全文获取类型
收费全文 | 2039篇 |
免费 | 241篇 |
国内免费 | 214篇 |
专业分类
化学 | 1217篇 |
晶体学 | 33篇 |
力学 | 90篇 |
综合类 | 45篇 |
数学 | 206篇 |
物理学 | 903篇 |
出版年
2024年 | 7篇 |
2023年 | 33篇 |
2022年 | 64篇 |
2021年 | 55篇 |
2020年 | 58篇 |
2019年 | 80篇 |
2018年 | 70篇 |
2017年 | 46篇 |
2016年 | 77篇 |
2015年 | 65篇 |
2014年 | 77篇 |
2013年 | 107篇 |
2012年 | 150篇 |
2011年 | 147篇 |
2010年 | 101篇 |
2009年 | 115篇 |
2008年 | 110篇 |
2007年 | 96篇 |
2006年 | 95篇 |
2005年 | 109篇 |
2004年 | 93篇 |
2003年 | 77篇 |
2002年 | 68篇 |
2001年 | 102篇 |
2000年 | 50篇 |
1999年 | 63篇 |
1998年 | 55篇 |
1997年 | 44篇 |
1996年 | 37篇 |
1995年 | 38篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 16篇 |
1991年 | 16篇 |
1990年 | 33篇 |
1989年 | 17篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 19篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有2494条查询结果,搜索用时 125 毫秒
821.
The activation of C-O bonds in allylic acetates in water as a suspension medium has been accelerated by carrying out the reactions in the presence of platinum complexes associated with ligands. The platinum-catalyzed allylation of aminonaphthalenes using allylic acetates gave the corresponding N-allylic aminonaphthalenes in good yields. 相似文献
822.
Aqueous solution of anionic surfactant,sodium oleate(NaOA),was studied by means of steady-state shear rheology and dynamic oscillatory technique.The system of NaOA/Na3PO4 showed high viscosity,strong viscoelasticity and good ability of countering Ca^2+,Mg^2+.The Maxwell model and Cole-Cole plot were applied to study the dynamic viscoelasticity of wormlike micelles.The microstructures of the wormlike micelles were characterized by FF-TEM. 相似文献
823.
Gan D Jia M Vaughan PP Falvey DE Blough NV 《The journal of physical chemistry. A》2008,112(13):2803-2812
Chemical trapping studies combined with optical and electron paramagnetic resonance measurements were employed to examine the mechanisms of the aqueous photochemistry of methyl-benzoquinone (mBQ) at both low and high quinone concentrations. At low [mBQ], dimethylsulfoxide (DMSO) reacted with a photogenerated intermediate to form a methyl radical, but methane did not, thereby unequivocally excluding the hydroxyl radical. DMSO at concentrations between 50 mM and 2 M completely suppressed the formation of the hydroxylated quinone, while only slowing the formation of the hydroquinone, suggesting reaction with either the triplet state or an intermediate arising from the triplet. Addition of Cl-, a putative physical quencher of the triplet, inhibited the DMSO reaction both noncompetitively and competitively in a fashion similar to that observed previously with nitrite, formate, and salicylic acid, thus providing further evidence for a reactive intermediate distinct from the triplet. This intermediate is attributed to a water-quinone exciplex. The relative yield of the methyl radical from the DMSO reaction decreased with increasing [mBQ], suggesting that at high concentrations, a bimolecular reaction of the triplet with the ground-state quinone outcompetes the formation of the quinone-water exciplex. 相似文献
824.
Addition of the ambident SCN group to a fullerendione derivative follows two different pathways in the presence and absence of Lewis acid. 相似文献
825.
826.
827.
Norfullerenes are fullerene-like compounds (fulleroids) resulting from partial deletion of fullerene skeleton carbons. The one carbon less norfullerene C59(O) 3 derivatives having three carbonyl groups on the rim of the orifice are prepared through peroxide-mediated reactions. A key step involves a novel PCl 5 initiated rearrangement of a hydroxyl amine adduct. Decarboxylation serves as the carbon removal step. 相似文献
828.
A novel and simple method based on layer-by-layer (LBL) technique has been developed for the modification of the channel in PDMS electrophoresis microchip to create a hydrophilic surface with a stable EOF. The functional surface was obtained by sequentially immobilizing chitosan and deoxyribonucleic acid (DNA) onto the microfluidic channel surface using the LBL assembly technique. Compared to the native PDMS microchips, the contact angle of the chitosan-DNA modified PDMS microchips decreased and the EOF increased. Experimental conditions were optimized in detail. The chitosan-DNA modified PDMS microchips exhibited good reproducibility and long-term stability. Separation of uric acid (UA) and ascorbic acid (AA) performed on the modified PDMS microchip generated 43,450 and 46,790 N/m theoretical plates compared with 4048 and 19,847 N/m with the native PDMS microchip. In addition, this method has been successfully applied to real human urine samples, without SPE, with recoveries of 97-105% for UA and AA. 相似文献
829.
Star-shaped PCL with one to five arms were synthesized by ROP. They have the same crystal structure as linear PCL, indicating that the central cores are located in amorphous regions. The influence of arm length and number on crystallization and melting behavior were studied by DSC, POM, and through the Avrami equation. A model is proposed to analyze the enzymatic degradation process of star-shaped polymers. The multi-arm structure and the limitation of the central cores on the chain mobility of each arm are considered to be the primary factors influencing the characteristic crystallization and enzymatic degradation behavior of star-shaped PCLs. 相似文献
830.
Haokun Li Gan Xu Shuchang Li Yuhao Wu Dr. Zhenpin Lu 《Chemical record (New York, N.Y.)》2023,23(12):e202300238
Electron-precise B−B bonded compounds are valuable reagents in organic syntheses, which can be used as key starting material for the synthesis of functionalized organoboranes. Bis(pinacolato)diborane(4) B2pin2 and its derivatives are among the most studied diboron species. However, their B−B bonds usually need to be activated by transition metal catalysts or bases for further transformations. Recently, many well-designed/reactive electron-precise B−B bonded compounds have been developed, which could facilitate direct reactions with small molecules, unsaturated substrates, and electrophiles. This review highlights the synthesis, structure, and reactivity of neutral and anionic B−B bonded compounds. 相似文献