全文获取类型
收费全文 | 297篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
化学 | 254篇 |
晶体学 | 1篇 |
数学 | 29篇 |
物理学 | 36篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 14篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 11篇 |
2014年 | 12篇 |
2013年 | 14篇 |
2012年 | 18篇 |
2011年 | 27篇 |
2010年 | 17篇 |
2009年 | 24篇 |
2008年 | 20篇 |
2007年 | 19篇 |
2006年 | 28篇 |
2005年 | 11篇 |
2004年 | 13篇 |
2003年 | 8篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 5篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有320条查询结果,搜索用时 15 毫秒
181.
182.
Kikushima K Holder JC Gatti M Stoltz BM 《Journal of the American Chemical Society》2011,133(18):6902-6905
The first enantioselective Pd-catalyzed construction of all-carbon quaternary stereocenters via 1,4-addition of arylboronic acids to β-substituted cyclic enones is reported. Reaction of a wide range of arylboronic acids and cyclic enones using a catalyst prepared from Pd(OCOCF(3))(2) and a chiral pyridinooxazoline ligand yields enantioenriched products bearing benzylic stereocenters. Notably, this transformation is tolerant to air and moisture, providing a practical and operationally simple method of synthesizing enantioenriched all-carbon quaternary stereocenters. 相似文献
183.
Masuda K Ishige T Yamada H Fujii K Uekusa H Miura K Yonemochi E Terada K 《Chemical & pharmaceutical bulletin》2011,59(1):57-62
The purpose of the current study was to evaluate the rate of the pseudo-crystalline transformation of thiamine hydrochloride form I to form II depending on the temperature and humidity. Changes in the appearance and weight of form I crystals were observed under humidified conditions using a water vapor sorption system equipped with a CCD camera. The form I crystals and tablets were stored under various temperature and humidity conditions (the saturation salt desiccator method), and the pseudo-crystalline transformation was observed using X-ray powder diffractometry with our laboratory equipment for drug substances and using synchrotron X-ray powder diffractometry for tablets. It was confirmed that the activation energy in the pseudo-crystalline transformation rate from form I to form II was dependent on humidity, and the calculated values were 121-155 kJ/mol at 70-90% relative humidity. Moreover, when thiamine hydrochloride was formulated as tablets, it was confirmed that the transformation rate was slower compared with the drug substances alone. The pseudo-crystalline transformation rate therefore declined after formulation in tablet form, perhaps due to the shielding effects of thiamine hydrochloride crystal from contact with water molecules by excipients, compaction, etc. 相似文献
184.
A range of arylboronic acids undergo a homocoupling reaction in the presence of catalytic amount of gold salts to yield symmetrical biaryls. Alkenylboronic acids, arylboronic esters, and arylborates also participate in the gold-catalyzed homocoupling reaction. 相似文献
185.
Parinayok P Yamashita M Yonezu K Ohashi H Watanabe K Okaue Y Yokoyama T 《Journal of colloid and interface science》2011,364(1):272-275
In order to develop a chemical technique for the recovery of gold (Au) and platinum (Pt) in the metallic state from spent catalysts, e.g., catalysts for environmental protection and automobile and petroleum catalysts, the coprecipitation behaviors of Au(III) and Pt(IV) complex ions with Fe(OH)(2) as a scavenging and reducing agent were investigated. The Au(III) complex ions were found to be stoichiometrically and rapidly reduced to metallic Au due to electron transfer in acidic aqueous solution prior to coprecipitation with Fe(OH)(2). Conversely, Pt(IV) complex ions were reduced only after coprecipitation with Fe(OH)(2) due to electron transfer through a Pt(IV)-O-Fe(II) bond on the solid Fe(OH)(2). Using this chemical technique, Au and Pt can be selectively and effectively recovered in the metallic state. 相似文献
186.
Huili Liu Masaaki Umehara Kotaro Yamada 《Bulletin of the Brazilian Mathematical Society》2011,42(1):131-152
In a joint work with Saji, the second and the third authors gave an intrinsic formulation of wave fronts and proved a realization
theorem for wave fronts in space forms. As an application, we show that the following four objects are essentially the same:
– |
conformally flat n-manifolds (n ≥ 3) with admissible singular points (i.e. admissible GCF-manifolds) 相似文献
187.
Yoshiyuki Yoshida Kotaro Iwata Naofumi Aso 《Journal of Physics and Chemistry of Solids》2011,72(5):559-561
We have measured magnetization curves and powder neutron diffraction of double-layered Ruddlesden-Popper type ruthenate Sr3−xCaxRu2O7 (x=1.5, 2.0 and 3.0). The field dependence of the magnetization revealed that the transition field of metamagnetic transition along the b-axis shifted to lower fields and that the transition became broad with increasing Sr content. The slope of the magnetization curve also increased with increasing Sr content below the metamagnetic transition. These results indicate that an itinerant component is partly introduced by the Sr substitution. From the magnetic reflection, on cooling below TN, an additional reflection was observed at (0 0 1) for each x, and the amplitude increased with decreasing temperature. The observed diffraction patterns are very similar to those of Ca3Ru2O7. We conclude that the magnetic structure of the antiferromagnetic ordered phase is basically the same structure with that of Ca3Ru2O7. 相似文献
188.
Kawai K Kaneko K Kawakami H Yonezawa T 《Langmuir : the ACS journal of surfaces and colloids》2011,27(16):9671-9675
This letter proposes the use of choline-like hydrophilic ionic liquids (ILs) to visualize hydrous samples (e.g., seaweed and other biological or food samples) for scanning electron microscopy (SEM) observation. Some of the water in the samples was successfully replaced with these ILs, which penetrated the cell membranes. The treated samples did not contract much even after drying. The ILs' ionic conductivity decreased the charging of sample surfaces, and good SEM images were obtained. 相似文献
189.
Takehito Suzuki Hiroki Yonamine Takuya Konno John C. Young Kotaro Murai Fumiaki Miyamaru Keisuke Takano Hideaki Kitahara Masanori Hangyo 《Applied Physics A: Materials Science & Processing》2014,115(2):495-500
This paper presents a three-dimensional concave lens constructed from a metallic slit array. The effective refractive index is estimated to be $0<n<1$ . The actual lens requires spacers in the slits. A lens using a low loss dielectric material for the terahertz frequency band is designed. The fast wave effect is enhanced in order to mitigate the slow wave effect of the dielectric material. Full wave analysis results are obtained by ANSYS HFSS and the focusing effect of the three-dimensional concave lens is confirmed in the terahertz frequency band. 相似文献
190.
We use a transient-grating (TG) process in a Kerr bulk medium to clean a femtosecond laser pulse. Using the technique, the temporal contrast of the generated TG signal is improved by more than two orders of magnitude in comparison with the incident pulse in a 0.5-mm-thick fused silica plate. The laser spectrum is smoothed and broadened, and the pulse duration is shortened simultaneously. We expect to extend this technique to a clean pulse with broadband spectral bandwidth at a wide spectral range because it is a phase-matched process. 相似文献
|