全文获取类型
收费全文 | 2324篇 |
免费 | 391篇 |
国内免费 | 252篇 |
专业分类
化学 | 498篇 |
晶体学 | 12篇 |
力学 | 232篇 |
综合类 | 54篇 |
数学 | 628篇 |
物理学 | 1543篇 |
出版年
2024年 | 3篇 |
2023年 | 16篇 |
2022年 | 56篇 |
2021年 | 50篇 |
2020年 | 48篇 |
2019年 | 53篇 |
2018年 | 52篇 |
2017年 | 93篇 |
2016年 | 97篇 |
2015年 | 61篇 |
2014年 | 113篇 |
2013年 | 167篇 |
2012年 | 127篇 |
2011年 | 161篇 |
2010年 | 126篇 |
2009年 | 134篇 |
2008年 | 161篇 |
2007年 | 163篇 |
2006年 | 141篇 |
2005年 | 166篇 |
2004年 | 102篇 |
2003年 | 112篇 |
2002年 | 121篇 |
2001年 | 116篇 |
2000年 | 90篇 |
1999年 | 81篇 |
1998年 | 73篇 |
1997年 | 52篇 |
1996年 | 44篇 |
1995年 | 33篇 |
1994年 | 32篇 |
1993年 | 19篇 |
1992年 | 12篇 |
1991年 | 18篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1970年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有2967条查询结果,搜索用时 125 毫秒
101.
Molecular‐level structures at poly(4‐vinyl pyridine)/acid interfaces probed by nonlinear vibrational spectroscopy 下载免费PDF全文
Mingcong Wang Bolin Li Zhan Chen Xiaolin Lu 《Journal of Polymer Science.Polymer Physics》2016,54(8):848-852
The molecular structures of the interfaces between a solid poly(4‐vinyl pyridine) (P4VP) surface and poly(acrylic acid) (PAA) as well as hydrochloric acid (HCl) solutions were probed using sum frequency generation (SFG) vibrational spectroscopy in situ in real time. Spectroscopic results clearly reveal that the PAA molecules are adsorbed onto the P4VP surface via hydrogen bonding at the P4VP/PAA solution interface while the P4VP surface is protonated at the P4VP/HCl solution interface. Consequently, the water molecules near the interfaces are strongly perturbed by these two interactions, exhibiting different orderings at the two interfaces. This work clearly demonstrates the power of studying the interfacial molecular‐level structures via nonlinear vibrational spectroscopy when molecular adsorption happens at the solid–liquid interface and paves a way for our future study on tracing the adsorption dynamics of polymer chains onto solid surfaces. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 848–852 相似文献
102.
基于对中西部地区15个省市农业转移人口就近城镇化意愿的问卷调查数据,以社会认同度为研究视角,构建多群组结构方程模型分析中西部地区人口就近城镇化的受教育程度差异及其影响因素。研究结果表明:个人特征差异性对中西部地区不同受教育程度的农业转移人口的就近城镇化意愿影响显著;中西部地区不同受教育程度的农业转移人口的社会认同度与其就近城镇化意愿显著正相关,且社会认同度对中西部地区小学及以下学历的农业转移人口就近城镇化意愿的影响最显著,大专及以上学历的农业转移人口的就近城镇化意愿受社会认同度的影响最小。 相似文献
103.
