全文获取类型
收费全文 | 247篇 |
免费 | 21篇 |
国内免费 | 9篇 |
专业分类
化学 | 44篇 |
晶体学 | 3篇 |
力学 | 6篇 |
综合类 | 2篇 |
数学 | 61篇 |
物理学 | 64篇 |
综合类 | 97篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 14篇 |
2012年 | 9篇 |
2011年 | 20篇 |
2010年 | 12篇 |
2009年 | 16篇 |
2008年 | 15篇 |
2007年 | 17篇 |
2006年 | 19篇 |
2005年 | 11篇 |
2004年 | 13篇 |
2003年 | 8篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 22篇 |
1999年 | 16篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有277条查询结果,搜索用时 15 毫秒
81.
Molybdenum-95 NMR spectra of a series of phosphine and phosphite substituted molybdenum carbonyls Mo(CO)6-n
L
n
[L=P(OCH3)3
n=1, 2, 3, 4, 5,L=P(OC2H5)3
n=1, 2, 3,L=P(C6H5)3
n=1] including isomers (cis,trans,fac,mer) are reported, A large range of chemical shifts is found for the title compounds. The coupling constants1
J(95Mo-31P) are derived either from95Mo-NMR spectra or31P-NMR spectra. Syntheses of the measured compounds were performed by thermal or photochemical ligand substitution.
Molybdän-95 NMR einer Reihe von Phosphin- und Phosphit-substituierten Molybdäncarbonylen Mo(CO)6–n(L) n (n=1, 2, 3, 4, 5)
Zusammenfassung Es werden die95Mo-NMR-Spektren der im Titel genannten Verbindungen mitL=P(OCH3)3 n=1–5,L=P(OC2H5)3 n=1–3 undL=P(C6H5)3 n=1, einschließlich von Isomeren (cis, trans, fac, mer) angegeben. Für die chemischen Verschiebungen wurde ein sehr weiter Bereich beobachtet. Die Kopplungskonstanten1 J(95Mo-31P) wurden entweder von den95Mo- oder31P-NMR-Spektren ermittelt. Die Synthese der Verbindungen erfolgte mittels thermischem oder photochemischem Ligandenaustausch.相似文献
82.
Zoran Samard?ijaRID=""ID="" To whom correspondence should be addressed Darko Makovec Miran ?eh 《Mikrochimica acta》2000,132(2-4):383-386
Yttrium-doped BaTiO3 ceramics have been studied as a potential material for positive temperature coefficient resistors (PTCR). The mechanism of
Y incorporation into BaTiO3 plays an important role for displaying good electrical properties. Determination of the amount of yttrium in the BaTiO3 as well as microstructure characterization of the samples were performed using SEM, EDS and WDS analysis. An optimized trace
element WDS quantitative analysis was applied to determine elemental concentrations for Ba, Ti and Y in the samples as accurately
as possible. BaTiO3 and Y2O3 were used as standards. Analysis was undertaken using a JEOL JXA 840A electron probe microanalyzer. WDS X-ray intensity measurements
were performed under 20 kV, 50 nA beam current and 0.2% preset standard counting deviation (σc) using a PET crystal. Measured k-ratios were quantified by ZAF matrix correction. Average results of WDS quantitative analysis showed 20.17 ± 0.08 at % Ti,
19.95 ± 0.09 at % Ba, 0.22 ± 0.03 at % Y, and 59.66 at % O. The results suggest incorporation of yttrium in the BaTiO3 preferentially at the Ba-sites, however partial incorporation of Y at Ti-sites could not be excluded. 相似文献
83.
《Arabian Journal of Chemistry》2022,15(7):103892
The purpose of this study was to illustrate the mechanism of “enzyme inactivation and toxicity reduction” of Fructus Tribuli (FT) after being heating processed. Ultra-high performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry (UHPLC-MS/MS) was used to quantitatively analyze the contents of four steroidal saponins in crude Fructus Tribuli (CFT) and stir-fried Fructus Tribuli (SFT) under different storage times at room temperature. The enzyme activity of β-D-glucosidase in CFT and SFT were determined and calculated by ultraviolet–visible spectrometry (UV-VIS spectrometry). In addition, the enzyme hydrolysates of FOT and tribuluside A were qualitatively analyzed by ultra-high-performance liquid chromatography coupled with quadruple-time-of-flight mass spectrometry (UHPLC-Q-TOF/MS). The hepatorenal toxicity of spirostanol saponins in FT were further confirmed by in vivo and in vitro experiment. This study confirmed that “enzyme inactivation and toxicity reduction” was one of the reasons why the stir-frying can reduce hepatorenal toxicity of FT, and further enriched the exploration on the mechanism of processing toxicity reduction. 相似文献
84.
