全文获取类型
收费全文 | 1520篇 |
免费 | 27篇 |
国内免费 | 5篇 |
专业分类
化学 | 1180篇 |
晶体学 | 18篇 |
力学 | 12篇 |
数学 | 54篇 |
物理学 | 288篇 |
出版年
2021年 | 9篇 |
2020年 | 12篇 |
2019年 | 14篇 |
2018年 | 12篇 |
2017年 | 8篇 |
2016年 | 15篇 |
2015年 | 14篇 |
2014年 | 35篇 |
2013年 | 60篇 |
2012年 | 86篇 |
2011年 | 88篇 |
2010年 | 30篇 |
2009年 | 46篇 |
2008年 | 99篇 |
2007年 | 72篇 |
2006年 | 65篇 |
2005年 | 70篇 |
2004年 | 78篇 |
2003年 | 79篇 |
2002年 | 72篇 |
2001年 | 47篇 |
2000年 | 19篇 |
1999年 | 22篇 |
1998年 | 23篇 |
1997年 | 15篇 |
1996年 | 22篇 |
1995年 | 18篇 |
1994年 | 13篇 |
1993年 | 14篇 |
1992年 | 18篇 |
1991年 | 20篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 19篇 |
1986年 | 21篇 |
1985年 | 23篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 17篇 |
1979年 | 22篇 |
1978年 | 21篇 |
1977年 | 19篇 |
1976年 | 19篇 |
1975年 | 22篇 |
1974年 | 9篇 |
1973年 | 17篇 |
1971年 | 8篇 |
排序方式: 共有1552条查询结果,搜索用时 15 毫秒
991.
992.
993.
Non‐destructive and non‐contact analysis has been in demand on numerous occasions. Confocal micro X‐ray fluorescence analysis enables depth‐selective elemental analysis of solid samples in the laboratory. In this paper, we applied this technique for imaging elemental distributions in solutions. A low‐carbon steel sheet was placed in artificial seawater (NaCl: 3.5 mass%), and the corrosion process in the solution was observed. A depth image of Fe Kα intensity in the NaCl solution was obtained by using this technique. The Fe Kα intensity in the solution was measured with corrosion time by sequential line analysis at a fixed lateral position. The corrosion of Fe from the steel sheet, the migration of Fe ions in solution, and their condensation near a polymer window were successfully monitored. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
994.
Feng Wang Rosie Jiang Keiko Takahashi John Gore Raymond C. Harris Takamune Takahashi C. Chad Quarles 《Magnetic resonance imaging》2014
The purpose of this study is to evaluate the utility of high-resolution non-invasive endogenous high-field MRI methods for the longitudinal structural and quantitative assessments of mouse kidney disease using the model of unilateral ureter obstruction (UUO). T1-weighted, T2-weighted and magnetization transfer (MT) imaging protocols were optimized to improve the regional contrast in mouse kidney. Conventional T1 and T2 weighted images were collected in UUO mice on day 0 (~ 3 h), day 1, day 3 and day 6 after injury, on a 7 T small animal MRI system. Cortical and medullary thickness, corticomedullary contrast and Magnetization Transfer Ratio (MTR) were assessed longitudinally. Masson trichrome staining was used to histologically assess changes in tissue microstructure. Over the course of UUO progression there were significant (p < 0.05) changes in thickness of cortex and outer medulla, and regional changes in T2 signal intensity and MTR values. Histological changes included tubular cell death, tubular dilation, urine retention, and interstitial fibrosis, assessed by histology. The MRI measures of renal cortical and medullary atrophy, cortical–medullary differentiation and MTR changes provide an endogenous, non-invasive and quantitative evaluation of renal morphology and tissue composition during UUO progression. 相似文献
995.
Susumu Shinohara Takehiro Fukushima Satoshi Sunada Takahisa Harayama Kenichi Arai Kazuyuki Yoshimura 《Optical Review》2014,21(2):113-116
Time-domain properties of the output from quasistadium-shaped microcavity semiconductor lasers are studied. Ring modes generating a bidirectional output are selectively excited by partial pumping. We observe a high anticorrelation between the two beams output from the ring modes. This can be considered as the generalization of alternate oscillations reported previously. We find that the outputs exhibit a robust slow modulation of 4–10 MHz, and explain it by the quasi-degeneracy of the resonator modes. 相似文献
996.
