全文获取类型
收费全文 | 5626篇 |
免费 | 165篇 |
国内免费 | 9篇 |
专业分类
化学 | 4016篇 |
晶体学 | 45篇 |
力学 | 116篇 |
数学 | 511篇 |
物理学 | 1112篇 |
出版年
2023年 | 48篇 |
2022年 | 197篇 |
2021年 | 194篇 |
2020年 | 142篇 |
2019年 | 153篇 |
2018年 | 133篇 |
2017年 | 96篇 |
2016年 | 219篇 |
2015年 | 182篇 |
2014年 | 233篇 |
2013年 | 335篇 |
2012年 | 375篇 |
2011年 | 429篇 |
2010年 | 281篇 |
2009年 | 285篇 |
2008年 | 365篇 |
2007年 | 305篇 |
2006年 | 272篇 |
2005年 | 225篇 |
2004年 | 190篇 |
2003年 | 144篇 |
2002年 | 121篇 |
2001年 | 97篇 |
2000年 | 87篇 |
1999年 | 58篇 |
1998年 | 50篇 |
1997年 | 46篇 |
1996年 | 40篇 |
1995年 | 39篇 |
1994年 | 43篇 |
1993年 | 45篇 |
1992年 | 46篇 |
1991年 | 25篇 |
1990年 | 28篇 |
1989年 | 18篇 |
1988年 | 21篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 18篇 |
1983年 | 21篇 |
1982年 | 10篇 |
1981年 | 22篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 16篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有5800条查询结果,搜索用时 0 毫秒
221.
Poliana Cristina Spricigo Banny Silva Barbosa Correia Karla Rodrigues Borba Isabela Barroso Taver Guilherme de Oliveira Machado Renan Ziemann Wilhelms Luiz Henrique Keng Queiroz Junior Angelo Pedro Jacomino Luiz Alberto Colnago 《Molecules (Basel, Switzerland)》2021,26(12)
The cambuci is a native Brazilian fruit from the Atlantic Forest biome. A soft and astringent pulp, a green color, and a sweet aroma are its main characteristics. Classical food quality attributes (fresh fruit mass, fruit height, diameters, total soluble solid, titratable acidity, and ratio) and the metabolic profile from ten accessions from three different locations were analyzed herein by analytical methods (refractometry and neutralization titration) and nuclear magnetic resonance spectroscopy. Concerning sugar content, sucrose was the predominant compound, with glucose and fructose alternating in second, depending on the accession. Citric acid was the most relevant acid, followed by shikimic and quinic acids in quite variable amounts. These three main acids vary in amounts for each accession. Ascorbic acid content emerges as an important quality attribute and makes this fruit nutritionally attractive, due to values comparable to those contained in citric fruits. The main amino acids identified in cambuci were glutamic acid individually or in comprising the tripeptide glutathione (glutamic acid, cysteine, glycine). The quality diversity of the evaluated accessions suggests the potentiality of cambuci use in future breeding programs. 相似文献
222.
Mozaniel Santana de Oliveira Jorddy Neves Cruz Oberdan Oliveira Ferreira Daniel Santiago Pereira Natanael Santiago Pereira Marcos Enê Chaves Oliveira Giorgio Cristino Venturieri Giselle Maria Skelding Pinheiro Guilhon Antnio Pedro da Silva Souza Filho Eloisa Helena de Aguiar Andrade 《Molecules (Basel, Switzerland)》2021,26(11)
Propolis is a balsamic product obtained from vegetable resins by exotic Africanized bees Apis mellifera L., transported and processed by them, originating from the activity that explores and maintains these individuals. Because of its vegetable and natural origins, propolis is a complex mixture of different compound classes; among them are the volatile compounds present in the aroma. In this sense, in the present study we evaluated the volatile fraction of propolis present in the aroma obtained by distillation and simultaneous extraction, and its chemical composition was determined using coupled gas chromatography, mass spectrometry, and flame ionization detection. The majority of compounds were sesquiterpene and hydrocarbons, comprising 8.2–22.19% α-copaene and 6.2–21.7% β-caryophyllene, with additional compounds identified in greater concentrations. Multivariate analysis showed that samples collected from one region may have different chemical compositions, which may be related to the location of the resin’s production. This may be related to other bee products. 相似文献
223.
Joshua Silva Eileen Carry Chen Xue Jifeng Zhang Jing Liang Jacques Y. Roberge Daryl L. Davies 《Molecules (Basel, Switzerland)》2021,26(6)
Alcohol use disorder (AUD) affects over 18 million people in the US. Unfortunately, pharmacotherapies available for AUD have limited clinical success and are under prescribed. Previously, we established that avermectin compounds (ivermectin [IVM] and moxidectin) reduce alcohol (ethanol/EtOH) consumption in mice, but these effects are limited by P-glycoprotein (Pgp/ABCB1) efflux. The current study tested the hypothesis that dihydromyricetin (DHM), a natural product suggested to inhibit Pgp, will enhance IVM potency as measured by changes in EtOH consumption. Using a within-subjects study design and two-bottle choice study, we tested the combination of DHM (10 mg/kg; i.p.) and IVM (0.5–2.5 mg/kg; i.p.) on EtOH intake and preference in male and female C57BL/6J mice. We also conducted molecular modeling studies of DHM with the nucleotide-binding domain of human Pgp that identified key binding residues associated with Pgp inhibition. We found that DHM increased the potency of IVM in reducing EtOH consumption, resulting in significant effects at the 1.0 mg/kg dose. This combination supports our hypothesis that inhibiting Pgp improves the potency of IVM in reducing EtOH consumption. Collectively, we demonstrate the feasibility of this novel combinatorial approach in reducing EtOH consumption and illustrate the utility of DHM in a novel combinatorial approach. 相似文献
224.
