全文获取类型
收费全文 | 5926篇 |
免费 | 1010篇 |
国内免费 | 583篇 |
专业分类
化学 | 3849篇 |
晶体学 | 56篇 |
力学 | 261篇 |
综合类 | 31篇 |
数学 | 771篇 |
物理学 | 2551篇 |
出版年
2024年 | 23篇 |
2023年 | 134篇 |
2022年 | 211篇 |
2021年 | 223篇 |
2020年 | 240篇 |
2019年 | 201篇 |
2018年 | 187篇 |
2017年 | 184篇 |
2016年 | 292篇 |
2015年 | 258篇 |
2014年 | 321篇 |
2013年 | 403篇 |
2012年 | 492篇 |
2011年 | 560篇 |
2010年 | 340篇 |
2009年 | 341篇 |
2008年 | 366篇 |
2007年 | 337篇 |
2006年 | 319篇 |
2005年 | 265篇 |
2004年 | 197篇 |
2003年 | 174篇 |
2002年 | 199篇 |
2001年 | 152篇 |
2000年 | 133篇 |
1999年 | 157篇 |
1998年 | 129篇 |
1997年 | 112篇 |
1996年 | 109篇 |
1995年 | 72篇 |
1994年 | 56篇 |
1993年 | 56篇 |
1992年 | 48篇 |
1991年 | 60篇 |
1990年 | 31篇 |
1989年 | 27篇 |
1988年 | 22篇 |
1987年 | 17篇 |
1986年 | 23篇 |
1985年 | 17篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有7519条查询结果,搜索用时 0 毫秒
51.
Wang Shutao Wang Enbo Hou Yu Li Yangguang Wang Li Yuan Mei Hu Changwen 《Transition Metal Chemistry》2003,28(6):616-620
A novel organic/inorganic hybrid molybdenum phosphate, [NH3(CH2CH2)2NH3]3[NH3(CH2CH2)2NH2]Na5-[Mo6O12(OH)3(PO4)(HPO4)3]2·4H2O (1), involving molybdenum presented in V oxidation, has been hydrothermally prepared and characterized by elemental analysis, i.r., u.v.–vis., x.p.s., t.g. and single crystal X-ray diffraction. The structure of the title compound (1) may be considered to consist of two [Mo6O12(OH)3(PO4)(HPO4)3] units bonded together with NaO6 octahedra, forming dimers. Further, these dimers connect with each other through four Na+ cations as bridges, giving rise to novel one-dimensional chain-like skeleton. Piperazines exist among inorganic chains acting as charge balancing cations. 相似文献
52.
Adam D. Martin Jonathan P. Wojciechowski Eric Y. Du Aditya Rawal Holly Stefen Carol G. Au Liming Hou Charles G. Cranfield Thomas Fath Lars M. Ittner Pall Thordarson 《Chemical science》2020,11(5):1375
Peptide-based nanofibres are a versatile class of tunable materials with applications in optoelectronics, sensing and tissue engineering. However, the understanding of the nanofibre surface at the molecular level is limited. Here, a series of homologous dilysine–diphenylalnine tetrapeptides were synthesised and shown to self-assemble into water-soluble nanofibres. Despite the peptide nanofibres displaying similar morphologies, as evaluated through atomic force microscopy and neutron scattering, significant differences were observed in their ability to support sensitive primary neurons. Contact angle and labelling experiments revealed that differential presentation of lysine moieties at the fibre surface did not affect neuronal viability; however the mobility of phenylalanine residues at the nanofibre surface, elucidated through solid- and gel-state NMR studies and confirmed through tethered bilayer lipid membrane experiments, was found to be the determining factor in governing the suitability of a given peptide as a scaffold for primary neurons. This work offers new insights into characterising and controlling the nanofibre surface at the molecular level.The mobility of hydrophobic moieties at a peptide nanofibre surface determines its suitability as a scaffold for sensitive primary cells. 相似文献
53.
Determination of pesticides in soil by liquid-phase microextraction and gas chromatography-mass spectrometry 总被引:4,自引:0,他引:4
Trace amounts of pesticides in soil were determined by liquid-phase microextraction (LPME) coupled to gas chromatography-mass spectrometry (GC-MS). The technique involved the use of a small amount (3 microl) of organic solvent impregnated in a hollow fiber membrane, which was attached to the needle of a conventional GC syringe. The organic solvent was repeatedly discharged into and withdrawn from the porous polypropylene hollow fiber by a syringe pump, with the pesticides being extracted from a 4 ml aqueous soil sample into the organic solvent within the hollow fiber. Aspects of the developed procedure such as organic solvent selection, extraction time, movement pattern of plunger, concentrations of humic acid and salt, and the proportion of organic solvent in the soil sample, were optimized. Limits of detection (LOD) were between 0.05 and 0.1 microg/g with GC-MS analysis under selected-ion monitoring (SIM). Also, this method provided good precision ranging from 6 to 13%; the relative standard deviations were lower than 10% for most target pesticides (at spiked levels of 0.5 microg/g in aqueous soil sample). Finally, the results were compared to those achieved using solid-phase microextraction (SPME). The results demonstrated that LPME was a fast (within 4 min) and accurate method to determine trace amounts of pesticides in soil. 相似文献
54.
