全文获取类型
收费全文 | 2643篇 |
免费 | 80篇 |
国内免费 | 5篇 |
专业分类
化学 | 2153篇 |
晶体学 | 14篇 |
力学 | 27篇 |
数学 | 269篇 |
物理学 | 265篇 |
出版年
2024年 | 3篇 |
2023年 | 24篇 |
2022年 | 77篇 |
2021年 | 81篇 |
2020年 | 64篇 |
2019年 | 54篇 |
2018年 | 28篇 |
2017年 | 30篇 |
2016年 | 82篇 |
2015年 | 88篇 |
2014年 | 92篇 |
2013年 | 153篇 |
2012年 | 175篇 |
2011年 | 207篇 |
2010年 | 121篇 |
2009年 | 116篇 |
2008年 | 199篇 |
2007年 | 203篇 |
2006年 | 166篇 |
2005年 | 155篇 |
2004年 | 112篇 |
2003年 | 109篇 |
2002年 | 77篇 |
2001年 | 22篇 |
2000年 | 35篇 |
1999年 | 20篇 |
1998年 | 11篇 |
1997年 | 17篇 |
1996年 | 17篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 14篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 13篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 18篇 |
1984年 | 16篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有2728条查询结果,搜索用时 0 毫秒
81.
Nincevic Gladan Z Ujevic I Milandri A Marasovic I Ceredi A Pigozzi S Arapov J Skejic S 《Molecules (Basel, Switzerland)》2011,16(1):888-899
Dinophysis spp. blooms and related shellfish toxicity events of diarrhetic shellfish poisoning (DSP) have been the most reported toxicity event through the Croatian National monitoring program. With the aim to characterize the DSP toxin profile in shellfish farmed in Croatia, for the first time a complete analysis of the toxin profile of Croatian mussels has been carried out using the LC-MS/MS technique. The obtained results showed okadaic acid (OA) as the main toxin contaminating Croatian mussels at that time. The maximum concentration of OA in shellfish tissue was recorded 12 days after the Dinophysis fortii bloom, thus suggesting that rapid growth of the toxin level in the shellfish occurred in the first week after the bloom while it was slower in the second week. Furthermore, the presence of only OA at concentrations which could endanger human health suggests D. fortii as the main organism responsible for the toxic event that occurred in Lim Bay. The presence of gymnodimine and spirolides in Croatian mussel has been detected for the first time, while the presence of yessotoxin and pectenotoxin-2 is confirmed. 相似文献
82.
Four novel benzamido-functionalized prolinamides have been prepared and tested as organocatalysts for enantioselective aldol reaction of aldehydes and cyclic ketones in water. In particular, prolinamide derived from achiral ethylene diamine was the best catalyst leading to anti aldols in excellent diastereomeric (up to 98/2) and enantiomeric (up to 99/1) ratios, thereby showing that lateral amide functionalities might be a key issue for facilitating "in water" chemistry. These catalysts are cheaper and easier to prepare than those previously described. 相似文献
83.
Silvia Dorn Peter Eggenberg Michael R. C. Gerstenberger Alois Haas Ulrich Niemann Peter Zobrist 《Helvetica chimica acta》1979,62(5):1442-1450
(Perhalomethylthio)heterocycles. X 1 IX. Mitt.: s. [1]. . Acid-catalyzed substitutions on (perchlorofluoromethylthio)pyrroles and their agro-biological activities In the presence of C4F9SO3H the (perhalomethylthio)pyrroles 1a–c react with Cl3?nFnCSCl (n = 1–3) to give mixtures of the 2,5- and 2,4-disubstituted pyrroles 2a–f and 3a–h . 2a and 3a react with CF3SCl (catalyst CF3SO3H) yielding 2,3,5-tris (trifloromethylthio)pyrrole ( 4a ), which under similar conditions reacts further to give 2,3,4,5-tetrakis (trifluoromethylthio)pyrrole ( 5 ). As a by-product during the conversion of 3a to 4a 2,3,4-tris (trifluoromethylthio)pyrrole ( 4b ) is formed. The pyrroles 2a , 4a and 5 form the mercury salts 6a–c ; compound 5 yields also a silver salt 7 . The 1H- and 19F-NMR. spectra are discussed and the agro-biological properties of the compounds investigated. 相似文献
84.
