全文获取类型
收费全文 | 578篇 |
免费 | 29篇 |
国内免费 | 5篇 |
专业分类
化学 | 445篇 |
力学 | 11篇 |
数学 | 70篇 |
物理学 | 86篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 11篇 |
2019年 | 16篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 15篇 |
2015年 | 8篇 |
2014年 | 13篇 |
2013年 | 26篇 |
2012年 | 40篇 |
2011年 | 50篇 |
2010年 | 31篇 |
2009年 | 18篇 |
2008年 | 38篇 |
2007年 | 36篇 |
2006年 | 38篇 |
2005年 | 30篇 |
2004年 | 14篇 |
2003年 | 19篇 |
2002年 | 20篇 |
2001年 | 22篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1980年 | 2篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1968年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有612条查询结果,搜索用时 0 毫秒
71.
Zhao X Yeung N Russell BS Garner DK Lu Y 《Journal of the American Chemical Society》2006,128(21):6766-6767
The effects of metal ions on the reduction of nitric oxide (NO) with a designed heme copper center in myoglobin (F43H/L29H sperm whale Mb, CuBMb) were investigated under reducing anaerobic conditions using UV-vis and EPR spectroscopic techniques as well as GC/MS. In the presence of Cu(I), catalytic reduction of NO to N2O by CuBMb was observed with turnover number of 2 mol NO.mol CuBMb-1.min-1, close to 3 mol NO.mol enzyme-1.min-1 reported for the ba3 oxidases from T. thermophilus. Formation of a His-heme-NO species was detected by UV-vis and EPR spectroscopy. In comparison to the EPR spectra of ferrous-CuBMb-NO in the absence of metal ions, the EPR spectra of ferrous-CuBMb-NO in the presence of Cu(I) showed less-resolved hyperfine splitting from the proximal histidine, probably due to weakening of the proximal His-heme bond. In the presence of Zn(II), formation of a five-coordinate ferrous-CuBMb-NO species, resulting from cleavage of the proximal heme Fe-His bond, was shown by UV-vis and EPR spectroscopic studies. The reduction of NO to N2O was not observed in the presence of Zn(II). Control experiments using wild-type myoglobin indicated no reduction of NO in the presence of either Cu(I) or Zn(II). These results suggest that both the identity and the oxidation state of the metal ion in the CuB center are important for NO reduction. A redox-active metal ion is required to deliver electrons, and a higher oxidation state is preferred to weaken the heme iron-proximal histidine toward a five-coordinate key intermediate in NO reduction. 相似文献
72.
A continuous-wave 280 nm light-emitting diode (LED) was used as the excitation source for native fluorescence detection of proteins in CE. The operating current and temperature of the LED were optimized in order to achieve high luminescence power. It was found that a forward current of 30 mA and a temperature of approximately 5 degrees C gave the best S/N. By using a set of two ball lenses to focus light from the LED, we achieved a spot of approximately 200 mum with a power of 0.1-0.2 mW on the detection window. Fluorescence was collected with a ball lens at 90 degrees angle through a bandpass filter onto a photomultiplier tube. In CZE an LOD of 20 nM for conalbumin was reached. In capillary gel electrophoresis all eight proteins from a commercial standard kit were detected with high S/N. For a 10 microg/mL total protein mixture, S/N was better than 3 for all proteins in solution. Further improvement in LOD should be possible on utilization of an LED with higher luminescence power. 相似文献
73.
Yeung WF Lau PH Lau TC Wei HY Sun HL Gao S Chen ZD Wong WT 《Inorganic chemistry》2005,44(19):6579-6590
The synthesis, structures, and magnetic properties of four cyano-bridged M(II)Ru(III)2 compounds prepared from the paramagnetic Ru(III) building blocks, trans-[Ru(salen)(CN)2]- 1 [H2salen = N,N'-ethylenebis(salicylideneimine)] and trans-[Ru(acac)2(CN)2]- (Hacac = acetylacetone), are described. Compound 2, {Mn(CH3OH)4[Ru(salen)(CN)2]2}.6CH3OH.2H2O, is a trinuclear complex that exhibits antiferromagnetic coupling between Mn(II) and Ru(III) centers. Compound 3, {Mn(H2O)2[Ru(salen)(CN)2]2.H2O}n, has a 2-D sheetlike structure that exhibits antiferromagnetic coupling between Mn and Ru, leading to ferrimagnetic-like behavior. Compound 4, {Ni(cyclam)[Ru(acac)2(CN)2]2}.2CH3OH.2H2O (cyclam = 1,4,8,11-tetraazacyclotetradecane), is a trinuclear complex that exhibits ferromagnetic coupling. Compound 5, {Co[Ru(acac)2(CN)2]2}n, has a 3-D diamond-like interpenetrating network that exhibits ferromagnetic ordering below 4.6 K. The density functional theory (DFT) method was used to calculate the molecular magnetic orbitals and the magnetic exchange interaction between Ru(III) and M(II) (Mn(II), Ni(II)) ions. 相似文献
74.
