全文获取类型
收费全文 | 2850篇 |
免费 | 96篇 |
国内免费 | 5篇 |
专业分类
化学 | 2233篇 |
晶体学 | 22篇 |
力学 | 32篇 |
数学 | 353篇 |
物理学 | 311篇 |
出版年
2023年 | 25篇 |
2022年 | 79篇 |
2021年 | 84篇 |
2020年 | 65篇 |
2019年 | 59篇 |
2018年 | 29篇 |
2017年 | 34篇 |
2016年 | 86篇 |
2015年 | 89篇 |
2014年 | 102篇 |
2013年 | 159篇 |
2012年 | 191篇 |
2011年 | 216篇 |
2010年 | 132篇 |
2009年 | 120篇 |
2008年 | 214篇 |
2007年 | 210篇 |
2006年 | 173篇 |
2005年 | 168篇 |
2004年 | 112篇 |
2003年 | 109篇 |
2002年 | 78篇 |
2001年 | 24篇 |
2000年 | 39篇 |
1999年 | 23篇 |
1998年 | 16篇 |
1997年 | 21篇 |
1996年 | 21篇 |
1995年 | 18篇 |
1994年 | 14篇 |
1993年 | 21篇 |
1992年 | 13篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1988年 | 9篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 27篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1969年 | 4篇 |
排序方式: 共有2951条查询结果,搜索用时 46 毫秒
991.
Facile acidic hydrolysis and displacement reactions of 2‐chloro‐and 2,9‐dichloro‐1,10‐phenanthroline
992.
Michieletti M Bracci A Compostella F De Libero G Mori L Fallarini S Lombardi G Panza L 《The Journal of organic chemistry》2008,73(22):9192-9195
A new practical synthesis of alpha-GalCer and of its analogues is presented, opening the chance to easily modify the sphingosine chain. The common precursor is a disaccharide, obtained by coupling tetra-O-benzyl-D-galactose with allyl 2,3-O-isopropylidene-D-lyxofuranoside. Introduction of alkyl chains via Wittig reaction (for alpha-GalCer and OCH) or via Williamson reaction (for oxa analogues) followed by standard synthetic steps allows one to efficiently obtain such compounds. The analogues are able to activate iNKT cells when presented by CD1d expressing cells. 相似文献
993.
Porto S Seco JM Espinosa JF Quiñoá E Riguera R 《The Journal of organic chemistry》2008,73(15):5714-5722
A general methodology for assigning the configuration of chiral mono- and polyfunctional compounds by NMR is presented. The approach is based on the use of polystyrene-bound chiral derivatizing agents (CDA-resins) specifically designed to achieve the high-yield formation of the covalent linkages (amide or ester bonds) between the substrate and the chiral auxiliary within the NMR tube, without the need for other manipulations, on a microscale level and in a short time. The deuterated NMR solvents (CDCl3, CD3CN, CS2/CD2Cl2) are also the reaction solvents and separations, purifications or workups of any kind are not necessary prior to recording the spectra. The CDA-resins prepared included MPA, 9-AMA, BPG, MTPA, and 2-NTBA as auxiliary agents incorporated either as single enantiomers or as mixed combinations of the (R)- and the (S)-enantiomers at unequal and known ratios. The high versatility of these systems was successfully demonstrated in a variety of ways based on double and single derivatization, low temperature experiments, or the formation of metal complexes. The approach allowed the absolute configurations of chiral primary amines, primary and secondary alcohols, cyanohydrins, thiols, diols, triols, and amino alcohols to be determined. Extensive high-resolution magic angle spinning (HR-MAS) NMR experiments allowed the characterization of the new CDA-resins and enabled the study of their stability and regioselectivity. 相似文献
994.
995.
Desyana Olenka Margaretta Mega Silvia Lestari Bebeh W. Nuryadin Mikrajuddin Abdullah 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(6):154
We introduce a new and general criterion for melting as an alternative to the commonly used Lindemann criterion. Nanostructures are modeled using a zipper model and the melting process is assumed to start from the outer layer and develop towards the center layer. Melting occurs when the logarithm of the partition function per number of layers is zero. The equation shows good consistency with experimental data for the melting of thin films, nanoparticles, and nanowires. We also introduce a degree-of-freedom parameter which seems to be universal for most metals. 相似文献
996.
Silvia Gazzola Enyinda Onunwor Lothar Reichel Giuseppe Rodriguez 《Numerical Linear Algebra with Applications》2016,23(1):187-204
The symmetric Lanczos method is commonly applied to reduce large‐scale symmetric linear discrete ill‐posed problems to small ones with a symmetric tridiagonal matrix. We investigate how quickly the nonnegative subdiagonal entries of this matrix decay to zero. Their fast decay to zero suggests that there is little benefit in expressing the solution of the discrete ill‐posed problems in terms of the eigenvectors of the matrix compared with using a basis of Lanczos vectors, which are cheaper to compute. Similarly, we show that the solution subspace determined by the LSQR method when applied to the solution of linear discrete ill‐posed problems with a nonsymmetric matrix often can be used instead of the solution subspace determined by the singular value decomposition without significant, if any, reduction of the quality of the computed solution. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
997.