Franciani C. Sentanin Willian R. Caliman Rodrigo C. Sabadini Carla C. S. Cavalheiro Rui F. P. Pereira Maria M. Silva Agnieszka Pawlicka 《Molecules (Basel, Switzerland)》2021,26(8)
Nanocomposite polymer electrolytes (NPEs) were synthesized using sodium alginate (Alg) and either sodium (SCa-3-Na+)- or lithium (SCa-3-Li+)-modified montmorillonite clays. The samples were characterized by structural, optical, and electrical properties. SCa-3-Na+ and SCa-3-Li+ clays’ X-ray structural analyses revealed peaks at 2θ = 7.2° and 6.7° that corresponded to the interlamellar distances of 12.3 and 12.8 Å, respectively. Alg-based NPEs X-ray diffractograms showed exfoliated structures for samples with low clay percentages. The increase of clay content promoted the formation of intercalated structures. Electrochemical Impedance Spectroscopy revealed that Alg-based NPEs with 5 wt% of SCa-3-Na+ clay presented the highest conductivity of 1.96 × 10−2 S/cm2, and Alg with 10 wt% of SCa-3-Li+ showed conductivity of 1.30 × 10−2 S/cm2, both measured at 70 °C. From UV-Vis spectroscopy, it was possible to infer that increasing concentration of clay promoted a decrease of the samples’ transmittance and, consequently, an increase of their reflectance. 相似文献
225.
Adriana Aniceto Julia Montenegro Rafael da Silva Cadena Anderson Junger Teodoro 《Molecules (Basel, Switzerland)》2021,26(2)
Amazonian fruits are excellent sources of bioactive compounds and can be used in beverages to improve the nutritional and sensorial characteristics. The present study aimed to develop a blend of murici (Byrsonima Crassifolia (L.) Kunth) and taperebá (Spondias Mombin L.) through experimental design and investigating the nutritional and sensorial characteristics of fruits and beverages. The murici was highlighted as higher vitamin C content (58.88 mg · 100 g−1) compared to taperebá (25.93 mg · 100 g−1). The murici and taperebá are good sources of total phenolic compounds (taperebá 1304.15 ± 19.14 mgGAE · 100 g−1 and the murici of 307.52 ± 19.73 mg GAE · 100 g−1) and flavonoids (174.87 ± 1.76 μgQE/g and 129.46 ± 10.68 μgQE/g, murici and taperebá, respectively), when compared to other Brazilian fruits. The antioxidant capacity in different methods revealed that the taperebá had a higher average in the results, only in the ORAC method and did not present a significant difference (p > 0.05) in relation to the murici. The beverage development was performed using experimental design 23, showed through sensory analysis and surface response methodology that murici and high sugar content (between 12.5 and 14.2% of sugar) influenced in sensory acceptance. Our findings indicate that beverages with improved nutrition and a sensory acceptance can be prepared using taperebá and murici fruits. 相似文献
226.
Artur V. da Silva Simoni M. P. Meneghetti Mario R. Meneghetti 《Molecules (Basel, Switzerland)》2021,26(9)
The synthesis of organometallic compounds with potential pharmacological activity has attracted the attention of many research groups, aiming to take advantage of aspects that the presence of the metal-carbon bond can bring to the design of new pharmaceutical drugs. In this context, we have gathered studies reported in the literature in which psychoactive benzodiazepine drugs were used as ligands in the preparation of organometallic and metal complexes and provide details on some of their biological effects. We also highlight that most commonly known benzodiazepine-based drugs display molecular features that allow the preparation of metallacycles via C-H activation. These organometallic compounds merit further attention regarding their potential biological effects, not only in terms of psychoactive drugs but also in the search for drug replacements, for example, for cancer treatments. 相似文献
227.
Lidiane Diniz do Nascimento Sebastio Gomes Silva Mrcia Moraes Cascaes Kauê Santana da Costa Pablo Luis Baia Figueiredo Cristiane Maria Leal Costa Eloisa Helena de Aguiar Andrade Lênio Jos Guerreiro de Faria 《Molecules (Basel, Switzerland)》2021,26(9)
Leaves of Lippia thymoides (Verbenaceae) were dried in an oven at 40, 50 and 60 °C and the kinetic of drying and the influence of the drying process on the chemical composition, yield, and DPPH radical scavenging activity of the obtained essential oils were evaluated. The composition of the essential oils was determined with gas chromatography-mass spectrometry and gas chromatography-flame ionization detection analyses. The influence of drying on the chemical composition of the essential oils of L. thymoides was evaluated by multivariate analysis, and their antioxidant activity was investigated via the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The Midilli model was the most appropriate to describe the behavior of drying kinetic data of L. thymoides leaves. Thymol was the major compound for all analyzed conditions; the maximum content was obtained from fresh leaves (62.78 ± 0.63%). The essential oils showed DPPH radical scavenging activity with an average of 73.10 ± 12.08%, and the fresh leaves showed higher inhibition (89.97 ± 0.31%). This is the first study to evaluate the influence of drying on the chemical composition and antioxidant activity of L. thymoides essential oils rich in thymol. 相似文献
228.
