全文获取类型
收费全文 | 3662篇 |
免费 | 78篇 |
国内免费 | 15篇 |
专业分类
化学 | 2799篇 |
晶体学 | 60篇 |
力学 | 39篇 |
数学 | 115篇 |
物理学 | 742篇 |
出版年
2022年 | 19篇 |
2021年 | 27篇 |
2020年 | 23篇 |
2019年 | 34篇 |
2018年 | 18篇 |
2017年 | 26篇 |
2016年 | 51篇 |
2015年 | 50篇 |
2014年 | 54篇 |
2013年 | 144篇 |
2012年 | 182篇 |
2011年 | 211篇 |
2010年 | 120篇 |
2009年 | 123篇 |
2008年 | 219篇 |
2007年 | 209篇 |
2006年 | 183篇 |
2005年 | 200篇 |
2004年 | 183篇 |
2003年 | 167篇 |
2002年 | 131篇 |
2001年 | 116篇 |
2000年 | 85篇 |
1999年 | 72篇 |
1998年 | 40篇 |
1997年 | 56篇 |
1996年 | 48篇 |
1995年 | 36篇 |
1994年 | 33篇 |
1993年 | 36篇 |
1992年 | 51篇 |
1991年 | 35篇 |
1990年 | 45篇 |
1989年 | 31篇 |
1988年 | 30篇 |
1987年 | 37篇 |
1986年 | 24篇 |
1985年 | 48篇 |
1984年 | 47篇 |
1983年 | 35篇 |
1982年 | 47篇 |
1981年 | 45篇 |
1980年 | 40篇 |
1979年 | 57篇 |
1978年 | 36篇 |
1977年 | 26篇 |
1976年 | 18篇 |
1975年 | 23篇 |
1974年 | 25篇 |
1973年 | 18篇 |
排序方式: 共有3755条查询结果,搜索用时 0 毫秒
991.
992.
The magnetic hyperfine splitting frequency of 82BrNi in an external magnetic field of 0.2 T has been measured by NMR-ON method at 8 mK. The centre of resonance frequency
was determined to be 18.7(2) MHz. With the known g-factor of g(82Br)= 0.3254(1), the hyperfine field of 82BrNi was deduced as Bhf(82BrNi)= 7.34(8) T. The measured value is compared with the calculated value based on band structure using bonding states.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
993.
We investigate the dynamics of probability distributions of an initially one-mode coherent field interacting with a four-state molecular system, which is a single magnet with a tunneling across an anisotropic barrier, using a numerically exact approach. The population for each state, the phase properties of and
, and
), the entropy are calculated for a model system. The model predicts that the molecule and field become asymptotically disentangled at half of the revival time, and that optical Schrödinger-cat and magnetic Schrödinger-cat states are generated.This paper was originally presented at the 5th International Conference on NEAR FIELD OPTICS and RELATED TECHNOLOGIES (NFO-5), which was held on December 6–10, 1998 at Coganoi Bay Hotel, Shirahama, Japan, in cooperation with the Japan Society of Applied Physics and Mombusho Grant-in Aid for Scientific Research on Priority Areas “Near-field Nano-optics” Project, sponsored by Japan Society for the Promotion of Science. 相似文献
994.
995.
Yuji Matsuura Yi-Wei Shi Yukio Abe Masaru Yaegashi Goro Takada Shintaro Mohri Mitsunobu Miyagi 《Optics & Laser Technology》2001,33(5)
Infrared Er : YAG laser delivery systems based on hollow fibers with an internal polymer layer has been developed. The system consists of a hollow fiber as the delivery medium, a launching coupler for effective coupling between the laser beam and the fiber, and a sealed hollow-fiber tip attached at the output end of the fiber. Fabrication process of the fiber and attachment of the delivery system is reported. 相似文献
996.
The effects of protonation on the excited states oftrans-3-styrylpyridine (StP) andtrans-4,4′-dipyridylethylene (DPE) have been studied through measurements of the time-resolved electron paramagnetic resonance (EPR), ultraviolet absorption, and fluorescence spectra in methanol-water mixtures at 77 K. The assignment of the transient EPR signals was carried out with the aid of the stretched poly(vinyl alcohol) films method. From the analysis of these spectra it is concluded that the single protonation appears to have little effect on the zero-field splitting parameters and the anisotropy in the sublevel populating rates of the lowest excited triplet (T1) states of StP and DPE. However, the decay rate constants of the fluorescent states decrease and fluorescence quantum yields increase on single protonation. These experimental results suggest that the single protonation causes a decrease in the intersystem crossing (ISC) rates for the three T1 sublevels. These results are explained in terms of the vibronic mixing between the1nπ* and1ππ* states in the lowest excited singlet state. The assignment of StP to the specified conformer was carried out through the analysis of the anisotropic ISC processes. 相似文献
997.