Yuki Obukuro Hiroyuki Nakamura Kenji Obata Shigenori Matsushima Masao Arai Kenkichiro Kobayashi 《Journal of Physics and Chemistry of Solids》2011,72(12):1477-1481
The electronic structure of Sr2Bi2O5 is calculated by the GGA approach. Both of the valence band maximum and the conduction band minimum are located at Γ-point. This means that Sr2Bi2O5 is a direct band-gap material. The wide energy-band dispersions near the valence band maximum and the conduction band minimum predict that holes and electrons generated by band gap excitation have a high mobility. The conduction band is composed of Bi 6p, Sr 4d and O 2p energy states. On the other hand, the valence band can be divided into two energy regions ranging from −9.5 to −7.9 eV (lower valence band) and from −4.13 to 0 eV (upper valence band). The former mainly consists of Bi 6s states hybridizing with O 2s and O 2p states, and the latter is mainly constructed from O 2p states strongly interacting with Bi 6s and Bi 6p states. 相似文献
997.
S. Shamoto S. Wakimoto K. Kodama M. Ishikado A.D. Christianson M.D. Lumsden R. Kajimoto M. Nakamura Y. Inamura M. Arai K. Kakurai F. Esaka A. Iyo H. Kito H. Eisaki 《Physica C: Superconductivity and its Applications》2011,471(21-22):639-642
Low-energy spin excitations have been studied on polycrystalline LaFeAsO1?xFx samples by inelastic neutron scattering. The Q-integrated dynamical spin susceptibility χ″(ω) of the superconducting samples is found to be comparable to that of the magnetically ordered parent sample. On the other hand, χ″(ω) almost vanishes at x = 0.158, where the superconducting transition temperature Tc is suppressed to 7 K. In addition, χ″(ω) in optimally doped LaFeAsO0.918F0.082 with Tc = 29 K exhibits a spin resonance mode. The peak energy, Eres, when scaled by kBTc is similar to the value of about 4.7 reported in other high-Tc iron-based superconductors. This result suggests that there is intimate relationship between the dynamical spin susceptibility and high-Tc superconductivity in iron-based superconductors, and is consistent with a nesting condition between Fermi surfaces at the Γ and M points. 相似文献
998.
Akira Shigenaga Hiroko HirakawaJun Yamamoto Keiji OguraMasaya Denda Keiko YamaguchiDaisuke Tsuji Kohji ItohAkira Otaka 《Tetrahedron》2011,67(22):3984-3990
Sphingolipids, recognized as membrane constructs and as key signaling molecules, have been studied to examine intracellular function. Some caged sphingolipids that release parent sphingolipids after exposure to UV-irradiation have been previously developed, but caged ceramide has yet to be reported. In this study, we report the design and synthesis of a caged ceramide. Photo-irradiation experiment clarified that the caged ceramide can be successfully converted to the parent ceramide by UV-irradiation. Introduction of an alkyne-handle moiety for further modification of the caged ceramide is also reported. 相似文献
999.
The catalytic asymmetric Friedel-Crafts/protonation of indoles and pyrroles with α-substituted nitroalkenes to give the corresponding adducts in a highly anti-selective manner was achieved by an imidazoline-aminophenol (L2)-Cu complex. The anti-adducts could be successfully transformed to biochemically important α-substituted β-heteroarylalkylamines. 相似文献
1000.
Inokuma Y Kojima N Arai T Fujita M 《Journal of the American Chemical Society》2011,133(49):19691-19693
Two substrates, 4-hydroxydiphenylamine (3) and ethyl isocyanate (4), were successively introduced into the crystals of networked M(6)L(4) cages 1. Because of the encapsulation effect, most of the initially introduced substrate 3 remained within the crystals during immersion in a solution of 4. X-ray analysis revealed that before the reaction, the nucleophilic NH group of 3 is effectively protected by tight packing within the cage units while the OH group is exposed to the incoming second substrate. Successive introduction of 4 into the crystal results in the chemoselective acylation of 3 at the less nucleophilic OH group. The observed chemoselectivity is consistent with that exhibited by discrete M(6)L(4) cage 2 in solution. 相似文献