全文获取类型
收费全文 | 2047篇 |
免费 | 289篇 |
国内免费 | 306篇 |
专业分类
化学 | 1667篇 |
晶体学 | 29篇 |
力学 | 97篇 |
综合类 | 23篇 |
数学 | 284篇 |
物理学 | 542篇 |
出版年
2024年 | 2篇 |
2023年 | 34篇 |
2022年 | 53篇 |
2021年 | 44篇 |
2020年 | 66篇 |
2019年 | 73篇 |
2018年 | 74篇 |
2017年 | 59篇 |
2016年 | 86篇 |
2015年 | 96篇 |
2014年 | 103篇 |
2013年 | 140篇 |
2012年 | 185篇 |
2011年 | 184篇 |
2010年 | 128篇 |
2009年 | 119篇 |
2008年 | 138篇 |
2007年 | 126篇 |
2006年 | 113篇 |
2005年 | 101篇 |
2004年 | 101篇 |
2003年 | 78篇 |
2002年 | 94篇 |
2001年 | 71篇 |
2000年 | 57篇 |
1999年 | 58篇 |
1998年 | 47篇 |
1997年 | 28篇 |
1996年 | 29篇 |
1995年 | 18篇 |
1994年 | 23篇 |
1993年 | 20篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有2642条查询结果,搜索用时 31 毫秒
71.
The synthesis of some new N‐[1‐(2,5‐dichlorophenyl)‐5‐methyl‐1,2,3‐triazol‐4‐yl]‐carbamic acid ester derivatives are reported in this paper. The yielded products 6a‐l were confirmed by Elemental analyses, NMR, MS, and IR spectra. 相似文献
72.
K.B. Helean S.V. Ushakov A. Navrotsky J. Lian J.M. Farmer 《Journal of solid state chemistry》2004,177(6):1858-1866
High-temperature oxide melt solution calorimetry and Rietveld refinements of powder X-ray diffraction data were used to investigate the structure (Fd3m; Z=8) and energetics of a series of RE2Ti2O7 (RE=Sm-Lu) compounds with the pyrochlore structure as well as La2Ti2O7 with a layered perovskite-type structure. All of the RE-titanates were found to be stable in enthalpy with respect to their oxides. In the pyrochlore series, Lu2Ti2O7 was least stable in enthalpy (ΔHf-ox at 298 K=−56.0±4.0 kJ/mol); the most stable materials were Gd-, Eu-, and Sm2Ti2O7 with ΔHf-ox at 298 K=−113.4±2.7, −106.1±4.2, −115.4±4.2 kJ/mol, respectively. In general, as the radius ratio of the A- to B-site cations, RA/RB, decreases, the pyrochlore structure becomes less stable. The trend of ionic radius of the RE3+ cation vs. ΔHf-ox at 298 K is non-linear and approximately parallels the increasing “resistance” to ion-beam-induced amorphization as RA/RB decreases. 相似文献
73.
A new dihydrobenzodioxane derivative, origalignanol ( 10 ), together with nine polyphenolic compounds, salvianolic acid A ( 1 ), salvianolic acid C ( 2 ), lithospermic acid ( 3 ), apigenin 7‐O‐β‐D‐glucuronide ( 4 ), apigenin 7‐O‐β‐D‐(6″‐methyl)glucuronide ( 5 ), luteolin, ( 6 ), luteolin 7‐O‐β‐D‐glucopyranoside ( 7 ), luteolin 7‐O‐β‐D‐glucuronide ( 8 ), and luteolin 7‐O‐β‐D‐xylopyranoside ( 9 ), were isolated from the aqueous ethanolic extract of the aerial parts of Origanum vulgare for the first time. The structure of new compound 10 was determined on the basis of spectroscopic methods. Compound 5 is probably an artifact formed during the isolation. Compounds 1, 2 and 3 showed strong DPPH radical scavenging activity with an EC50 of 7.2 ± 0.4, 9.6 ± 0.9, and 9.5 ± 0.7 μM, respectively, and protected rat hepatocytes from CCl4‐damage at 100 μM. 相似文献
74.
Kam Yee Yoon Wen Siang Tan Beng Ti Tey Khai Wooi Lee Kok Lian Ho 《Electrophoresis》2013,34(2):244-253
Hepatitis B core antigen (HBcAg) expressed in Escherichia coli is able to self‐assemble into large and small capsids comprising 240 (triangulation number T = 4) and 180 (triangulation number T = 3) subunits, respectively. Conventionally, sucrose density gradient ultracentrifugation and SEC have been used to separate these capsids. However, good separation of the large and small particles with these methods is never achieved. In the present study, we employed a simple, fast, and cost‐effective method to separate the T = 3 and T = 4 HBcAg capsids by using native agarose gel electrophoresis followed by an electroelution method (NAGE‐EE). This is a direct, fast, and economic method for isolating the large and small HBcAg particles homogenously based on the hydrodynamic radius of the spherical particles. Dynamic light scattering analysis demonstrated that the T = 3 and T = 4 HBcAg capsids prepared using the NAGE‐EE method are monodisperse with polydispersity values of ~15% and ~13%, respectively. ELISA proved that the antigenicity of the capsids was not affected in the purification process. Overall, NAGE‐EE produced T = 3 and T = 4 capsids with a purity above 90%, and the recovery was 34% and 50%, respectively (total recovery of HBcAg is ~84%), and the operation time is 15 and 4 times lesser than that of the sucrose density gradient ultracentrifugation and SEC, respectively. 相似文献
75.
