全文获取类型
收费全文 | 29194篇 |
免费 | 3644篇 |
国内免费 | 3169篇 |
专业分类
化学 | 21089篇 |
晶体学 | 363篇 |
力学 | 1431篇 |
综合类 | 234篇 |
数学 | 3544篇 |
物理学 | 9346篇 |
出版年
2024年 | 77篇 |
2023年 | 453篇 |
2022年 | 795篇 |
2021年 | 883篇 |
2020年 | 926篇 |
2019年 | 940篇 |
2018年 | 807篇 |
2017年 | 771篇 |
2016年 | 1150篇 |
2015年 | 1179篇 |
2014年 | 1397篇 |
2013年 | 1956篇 |
2012年 | 2308篇 |
2011年 | 2509篇 |
2010年 | 1763篇 |
2009年 | 1734篇 |
2008年 | 1933篇 |
2007年 | 1759篇 |
2006年 | 1579篇 |
2005年 | 1393篇 |
2004年 | 1109篇 |
2003年 | 904篇 |
2002年 | 882篇 |
2001年 | 740篇 |
2000年 | 624篇 |
1999年 | 580篇 |
1998年 | 504篇 |
1997年 | 443篇 |
1996年 | 474篇 |
1995年 | 386篇 |
1994年 | 370篇 |
1993年 | 342篇 |
1992年 | 323篇 |
1991年 | 277篇 |
1990年 | 232篇 |
1989年 | 191篇 |
1988年 | 167篇 |
1987年 | 129篇 |
1986年 | 142篇 |
1985年 | 155篇 |
1984年 | 101篇 |
1983年 | 64篇 |
1982年 | 71篇 |
1981年 | 53篇 |
1980年 | 52篇 |
1979年 | 58篇 |
1978年 | 40篇 |
1976年 | 37篇 |
1974年 | 40篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Prof. Songping Wu Dr. Cuiping Han James Iocozzia Mingjia Lu Rongyun Ge Rui Xu Prof. Zhiqun Lin 《Angewandte Chemie (International ed. in English)》2016,55(28):7898-7922
Germanium‐based nanomaterials have emerged as important candidates for next‐generation energy‐storage devices owing to their unique chemical and physical properties. In this Review, we provide a review of the current state‐of‐the‐art in germanium‐based materials design, synthesis, processing, and application in battery technology. The most recent advances in the area of Ge‐based nanocomposite electrode materials and electrolytes for solid‐state batteries are summarized. The limitations of Ge‐based materials for energy‐storage applications are discussed, and potential research directions are also presented with an emphasis on commercial products and theoretical investigations. 相似文献
992.
A Single Excitation‐Duplexed Imaging Strategy for Profiling Cell Surface Protein‐Specific Glycoforms 下载免费PDF全文
Na Wu Lei Bao Prof. Dr. Lin Ding Prof. Dr. Huangxian Ju 《Angewandte Chemie (International ed. in English)》2016,55(17):5220-5224
This work develops a site‐specific duplexed luminescence resonance energy transfer system on cell surface for simultaneous imaging of two kinds of monosaccharides on a specific protein by single near‐infrared excitation. The single excitation‐duplexed imaging system utilizes aptamer modified upconversion luminescent nanoparticles as an energy donor to target the protein, and two fluorescent dye acceptors to tag two kinds of cell surface monosaccharides by a dual metabolic labeling technique. Upon excitation at 980 nm, only the dyes linked to protein‐specific glycans can be lit up by the donor by two parallel energy transfer processes, for in situ duplexed imaging of glycoforms on specific protein. Using MUC1 as the model, this strategy can visualize distinct glycoforms of MUC1 on various cell types and quantitatively track terminal monosaccharide pattern. This approach provides a versatile platform for profiling protein‐specific glycoforms, thus contributing to the study of the regulation mechanisms of protein functions by glycosylation. 相似文献
993.
Shu‐Jin Li De‐Chun Zhang Zhong‐Lin Huang Yan‐Qiu Zhang Kai‐Bei Yu 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(9):1122-1123
In the cation of the title compound, C15H16NO+·C24H20B?, the pyridyl ring makes a dihedral angle of 14.03° with the phenyl ring. The anion has a slightly distorted tetrahedral geometry and forms honeycomb‐like sheets which extend along the b axis, forming channels containing the cations. A comparison of packing energies reveals a difference between the title compound and a similar material which has non‐linear optical properties. 相似文献
994.
