全文获取类型
收费全文 | 928篇 |
免费 | 20篇 |
国内免费 | 3篇 |
专业分类
化学 | 656篇 |
晶体学 | 8篇 |
力学 | 33篇 |
数学 | 97篇 |
物理学 | 157篇 |
出版年
2023年 | 4篇 |
2022年 | 26篇 |
2021年 | 28篇 |
2020年 | 28篇 |
2019年 | 28篇 |
2018年 | 26篇 |
2017年 | 23篇 |
2016年 | 33篇 |
2015年 | 28篇 |
2014年 | 31篇 |
2013年 | 49篇 |
2012年 | 52篇 |
2011年 | 77篇 |
2010年 | 60篇 |
2009年 | 42篇 |
2008年 | 84篇 |
2007年 | 48篇 |
2006年 | 41篇 |
2005年 | 42篇 |
2004年 | 27篇 |
2003年 | 33篇 |
2002年 | 28篇 |
2001年 | 17篇 |
2000年 | 24篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有951条查询结果,搜索用时 15 毫秒
201.
Lozano Katherine da Rocha Ferreira Fabricia da Silva Emanuella G. dos Santos Renata Costa Goulart Marilia O. F. Souza Samuel T. Fonseca Eduardo J. S. Yañez Claudia Sierra-Rosales Paulina de Abreu Fabiane Caxico 《Journal of Solid State Electrochemistry》2018,22(5):1483-1493
Journal of Solid State Electrochemistry - Thymol, a potent agent for microbial, fungal, and bacterial disease, has low aqueous solubility and it is genotoxic, i.e., is capable of damaging... 相似文献
202.
Pinho e Melo TM Soares MI Gonsalves AM Paixão JA Beja AM Silva MR 《The Journal of organic chemistry》2005,70(17):6629-6638
1-Azafulvenium methides, generated from pyrrolo[1,2-c]thiazole-2,2-dioxides' thermal extrusion of sulfur dioxide, led to the synthesis of functionalized pyrroles. The intramolecular trapping of these transient 8pi 1,7-dipoles in pericyclic reactions, namely sigmatropic [1,8]H shifts and 1,7-electrocyclization, allowed the synthesis of N-vinylpyrroles and C-vinylpyrroles which, under flash vacuum pyrolysis conditions, are converted into 5-oxo-5H-pyrrolizines or 4-oxo-1,4-dihydro-1-aza-benzo[f]azulenes, respectively. These heterocycles can also be obtained directly from FVP of pyrrolo[1,2-c]thiazole 2,2-dioxides. The synthesis and X-ray structure of a new 6-oxocyclopenta[b]pyrrole derivative is also reported. 相似文献
203.
Renata Galvão de Lima Marilia Gama Sauaia Camila Ferezin Iuri Muniz Pepe Nádia Mamede José Lusiane M. Bendhack Zênis Novais da Rocha Roberto Santana da Silva 《Polyhedron》2007
The entrapped [Ru(terpy)(L)NO](PF6)3, where terpy = 2,2′:6′,2″-terpyridine and L = 2,2′-bipyridine (bpy) and 3,4-diiminebenzoic acid (NH · NHq) complexes into sol–gel processed polysiloxane and silicone matrices, shows NO release characteristics when submitted to light irradiation at 355 and 532 nm, as judged by NO measurement using a NO-sensor electrode. The pharmacological properties of doped matrix showed vasodilator characteristics by visible light irradiation, which is of great interest because the target delivery system can avoid the occurrence of side effects possibly by the aquo ruthenium species. All matrices obtained showed to be amorphous materials. The scanning electron micrographs of the matrices showed irregularly shaped particles, with a broad size of 1000 μm for both matrices and homogeneous distribution. 相似文献
204.
A new method based on separation with gas chromatography and detection with a quartz crystal microbalance was used for quantification of nitrobenzene, 2-, 3- and 4-nitrotoluene in landfill gas. The analytical error, the analysis time and general analytical performance were identical for gas chromatography-mass spectrometry (GC-MS) and gas chromatography-quartz crystal microbalance (GC-QCM). GC-QCM constitutes a very inexpensive alternative to GC-MS for monitoring nitroaromatic compounds in landfill gas. 相似文献
205.
Analysis of application of Langmuir isotherm to heterogeneous systems: high-pressure conditions 总被引:2,自引:0,他引:2
Cordeiro CN da Rocha MS Faleiros AC Iha K 《Journal of colloid and interface science》2005,286(2):459-461
In this paper, an adsorption model that is based on the statistical mechanics approach was applied to study the saturation phenomena in adsorption to calculate the minimum pressure needed to attain the complete surface coverage on a physical adsorption. The fundamental integral equation, Theta(T)(Q)=integral N(Q)Theta(Q)dQ, for the calculation of the coverage degree of the surface was developed for an exponential distribution function, N(Q)=(m/RT)exp(-mQ/RT), and the representation of local adsorption sites is given by the Langmuir expression, Theta(Q)=b(0)C exp(Q/RT)/(1+b(0)C exp(Q/RT)). At high values of the pressure C, a solution of the fundamental integral equation was obtained by imposing the condition b(0)C>1. The expression for the saturation condition, b(0)C>m/(m+1), was obtained; that is, the saturation phenomenon is dependent on two parameters, correlated with the energetic heterogeneity and adsorption energy of the system. The pressure in the analysis of the cited expression shows that, for low m values (more heterogeneous systems), saturation is attained for b(0)C>m, while for m congruent with 1 (more homogeneous systems), the saturation is attained for b(0)C>0.5. 相似文献
206.
