全文获取类型
收费全文 | 1327篇 |
免费 | 53篇 |
国内免费 | 4篇 |
专业分类
化学 | 992篇 |
晶体学 | 3篇 |
力学 | 45篇 |
数学 | 203篇 |
物理学 | 141篇 |
出版年
2023年 | 17篇 |
2022年 | 22篇 |
2021年 | 38篇 |
2020年 | 27篇 |
2019年 | 25篇 |
2018年 | 15篇 |
2017年 | 19篇 |
2016年 | 43篇 |
2015年 | 46篇 |
2014年 | 39篇 |
2013年 | 66篇 |
2012年 | 77篇 |
2011年 | 106篇 |
2010年 | 72篇 |
2009年 | 50篇 |
2008年 | 70篇 |
2007年 | 86篇 |
2006年 | 74篇 |
2005年 | 67篇 |
2004年 | 58篇 |
2003年 | 51篇 |
2002年 | 46篇 |
2001年 | 15篇 |
2000年 | 13篇 |
1999年 | 21篇 |
1998年 | 11篇 |
1997年 | 19篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 11篇 |
1978年 | 5篇 |
1976年 | 10篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1970年 | 3篇 |
排序方式: 共有1384条查询结果,搜索用时 15 毫秒
901.
902.
Dr. Irene Gómez‐Pinto Empar Vengut‐Climent Dr. Ricardo Lucas Dr. Anna Aviñó Prof. Dr. Ramón Eritja Prof. Dr. Carlos González Dr. Juan Carlos Morales 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(6):1920-1927
Quadruplex DNA structures are attracting an enormous interest in many areas of chemistry, ranging from chemical biology, supramolecular chemistry to nanoscience. We have prepared carbohydrate–DNA conjugates containing the oligonucleotide sequences of G‐quadruplexes (thrombin binding aptamer (TBA) and human telomere (TEL)), measured their thermal stability and studied their structure in solution by using NMR and molecular dynamics. The solution structure of a fucose–TBA conjugate shows stacking interactions between the carbohydrate and the DNA G‐tetrad in addition to hydrogen bonding and hydrophobic contacts. We have also shown that attaching carbohydrates at the 5′‐end of a quadruplex telomeric sequence can alter its folding topology. These results suggest the possibility of modulating the folding of the G‐quadruplex by linking carbohydrates and have clear implications in molecular recognition and the design of new G‐quadruplex ligands. 相似文献
903.
Irene Núñez Dr. Estíbaliz Merino Dr. Mercedes Lecea Dr. Silvia Pieraccini Prof. Dr. Gian Piero Spada Dr. Giuseppe Mazzeo Dr. María Ribagorda Prof. Dr. M. Carmen Carreño 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(10):3397-3406
A new class of enantiopure ortho,ortho‐disubstituted azobenzene photoswitches has been synthesized from (S)‐2‐(p‐tolylsulfinyl)benzoquinone and arylhydrazines. The sulfoxide acts as a unidirectional controller of the helical chirality that arises in the Z isomer after photoisomerization. Highly congested E‐azobenzenes 5 c showed two atropisomeric diastereoconformers in the solid state that converged upon irradiation into a unique Z isomer with defined helicity (M), as evident in the X‐ray structure. The chiroptical properties of this three‐state enantiopure switch can be externally tuned both photochemically and/or thermally. Theoretical CD spectra calculated by using time‐dependent DFT methods support the existence of two atropoisomeric E isomers and only one Z isomer with (M) helicity. Complementary to the classical azobenzene‐based switches, the photoswiching event is promoted under green/blue light and do not occur under UV irradiation. 相似文献
904.
