全文获取类型
收费全文 | 3628篇 |
免费 | 716篇 |
国内免费 | 632篇 |
专业分类
化学 | 2603篇 |
晶体学 | 58篇 |
力学 | 220篇 |
综合类 | 53篇 |
数学 | 259篇 |
物理学 | 1783篇 |
出版年
2024年 | 11篇 |
2023年 | 71篇 |
2022年 | 122篇 |
2021年 | 170篇 |
2020年 | 190篇 |
2019年 | 160篇 |
2018年 | 142篇 |
2017年 | 172篇 |
2016年 | 207篇 |
2015年 | 227篇 |
2014年 | 271篇 |
2013年 | 292篇 |
2012年 | 349篇 |
2011年 | 343篇 |
2010年 | 258篇 |
2009年 | 260篇 |
2008年 | 316篇 |
2007年 | 211篇 |
2006年 | 196篇 |
2005年 | 179篇 |
2004年 | 143篇 |
2003年 | 104篇 |
2002年 | 137篇 |
2001年 | 96篇 |
2000年 | 104篇 |
1999年 | 49篇 |
1998年 | 27篇 |
1997年 | 40篇 |
1996年 | 12篇 |
1995年 | 22篇 |
1994年 | 12篇 |
1993年 | 16篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1981年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1966年 | 2篇 |
1963年 | 1篇 |
1957年 | 1篇 |
1911年 | 4篇 |
排序方式: 共有4976条查询结果,搜索用时 15 毫秒
61.
Aihua Zhang Kun Liu Lan Li Siyu Ma Zonghe Li 《International journal of quantum chemistry》2005,104(3):373-378
The ring‐closing reaction of 5′‐adenosine monophosphate (5′‐AMP) to generate cyclic 3′, 5′‐adenosine monophosphate (cAMP) and H2O was theoretically investigated at the B3LYP/6‐31G**level. It was found that the ring‐closing reaction of 5′‐AMP may proceed in a synchronous way or in a stepwise way. For the latter, the reaction is a multichannel elimination reaction including inner H transfer. The potential energy surface of Path 3 is lowest in all the ring‐closing reaction paths. In addition, H shuttling reaction with the participation of a water molecule to act as a shuttle were also studied at the same level. The calculations indicate that the participation of a water molecule facilitates hydrogen transfer reaction. Our present calculations rationalized all the possible reaction channels. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
62.
超声波作用下的糖精相转移催化N-苄基化反应的研究嵇学林刘华黄昆(江苏镇江医学院有机化学教研室镇江212001)关键词超声波相转换催化糖精苄基化有机声化学近年来,由于超声波(Ultrasoun,缩写U.S)在有机合成中应用的不断发展,逐渐形成了一门新兴... 相似文献
63.
Qiang ZHAO Qian Kun ZHUANG 《中国化学快报》2005,16(9):1237-1240
With 1-Pymnebutyric acid (PBA) and multiwalled carbon nanotubes (MWNTs), glassy carbon electrode modified was successfully prepared. In phosphate buffer solution (pH 7,0), the direct electrochemistry of cytochrome C (Cyt C) was realized. In the cyclic voltammetry experiment two pairs of redox peaks ofCyt C were observed at 0.018 V and -0.314 V (vs. SCE), respectively. The redox reaction at 0.018 V was diffusion controlled, while the redox reaction at -0.314 V was adsorption controlled. 相似文献
64.
Simultaneous determination of triterpene saponins in ginseng drugs by high-performance liquid chromatography 总被引:3,自引:0,他引:3
A HPLC method for the simultaneous determination of 11 triterpene saponins with four-type aglycones (protopanaxadiol, protopanaxatriol, ocotillol and oleanolic acid types) in Ginseng drugs was developed and validated. Using a gradient of acetonitrile and 10 mM K-phosphate buffer (pH 5.80) as the mobile phase and UV detection at 196 nm, more than 18 ginsenosides with different aglycones were separated satisfactorily within 60 min. The detection limits (signal/noise> or =3) were 0.1 microg for ginsenosides Rb1, Rc, Rd, Re and Rg1, chikusetsusaponin III, and notoginsenoside R2, 0.2 microg for gisenoside Ro and chikusetsusaponin IVa, 0.3 microg for chikusetsusaponin IV, and 3 microg for majonoside R2. The calibration curve of each saponin had a correlation coefficient close to 1. Intra- and interday precisions were less than 2.1% (n=5) and 3.3% (n=15), respectively. The recovery rates of extraction were in the range of 96.4-102.7% for all ginsenosides. By adopting this method, the determinations of 11 ginsenosides in three Ginseng drugs derived from Panax ginseng, Panax vietnamensis var. fuscidiscus and Panax japonicus (Japan) were achieved. 相似文献
65.
