全文获取类型
收费全文 | 3750篇 |
免费 | 69篇 |
国内免费 | 10篇 |
专业分类
化学 | 2574篇 |
晶体学 | 50篇 |
力学 | 67篇 |
数学 | 184篇 |
物理学 | 954篇 |
出版年
2021年 | 26篇 |
2020年 | 50篇 |
2019年 | 49篇 |
2018年 | 42篇 |
2017年 | 25篇 |
2016年 | 55篇 |
2015年 | 54篇 |
2014年 | 71篇 |
2013年 | 165篇 |
2012年 | 149篇 |
2011年 | 191篇 |
2010年 | 128篇 |
2009年 | 119篇 |
2008年 | 193篇 |
2007年 | 218篇 |
2006年 | 201篇 |
2005年 | 147篇 |
2004年 | 134篇 |
2003年 | 143篇 |
2002年 | 138篇 |
2001年 | 114篇 |
2000年 | 128篇 |
1999年 | 81篇 |
1998年 | 53篇 |
1997年 | 54篇 |
1996年 | 44篇 |
1995年 | 42篇 |
1994年 | 44篇 |
1993年 | 55篇 |
1992年 | 49篇 |
1991年 | 50篇 |
1990年 | 36篇 |
1989年 | 49篇 |
1988年 | 50篇 |
1987年 | 42篇 |
1986年 | 36篇 |
1985年 | 49篇 |
1984年 | 51篇 |
1983年 | 48篇 |
1982年 | 46篇 |
1981年 | 30篇 |
1980年 | 33篇 |
1979年 | 48篇 |
1978年 | 43篇 |
1977年 | 47篇 |
1976年 | 16篇 |
1975年 | 26篇 |
1974年 | 30篇 |
1973年 | 15篇 |
1967年 | 16篇 |
排序方式: 共有3829条查询结果,搜索用时 12 毫秒
91.
92.
93.
The intermolecular partial wave expansion of the atom-atom potential U is reviewed briefly and developed, by using results due to Sack, so that the radial components of the expansion can be evaluated to arbitrary accuracy for all relevant partial wave orders and values of the intermolecular distance r. These results are used to study the convergence of the partial wave expansion of U as a function of partial wave order, r, intermolecular orientation, and the anisotropy of the interacting molecules. In marked contrast to previous work it is found that many of the higher order partial wave components of U are important relative to the isotropic term even for the interaction of relatively spherical molecules and that the results obtained from a truncated partial wave expansion depend significantly upon the method of summation due to the generally poor convergence of the expansion. The validity of the atom-atom potential as a representation of the correct attractive intermolecular potential is also discussed in some detail. There are basic problems associated with the representations furnished by both the isotropic and the anisotropic parts of the atom-atom potential at intermediate and large r. The different convergence properties of the r -1 expansions of the partial wave expansions of U and of the correct potential for these values of r is illustrated by using model interactions. While it appears that it may be possible to obtain a qualitatively reasonable representation of the attractive part of an intermolecular potential over a useful range of r from atom-atom results, this apparently cannot be achieved for wider ranges of r or for the purely anisotropic part of the potential. 相似文献
94.
Isao Watanabe Kusuo Nishiyama Kanetada Nagamine Kenji Kawano Ken-ichi Kumagai 《Hyperfine Interactions》1994,86(1):603-608
Zero field positive muon spin rotation method (
+SR) is applied on La2–x
Sr
x
CuO4 around forx=0.12 at which the high-T
c
superconductivity (SC) is suppressed. The magnetically ordered state of Cu-moments, which is not a spin glass state but an antiferromagnetic like state, appears below 15 K for 0.105x0.120. The magnetic phase boundary is very similar to the one of the La2–x
Ba
x
CuO4 in which the structural transition from the low temperature orthorhombic (LTO) phase to the low temperature tetragonal (LTT) phase is observed aroundx=0.12. The present study suggests that there is no big difference of the electronic state of the CuO2 plane between the La-Ba system and the La-Sr system and that the magnetic ordering of Cu-moments plays an important role for the suppression of the high-T
c
SC aroundx=0.12 in both of the systems, although the LTO-LTT structural transition has not been observed yet in the La-Sr system. 相似文献
95.
Takashi Hara Tetsuya Hattori Hiroshi Watanabe 《Communications in Mathematical Physics》2001,220(1):13-40
Existence of critical renormalization group trajectory for a hierarchical Ising model in 4 dimensions is shown. After 70
iterations of renormalization group transformations, the critical Ising model is mapped into a vicinity of the Gaussian fixed
point. Convergence of the subsequent trajectory to the Gaussian fixed point is shown by power decay of the effective coupling
constant. The analysis in the strong coupling regime is computer-aided and Newman's inequalities on truncated correlations
are used to give mathematical rigor to the numerical bounds. In order to obtain a criterion for convergence to the Gaussian
fixed point, characteristic functions and Newman's inequalities are systematically used.
