全文获取类型
收费全文 | 1243篇 |
免费 | 28篇 |
国内免费 | 8篇 |
专业分类
化学 | 919篇 |
晶体学 | 3篇 |
力学 | 26篇 |
数学 | 177篇 |
物理学 | 154篇 |
出版年
2023年 | 8篇 |
2022年 | 13篇 |
2021年 | 20篇 |
2020年 | 23篇 |
2019年 | 12篇 |
2018年 | 17篇 |
2017年 | 14篇 |
2016年 | 40篇 |
2015年 | 41篇 |
2014年 | 27篇 |
2013年 | 59篇 |
2012年 | 90篇 |
2011年 | 90篇 |
2010年 | 61篇 |
2009年 | 57篇 |
2008年 | 79篇 |
2007年 | 77篇 |
2006年 | 79篇 |
2005年 | 68篇 |
2004年 | 72篇 |
2003年 | 53篇 |
2002年 | 44篇 |
2001年 | 36篇 |
2000年 | 28篇 |
1999年 | 13篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1996年 | 18篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 11篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有1279条查询结果,搜索用时 15 毫秒
991.
Barluenga J Riesgo L Vicente R López LA Tomás M 《Journal of the American Chemical Society》2008,130(41):13528-13529
Polysubstituted furan derivatives are regioselective obtained from (bis-alkynyl)methyl carboxylates in the presence of catalytic amounts of copper(I) salts. This multistep process is consistent with the intermediacy of a copper(I) (2-furyl)carbene complex which is intercepted by suitable trapping reagents. 相似文献
992.
Boufi S Rei Vilar M Parra V Ferraria AM Botelho do Rego AM 《Langmuir : the ACS journal of surfaces and colloids》2008,24(14):7309-7315
Ultrathin films of cellulose were functionalized with iron protoporphyrin IX (FePP). Spin-coating allows the production of silylated cellulose films in a controlled way. Cellulose regeneration is achieved through the hydrolyzation of the silane groups, exposing the film to acidic vapors. To enhance the reactivity of the cellulose surface to the protoporphyrin, carbonyldiimidazole (CDI) was used as an activator. The effect of different spacers on the porphyrin grafting such as 1,8-diaminooctane and 1,4-phenylenediamine was studied. The highest level of cellulose functionalization with FePP was achieved when both the cellulose film and FePP were activated by CDI and a diaminoalkane was used as a spacer between the surface and the FePP. ATR/MIR (attenuated total reflection in multiple internal reflections) was performed in situ to follow the kinetics of the different chemical reactions with the cellulose surface. ATR/MIR proved again to be a powerful tool for probing the surface reaction. X-ray photoelectron spectroscopy permitted the elemental analysis of the cellulose surface after the chemical modification. 相似文献
993.
Fernández I Mancheño MJ Vicente R López LA Sierra MA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(35):11222-11230
Transmetalation reactions from chromium(0) Fischer carbene complexes to late-transition-metal complexes (palladium(0), copper(I), and rhodium(I)) have been studied computationally by density functional theory. The computational data were compared with the available experimental data. In this study, the different reaction pathways involving the different metal atoms have been compared with each other in terms of their activation barriers and reaction energies. Although the reaction profiles for the transmetalation reactions to palladium and copper are quite similar, the computed energy values indicate that the process involving palladium as catalyst is more favorable than that involving copper. In contrast to these transformations, which occur via triangular heterobimetallic species, the transmetalation reaction to rhodium leads to a new heterobimetallic species in which a carbonyl ligand is also transferred from the Fischer carbene to the rhodium catalyst. Moreover, the structure and bonding situation of the so far elusive heterobimetallic complexes are briefly discussed. 相似文献
994.
Maximum Incident Erythemally Effective UV Exposure Received by Construction Workers,in Valencia,Spain 下载免费PDF全文
Vicente Blanca Giménez Gonzalo Gurrea Ysasi Juan Carlos Moreno María Antonia Serrano 《Photochemistry and photobiology》2015,91(6):1505-1509
This article analyzes the influence of Ultraviolet Erythematic Radiation (UVER) dose received by construction workers in Valencia highlighting the upper limit of the dose received for a worker in different periods of a year. Building construction usually implies workers to stand for several hours outdoors while working until roof top is finished. In Valencia, construction carried out near the coastline has been very intense in the last few years with the construction of a great amount of summer flats. This article focuses on the maximum values UVER can reach in different seasons of the year for cities with similar latitude to Valencia (39°28′N, 0°22′W), as an important way of warning construction workers about the necessity of taking preventive actions. Viospor dosimeters placed on a mannequin have been used in this study. The measurements took place between 2012 December and 2013 July. 相似文献
995.