We consider the augmented Lagrangian method (ALM) as a solver for the fused lasso signal approximator (FLSA) problem. The ALM is a dual method in which squares of the constraint functions are added as penalties to the Lagrangian. In order to apply this method to FLSA, two types of auxiliary variables are introduced to transform the original unconstrained minimization problem into a linearly constrained minimization problem. Each updating in this iterative algorithm consists of just a simple one-dimensional convex programming problem, with closed form solution in many cases. While the existing literature mostly focused on the quadratic loss function, our algorithm can be easily implemented for general convex loss. We also provide some convergence analysis of the algorithm. Finally, the method is illustrated with some simulation datasets. 相似文献
76.
Oscillatory interaction between two like‐charged nanoparticles induced by polyelectrolyte brush–solvent interface 下载免费PDF全文
We use two‐dimensional (2D) self‐consistent field theory to study the effective interactions between two like‐charged cylindrical nanoparticles mediated by an oppositely weakly charged polyelectrolyte brush in a solvent solution. In a poor solvent, where a sharp brush–solvent interface forms, an oscillatory interaction is observed when two nanoparticles are both located at the brush–solvent interface. This oscillatory interaction depends on the penetration depths of the particles and their geometric orientations with respect to the substrate. When the particles are both immersed in the brush and/or the particles are oriented vertically or diagonally with large angles to the substrate, the oscillatory behavior disappears. We interpret our findings by analyzing in detail the contributions to the free energy from electrostatic interaction, nonelectrostatic interaction, and entropies, separately. Briefly, the deformations of the interface and the ion layers formed in the vicinity of the interface are responsible for this oscillatory behavior. In a good solvent, where the narrow brush–solvent interface vanishes, the effective particle–particle interactions behave like that for both particles immersed into the brush with poor solvent. They are found to be repulsive. The influences of the particle size, grafting density, and amount of charges and ions are also briefly discussed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1458–1468 相似文献
77.
Two water‐soluble 6‐(pyrazin‐2‐yl)‐1,3,5‐triazine‐2,4‐diamino (pzta)‐based Cu(II) complexes, namely [Cu(l ‐Val)(pzta)(H2O)]ClO4 ( 1 ) and [Cu(l ‐Thr)(pzta)(H2O)]ClO4 ( 2 ) (l ‐Val: l ‐valinate; l ‐Thr: l ‐threoninate), were synthesized and characterized using elemental analyses, molar conductance measurements, spectroscopic methods and single‐crystal X‐ray diffraction. The results indicated that the molecular structures of the complexes are five‐coordinated and show a distorted square‐pyramidal geometry, in which the central copper ions are coordinated to N,N atoms of pzta and N,O atoms of amino acids. The interactions of the complexes with DNA were investigated using electronic absorption, competitive fluorescence titration, circular dichroism and viscosity measurements. These studies confirmed that the complexes bind to DNA through a groove binding mode with certain affinities (Kb = 4.71 × 103 and 1.98 × 103 M?1 for 1 and 2 , respectively). The human serum albumin (HSA) binding properties of the complexes were also evaluated using fluorescence and synchronous fluorescence spectroscopies, indicating that the complexes could quench the intrinsic fluorescence of HSA in a static quenching process. The relevant thermodynamic parameters revealed the involvement of van der Waals forces and hydrogen bonds in the formation of complex–HSA systems. Finally, molecular docking technology was also used to further verify the interactions of the complexes with DNA/HSA. 相似文献
78.
A Resettable Keypad Lock with Visible Readout Based on Closed Bipolar Electrochemistry and Electrochromic Poly(3‐methylthiophene) Films 下载免费PDF全文
Lei Wang Wenjing Lian Hongyun Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(14):4825-4832
A closed bipolar electrode (BPE) system was developed with electrochromic poly(3‐methylthiophene) (PMT) films electropolymerized on the ITO/rGO electrode as one pole of BPE in the reporting reservoir and the bare ITO electrode as another pole of BPE in the analyte reservoir, in which rGO represents reduced graphene oxide. Under a suitable driving voltage (Vtot), the electrochemical reduction/oxidation of electroactive probes, such as H2O2/glutathione (Glu), in the analyte reservoir could induce the reversible color change of PMT films in the reporting reservoir between blue and red. Based on this, a keypad lock with H2O2, Glu, and Vtot=?3.0 V as the three inputs and the color change of PMT films as the visible output was established. This system was easily operated and did not need to synthesize the complex compounds or DNA molecules. The security system was easy to reset and could be used repeatedly. 相似文献
79.
Chen Chen Weng Xinliang Xu Xiao Xia Xiong Xiu Lian Lu Yi Feng Zhou 《Russian Journal of General Chemistry》2013,83(12):2447-2452
We have demonstrated that the fragments of Telaprevir can act as organocatalysts for asymmetric aldol reactions between aromatic aldehydes and acetone under mild conditions. The reaction conditions have been optimized in terms of the catalyst nature, choice of temperature, solvent, additive, and the catalyst loading. Under proper conditions, fairly good yield and enantioselectivity have been achieved. 相似文献
80.