Effects of substituent and solvent on the structure and spectral properties of maleimide derivatives
Chin-Kuen Tai Yih-Jiun Lin Pao-Ling Yeh Yi-Ren Tzeng Yu-Ma Chou Bo-Cheng Wang 《Journal of Molecular Structure》2008,860(1-3):58-63
The maximum absorption wavelength , emission wavelength (λem) and the related oscillator strength (f) of the maleimides in the ground and first excited states were calculated by using the DFT, CIS and the time-dependent density functional theory (TD-DFT) methods, where the molecular structures were optimized by DFT/B3LYP/6-31G* calculation. Solvent effects on the maleimides were examined using the PCM simulation at DFT/B3LYP level with the 6-31G* basis set. For N-substituted maleimide, the substituent gives only a slight influence on the maleimide chromophore, while planar conformation of PhMLH leads to the improvement in π-delocalization from substituent to maleimide unit. For 3,4-substituted maleimide, the steric repulsion between substituent and maleimide chromophore influences the extent of π-delocalization and the molecular conformation. The calculated and λem of maleimides are in good agreement with the experimental data. In the gas phase, both absorption and emission peaks are red-shift as compared to the non-substituted maleimide. Under solvent environment, the more planar conformation of PhMLH shows a blue-shift in the calculated and λem as compared with other N-substituted maleimides. For 3,4-substituted maleimides, the effect of substitution produces the most significant spectral red-shift as compared to other maleimides. 相似文献
995.
Lin N Santoro F Zhao X Rizzo A Barone V 《The journal of physical chemistry. A》2008,112(48):12401-12411
The vibrationally resolved electronic circular dichroism (ECD) spectra of the two dominant conformers of (R)-(+)-3-methylcyclopentanone in gas phase are computed by density functional response theory, with a full account of Franck-Condon and Herzberg-Teller vibrational contributions at the harmonic level. Proper inclusion of the latter contributions was made possible by the recent implementation of effective-scaling computations of vibrational overlaps and of analytical gradients of time dependent DFT. The Coulomb-attenuated Becke three parameters Lee-Yang-Parr (CAM-B3LYP) functional reproduces both the position and the intensity of the experimental peaks, providing a remarkable improvement over the spectra obtained with the popular hybrid B3LYP functional, and allowing a confident assignment of the CD fine vibrational structure. Franck-Condon and Herzberg-Teller contributions are discussed in detail. The computed decrease of the CD intensity in the gas phase upon increase of the temperature of the sample follows the trend observed experimentally in different solvents. 相似文献
996.
Fang J Shan XQ Wen B Lin JM Lu XC Liu XD Owens G 《Langmuir : the ACS journal of surfaces and colloids》2008,24(19):10929-10935
The sorption and desorption of phenanthrene by three engineered nanoparticles including nanosize zerovalent iron (NZVI), copper (NZVC), and silicon dioxide (NSiO2) were investigated. The sorption of phenanthrene onto NSiO2 was linear and reversible due to the hydrophilic properties of NSiO2. In comparison, sorption of phenanthrene onto NZVI and NZVC was nonlinear and irreversible, which was potentially due to the existence of significantly heterogeneous surface energy distribution patterns detected by a standard molecular probe technique. Naphthalene exerted significant competitive sorption with phenanthrene for NZVI and NZVC, and the isotherm of phenanthrene changed from being significantly nonlinear to nearly linear when naphthalene was simultaneously absorbed. A surface adsorption mechanism was proposed to explain the observed sorption and competition of phenanthrene on both NZVI and NZVC. In contrast, no competition was observed for sorption onto NSiO2. The sorption of phenanthrene on all three nanoparticles significantly decreased with increasing pH. The sorption irreversibility of phenanthrene on NZVI and NZVC were significantly enhanced with decreasing pH. A pH-dependent hydrophobic effect and dipole interactions between the charged surface (electron acceptors) and phenanthrene with electron-rich pi systems (electron donors) were proposed to explain the observed pH-dependent sorption. 相似文献
997.
