全文获取类型
收费全文 | 491篇 |
免费 | 11篇 |
专业分类
化学 | 336篇 |
晶体学 | 8篇 |
力学 | 3篇 |
数学 | 7篇 |
物理学 | 148篇 |
出版年
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 13篇 |
2013年 | 16篇 |
2012年 | 10篇 |
2011年 | 19篇 |
2010年 | 19篇 |
2009年 | 11篇 |
2008年 | 19篇 |
2007年 | 25篇 |
2006年 | 33篇 |
2005年 | 24篇 |
2004年 | 19篇 |
2003年 | 19篇 |
2002年 | 21篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 14篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 11篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1968年 | 5篇 |
1967年 | 3篇 |
排序方式: 共有502条查询结果,搜索用时 78 毫秒
431.
Daniel Citterio Jun Yagi Hideaki Hisamoto Shin-ichi Sasaki Koji Suzuki 《Analytica chimica acta》2003,482(1):19-28
In this paper, new “multiinformation dyes” (MIDs) with extended spectral sensitivity reporting on both changes in solvent polarity (solvatochromism) and in pH (halochromism) by changes in their visible absorption spectra, are presented. The merocyanine dyes 2,6-dibromo-4-[4-(1-dodecyl-4(1H)-pyridinylidene)-2-butenylidene]-2,5-cyclohexadien-1-one (KD-M301) and 2,6-dibromo-4-[4-(1-dodecyl-4(1H)-quinolinylidene)-2-butenylidene]-2,5-cyclohexadien-1-one (KD-M402) were designed, synthesized, and characterized regarding analytical applications. The spectral sensitivity for the MIDs was extended into the near-infrared (NIR) wavelength range (λmax=800 nm in CHCl3 for KD-M402) and at the same time, the degree of solvent polarity-induced spectral shifts was strongly enhanced (Δλmax=202 nm for KD-M402 between tetrahydrofuran (THF) and methanol), reaching similar values to the standard solvatochromic dye Dimroth-Reichardt’s betaine on which the empirical ET(30) classification of solvent polarity is based. Compared to Dimroth-Reichardt’s betaine dye, the molar absorption coefficient ε, is increased more than 10-fold (ε of KD-M402 in THF: 7.7×104 M−1 cm−1), allowing sensitive measurements at low concentrations of the dye. The dodecyl-substituted KD-M402 is suitable as a lipophilic pH indicator in ion-exchange type optical sensors (optodes) with optical detection in the near-infrared wavelength range. 相似文献
432.
Multielement determinations in the certified reference materials of soils (IAEA soil-5 and 7) have been studied fundamentally by instrumental photon activation analysis using the internal standard method coupled with the standard addition method. For the soil-5 sample, in the first place, the qualities of the comparative standards prepared by two processing methods were compared with each other. As a result, it was demonstrated that a highly accurate and precise multielement determination can be achieved easily by minor improvement in the processing method of the comparative standard to ensure homogeneity. The utility of this processing method for soil samples was proved further through a similar analysis in another soil sample (IAEA soil-7). 相似文献
433.
Yagi S Minami N Fujita J Hyodo Y Nakazumi H Yazawa T Kami T Ali AH 《Chemical communications (Cambridge, England)》2002,(20):2444-2445
N2 and CO2 gas permeability of mesoporous silica glass bearing photochromic indolinospironaphth[2,1-b][1,4]oxazine through a covalent linkage was controlled by photo-irradiation: the photo-isomerization of the spironaphthoxazine to the photomerocyanine form suppressed the gas permeation of the glass. 相似文献
434.
Adenosine diphosphatase (ADPase) activity was solubilized with a non-ionic detergent, Tween 20, from human umbilical vessels and purified to homogeneity by diethylaminoethyl-Sepharose CL-6B, adenosine 5'-monophosphate-Sepharose 4B, and concanavalin A-Sepharose chromatography. The apparent molecular mass was 75 kDa. The purified enzyme hydrolyzed pyrophosphate bonds of nucleoside di- and triphosphates in the presence of calcium ion. It was insensitive to the adenosine triphosphatase (ATPase) inhibitors, oligomycin and ouabain, and sensitive to sodium azide. Therefore, we concluded that the ADPase activity in human umbilical vessels does not derive from ADPase degrading only ADP but from ATP diphosphohydrolase (EC 3.6.1.5). The broad substrate specificity and the sensitivity to various inhibitors and calcium ion are common to ATP diphosphohydrolase from bovine aorta. However, there might exist some structural difference around the active site, because the antiserum raised in rabbit against the bovine aorta enzyme scarcely inhibited the human umbilical enzyme. 相似文献
435.
In order to apply the stable-isotope dilution method to charged-particle activation analysis, determination of strontium in biological materials has been studied by proton activation using isotopically enriched86Sr as a spike. To avoid thermal decomposition of biological materials due to the low penetrating power of proton beam, and to eliminate interfering nuclear reactions due to the matrix elements, strontium in the sample and/or isotopic mixture as a comparator was separated chemically together with most of calcium before bombardment, and the fraction isolated was converted to a silica-gel pellet as a most suitable physical and chemical form for bombardment. By processing as above, it was demonstrated that the strontium contents in the biological materials can be determined accurately, precisely and easily. Through a series of experiments, the method was also proved to be applicable for charged-particle activation analysis. 相似文献
436.
A more exact and reliable irradiation system for the photon activation analysis by the use of high power electron linear accelerator
was originally designed and tested. Applications of a simple beam position monitor and a thin beryllium oxide ceramic disk
in this system made possible to control the beam position on the center axis of sample during irradiation, and also permitted
the reproducible irradiations in situ. 相似文献
437.
Kaori Yagi 《Tetrahedron》2006,62(20):4933-4940
CuCN-catalyzed reaction of the (1R)-isomer of 4-cyclopentene-1,3-diol monoacetate with TBDPSO(CH2)6MgCl produced an SN2-type product regioselectively in high yield. Mitsunobu inversion of the product and subsequent Claisen rearrangement furnished aldehyde with the two side chains, from which the title compounds were synthesized efficiently. 相似文献
438.
Takeshi Imanishi Hiroaki Shin Noriyuki Yagi Miyoji Hanaoka 《Tetrahedron letters》1980,21(34):3285-3288
Formal synthesis of (±)-tabersonine (3) and (±)-catharanthine (4) has been achieved starting from ethyl 1,6-dihydro-3 (2H)-pyridinone-1-carboxylate (1a) as a common synthon. 相似文献
439.
Masami Sakamoto Tadao Yagi Shuichiro Kobaru Takashi Mino Tsutomu Fujita 《Tetrahedron letters》2004,45(23):4437-4440
Irradiation of a benzene solution of 2-alkoxy-3-cyanopyridines in the presence of 2-cyanofuran gave 4+4 photoadducts in good yields, and the structure was established by X-ray single crystal analysis. 相似文献
440.
Multielement determinations of coal fly ashes (NIST SRM-1633a and BCR CRM-38) have been carried out by instrumental photon activation analysis using 30 MeV bremsstrahlung and the internal standard method coupled with the standard addition method. In these determinations, some major and minor constituent elements in the samples were properly used as effective internal standards. As a result, it was demonstrated that concentrations of 18 elements were determined accurately and precisely. Furthermore, a similar multielement determination has also been examined using 20 MeV bremsstrahlung. In this case, it was proved that better results can be achieved, because all interfering reactions were eliminated completely. 相似文献