Moro AV Nogueira CW Barbosa NB Menezes PH da Rocha JB Zeni G 《The Journal of organic chemistry》2005,70(13):5257-5268
We present here the reaction of diorganoyl dichalcogenides with terminal alkynes under catalyst-free conditions, by a one-pot procedure, to prepare bis- and tris-chalcogenide alkenes selectively, avoiding the previous preparation of chalcogen alkynes. The reaction proceeded cleanly under mild reaction conditions, and the addition of dichalcogenides to alkynes occurred stereoselectively to give exclusively the corresponding Z isomers. We observed that the selectivity control was governed by the effective participation of the hydroxyl group from propargyl alcohols. In addition, the bis-chalcogenide alkenes were exclusively obtained with propargyl alcohol having the acidic hydroxyl group proton. Conversely, the alkynes with no potentially acidic hydroxyl group proton, at propargyl positions, gave exclusively the tris-chalcogenide alkenes. 相似文献
207.
Scale inhibitors based on phosphinepolycarboxylic acid (PPCA) have been successfully used in offshore oil production for preventing deposition of barium and strontium sulfates. A system was developed for the automated pretreatment of PPCA-containing water samples, followed on-line or off-line by phosphorus determination using ICP mass spectrometry. During pretreatment, the previously acidified inhibitor solution is adsorbed on a C18-reversed phase column and then eluted with 0.025 mol l−1 borate solution. Using a 3.5-ml sample volume, analytical frequency in the on-line mode is about 9 samples per hour and 17 in off-line operation. Detection limit of phosphorus in the borate solution was 0.20 μg l−1, using a crossflow nebulizer and a Ryton® spray chamber. Recoveries were, typically, in the range of 90% to 100% and repeatability about 5%. The method has been applied for monitoring inhibitor concentrations during laboratory and field squeeze tests. 相似文献
208.
Gilson Zeni Cristina W. NogueiraDagoberto O. Silva Paulo H. MenezesAntonio L. Braga Hélio A. StefaniJoão B.T. Rocha 《Tetrahedron letters》2003,44(4):685-688
Both symmetrically and unsymmetrically substituted 2,5-bis-(acetylenic) thiophene derivatives were obtained in good yields under mild conditions through palladium-catalyzed cross coupling reaction of 2,5-bis-(butyltelluro) thiophene 2 and terminal alkynes. The methodology represents a general and efficient protocol for carrying out the synthesis of thiophene derivatives with potential biological activities. 相似文献
209.
Martínez-Núñez E Vazquez SA Borges I Rocha AB Estévez CM Castillo JF Aoiz FJ 《The journal of physical chemistry. A》2005,109(12):2836-2839
The photodissociation of formic acid at 248 and 193 nm was investigated by classical trajectory and RRKM calculations using an interpolated potential energy surface, iteratively constructed using the B3LYP/aug-cc-pVDZ level of calculation. Several sampling schemes in the ground electronic state were employed to explore the possibility of conformational memory in formic acid. The CO/CO2 branching ratios obtained from trajectories initiated at the cis and at the trans conformers are almost identical to each other and in very good accordance with the RRKM results. In addition, when a specific initial excitation that simulates more rigorously the internal conversion process is used, the calculated branching ratio does not vary with respect to those obtained from cis and trans initializations. This result is at odds with the idea of conformational memory in the ground state proposed recently for the interpretation of the experimental results. It was also found that the calculated CO vibrational distributions after dissociation of the parent molecule at 248 nm are in agreement with the experimental available data. 相似文献
210.
Optimised hydrothermal synthesis of multi-dimensional hybrid coordination polymers containing flexible organic ligands 总被引:2,自引:0,他引:2
Filipe A. Almeida Paz Joo Rocha Jacek Klinowski Tito Trindade Fa-Nian Shi Luís Mafra 《Progress in Solid State Chemistry》2005,33(2-4):113-125
In this paper, we summarise our recent research interest in the hydrothermal synthesis and structural characterisation of multi-dimensional coordination polymers. The use of N-(phosphonomethyl)iminodiacetic acid (also referred to as H4pmida) in the literature as a versatile chelating organic ligand is briefly reviewed. This molecule plays an important role in the formation of centrosymmetric dimeric [V2O2(pmida)2]4− anionic units, which were first used by us as building blocks to construct novel coordination polymers. Starting with [V2O2(pmida)2]4− in solution, we have isolated [M2V2O2(pmida)2(H2O)10] species (where M2+ = Mn2+, Co2+ or Cd2+) via the hydrothermal synthetic approach, which were then employed for the construction of [CdVO(pmida)(4,4′-bpy)(H2O)2]·(4,4′-bpy)0.5·(H2O), [CoVO(pmida)(4,4′-bpy)(H2O)2]·(4,4′-bpy)0.5, [Co(H2O)6][CoV2O2(pmida)2(pyr)(H2O)2]·2(H2O) and [Cd2V2O2(pmida)2(pyr)2(H2O)4]·4(H2O) by the inclusion of bridging organic ligands in the reactive mixtures, such as pyrazine (pyr) and 4,4′-bipyridine (4,4′-bpy). These materials can contain channel systems, and exhibit magnetic behaviour, not only due to the V4+ centres but also to the transition metal centres which establish the links between neighbouring dimeric [V2O2(pmida)2]4− anionic units. A closely related anionic moiety, [Ge2(pmida)2(OH)2]2−, was engineered to allow the study of such crystalline hybrid materials using one- and two-dimensional high-resolution solid-state NMR. 相似文献