全文获取类型
收费全文 | 373篇 |
免费 | 20篇 |
专业分类
化学 | 283篇 |
晶体学 | 11篇 |
力学 | 8篇 |
数学 | 13篇 |
物理学 | 78篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 22篇 |
2021年 | 27篇 |
2020年 | 16篇 |
2019年 | 17篇 |
2018年 | 16篇 |
2017年 | 19篇 |
2016年 | 20篇 |
2015年 | 11篇 |
2014年 | 28篇 |
2013年 | 28篇 |
2012年 | 23篇 |
2011年 | 25篇 |
2010年 | 16篇 |
2009年 | 11篇 |
2008年 | 25篇 |
2007年 | 16篇 |
2006年 | 15篇 |
2005年 | 14篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有393条查询结果,搜索用时 15 毫秒
91.
A new ligand, 1-(2-furanthiocarbo)-3-thiosemicarbazide (H2ftsc), prepared from thiosemicarbazide and carboxymethyl-2-furandithioate, forms complexes [Mn(ftsc)(H2O)2], [Pd(ftsc)] · 2H2O, [M(Hftsc)(acac)2] (M=CoIII or CrIII), [M(Hftsc)2(acac)] (M=MnIII or FeIII) and [Zn(Hftsc)2] · 2H2O, which were characterized by elemental analyses, magnetic susceptibility, i.r., electronic and n.m.r. spectral data. The Mössbauer spectra of [Fe(Hftsc)2(acac)] at 298K and 80K suggest the presence of high-spin iron(III) with an S=5/2 state. In vivo and in vitro antitumour activity of the ligand and the complexes have been screened towards several tumour cell-lines. 相似文献
92.
Homo- and heteroleptic aryloxides of the type MX4–x(OAr)x [M = TiIV, ZrIV; X = OPri, Cl; x = 1,2,3,4; OAr = OC6H4Pri-4(OAr1), OC6H3Me-2-Pri-5(OAr2), OC6H3Me-5-Pri-2(OAr3), OC6H2Me3-2,4,6(OAr4), OC6H3But2-2,4(OAr5), OC6H3But2-2,6(OAr6)] have been prepared either by alkoxo–aryloxo or chloro-aryloxo exchange reactions in benzene or tetrahydrofuran. All these new derivatives have been characterized by elemental analyses, spectroscopic (i.r., 1H-, 13C-n.m.r.) studies and molecular weight measurements. The FAB mass spectral studies of four representative derivatives Support a dimeric nature for [Ti(OC6H3Me-5-Pri-2)4], [TiCl2(OC6H3Me-5-Pri-2)2], and [Zr(OC6H3But2-2,4)4(thf)], whereas the derivative [ZrCl(OC6H3But2-2,4)3(thf)] is monomeric. 相似文献
93.
The aim of preclarification is to minimize sludge going to yeast separators. This purpose is partially fulfilled. However,
it has been measured during the plant trial runs that preclarification does not noticeably improve fermentation.
The aim of postclarification is to minimize sludge going to distillation. This purpose is well served as noted from the fact
that cycle run of distillation columns using postclarification is three times longer (9–12 mo) as compared to the normal one
(3–4 mo). 相似文献
94.
Christodoulides N Mohanty S Miller CS Langub MC Floriano PN Dharshan P Ali MF Bernard B Romanovicz D Anslyn E Fox PC McDevitt JT 《Lab on a chip》2005,5(3):261-269
In the last decade, saliva has been advocated as a non-invasive alternative to blood as a diagnostic fluid. However, use of saliva has been hindered by the inadequate sensitivity of current methods to detect the lower salivary concentrations of many constituents compared to serum. Furthermore, developments in the areas related to lab-on-a-chip systems for saliva-based point of care diagnostics are complicated by the high viscosity and heterogeneous properties associated with this diagnostic fluid. The biomarker C-reactive protein (CRP) is an acute phase reactant and a well-accepted indicator of inflammation. Numerous clinical studies have established elevated serum CRP as a strong, independent risk factor for the development of cardiovascular disease (CVD). CVD has also been associated with oral infections (i.e. periodontal diseases) and there is evidence that systemic CRP may be a link between the two. Clinical measurements of CRP in serum are currently performed with "high sensitivity" CRP (hsCRP) enzyme-linked immunosorbent assay (ELISA) tests that lack the sensitivity for the detection of this important biomarker in saliva. Because measurement of salivary CRP may represent a novel approach for diagnosing and monitoring chronic inflammatory disease, including CVD and periodontal diseases, the objective of this study was to apply an ultra-sensitive microchip assay system for the measurement of CRP in human saliva. Here, we describe this novel lab-on-a-chip system in its first application for the measurement of CRP in saliva and demonstrate its advantages over the traditional ELISA method. The increased sensitivity of the microchip system (10 pg ml(-1) of CRP with 1000-fold dilution of saliva sample) is attributed to its inherent increased signal to noise ratio, resulting from the higher bead surface area available for antigen/antibody interactions and the high stringency washes associated with this approach. Finally, the microchip assay system was utilized in this study to provide direct experimental evidence that chronic periodontal disease may be associated with higher levels of salivary CRP. 相似文献
95.
