全文获取类型
收费全文 | 379篇 |
免费 | 14篇 |
国内免费 | 2篇 |
专业分类
化学 | 270篇 |
晶体学 | 6篇 |
力学 | 6篇 |
数学 | 55篇 |
物理学 | 58篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 14篇 |
2015年 | 8篇 |
2014年 | 7篇 |
2013年 | 25篇 |
2012年 | 18篇 |
2011年 | 34篇 |
2010年 | 26篇 |
2009年 | 19篇 |
2008年 | 32篇 |
2007年 | 33篇 |
2006年 | 20篇 |
2005年 | 20篇 |
2004年 | 13篇 |
2003年 | 11篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 12篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有395条查询结果,搜索用时 15 毫秒
161.
Hernández S Moreno I SanMartin R Herrero MT Domínguez E 《Organic & biomolecular chemistry》2011,9(7):2251-2257
A series of novel pyrazolodibenzo[1,4]diazepines has been synthesized with good overall yields. The diarylpyrazole intermediates, with structure similarity to biologically relevant compounds such as currently marketed drugs like rimonabant or celecoxib, were prepared by a tandem sequence amine-exchange/heterocyclization starting from readily available enaminones and arylhydrazines. The key step of this efficient methodology was C(aryl)-N bond construction, accomplished by a palladium-catalyzed intramolecular N-arylation reaction, which was conducted in both homogeneous and polymer-supported versions. Reaction scope of such protocols and recycling of the heterogeneous catalyst were also examined. 相似文献
162.
Díaz-Ortiz A de la Hoz A Alcázar J Carrillo JR Herrero MA Fontana A Muñoz Jde M Prieto P de Cózar A 《Combinatorial chemistry & high throughput screening》2011,14(2):109-116
Organic reactions performed in the absence of solvent in domestic ovens without appropriate temperature control are generally considered as not reproducible, particularly when different instruments are used. For this reason, reproducibility has historically been one of the major issues associated with Microwave-Assisted Organic Synthesis (MAOS) especially when domestic ovens are involved. The lack of reproducibility limits the general applicability and the scale up of these reactions. In this work several solvent-free reactions previously carried out in domestic ovens have been translated into a single-mode microwave reactor and then scaled up in a multimode oven. The results show that most of these reactions, although not considered as reproducible, can be easily updated and applied in microwave reactors using temperature-controlled conditions. Furthermore, computational calculations can assist to explain and/or predict whether a reaction will be reproducible or not. 相似文献
163.
164.
Vidal-de-Miguel G Herrero A 《Journal of the American Society for Mass Spectrometry》2012,23(6):1085-1096
In secondary electrospray ionization (SESI) systems, gaseous analytes exposed to an electrospray plume become ionized after
charge is transferred from the charging electrosprayed particles (the charging agent) to the vapor species. Currently available
SESI models are valid for simplified systems having only one type of electrosprayed species, which ionizes only one single
vapor species, and for the limit of low vapor concentration. More realistic models require considering other effects. Here
we develop a theoretical model that accounts for the effects of high vapor concentration, saturation effects, interferences
between different vapor species, and electrosprays producing different types of species from the liquid phase. In spite of
the relatively high complexity of the problem, we find simple relations between the different ionic species concentrations
that hold independently of the particular ion source configuration. Our model suggests that an ideal SESI system should use
highly concentrated charging agents composed preferably of only one dominating species with low mobility. Experimental measurements
with a MeOH-H2O-NH3 electrospray and a mixture of fatty acids and lactic acid served to test the theory, which gives good qualitative results.
These results also suggest that the SESI ionization mechanism is primarily based on ions rather than on charged droplets. 相似文献
165.
Raul SanMartin Blanca Inés María Jesús Moure María Teresa Herrero Esther Domínguez 《Helvetica chimica acta》2012,95(6):955-962
The catalytic activity of two CNC palladium pincer complexes is evaluated in two fundamental C? C bond‐forming reactions: Mizoroki? Heck and Sonogashira cross‐couplings. After several optimization attempts and a brief comparison with a PCN pincer catalyst, a number of arylated alkenes and diarylethynes are synthesized by procedures based on the catalytic use of the above mentioned CNC Pd pincers in H2O and DMF. 相似文献
166.