P. Staszczuk 《Journal of Thermal Analysis and Calorimetry》1997,48(4):755-767
This paper presents investigations of phase and structural transitions occurring in water adsorbed on the surface of bovine serum albumin (BSA) and on the so-called intelligentrs or smart silica gel surface covered with a chemically bonded BSA phase. Cyclic changes of heat flow (HF) were observed in the samples studied during cooling and heating of the measuring cell of the differential scanning calorimetry (DSC) apparatus. These cyclic changes reflect structural transitions occurring in the water adsorbed on the surface at subambient and elevated temperatures. This is connected with cyclic changes (decay and reproduction) of ice-like structures existing in the adsorbed water layers. On the basis of quantitative investigations it appears that, depending on the direction of the cooling or heating process of the samples studied, the number of ice-like water structures in the surface film increases or decreases. It has been stated that the observed fluctuations occur spontaneously and suddenly in the whole volume of adsorbed water in different and not regular temperature ranges, especially at the paradoxical effect temperatures.Support from the Research Council (Dr. R. K. Gilpin and Dr. M. Jaroniec) of Kent State University (Ohio, USA) is acknowledged. The author thanks Dr. V. Tittlebach for providing the samples of pure BSA and silica gel with chemically, bonded BSA phase. 相似文献
85.
86.
以苯甲硫醚(Ph SMe)为化学毒剂芥子气的模拟剂,研究了Na2Mo O4催化H2O2溶液氧化Ph SMe的两阶段反应动力学及产物分布.Ph SMe在Na2Mo O4催化H2O2溶液中生成了苯甲亚砜(Ph S(O)Me)和苯甲砜(Ph S(O)2Me).相对无催化H2O2溶液,Na2Mo O4催化在加快Ph SMe氧化为Ph S(O)Me的同时,也将过度氧化产物Ph S(O)2Me的产率提高了两个数量级.95Mo NMR测试表明,Mo O42-与H2O2反应生成了钼酸盐过氧配合物Mo Ox(OO)(4-x)2-,当H2O2/Mo O42-5时,Mo(O2)42-是主要的活性物种,通过直接氧转移方式导致硫醚→亚砜→砜的氧化. 相似文献
87.
Delphi高级接口技术及其在数据处理中的应用 总被引:3,自引:0,他引:3
在Delphi7.0环境下利用OLE Automation技术实现了Delphi,Fortran,Surfer和AutoCAD的无缝集成,并编制出一套地震面波频散曲线自动成图以及频散数据自动读取的应用软件,同时给出了在地震海量数据处理方面的应用实例. 相似文献
88.
The effect of input power fluctuation on photo-thermal shot noise in the end mirrors of a laser interferometer gravitational-wave observatory (LIGO) is analysed according to the statistical optics, which is a supplement of Braginsky's research. The laser light folding in LIGO increases a correlation of input power fluctuation in the photo-thermal shot noise. This part of noise has spectral density proportional to -2 in low frequency bands, and -4 in high frequency bands. It is not a white noise and may affect the processing about data of interferometers. To obtain an advanced LIGO, photo-thermal shot noise in end mirrors due to correlation of input power fluctuation is up to Braginsky's photo-thermal noise in the frequency range 1-100 Hz. 相似文献
89.
以溶胶-凝胶法合成了阴阳离子复合掺杂尖晶石型锰酸锂正极材料LiCu0.05M0.95O3.9F0.1 ,XRD表征合成产物具有良好的尖晶石结构;SEM测试表明所合成产物的颗粒达到了亚微米级,且分布均匀,形貌较好。以该物质作为锂离子电池的正极材料组装成扣式电池,经充放电循环测试可知:LiCu0.05Mn1.95O3.9F0.1材料比LiMn2O4正极材料能够更好地抑制电池的可逆容量在充放电过程中的衰减,循环性能有了很大改善,表现出很好的电化学可逆特性。 相似文献
90.
Shao jun Zhang Qingpu Wang Zhaobing Tian Xin Yin Huaijin Zhang Yunchu Li Shichen Li 《Optics & Laser Technology》2005,37(8):2085
The polarization rotating coefficient and the laser-damage threshold of La3Ga5SiO14 crystal at 1064 nm are measured, which are 1.1 deg/mm and , respectively. The working principle and the design method of electrooptic Q-switch based on La3Ga5SiO14 crystal, which has the optical activity, are reported. The performance of Nd:YLF laser with the electrooptic Q-switch of La3Ga5SiO14 crystal was studied. The output pulses with an energy of 379 mJ, a duration of 8.7 ns and repetition of 10 Hz are achieved. 相似文献