全文获取类型
收费全文 | 3094篇 |
免费 | 406篇 |
国内免费 | 251篇 |
专业分类
化学 | 1820篇 |
晶体学 | 58篇 |
力学 | 679篇 |
综合类 | 44篇 |
数学 | 349篇 |
物理学 | 801篇 |
出版年
2024年 | 14篇 |
2023年 | 38篇 |
2022年 | 109篇 |
2021年 | 142篇 |
2020年 | 142篇 |
2019年 | 107篇 |
2018年 | 87篇 |
2017年 | 98篇 |
2016年 | 154篇 |
2015年 | 94篇 |
2014年 | 132篇 |
2013年 | 328篇 |
2012年 | 137篇 |
2011年 | 122篇 |
2010年 | 132篇 |
2009年 | 136篇 |
2008年 | 131篇 |
2007年 | 167篇 |
2006年 | 151篇 |
2005年 | 139篇 |
2004年 | 118篇 |
2003年 | 136篇 |
2002年 | 100篇 |
2001年 | 85篇 |
2000年 | 89篇 |
1999年 | 61篇 |
1998年 | 64篇 |
1997年 | 83篇 |
1996年 | 74篇 |
1995年 | 79篇 |
1994年 | 64篇 |
1993年 | 52篇 |
1992年 | 37篇 |
1991年 | 27篇 |
1990年 | 20篇 |
1989年 | 17篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1982年 | 9篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 9篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有3751条查询结果,搜索用时 703 毫秒
111.
In Situ Synthesis and Characterization of Poly(aryleneethynylene)‐Grafted Reduced Graphene Oxide
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Sai Sun Dr. Xiaodong Zhuang Prof. Dr. Bo Liu Luxing Wang Linfeng Gu Prof. Dr. Sannian Song Prof. Dr. Bin Zhang Prof. Dr. Yu Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(7):2247-2252
Using highly soluble bromo‐functionalized reduced graphene oxide (RGBr) as a key graphene template for surface‐directing Sonogashira–Hagihara polymerization, a novel soluble poly(arylene‐ethynylene)‐grafted reduced graphene oxide, hereafter abbreviated as PAE‐g‐RGO, was prepared in situ. The entirely different electron distribution of LUMO and HOMO of PAE‐g‐RGO suggested the existence of a charge‐transfer (CT) state (PAE.?–RGO.+). The negative ΔGCS value (?2.57 eV) indicates that the occurrence of the charge separation via 1RGO* in o‐DCB is exothermic and favorable. Upon irradiation with 365 nm light, the light‐induced electron paramagnetic resonance (LEPR) spectrum of PAE‐g‐RGO showed a decrease in the spin‐state density owing to photoinduced intramolecular electron transfer events in this system. A sandwich‐type Al/PAE‐g‐RGO/ITO device showed representative bistable electrical switching behavior. The nonvolatile memory performance was attributed to the CT‐induced conductance changes, which was supported by molecular computation results and conductive atomic force microscopy (C‐AFM) images. 相似文献
112.
Abdulnasir A. Majeed Mostafa M.H. Khalil Ahmed Fetoh Ayman A. Abdel Aziz G.M. Abu El‐Reash 《应用有机金属化学》2021,35(1)
In this work, (Z)‐N‐benzoyl‐N′‐(1H‐1,2,4‐triazol‐3‐yl)carbamimidothioic acid and its Mn(II), Co(II), Cu(II) and Cd(II) complexes were introduced for the first time. This carbonyl thiourea ligand was prepared by the reaction of 1H‐1,2,4‐triazol‐3‐amine with benzoyl isothiocyanate. The structural elucidation of these compounds was performed using elemental analysis and spectral and magnetic measurements. Octahedral structures of all complexes, except Cd(II) complex with a tetrahedral geometry, were confirmed by applying DFT structural optimization. The thermal decomposition behaviour of metal complexes of carbonyl thiourea ligand is discussed. The calculation of kinetic parameters for prepared complexes (Ea, A, ΔH*, ΔS* and ΔG*) of all thermal degradation stages has been evaluated using two comparable approaches. Antimicrobial and ABTS‐antioxidant studies indicated potent activity of Cd(II) complex compared with the other investigated compounds. The cytotoxic activity of the prepared compounds was investigated in vitro. The results indicated potent activity of Mn(II) complex against both HePG2 (liver carcinoma) and MCF‐7 (breast carcinoma) cancer cells. 相似文献
113.
《Mendeleev Communications》2020,30(5):666-668
- Download : Download high-res image (112KB)
- Download : Download full-size image
114.
Cephalotanins A–D,Four Norditerpenoids Represent Three Highly Rigid Carbon Skeletons from Cephalotaxus sinensis
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Jin‐Biao Xu Dr. Yao‐Yue Fan Prof. Dr. Li‐She Gan Dr. Yu‐Bo Zhou Prof. Dr. Jia Li Prof. Dr. Jian‐Min Yue 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(41):14648-14654
Four polycyclic norditerpenoids, cephalotanins A–D ( 1 – 4 ) representing three unprecedented carbon skeletons with highly rigid ring systems, were isolated from Cephalotaxus sinensis and structurally characterized by a combination of various methods. Compounds 1 and 2 are new skeletal norditerpenoid trilactones, while 3 and 4 are two norditerpenoids featuring different new carbon skeletons. Biosynthetic pathways for 1 – 4 were proposed by involving diverse and very fascinating chemical events with the coexisting cephalotane troponoids as the precursors. Compound 1 exhibited good NF‐κB inhibition with an IC50 value of 4.12±0.61 μΜ. 相似文献
115.
116.
