全文获取类型
收费全文 | 1783篇 |
免费 | 45篇 |
国内免费 | 7篇 |
专业分类
化学 | 1405篇 |
晶体学 | 30篇 |
力学 | 20篇 |
数学 | 122篇 |
物理学 | 258篇 |
出版年
2021年 | 18篇 |
2020年 | 12篇 |
2019年 | 20篇 |
2018年 | 14篇 |
2016年 | 23篇 |
2015年 | 19篇 |
2014年 | 28篇 |
2013年 | 66篇 |
2012年 | 73篇 |
2011年 | 86篇 |
2010年 | 57篇 |
2009年 | 37篇 |
2008年 | 80篇 |
2007年 | 97篇 |
2006年 | 101篇 |
2005年 | 111篇 |
2004年 | 83篇 |
2003年 | 59篇 |
2002年 | 83篇 |
2001年 | 14篇 |
2000年 | 21篇 |
1999年 | 25篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 28篇 |
1995年 | 26篇 |
1994年 | 16篇 |
1993年 | 26篇 |
1992年 | 16篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 19篇 |
1987年 | 21篇 |
1986年 | 18篇 |
1985年 | 37篇 |
1984年 | 40篇 |
1983年 | 26篇 |
1982年 | 31篇 |
1981年 | 29篇 |
1980年 | 23篇 |
1979年 | 28篇 |
1978年 | 31篇 |
1977年 | 26篇 |
1976年 | 36篇 |
1975年 | 26篇 |
1974年 | 25篇 |
1973年 | 25篇 |
1972年 | 11篇 |
1971年 | 9篇 |
排序方式: 共有1835条查询结果,搜索用时 15 毫秒
101.
102.
Nakano H Takahashi K Okuyama Y Senoo C Tsugawa N Suzuki Y Fujita R Sasaki K Kabuto C 《The Journal of organic chemistry》2004,69(21):7092-7100
Cationic palladium (Pd)- and platinum (Pt)-phosphinooxazolidine catalysts 13a-c, 15a-d, 17a-c, and 19a-c were prepared from phosphinooxazolidine ligands 1-3, MCl(2) (M = Pd and Pt), and counterions, and the activities of the catalysts in the asymmetric Diels-Alder (DA) reactions of cyclic or acyclic dienes with imide dienophiles were investigated. These catalysts demonstrated high levels of catalytic activity. The cationic Pd-POZ complex 13c provided particularly excellent enantioselectivity (98% ee) in the DA reactions of cyclopentadiene with acryloyl-, crotonyl-, and fumaroyl-1,3-oxazolidin-2-ones (20a-c). 相似文献
103.
Lee HJ Jin ZX Aleshin AN Lee JY Goh MJ Akagi K Kim YS Kim DW Park YW 《Journal of the American Chemical Society》2004,126(51):16722-16723
To study the transport properties of individual helical polyacetylene (PA) fibers, we developed a method to extract a single fiber from tightly entangled ropes of helical PA bulk film. After a few minutes of sonication of a piece of helical PA bulk film in an organic solution containing surfactant, a droplet of solution is deposited on the pre-pattened electrode under argon atmosphere. AFM images show that extracted helical PA fibers are typically 10 mum in length and 100-200 nm in diameter. We found that the helicity of bulk materials is conserved. We present the temperature dependencies of current-voltage characteristics of individual helical PA fibers doped with iodine. 相似文献
104.
105.
Ashihara S Shimura T Kuroda K Yu NE Kurimura S Kitamura K Ro JH Cha M Taira T 《Optics letters》2003,28(16):1442-1444
Large nonlinear phase shifts were generated with femtosecond pulses at 1560 nm through cascaded quadratic interactions in periodically poled MgO-doped LiNbO3. The off-diagonal component of the nonlinear coefficient was utilized for simultaneous quasi phase matching and group-velocity matching. The effective nonlinear refractive index was varied from -2.9 x 10(-14) to +3.3 x 10(-14) cm2/W by tuning the phase-mismatch conditions. 相似文献
106.
Abe S Fujishima T Tsubone T Fujimura R Ono H Matoba O Oda K Shimura T Kuroda K 《Optics letters》2003,28(6):420-422
The photorefractive effect in a nominally undoped 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 single crystal is measured. We report what is, to our knowledge, the first observation of the photorefractive effect in Pb-based relaxor ferroelectric crystals. The crystal is grown by the flux solution method. Then it is cut into a 2 mm x 4 mm x 8 mm piece and electrically poled along the [111] direction. The coupling constant of the two-wave mixing is 17 cm(-1), and the normalized time constant under 1-W/cm(2) illumination is 12 s at a wave-length of 476 nm. The effective trap density is calculated as 5 x 10(16) cm(-3) from the Debye screening length under the assumption of Kukhtarev's band-transport model. The dominant carrier is identified to be holes from the direction of two-wave mixing energy transfer. 相似文献
107.
Kazuo Akutagawa 《Mathematische Zeitschrift》2003,243(1):85-98
For a supergroup , we describe an obstruction to the existence of positive scalar curvature metrics with minimal boundary condition on a compact
n-dimensional -manifold W with nonempty boundary M, , in terms of the bordism class [M] in the Stolz obstruction group associated to [St2]. In par ticular, when W is a 5-dimensional spin manifold and the -invariant of a connected component of M is nonzero, we prove that W does not admit a positive scalar curvature metric with minimal boundary condition.
Received: 4 July 2001; in final form: 5 February 2002 / Published online: 8 November 2002
RID="*"
ID="*" Partially supported by the Grants-in-Aid for Scientific Research (C), Japan Society for the Promotion of Science, No.
11640070. 相似文献
108.
Yoshiki Kaneoke Masahiro Furuse Suguru Inao Katsuyoshi Saso Kazuo Yoshida Yoshimasa Motegi Motomu Mizuno Akira Izawa 《Magnetic resonance imaging》1987,5(6):415-420
Measurements were made of T1 of bound water (T1b) and bound water fraction () for gelatin solutions and human tissues (sera, brain tumor, cerebral white matter). Bound water fraction in each sample was measured by means of thermal analysis (differential scanning calorimetry: DSC). T1 values were measured by FONAR QED 80-. T1b values were calculated by an equation derived from the fast-exchange two-state model. In the study of gelatin solutions, the relationship between T1 and water content differed depending on the sort of solutions. This was considered to be due to differences in T1b values. In each biological tissue the values of T1b and had different distributions. These results indicate that values of T1b and for biological tissues may be altered in correspondence to the changes in pathophysiological states in those tissues. 相似文献
109.
Inhibition of the mevalonate pathway by an HMG-CoA reductase inhibitor, mevalotin, in Streptomyces prunicolor possessing both mevalonate and MEP pathways resulted in the production of a new metabolite mevashuntin that consisted of conjugated thiazolone and pyranonaphthoquinone moieties. 相似文献
110.
Minghui Song Kazutaka Mitsuishi Kazuo Furuya 《Physica E: Low-dimensional Systems and Nanostructures》2005,29(3-4):575
Nanometer-sized W-dendrites are fabricated on Al2O3 substrates with an electron-beam-induced deposition process. Dependence of growth of nanodendrite on surface topography is investigated with transmission electron microscopy. It is confirmed that the nanodendrite grows on convex surfaces but not around a hole on a substrate. These are attributed to different distribution of charges on surfaces with different topographies during electron beam irradiation when charges are produced on the surface due to emission of second electrons. The charges accumulate on convex surface and do not distribute around a hole. Therefore, the nanodendrite grows on the former and not on the latter. 相似文献