996.
A Photoactivatable Platinum(IV) Anticancer Complex Conjugated to the RNA Ligand Guanidinoneomycin 下载免费PDF全文
Dr. Evyenia Shaili Marta Fernández‐Giménez Savina Rodríguez‐Astor Albert Gandioso Lluís Sandín Carlos García‐Vélez Dr. Anna Massaguer Dr. Guy J. Clarkson Dr. Julie A. Woods Prof. Peter J. Sadler Dr. Vicente Marchán 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(50):18474-18486
A photoactivatable platinum(IV) complex, trans,trans,trans‐[Pt(N3)2(OH)(succ)(py)2] (succ=succinylate, py=pyridine), has been conjugated to guanidinoneomycin to study the effect of this guanidinum‐rich compound on the photoactivation, intracellular accumulation and phototoxicity of the pro‐drug. Surprisingly, trifluoroacetic acid treatment causes the replacement of an azido ligand and the axial hydroxide ligand by trifluoroacetate, as shown by NMR spectroscopy, MS and X‐ray crystallography. Photoactivation of the platinum–guanidinoneomycin conjugate in the presence of 5′‐guanosine monophosphate (5′‐GMP) led to the formation of trans‐[Pt(N3)(py)2(5′‐GMP)]+, as does the parent platinum(IV) complex. Binding of the platinum(II) photoproduct {PtN3(py)2}+ to guanine nucleobases in a short single‐stranded oligonucleotide was also observed. Finally, cellular uptake studies showed that guanidinoneomycin conjugation improved the intracellular accumulation of the platinum(IV) pro‐drug in two cancer cell lines, particularly in SK‐MEL‐28 cells. Notably, the higher phototoxicity of the conjugate in SK‐MEL‐28 cells than in DU‐145 cells suggests a degree of selectivity towards the malignant melanoma cell line. 相似文献
997.
Zinc‐Catalyzed Alkene Cyclopropanation through Zinc Vinyl Carbenoids Generated from Cyclopropenes 下载免费PDF全文
María J. González Dr. Javier González Dr. Luís A. López Dr. Rubén Vicente 《Angewandte Chemie (International ed. in English)》2015,54(41):12139-12143
The zinc‐catalyzed reaction of cyclopropenes with alkenes leading to vinylcyclopropane derivatives is reported. A broad range of alkenes (including highly substituted or functionalized alkenes) is compatible with this protocol. On the basis of trapping experiments and computational studies, this cyclopropanation reaction is proposed to proceed through initial formation of an electrophilic zinc vinyl carbenoid intermediate, which may be involved in a concerted cyclopropanation reaction. The reported protocol represents an unprecedented and simple strategy for the catalytic generation of zinc vinyl carbenoids, which are promising intermediates in organic synthesis. 相似文献
998.
Vicente J. Margarit Marta E. Martínez‐Armero Dr. M. Teresa Navarro Dr. Cristina Martínez Prof. Avelino Corma 《Angewandte Chemie (International ed. in English)》2015,54(46):13724-13728
A two‐dimensional zeolite with the topology of MWW sheets has been obtained by direct synthesis with a combination of two organic structure‐directing agents. The resultant material consists of approximately 70 % single and double layers and displays a well‐structured external surface area of about 300 m2 g?1. The delaminated zeolite prepared by means of this single‐step synthetic route has a high delamination degree, and the structural integrity of the MWW layers is well preserved. The new zeolite material displayed excellent activity, selectivity, and stability when used as a catalyst for the alkylation of benzene with propylene and found to be superior to the catalysts that are currently used for producing cumene. 相似文献
999.
1000.
Aldo-Jonathan Muñoz-Vázquez Vicente Parra-Vega Anand Sánchez-Orta 《Nonlinear dynamics》2017,87(2):895-901
Memory and heritage of differintegral operators require knowledge of the error manifold derivative at the initial time to sustain a sliding motion for any initial condition. Moreover, when the system is subject to (unknown) disturbances, such initial condition is unknown; thus, the enforcement of an integral sliding motion has been elusive with a chatter-less controller. In this paper, a novel fractional-order integral sliding mode (FISM) is proposed to maintain an invariant sliding mode due to an exact estimation of disturbances at first step. Our scheme is continuous after initial condition, avoiding chattering effects thanks to the topological properties of differintegral operators. In contrast to other FISM approaches, the proposed scheme induces a fractional-order reaching dynamics of order \((1+\nu )\in (1,2)\) to enforce an integral sliding mode for any initial condition, even in the presence of Hölder (continuous but not necessarily differentiable) disturbances and model uncertainties. Simulations show the reliability of the proposed scheme. 相似文献