全文获取类型
收费全文 | 1666篇 |
免费 | 86篇 |
国内免费 | 5篇 |
专业分类
化学 | 1451篇 |
晶体学 | 9篇 |
力学 | 33篇 |
数学 | 125篇 |
物理学 | 139篇 |
出版年
2023年 | 24篇 |
2022年 | 24篇 |
2021年 | 58篇 |
2020年 | 62篇 |
2019年 | 58篇 |
2018年 | 39篇 |
2017年 | 47篇 |
2016年 | 79篇 |
2015年 | 78篇 |
2014年 | 80篇 |
2013年 | 119篇 |
2012年 | 150篇 |
2011年 | 149篇 |
2010年 | 100篇 |
2009年 | 90篇 |
2008年 | 110篇 |
2007年 | 109篇 |
2006年 | 79篇 |
2005年 | 70篇 |
2004年 | 44篇 |
2003年 | 37篇 |
2002年 | 32篇 |
2001年 | 13篇 |
2000年 | 7篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 9篇 |
1993年 | 2篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1971年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有1757条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Generation of a Genetically Encoded,Photoactivatable Intein for the Controlled Production of Cyclic Peptides
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)
M. Sc. Jana K. Böcker M. Sc. Kristina Friedel M. Sc. Julian C. J. Matern M. Sc. Anne‐Lena Bachmann Prof. Dr. Henning D. Mootz 《Angewandte Chemie (International ed. in English)》2015,54(7):2116-2120
Cyclic peptides are important natural products and hold great promise for the identification of new bioactive molecules. The split‐intein‐mediated SICLOPPS technology provides a generic access to fully genetically encoded head‐to‐tail cyclized peptides and large libraries thereof (SICLOPPS=split‐intein circular ligation of peptides and proteins). However, owing to the spontaneous protein splicing reaction, product formation occurs inside cells, making peptide isolation inconvenient and precluding traditional in vitro assays for inhibitor discovery. The design of a genetically encoded, light‐dependent intein using the photocaged tyrosine derivative ortho‐nitrobenzyltyrosine incorporated at an internal, non‐catalytic position is now reported. Stable intein precursors were purified from the E. coli expression host and subsequently subjected to light activation in vitro for both the regular protein splicing format and cyclic peptide production, including the natural product segetalin H as an example. The activity of the intein could also be triggered in living cells. 相似文献
995.
P. Dasgupta Y.M. Jana R. Higashinaka D. Ghosh 《Journal of Physics and Chemistry of Solids》2007,68(3):347-354
Magnetic susceptibility obtained from magnetization measurement (for fields H=0.1 and 1.0 T) of polycrystalline Eu2Ti2O7 shows two distinct features. Firstly, increases on cooling below 300 K and attains a temperature-independent constant value at 68 K (Tmax). Secondly, shows an antiferromagnetic increase below 4.9±0.1 K. The former behavior is explained by crystal field (CF) theory. CF levels and wave functions of ground and excited states are determined accurately from analyses of and earlier reported Mössbauer and optical spectra. Analysis of vs. 1/T curve at low temperatures gives the classical nearest-neighbor exchange interaction Jcl=−0.76 K and a weak dipolar interaction Dnn=0.0056 K. CP of polycrystalline sample of Eu2Ti2O7 and Y2Ti2O7 are measured between 1.8-35 and 1.8-120 K respectively and θD vs. T (K) curves are calculated. At 4 K, θD of Eu2Ti2O7 shows a kink and dCP/dT curve show a maximum. Optical results show energy exchange between Eu3+ ions at intrinsic and extrinsic (defect) sites via super-exchange interaction at low temperature which may account for the observed anomalous behavior of and CP. 相似文献
996.
The formulae for the free energy, when the driving distributions in Generalized Random Energy Model (GREM) are of the form
for γ ≥ 1 are derived. The large deviation technique allows the use of different distributions at different levels of the
GREM. As an illustration we consider, in detail, a two level GREM with exponential and Gaussian distributions. This simple
case itself leads to interesting phenomena. 相似文献
997.
