全文获取类型
收费全文 | 1120篇 |
免费 | 50篇 |
国内免费 | 2篇 |
专业分类
化学 | 777篇 |
晶体学 | 25篇 |
力学 | 19篇 |
数学 | 141篇 |
物理学 | 210篇 |
出版年
2023年 | 17篇 |
2022年 | 20篇 |
2021年 | 21篇 |
2020年 | 40篇 |
2019年 | 34篇 |
2018年 | 33篇 |
2017年 | 22篇 |
2016年 | 36篇 |
2015年 | 26篇 |
2014年 | 37篇 |
2013年 | 65篇 |
2012年 | 75篇 |
2011年 | 103篇 |
2010年 | 38篇 |
2009年 | 37篇 |
2008年 | 69篇 |
2007年 | 68篇 |
2006年 | 41篇 |
2005年 | 46篇 |
2004年 | 27篇 |
2003年 | 26篇 |
2002年 | 24篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 8篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1991年 | 7篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1983年 | 5篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1971年 | 6篇 |
1970年 | 6篇 |
1969年 | 8篇 |
1968年 | 8篇 |
1963年 | 6篇 |
1962年 | 8篇 |
1961年 | 11篇 |
1958年 | 7篇 |
1955年 | 5篇 |
排序方式: 共有1172条查询结果,搜索用时 109 毫秒
51.
Sulfur K-edge X-ray absorption spectroscopy of a hydrogen-bonded elongated [Fe4S4]2+ cube is reported. The data show that this synthetic cube is less covalent than a normal compressed cube with no hydrogen bonding. DFT calculations reveal that the observed difference in electronic structure has significant contributions from both the cluster distortion and from hydrogen bonding. The elongated and compressed Fe4S4 structures are found to have different spin topologies (i.e., orientation of the delocalized Fe2S2 subclusters which are antiferromagnetically coupled to each other). It is suggested that the H-bonding interaction with the counterion does not contribute to the cluster elongation. A magneto-structural correlation is developed for the Fe4S4 cube that is used to identify the redox-active Fe2S2 subclusters in active sites of HiPIP and ferredoxin proteins involving these clusters. 相似文献
52.
F. Moritz M. Dey K. Zipperer S. Prinke J. Grotemeyer 《Journal of mass spectrometry : JMS》1993,28(12):1467-1475
Some details of the generation of electrons by impinging a laser beam on a metal surface are described. It is shown that highly efficient electron generation is observed only during the laser pulse. Therefore, this technique delivers intense pulses of electrons. The process is investigated and different ion source set-ups are discussed. In conjunction with a time-of-flight mass spectrometer this technique can be used to produce mass spectra of different samples ranging from simple organic molecules to peptides. 相似文献
53.
Samik Gupta Anil Kumar Barik Sachindranath Pal Arijit Hazra Somnath Roy Ray J. Butcher Susanta Kumar Kar 《Polyhedron》2007
Four cis-dioxomolybdenum complexes of general formula [MoO2(Ln)EtOH] (n = 1–4) and one oxomolybdenum(IV) complex [MoO(L4)EtOH], with potentially tridentate Schiff bases derived from 5-methyl pyrazole-3-carbohydrazide and salicylaldehyde/substituted salicylaldehyde/o-hydroxy acetophenone have been prepared. The Mo(IV) complex is derived from the Mo(VI) dioxo complex by oxotransfer reaction with PPh3. The complexes are characterized by elemental analysis, electronic spectra, IR, 1H NMR, and by cyclic voltammetry. All the Mo(VI) species are crystallographically characterized. The complexes have a distorted octahedral structure in which the ligand behaves as a binegative donor one, leaving the pyrazole –N uncoordinated towards the metal center. It is also revealed from the crystal structure that the Mo(VI) center enjoys an NO5 donor environment. 相似文献
54.
Two diorganotin(IV) complexes of the general formula R2Sn[Ph(O)CCH-C(Me)N-NC(O)Ph] (R=Ph, 1; R=Me, 2) have been synthesised from the corresponding diorganotin(IV) dichloride and the ligand 4-phenyl-2,4-butanedionebenzoylhydrazone(2−) (H2L), derived from benzoyl acetone and benzoyl hydrazide in methanol at room temperature in presence of triethylamine. The syntheses were performed under very mild conditions, at room temperature and without exclusion of air or moisture from the reaction vessel. Previously, rigorous conditions have been considered necessary for these species. The two compounds have been characterised by elemental analysis, IR and 1H, 13C, 15N, 119Sn NMR spectra, and their structures have been confirmed single crystal X-ray structure analysis. The central tin atom of both complexes adopts a distorted trigonal bipyramidal coordination with two ligand oxygen atoms in axial positions, the nitrogen atom of the ligand and two organic groups on tin occupying equatorial sites. 2 has crystallised with two crystallographically independent molecules in the asymmetric unit. The δ(119Sn) values for the complexes 1 and 2 are −151.5 and −146.8 ppm, respectively, thus indicating penta-coordinated tin centres. 相似文献
55.
56.
JPC – Journal of Planar Chromatography – Modern TLC - The four new spray reagents (Benzoic acid and some of its parahaloderivatives) have been introduced. These reagents enable... 相似文献
57.
Mixed Polymer‐Coated Magnetic Nanoparticles as Forward Osmosis Draw Agents of Tuned Hydrophilicity
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. Priyanka Dey Dr. Emad L. Izake 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(32):11253-11260
We recently reported a polymer‐coated magnetic nanoparticle (MNP) draw agent for the forward osmosis (FO) water desalination process. The water flux was found to increase when the polymer poly(sodium acrylate) (PSA) was anchored to the MNP surface as compared to the polymer (or polyelectrolyte solution) alone, due to the polymer chains being stretched out and most of the hydrophilic groups on the polymer contributing to water flux. We herein report the use of a secondary polymer poly(N‐isopropylacrylamide) PNIPAM to manipulate the PSA polymer conformation and influence inter‐ and intrachain interactions to enhance the efficiency of the FO draw agent. These PSA–PNIPAM‐coated MNPs generated a much higher water flux of ~11.66 LMH when compared to the 100 % PSA‐coated MNPs featuring a value of ~5.32 LMH under identical FO conditions. The osmotic pressure and water flux driven by the mixed polymer‐coated MNPs were found to be a strong function of the net polymer coverage on MNPs, that is, net available hydrophilic groups. Our new draw agent demonstrates potential for use in the water industry due to its improved efficiency and cost effectiveness as it uses only ~0.062 % (w/v) of the draw agent solution. 相似文献
58.
59.
60.