全文获取类型
收费全文 | 399篇 |
免费 | 6篇 |
国内免费 | 5篇 |
专业分类
化学 | 240篇 |
晶体学 | 2篇 |
力学 | 7篇 |
数学 | 69篇 |
物理学 | 92篇 |
出版年
2023年 | 4篇 |
2022年 | 2篇 |
2020年 | 3篇 |
2019年 | 14篇 |
2018年 | 5篇 |
2017年 | 10篇 |
2016年 | 17篇 |
2015年 | 10篇 |
2014年 | 25篇 |
2013年 | 36篇 |
2012年 | 32篇 |
2011年 | 27篇 |
2010年 | 16篇 |
2009年 | 17篇 |
2008年 | 6篇 |
2007年 | 28篇 |
2006年 | 17篇 |
2005年 | 14篇 |
2004年 | 11篇 |
2003年 | 13篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1957年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有410条查询结果,搜索用时 15 毫秒
1.
The sub-millisecond protonation dynamics of the chromophore in S65T mutant form of the green fluorescent protein (GFP) was
tracked after a rapid pH jump following laser-induced proton release from the caged photolabile compoundo-nitrobenzaldehyde. Following a jump in pH from 8 to 5 (which is achieved within 2 μs), the fluorescence of S65T GFP decreased
as a single exponential with a time constant of ∼90 μs. This decay is interpreted as the conversion of the deprotonated fluorescent
GFP chromophore to a protonated non-fluorescent species. The protonation kinetics showed dependence on the bulk viscosity
of the solvent, and therefore implicates bulk solvent-controlled protein dynamics in the protonation process. The protonation
is proposed to be a sequential process involving two steps: (a) proton transfer from solvent to the chromophore, and (b) internal
structural rearrangements to stabilize a protonated chromophore. The possible implications of these observations to protein
dynamics in general is discussed 相似文献
2.
G. Jyothi Chanchal K. Mitra G. Krishnamoorthy 《Journal of Electroanalytical Chemistry》1991,321(3):395-402
The exchange of gramicidin between liposomes made of two different kinds of phospholipids has been studied using a fluorescent probe (pyranine). The experimentally observed rate of exchange is compared with that of nigericin, which is a simple carrier. Possible reasons for the difference in the rate of exchange are discussed and probable mechanisms suggested. It is proposed that gramicidin exchanges between vesicles by a contact mechanism. 相似文献
3.
4.
5.
Synthesis and structure of nanocrystalline TiO2 with lower band gap showing high photocatalytic activity 总被引:15,自引:0,他引:15
Nagaveni K Hegde MS Ravishankar N Subbanna GN Madras G 《Langmuir : the ACS journal of surfaces and colloids》2004,20(7):2900-2907
Nanocrystalline TiO2 was synthesized by the solution combustion method using titanyl nitrate and various fuels such as glycine, hexamethylenetetramine, and oxalyldihydrazide. These catalysts are active under visible light, have optical absorption wavelengths below 600 nm, and show superior photocatalytic activity for the degradation of methylene blue and phenol under UV and solar conditions compared to commercial TiO2, Degussa P-25. The higher photocatalytic activity is attributed to the structure of the catalyst. Various studies such as X-ray diffraction, Raman spectroscopy, Brunauer-Emmett-Teller surface area, thermogravimetric-differential thermal analysis, FT-IR spectroscopy, NMR, UV-vis spectroscopy, and surface acidity measurements were conducted. It was concluded that the primary factor for the enhanced activity of combustion-synthesized catalyst is a larger amount of surface hydroxyl groups and a lowered band gap. The lower band gap can be attributed to the carbon inclusion into the TiO2 giving TiO(2-2x)C(x) VO2**. 相似文献
6.
Wender PA Hegde SG Hubbard RD Zhang L 《Journal of the American Chemical Society》2002,124(18):4956-4957
(-)-Laulimalide (1), a structurally novel macrolide isolated in trace amounts from marine sponges, promotes abnormal tubulin polymerization and apoptosis in vitro, with a similar mode of action to that of Taxol(R), but with potentially less susceptibility to multidrug resistance. Herein, a flexible and convergent asymmetric synthesis of (-)-laulimalide is described. This synthesis featured a highly diastereoselective Sakurai reaction of 2 with 3 and a regioselective macrolactonization of an unprotected vicinal diol. Laulimalide was synthesized in 25 steps (longest linear; 36 overall) in 3.5% overall yield, providing a uniquely short and efficient route to 1 and its analogues. 相似文献
7.
The kinetics of oxidation of thiocarbohydrazide in the free and zinc(Ⅱ)-bound states byacid bromate have been studied in aqueous and water-acetic acid(1:1,V/V)media under varyingconditions,both in the absence and presence of added bromide ion.The rates of oxidations show firstorder kinetics in[bromate]in all the cases,but exhibit different kinetic behaviour in[substrate]and[H~+].Oxidation of TCH in aqueous medium shows zero order in[TCH]and nearly second order in[H~+],while oxidation in aqueous acetic acid shows two ranges in[H~+].The rate shows first and fractionalorder kinetics in[TCH]in the first and second acid ranges.Kinetics observed in the presence of Br~-are similar to those observed for oxidation of TCH in second acid range.In addition,the reactionshows fractional order in[Br~-].Oxidation of TCH in Zn(Ⅱ)-bound state exhibits first order kinetics in[substrate]and second order in[H~+].Increase in ionic strength of the medium decreases the rate in allthe cases.Increase in acetic acid composition of the solvent increases the rate.Mechanisms consistentwith the observed results have been considered and the rate laws deduced.The rate limiting steps havebeen identified and the coefficients of these steps have been calculated at different temperatures.Therelated activation parameters have also been computed.The validity of the deduced rate laws has alsobeen tested by recalculating the rate constants from them as[TCH]and[H~+]are varied. 相似文献
8.
9.
Pasupathy Krishnamoorthy 《Tetrahedron》2006,62(45):10555-10566
In the context of synthetic studies toward the oroidin family of pyrrole-imidazole alkaloids, we required an efficient method for conducting substitution reactions of allylic alcohols derived from urocanic acid. While in some cases this could be accomplished quite readily by classical nucleophilic substitution, it was complicated by allylic transposition in others. Application of Pd-catalyzed π-allyl chemistry provided a convenient solution, giving substitution without allylic transposition. Herein we describe the scope of this reaction in imidazole-containing substrates, and the elaboration of one adduct into a homologated histidine derivative, and into a cyclic homohistidine derivative. 相似文献
10.
Copper(I)-catalyzed 1,3-dipolar cycloaddition reaction of nonfluorescent 3-azidocoumarins and terminal alkynes afforded intense fluorescent 1,2,3-triazole products. The mild condition of this reaction allowed us to construct a large library of pure fluorescent coumarin dyes. Since both azide and alkyne are quite inert to biological systems, this reaction has potential in bioconjugation and bioimaging applications. [reaction: see text] 相似文献