全文获取类型
收费全文 | 450篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
化学 | 142篇 |
晶体学 | 1篇 |
力学 | 40篇 |
数学 | 76篇 |
物理学 | 193篇 |
出版年
2022年 | 2篇 |
2019年 | 2篇 |
2017年 | 5篇 |
2015年 | 4篇 |
2014年 | 2篇 |
2013年 | 9篇 |
2012年 | 16篇 |
2011年 | 18篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 11篇 |
2007年 | 16篇 |
2006年 | 15篇 |
2005年 | 16篇 |
2004年 | 12篇 |
2003年 | 14篇 |
2002年 | 15篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 6篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 15篇 |
1990年 | 20篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1970年 | 2篇 |
1938年 | 2篇 |
1935年 | 2篇 |
1867年 | 6篇 |
1866年 | 3篇 |
1863年 | 4篇 |
1862年 | 3篇 |
排序方式: 共有452条查询结果,搜索用时 15 毫秒
331.
Abe F Amidei D Apollinari G Atac M Auchincloss P Baden AR Bacchetta N Bailey MW Bamberger A de Barbaro P Barnett BA Barbaro-Galtieri A Barnes VE Baumann T Bedeschi F Behrends S Belforte S Bellettini G Bellinger J Benjamin D Bensinger J Beretvas A Berge JP Bertolucci S Bhadra S Binkley M Blair R Blocker C Bolognesi V Booth AW Boswell C Brandenburg G Brown D Buckley-Geer E Budd HS Busetto G Byon-Wagner A Byrum KL Campagnari C Campbell M Caner A Carey R Carithers W Carlsmith D Carroll JT 《Physical review D: Particles and fields》1992,45(11):3921-3948
332.
Alverson G Baker WF Ballocchi G Benson R Berg D Blusk S Bromberg C Brown D Carey D Chand T Chandlee C Choudhary BC Chung WH de Barbaro L DeSoi W Dlugosz W Dunlea J Easo S Engels E Faissler W Fanourakis G Ferbel T Garelick D Ginther G Glass G Glaubman M Gutierrez P Hartman K Huston J Johnstone C Kapoor V Kourbanis I Lanaro A Lirakis C Lobkowicz F Lukens P Mani S Maul A Mansour J Miller R Nelson CA Oh B Orris D Pothier E Prebys E Rajaram BM Roser R Ruddick K Shepard P Shivpuri RK Sinanidis A 《Physical review D: Particles and fields》1992,45(11):R3899-R3902
333.
Raman spectroscopic characterization of secondary structure in natively unfolded proteins: alpha-synuclein 总被引:2,自引:0,他引:2
Maiti NC Apetri MM Zagorski MG Carey PR Anderson VE 《Journal of the American Chemical Society》2004,126(8):2399-2408
The application of Raman spectroscopy to characterize natively unfolded proteins has been underdeveloped, even though it has significant technical advantages. We propose that a simple three-component band fitting of the amide I region can assist in the conformational characterization of the ensemble of structures present in natively unfolded proteins. The Raman spectra of alpha-synuclein, a prototypical natively unfolded protein, were obtained in the presence and absence of methanol, sodium dodecyl sulfate (SDS), and hexafluoro-2-propanol (HFIP). Consistent with previous CD studies, the secondary structure becomes largely alpha-helical in HFIP and SDS and predominantly beta-sheet in 25% methanol in water. In SDS, an increase in alpha-helical conformation is indicated by the predominant Raman amide I marker band at 1654 cm(-1) and the typical double minimum in the CD spectrum. In 25% HFIP the amide I Raman marker band appears at 1653 cm(-1) with a peak width at half-height of approximately 33 cm(-1), and in 25% methanol the amide I Raman band shifts to 1667 cm(-1) with a peak width at half-height of approximately 26 cm(-1). These well-characterized structural states provide the unequivocal assignment of amide I marker bands in the Raman spectrum of alpha-synuclein and by extrapolation to other natively unfolded proteins. The Raman spectrum of monomeric alpha-synuclein in aqueous solution suggests that the peptide bonds are distributed in both the alpha-helical and extended beta-regions of Ramachandran space. A higher frequency feature of the alpha-synuclein Raman amide I band resembles the Raman amide I band of ionized polyglutamate and polylysine, peptides which adopt a polyproline II helical conformation. Thus, a three-component band fitting is used to characterize the Raman amide I band of alpha-synuclein, phosvitin, alpha-casein, beta-casein, and the non-A beta component (NAC) of Alzheimer's plaque. These analyses demonstrate the ability of Raman spectroscopy to characterize the ensemble of secondary structures present in natively unfolded proteins. 相似文献
334.
Slater MJ Amphlett EM Andrews DM Bamborough P Carey SJ Johnson MR Jones PS Mills G Parry NR Somers DO Stewart AJ Skarzynski T 《Organic letters》2003,5(24):4627-4630
[reaction: see text] In this, the first of two Letters, we describe how a P3/P4 urea linking unit was used to greatly enhance the biochemical and replicon potency of inhibitors based upon the pyrrolidine-5,5-trans-lactam template. Compound 7b demonstrated a 100 nM IC(50) in the replicon cell-based surrogate HCV assay. 相似文献
335.
