fluorescence of Courmarin 343 (C343) is intense. At intermediate pH, C343 is deprotonated and coordinates to the Cu2+ centre in its apical position, with fluorescence quenching. At higher pH the deprotonated C343 is displaced from Cu2+ by the formation of an OH? complex, and the fluorescence is revived. This allows the system to carry out its first task as it behaves as an “on–off–on” fluorescent sensor for pH windows. The “off” part of the window ranges from pH 6 to 8. In this interval, in which the carboxylate form of C343 is apically coordinated to the Cu2+ complex inside micelles, the device carries out its second task, that is, it behaves as a gauge for lipophilicity. For pHs between 6 and 8, molecules containing a COOH group are in their COO? form and distribute between bulk water and micelles proportionally to their lipophilicity. Upon entering the micelle, their COO? moiety competes for coordination with C343, displacing it from the Cu2+ centre, and this results in fluorescence revival, the intensity of which is also proportional to the lipophilicity of the examined molecule. We have chosen the physiological pH value (7.4) as the working pH, and we have examined the lipophilicity of fatty acids and of the widely used family of non‐steroidal anti‐inflammatory drugs (NSAIDs). The device successfully measures their lipophilicity, expressing it with an “off–on” type fluorescent signal, as demonstrated by the correlation of the fluorescence increase with the logarithmic water/octanol partition coefficient (log P) and with the difference between the pKa observed in micelles and that measured in water for NSAIDs. 相似文献
999.
1000.