全文获取类型
收费全文 | 8297篇 |
免费 | 351篇 |
国内免费 | 126篇 |
专业分类
化学 | 6197篇 |
晶体学 | 42篇 |
力学 | 439篇 |
数学 | 881篇 |
物理学 | 1215篇 |
出版年
2024年 | 16篇 |
2023年 | 66篇 |
2022年 | 288篇 |
2021年 | 394篇 |
2020年 | 398篇 |
2019年 | 418篇 |
2018年 | 422篇 |
2017年 | 412篇 |
2016年 | 561篇 |
2015年 | 388篇 |
2014年 | 514篇 |
2013年 | 936篇 |
2012年 | 682篇 |
2011年 | 616篇 |
2010年 | 405篇 |
2009年 | 385篇 |
2008年 | 379篇 |
2007年 | 315篇 |
2006年 | 218篇 |
2005年 | 183篇 |
2004年 | 137篇 |
2003年 | 125篇 |
2002年 | 104篇 |
2001年 | 40篇 |
2000年 | 18篇 |
1999年 | 26篇 |
1998年 | 21篇 |
1997年 | 26篇 |
1996年 | 27篇 |
1995年 | 15篇 |
1994年 | 20篇 |
1993年 | 10篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 16篇 |
1986年 | 7篇 |
1985年 | 17篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有8774条查询结果,搜索用时 15 毫秒
981.
Mohammad Ali Zolfigol Kamal Amani Maryam Hajjami Arash Ghorbani-Choghamarani 《Monatshefte für Chemie / Chemical Monthly》2008,121(4):895-899
A wide range of aliphatic or aromatic sulfides are selectively oxidized to the corresponding sulfoxides using ammonium cerium
(IV) nitrate (CAN) and a catalytic amount of KBr or NaBr in the presence of wet SiO2 in CH2Cl2 under heterogeneous conditions in moderate to high yields. 相似文献
982.
S-allyl-β-N-[(2-hydroxyphenyl)methylene]hyrazinecarbodithioate) (1, H2L), the Schiff base of dithiocarbazate with unsaturated allyl substitution, can act as a new tridentate SNO ligand H2–L and react with cobalt(II) nitrate hexahydrate to form the novel linear trinuclear isovalence Co(II) complex, [Co3(H–L)2(L)2] 2C2H5OH (2). The compounds were characterized by elemental analysis, infrared, and ultraviolet spectroscopy. Compound 2 was also characterized by single-crystal X-ray analysis and crystallizes in the orthorhombic space group, Pbcn, with a = 30.643(1) Å, b = 9.118(4) Å, c = 19.017(7) Å, α = β = γ = 90°, V = 5312.95 Å3, Z = 4, and R 1 = 0.0790, (wR 2) = 0.1223. The six-coordinate central Co(II) atom is bonded to two deprotonated metal-containing ligands. The terminal Co(II) atoms are in a square planar SNON four-coordinate environment and connected to the central Co(II) by N-atoms from the ligand backbone. For quantifying the intermolecular interactions in crystal lattice, the new d norm surface and the breakdown of fingerprint plots have been used for visualizing and exploring the compound 2. 相似文献
983.
Mohammad Ali Zolfigol Kamal Amani Maryam Hajjami Arash Ghorbani-Choghamarani 《Monatshefte für Chemie / Chemical Monthly》2008,139(8):895-899
A wide range of aliphatic or aromatic sulfides are selectively oxidized to the corresponding sulfoxides using ammonium cerium
(IV) nitrate (CAN) and a catalytic amount of KBr or NaBr in the presence of wet SiO2 in CH2Cl2 under heterogeneous conditions in moderate to high yields.
Correspondence: Mohammad Ali Zolfigol, Faculty of Chemistry, Bu-Ali Sina University, P.O. Box 6517838683, Hamadan, Iran; Kamal
Amani, Department of Chemistry, Faculty of Science, University of Kurdistan, P.O. Box 6617715175, Sanandaj, Iran. 相似文献
984.