Andrews DM Carey SJ Chaignot H Coomber BA Gray NM Hind SL Jones PS Mills G Robinson JE Slater MJ 《Organic letters》2002,4(25):4475-4478
[reaction: see text] In this, the first of two letters, we outline the use of the pyrrolidine-5,5-trans-lactam template to design small, neutral, mechanism-based inhibitors of hepatitis C NS3/4A protease. The hitherto unreported reaction of the acyl iminium ion precursor 4 with dialkyl-substituted silyl ketene acetals (e.g., 8b) is described. Compound 12b, with a spirocyclobutyl P1 substituent and a cyclopropylacyl substituent on the lactam nitrogen, has a k(obs)/I of 400 M(-)(1) s(-)(1) and demonstrates activity in a replicon cell-based surrogate HCV assay. 相似文献
336.
337.
Structural chemistry of a green fluorescent protein Zn biosensor 总被引:5,自引:0,他引:5
Barondeau DP Kassmann CJ Tainer JA Getzoff ED 《Journal of the American Chemical Society》2002,124(14):3522-3524
We designed a green fluorescent protein mutant (BFPms1) that preferentially binds Zn(II) (enhancing fluorescence intensity) and Cu(II) (quenching fluorescence) directly to a chromophore ligand that resembles a dipyrrole unit of a porphyrin. Crystallographic structure determination of apo, Zn(II)-bound, and Cu(II)-bound BFPms1 to better than 1.5 A resolution allowed us to refine metal centers without geometric restraints, to calculate experimental standard uncertainty errors for bond lengths and angles, and to model thermal displacement parameters anisotropically. The BFPms1 Zn(II) site (KD = 50 muM) displays distorted trigonal bipyrimidal geometry, with Zn(II) binding to Glu222, to a water molecule, and tridentate to the chromophore ligand. In contrast, the BFPms1 Cu(II) site (KD = 24 muM) exhibits square planar geometry similar to metalated porphyrins, with Cu(II) binding to the chromophore chelate and Glu222. The apo structure reveals a large electropositive region near the designed metal insertion channel, suggesting a basis for the measured metal cation binding kinetics. The preorganized tridentate ligand is accommodated in both coordination geometries by a 0.4 A difference between the Zn and Cu positions and by distinct rearrangements of Glu222. The highly accurate metal ligand bond lengths reveal different protonation states for the same oxygen bound to Zn vs Cu, with implications for the observed metal ion specificity. Crystallographic anisotropic thermal factor analysis validates metal ion rigidification of the chromophore in enhancement of fluorescence intensity upon Zn(II) binding. Thus, our high-resolution structures reveal how structure-based design has effectively linked selective metal binding to changes in fluorescent properties. Furthermore, this protein Zn(II) biosensor provides a prototype suitable for further optimization by directed evolution to generate metalloprotein variants with desirable physical or biochemical properties. 相似文献
338.
This paper reports the development of a technique for identifying and confirming chlorinated fatty acids previously detected in fish by gas chromatography (GC) with halogen-specific detection (XSD). Fatty acid methyl esters (FAMEs) including chlorinated FAMEs within fractions of reversed-phase high-performance liquid chromatography of transesterified fish extracts were derivatized to pentafluorobenzyl esters, which were subjected to GC/mass spectrometry (MS) with negative ion chemical ionization (NICI). Pentafluorobenzyl esters displayed reasonably good GC characteristics, a very high ionization efficiency and a low degree of fragmentation. Chloride ion chromatograms extracted at m/z 35 and 37 from full scans were utilized for locating traces of chlorinated unknowns in the GC elution profile so that their mass spectra could be readily displayed. Significant ions displayed in the mass spectrum scanned in a narrow range of retention time where a chlorinated unknown was located were evaluated using ion chromatograms extracted at the m/z of these ions. The chromatographic peaks of those ions derived from the analyte were expected to center at that specific retention time, whereas those originating from matrix compounds were not. The isotopic patterns of chlorinated ions were also examined against their theoretical relative abundances. Using this approach, three metabolism-related dichloro fatty acids previously identified by GC/XSD in filet extracts of white sucker sampled downstream from a bleached kraft pulp mill were confirmed: dichlorooctadecanoic, dichlorohexadecanoic and dichlorotetradecanoic acids. In addition, an isomer of dichlorotetradecanoic acid was found in a reference fish sample. As sample preparation is critical in this application, improved conditions for hydrolysis and pentafluorobenzyl esterification are also discussed. 相似文献
339.
We show that there is a natural relationship between the Jensen function of certain analytic almost periodic functions h and the principal function of an associated Toeplitz operator Wh in type von-Neumann algebra. We show that the principal function is a generalized winding number of a part of the essential spectrum of Wh with Hausdorff dimension one, and we use facts from geometric measure theory to analyze the stability of the mean motion. This is another example of our extension of the index onto a "thick" essential spectrum. 相似文献
340.
Leitch MJ Lee WM Beddo ME Brown CN Carey TA Chang TH Cooper WE Gagliardi CA Garvey GT Geesaman DF Hawker EA He XC Isenhower LD Kaplan DM Kaufman SB Koetke DD McGaughey PL Moss JM Mueller BA Papavassiliou V Peng JC Petitt G Reimer PE Sadler ME Sondheim WE Stankus PW 《Physical review letters》2000,84(15):3256-3260
Measurements of the suppression of the yield per nucleon of J/psi and psi(') production for 800 GeV/ c protons incident on heavy nuclear targets, relative to light nuclear targets, have been made with very broad coverage in x(F) and p(T). The observed suppression is smallest at x(F) values of 0.25 and below, and increases at larger values of x(F). It is also strongest at small p(T). Substantial differences between psi(') and J/psi production are observed for the first time in p-A collisions. The suppression for psi(') production is stronger than that for J/psi for x(F) near zero, but becomes comparable to that for J/psi for x(F)>0.6. 相似文献