167.
Garazi Urgoitia Maria Teresa Herrero Ftima Churruca Nerea Conde Raul SanMartin 《Molecules (Basel, Switzerland)》2021,26(14)
Direct arylation is an atom-economical alternative to more established procedures such as Stille, Suzuki or Negishi arylation reactions. In comparison with other palladium sources and ligands, the use of palladium pincer complexes as catalysts or pre-catalysts for direct arylation has resulted in improved efficiency, higher reaction yields, and advantageous reaction conditions. In addition to a revision of the literature concerning intra- and intermolecular direct arylation reactions performed in the presence of palladium pincer complexes, the role of these remarkably active catalysts will also be discussed. 相似文献
168.
In this paper we analyse convective solutions of a two dimensional fluid layer in which viscosity depends exponentially on temperature. This problem takes in features of mantle convection, since large viscosity variations are to be expected in the Earth’s interior. These solutions are compared with solutions obtained at constant viscosity. Special attention is paid to the influence of the aspect ratio in the solutions presented. The analysis is assisted by bifurcation techniques such as branch continuation, which has proven to be a useful, systematic method for gaining insight into the possible stationary solutions satisfied by the basic equations. One feature presented by the fluid with non constant viscosity is the presence of pitchfork and saddle-node subcritical bifurcations and the presence of convective solutions below the linear critical threshold. The analysis also provides limits of existence of stationary solutions and draws the boundaries for time dependent convection. 相似文献
169.
Photo‐polymerized lauryl methacrylate monolithic columns for CEC using lauroyl peroxide as initiator
Virginia Bernabé‐Zafón Miriam Beneito‐Cambra Ernesto F. Simó‐Alfonso Guillermo Ramis‐Ramos José Manuel Herrero‐Martínez 《Electrophoresis》2009,30(21):3748-3756
Lauryl methacrylate (LMA)‐ester based monolithic columns photo‐polymerized using lauroyl peroxide (LPO) as initiator were prepared, and their morphological and CEC properties were studied. The composition of the polymerization mixture (i.e. ratios of monomers/porogenic solvents, 1,4‐butanediol/1‐propanol and LMA/crosslinker) was optimized. The morphological and chromatographic properties of LMA columns were evaluated by means of SEM pictures and van Deemter plots of PAHs, respectively. The polymerization mixture selected as optimal provided a fast separation of a mixture of PAHs with excellent efficiencies (minimum plate heights of 8.9–11.1 μm). Satisfactory column‐to‐column (RSD<4.5%) and batch‐to‐batch reproducibilities (RSD<6.3%) were achieved. The LMA columns photo‐polymerized with LPO were compared with those prepared with AIBN. Using PAHs, alkylbenzenes and basic compounds for testing, the columns obtained with LPO gave the best compromise between efficiency, resolution and analysis time. 相似文献
170.
C.M.C. Pereira M. Herrero F.M. Labajos A.T. Marques V. Rives 《Polymer Degradation and Stability》2009,94(6):939-946
The preparation of new layered double hydroxides/unsaturated polyester (LDH/UP) nanocomposites was performed and the effect of LDH on the resin properties was studied. Two different organo-LDHs have been prepared, adipate-LDH (A-LDH) and 2-methyl-2-propene-1-sulfonate-LDH (S-LDH); in order to evaluate the influence of these nanofillers, samples with two different concentrations were dispersed in the matrix. The physical, thermal, mechanical and fire reaction properties of nanocomposites were studied. Intercalated layered structures were observed for the different organo-LDH loadings (1 and 5 wt%). Mechanical properties studied under flexural tests show that incorporation of organo-LDH in the resin reduces the flexural strength of polyester resin while the flexural modulus is unchanged for the S-LDH/UP composites and increased with 1 wt% of A-LDH. Adding 1 wt% of A-LDH to the resin produces an important reduction on the flexural strength, but an increase of the flexural modulus. The study of fire reaction properties, using cone calorimeter, suggested a significant reduction in the UP flammability, by 46 and 32%, by incorporating 1 wt% of A-LDH and 5 wt% S-LDH, respectively. Mass loss curves show enhanced char formation with the different loads tested while the amount of evolved smoke remains quite unchanged. 相似文献