全文获取类型
收费全文 | 402篇 |
免费 | 4篇 |
专业分类
化学 | 332篇 |
晶体学 | 9篇 |
力学 | 7篇 |
数学 | 22篇 |
物理学 | 36篇 |
出版年
2023年 | 2篇 |
2022年 | 32篇 |
2021年 | 30篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 25篇 |
2012年 | 18篇 |
2011年 | 22篇 |
2010年 | 18篇 |
2009年 | 18篇 |
2008年 | 25篇 |
2007年 | 22篇 |
2006年 | 24篇 |
2005年 | 22篇 |
2004年 | 17篇 |
2003年 | 12篇 |
2002年 | 17篇 |
2001年 | 16篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有406条查询结果,搜索用时 0 毫秒
291.
The paper describes deposition of plasma polymerized allyl alcohol on polysulfone film. It is shown that film surface becomes more hydrophilic after plasma treatment independently on presence of argon in a reaction mixture. The chemistry of the new surface layer was established by FTIR-ATR and ESCA spectroscopy. The substrate placed close to the plasma edge was the most hydrophilic but the amount of hydoxyl groups was not the highest there. Presence of argon stabilized the plasma but the deposited layer contained relatively less oxygen-bearing functionalities. The plasma treated polymer was subjected to xylose isomerase immobilization. For this purpose the divinylsulfone method was adapted. The studies revealed no correlation between the surface hydrophilicity and efficiency of immobilization. 相似文献
292.
293.
Triplet blinking is a phenomenon observed commonly in single molecule fluorescence spectroscopy. At high to moderate excitation intensities one can distinguish bright (on) and dark (off) periods in the fluorescence intensity trajectory caused by sojourns into the nonemissive triplet state. In this work, we focus on triplet blinking of an immobilized molecule in the low excitation regime, where a threshold between on and off intensity levels cannot be set, and, therefore, a standard on/off analysis of fluorescence intensity trajectories is not possible. In the low excitation regime triplet blinking parameters can be recovered from photon arrival time trajectories, i.e., records of individual photon arrival time. We use computer-generated data to compare the recovery of the triplet blinking parameters from the intensity correlation function (ICF) and the histogram of interarrival time. We have found that the ICF offers a better statistics for the recovery of the triplet blinking parameters. 相似文献
294.
Let E be a Banach space, and let E* be its dual. For understanding the main results of this paper it is enough to consider E=
n
. A symmetric random vector X taking values in E is called pseudo-isotropic if all its one-dimensional projections have identical distributions up to a scale parameter, i.e., for every E* there exists a positive constant c() such that (, X) has the same distribution as c() X
0, where X
0 is a fixed nondegenerate symmetric random variable. The function c defines a quasi-norm on E*. Symmetric Gaussian random vectors and symmetric stable random vectors are the best known examples of pseudo-isotropic vectors. Another well known example is a family of elliptically contoured vectors which are defined as pseudo-isotropic with the quasi-norm c being a norm given by an inner product on E*. We show that if X and Y are independent, pseudo-isotropic and such that X+Y is also pseudo-isotropic, then either X and Y are both symmetric -stable, for some (0, 2], or they define the same quasi-norm c on E*. The result seems to be especially natural when restricted to elliptically contoured random vectors, namely: if X and Y are symmetric, elliptically contoured and such that X+Y is also elliptically contoured, then either X and Y are both symmetric Gaussian, or their densities have the same level curves. However, even in this simpler form, this theorem has not been proven earlier. Our proof is based upon investigation of the following functional equation:
which we solve in the class of real characteristic functions. 相似文献
295.
In this paper we study a general notion of a uniform convergence structure. Morphisms of various supremum-complete subsets of the complete lattice of all uniform convergence structures are investigated. They provide a satisfactory framework for the uniformization of arbitrary convergences. 相似文献
296.
Preliminary study on application of impregnated synthetic peptide TLC stationary phases for the pre-screening of 5-HT1A ligands 总被引:1,自引:0,他引:1
Zajdel P Bojarski AJ Byrtus H Chłoń-Rzepa G Obniska J Chevallet P Martinez J Pawłowski M 《Biomedical chromatography : BMC》2003,17(5):312-317
Chromatographic parameters (deltaR(f)), defined as a difference in the migration of tested compound on the control and peptide impregnated silica gel TLC plates, were determined for 42 arylpiperazine derivatives. An amino acid sequence of the peptide used for impregnation was derived from the III transmembrane segment of the 5-HT(1A) receptor in the close vicinity of aspartic acid (Asp 166) residue. It was found that the deltaR(f) values obtained in a model employing tetrapeptide P4LA (ADVL), as well as the calculated logP correlate with 5-HT(1A) receptor affinity of the studied compounds. 相似文献
297.
In presence of acides (HF/pyridine) substitutes 3-ethoxycarbonyl-6-oxal-azabicyclo[3.1.0[hexanes 1 afforded subtituted 3-ethoxycarbonyl-pyrroles 3 in stereospecific manner. Spiro substrates gave polycyclic product under the conditions used. 相似文献
298.
Krzysztof Marciniec Jolanta Bafeltowska Maria J. Maślankiewicz Ewa Buszman Stanisław Boryczka 《液相色谱法及相关技术杂志》2016,39(15):702-709
Reversed-phase high-performance liquid chromatography analyses were used for the determination of the retention factor (log k) of a set of quinolinesulfonamides. The analyses utilized a mixture of acetonitrile/water as the mobile phase. The log k values were linearly dependent on the concentration of acetonitrile and extrapolated to 100% water and gave the lipophilicity parameter log kw. The parameter log PHPLC was determined from log kw values using the calibration curve obtained for five standards. The log PHPLC parameters are discussed in terms of structure–lipophilicity relationships. Furthermore, the theoretical lipophilic parameters (log Pcalc) for all compounds were calculated using chemical programs (e.g., Advanced Chemistry Development (ACD/ logP), miLogP, AlogP, ClogP, and Pallas). The determined log PHPLC and calculated log Pcalc values were compared by linear regression analysis. 相似文献
299.
Djedovic N Ferdani R Harder E Pajewska J Pajewski R Schlesinger PH Gokel GW 《Chemical communications (Cambridge, England)》2003,(23):2862-2863
Five heptapeptide derivatives, [CH3(CH2)17]2NCOCH2OCH2CO-Gly-Gly-Gly-Pro-Gly-Gly-Gly-OR, in which R = ethyl, 2-propyl, heptyl, benzyl, and cyclohexylmethyl, were found to transport chloride anion through a phospholipid bilayer to varying extents dependent on the identity of R. It was concluded that the R group is a membrane anchor for the synthetic chloride channels. 相似文献
300.
Agnieszka J. Rybarczyk-Pirek Alina T. Dubis Sawomir J. Grabowski Jolanta Nawrot-Modranka 《Chemical physics》2006,320(2-3):247-258
The crystal structures of two new benzopyrane derivatives are analyzed and compared with previous X-ray investigations on related compounds. A particular attention is focused on intramolecular interactions. For the chromone derivatives (1 and 3) only one kind of interaction is possible, i.e., N–HO, whereas for the coumarine derivatives (2 and 4) two types of intramolecular hydrogen bonding are observed – N–HO and O–HN. Two types of H-bond for coumarine derivatives are the result of the existence of two tautomeric forms – enamine and iminoenol. Combined spectroscopic, NMR and IR measurements confirm such tautomeric equilibrium in solution. The influence of the additional intermolecular hydrogen bonds on the stabilization of tautomeric forms in crystals is also discussed here. 相似文献