Lara R. S. Fonseca Gonalo R. Silva ngelo Luís Henrique J. Cardoso Sara Correia Ctia V. Vaz Ana P. Duarte Sílvia Socorro 《Molecules (Basel, Switzerland)》2021,26(10)
Sweet cherries (Prunus avium L.) are among the most appreciated fruits worldwide because of their organoleptic properties and nutritional value. The accurate phytochemical composition and nutritional value of sweet cherries depends on the climatic region, cultivar, and bioaccessibility and bioavailability of specific compounds. Nevertheless, sweet cherry extracts are highly enriched in several phenolic compounds with relevant bioactivity. Over the years, technological advances in chemical analysis and fields as varied as proteomics, genomics and bioinformatics, have allowed the detailed characterization of the sweet cherry bioactive phytonutrients and their biological function. In this context, the effect of sweet cherries on suppressing important events in the carcinogenic process, such as oxidative stress and inflammation, was widely documented. Interestingly, results from our research group and others have widened the action of sweet cherries to many hallmarks of cancer, namely metabolic reprogramming. The present review discusses the anticarcinogenic potential of sweet cherries by addressing their phytochemical composition, the bioaccessibility and bioavailability of specific bioactive compounds, and the existing knowledge concerning the effects against oxidative stress, chronic inflammation, deregulated cell proliferation and apoptosis, invasion and metastization, and metabolic alterations. Globally, this review highlights the prospective use of sweet cherries as a dietary supplement or in cancer treatment. 相似文献
229.
Daniela Nunes da Silva Hanna Leijoto de Oliveira Keyller Bastos Borges Arnaldo César Pereira 《Electroanalysis》2021,33(2):506-514
The analysis of 17β-estradiol with high sensitivity and selectivity is extremely relevant to control the impacts that this compound can cause on health and the environment. Thus, we describe the development and application of a magneto carbon paste electrode based on magnetic molecularly imprinted polymer (MCPE-MMIP) for determination of 17β-estradiol. The analyte adsorbed on the MMIP was immobilized on the electrode surface by magnetic capture. The morphological and structural characterization of the obtained MMIP suggests that the material was effectively synthesized. MCPE-MMIP showed an improvement in the sensitivity for 17β-estradiol detection when compared to electrode configurations in the absence of this material. The optimum conditions (0.10 mol L−1 phosphate buffer pH 7.0) were reached by differential pulse adsorptive stripping voltammetry (DPAdSV), in which the method presented linearity ranged from 0.06 to 175 μmol L−1 with limits of detection and quantification of 0.02 and 0.06 μmol L−1, respectively. The proposed sensor was applied effectively in the analysis of 17β-estradiol in river water and raw milk samples, exhibiting excellent recovery values (between 96.20 and 104 %), which were confirmed by HPLC analysis. 相似文献
230.
Jonatas de Oliveira S. Silva Prof. Mércia V. S. Sant'Anna Dr. Ava Gevaerd MSc. Jéssica B. S. Lima MSc. Michael D. S. Monteiro Dr. Sanny W. M. M. Carvalho Dr. Eliana Midori Sussuchi 《Electroanalysis》2021,33(10):2152-2160
This study introduces modified carbon paste electrodes with carbon nitride nanosheets (CNNS) and outlines their application for the determination of hydroxychloroquine sulfate (HCQ) in tablets and synthetic urine samples. CNNS were synthesized by hydrothermal route (200 °C, 10 h) using melamine and citric acid as their precursors. The carbon nitride nanosheets-based electrode (CNNS/E) presented a linear dynamic range for HCQ (LDR), ranging from 10.0 nmol l−1 to 6.92 μmol l−1, and detection (LOD) and quantification limits (LOQ) of 0.16 nmol l−1 and 0.52 nmol l−1, respectively. LOD and LOQ were calculated by the equations: LOD=3(Sd/b), and LOQ=10(Sd/b). The modified sensor presented excellent relative standard deviations for parameters such as repeatability (2.39 % and 1.87 %) and reproducibility (3.22 % and 2.32 %) in HCQ oxidation peaks (1 and 2). The CNNS/E has not shown significant variations in its anodic signal intensity in the presence of some organic and inorganic substances. It is worth bearing in mind that CNNS/E can be easily manufactured and the sensor has the lowest HCQ detection limits reported so far. The proposed sensor was successfully applied for HCQ determination in tablets and synthetic urine, showing good recovery values and an error of 0.60 % about comparative method in tablet samples, assuring the quality of the method. 相似文献