Irene Ojeda María Moreno‐Guzmán Araceli González‐Cortés Paloma Yáñez‐Sedeño José M. Pingarrón 《Electroanalysis》2013,25(9):2166-2174
Electrochemical immunosensors for ceruloplasmin (Cp) are reported for the first time. Two configurations involving magnetic beads (MBs) functionalized with Protein A or Streptavidin for immobilization of Cp antibodies were compared, using competitive immunoassay with synthesized alkaline phosphatase‐Cp conjugate. Upon capturing MBs‐immunoconjugates onto screen‐printed carbon electrodes, quantification of Cp was accomplished by DPV measurement of 1‐naphthol generated after 1‐naphthylphosphate addition. Linear ranges of calibration curves and detection limits were 0.1–1000 µg/mL and 0.040 µg/mL (Protein A‐MBs), and 0.025–20 µg/mL and 0.018 µg/mL (Strept‐MBs). Good results were obtained in the determination of Cp in spiked human serum samples. 相似文献
905.
Dr. Mohsen M. T. El-Tahawy Dr. Irene Conti Dr. Matteo Bonfanti Dr. Artur Nenov Prof. Dr. Marco Garavelli 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20800-20808
Controlling the spectral tunability and isomerization activity is currently one of the hot topics in the design of photoreversible molecular switches for application in optoelectronic devices. The present work demonstrates how to manipulate the absorption of the retinal protonated Schiff base (rPSB) chromophore over the entire visible range by targeted functionalization of the retinal backbone. Moreover, a correlation between the vertical excitation energy and the profile of the potential energy surface of the bright excited state responsible for the photoreactivity of rPSB is established. This correlation was exploited to rank the functionalized rPSBs into different classes with characteristic photoisomerization activity. Eventually, the synergic effects of functionalization and of external electric fields in the range of a few MV cm−1 were applied to achieve reversable and regioselective control of the photoisomerization propensity of selected rPBS derivatives. 相似文献
906.
Andreas Kakouris Victoria Samara Anastasia Kalaskani Irene Panderi 《Chromatographia》2014,77(5-6):447-457
A gradient HPLC method coupled with diode array detection was developed and fully validated for the analysis of impurities in ropinirole using a Kromasil® C8 100 Å (250 × 4.6 mm, 5 μm) column with a flow rate 1.0 mL min?1 and detection at 250 nm. The mobile phase component A consisted of a mixture of 19.6 mM aqueous potassium dihydrogen phosphate–acetonitrile (98:2 v/v), pH adjusted to 7.0 with triethylamine and the mobile phase component B consisted of acetonitrile. The method was validated in terms of linearity, sensitivity, precision, accuracy and stability. The calibration curves for ropinirole and its five impurities showed good linearity (r > 0.998) within the calibration ranges tested. The intra- and inter-day RSD values were <3.9 %, while the relative percentage error E r was <5.8 % for all compounds. Accelerated stability studies performed under various stress conditions including oxidation, hydrolysis and UV light irradiation at 254 nm proved the selectivity of the procedure. Long-term stability studies performed on blistered tablets and under various conditions of heat and humidity indicate the presence of four of the studied impurities in less than 0.07 %. The method was applied successfully to the detection and determination of ropinirole impurities in pharmaceutical formulations. 相似文献
907.
Marta Martin‐Lorenzo Laura Gonzalez‐Calero Irene Zubiri Pedro J. Diaz‐Payno Aroa Sanz‐Maroto Maria Posada‐Ayala Alberto Ortiz Fernando Vivanco Gloria Alvarez‐Llamas 《Electrophoresis》2014,35(18):2634-2641
Urine is a source of potential markers of disease. In the context of renal disease, urine is particularly important as it may directly reflect kidney injury. Current markers of renal dysfunction lack both optimal specificity and sensitivity, and improved technologies and approaches are needed. There is no clear consensus about the best sample pretreatment procedure for 2DE analysis of the urine proteome. Sample pretreatment conditions spots resolution and detection sensitivity, critically. As a first goal, we exhaustively compared eight different sample cleaning and protein purification methodologies for 2DE analysis of urine from healthy individuals. Oasis® HLB cartridges allowed the detection of the highest number of low molecular weight proteins; while PD10 desalting columns resulted in the highest number of detected spots in the high molecular weight area. Sample pretreatment strategies were also explored in the context of proteinuria, a clinical condition often associated to renal damage. Testing of urine samples from 13 patients with hypertension or kidney disease and different levels of proteinuria identified Oasis® HLB cartridge purification in combination with albumin depletion by ProteoPrep kit as the best option for urine proteome profiling from patients with proteinuric (> 30 mg/L albumin in urine) renal disease. 相似文献
908.