This paper is the study of the fluorescence enhancement of Eu3+-1-ethyl-6-fluoro-4-oxo-7-(1-piperazinyl)-1,8-naphthyridin-3-carbonic acid (enoxacin, EFLX) system by surfactants. It was
found that sodium dodecylbenzenesulfonate (SDBS) exhibits great enhancement on the fluorescence of the Eu-EFLX system. The
molar ratio is 1:2:1 for Eu:EFLX: SDBS. Under the optimum conditions, the fluorescence intensity is a linear function of europium
in the range of 1.0 × 10−8 ∼ 5.0 × 10−6 mol/L, the detection limit is 1.0 × 10−9 mol/L. The application of the Eu-EFLX-SDBS system for the determination of trace europium in rare earth samples gave satisfactory
results.
Received October 19, 2000. Revision August 10, 2001. 相似文献
66.
A new approach to isoprostanes and neuroprostanes featuring cis-dialkyl stereochemistry at the cyclopentane ring has been developed by employing an intramolecular cross-coupling reaction of an alkyl iodide and a tethered alkenylsiloxane for stereoselective installation of a functionalized omega-side chain. 相似文献
67.
The interaction of pinacyanol chloride(PC) with nucleic acids has been investigated by a series of experiments.Extensive hypochromism,appreciable peak shifts,isosbestic points and new peaks of the product of binding to nucleic acids in the spectra were observed.They showed that the interaction between PC and nucleic acids occurred.The results from absorption spectra of DNA,DNA melting,electrophoresis and fluorescence polarization studies have indicated that PC binds to DNA in nonintercalative way.Consistent with the nonintercalation,the studies of fluorescence titration and absorption titration specified that the binding of PC to nucleic acids occurred by an outside stacking binding,in which nucleic acids served for acting templates,The fact that the new absorption peaks of bound PC at ca,485nm are just close to the absorption bands of Haggregate of PC at high concentrations without DNA further supports the outside stacking binding mode,In addition,other evidence indicated that the interaction between PC and nucleic acids is not purely electrostatic. 相似文献
68.
69.
Synthesis, Characterization and Two-Photon Absorption Properties of a Novel Pyridinium Salt 总被引:2,自引:0,他引:2
A novel pyridinium salt, 2,4-bis[p-(N,N-dimethylamino)styryll-N-metlayl pyridinium iodide (BMSPI) was synthesized and characterized by TG, ^1H NMR spectroscopy and elemental analysis, and the reaction process was studied by using ES-MS. When BMSPI was pumped by a pulsed 1064 nm, 50 ps laser beam, it manifests highly efficient TPA (Two-Photon Absorption) and up-conversion superradiance. The up-conversion efficiency was 6.0% at the pump energy of 4-6 mJ and the lifetime of two-photon fluorescence was measured as 59 ps. 相似文献
70.
Ahn YH Park EJ Cho K Kim JY Ha SH Ryu SH Yoo JS 《Rapid communications in mass spectrometry : RCM》2004,18(20):2495-2501
The enrichment of phosphopeptides using immobilized metal ion affinity chromatography (IMAC) and subsequent mass spectrometric analysis is a powerful protocol for detecting phosphopeptides and analyzing their phosphorylation state. However, nonspecific binding peptides, such as acidic, nonphosphorylated peptides, often coelute and make analyses of mass spectra difficult. This study used a partial chemical tagging reaction of a phosphopeptide mixture, enriched by IMAC and contaminated with nonspecific binding peptides, following a modified beta-elimination/Michael addition method, and dynamic mass analysis of the resulting peptide pool. Mercaptoethanol was used as a chemical tag and nitrilotriacetic acid (NTA) immobilized on Sepharose beads was used for IMAC enrichment. The time-dependent dynamic mass analysis of the partially tagged reaction mixture detected intact phosphopeptides and their mercaptoethanol-tagged derivatives simultaneously by their mass difference (-20 Da for each phosphorylation site). The number of new peaks appearing with the mass shift gave the number of multiply phosphorylated sites in a phosphopeptide. Therefore, this partial chemical tagging/dynamic mass analysis method can be a powerful tool for rapid and efficient phosphopeptide identification and analysis of the phosphorylation state concurrently using only MS analysis data. 相似文献