Received: 27 April 2000 / Accepted: 5 January 2001 相似文献
96.
97.
Two flame spray methods, emulsion combustion method (ECM) and flame spray pyrolysis (FSP), were compared for synthesis of pure and mixed SiO2 and ZnO nanoparticles. The effect of silicon precursor was investigated using liquid hexamethyldisiloxane (HMDSO) or SiO2 sol, while for ZnO zinc acetate (ZA) was used. Gas phase reaction took place when using HMDSO as Si precursor, forming nanoparticles, whereas the SiO2 sol used as Si source was not evaporated in the flame, creating large aggregates of the sol particles (e.g. 1 m). The FSP of ZA produced ZnO homogeneous nanoparticles. Lower flame temperatures in ECM than in FSP resulted in mixed gas and liquid phase reaction, forming ZnO particles with inhomogeneous sizes. The FSP of HMDSO and ZA led to intimate gas-phase mixing of Zn and Si, suppressing each other's particle growth, forming nanoparticles of 19 nm in BET-equivalent average primary particle diameter. Nucleation of ZnO and SiO2 occurred independently by ECM of HMDSO and ZA as well as by FSP of the SiO2 sol and ZA, creating a ZnO and SiO2 mixture. The reaction of ZnO with SiO2 was likely to be enhanced by ECM of the SiO2 sol and ZA where both Zn and Si species were not evaporated completely, resulting in ZnO, -willemite and Zn1.7SiO4 mixed phase. 相似文献
98.
Reliability of mean transit time obtained using perfusion-weighted MR imaging; comparison with positron emission tomography 总被引:2,自引:0,他引:2
Mihara F Kuwabara Y Tanaka A Yoshiura T Sasaki M Yoshida T Masuda K Matsushima T 《Magnetic resonance imaging》2003,21(1):33-39
The purpose of this project was to assess the reliability of the cerebral mean transit time (MTT) obtained using perfusion-weighted MR imaging by comparing it with the MTT obtained when performing positron emission tomography (PET). Ten patients with chronic occlusive cerebrovascular disease were investigated. They had either unilateral internal carotid artery occlusion or middle cerebral artery occlusion. The regions-of-interest were placed in non-infarcted areas within the territory of the middle cerebral artery on the affected side. Control regions-of-interest were placed in mirrored regions of the contralateral side. Linear regression analyses were performed using the parameters of the MTT obtained with perfusion-weighted MR imaging and the MTT, cerebral blood flow, vascular reactivity, and oxygen extraction fraction obtained with PET. The respective MTTs of the affected and non-affected sides obtained with perfusion-weighted MR imaging versus those with PET were 7.3 +/- 2.2 s and 6.0 +/- 1.2 s versus 8.2 +/- 3.0 s and 6.4 +/- 1.7 s. The MTT obtained using perfusion-weighted MR imaging and PET demonstrated statistically significant correlation (r = 0.87, p < 0.0001). The MTT obtained with perfusion-weighted MR imaging correlated statistically with cerebral blood flow (r = -0.74, p < 0.001), vascular reactivity (r = -0.73, p < 0.001) and oxygen extraction fraction (r = 0.61, p < 0.01). Similarly, the MTT obtained using PET statistically correlated with cerebral blood flow (r = -0.78, p < 0.0001), vascular reactivity (r = -0.51, p < 0.05) and oxygen extraction fraction (r = 0.68, p < 0.01). The reliability of the MTT obtained using perfusion-weighted MR imaging appears to be approximately equal to that obtained with positron emission tomography. 相似文献
99.
We demonstrate an optical parametric chirped-pulse amplification (OPCPA) system with the pulse energy of 1.5 mJ at a 1 kHz repetition rate. The newly developed 100 ps Ti:sapphire pump laser system, which was optically synchronized with OPCPA seed pulses, delivered 10 mJ, 400 nm pump pulses. After three-stage parametric amplification, recompression of the amplifier output from 45 ps to 6.4 fs was performed. The pulse width of 6.4 fs is, to our knowledge, the shortest ever obtained by OPCPA, and the average power of 1.5 W (1.5 mJ, 1 kHz) is believed to be the highest among few-cycle OPCPA systems. 相似文献
100.
35Cl NQR as well as heat capacity measurements of [(PyO)H][AuCl4] and its deuterated analog [(PyO)D][AuCl4] revealed successive phase transitions at 70.5 and 62.5 K, and at 71 and 63 K, respectively. The NQR frequency varied continuously through the upper transition point while discontinuously through the lower transition point. In the intermediate-temperature phase a remarkable decrease in the signal intensity was observed. These NQR observations as well as the feature of the heat capacity anomaly in which a broad peak is succeeded by a sharp peak with decreasing temperature suggest a possibility of normal-incommensurate-commensurate phase sequence. 相似文献