Metabolic profiling for the identification of Huntington biomarkers by on‐line solid‐phase extraction capillary electrophoresis mass spectrometry combined with advanced data analysis tools
下载免费PDF全文
![点击此处可从《Electrophoresis》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Laura Pont Fernando Benavente Joaquim Jaumot Romà Tauler Jordi Alberch Silvia Ginés José Barbosa Victoria Sanz‐Nebot 《Electrophoresis》2016,37(5-6):795-808
In this work, an untargeted metabolomic approach based on sensitive analysis by on‐line solid‐phase extraction capillary electrophoresis mass spectrometry (SPE‐CE‐MS) in combination with multivariate data analysis is proposed as an efficient method for the identification of biomarkers of Huntington's disease (HD) progression in plasma. For this purpose, plasma samples from wild‐type (wt) and HD (R6/1) mice of different ages (8, 12, and 30 weeks), were analyzed by C18‐SPE‐CE‐MS in order to obtain the characteristic electrophoretic profiles of low molecular mass compounds. Then, multivariate curve resolution alternating least squares (MCR‐ALS) was applied to the multiple full scan MS datasets. This strategy permitted the resolution of a large number of metabolites being characterized by their electrophoretic peaks and their corresponding mass spectra. A total number of 29 compounds were relevant to discriminate between wt and HD plasma samples, as well as to follow‐up the HD progression. The intracellular signaling was found to be the most affected metabolic pathway in HD mice after 12 weeks of birth, when mice already showed motor coordination deficiencies and cognitive decline. This fact agreed with the atrophy and dysfunction of specific neurons, loss of several types of receptors, and changed expression of neurotransmitters. 相似文献
998.
The production of a high-content galacto-oligosaccharides mixture (GOS) by immobilised β-galactosidase and yeasts in LentiKats® lens-shaped polyvinylalcohol (PVA) capsules was evaluated. Galacto-oligosaccharides were produced from lactose (300 g L?1) by immobilised fungal β-galactosidase and the yeast Kluyveromyces marxianus in polyvinylalcohol hydrogel in batch mode. The low-content GOS mixture produced by the immobilised enzyme consisted of 71.7 g L?1 with a final purity of 22.7 % after 30 h of transgalactosylation reaction at 30·C and pH 4.5. The lowcontent GOS mixtures were subsequently used in 20 repeated batch runs with immobilised yeasts for increasing the GOS content. Digestible sugars were fermented to ethanol and the resulting mixture consisted of 88 mass % of GOS after 26 h of fermentation. The PVA lenses exhibited high fermentative stability without any mechanical deformations. 相似文献
999.
Riikka Peltomaa Silvia Vaghini Belén Patiño Elena Benito-Peña María C. Moreno-Bondi 《Analytica chimica acta》2016
Plant-pathogenic Fusarium species, Fusarium verticillioides and Fusarium proliferatum, are the major producers of fumonisins which are one of the most common mycotoxins found in maize. Herein, we report the development of specific and sensitive genosensors for detecting these two closely related Fusarium species in food samples. The sensors are based on species-specific capture and detection probes, which bind to the intergenic spacer region of rDNA (IGS). Oligonucleotide functionalized magnetic microbeads are used to capture the target DNA which is then detected using biotinylated detection probes and a streptavidin-coupled label. The developed genosensors had detection limits of 1.8 pM and 3.0 pM for F. proliferatum and F. verticillioides, respectively, using synthetic DNA targets. Furthermore, the biosensors were used to analyze natural fungal contamination of commercial maize samples. After amplification of the genomic DNA the sensors detected the presence of the fungi, in accordance with previous results obtained with PCR. No cross-reactivity between F. verticillioides and F. proliferatum, or other fungi species tested, was observed. The developed biosensors can provide a valuable tool to evaluate the potential for mycotoxin contamination in conditions where detection of mycotoxins directly is challenging. 相似文献
1000.
Alkoxide bridged Copper(II) Hinokitiolato and Tropolonato Complexes: Polymorphism,Reconstructive Phase Transition,and Magnetic Properties
下载免费PDF全文
![点击此处可从《无机化学与普通化学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Silvia Schnitzler Kevin Lamberts Manfred Speldrich Paul Kögerler Ulli Englert 《无机化学与普通化学杂志》2016,642(3):222-230
Polymorphism and an unexpected reconstructive phase transition in [Cu(trop)(μ‐OMe)]2 (trop = tropolonate) were studied by single crystal and powder X‐ray diffraction; the phase transition is associated with a huge hysteresis of ca. 200 °C. In the readily reproducible crystal form, the methoxide‐bridged dinuclear subunits aggregate to infinite chains by longer bonds in the Jahn‐Teller distorted coordination sphere. Analogous alkoxide‐bridged derivatives with the substituted ligand hinokitiol (hino), [Cu(hino)(μ‐OR)]2 (R = Me, Et, iPr) form pairs of dinuclear complexes and aggregate to discrete tetranuclear molecules. The inter‐cation distance patterns are reflected in the magnetic properties of these two structure types: Strong antiferromagnetic coupling within the dinuclear subunits is observed in either case, but susceptibility measurements confirm differences in exchange coupling between neighboring central CuII atoms. 相似文献