全文获取类型
收费全文 | 1646篇 |
免费 | 70篇 |
国内免费 | 11篇 |
专业分类
化学 | 1150篇 |
晶体学 | 14篇 |
力学 | 55篇 |
数学 | 154篇 |
物理学 | 354篇 |
出版年
2023年 | 8篇 |
2022年 | 8篇 |
2021年 | 35篇 |
2020年 | 36篇 |
2019年 | 37篇 |
2018年 | 28篇 |
2017年 | 25篇 |
2016年 | 53篇 |
2015年 | 49篇 |
2014年 | 51篇 |
2013年 | 77篇 |
2012年 | 120篇 |
2011年 | 132篇 |
2010年 | 93篇 |
2009年 | 93篇 |
2008年 | 138篇 |
2007年 | 104篇 |
2006年 | 83篇 |
2005年 | 85篇 |
2004年 | 73篇 |
2003年 | 57篇 |
2002年 | 66篇 |
2001年 | 21篇 |
2000年 | 39篇 |
1999年 | 28篇 |
1998年 | 22篇 |
1997年 | 14篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1970年 | 4篇 |
1966年 | 2篇 |
1965年 | 3篇 |
排序方式: 共有1727条查询结果,搜索用时 46 毫秒
101.
Kim MR Moon HI Chung JH Moon YH Hahm KS Woo ER 《Chemical & pharmaceutical bulletin》2004,52(12):1466-1469
A bioassay-guided fractionation of the ethyl acetate soluble fraction from the stem bark of Styrax japonica S. et Z. (Styracaceae) yielded two new lignan compounds, styraxjaponoside A (1) and styraxjaponoside B (2), along with three known compounds, matairesinoside (3), egonol glucoside (4), and dihydrodehydrodiconiferyl alcohol 9'-O-glucoside (5). The structures of compounds 1-5 were determined by spectroscopic method, as well as 1D- and 2D-NMR (HSQC, 1H-1H COSY, and HMBC) spectroscopy. Among them, compound 2 exhibited potent inhibitory activity against matrix metalloproteinase (MMP)-1, and prevented the UV-induced changes in the MMP-1 expression. In addition, compounds 3 and 5 were isolated from this plant for the first time. 相似文献
102.
The effects of inorganic substances on water splitting in ion-exchange membranes (IEMs) were investigated. In this study, iron hydroxide/ oxide and silica sol were immobilized on the surface of the IEMs. The water-splitting capabilities of the metal-embedded cation-exchange membranes were 10(4)-10(5) times greater than those of the virgin membranes at the same current density. Similarly, silica sol (i.e., triple bond Si-OH groups) deposited on the anion-exchange membrane surface also drastically increased the proton transport numbers. It was thought that the bipolar structure consisting of H- and OH-affinity groups immobilized on the IEM surface increased water-splitting due to the enhancement of water polarization with the help of strong electric fields. This study revealed that metal oxides or silica groups (triple bond Si-OH), as well as metal hydroxides, can be used as catalysts for water splitting. 相似文献
103.
Choi WJ Moon HR Kim HO Yoo BN Lee JA Shin DH Jeong LS 《The Journal of organic chemistry》2004,69(7):2634-2636
The preparative and stereoselective synthesis (45-50% overall yields) of the target compound 17 has been accomplished from D-ribose. The bulky protecting groups such as TBDPS and Trityl enforced the facial selectivity during Grignard reaction to give the tertiary beta-allylic alcohol 16 as the sole product, which was oxidatively rearranged to the key molecule 17 in excellent yield. 相似文献
104.
The thermoreversible fcc-bcc transition in concentrated block copolymer micellar solutions is shown to be driven by decreases in the aggregation number as the solvent penetrates the core, leading to a softer intermicelle potential. Small-angle neutron scattering measurements in a dilute solution are used to quantify the temperature-dependent micellar characteristics. The observed phase boundary is in excellent agreement with recent simulations of highly branched star polymers. 相似文献
105.
H.Y.?RyuEmail author D.?Lee K.-D.?Park W.-K.?Lee H.S.?Moon S.K.?Kim H.-S.?Suh 《Applied physics. B, Lasers and optics》2004,79(5):583-586
We report the fabrication of a discretely tunable erbium-doped fiber ring laser with a novel scheme that can select ITU-T grids of 50-GHz spacing in both C and L bands. Wavelength selections of 273 channels are demonstrated with a signal to source spontaneous emission ratio of 60 dB/nm and excellent power flatness over 111-nm bandwidth. This was realized by incorporating both a solid Fabry–Pérot interferometer and a fiber Fabry–Pérot tunable filter into the ring laser. To our knowledge, our experimental result has the widest tuning range ever reported for a discretely tunable fiber laser with 50-GHz channel spacing that matches the ITU-T grids and is the first equipment that can operate in both C and L bands. PACS 42.55.Wd; 42.60.Da; 42.60.-v 相似文献
106.
A simple quantum-mechanics/molecular-mechanics (QM/MM) approach for calculating NMR shielding tensors (sigma) is presented. The method involves capping the QM region with quantum capping potentials (QCPs) and representing the MM region with point charges. Test calculations on simple systems without MM charges show that calculated sigma values improve relative to the full QM results with increasing distance between the capped bond and chromophore. Calculations on the histidine amino acid and cytosine monophosphate (CMP) nucleic acid show that the use of QCPs with point charges result in mean errors in the isotropic component of sigma that are less than 1.6 ppm. The results also reveal that, contrary to previous work, the explicit effect of point charges on sigma through coupling with gauge factors, as in the gauge including atomic orbital approach, is minimal for the CMP molecule. The present QM/MM approach for calculating sigma is easy to apply and requires no code modification. 相似文献
107.
108.
Cho YS Karupaiyan K Kang HJ Pae AN Cha JH Koh HY Chang MH 《Chemical communications (Cambridge, England)》2003,(18):2346-2347
Synthesis of novel substituted tetrahydropyrans with adjacent exo-methylene groups at the C3 and C4 positions via Prins-type cyclization has been described. 相似文献
109.
110.
The Ba/Si(111) surface, previously known as a 3 x 1 phase, is found to have a 3 x 2 periodicity and a semiconducting band gap. The substrate reconstructs into the honeycomb chain-channel (HCC) structure with Ba atoms in the channel, as in the alkali-metal-induced Si(111)-(3 x 1). However, the metal coverage is determined to be 1/6 monolayers, half the alkali-metal coverage. We propose that the structure and the metal coverage determined for the Ba adsorbate is universal for other alkaline-earth-metal adsorbates. With the alkali-metal-induced 3 x 1 case, our results lead to a rule that one donated electron per 3 x 1 surface unit is necessary to stabilize the HCC reconstruction of Si. 相似文献