96.
N. Vishnu Priya M. Senthilvelan Govindan Rangarajan M. Lakshmanan 《Physics letters. A》2019,383(1):15-26
We construct symmetry preserving and symmetry broken N-bright, dark and antidark soliton solutions of a nonlocal nonlinear Schrödinger equation. To obtain these solutions, we use appropriate eigenfunctions in Darboux transformation (DT) method. We present explicit one and two bright soliton solutions and show that they exhibit stable structures only when we combine the field and parity transformed complex conjugate field. Further, we derive two dark/antidark soliton solution with the help of DT method. Unlike the bright soliton case, dark/antidark soliton solution exhibits stable structure for the field and the parity transformed conjugate field separately. In the dark/antidark soliton solution case we observe a contrasting behaviour between the envelope of the field and parity transformed complex conjugate envelope of the field. For a particular parametric choice, we get dark (antidark) soliton for the field while the parity transformed complex conjugate field exhibits antidark (dark) soliton. Due to this surprising result, both the field and PT transformed complex conjugate field exhibit sixteen different combinations of collision scenario. We classify the parametric regions of dark and antidark solitons in both the field and parity transformed complex conjugate field by carrying out relevant asymptotic analysis. Further we present 2N-dark/antidark soliton solution formula and demonstrate that this solution may have combinations of collisions. 相似文献
97.
Nandhakumar E. Priya P. Rajeswari R. Aravindhan V. Sasikumar A. Senthilkumar N. 《Research on Chemical Intermediates》2019,45(5):2657-2671
Research on Chemical Intermediates - In the present work, Fe3O4 (NR)/ZrO2 core/shell nanocomposites (CSNCs) were synthesized using a green approach. The Argemone mexicana L. leaf extract acts as... 相似文献
98.
Dr. Esther Frederick Dr. Quinn Campbell Dr. Igor V. Kolesnichenko Dr. Luis F. Peña Dr. Angelica Benavidez Dr. Evan M. Anderson Dr. David R. Wheeler Dr. Shashank Misra 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(53):13337-13341
Ultradoping introduces unprecedented dopant levels into Si, which transforms its electronic behavior and enables its use as a next-generation electronic material. Commercialization of ultradoping is currently limited by gas-phase ultra-high vacuum requirements. Solvothermal chemistry is amenable to scale-up. However, an integral part of ultradoping is a direct chemical bond between dopants and Si, and solvothermal dopant-Si surface reactions are not well-developed. This work provides the first quantified demonstration of achieving ultradoping concentrations of boron (∼1e14 cm2) by using a solvothermal process. Surface characterizations indicate the catalyst cross-reacted, which led to multiple surface products and caused ambiguity in experimental confirmation of direct surface attachment. Density functional theory computations elucidate that the reaction results in direct B−Si surface bonds. This proof-of-principle work lays groundwork for emerging solvothermal ultradoping processes. 相似文献
99.
In this study, the bark of an important medicinal plant, Indigofera aspalathoides is utilized as a bioreductant for the synthesis of silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs). The formation of nanoparticles was monitored, and the reaction parameters were optimized by UV–Vis spectroscopy. The attachment of biocomponents as stabilizer was proved employing Fourier‐transform infrared (FT‐IR) studies. Through transmission electron microscopy (TEM), the morphology was found to be predominantly spherical and a mixture of triangle and hexagon in the case of AgNPs and AuNPs, respectively. The crystallite size of AgNPs and AuNPs was affirmed through X‐ray diffraction (XRD) studies using Sherrer formula as 22.03 and 47.70 nm, respectively. DPPH method was adopted to analyse the free‐radical quenching ability, and the AgNPs, AuNPs and extract showed inhibition of 76%, 89% and 59% at a concentration of 200 μg ml?1, and the corresponding IC50 values were 86.49, 55.20 and 149.19 μg ml?1. The binding of nanoparticles to calf‐thymus DNA (CT‐DNA) was through groove and the high binding constants (8.49 × 106 M?1 and 2.34 × 107 M?1 for AgNPs and AuNPs) point out the potential of these nanoparticles as curative drugs. The MTT assay showed that AgNPs were 100% toxic, and the low IC50 value suggests that this can be used in the medicinal field as a safe drug. 相似文献
100.