One- and two-photon circular dichroism spectra of R-(+)-3-methyl-cyclopentanone, a system that has been the subject of recent experimental studies of (2+1) resonance-enhanced multiphoton ionization circular dichroism, have been calculated with an origin-invariant density functional theory approximation in the region of the lowest electronic excited states, both for the gas phase and for a selection of solvents. A polarizable continuum model is used in the calculations performed on the solvated system. Two low-lying conformers are analyzed, and a comparison of the intensities and characteristic features is made with the corresponding two-photon absorption for each species, also for the Boltzmann-averaged spectra. The effect of the choice of geometry, basis set, and exchange-correlation functional is carefully analyzed. It is found that a density functional theory approach using the Coulomb attenuating method variant of Becke's three-parameter exchange and the Lee-Yang-Parr correlation functionals with correlation-consistent basis sets of double-zeta quality can reproduce the experimental electronic circular dichroism spectra very well. The features appearing in experiment are characterized in terms of molecular excitations, and the differences in the response of each state in the one- and two-photon processes are highlighted. 相似文献
998.
Certain characteristic fragmentations of tryptamines (indoleethylamine) and phenethylamines are described. Based on the GC-EI/MS, LC-ESI/MS and MALDI/TOFMS, the mass fragmentations of 13 standard compounds, including alpha-methyltryptamine (AMT), N,N-dimethyltryptamine (DMT), 5-methoxy-alpha-methyltryptamine (5-MeO-AMT), N,N-diethyltryptamine (DET), N,N-dipropyltryptamine (DPT), N,N-dibutyltryptamine (DBT), N,N-diisopropyltryptamine (DIPT), 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT), 5-methoxy-N,N-diisopropyltryptamine (5-MeO-DIPT), methamphetamine (MAMP), 3,4-methylenedioxyamphetamine (3,4-MDA), 3,4-methylenedioxymethamphetamine (3,4-MDMA) and 2-methylamino-1-(3,4-methylenedioxyphenyl)butane (MBDB), were compared. As a result, the parent ions of these analytes were hard to be obtained by GC/MS whereas the protonated molecular ions can be observed clearly by means of ESI/MS and MALDI/TOFMS. Furthermore, two major characteristic fragmentations, namely and alpha-cleavage ([M+H](+)-->[3-vinylindole](+)) and beta-cleavage ([M+H](+)-->[CH(2)N(+)R(N1)R(N2)]), are produced when the ESI and MALDI modes are used, respectively. In the case of ESI/MS, the fragment obtained from alpha-cleavage is the major process. In contrast to this, in the case of MALDI/TOFMS, the major fragment is produced via beta-cleavage. The ionization efficiency and fragments formed from either alpha- or beta-cleavages are closely related to the degree of alkylation of the side chain nitrogen in both cases. 相似文献
999.
Highly sensitive sensor for detection of NADH based on catalytic growth of Au nanoparticles on glassy carbon electrode 总被引:1,自引:0,他引:1
Lin Tang Guangming Zeng Guoli Shen Yi Zhang Yuanping Li Changzheng Fan Can Liu Chenggang Niu 《Analytical and bioanalytical chemistry》2009,393(6-7):1677-1684
In this work, an electrochemical dihydronicotinamide adenine dinucleotide (NADH) sensor based on the catalytic growth of Au nanoparticles (Au NPs) on glassy carbon electrode was developed. Catalyzed by Au NPs immobilized on pretreated glassy carbon electrode, the reduction of AuCl4 ? in the presence of hydroquinone and cetyltrimethyl ammonium chloride led to the formation of enlarged Au NPs on the electrode surface. Spectrophotometry and high-resolution scanning electronic microscope (SEM) analysis of the sensor morphologies before and after biocatalytic reaction revealed a diameter growth of the nanoparticles. The catalytic growth of Au NPs on electrode surface remarkably facilitated the electron transfer and improved the performance of the sensor. Under optimal conditions, NADH could be detected in the range from 1.25?×?10?6 to 3.08?×?10?4 M, and the detection limit was 2.5?×?10?7 M. The advantages of the proposed sensor, such as high precision and sensitivity, fast response, low cost, and good storage stability, made it suitable for on-line detection of NADH in complex biological systems and contaminant degradation processes. Figure
Schematic presentation of the bioelectrocatalytic sensing of NADH 相似文献
1000.