Herbert Hommer Gabriel Cuevas Barbara Gordillo 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2421-2437
By following a previously reported method,1 the synthesis of r-2-alkoxy-cis-4-cis-5-dimethyl-1,3,2-λ3-dioxaphospholanes ligands (1 and 3) was carried out. The purpose of this work is the kinetic study of the inversion barrier at phosphorus for 1 and 3 and the comparison with the already informed dioxaphospholane 2. The kinetic measurements of the thermal isomerization cis-to-trans were performed by 31P NMR spectroscopy, observing a first order kinetics for both compounds. The energy of activation (Ea) for the epimerization of compounds cis-1 and cis-3 was calculated to be 16.0 ± 0.6 and 11.8 ± 0.8 kcal/mol, respectively. The values of the thermodynamic parameters of the transition state (Δ H≠, Δ S≠, Δ G≠) suggest that the inversion at phosphorus not only depends on the spatial requirements of the alkoxy substituent but also on entropic effects. The thermodynamic parameters Δ H°, Δ S°, and Δ G° were also evaluated and they show that the cis isomers are preferred from enthalpic point of view, but entropic effects dominate the equilibrium trans ? cis leading to the entropically favored trans isomers. Furthermore, the results are supported by density functional theory calculations of 1–4 at the B3LYP/6-31G** level. 相似文献
104.
105.
The π–π interactions between CO2 and three aromatic molecules, namely benzene (C6H6), pyridine (C5H5N), and pyrrole (C4H5N), which represent common functional groups in metal‐organic/zeoliticimidazolate framework materials, were characterized using high‐level ab initio methods. The coupled‐cluster with single and double excitations and perturbative treatment of triple excitations (CCSD(T)) method with a complete basis set (CBS) was used to calibrate Hartree–Fock, density functional theory, and second‐order M?ller–Plesset (MP2) with resolution of the identity approximation calculations. Results at the MP2/def2‐QZVPP level showed the smallest deviations (only about 1 kJ/mol) compared with those at the CCSD(T)/CBS level of theory. The strength of π–π binding energies (BEs) followed the order C4H5N > C6H6 ~ C5H5N and was roughly correlated with the aromaticity and the charge transfer between CO2 and aromatic molecule in clusters. Compared with hydrogen‐bond or electron donor–acceptor interactions observed during BE calculations at the MP2/def2‐QZVPP level of theory, π–π interactions significantly contribute to the total interactions between CO2 and aromatic molecules. © 2013 Wiley Periodicals, Inc. 相似文献
106.
Marcus V. P. dos Santos Eduardo C. Aguiar João Bosco P. da Silva Ricardo L. Longo 《Journal of computational chemistry》2013,34(8):611-621
A new approach Procedure for Investigating Categories of Vibrations (PICVib) for estimating vibrational frequencies of selected modes using only the structure and energy calculations at a more demanding computational level is presented and explored. The PICVib has an excellent performance at only a small fraction of the computational demand required for a complete analytical calculation. The errors are smaller than ca. 0.5% when DFT functionals are combined with high level ab initio methods. The approach is general because it can use any quantum chemical program and electronic structure method. It is very robust because it was validated for a wide range of frequency values (ca. 20–4800 cm–1) and systems: XH3 (D3h) with X = B, Al, Ga, N, P, As, O, S, and Se, YH4 (D4h) with Y = C, Si, and Ge, conformers of RDX, SN2 and E2 reactions, [W(dppe)2(NNC5H10)] complex, carbon nanotubes, and hydrogen‐bonded complexes including guanine‐cytosine pair. © 2012 Wiley Periodicals, Inc. 相似文献
107.
采用高温固相反应法在弱还原气氛下制备了Ca2Y7.9(SiO4)6O2-0.5xFx:Eu(2+,3+)0.1(x=0~4)系列荧光粉。晶胞参数a,c和晶胞体积V均随着F-置换量的增加呈线性减小,晶胞参数a和c的变化率相近。荧光体中Eu2+和Eu3+共存,Eu2+3d5/2与Eu3+3d5/2电子结合能分别为1128.4和1136.3 eV,Eu2+的3d5/2与3d3/2的电子结合能差为28.4 eV。Eu2+和Eu3+的3d5/2态XPS峰面积比为6.9∶1。激发光谱由Eu3+的两个电荷迁移(CTS)带和f-f跃迁激发线组成,x=0,1的试样中出现了Eu2+的f-d跃迁强激发谱带。激发到Eu3+的电荷迁移态或激发Eu2+,除了来自Eu3+的5D0能级的发射之外,还观察到了5D1能级的强发射和5D2能级的弱发射,并且激发Eu2+时5D1→7F4发射强度超过5D0→7F2,没有出现Eu2+的明显发射,Eu2+对Eu3+发光起到很好的敏化作用。5DJ(J>0)高能级发射来自4f格位的Eu3+发光中心,Eu2+的敏化起关键作用。Eu3+在4f和6h两种格位的分布比为4∶6。 相似文献
108.