Matsuta K. Fukuda M. Tanigaki M. Minamisono T. Nojiri Y. Akai H. Izumikawa T. Nakazato M. Mihara M. Yamaguchi T. Harada A. Sasaki M. Miyake T. Onishi T. Minamisono K. Fukao T. Sato K. Matsumoto Y. Ohtsubo T. Fukuda S. Yoshida K. Ozawa A. Momota S. Kobayashi T. Tanihata I. Alonso J. R. Krebs G. F. Symons T. J. M. 《Hyperfine Interactions》1996,97(1):501-508
The spin relaxation timeT
1 for short-lived beta emitters13O and23Mg implanted in Pt have been measured for the first time;T
1T13O) = 2.90 ±0.65 Ks andT
1
T(23Mg) = 1665 ±140 Ks. The Knight shift for13O in Pt was measured at 300 K to beK(13O) = +(4.23 ±0.14) × 10–3. In the case of13O, the Knight shift is unusually large and the relaxation time is unusually fast compared with other interstitial impurities in Pt. A KKR band-structure calculation reproduces the present large Knight shift fairly well. 相似文献
998.
Local density of states of quasiparticles around the magnetic impurity in superconductors are calculated on the basis of a pair potential the spatial dependence of which is determined self-consistently using negative Hubbard model. The spatial dependence of the tunneling conductance observed by Scanning tunneling spectroscopy (STS) strongly depends on the magnitude of the impurity potentials. 相似文献
999.
In the presence of an easily prepared supported ruthenium hydroxide catalyst, Ru(OH)(x)/Al(2)O(3), various kinds of structurally diverse primary azides including benzylic, allylic, and aliphatic ones could be converted into the corresponding nitriles in moderate to high yields (13 examples, 65-94% yields). The gram-scale (1 g) transformation of benzyl azide efficiently proceeded to give benzonitrile (0.7 g, 90% yield) without any decrease in the performance in comparison with the small-scale (0.5 mmol) transformation. The catalysis was truly heterogeneous, and the retrieved catalyst could be reused for the transformation of benzyl azide without an appreciable loss of its high performance. The present transformation of primary azides to nitriles likely proceeds via sequential reactions of imide formation, followed by dehydrogenation (β-elimination) to produce the corresponding nitriles. The Ru(OH)(x)/Al(2)O(3) catalyst could be further employed for synthesis of amides in water through the transformation of primary azides (benzylic and aliphatic ones) to nitriles, followed by sequent hydration of the nitriles formed. Additionally, direct one-pot synthesis from alkyl halides and TBAN(3) (TBA = tetra-n-butylammonium) could be realized with Ru(OH)(x)/Al(2)O(3), giving the corresponding nitriles in moderate to high yields (10 examples, 64-84% yields). 相似文献
1000.
The Beryllium tetramer: profiling an elusive molecule 总被引:1,自引:0,他引:1
Ascik PN Wilke JJ Simmonett AC Yamaguchi Y Schaefer HF 《The Journal of chemical physics》2011,134(7):074110
The structure and energetics of Be(4) are investigated using state-of-the-art coupled-cluster methods. We compute the optimized bond length, dissociation energy, and anharmonic vibrational frequencies. A composite approach is employed, starting from coupled-cluster theory with single, double, and perturbative triple excitations extrapolated to the complete basis set (CBS) limit using Dunning's correlation consistent cc-pCVQZ and cc-pCV5Z basis sets. A correction for full triple and connected quadruple excitations in the smaller cc-pCVDZ basis set is then added, yielding an approximation to CCSDT(Q)/CBS denoted c~CCSDT(Q). Corrections are included for relativistic and non-Born-Oppenheimer effects. We obtain D(e) = 89.7 kcal mol(-1), D(0) = 84.9 kcal mol(-1), and r(e) = 2.043 A?. Second-order vibrational perturbation theory (VPT2) is applied to a full quartic force field computed at the c~CCSDT(Q) level of theory, yielding B(e) = 0.448 cm(-1) and fundamental frequencies of 666 (a(1)), 468 (e), and 571 (t(2)) cm(-1). Computations on the spectroscopically characterized Be(2) molecule are reported for the purpose of benchmarking our methods. Perturbative estimates of the effect of quadruple excitations are found to be essential to computing accurate parameters for Be(2); however, they seem to exert a much smaller influence on the structure and energetics of Be(4). Our extensive characterization of the Be(4) bonding potential energy surface should aid in the experimental identification of this thermodynamically viable but elusive molecule. 相似文献