Silvia E. Braslavsky Alfred R. Holzwarth Harald Lehner Kurt Schaffner 《Helvetica chimica acta》1978,61(6):2219-2222
Freshly prepared solutions of biliverdin dimethyl ester ( 2 ) in ethanol showed fluorescence maxima at 710 and 770 nm [ΦF = 1.1. 10?4 (room temperature) and 5.0 10?4 (77 K)]. The maxima of monoprotonated 2 at 77 K were shifted to 725 and 806 nm and the quantum yield was increased to 2.6. 10?2. This acid effect was reversible by neutralization with base. When a neutral solution was kept standing in the dark at room temperature, or when an acidic solution was neutralized by base, an additional fluorescence maximum at 500 nm with a mirror image excitation spectrum with λmax = 470 nm developed, which disappeared on addition of acid and which is attributed to a chemical change of 2 . 相似文献
85.
The applicability of the headspace coupled to mass spectrometry for evaluation of the sensory quality of virgin olive oil samples is presented. The volatiles of the oil are directly transferred from the sample vial to the detector without chromatographic separation. The mass spectrum obtained can be considered as a fingerprint of the oil sample and can be used for classification purposes. After a training step with samples previously qualified following the official method, a classification model was created using the supervised technique soft independent modeling of class analogy (SIMCA). Eight negative (rancid, winey-vinegary, muddy sediment, hay-wood, vegetable water, earthy, fusty and musty-humidity) and three principal positive attributes (fruity, bitter and pungent) have been included in this study. With them, a classification model consisting of two main classes (extra- and lampante-virgin olive oil) was constructed. In addition, the unsupervised technique cluster analysis permited the discrimination among oils with different negative attributes. The proposed procedure has been applied to the classification of commercial samples (as extra- or lampante-virgin olive oils) and the results were compared with those provided by the expert's panel with acceptable correlation. 相似文献
86.
Pawel J. Kulesza Silvia Zamponi Marcin A. Malik Krzysztof Miecznikowski Mario Berrettoni Roberto Marassi 《Journal of Solid State Electrochemistry》1997,1(1):88-93
Using Prussian blue (PB) electrodeposited on gold-covered foil as a model system, we have demonstrated the usefulness of
the time-derivative measurements of absorbance versus potential (linear potential-scan voltabsorptometry) for spectroelectrochemical
characterization of thin electrochromic films. The time-derivative signals were monitored for PB at 680 and 420 nm in potassium,
sodium and lithium electrolytes. Information obtained from cyclic voltabsorptometry is equivalent or complementary to that
from conventional cyclic voltammetry. In the case of PB films investigated in lithium electrolyte, the voltabsorptometric
time-derivative peaks are better defined than the respective voltammetric peaks. The combination of voltabsorptometry with
voltammetry enables molar absorptivity and/or film loading to be determined. Also, concentration changes of differently colored
mixed-valence redox centers can be monitored as a function of applied potential.
Received: 16 January 1997 / Accepted: 11 March 1997 相似文献
87.
