首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   285篇
  免费   7篇
  国内免费   14篇
化学   241篇
晶体学   1篇
力学   8篇
综合类   1篇
数学   27篇
物理学   28篇
  2023年   2篇
  2022年   6篇
  2021年   8篇
  2020年   5篇
  2019年   3篇
  2018年   5篇
  2017年   3篇
  2016年   9篇
  2015年   2篇
  2014年   6篇
  2013年   25篇
  2012年   24篇
  2011年   25篇
  2010年   12篇
  2009年   37篇
  2008年   11篇
  2007年   8篇
  2006年   13篇
  2005年   10篇
  2004年   4篇
  2003年   11篇
  2002年   4篇
  2001年   1篇
  2000年   8篇
  1999年   4篇
  1998年   5篇
  1997年   3篇
  1996年   3篇
  1995年   3篇
  1994年   1篇
  1993年   2篇
  1992年   6篇
  1991年   3篇
  1990年   4篇
  1988年   5篇
  1987年   3篇
  1986年   2篇
  1985年   3篇
  1984年   2篇
  1983年   1篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1976年   1篇
  1974年   4篇
  1973年   1篇
  1970年   1篇
  1969年   1篇
排序方式: 共有306条查询结果,搜索用时 15 毫秒
291.
Reactions of 3-(furan-2-yl)propenoic acids and their esters with arenes in Brønsted superacid TfOH affords products of hydroarylation of the carbon–carbon double bond, 3-aryl-3-(furan-2-yl)propenoic acid derivatives. According to NMR and DFT studies, the corresponding O,C-diprotonated forms of the starting furan acids and esters should be reactive electrophilic species in these transformations. Starting compounds and their hydroarylation products, at a concentration of 64 µg/mL, demonstrate good antimicrobial activity against yeast-like fungi Candida albicans. Apart from that, these compounds suppress Escherichia coli and Staphylococcus aureus.  相似文献   
292.
In this paper we report an innovative use of Poly(DiMethyl)Siloxane (PDMS) to design a microfluidic device that combines, for the first time, in one single reaction chamber, DNA purification from a complex biological sample (blood) without elution and PCR without surface passivation agents. This result is achieved by exploiting the spontaneous chemical structure and nanomorphology of the material after casting. The observed surface organization leads to spontaneous DNA adsorption. This property allows on-chip complete protocols of purification of complex biological samples to be performed directly, starting from cells lysis. Amplification by PCR is performed directly on the adsorbed DNA, avoiding the elution process that is normally required by DNA purification protocols. The use of one single microfluidic volume for both DNA purification and amplification dramatically simplifies the structure of microfluidic devices for DNA preparation. X-Ray Photoelectron Spectroscopy (XPS) was used to analyze the surface chemical composition. Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FESEM) were employed to assess the morphological nanostructure of the PDMS-chips. A confocal fluorescence analysis was utilized to check DNA distribution inside the chip.  相似文献   
293.
Oil-in-water emulsions were developed employing the HLB system and emulsion phase inversion (EPI) method. X-ray diffraction revealed that the anisotropic structures around the inner phase globules were lamellar gel network phases. The calculated distances between the lamellae made after preparation and 3 month latter showed that there was no swelling of the lamellar gel network indicating good stability and few changes during storage. The developed emulsions were stable and have potential to be employed for cosmetic and pharmaceutical purposes. The gel phase network and vegetal components seemed to be contributing factors.   相似文献   
294.
Well-defined amphiphilic tri-block copolymer PVP-b-PMMA-b-PVP was prepared for the first time via successive reversible addition fragmentation chain transfer(RAFT) polymerization using carboxyl-terminated trithiocarbonate as the RAFT agent.The structure of the copolymer was characterized using FTIR,GPC and ~1H NMR.The block copolymer could be directly blended with polyethersulfone(PES) as a macromolecule additive using N-methyl-2-pyrrolidone(NMP) as the solvent to prepare membranes. The water contact angles for the modified membranes decreased obviously,and therefore,the protein adsorption amount on the membrane surface decreased.  相似文献   
295.
