全文获取类型
收费全文 | 441篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
化学 | 390篇 |
晶体学 | 4篇 |
力学 | 5篇 |
数学 | 21篇 |
物理学 | 36篇 |
出版年
2023年 | 4篇 |
2022年 | 45篇 |
2021年 | 23篇 |
2020年 | 15篇 |
2019年 | 17篇 |
2018年 | 15篇 |
2017年 | 12篇 |
2016年 | 17篇 |
2015年 | 15篇 |
2014年 | 16篇 |
2013年 | 20篇 |
2012年 | 18篇 |
2011年 | 46篇 |
2010年 | 16篇 |
2009年 | 16篇 |
2008年 | 26篇 |
2007年 | 25篇 |
2006年 | 11篇 |
2005年 | 14篇 |
2004年 | 16篇 |
2003年 | 10篇 |
2002年 | 11篇 |
2000年 | 10篇 |
1999年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1975年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有456条查询结果,搜索用时 15 毫秒
11.
Aicha Benabad Karima Bakhous Fatima Cherkaoui Elizabeth M. Holt 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(11):1292-1293
BiV0.4Fe3IIIO(PO4)3 crystallizes with two Fe atoms (one on an inversion centre and one on a mirror plane) displaying octahedral geometry and a third Fe atom (on a mirror plane) with trigonal bipyramidal coordination. Fe atoms are seen in oxygen‐bridged chains. BiV atoms are found in the interstitial sites between these chains. Bi shows sevenfold coordination, with Bi—O distances between 2.357 (7) and 2.529 (6) Å. 相似文献
12.
Maria de Fatima Pereira 《Tetrahedron》2007,63(4):847-854
The work described in this paper is a further example of the utility of Appel's salt in the conception of novel heterocyclic rings. We confirmed that primary alkyldiamines may react easily with the methyl N-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)-anthranilates to afford quinazolines, which are very interesting starting materials for the access to novel 2,3-condensed quinazolin-4-ones. On the other side, aromatic amines allow the synthesis of polycyclic molecules, which are structurally close to the model natural products (e.g., rutaecarpine, luotonine, tryptanthrine and vasicinone). 相似文献
13.
Fatima Flores-Galicia Alexander Eden Antoine Pallandre Sumita Pennathur Anne-Marie Haghiri-Gosnet 《Electrophoresis》2022,43(5-6):741-751
We report on the investigation of electropreconcentration phenomena in micro-/nanofluidic devices integrating 100 μm long nanochannels using 2D COMSOL simulations based on the coupled Poisson–Nernst–Planck and Navier–Stokes system of equations. Our numerical model is used to demonstrate the influence of key governing parameters such as electrolyte concentration, surface charge density, and applied axial electric field on ion concentration polarization (ICP) dynamics in our system. Under sufficiently extreme surface-charge-governed transport conditions, ICP propagation is shown to enable various transient and stationary stacking and counter-flow gradient focusing mechanisms of anionic analytes. We resolve these spatiotemporal dynamics of analytes and electrolyte ICP over disparate time and length scales, and confirm previous findings that the greatest enhancement is observed when a system is tuned for analyte focusing at the charge, excluding microchannel, nanochannel electrical double layer (EDL) interface. Moreover, we demonstrate that such tuning can readily be achieved by including additional nanochannels oriented parallel to the electric field between two microchannels, effectively increasing the overall perm-selectivity and leading to enhanced focusing at the EDL interfaces. This approach shows promise in providing added control over the extent of ICP in electrokinetic systems, particularly under circumstances in which relatively weak ICP effects are observed using only a single channel. 相似文献
14.