采用单、双取代包括三重激发的二次组态相互作用[QCISD(T)]方法和单、双取代包括非迭代三重激发的耦合簇理论[CCSD(T)]方法, 结合相关一致基组aug-cc-pVXZ (X=D, T, Q, 5)对基态35ClF-和37ClF- (X2Σ+)分子离子进行了结构优化计算. 对CCSD(T)方法的计算结果用四种方法分别外推至基组极限, 得到了体系在基组极限的平衡结构常数. 在CCSD(T)/aug-cc-pVXZ (X=D, T, Q, 5)理论水平进行了单点能扫描. 对扫描计算结果进行基组外推并用Murrell-Sorbie 势能函数拟合得到了体系的解析势能函数表达式, 并进一步得到了35ClF-和37ClF-的光谱常数. 拟合所得势能曲线准确地再现了其离解能和平衡结构特征. 对ClF 中性自由基采用完全相同的理论方法进行了计算. 所得结果与有关文献中的实验结果符合得很好, 而且在一定程度上证明了将该理论方法应用于ClF-分子离子的计算是合适而可靠的. ClF 自由基的优化计算结果还被用于计算其电子亲和能.ClF-的垂直解离能也同时计算得出. 基于ClF-的结构优化和单点能扫描计算结果, 通过求解核运动的径向薛定谔方程, 得到了无转动35ClF-和37ClF-(X2Σ+)的全部振动态及相应的分子常数. 相似文献
109.
以能斯特方程为基础, 通过分析电流密度与氧化还原物种活度变化, 即载流子浓度变化的关系, 计算出有机半导体材料电极电势的变化, 从而建立起有机半导体前线轨道, 即最高占据分子轨道(HOMO)能级和最低未被占据分子轨道(LUMO)能级相对于热力学平衡态的能量位移随电流密度变化的数学关系. 进而依据能级能量位移引起的能隙变化, 提出了有机电致发光显示器(OLED)中“热激子”的产生机制. 相似文献
110.
R. Shanmugam J. Ganesamurthi T.-W. Chen S.-M. Chen M. Balamurugan M.A. Ali A.M. Al-Mohaimeed W.A. Al-onazi K. Alagumalai 《Materials Today Chemistry》2022
Herein, we reported the fabrication of porous iron oxide/carbon black (P–Fe2O3/CB) composite through a two-step engineering method. At first, Prussian blue microcubes were used as a precursor and further calcined to form P–Fe2O3 microcubes. The intercalation of CB nanoparticles with P–Fe2O3 nanocubes was processed through the ultrasonication method. The obtained P–Fe2O3/CB were successfully scrutinized through various physiochemical characterization methods. The proposed P–Fe2O3/CB-modified glassy carbon electrode sensor was successfully implemented in the electrochemical sensing of chlorpromazine hydrochloride due to its very low charge transfer resistance (Rct) compared to the other electrode modifiers. The sensitive detection of CPMH through differential pulse voltammetry exemplifies an excellent electroanalytical performance such as a wide linear range of 0.5–1472 μM, a lower detection limit (0.001 μM), and an appraisable sensitivity of 1.99 μA/μM cm?2 due to its availability of a high number of active sites and its large surface area, respectively. It also expresses excellent selectivity, repeatability, reproducibility, and stability results. Moreover, the practical feasibility of the as-fabricated P–Fe2O3/CB/glassy carbon electrode sensor shows exquisite recovery (98.1–100.8%) results with an appraisable current response in various biological, pharmaceutical, and environmental samples. 相似文献