全文获取类型
收费全文 | 4138篇 |
免费 | 173篇 |
国内免费 | 13篇 |
专业分类
化学 | 3342篇 |
晶体学 | 36篇 |
力学 | 37篇 |
数学 | 241篇 |
物理学 | 668篇 |
出版年
2023年 | 28篇 |
2022年 | 19篇 |
2021年 | 50篇 |
2020年 | 91篇 |
2019年 | 77篇 |
2018年 | 38篇 |
2017年 | 22篇 |
2016年 | 90篇 |
2015年 | 88篇 |
2014年 | 118篇 |
2013年 | 238篇 |
2012年 | 244篇 |
2011年 | 291篇 |
2010年 | 148篇 |
2009年 | 126篇 |
2008年 | 279篇 |
2007年 | 266篇 |
2006年 | 265篇 |
2005年 | 243篇 |
2004年 | 234篇 |
2003年 | 186篇 |
2002年 | 177篇 |
2001年 | 76篇 |
2000年 | 66篇 |
1999年 | 70篇 |
1998年 | 54篇 |
1997年 | 59篇 |
1996年 | 39篇 |
1995年 | 38篇 |
1994年 | 38篇 |
1993年 | 30篇 |
1992年 | 31篇 |
1991年 | 24篇 |
1990年 | 23篇 |
1989年 | 36篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 45篇 |
1984年 | 34篇 |
1983年 | 24篇 |
1982年 | 30篇 |
1981年 | 37篇 |
1980年 | 33篇 |
1979年 | 23篇 |
1978年 | 19篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1975年 | 18篇 |
1973年 | 20篇 |
排序方式: 共有4324条查询结果,搜索用时 15 毫秒
991.
Akira Mori Nobuo Kato Hitoshi Takeshita Ryuko Nimura Masahiro Isobe Chihiro Jin 《Liquid crystals》2013,40(9):1425-1433
The mesomorphic properties of 2-(4-alkoxybenzoyloxy)-5-alkylaminotropones and 5-alkoxy-2-(4-alkylaminobenzoyloxy)tropones are discussed on the basis of results obtained by X-ray crystallographic and X-ray diffraction studies, as well as temperature-dependent FTIR spectral measurements. The X-ray crystallographic analysis of 2-(4-dodecylaminobenzoyloxy)-5-tetradecyloxytropone (2f) indicated that it formed a head-to-tail dimer through an intermolecular hydrogen bond between the NH and the tropone carbonyl group. The X-ray diffraction study of compound 2f suggested that the molecules formed interdigitated bilayer smectic C phases with a tilt angle of as much as c. 40° to a layer plane. The corresponding benzenoids, however, were non-mesomorphic, with higher melting points than the troponoids. In the troponoids, sigmatropic migration of the benzoyl group weakened the intermolecular hydrogen bonding and assisted the occurrence of mesomorphic properties. 相似文献
992.
993.
Masahiko Suzuki Yukio Yamamoto Masahiro Irie Koichiro Hayashi 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):1607-1622
Photopolymerization of styrene in the presence of pyromellitic dianhydride, an electron acceptor which forms a charge-transfer complex with the monomer, was studied. Polymerization was initiated by illumination with a light of wavelength longer than 350 nm, where only the charge-transfer absorption band exists. It was found that the reaction involves cationic and radical polymerizations and that the reaction course strongly depends on polarity of the system. It was also suggested by the dependence of the rate of polymerization on light intensity and temperature that the cationic polymerization consists of free ion and ion-pair polymerizations. These results were compared with those of the photoinduced cationic polymerization of α-methylstyrene, which has previously been studied. 相似文献
994.
The effect of the polarization electric field on helix-unwinding in a thin planar chiral smectic C liquid-crystal cell is studied by using the nematic-like expression for the elastic deformation free-energy density. It is found that the elongation of the helical pitch when the cell thickness decreases is greater when the spontaneous polarization is larger. This is due to the Coulomb repulsion between polarization charges concentrated at ± 2π disclinations. 相似文献
995.
Tetsuro Yamashita Shigeo Ohara Isao Sakamoto 《Physica C: Superconductivity and its Applications》2011,471(23-24):1655-1659
We have grown high purity single crystals of Ce2CoIn8 using the self-flux technique, and have investigated its transport, thermal, and magnetic properties, including the anisotropic features. Single crystals of Ce2CoIn8 were grown in the lower temperature region to avoid the formation of un-wanted phases such as CeCoIn5 and CeIn3 impurities. The results of the structural and physical measurements imply that the present single crystals have high purity. The electrical resistivity and specific heat measurements demonstrate that Ce2CoIn8 has a superconducting ground state with a distinct non-Fermi liquid character. This indicates that the superconductivity in Ce2CoIn8 arises out of the verge of the underlying quantum critical instability mediated by the antiferromagnetic correlations. Additionally, we investigate the crystalline electric field (CEF) energy scheme based on the temperature dependence of the specific heat and the anisotropic features in the susceptibility. We propose one of the CEF level schemes calculated on the basis of the CEF model that the first and second CEF states are located at Δ1 = 82 K and Δ2 = 102 K above the ground state doublet, respectively. 相似文献
996.
997.
998.
999.
Arylacetate was directly converted to the corresponding alkyl-aryl ether by treatment with sodium hydride and alkyl halide in THF and HMPA. 相似文献
1000.
Takeshi Hasegawa Hiroaki Kubo Koichi Shinozaki Masahiko Nowatari Masahiro Ishii 《Biomedical chromatography : BMC》2010,24(6):613-619
A simple, sensitive and specific chemiluminescent high‐performance liquid chromatography method, based on the luminol reaction, for determination of serum cortisol and cortisone, was established. In infants, placental 11β‐hydroxysteroid dehydrogenase type 2 enzyme (11β‐HSD2) activity may affect adrenal function early after birth. The cortisol–cortisone ratio of serum concentrations in umbilical cord blood is an indicator of placental 11β‐HSD2 activity. The optimum conditions for the luminol reaction were determined to be 1.5 mM luminol, 0.6 M sodium hydroxide, 0.15 mm potassium hexacyanoferrate(III) and 200 mM potassium hexacyanoferrate (II). The calibration curves for cortisol and cortisone exhibited good linearity. The correlation coefficients of the calibration curves were 0.996. The intra‐ and inter‐day precisions were in the ranges: cortisol 7.0–12.2 and 4.4–9.2%, cortisone 5.3–7.0 and 6.2–9.9%. The recoveries of these steroids were in the ranges: cortisol 97–105%, cortisone 94–102%. The limits of detection were as follows: cortisol, 0.17 μg/dl; cortisone 0.15 μg/dl. This assay could be successfully applied to determination of the cortisol–cortiosone ratio of serum concentrations in umbilical cord bloods. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献