全文获取类型
收费全文 | 232篇 |
免费 | 13篇 |
专业分类
化学 | 193篇 |
力学 | 2篇 |
数学 | 29篇 |
物理学 | 21篇 |
出版年
2023年 | 6篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 10篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 15篇 |
2012年 | 14篇 |
2011年 | 17篇 |
2010年 | 7篇 |
2009年 | 9篇 |
2008年 | 16篇 |
2007年 | 22篇 |
2006年 | 20篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 13篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1994年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1974年 | 2篇 |
1965年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有245条查询结果,搜索用时 140 毫秒
121.
Laura Castoldi Ester Maria Di Tommaso Marcus Reitti Barbara Grfen Berit Olofsson 《Angewandte Chemie (International ed. in English)》2020,59(36):15512-15516
The iodine(III) reagents vinylbenziodoxolones (VBX) were employed to vinylate a series of aliphatic and aromatic thiols, providing E‐alkenyl sulfides with complete chemo‐ and regioselectivity, as well as excellent stereoselectivity. The methodology displays high functional group tolerance and proceeds under mild and transition metal‐free conditions without the need for excess substrate or reagents. Mercaptothiazoles could be vinylated under modified conditions, resulting in opposite stereoselectivity compared to previous reactions with vinyliodonium salts. Novel VBX reagents with substituted benziodoxolone cores were prepared, and improved reactivity was discovered with a dimethyl‐substituted core. 相似文献
122.
Dr. Ester Rossi Dr. Alessia Colombo Dr. Claudia Dragonetti Dr. Stefania Righetto Prof. Dr. Dominique Roberto Prof. Dr. Renato Ugo Dr. Adriana Valore Prof. Dr. J. A. Gareth Williams Dr. Maria Grazia Lobello Dr. Filippo De Angelis Dr. Simona Fantacci Prof. Dr. Isabelle Ledoux‐Rak Dr. Anu Singh Prof. Dr. Joseph Zyss 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(30):9875-9883
Appropriate functionalization of the cyclometalated ligand, L , and the choice of the ancillary ligand, X, allows the dipolar second‐order nonlinear optical response of luminescent [Pt L X] complexes—in which L is an N^C^N‐coordinated 1,3‐di(2‐pyridyl)benzene ligand and X is a monodentate halide or acetylide ligand—to be controlled. The complementary use of electric‐field‐induced second‐harmonic (EFISH) generation and harmonic light scattering (HLS) measurements demonstrates how the quadratic hyperpolarizability of this appealing family of multifunctional chromophores, characterized by a good transparency throughout much of the visible region, is dominated by an octupolar contribution. 相似文献
123.
The first example of microwave-promoted solid-state synthesis of an alkali complex derived from a heteromacrocyclic compound has been described. The 15-membered mixed dioxa-diaza macrocycle 5,6,14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadeca-5,14-diene (L) by reaction with sodium ethyl [4-α-(benzeneazoanilino)-N-benzyl]phosphonate (NaEP · 1.5H2O) yielded the sodium complex [Na(L)(μ-EP) · H2O]2, as a diphosphonate-bridged dinuclear species. The new complex was identified and characterized on the basis of elemental and thermal (TG and DTA) analyses as well as by IR, 1H and 13C nuclear magnetic resonance, and ESI and LDI mass spectroscopic studies. The results obtained by the reaction carried out under focused microwave conditions are compared with those obtained by conventional thermal reactions, both in the solid-state and in solution. 相似文献
124.
José L. López Ester Pérez Sinusía 《Journal of Mathematical Analysis and Applications》2007,328(2):931-945
We consider three singularly perturbed convection-diffusion problems defined in three-dimensional domains: (i) a parabolic problem −?(uxx+uyy)+ut+v1ux+v2uy=0 in an octant, (ii) an elliptic problem −?(uxx+uyy+uzz)+v1ux+v2uy+v3uz=0 in an octant and (iii) the same elliptic problem in a half-space. We consider for all of these problems discontinuous boundary conditions at certain regions of the boundaries of the domains. For each problem, an asymptotic approximation of the solution is obtained from an integral representation when the singular parameter ?→0+. The solution is approximated by a product of two error functions, and this approximation characterizes the effect of the discontinuities on the small ?− behaviour of the solution and its derivatives in the boundary layers or the internal layers. 相似文献
125.
