全文获取类型
收费全文 | 1103篇 |
免费 | 41篇 |
国内免费 | 2篇 |
专业分类
化学 | 946篇 |
晶体学 | 5篇 |
力学 | 22篇 |
数学 | 48篇 |
物理学 | 125篇 |
出版年
2024年 | 4篇 |
2023年 | 11篇 |
2022年 | 25篇 |
2021年 | 43篇 |
2020年 | 21篇 |
2019年 | 23篇 |
2018年 | 15篇 |
2017年 | 16篇 |
2016年 | 27篇 |
2015年 | 25篇 |
2014年 | 39篇 |
2013年 | 74篇 |
2012年 | 83篇 |
2011年 | 77篇 |
2010年 | 46篇 |
2009年 | 36篇 |
2008年 | 69篇 |
2007年 | 79篇 |
2006年 | 74篇 |
2005年 | 71篇 |
2004年 | 71篇 |
2003年 | 59篇 |
2002年 | 41篇 |
2001年 | 15篇 |
2000年 | 10篇 |
1999年 | 14篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1991年 | 3篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1975年 | 3篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1904年 | 1篇 |
1899年 | 1篇 |
1892年 | 1篇 |
1890年 | 2篇 |
排序方式: 共有1146条查询结果,搜索用时 62 毫秒
41.
The lipase catalyzed resolution of trans-3,4-tetrahydrofuran and pyrrolidine bromohydrins by acylation or hydrolysis of their acylated derivatives has been studied. For both heterocycles, the best enantioselectivity was obtained using Candida antarctica lipase B as the catalyst in the hydrolytic processes. The enantiomerically pure bromohydrins are useful intermediates for the preparation of 3,4-fuctionalized cis-heterocycles. 相似文献
42.
Davide Toniolo Aurélien R. Willauer Dr. Julie Andrez Yan Yang Dr. Rosario Scopelliti Prof. Laurent Maron Prof. Marinella Mazzanti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(33):7831-7834
The activation of CS2 is of interest in a broad range of fields and, more particularly, in the context of creating new C−C bonds. The reaction of the dinuclear ytterbium(II) complex [Yb2L4], 1 , [L=(OtBu)3SiO−] with carbon disulfide led to the isolation of unprecedented reduction products. In particular, the crystallographic characterization of complex [Yb2L4(μ-C2S2)], 2 , provided the first example of an acetylenedithiolate ligand formed from metal reduction of CS2. Computational studies indicated that this unprecedented reactivity can be ascribed to the unusual binding mode of CS22− in the isolated “key intermediate” [Yb2L4(μ-CS2)], 3 , which results from the dinuclear nature of 1 . 相似文献
43.
44.
45.
The resolutions of determinantal ideals exhibit a remarkable stability property: for fixed rank but growing dimension, the terms of the resolution stabilize (in an appropriate sense). One may wonder if other sequences of ideals or modules over coordinate rings of matrices exhibit similar behavior. We show that this is indeed the case. In fact, our main theorem is more fundamental in nature: It states that certain large algebraic structures (which are examples of twisted commutative algebras) are noetherian. These are important new examples of large noetherian algebraic structures, and ones that are in some ways quite different from previous examples. 相似文献
46.
Rosa M. Claramunt Pilar Cornago M. Dolores Santa María Verónica Torres Elena Pinilla M. Rosario Torres 《Supramolecular chemistry》2013,25(4):349-356
The X-ray structure and the solid-state NMR measurements, mainly 15N CPMAS of the labelled compound, allow to determine the static and dynamic properties of 3(5)-ethyl-5(3)-phenyl-1H-pyrazole. The compound is a tetramer formed by three 5-ethyl-3-phenyl-1H-pyrazole and one 3-ethyl-5-phenyl-1H-pyrazole tautomers in dynamic equilibrium with the complementary situation. 相似文献
47.
Jitender Gaur Shilpa Jain Rohit Bhatia Arun Lal Narender Kumar Kaushik 《Journal of Thermal Analysis and Calorimetry》2013,112(2):1137-1143
We demonstrate synthesis of water insoluble, novel copolymer PA1 from condensation of glyoxal dihydrazone and glyoxal dihydrazone bis(dithiocarbamate) monomers having high capacity to remove metal ions from aqueous solution. The presence of a high atomic percentage of nitrogen and sulfur atoms in PA1 leads to strong ligating ability with metal ions. The monomers and the polymer have been characterized by FTIR, UV–Visible spectroscopy, CHNS elemental analysis, NMR, MALDI-MS, and TG/DTA. As a proof of concept, the PA1 is tested for its ability to remove heavy metal ions Cu2+, Co2+, Fe2+, Ni2+, Mn2+, and CrO 7 2? from aqueous solutions. PA1 efficiently removed metals ions from the metal solutions. The highest absorption ability has been observed toward the iron salts where 0.969 g metal salt is absorbed by 1 g polymer. This study has implication for inexpensive and efficient polymer for purification of water. 相似文献
48.
