全文获取类型
收费全文 | 471篇 |
免费 | 35篇 |
国内免费 | 1篇 |
专业分类
化学 | 371篇 |
晶体学 | 7篇 |
力学 | 4篇 |
数学 | 59篇 |
物理学 | 66篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 21篇 |
2019年 | 23篇 |
2018年 | 25篇 |
2017年 | 7篇 |
2016年 | 25篇 |
2015年 | 25篇 |
2014年 | 19篇 |
2013年 | 33篇 |
2012年 | 30篇 |
2011年 | 45篇 |
2010年 | 29篇 |
2009年 | 17篇 |
2008年 | 36篇 |
2007年 | 33篇 |
2006年 | 26篇 |
2005年 | 18篇 |
2004年 | 11篇 |
2003年 | 10篇 |
2002年 | 11篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1981年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1975年 | 3篇 |
排序方式: 共有507条查询结果,搜索用时 640 毫秒
41.
A novel procedure for an observation of a liquid crystal texture is proposed by using a UV curable liquid crystal. Optical observations from a cross-section of the Cano wedge cell are demonstrated and layered structures of cholesteric LC are visualized clearly. The structures near the Grandjean lines are then revealed in detail from images. From the observations, it is confirmed that the texture near the Grandjean line is similar to fingerprint texture 相似文献
42.
43.
Atsuo Konda Kenkichi Nose Hiroshi Ishikawa 《Journal of Polymer Science.Polymer Physics》1976,14(8):1495-1512
Unoriented T-die flat films of nylon 6 and PET films annealed at 90°C were stretched in water at 80°C. Amorphous PET films were stretched in water at 65–75°C. Changes in the light scattering patterns from these samples upon stretching were investigated. One of the observed LS patterns from the stretched samples is the Hv eight-leaf pattern consisting of four lobes and streaks. In the nylon 6 and heat-treated PET showing this pattern, spherulitic patterns can be seen in polarization microscopy. The microscopic spherulitic superstructure may possibly be the factor responsible for producing the lobe-and-streak pattern. On the other hand, many microscopic eight-leaf patterns can be observed in amorphous unannealed PET showing the lobe-and-streak pattern. These microscopic patterns are due to retardation at stress concentrations around impurities and nuclei. The superstructure giving these microscopic patterns must be the origin of the lobe-and-streak pattern from unannealed PET. Another scattering pattern, the Vv cruciform pattern, was observed in both stretched nylon 6 and unannealed PET. This pattern is due to an orientation change across the slip lines observed under a polarizing microscope. It is noted (1) that the appearance of the slip lines in PET coincides with the occurrence of oriented crystallization on stretching, (2) that the lobe-and-streak pattern from PET in which orientation crystallization has taken place is fairly stable to heat treatment and does not disappear until just before melting, and (3) that the superstructures produced at low stretching seem to be deformed on further stretching, in accordance with affine deformation theory. 相似文献
44.
Kazutoshi Nose Yoko Nunome Takaharu Kondo Syuki Araki Takao Tsuda 《Analytical sciences》2005,21(6):625-628
We investigated whether methane, ethylene and ethane gas can be detected in gas emanating from human skin, which is called skin gas. Skin gas was collected with a homemade stainless-steel trap system, which was cooled with liquid nitrogen, and analyzed with a gas chromatograph fitted with a flame ionization detector (FID). Skin-gas samples were obtained by covering a hand for 30 min with a polyfluorovinyl bag in which pure helium gas was introduced. The bag, the trap system and GC were set up online to avoid any contamination by air. Methane, ethylene and ethane in skin gas were successfully collected at an average amount emanated for 30 min (from ten subjects) of 150 +/- 63, 20 +/- 11 and 17 +/- 8 [mean +/- SD] pg/cm2, respectively. 相似文献
45.