Khazangul A. Ibrahimova Abdulsaid A. Azizov Ofeliya O. Balayeva Rasim M. Alosmanov Sevinj C. Mammadyarova 《Mendeleev Communications》2021,31(1):100-103
- Download : Download high-res image (140KB)
- Download : Download full-size image
117.
《应用有机金属化学》2017,31(7)
The reactions of R3SnCl (R = Me, Bu or Ph) with sodium 4‐phenylbutyrate, Na(OPhb), in EtOH yielded three polymeric triorganotin carboxylates, namely [R3Sn(OPhb)]n (R = Me ( 1 ), Bu ( 2 ) or Ph ( 3 )). All complexes were spectroscopically characterized using Fourier transform infrared, 119Sn Mössbauer, 1H NMR, 13C{1H} NMR and 119Sn{1H} NMR spectral techniques. In addition, the crystal structures of 1 and 3 were determined using single‐crystal X‐ray diffraction. Their polymeric structures are sustained by bridging carboxylates which connect two five‐coordinate Sn(IV) centres. Each metallic cation displays a distorted trigonal bipyramidal coordination geometry (Addison's parameters ranging from 0.84 in 1 to 0.77–0.91 in 3 ), with the oxygen atoms occupying the apical positions and the organic groups at the equatorial corners. The one‐dimensional zigzag chains of 1 propagate along the b ‐axis, whereas 3 displays wave‐like double polymeric chains along the b ‐axis. For both 1 and 3 , parallel one‐dimensional polymeric chains are interconnected by C─H⋅⋅⋅π interactions. The antifungal activity of 1 – 3 was screened against Candida albicans (ATCC 18804), C. tropicalis (ATCC 750), C. glabrata (ATCC 90030), C. parapsilosis (ATCC 22019), C. lusitaniae (CBS 6936) and C. dubliniensis (clinical isolate 28). The antifungal activity of 3 was noteworthy since it was not only more active than 1 and 2 , but also more active than the control drugs (nystatin and fluconazole nitrate) in some cases. 相似文献
118.
Transition metal complexes of Mn(II) and Ni(II) have been synthesized with novel bioactive Schiff's base ligand. Schiff's base ligand i.e. benzoylacetone‐bis(2‐amino‐4‐methylbenzothioazole) has been synthesized via condensation reaction between 2‐amino‐4‐methylbenzothioazole and benzoylacetone in 2:1 ratio, respectively. Synthesized ligand has been characterized using elemental analysis, infra‐red, 1H–NMR and mass spectroscopy techniques. Characterization of complexes was based on magnetic moment, molar conductance, elemental analysis, electronic spectra, infra‐red and EPR spectroscopic techniques. Molar conductance data suggest that metal complexes are non‐electrolytic in nature. Therefore, these complexes are formulated as [M(L)X2], where M = Mn(II), Ni(II), L = Schiff's base ligand, X = Cl?, CH3COO?, NO3?. Data of characterization study suggest octahedral geometry for Mn(II) and Ni(II) complexes. Geometry of metal complexes was also optimized with the help of computational study i.e. molecular modelling. Computational study also suggests octahedral geometry for complexes. Free ligand as well as its all metal complexes have been screened against the growth of pathogenic bacteria (E.coli, S.aureus) and fungi (C.albicans, C.krusei, C.parapsilosis, C.tropicalis) to assess their inhibition potential. The inhibition data revealed that metal complexes exhibit higher inhibition potential against the growth of bacteria and fungi microorganisms than free ligand. 相似文献
119.
The structure of liquid indium in a wide temperature range has been investigated by means of X-ray diffraction and reverse Monte Carlo methods. Analysis of temperature dependence of the interatomic distances and coordination numbers allowed us to determine the existence of structural transformation in a liquid state. Moreover, it was found that at a temperature of 640 K thermal expansion coefficients, estimated from temperature dependence of interatomic distances, change its sign from negative to positive confirming the transformations in structure of liquid indium which are observed by temperature variations. 相似文献
120.
Direct and adjoint global stability analysis of turbulent transonic flows over a NACA0012 profile
下载免费PDF全文
![点击此处可从《国际流体数值方法杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this work, various turbulent solutions of the two‐dimensional (2D) and three‐dimensional compressible Reynolds averaged Navier–Stokes equations are analyzed using global stability theory. This analysis is motivated by the onset of flow unsteadiness (Hopf bifurcation) for transonic buffet conditions where moderately high Reynolds numbers and compressible effects must be considered. The buffet phenomenon involves a complex interaction between the separated flow and a shock wave. The efficient numerical methodology presented in this paper predicts the critical parameters, namely, the angle of attack and Mach and Reynolds numbers beyond which the onset of flow unsteadiness appears. The geometry, a NACA0012 profile, and flow parameters selected reproduce situations of practical interest for aeronautical applications. The numerical computation is performed in three steps. First, a steady baseflow solution is obtained; second, the Jacobian matrix for the RANS equations based on a finite volume discretization is computed; and finally, the generalized eigenvalue problem is derived when the baseflow is linearly perturbed. The methodology is validated predicting the 2D Hopf bifurcation for a circular cylinder under laminar flow condition. This benchmark shows good agreement with the previous published computations and experimental data. In the transonic buffet case, the baseflow is computed using the Spalart–Allmaras turbulence model and represents a mean flow where the high frequency content and length scales of the order of the shear‐layer thickness have been averaged. The lower frequency content is assumed to be decoupled from the high frequencies, thus allowing a stability analysis to be performed on the low frequency range. In addition, results of the corresponding adjoint problem and the sensitivity map are provided for the first time for the buffet problem. Finally, an extruded three‐dimensional geometry of the NACA0012 airfoil, where all velocity components are considered, was also analyzed as a Triglobal stability case, and the outcoming results were compared to the previous 2D limited model, confirming that the buffet onset is well detected. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献