A generalized Kohn-Sham (GKS) approach to density functional theory (DFT), based on the Baer-Neuhauser-Livshits range-separated hybrid, combined with ab initio motivated range-parameter tuning is used to study properties of water dimer and pentamer cations. The water dimer is first used as a benchmark system to check the approach. The present brand of DFT localizes the positive charge (hole), stabilizing the proton transferred geometry in agreement with recent coupled-cluster calculations. Relative energies of various conformers of the water dimer cation compare well with previously published coupled cluster results. The GKS orbital energies are good approximations to the experimental ionization potentials of the system. Low-lying excitation energies calculated from time-dependent DFT based on the present method compare well with recently published high-level "equation of motion-coupled-cluster" calculations. The harmonic frequencies of the water dimer cation are in good agreement with experimental and wave function calculations where available. The method is applied to study the water pentamer cation. Three conformers are identified: two are Eigen type and one is a Zundel type. The structure and harmonic vibrational structure are analyzed. The ionization dynamics of a pentamer water cluster at 0 K shows a fast <50 fs transient for transferring a proton from one of the water molecules, releasing a hydroxyl radical and creating a protonated tetramer carrying the excess hole. 相似文献
126.
León V Quintana M Herrero MA Fierro JL de la Hoz A Prato M Vázquez E 《Chemical communications (Cambridge, England)》2011,47(39):10936-10938
We report a simple, practical scalable procedure to produce few-layer graphene sheets using ball-milling. Commercially available melamine can be efficiently used to exfoliate graphite and generate concentrated water or DMF dispersions. 相似文献
127.
Falletta E Ridi F Fratini E Vannucci C Canton P Bianchi S Castelvetro V Baglioni P 《Journal of colloid and interface science》2011,357(1):88-94
Stable ultra-small gold nanoparticles have been synthesized in aqueous phase by using a tri-block copolymer (BMB) as a templating agent consisting of two PEG-methylacrylate chains (B blocks) anchored to a poly(methacrylic) moiety containing a trithiocarbonate unit (M block). The effect of the BMB/Au molar ratios on the final particle size, shape and monodispersity has been investigated. The synthesized nanosols have been characterized by means of Visible Absorption, Small Angle X-ray Scattering (SAXS), and Transmission Electron Microscopy (TEM). Results clearly indicate that the polymer plays a key role in determining the size and shape of gold particles, from fractal-like structures to monodisperse spherical particles with a mean diameter of about 3 nm. The aggregation behavior of these nanostructures has been characterized both in solution (SAXS) as well as on mica substrate (AFM) and has been proven to be driven by the polymer to gold concentration ratio. 相似文献
128.
Rok Tomi
David Heath Ester Heath Jernej Markelj Andreja Kandolf Borovak Helena Prosen 《Molecules (Basel, Switzerland)》2020,25(24)
In this study, a method was developed for the determination of five neonicotinoid pesticides (acetamiprid, clothianidin, imidacloprid, thiacloprid, and thiamethoxam) in propolis. Two sample preparation methods were tested: solid-phase extraction and the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. The identities of analytes were confirmed using liquid chromatography–tandem mass spectrometry (LC-MS/MS) in the selected reaction monitoring mode. Solid-phase extraction resulted in cleaner extracts; therefore, the SPE-LC-MS/MS method was validated according to the SANTE protocol in triplicate at two spiking levels (10 ng/g and 50 ng/g). The average recoveries of analytes ranged from 61% to 101%, except for clothianidin (10–20%). The LOD ranged from 0.2 ng/g to 4.4 ng/g, whereas the LOQ was in the range of 0.8 ng/g–14.7 ng/g. In order to compensate for the matrix effect, matrix-matched calibration was used. Good accuracy (relative error: 1.9–10.4%) and good linearity (R2 > 0.991) were obtained for all compounds. The optimised method was applied to 30 samples: 18 raw propolis and 12 ethanol tinctures. Acetamiprid, imidacloprid, and thiacloprid were detectable in seven samples but were still below the LOQ. This study is the first to report the determination of several neonicotinoid residues in propolis. 相似文献
129.
130.