全文获取类型
收费全文 | 339篇 |
免费 | 34篇 |
国内免费 | 16篇 |
专业分类
化学 | 201篇 |
晶体学 | 7篇 |
力学 | 34篇 |
综合类 | 2篇 |
数学 | 35篇 |
物理学 | 110篇 |
出版年
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 18篇 |
2015年 | 13篇 |
2014年 | 23篇 |
2013年 | 24篇 |
2012年 | 31篇 |
2011年 | 25篇 |
2010年 | 17篇 |
2009年 | 9篇 |
2008年 | 18篇 |
2007年 | 10篇 |
2006年 | 9篇 |
2005年 | 11篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 1篇 |
排序方式: 共有389条查询结果,搜索用时 15 毫秒
101.
The asymptotic-planarity argument that explains the pomeron as a cylinder-shifted f, when applied to unnatural parity, predicts near t = 0 a high-lying small-slope H trajectory, with the corresponding I = 0, 1+, C = ? meson mass near 1 GeV. H couplings near t = 0 will be close to pure SU3 singlet. 相似文献
102.
A mechanism is exhibited that monotonically depresses the cylinder component of the topological expansion with increasing t, and it is conjectured that all non-planar S-matrix components diminish as t increases, exchange degeneracy and the Okubo-Zweig-Iizuka rule becoming more accurately satisfied. Such asymptotic planarity is compared to the field-theoretical concept of asymptotic freedom. The characteristics low-t cylinder “quenching interval” is found to be the inverse of the mean value over a two-reggeon loop, of are the squared masses of the loop reggeons and α′ is the trajectory slope. For leading trajectories the low-t cylinder quenching interval is predicted by this formula to be roughly 0.5 GeV2-consistent with the observed pomeron intercept and slope, with the p-ω and f-A2 mass differences and with the (φ,ω) deviation from ideal mixing. As t grows negatively over a corresponding interval, it is predicted that the pomeron will become nearly a pure SU(3) singlet. If the pion mass helps to set the scale for reggeon loops coupled to unnatural-parity trajectories, the cylinder quenching interval will be larger, explaining the large (η, η′) deviation from ideal mixing as well as the large π-η mass difference. Even when the small-t cylinder quenching is rapid (“precocious planarity”) the large-t approach to the planar limit turns out to be gentle. A by-product of this study is an explanation of the approximate reality and linearity of trajectories at large t. 相似文献
103.
Promoted by SmI2, 3‐aryl‐2,1‐benzi‐ soxazoles underwent reductive cleavage of the N O bond leading to 2‐aminobenzophenones in high yields upon protonation. Otherwise, if ketones with active methylene group were added to the reaction mixture prior to protonation, the desired polysubstituted quinolines could be obtained under mild conditions in a one‐pot manner. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:637–643, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20164 相似文献
104.
浅谈萘的α位和β位的活性次序问题 总被引:1,自引:0,他引:1
利用HMO法、PMO法和共振论解释了萘分子中α位比 β位活泼的原因。 相似文献
105.
106.
Shuxiang Wang Wenhao Chu Yuechai Wang Siyuan Liu Jinchao Zhang Shenghui Li Haiying Wei Guoqiang Zhou Xinying Qin 《应用有机金属化学》2013,27(7):373-379
Eight novel Pt(II), Pd(II), Cu(II) and Zn(II) complexes with 4’‐substituted terpyridine were synthesized and characterized by elemental analysis, UV, IR, NMR, electron paramagnetic resonance, high‐resolution mass spectrometry and molar conductivity measurements. The cytotoxicity of these complexes against HL‐60, BGC‐823, KB and Bel‐7402 cell lines was evaluated by MTT assay. All the complexes displayed cytotoxicity with low IC50 values (<20 μm ) and showed selectivity. Complexes 3 , 5 , 7 and 8 exerted 9‐, 5‐, 12‐ and 7‐fold higher cytotoxicity than cisplatin against Bel‐7402 cell line. The cytotoxicity of complexes 3 , 5 , 6 , 7 and 8 was higher than that of cisplatin against BGC‐823 cell line. Complexes 3 , 7 and 8 showed similar cytotoxicity to cisplatin against KB cell line. Complex 7 exhibited higher cytotoxicity than cisplatin against HL‐60 cell line. Among these complexes, complex 7 demonstrated the highest in vitro cytotoxicity, with IC50 values of 1.62, 3.59, 2.28 and 0.63 μm against HL‐60, BGC‐823, Bel‐7402 and KB cells lines, respectively. The results suggest that the cytotoxicity of these complexes is related to the nature of the terminal group of the ligand, the metal center and the leaving groups. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
107.
Peirong Chen Ly May Chew Aleksander Kostka Kunpeng Xie Martin Muhler Wei Xia 《天然气化学杂志》2013,(2):312-320
Oxygen-and nitrogen-functionalized carbon nanotubes (OCNTs and NCNTs) were applied as metal-free catalysts in selective olefin hydrogenation. A series of NCNTs was synthesized by NH3 post-treatment of OCNTs. Temperature-programmed desorption, N2 physisorption, Raman spectroscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were employed to characterize the surface properties of OCNTs and NCNTs, aiming at a detailed analysis of the type and amount of oxygenand nitrogen-containing groups as well as surface defects. The gas-phase treatments applied for oxygen and nitrogen functionalization at elevated temperatures up to 600 C led to the increase of surface defects, but did not cause structural damages in the bulk. NCNTs showed a clearly higher activity than the pristine CNTs and OCNTs in the hydrogenation of 1,5-cyclooctadiene, and also the selectivity to cyclooctene was higher. The favorable catalytic properties are ascribed to the nitrogen-containing surface functional groups as well as surface defects related to nitrogen species. In contrast, oxygen-containing surface groups and the surface defects caused by oxygen species did not show clear contribution to the hydrogenation catalysis. 相似文献
108.
This study attempts to analyze the measured wall shear stress distribution downstream of single and tandem BLADEs in fully developed pipe flow. Previous works have indicated the adverse effect of overall drag increase with the single BLADE in both channel and pipe flows, and an even larger drag increase with the tandem BLADES. This is contrary to that observed for external boundary layer flow. Extensive comparisons are then made to the wall shear stress distribution following BLADEs in boundary layer flow, leading to the conclusion of little or no potential in the application of BLADEs alone to pipe flow. 相似文献
109.
A specially-designed rotating rig for producing near Couette flow was used in the calibration of a marginally elevated hot-wire
shear stress probe. The probe was then used for measurements in both the turbulent boundary layer and pipe flows. Results
showed that the mean wall shear stress can be accurately predicted and the near wall statistical quantities of intensity,
skewness and flatness of shear stress fluctuations concurred well with previous works, thereby supporting the notion of a
time-resolved shear stress probe for turbulent flows. 相似文献
110.
The present paper numerically investigates the near-wall correction of velocity readings when using hot wires to measure the flows very close to walls. It is found that the near-wall correction is necessary not only for the conducting wall but also for the adiabatic wall. For an infinitely long 5-μm diameter hot wire, measurement error begins to appear at Y+ < 5 for an infinitely conducting wall and at Y+ < 2 for an adiabatic wall. In addition to the distance from wall, the wire diameter also exerts significant influence on the velocity measurements. However, provided the flow is two-dimensional (2-D), the effect of operating overheat ratio seems to be insignificant. 相似文献