Bang JK Naka H Teruya K Aimoto S Konno H Nosaka K Tatsumi T Akaji K 《The Journal of organic chemistry》2005,70(25):10596-10599
[reaction: see text] The solid-phase Horner-Emmons reaction was successfully applied for the convenient syntheses of olefin-containing protease inhibitors. The isomerization during the solid-phase Horner-Emmons reaction can be minimized simply by the use of an appropriate amount of the base. The synthesized olefin peptides, which have an olefin gamma-amino acid at the scissile site, were found to act as effective inhibitors for the HTLV-1 protease for the first time. 相似文献
46.
Umebayashi Y Mroz B Asada M Fujii K Matsumoto K Mune Y Probst M Ishiguro S 《The journal of physical chemistry. A》2005,109(21):4862-4868
Solvation structure of the zinc(II) ion in N,N-dimethylpropionamide (DMPA) was studied by Raman spectroscopy at varying temperature and by quantum mechanical calculations. No significant ion-pair formation was found for the Zn(ClO4)2 solution in the molality range m(Zn) < 1.5 mol kg(-1), and the solvation number of the zinc(II) ion was determined to be 4, indicating that 6-coordination of DMPA is sterically hindered. Interestingly, DMPA molecules are under equilibrium between planar cis and nonplanar staggered conformers, and the latter is more preferred in the coordination sphere, while the reverse is the case in the bulk. The DeltaG degrees , DeltaH degrees , and TDeltaS degrees values of conformational change from planar cis to nonplanar staggered in the coordination sphere were obtained to be -0.9, -8.5, and -7.5 kJ mol(-1), respectively. Density functional theory (DFT) calculations show that the planar cis conformer is more favorable than the nonplanar staggered one in the 1:2 cluster, as is the case for a single DMPA molecule and H(DMPA)+, indicating that there hardly occurs solvent-solvent interaction through the metal ion in the Zn2+-DMPA 1:2 cluster. On the other hand, the SCF energy of [Zn(planar cis-DMPA)4-n(nonplanar staggered DMPA)n]2+ (n = 0-4) decreases with increasing n, implying that the nonplanar staggered conformer is preferred in the solvate ion. It is thus concluded that solvent-solvent interaction through space, or solvation steric effect, plays a crucial role in the conformational equilibrium in the coordination sphere of the four-solvate metal ion. 相似文献
47.
Tetraalkylphosphonium-based amino-acid ionic liquids show lower viscosities and higher decomposition temperatures (>300 degrees C) than previously reported ammonium-based amino-acid ionic liquids. 相似文献
48.
Kawasaki T Suzuki K Hatase K Otsuka M Koshima H Soai K 《Chemical communications (Cambridge, England)》2006,(17):1869-1871
Enantiomorphous crystals composed of achiral hippuric acid, i.e., naturally occurring N-benzoylglycine, have been used successfully as chiral inducers in enantioselective synthesis in combination with asymmetric autocatalysis to afford the product with extremely high enantiomeric excess. 相似文献
49.
50.
Shimada T Kondoh H Iwasaki M Nakai I Nagasaka M Amemiya K Orita H Ohta T 《The journal of physical chemistry. B》2006,110(41):20507-20512
The adsorption structure of NO on the reconstructed Pt(110)-(1 x 2) surface was studied with X-ray photoelectron spectroscopy (XPS), X-ray photoelectron diffraction (XPD), low-energy scanned-angle photoelectron diffraction (LESA-PD), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The experiments were performed at 180 K, where no surface lifting from (1 x 2) to (1 x 1) takes place after NO adsorption. XPS indicates that the (1 x 2) unit cell of the Pt(110) surface contains 1.5 NO molecules at the saturated coverage. XPD and LESA-PD analyses allow us to propose a structural model for the NO adlayer, where two-thirds of the NO molecules in the (1 x 2) unit cell are adsorbed on the atop site of the close-packed Pt rows (ridges) along the [10] direction with an inclined geometry and one-third of the NO molecules adsorb on the bridge site between the Pt ridges with an upright configuration. This model is supported by the N K-edge NEXAFS experiments and is consistent with the recently reported model based on the density functional theory (Orita, H.; Nakamura, I.; Fujitani, T. J. Phys. Chem. B 2005, 109, 10312). 相似文献