Ioana Konz Beatriz Fernández M. Luisa Fernández Rosario Pereiro Héctor González Lydia Álvarez Miguel Coca-Prados Alfredo Sanz-Medel 《Analytical and bioanalytical chemistry》2013,405(10):3091-3096
Laser ablation coupled to inductively coupled plasma mass spectrometry has been developed for the elemental imaging of Mg, Fe and Cu distribution in histological tissue sections of fixed eyes, embedded in paraffin, from human donors (cadavers). This work presents the development of a novel internal standard correction methodology based on the deposition of a homogeneous thin gold film on the tissue surface and the use of the 197Au+ signal as internal standard. Sample preparation (tissue section thickness) and laser conditions were carefully optimized, and internal normalisation using 197Au+ was compared with 13C+ correction for imaging applications. 24Mg+, 56Fe+ and 63Cu+ distributions were investigated in histological sections of the anterior segment of the eye (including the iris, ciliary body, cornea and trabecular meshwork) and were shown to be heterogeneously distributed along those tissue structures. Reproducibility was assessed by imaging different human eye sections from the same donor and from ten different eyes from adult normal donors, which showed that similar spatial maps were obtained and therefore demonstrate the analytical potential of using 197Au+ as internal standard. The proposed analytical approach could offer a robust tool with great practical interest for clinical studies, e.g. to investigate trace element distribution of metals and their alterations in ocular diseases. Figure
Development of a new internal standard correction methodology for qualitative elemental imaging by LA-ICP-MS 相似文献
49.
Jorge Pisonero Nerea Bordel Claudia Gonzalez de Vega Beatriz Fernández Rosario Pereiro Alfredo Sanz-Medel 《Analytical and bioanalytical chemistry》2013,405(17):5655-5662
The combination of radiofrequency pulsed glow discharge (RF-PGD) analytical plasmas with time-of-flight mass spectrometry (TOFMS) has promoted the applicability of this ion source to direct analysis of innovative materials. In this sense, this emerging technique enables multi-elemental depth profiling with high depth resolution and sensitivity, and simultaneous production of elemental, structural, and molecular information. The analytical potential and trends of this technique are critically presented, including comparison with other complementary and well-established techniques (e.g. SIMS, GD–OES, etc.). An overview of recent applications of RF-PGD–TOFMS is given, including analysis of nano-structured materials, coated-glasses, photovoltaic materials, and polymer coatings 相似文献
50.
Aline Bruna da Silva Juliano Marini Genaro Gelves Uttandaraman Sundararaj Rinaldo Gregório Jr. Rosario E.S. Bretas 《European Polymer Journal》2013
The objective of this work was to prepare novel conductive blends of poly(vinylidene fluoride) (PVDF) with polypyrrole (PPy) and to compare their performance with PVDF/multiwall carbon nanotube (MWCNT) composites and novel PVDF/PPy/MWCNT hybrid systems. All the compositions were prepared by melt mixing using a miniature mixer. The mixtures were characterized by Fourier transformed infrared (FTIR), wide angle X-ray diffraction (WAXD), thermogravimetric analyses (TGA), scanning and transmission electron microscopy (SEM and TEM, respectively) and volume electrical resistivity. For the binary PVDF/PPy and PVDF/MWCNT systems, percolation thresholds of 10 and 0.3 wt%, respectively, were found. In the hybrid systems, however, the percolation threshold for each filler was lower than in the binary systems, but the electrical conductivities were always much higher at all concentrations than the conductivities of the binary systems. Therefore, the addition of both fillers had a synergistic effect on the hybrid system conductivity, which was attributed to its morphology: the PPy increased the homogeneity of the MWCNT distribution and decreased the available free volume for the MWCNT; as a result the MWCNT rolled around the PPy particles bridging them through the PVDF matrix, increasing the quantum tunneling effect and thus, the electrical conductivity of the system. 相似文献