全文获取类型
收费全文 | 948篇 |
免费 | 36篇 |
国内免费 | 3篇 |
专业分类
化学 | 755篇 |
晶体学 | 8篇 |
力学 | 13篇 |
数学 | 53篇 |
物理学 | 158篇 |
出版年
2022年 | 4篇 |
2021年 | 17篇 |
2020年 | 17篇 |
2019年 | 21篇 |
2018年 | 18篇 |
2017年 | 11篇 |
2016年 | 24篇 |
2015年 | 21篇 |
2014年 | 22篇 |
2013年 | 42篇 |
2012年 | 59篇 |
2011年 | 70篇 |
2010年 | 30篇 |
2009年 | 17篇 |
2008年 | 58篇 |
2007年 | 59篇 |
2006年 | 64篇 |
2005年 | 57篇 |
2004年 | 57篇 |
2003年 | 59篇 |
2002年 | 45篇 |
2001年 | 20篇 |
2000年 | 22篇 |
1999年 | 14篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1936年 | 3篇 |
排序方式: 共有987条查询结果,搜索用时 31 毫秒
941.
A novel approach to fabricate periodic one-dimensional (1D) nanostructured arrays is developed using monolayer colloidal crystals as templates or masks. This approach is more flexible and less costly than traditional lithographic techniques. The morphology and structural parameters of periodic arrays can be easily controlled, further resulting in optimized properties. Herein we introduce recent work to create periodic 1D nanostructured arrays by combining colloidal templates with other techniques, such as solution techniques, electrodeposition, wet chemical etching, reactive ion etching (RIE), pulsed laser deposition (PLD), and sputtering. These periodic 1D nanostructured arrays with controllable morphology and structural parameters have extensive applications in areas such as nanophotonics, field emitters, solar cells, light-emitting diodes, and microfluidic devices. 相似文献
942.
Hayashi N Sato K Sato Y Iwagami M Nishimura N Yoshino J Higuchi H Sato T 《The Journal of organic chemistry》2011,76(14):5747-5758
Statistical studies using the Cambridge Structural Database have revealed that there are several elongated phenoxide C-O bonds. They are characterized by the formation of 3-fold (or occasionally 2-fold) hydrogen bonds to the phenoxide oxygen atoms, and their mean bond length extends up to 1.320 ?, which is quite different from the theoretically predicted carbon-oxygen bond length of C(6)H(5)O(-) (1.26 ?). Elongated phenoxide C-O bonds associated with the formation of 3-fold hydrogen bonds were also observed in the X-ray structures of proton-transfer complexes (2X-O(-))(TEAH(+))s derived from 5'-X-substituted 5,5'-dimethyl-1,1':3',1'-terphenyl-2,2',2'-triols (2X-OHs, where X = NO(2), CN, COOCH(3), Cl, F, H, and CH(3)) and triethylamine (TEA). By comparing the X-ray structures, C-O bond elongation was found to be only slightly affected by an electron-withdrawing substituent at the para position (X). This along with strong bathochromic shifts of N-H(···O(-)) and O-H(···O(-)) stretching vibrations in the IR spectra indicates that the elongated C-O bonds in (2X-O(-))(TEAH(+))s essentially have single-bond character. This is further confirmed by molecular orbital calculations on a model complex, showing that the negatively charged phenoxide oxygen atom is no longer conjugated to the central benzene ring, and the NICS values of the three benzene rings are virtually identical. However, C-O bond elongation in (2X-O(-))(TEAH(+))s was considerably influenced by a change in the hydrogen-bond geometry. This also suggests that hydrogen bonds significantly affect phenoxide C-O bond elongation. 相似文献
943.
Li Z Kishi N Hasegawa K Akita M Yoshizawa M 《Chemical communications (Cambridge, England)》2011,47(30):8605-8607
M(2)L(4) molecular capsules self-assembled from M(II) ions (where M = Zn, Ni, and Pd) and bent bidentate ligands constructed from anthracene fluorophores. The Ni(II) and Zn(II) capsules exhibited weak to strong blue emission unlike traditional Pd(II) cages and capsules. 相似文献
944.
Morita Y Nagaya N Shibata Y Kwon E Oikawa H Nakanishi H Kira M Sakamoto K 《Chemical communications (Cambridge, England)》2011,47(8):2315-2317
Nanocrystals of several oligosilanes have been fabricated easily by using a reprecipitation method. The nanocrystals reveal an intense absorption band at the UVB region (280 to 320 nm) and a fluorescence band with large Stokes shift. These photophysical properties show that the nanocrystals exhibit an excitonic interaction of the H-aggregate type. 相似文献
945.
