全文获取类型
收费全文 | 2473篇 |
免费 | 45篇 |
国内免费 | 13篇 |
专业分类
化学 | 1735篇 |
晶体学 | 33篇 |
力学 | 29篇 |
数学 | 120篇 |
物理学 | 614篇 |
出版年
2022年 | 13篇 |
2021年 | 14篇 |
2019年 | 31篇 |
2018年 | 14篇 |
2016年 | 34篇 |
2015年 | 39篇 |
2014年 | 34篇 |
2013年 | 205篇 |
2012年 | 91篇 |
2011年 | 119篇 |
2010年 | 64篇 |
2009年 | 70篇 |
2008年 | 112篇 |
2007年 | 137篇 |
2006年 | 130篇 |
2005年 | 120篇 |
2004年 | 107篇 |
2003年 | 110篇 |
2002年 | 112篇 |
2001年 | 53篇 |
2000年 | 68篇 |
1999年 | 37篇 |
1998年 | 39篇 |
1997年 | 33篇 |
1996年 | 33篇 |
1995年 | 33篇 |
1994年 | 36篇 |
1993年 | 38篇 |
1992年 | 40篇 |
1991年 | 28篇 |
1990年 | 22篇 |
1989年 | 19篇 |
1988年 | 28篇 |
1987年 | 18篇 |
1986年 | 21篇 |
1985年 | 36篇 |
1984年 | 36篇 |
1983年 | 25篇 |
1982年 | 25篇 |
1981年 | 35篇 |
1980年 | 14篇 |
1979年 | 34篇 |
1978年 | 31篇 |
1977年 | 28篇 |
1976年 | 18篇 |
1975年 | 28篇 |
1974年 | 25篇 |
1973年 | 12篇 |
1972年 | 12篇 |
1969年 | 11篇 |
排序方式: 共有2531条查询结果,搜索用时 15 毫秒
61.
62.
A. Kawasuso M. Hasegawa M. Suezawa S. Yamaguchi K. Sumino 《Hyperfine Interactions》1994,84(1):397-406
The charge state dependence of positron lifetime and trapping at divacancy (V2) in Si doped with phosphorus or boron has been studied after 15 McV electron irradiation up to a fluence of 8.0×1017 e/cm2. The positron trapping cross sections for V
2
2–
, V
2
–
and V
2
0
at 300 K were about 6×10–14, 3×10–14 and 0.1–3×10–14 cm2, respectively. For V
2
+
, however, no positron trapping was observed. The marked difference in the cross sections comes from Coulomb interaction between the positron and the charged divacancy. The trapping rates for V
2
0
and V
2
2–
have been found to increase with decreasing temperature in the temperature range of 10–300 K. These results are well interpreted by a two-stage trapping model having shallow levels with energy of 9 meV (V
2
0
) and 21 meV (V
2
2–
). The appearance of a shallow level for V
2
0
can not be explained by a conventional Rydberg state model. The lifetime (290–300 ps) in V
2
0
is nearly constant in the temperature range from 10 to 300 K, while that in V
2
2–
increases from 260 ps at 10 K to 320 ps at 300 K. The lifetime (260 ps) in V
2
2–
is shorter than that in V
2
0
at low temperature, which is due to the excess electron density in V
2
2–
. At high temperature, however, the longer lifetime of V
2
2–
than that of V
2
0
is attributed to lattice relaxation around V
2
2–
. 相似文献
63.
We analyse a scheme of transition from the Poissonian statistics for quantum levels to the Gaussian one of random matrix ensembles in the framework of level dynamics discussed by Yukawa. We propose a means of connecting these two limiting statistics by showing a result that Yukawa's parameter / of the exponential family can be efficiently replaced by the ratio <E>/<Q> which reflects directly a degree of the eigenvalue correlations of each sample matrix in the ensemble. On this basis, we discuss a correspondence between the level statistics of a generic quantum system and its classical regular/chaotic dynamics in terms of the semiclassical power spectrum and its second moment formulated by Feingold-Peres and Prosen-Robnik. We also discuss some limiting proceduresN (infinite limit of the matrix dimension) pertinent to the Gaussian ensembles, and remark about the possibility offractional power law of Brody's type. 相似文献
64.
65.
Yoshitsugu Hasegawa Suguru Kontani Isao Tomita 《Journal of inclusion phenomena and macrocyclic chemistry》1993,16(4):329-337
Intercalation of alkylalcohols into -zirconium phosphate was investigated at 25°C and/or under reflux.n-Alcohols having two to five carbons and 2-propanol were taken up at 25°C. These alcohols, andn-hexanol and heptanol, also intercalated under reflux.n-Alcohols having eight to eighteen carbon atoms intercalated when a stepwise method was employed. 2-Butanol and tertiary amylalcohols intercalated under reflux using a butanol intercalate as a starting material. Ethanol-to-butanol intercalates were unstable at room temperature, losing alcohols and changing to -zirconium phosphate. The particle size of the -zirconium phosphate did not affect the intercalation of alcohols. 相似文献
66.
67.
68.
The concise synthesis of Amaryllidaceae alkaloids, such as anhydrolycorinone, anhydrolycorin-7-one, assoanine, and oxoassoanine, which have a pyrrolophenanthridine skeleton, was achieved in moderate yield using the Pd-mediated biaryl coupling reaction of 1-(2-halobenzyl)-2,3-dihydroindole, which applied the regioselective C-H activation method with intramolecular coordination of the benzylamino group to Pd. 相似文献
69.
Eietsu Hasegawa Shinya Takizawa Akira Yamaguchi Naoki Chiba Hiroshi Ikeda 《Tetrahedron》2006,62(27):6581-6588
Photoinduced electron-transfer reactions of several ketone substrates were studied to evaluate the utilities of 1,6-bis(dimethylamino)pyrene (BDMAP), 1,6-dimethoxypyrene (DMP), 9,10-bis(dimethylamino)anthracene (BDMAA), and 9,10-dimethoxyanthracene (DMA) as electron-donating sensitizers cooperating with 2-aryl-1,3-dimethylbenzimidazolines. BDMAP and DMP generally led higher conversion of ketones and better yield of reduction products compared to BDMAA and DMA. 相似文献
70.