Water-soluble non-structural carbohydrates (NSC) in the needles of Norway spruce Picea abies [L.] Karst have been studied by using a combination of several separation techniques, having various detectors, with mass spectrometry. The intent was to find a suitable methodology that enables the characterization and determination of NSC, covering a wide range of molar masses, and being suitable to assess how NCS are influenced by both external conditions, e.g. different carbon dioxide (CO(2)) concentrations, light intensity, and by internal conditions such as the needle age. The techniques were liquid-liquid extraction, high performance liquid chromatography (HPLC), size exclusion chromatography (SEC), asymmetrical flow field-flow fractionation (AsFlFFF), electrospray ionization mass spectrometry (ESI-MS), and matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). NSC were extracted by a methanol/chloroform/water mixture into the water-rich phase. Application of AsFlFFF and SEC, using refractive index (RI) and multi-angle light scattering (MALS) detectors to the water-rich extracts resulted in three or four main fractions covering molar masses from 10(3) to 10(6)g/mol. Individual fractions collected from SEC were directly subjected to both MALDI and ESI-MS analysis in order to identify NSC. MALDI mass spectra confirmed the presence of hexose oligomers in individual fractions while ESI-MS was used for evaluation of low mass NSC. HPLC-RI was used for quantification of NSC and predominant carbohydrates were found to be fructose, glucose, and sucrose. The changes in their content during seasonal course were studied in detail. HPLC coupled to ESI-MS enabled the identification of low concentration NSC like raffinose that occurred in the needles of autumn samplings. An influence of the increased CO(2) concentration on sucrose and glucose accumulation was observed and it was found that the light intensity as well as the needle age has significant influence on the sucrose content. 相似文献
998.
Basu S Ghosh SK Kundu S Panigrahi S Praharaj S Pande S Jana S Pal T 《Journal of colloid and interface science》2007,313(2):724-734
Gold nanoparticles of variable sizes have been prepared by reducing HAuCl(4) with trisodium citrate by Frens' method. It has been found that the gold particles under consideration produce well-ordered aggregates upon interaction with a biomolecule, glutathione in variable acidic pH condition and exhibit pronounced changes in their optical properties arising due to electromagnetic interaction in the close-packed assembly. The effect of nanoparticle size on the nature of aggregation as well as the variation in the optical response due to variable degree of interparticle coupling effects amongst the gold particles have been investigated. The optical properties of the gold aggregates have been accounted in the light of Maxwell-Garnett effective medium theory considering the changes in the filling factor in different aggregates produced by variable sizes of gold colloids. The aggregates have been characterized by UV-vis spectroscopy, FTIR, Raman, XRD and TEM studies. It has been observed that a new peak appearing at a longer wavelength intensifies and shifts further to the red from the original peak position depends on the particle size, concentration of glutathione and pH of the solution. On the basis of the first appearance of a clearly defined new peak at longer wavelength, a higher sensitivity of glutathione detection has been achieved with gold nanoparticles of larger dimension. 相似文献
999.
Mishra T Hait J Aman N Jana RK Chakravarty S 《Journal of colloid and interface science》2007,316(1):80-84
Uniform sized silica and zirconia mixed titania samples were prepared in presence of a surfactant (CETAB) using controlled hydrolysis of corresponding metal alkoxides. Photocatalytic activity towards reduction of lead and cadmium metal in aqueous solution was evaluated both in UV and visible light in a 100 ml capacity reactor. In particular mixing of 10 wt% silica with titania not only increases the surface area of the material but also increases the photocatalytic activity in UV light. Whereas mixing of zirconia with titania proved to be beneficial for visible light reaction. However, addition of hole scavenger increases the activity many folds and complete removal of Pb(2+) and Cd(2+) was possible in 60 min of reaction using synthesized catalysts. Among all the organic hole scavengers used, sodium formate is found to be the most active one. Interestingly quite high metal removal (89%) is also observed in presence of visible light within 60 min of reaction. Thus the above study indicates that the presence of certain oxides in low quantity (10 wt%) with titania can facilitates the photocatalytic process selectively in UV as well as visible light. 相似文献
1000.
A basic ionic liquid, [bmIm]OH, efficiently promotes a one-pot, three-component condensation of aldehydes, malononitrile, and thiophenols to produce highly substituted pyridines in high yields at room temperature. This reaction does not involve any hazardous organic solvent and toxic catalyst. The ionic liquid is recovered and recycled for subsequent reactions. 相似文献