Yamada I Yamashita N Tani K Einishi T Saito M Fukumi K Nishii J 《Optics letters》2011,36(19):3882-3884
A mid-IR wire-grid polarizer with a 500 nm pitch was fabricated on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) by the thermal imprinting of periodic grating followed by the thermal evaporation of Al metal. After imprinting, deposition of Al on the grating at an oblique angle produced a wire-grid polarizer. The fabricated polarizer showed polarization with TM transmittance greater than 60% at 5-9 μm wavelengths and an extinction ratio greater than 20 dB at 3.5-11 μm wavelengths. This polarizer with a high extinction ratio can be fabricated more simply and less expensively than conventional IR polarizers. 相似文献
946.
A kind of high-repetition-rate distributed Brillouin sensor is proposed and experimentally demonstrated based on optical correlation-domain analysis with differential frequency modulation, where the optical frequencies of the pump and the probe waves are modulated at slightly different RFs so that the temporal position of the measurement is continuously and repeatedly swept along a fiber under test. A distribution map of Brillouin frequency variation along a 100 m optical fiber is acquired at a repetition rate of 20 Hz with an accuracy of ±2.5 MHz and a spatial resolution of about 80 cm. 相似文献
947.
948.
We have synthesized new phenylacetylene-based liquid crystals containing a cyclohexyl or cyclohexylethyl group and evaluated their physical properties in order to develop a range of materials having high value of birefringence. The cyclohexyl-containing compounds exhibited nematic behaviour near room temperature and moderate values of δn of around 0.3. The cyclohexylethyl-containing compounds had a very wide nematic range with a high TNI and very high values of δn of over 0.4. They also exhibited low viscosities. The order parameter was not affected by introducing either a cyclohexyl or a cyclohexylethyl group and the values of δn based on calculated polarizabilities were obtained experimentally. 相似文献
949.
Dr. Shabbir Muhammad Kotaro Fukuda Takuya Minami Dr. Ryohei Kishi Dr. Yasuteru Shigeta Dr. Masayoshi Nakano 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(5):1677-1685
To reveal new structure–property relationships in the nonlinear optical (NLO) properties of fullerenes that are associated with their open‐shell character, we investigated the interplay between the diradical character (yi) and second hyperpolarizability (longitudinal component, γzzzz) in several fullerenes, including C20 , C26 , C30 , C36 , C40 , C42 , C48 , C60 , and C70 , by using the broken‐symmetry density functional theory (DFT; LC‐UBLYP (μ=0.33)/6‐31G*//UB3LYP/6‐31G*). We found that the large differences between the geometry and topology of fullerenes have a significant effect on the diradical character of each fullerene. On the basis of their different diradical character, these fullerenes were categorized into three groups, that is, closed‐shell (yi=0), intermediate open‐shell (0<yi<1), and almost pure open‐shell compounds (yi?1), which originated from their diverse topological features, as explained by odd‐electron‐density and spin‐density diagrams. For example, we found that closed‐shell fullerenes include C20 , C60 , and C70 , whereas fullerenes C26 and C36 and C30 , C40 , C42 , and C48 are pure and intermediate open‐shell compounds, respectively. Interestingly, the γzzzz enhancement ratios between C30 / C36 and C40 / C60 are 4.42 and 11.75, respectively, regardless of the smaller π‐conjugation size in C30 and C40 than in C36 and C60 . Larger γzzzz values were obtained for other fullerenes that had intermediate diradical character, in accordance with our previous valence configuration interaction (VCI) results for the two‐site diradical model. The γzzzz density analysis shows that the large positive contributions originate from the large γzzzz density distributions on the right‐ and left‐extended edges of the fullerenes, between which significant spin polarizations (related to their intermediate diradical character) appear within the spin‐unrestricted DFT level of theory. 相似文献
950.
Abstract Inclusion behavior of structurally similar host compounds, 1,4-bis[1-(9-anthryl)-3-propen-1-on-3-yl]benzene (1) and 1,4-bis[3-(9-anthryl)-3-propen-1-on-1-yl]benzene (2), has been studied. Both hosts preferred cyclic, non-branched small molecules as a guest component, to yield 1:2 clathrates specifically. X-ray powder diffraction studies revealed that those 1:2 clathrates of 1 and 2 were respectively isostructural. X-ray analyses of (1)(THF)2 (P 1, a = 10.910(2), b = 19.656(5), c = 9.172(4) Å, α = 95.58(3), β = 93.67(2), γ = 103.30(2)°, D calc = 1.195 g cm?3, Z = 2, and R = 0.067 for 8644 observed reflections) and (2)(1,4-dioxane)2, (P21/n, a = 5.661(1), b = 17.971(3), c = 18.619(3) Å, β = 91.37(2)°, D calc = 1.254 g cm?3, Z = 2, and R = 0.097 for 4353 observed reflections) illuminated that their guest preference should be ascribed to the commonly observed π-sandwich” structure, in which guest molecules are enclathrated between two anthracene planes of the host molecules. 相似文献