A computer-controlled galvanometer scanner is adapted for scanning a focused laser beam across a 96-capillary array for laser-induced fluorescence detection. The signal at a single photomultiplier tube is temporally sorted to distinguish among the capillaries. The limit of detection for fluoresceins is 3 x 10(-11) M (S/N = 3) for 5 mW of total laser power scanned at 4 Hz. The observed cross-talk among capillaries is 0.2%. Advantages include the efficient utilization of light due to the high duty-cycle of step scan, good detection performance due to the reduction of stray light, ruggedness due to the small mass of the galvanometer mirror, low cost due to the simplicity of components, and flexibility due to the independent paths for excitation and emission. 相似文献
75.
Li Liu Ling‐Xiang Qiao Shi‐Zhong Liu Dong‐Mei Cui Chun‐Mei Zhang Zheng‐Ji Zhou Zu‐Liang Du Wai‐Yeung Wong 《Journal of polymer science. Part A, Polymer chemistry》2008,46(10):3193-3206
A new family of organometallic/inorganic composite Langmuir‐Blodgett (LB) films consisting of rigid‐rod polyplatinayne polymer ([Pt‐T(OMe‐Fl)T]∞ or [Pt‐T(F‐Fl)T]∞, where the triplet bonds are abbreviated by T, and fluorene ring by Fl) as the π‐conjugated organometallic molecule, polyoxometalate (POM, POM = K3PMo12O40, H3PW12O40, or H6P2W18O62) of the Keggin and Dawson structures as the inorganic component, and dimethyldioctadecylammonium bromide (DODA) or a mixture of octadecanoic acid (OA) and docosanoic acid (DA) as the auxiliary film‐forming agent were prepared and characterized by π–A isotherms, UV–Vis absorption spectra, photoluminescence spectra, atomic force microscopy imaging, scanning tunneling microscopy, and low‐angle X‐ray diffraction. Our experimental results indicate that steady, even, and ordered Langmuir and LB films are formed in pure water and polyoxometalate subphases. It was shown that the POM molecules are probably embedded inside the polyplatinayne molecules in the LB film structure and they can quench the luminescence of the Pt polyyne. These Pt‐polyyne based LB films display interesting electric conductivity behavior. [Pt‐T(OMe‐Fl)T]∞/DODA/HPW12 monolayer film shows a good electrical conductivity, and the tunneling current amounts to ±100 nA when the voltage is set at ±8 V. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3193–3206, 2008 相似文献
76.
Zhou L Tan CK Jiang X Chen F Yeung YY 《Journal of the American Chemical Society》2010,132(44):15474-15476
A novel amino-thiocarbamate-catalyzed bromolactonization of unsaturated carboxylic acids has been developed. The scope of the reaction is evidenced by 22 examples of γ-lactones with up to 99% yield and 93% ee. The protocol was applied in the enantioselective synthesis of the key intermediates of VLA-4 antagonists. 相似文献
77.
David W. K. Yeung 《Annals of Operations Research》2014,220(1):181-204
Adoption of environment-preserving production technique plays a key role to effectively solving the continual worsening global industrial pollution problem. Due to the global nature of environmental effects and trade, unilateral response on the part of one nation is often ineffective. Cooperation in environmental management holds out the best promise of effective action. For cooperation over time to be credible, a dynamic consistency condition which requires the agreed-upon optimality principle to remain in effect throughout the collaboration duration has to hold. In this paper, we present a cooperative dynamic game of collaborative environmental management with production technique choices. A dynamically consistent cooperative scheme is derived. It is the first time that dynamically consistent solution is obtained for dynamic games in collaborative environmental management with production technique choices. The analysis widens the scope of study in global environmental management. 相似文献
78.
79.
80.
An improved synthesis of chiral diols via the asymmetric catalytic hydrogenation of prochiral diones
The rates of the asymmetric hydrogenation of prochiral diketones catalyzed by Ru(BINAP) catalysts were substantially accelerated in the presence of small amounts of a strong acid. 相似文献