Sherif Aly El-Kafrawy Sayed Sartaj Sohrab Zeenat Mirza Ahmed M. Hassan Fatima Alsaqaf Esam Ibraheem Azhar 《Molecules (Basel, Switzerland)》2021,26(9)
MERS-CoV was identified for the first time in Jeddah, Saudi Arabia in 2012 in a hospitalized patient. This virus subsequently spread to 27 countries with a total of 939 deaths and 2586 confirmed cases and now has become a serious concern globally. Camels are well known for the transmission of the virus to the human population. In this report, we have discussed the prediction, designing, and evaluation of potential siRNA targeting the ORF1ab gene for the inhibition of MERS-CoV replication. The online software, siDirect 2.0 was used to predict and design the siRNAs, their secondary structure and their target accessibility. ORF1ab gene folding was performed by RNAxs and RNAfold software. A total of twenty-one siRNAs were selected from 462 siRNAs according to their scoring and specificity. siRNAs were evaluated in vitro for their cytotoxicity and antiviral efficacy in Huh7 cell line. No significant cytotoxicity was observed for all siRNAs in Huh7 cells. The in vitro study showed the inhibition of viral replication by three siRNAs. The data generated in this study provide preliminary and encouraging information to evaluate the siRNAs separately as well as in combination against MERS-CoV replication in other cell lines. The prediction of siRNAs using online software resulted in the filtration and selection of potential siRNAs with high accuracy and strength. This computational approach resulted in three effective siRNAs that can be taken further to in vivo animal studies and can be used to develop safe and effective antiviral therapies for other prevalent disease-causing viruses. 相似文献
15.
Mameri Fatima Koutchoukali Ouahiba Koutchoukali Mohamed Salah Hartwig Anne Nemdili Leila Ulrich Joachim 《Journal of Thermal Analysis and Calorimetry》2019,136(2):833-842
Journal of Thermal Analysis and Calorimetry - The aim of this work is to apply the melt crystallization technology to manufacture ibuprofen tablets coated with polyethylene glycol in a single step.... 相似文献
16.
Rabia Javeed Dilshad Hussain Fahmida Jabeen Adeela Saeed Batool Fatima Muhammad Naeem Ashiq Muhammad Najam-ul-Haq 《Biomedical chromatography : BMC》2020,34(1):e4693
High-density lipoproteins (HDLs) have anti-inflammatory and antioxidant properties and are potentially cardio-protective. Defective HDL function is caused by alterations in both the proteome and lipidome of HDL particles. As potential biomarkers, the development of analytical methods is necessary for the enrichment of HDLs. Therefore, a method for selective enrichment of HDLs using immobilized metal ion affinity chromatography (IMAC) and metal oxide affinity chromatography (MOAC) is presented. SPE-based isolation of HDLs from whole serum is adopted as an alternative to traditional ultracentrifugation methods followed by SDS–PAGE. The enrichment mechanism relies on isoelectric points of lipoproteins and metal oxide. Negatively charged lipoprotein particles interact with positively charged metal oxides and IMAC affinity, which acts as a cation. Identified proteins from HDL through MALDI–MS analysis are apo AI, AII, AIV, CI, CIII, E, J, M, H, serum amyloid A and other nonapoproteins that are part of HDL particles and perform cellular functions. This serum-based proteomics approach gives insight into the functional role of HDL. HDL-associated phospholipids have also been analyzed by LDI–MS. Results suggest that the adopted analytical strategy is a feasible idea to extract lipoproteins from serum. A comparative study of healthy and diseased samples using this approach will provide valuable information in future. 相似文献
17.
Macrocyclic Gd3+ Complexes with Pendant Crown Ethers Designed for Binding Zwitterionic Neurotransmitters 下载免费PDF全文
Dr. Fatima Oukhatar Hervé Meudal Dr. Céline Landon Prof. Dr. Nikos K. Logothetis Prof. Dr. Carlos Platas‐Iglesias Priv.‐Doz. Dr. Goran Angelovski Dr. Éva Tóth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(31):11226-11237
A series of Gd3+ complexes exhibiting a relaxometric response to zwitterionic amino acid neurotransmitters was synthesized. The design concept involves ditopic interactions 1) between a positively charged and coordinatively unsaturated Gd3+ chelate and the carboxylate group of the neurotransmitters and 2) between an azacrown ether appended to the chelate and the amino group of the neurotransmitters. The chelates differ in the nature and length of the linker connecting the cyclen‐type macrocycle that binds the Ln3+ ion and the crown ether. The complexes are monohydrated, but they exhibit high proton relaxivities (up to 7.7 mM ?1 s?1 at 60 MHz, 310 K) due to slow molecular tumbling. The formation of ternary complexes with neurotransmitters was monitored by 1H relaxometric titrations of the Gd3+ complexes and by luminescence measurements on the Eu3+ and Tb3+ analogues at pH 7.4. The remarkable relaxivity decrease (≈80 %) observed on neurotransmitter binding is related to the decrease in the hydration number, as evidenced by luminescence lifetime measurements on the Eu3+ complexes. These complexes show affinity for amino acid neurotransmitters in the millimolar range, which can be suited to imaging concentrations of synaptically released neurotransmitters. They display good selectivity over non‐amino acid neurotransmitters (acetylcholine, serotonin, and noradrenaline) and hydrogenphosphate, but selectivity over hydrogencarbonate was not achieved. 相似文献
18.