A new phenylethanoid glycoside,seulponisidc(1) was isolated from the aerial parts of Isodon sculponeatus(Vaniot) Kudo, along with six known compounds martynoside(2),verbascoside(3),(+)-hydroxypinoresinol-8-O- β-D-glucoside(4),cedrusin(5), 7-megastigmene-3S,5R,6R,7E,9S-tetrol(6) and 4-oxo- β-ionol- β-D-glucopyranoside(7).Their chemical structures were elucidated from physieochemical data and by acidic hydrolysis.  相似文献   
296.
<正>A new method for the preparation of microcapsule-supported palladium catalyst was described.The highly monodisperse crosslinked polystyrene microcapsules containing phosphine ligand were synthesized by the self-assembling of phase separated polymer (SaPSeP) method using diphenyl(4-vinylphenyl) phosphine and divinylbenzene as a monomer and crosslinking agent,respectively, and 2,2'-azobisisobutyronitrile(AIBN) as an initiator within the droplets of oil-in-water(O/W) emulsions,which were prepared by using the Shirasu Porous Glass(SPG) membrane emulsification technique.The prepared microcapsule-supported palladium catalyst exhibited high catalytic activity for Heck reaction and can be reused several times without loss of activity.  相似文献   
297.
There is an increasing need to develop biosensors for the detection of harmful pesticide residues in food and water. Here, we report on a versatile strategy to synthesize functionalized graphene oxide nanomaterials with abundant affinity groups that can capture histidine (His)-tagged acetylcholinesterase (AChE) for the fabrication of paraoxon biosensors. Initially, exfoliated graphene oxide (GO) was functionalized by a diazonium reaction to introduce abundant carboxyl groups. Then, Nα,Nα-bis(carboxymethyl)-l-lysine hydrate (NTA-NH2) and Ni2+ were anchored onto the GO based materials step by step. AChE was immobilized on the functionalized graphene oxide (FGO) through the specific binding between Ni-NTA and His-tag. A low anodic oxidation potential was observed due to an enhanced electrocatalytic activity and a large surface area brought about by the use of FGO. Furthermore, a sensitivity of 2.23 μA mM−1 to the acetylthiocholine chloride (ATChCl) substrate was found for our composite covered electrodes. The electrodes also showed a wide linear response range from 10 μM to 1 mM (R2 = 0.996), with an estimated detection limit of 3 μM based on an S/N = 3. The stable chelation between Ni-NTA and His-tagged AChE endowed our electrodes with great short-term and long-term stability. In addition, a linear correlation was found between paraoxon concentration and the inhibition response of the electrodes to paraoxon, with a detection limit of 6.5 × 10−10 M. This versatile strategy provides a platform to fabricate graphene oxide based nanomaterials for biosensor applications.  相似文献   
298.
Photo correlation spectroscopy was used to measure the particle size distribution of TiO2 films. Other parameters, such as porosity, BET surface area, average pore size, crystallite size D101, distribution of pore size etc. were also measured. The effects of these parameters on the ionic liquid based dye-sensitized solar cells (DSC) were studied. It was concluded that the particle size distribution of nanocrystalline TiO2 played an important role on the performance of DSC. The narrow particle size distribution of nanocrystalline TiO2 increased the efficiency of DSC, while the wide distribution decreased the efficiency of DSC. From the result above, it was also concluded that the photo correlation spectroscopy was a good method to identify the performance of TiO2 films. Based on electrochemical impedance spectroscopy, we found that the particle size distribution could affect the electronic contact between the TiO2 layers as well. The narrow particle size distribution made the electronic contact between TiO2 layers better than the wide particle size distribution of the TiO2 films, and then better the electronic contact, higher the efficiency of the DSC.  相似文献   
299.
A novel triazatruxene-based fluorescent glycocluster was synthesized and its selective binding interactions with PNA lectin were investigated by fluorescence spectroscopy,CD spectroscopy,and a turbidity assay.The glycocluster exhibited a strong binding affinity for PNA lectin with a Stern-Volmer quenching constant of 5.8×105 mol-1L  相似文献   
300.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号