High‐resolution high‐performance liquid chromatography with electrospray ionization mass spectrometry and tandem mass spectrometry characterization of a new isoform of human salivary acidic proline‐rich proteins named Roma‐Boston Ser22(Phos) → Phe variant
下载免费PDF全文
![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Na Tian Tiziana Cabras Irene Messana Eva J. Helmerhorst Frank G. Oppenheim Massimo Castagnola 《Journal of separation science》2014,37(14):1896-1902
During a survey of human saliva by a top‐down reversed‐phase high‐performance liquid chromatography with electrospray ionization mass spectrometry approach, two proteins eluting at 27.4 and 28.4 min, with average masses of 15 494 ± 1 and 11 142 ± 1 Da, were detected in a subject from Boston. The Δmass value (4352 Da) of the two proteins was similar to the difference in mass values between intact (150 amino acids, [a.a.]) and truncated acidic proline‐rich proteins (aPRPs; 106 a.a.) suggesting an a.a. substitution in the first 106 residues resulting in a strong reduction in polarity, since under the same experimental conditions aPRPs eluted at ~22.5 min (intact) and 23.5 min (truncated forms). Manual inspection of the high‐resolution high‐performance liquid chromatography with electrospray ionization tandem mass spectra of the truncated isoform showed the replacement of the phosphorylated Ser‐22 in PRP‐3 with a Phe residue. Inspection of the tandem mass spectra of the intact isoform confirmed the substitution, which is allowed by the code transition TCT→TTT and is in agreement with the dramatic increase in elution time. The isoform was also detected in two other subjects, one from Boston (unrelated to the previous) and one from Rome. For this reason we propose to name this variant PRP‐1 (PRP‐3) RB (Roma‐Boston) Ser22(phos)→Phe. 相似文献
909.
Stéphane Brézillon Valérie Untereiner Lila Lovergne Irene Tadeo Rosa Noguera François-Xavier Maquart Yanusz Wegrowski Ganesh D. Sockalingum 《Analytical and bioanalytical chemistry》2014,406(24):5795-5803
We recently identified vibrational spectroscopic markers characteristic of standard glycosaminoglycan (GAG) molecules. The aims of the present work were to further this investigation to more complex biological systems and to characterize, via their spectral profiles, cell types with different capacities for GAG synthesis. After recording spectral information from individual GAG standards (hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparan sulfate) and GAG-GAG mixtures, GAG-defective mutant Chinese hamster ovary (CHO)-745 cells, wild-type CHO cells, and chondrocytes were analyzed as suspensions by high-throughput infrared spectroscopy and as single isolated cells by infrared imaging. Spectral data were processed and interpreted by exploratory unsupervised chemometric methods based on hierarchical cluster analysis and principal component analysis. Our results showed that the spectral information obtained was discriminant enough to clearly delineate between the different cell types both at the cell suspension and single-cell levels. The abilities of the technique are to perform spectral profiling and to identify single cells with different potentials to synthesize GAGs. Infrared microspectroscopy/imaging could therefore be developed for cell screening purposes and further for identifying GAG molecules in normal tissues during physiological conditions (aging, healing process) and numerous pathological states (arthritis, cancer). Figure
910.
Direct Catalytic Enantio‐ and Diastereoselective Mannich Reaction of Isocyanoacetates and Ketimines
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Irene Ortín Prof. Dr. Darren J. Dixon 《Angewandte Chemie (International ed. in English)》2014,53(13):3462-3465
A catalytic asymmetric synthesis of imidazolines with a fully substituted β‐carbon atom by a Mannich‐type addition/cyclization reaction of isocyanoacetate pronucleophiles and N‐diphenylphosphinoyl ketimines has been developed. When a combination of a cinchona‐derived aminophosphine precatalyst and silver oxide was employed as a binary catalyst system, good reactivity, high diastereoselectivities (up to 99:1 d.r.), and excellent enantioselectivities (up to 99 % ee) were obtained for a range of substrates. 相似文献