Solidified floating organic drop microextraction (SFODME) was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GFAAS). 20 μL of 1-undecanol containing dithizone as the chelating agent (2 × 10−4 mol L−1) was transferred to the water samples containing lead ions, and the solution was stirred for the prescribed time. The sample vial was cooled in an ice bath for 5 min. The solidified extract was transferred into a conical vial where it melted immediately, and then 10 μL of it was analyzed by GFAAS.Factors that influence the extraction and complex formation, such as pH, concentration of dithizone, extraction time, sample volume, and ionic strength were optimized. Under the optimized conditions, a good relative standard deviation of ±5.4% at 10 ng L−1 and detection limit of 0.9 ng L−1 were obtained. The procedure was applied to tap water, well water, river water and sea water, and accuracy was assessed through the analysis of certified reference water or recovery experiments. 相似文献
985.
M. Mohsen-Nia F.S. Mohammad Doulabi V.I. Manousiouthakis 《The Journal of chemical thermodynamics》2008,40(8):1269-1273
Tie-line data for ternary systems of (ethylene glycol + toluene + n-octane) at three temperatures (295.15, 301.15, and 307.15) K are reported. The compositions of liquid phases at equilibrium were determined and the results were correlated with the UNIQUAC and NRTL activity coefficient models. The partition coefficients and the selectivity factor of ethylene glycol are calculated and compared to suggest which ethylene glycol is more suitable for extracting of toluene from n-octane. The phase diagrams for the studied ternary mixtures including both the experimental and correlated tie lines are presented. From the phase diagrams and the selectivity factors, it is concluded that ethylene glycol may be used as a suitable solvent in extraction of toluene from n-octane mixtures. 相似文献
986.
Mohammad Joshaghani Marzieh Daryanavard Ezzat Rafiee Shirin Nadri 《Journal of organometallic chemistry》2008,693(19):3135-3140
The reaction of biphenyl-based phosphine P(o-C6H4Me)Ph2 (1) with Pd(OAc)2 in toluene affords the air and water stable palladacycle (2) as a binuclear compound which has been characterized by multi-nuclear NMR spectroscopy and elemental analysis as a mixture of cis and trans isomers with relative intensity of 1:3, respectively. This palladacycle is a highly efficient catalyst precursor for the coupling of aryl boronic acids and aryl halides. Both activated and deactivated aryl bromides and chlorides are efficiently coupled in the presence of 2 to furnish the corresponding cross-coupled products in excellent yields, and a wide variety of functional groups are tolerated in aryl halides. This methodology has also been extended for the coupling of bromoarylphosphines and bromoarylphosphine oxides with aryl boronic acids for the generation of hindered corresponding products. 相似文献
987.
988.
Mohammad Ali Taher Mohammad Esfandyarpour Shahryar Abbasi Alireza Mohadesi 《Electroanalysis》2008,20(4):374-378
Traces of copper(II) can be determined by adsorptive stripping voltammetry using 2‐carboxy‐2′‐hydroxy‐5′‐sulfoformazyl benzene (Zincon) as complex forming reagent. First in phosphate buffer pH 6.4, copper(II)‐Zincon complex was adsorbed on carbon paste electrode (CPE) with an accumulation potential of 0.6 V. Following this, adsorbed complex was oxidized and detected by differential pulse voltammetric (DPV) scan from 0.6 to 1.0 V. The effective parameters in sensor response were examined. The detection limit (DL) of copper(II) was 1.1 μg/L and relative standard deviations (RSDs) for 10 and 200 μg/L Cu(II) were 1.81 and 1.03%, respectively. The calibration curve was linear for 2–220 μg/L copper(II). The resulting CPE does not use mercury and therefore, has a positive environmental benefit. The method, which is reasonably sensitive and selective, has been successfully applied to the determination of trace amount of copper in water and human hair samples. 相似文献
989.