Secondary ion mass spectrometry and alpha-spectrometry of electrodeposited thorium films 总被引:1,自引:0,他引:1
Jozef Kuruc Jana Strišovská Dušan Galanda Silvia Dulanská Ľubomír Mátel Monika Jerigová Dušan Velič 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(3):973-981
The main aim of this work was the preparation of samples with thorium content on the steel discs by electrodeposition for determination of natural thorium isotope by alpha spectrometry and secondary ion mass spectrometry and finding out their possible linear correlation between these methods. The analysis of the composition of surface was other aim of study. Discs were measured by alpha spectrometer. After that, alpha spectrometry discs were analyzed by TOF-SIMS IV, which is installed in the International Laser Centre in Bratislava. The integral and normalized intensities of isotope of 232Th and intensities of ions of ThO+, ThOH+, ThO2H+, Th2O4H+, ThO2 ?, ThO3H?, ThH3O3 ? a ThN2O5H? were measured. The linear correlation is between surface’s weights of Th and intensities of ions of Th+ from identified in SIMS spectra. We found out the chemical binding between thorium and oxygen and hydrogen on the surface of samples by SIMS method. Obtained intensities of ions 232ThO+, 232ThOH+, 232ThO2H+ prove the presence of oxidized forms of thorium in the upper layers of surface. The oxidized ions predominate in univalent form of thorium up to deep about 3,000 nm. 相似文献
88.
Hierarchical MoS2@TiO2 Heterojunctions for Enhanced Photocatalytic Performance and Electrocatalytic Hydrogen Evolution 下载免费PDF全文
Yu Dong Sheng‐You Chen Yi Lu Yu‐Xuan Xiao Jie Hu Si‐Ming Wu Dr. Zhao Deng Prof. Ge Tian Prof. Gang‐Gang Chang Prof. Jing Li Prof. Silvia Lenaerts Prof. Christoph Janiak Prof. Xiao‐Yu Yang Prof. Bao‐Lian Su 《化学:亚洲杂志》2018,13(12):1609-1615
Hierarchical MoS2@TiO2 heterojunctions were synthesized through a one‐step hydrothermal method by using protonic titanate nanosheets as the precursor. The TiO2 nanosheets prevent the aggregation of MoS2 and promote the carrier transfer efficiency, and thus enhance the photocatalytic and electrocatalytic activity of the nanostructured MoS2. The obtained MoS2@TiO2 has significantly enhanced photocatalytic activity in the degradation of rhodamine B (over 5.2 times compared with pure MoS2) and acetone (over 2.8 times compared with pure MoS2). MoS2@TiO2 is also beneficial for electrocatalytic hydrogen evolution (26 times compared with pure MoS2, based on the cathodic current density). This work offers a promising way to prevent the self‐aggregation of MoS2 and provides a new insight for the design of heterojunctions for materials with lattice mismatches. 相似文献
89.
Lodi Andrea Nap Cees-Jan Metzger-Maurer Silvia Schwartzenberger Christelle 《Accreditation and quality assurance》2018,23(4):211-218
Accreditation and Quality Assurance - Two approaches were used to determine the mass fraction of a sample of folic acid, one indirect (mass balance) where the components other than folic acid were... 相似文献
90.
Vladislava Mičková Silvia Ružičková Dagmar Remeteiová Martina Laubertová Marianna Dorková 《Chemical Papers》2018,72(5):1231-1238
Sampling is the most important procedure in arriving at the value of an electronic scrap. Inappropriate sampling makes other procedures, including assaying, valueless, as the sample must really represent the electronic scrap from which it was taken. The aim of this study was to develop the procedure to investigate the composition of heterogeneous printed circuit boards (PCBs) material and to show its applicability as well as its related limitations. The contents of Cu, Pb, Ni, and Zn in PCBs from wasted mobile phones were determined. Mixtures of aqua regia, hydrogen peroxide and hydrofluoric acid were applied to sample digestion. Open and closed vessel wet digestion with or without heating and microwave-assisted one was realized. For these purposes different sample amounts (0.2, 0.4, and 0.5 g) were applied and on the basis of calculated relative standard deviation values (RSD), the precision of repeated the most effective digestion was evaluated. The microwave-assisted wet digestion and mixture of aqua regia and hydrogen peroxide was found as the most effective one of the compared mixtures and applied conditions. A sample amount of 0.5 g was found as the most suitable. RSD values confirm the importance of electronic waste material sample preparation. 相似文献