The adsorption properties of NO molecule on anionic, cationic, and neutral Au(n) clusters (n=1-6) are studied using the density functional theory with the generalized gradient approximation, and with the hybrid functional. For anionic and cationic clusters, the charge transfer between the Au clusters and NO molecule and the corresponding weakening and elongation of the N-O bond are essential factors of the adsorption. The neutral Au clusters have also remarkable adsorption ability to NO molecule. The adsorption energies of NO on the cationic clusters are generally greater than those on the neutral and anionic clusters. 相似文献
55.
The isospecific 3,4-polymerization of isoprene has been achieved for the first time by use of a combination of a binuclear rare earth metal dialkyl complex, such as [Me2Si(C5Me4)(mu-PCy)YCH2SiMe3]2 (Cy = cyclohexyl), and an equimolar amount of [Ph3C][B(C6F5)4] as a catalyst system. A DFT calculation suggested that a binuclear monocationic monoalkyl species, such as [Me2Si(C5Me4)(mu-PCy)Y(mu-CH2SiMe3)Y(mu-PCy)(C5Me4)SiMe2]+, in which the alkyl group bridges the two metal centers, could be the true catalyst species. 相似文献
56.
π‐Allyl (η3‐C3H5), a four‐electron donor, was used as a ligand model to replace η5‐C5Me4SiMe3 in DFT calculations on the tetranuclear yttrium polyhydrido complex (η5‐C5Me4SiMe3)4Y4H8 containing a Y4H8 tetrahedral core structure, which may separate the four π‐allyl groups and hence suppress the allyl ligand coupling during the computation. In terms of the calculated core geometry, isomerization energy barrier, charge population, and frontier orbital features of the complex, the η3‐C3H5 ligand model is comparable to η5‐C5H5. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
57.
What is the most favorite and original chemistry developed in your research group? We focus on developing new organic photovoltaic materials and exploring their applications in photovoltaic devices. Based on the new materials, we can figure out the correlations among chemical strictures, optoelectronic properties, and photovoltaic behaviors. Our group originally demonstrated quite a few build blocks for making conjugated polymers for photovoltaic applications, some of them have been broadly used by the researchers in the field. How do you get into this specific field? Could you please share some experiences with our readers? I got into this field when I was a graduate student in 2002, just because my supervisor gave me a research topic for synthesis of new conjugated polymers. At that moment, as a fresh graduate student, I had no chance to say yes or no, but to do it. The field of organic solar cells is oriented by the new organic photovoltaic materials. In the past decades, the materials have been updated for a few generations, which promoted the device performance to be higher and closer to practical applications. We have to concentrate on the fundamental problems but also need to follow the pace of the filed. How do you supervise your students? In my opinion, the students need more specific projects to get into the field so as to be well trained at the beginning. In the later stage, I prefer to encourage them to find and creatively figure out the real fundamental problems. I used to give them a few questions: Why do you need to do this project? How to make a clear definition for the problem? Can you suggest a new and better approach to solve it? What is the most important personality for scientific research? Passion, perseverance and sense of innovation. What is your favorite journal(s)? The journals publishing the latest and/or systematic research works in chemistry and material science. 相似文献
58.
A simple method was used to prepare a "switchable" electrode surface by using self-assembled monolayers of dodecanethiol on a gold electrode. The dodecane-modified electrode was electrochemically inactive until the monolayer was soaked in solutions of 1,10-phenanthroline or 2,2'-bipyridine. The electroactive form of the electrode could be reverted back to the nonelectroactive form by rinsing the electrode. Surface IR results showed that both dodecanethiol and 1,10-phenanthroline exist in the mixed monolayer. 相似文献
59.
The surfactant-encapsulated cluster (SEC) composed of a hydrophobic dimethyl dioctadecyl ammonium (DODA) shell and an encapsulated hydrophilic polyoxoanion core can form casting films. The structure of the casting film is influenced by evaporation rates of organic solvent. When the casting films are prepared by slow evaporation of chloroform, the alkyl chains are considered to possess a partial interdigitation, and the interdigitated length is 1.6 nm. The casting film structure is characterized by scanning force microscopy (SFM), Fourier transformation infrared (FT-IR), wide-angle X-ray diffraction, and differential scanning calorimetry (DSC). 相似文献
60.
Ye Xu Dr. Huifeng Yao Lijiao Ma Ling Hong Jiayao Li Qing Liao Yunfei Zu Jingwen Wang Mengyuan Gao Prof. Long Ye Prof. Jianhui Hou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9089-9095
Decreasing the energy loss is one of the most feasible ways to improve the efficiencies of organic photovoltaic (OPV) cells. Recent studies have suggested that non-radiative energy loss ( ) is the dominant factor that hinders further improvements in state-of-the-art OPV cells. However, there is no rational molecular design strategy for OPV materials with suppressed . Herein, taking molecular surface electrostatic potential (ESP) as a quantitative parameter, we establish a general relationship between chemical structure and intermolecular interactions. The results reveal that increasing the ESP difference between donor and acceptor will enhance the intermolecular interaction. In the OPV cells, the enhanced intermolecular interaction will increase the charge-transfer (CT) state ratio in its hybridization with the local exciton state to facilitate charge generation, but simultaneously result in a larger . These results suggest that finely tuning the ESP of OPV materials is a feasible method to further improve the efficiencies of OPV cells. 相似文献