Noorjahan Begum Mohammad A. Rahman Mohammad R. Hassan Derek A. Tocher Ebbe Nordlander Graeme Hogarth Shariff E. Kabir 《Journal of organometallic chemistry》2008,693(8-9):1645-1655
Reaction of [Ru3(CO)12] with tri(2-furyl)phosphine, P(C4H3O)3, at 40 °C in the presence of a catalytic amount of Na[Ph2CO] furnishes two triruthenium complexes [Ru3(CO)10{P(C4H3O)3}2] (1) and [Ru3(CO)9{P(C4H3O)3}3] (2) with the ligand coordinated through the phosphorus atom. Treatment of 1 and 2 with Me3NO at 40 °C affords the dinuclear phosphido-bridged complexes [Ru2(CO)6(μ-η1,η2-C4H3O){μ-P(C4H3O)2}] (3) and [Ru2(CO)5(μ-η1,η2-C4H3O){μ-P(C4H3O)2}{P(C4H3O)3}] (4), respectively, that are formed via phosphorus–carbon bond cleavage of a coordinated phosphine followed by coordination of the dissociated furyl moiety to the diruthenium center in a σ,π-alkenyl mode. Reaction of [Ru3(CO)12] with tri(2-furyl)phosphine in refluxing benzene gives, in addition to 3 and 4, low yields of the cyclometallated complex [Ru3(CO)9{μ-η1,η1-P(C4H3O)2(C4H2O)}2] (5). Treatment of 3 with EPh3 (E = P, As, Sb) at room temperature yields the monosubstituted derivatives [Ru2(CO)5(μ-η1,η2-C4H3O){μ-P(C4H3O)2}(EPh3)] (E = P, 8; E = As, 9; E = Sb, 10). Similar reactions of 3 with P(C4H3O)3, P(OMe)3 and ButNC yield 4, [Ru2(CO)5(μ-η1,η2-C4H3O){μ-P(C4H3O)2}{P(OMe)3}] (11) and [Ru2(CO)5(μ-η1,η2-C4H3O){μ-P(C4H3O)2}(NCBut)] (12), respectively. The molecular structures of complexes 3, 4 and 8 have been elucidated by single crystal X-ray diffraction studies. Each complex contains a bridging σ,π-alkenyl group and while in 4 the phosphine is bound to the σ-coordinated metal atom, in 8 it is at the π-bound atom. Protonation of 3 and 4 gives the hydride complexes [(μ-H)Ru2(CO)6(μ-η1,η2-C4H3O){μ-P(C4H3O)2}]+ (6) and [(μ-H)Ru2(CO)5(μ-η1,η2-C4H3O){μ-P(C4H3O)2}{P(C4H3O)3}]+ (7), respectively, while heating 3 with dimethylacetylenedicarboxylate (DMAD) in refluxing toluene gives the cyclotrimerization product, C6(CO2Me)6. 相似文献
990.
Roghieh Jamjah Gholam Hossein Zohuri Mohsen Javaheri Mehdi Nekoomanesh Saeid Ahmadjo Ali Farhadi 《Macromolecular Symposia》2008,274(1):148-153
Summery: A Ziegler-Natta catalyst of MgCl2 (ethoxide type)/TiCl4 has been synthesized. In order to obtain ultra high molecular weight polyethylene (UHMWPE) tri-isobutylaluminum which is less active to chain transfer was used as cocatalyst. Slurry polymerization was carried out for the polymerization of ethylene while, dilute solution viscometry was performed for the viscosity average molecular weight (Mv) measurement. The effect of [Al]/[Ti] molar ratio, temperature, monomer pressure and polymerization time on the Mv and productivity of the catalyst have been investigated. The results showed increasing [Al]/[Ti] ratio in the range of 78–117, decreased the Mv of the obtained polymer from 7.8 × 106 to 3.7 × 106 however, further increase of the ratio, resulted in decreased of by much slower rate up to [Al]/[Ti] = 588. The higher pressure in the range of 1–7 bars showed the higher the Mv of the polymer obtained, while increasing temperature in the range of 50 to 90 °C decreased the Mv from 9.3 × 106 to 3.7 × 106. The Mv rapidly increase with polymerization time in the first 15 minutes of the reaction, this increase was slowly up to the end of the reaction (120 min). Increasing [Al]/[Ti] ratio raised productivity of the catalyst in the range studied. Rising reaction temperature from 50 to 75 °C increased the productivity of the catalyst however, further increase in the temperature up to the 90 °C decreased activity of the catalyst. Monomer pressure in the range 1 to 7 bars yields higher productivity of the catalyst. Also by varying polymerization conditions synthesizing of UHMWPE with Mv in the range of 3 × 106 to 9 × 106 was feasible. 相似文献