Zouaoui Setifi Mehdi Boutebdja Fatima Setifi Hocine Merazig Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(7):702-706
In the title compound, catena‐poly[bis[(2,2′‐bipyridine‐κ2N,N′)(1,1,3,3‐tetracyano‐2‐ethoxypropenido‐κN)copper(II)]‐μ4‐hexanedioato‐κ6O1,O1′:O1:O6,O6′:O6], [Cu2(C9H5N4O)2(C6H8O4)(C10H8N2)2]n, the adipate (hexanedioate) dianion lies across a centre of inversion in the space group P. The CuII centre adopts a distorted form of axially elongated (4+2) coordination, and the CuII and adipate components form a one‐dimensional coordination polymer from which the 2,2′‐bipyridine and 1,1,3,3‐tetracyano‐2‐ethoxypropenide components are pendent, and where each adipate dianion is bonded to four different CuII centres. The coordination polymer chains are linked into a three‐dimensional framework structure by a combination of C—H...N and C—H...O hydrogen bonds, augmented by a π–π stacking interaction. 相似文献
19.
Indermeet Kohli Taylor L. Braunberger Amanda F. Nahhas Fatima N. Mirza Mohsen Mokhtari Alexis B. Lyons Nikiforos Kollias Eduardo Ruvolo Henry W. Lim Iltefat H. Hamzavi 《Photochemistry and photobiology》2020,96(1):208-214
Human skin is exposed to visible light (VL; 400–700 nm) and long-wavelength ultraviolet A1 (UVA1) radiation (370–400 nm) after the application of organic broad-spectrum sunscreens. The biologic effects of these wavelengths have been demonstrated; however, a dose–response has not been investigated. Ten subjects with Fitzpatrick skin phototype IV-VI were enrolled. Subjects were irradiated with 2 light sources (80–480 J cm−2): one comprising VL with less than 0.5% UVA1 (VL+UVA1) and the other pure VL. Skin responses were evaluated for 2 weeks using clinical and spectroscopic assessments. 4-mm punch biopsies were obtained from nonirradiated skin and sites irradiated with 480 J cm−2 of VL+UVA1 and pure VL 24 h after irradiation. Clinical and spectroscopic assessments demonstrated a robust response at VL+UVA1 sites compared with pure VL. Histology findings demonstrated a statistically significant increase in the marker of inflammation (P < 0.05) and proliferation (P < 0.05) at the irradiated sites compared with nonirradiated control. Threshold doses of VL+UVA1 resulting in biologic responses were calculated. Results indicate that approximately 2 h of sun exposure, which equates to VL+UVA1 dose (~400 J cm−2), is capable of inducing inflammation, immediate erythema and delayed tanning. These findings reinforce the need of photoprotection beyond the UV range. 相似文献
20.
The objective of this work was to prepare the mechanically stable hydrophobic biocomposites by incorporating the cellulose fibers into the polymer matrices for their applications in biomedical and food packaging. Herein, two different types of biocomposites were prepared by mixing polylactic acid (PLA) and polyhydroxybutyrate (PHB) with the agro-extracted cellulose, separately at 170 °C. The influence of the cellulose fibers on the thermal, mechanical, and barrier properties of polymer matrices (PLA and PHB) was observed. With an increase in the cellulose content in PLA and PHB, the tensile strength of the biocomposite materials significantly improved with the enhancement of 24.45% and 32.08%, respectively, compared with the pure PLA and PHB. Furthermore, a decrease of 74.16% and 73.49% in the water vapor transmission rate and oxygen transmission rate, respectively, was observed for cellulose/PHB biocomposites. This study highlights that adding cellulose fibers significantly improves the mechanical and the barrier properties of PLA and PHB, suggesting their biocomposites for use in biodegradable polymer industries. 相似文献