全文获取类型
收费全文 | 1058篇 |
免费 | 49篇 |
国内免费 | 10篇 |
专业分类
化学 | 914篇 |
晶体学 | 2篇 |
力学 | 11篇 |
数学 | 84篇 |
物理学 | 106篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 35篇 |
2021年 | 48篇 |
2020年 | 37篇 |
2019年 | 30篇 |
2018年 | 27篇 |
2017年 | 18篇 |
2016年 | 40篇 |
2015年 | 25篇 |
2014年 | 42篇 |
2013年 | 62篇 |
2012年 | 62篇 |
2011年 | 69篇 |
2010年 | 61篇 |
2009年 | 53篇 |
2008年 | 68篇 |
2007年 | 62篇 |
2006年 | 54篇 |
2005年 | 61篇 |
2004年 | 44篇 |
2003年 | 37篇 |
2002年 | 34篇 |
2001年 | 11篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1998年 | 13篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 9篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1117条查询结果,搜索用时 953 毫秒
991.
Luna Jde S De Carvalho JM De Lima MR Bieber LW Bento Ede S Franck X Sant'ana AE 《Natural product research》2006,20(3):253-257
An ethanolic extract of the leaves of Annona muricata was shown to be toxic to adult forms of the snail Biomphalaria glabrata (LC50 9.32 microg mL(-1)) and to larvae of the brine shrimp Artemia salina (LC50 0.49 microg mL(-1)). Activity-guided fractionation of the extract gave rise to a sample with high molluscicidal activity that contained the acetogenins, annonacin (90%), isoannonacin (6%) and goniothalamicin (4%). 相似文献
992.
Three Eu(III) luminescent compounds were separately entrapped in a xerogel porous silica matrix and finely ground particles of it were deposited on a glass support with polyvinylacetate (PVAc) as a binder to build a thin film sensor. These 3 devices were immersed in aqueous solutions of Cu(II) and the content of this metal was evaluated by emission-quenching experiments. The sensor containing the highly luminescent antenna chelate of diethylenetriaminepentaacetic acid (dtpa) sensitized with Coumarin120 rendered the largest Stern-Volmer constant (K(SV) = 1.49 x 10(4) M(-1)), showing no leaching of the Eu(III) complex to the aqueous solution and a reproducible value of the luminescence ratio between water and Cu(II) solution. The in situ sensor we developed can measure the concentration of Cu(II) in aqueous media down to the ppm level by emission-quenching experiments. This methodology permits a simple calibration of the sensor and an easy to use reusable device. 相似文献
993.
The reaction of enantiopure 4-oxoazetidine-2-carbaldehydes with unmodified ketones was catalyzed by L-proline as well as by D-proline, to give the corresponding gamma-amino-beta-hydroxy ketones with good yields and diastereoselectivities. The obtained results implied that (2R,3R)-4-oxoazetidine-2-carbaldehydes and L-proline are a matched pair for diastereoselective induction. 相似文献
994.
Elena Mas-Marzá Eduardo Peris Beatriz Royo 《Journal of organometallic chemistry》2006,691(12):2708-2712
Compound MoO2Cl2(THF)2 reacts with two equivalents of 1,3-dialkyl substituted 4,5-dimethylimidazol-2-ylidenes to give the dioxomolybdenum(VI) complexes MoO2Cl2(LR)2 [R = Me (1), i-Pr (2)]. Treatment of MoO2Cl2(THF)2 with one equivalent of the N-heterocyclic carbenes LMe, Li-Pr and C1Ln-Bu (LMe = 1,3,4,5-tetramethylimidazol-2-ylidene, Li-Pr = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, and C1Ln-Bu = 1,3-dibutyl-4,5-dichloroimidazol-2-ylidene) affords the monocarbene adducts MoO2Cl2(LR) [R = Me (3), i-Pr (4)] and MoO2Cl2(C1Ln-Bu) (5), respectively. Decomposition of complexes 1-5 affords a molybdenum oxychloride anion [Mo2O5Cl4]2− as an imidazolium salt. 相似文献
995.
Titanium complexes bearing an unprecedented tridentate cyclopentadienyl-silsesquioxanate ligand provide a new class of efficient and selective catalysts for epoxidation of olefins with aqueous hydrogen peroxide under homogeneous conditions. 相似文献
996.
997.
Angulo B García JI Herrerías CI Mayoral JA Miñana AC 《The Journal of organic chemistry》2012,77(13):5525-5532
An efficient release-capture strategy for the recovery and reuse of enantioselective catalysts in the Henry reaction is described. This strategy is based on the precipitation of an insoluble coordination polymer at the end of each reaction, allowing easy separation from products. The coordination polymer is formed through aggregation of Cu(II) ions with ditopic bisoxazoline-based chiral ligands. Up to 11 catalytic cycles have been conducted keeping good yields and enantioselectivities. 相似文献
998.
Mignone RA Martin MV Vieyra FE Palazzi VI de Mishima BL Mártire DO Borsarelli CD 《Photochemistry and photobiology》2012,88(4):792-800
In this study, we show that several UV-Vis absorbance, steady-state and time-resolved fluorescence parameters of a series of dissolved humic substances (DHS) from different sources (e.g. terrestrial fulvic and humic acids, and humic acid-like molecules extracted from composted and vermicomposted wastes) correlate with the molar absorptivity at 280 nm per mole of organic carbon (ε(280)), which in turn is proportional to the molecular complexity (e.g. molecular size, aromaticity and oxidation degree) of the DHS. Both absorbance and fluorescence spectral responses were sensitive to the molecular complexity associated with the maturation degree of the DHS. Depending on the DHS, different emitting responses by excitation at the UVA (340 nm) and VIS (460 nm) regions of the absorption spectra were observed. The results were explained in terms of the extent of intramolecular electronic interactions between electron donor groups, such as polyhydroxylated aromatics and indoles, and more oxidized acceptor groups (e.g. quinones or other oxidized aromatics) as the molecular complexity of the DHS increased. 相似文献
999.
Elena Galán Raquel Andreu Javier Garín Laura Mosteo Jesús Orduna Belén Villacampa Beatriz E. Diosdado 《Tetrahedron》2012,68(32):6427-6437
Two series of matched and mismatched donor–thiazole–acceptor chromophores have been synthesized to disclose the role that the orientation of the thiazole ring plays on their second-order nonlinear optical (NLO) properties. Whereas previous theoretical studies predict that the matched systems show markedly higher NLO responses, our experimental results do not parallel this trend, showing differences between regioisomers much lower than those predicted. 相似文献
1000.
Fernández-Calviño D Bermúdez-Couso A Garrido-Rodríguez B Peña Rodríguez S Arias-Estévez M 《Journal of colloid and interface science》2012,367(1):422-428
The effect of pH and ionic strength on copper release in a long-term Cu-polluted soil was studied using a stirred flow chamber. The presence of Ca(2+) and Na(+) was also evaluated. More copper was released as the ionic strength increased, and it was significantly higher in the presence of Ca(2+) than in the presence of Na(+). The maximum amount of Cu that could be released under experimental conditions increased logarithmically as the ionic strength increased, and the release rate parameters were not significantly correlated with ionic strength values. The maximum amount of Cu that could be released was similar for solutions with pH values between 5.5 and 8.5. For solutions with a pH value below 4.5, the amount of Cu released increased exponentially as the pH decreased. The release rate parameters and Cu release pattern were affected by pH, especially for more acidic solutions (pH values of 2.5 and 3.5). 相似文献