全文获取类型
收费全文 | 1431篇 |
免费 | 147篇 |
国内免费 | 222篇 |
专业分类
化学 | 1405篇 |
晶体学 | 3篇 |
力学 | 15篇 |
综合类 | 52篇 |
数学 | 82篇 |
物理学 | 243篇 |
出版年
2024年 | 2篇 |
2023年 | 31篇 |
2022年 | 68篇 |
2021年 | 115篇 |
2020年 | 111篇 |
2019年 | 61篇 |
2018年 | 56篇 |
2017年 | 41篇 |
2016年 | 67篇 |
2015年 | 50篇 |
2014年 | 60篇 |
2013年 | 95篇 |
2012年 | 81篇 |
2011年 | 107篇 |
2010年 | 65篇 |
2009年 | 69篇 |
2008年 | 71篇 |
2007年 | 74篇 |
2006年 | 79篇 |
2005年 | 79篇 |
2004年 | 37篇 |
2003年 | 40篇 |
2002年 | 41篇 |
2001年 | 20篇 |
2000年 | 32篇 |
1999年 | 24篇 |
1998年 | 26篇 |
1997年 | 24篇 |
1996年 | 35篇 |
1995年 | 31篇 |
1994年 | 19篇 |
1993年 | 22篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有1800条查询结果,搜索用时 15 毫秒
71.
《Journal of Coordination Chemistry》2012,65(3):417-426
Abstract The electrochemical behavior of VOQ2OH or [VOQ2-OVOQ2] (Q = 8-hydroxyquinohnate anion) has been investigated by cyclic voltammetry in acetonitnie solutions. Although both species exist simultaneously at every condition analyzed, they can be clearly differentiated by this method. The effect of trace amounts of water on the electrochemical behavior is also discussed. 相似文献
72.
Exhaled breath condensate is a promising, non-invasive, diagnostic sample obtained by condensation of exhaled breath. Starting from a historical perspective of early attempts of breath testing towards the contemporary state-of-the-art breath analysis, this review article focuses mainly on the progress in determination of non-volatile compounds in exhaled breath condensate. The mechanisms by which the aerosols/droplets of non-volatile compounds are formed in the airways are discussed with methodological consequences for sampling. Dilution of respiratory droplets is a major problem for correct clinical interpretation of the measured data and there is an urgent need for standardization of EBC. This applies also for collection instrumentation and therefore various commercial and in-house built devices are described and compared with regard to their design, function and collection parameters. The analytical techniques and methods for determination of non-volatile compounds as potential markers of oxidative stress and lung inflammation are scrutinized with an emphasis on method suitability, sensitivity and appropriateness. The relevance of clinical findings for each group of possible non-volatile markers of selected pulmonary diseases and methodological recommendations with emphasis on interdisciplinary collaboration that is essential for future development into a fully validated clinical diagnostic tool are given. 相似文献
73.
Environmental Fenton chemistry has been poorly constrained within the marine environment at a multi-component level. A simple, unique, reconfiguration of a flow-injection analytical system combined with luminol chemiluminescence allows quasi-simultaneously the measurement, using a single load-inject valve and a single photon multiplier tube, of reduced iron, Fe(II), and hydrogen peroxide. The system enables rapid, every 22 s, measurements with good accuracy at environmentally relevant concentrations, less than 5% relative standard deviations on both a 5 nM Fe(II) standard and a 60 nM hydrogen peroxide standard. Limits of detection were as low as 40 pM Fe(II) and 100 pM hydrogen peroxide. The system showed excellent capability by measuring from within an organic rich seawater the photochemically induced production of Fe(II) and hydrogen peroxide and their subsequent cycling and Fenton like interactions. 相似文献
74.
Zhongxian Song Yun Xing Tingji Zhang Jinggang Zhao Junkai Wang Yanli Mao Baolin Zhao Xuejun Zhang Min Zhao Ziang Ma 《应用有机金属化学》2020,34(3):e5446
A series of Ce-Fe-Ox catalysts prepared by the different calcination temperatures (marked as CF-X, where X represented calcination temperature) were used to the selectivity catalytic reduction of NOx by NH3. The results explained the relationship between calcination temperature and the sulfate species over Ce-Fe-Ox, and then investigated the surface acidity and catalytic performance. The large amounts of sulfate species were formed over CF-450 and CF-550 while it was decomposed with further the increasing of calcination temperature, which resulted in the loss of surface acidity, causing a decrease in the catalytic activity over Ce-Fe-Ox. Thereby, the CF-450 catalyst showed the best catalytic activity and over 90% NOx conversion was obtained at 244–450 °C. Besides, the favored pore structure, more Fe3+ active species, higher Ce3+ concentration and the abundance of chemical adsorbed oxygen species, as well as the surface acid sites, would together contribute to the excellent catalytic activity of CF-450 catalyst. 相似文献
75.
Dr. Wenyan Hao Yuchen Sha Dr. Yi Deng Yi Luo Li Zeng Shan Tang Dr. Yue Weng Prof. Dr. Chien-Wei Chiang Prof. Dr. Aiwen Lei 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(19):4931-4934
An in situ generated oxidation species of nickel quinolinylpropioamide intermediate was produced. Characterization by X-ray absorption near edge structure (XANES) and EPR provides complementary insights into this oxidized nickel species. With aliphatic amides and isocyanides as substrates, a nickel-catalyzed facile synthesis of structurally diverse five-membered lactams could be achieved. 相似文献
76.
Dr. Franck Ulm Dr. Yann Cornaton Dr. Jean-Pierre Djukic Prof. Michael J. Chetcuti Prof. Vincent Ritleng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(41):8916-8925
The pentamethylcyclopentadienyl N-heterocyclic carbene nickel complex [Ni(η5-C5Me5)Cl(IMes)] (IMes=1,3-dimesitylimidazol-2-ylidene) efficiently catalyses the anti-Markovnikov hydroboration of alkenes with catecholborane in the presence of a catalytic amount of potassium tert-butoxide, and joins the very exclusive club of nickel catalysts for this important transformation. Interestingly, the regioselectivity can be reversed in some cases by using pinacolborane instead of catecholborane. Mechanistic investigations involving control experiments, 1H and 11B NMR spectroscopy, cyclic voltammetry, piezometric measurements and DFT calculations suggest an initial reduction of the NiII precursor to a NiI active species with the concomitant release of H2. The crucial role of the alkoxo-catecholato-borohydride species resulting from the reaction of potassium tert-butoxide with catecholborane in the formation of an intermediate nickel-hydride species that would then be reduced to the NiI active species, is highlighted. 相似文献
77.
Juechen Ni Yijia Wang Haoke Zhang Jing Zhi Sun Ben Zhong Tang 《Molecules (Basel, Switzerland)》2021,26(2)
Luminogens with aggregation-induced emission (AIEgens) have been widely applied in the field of photodynamic therapy. Among them, aggregation-induced emission photosensitizers (AIE–PSs) are demonstrated with high capability in fluorescence and photoacoustic bimodal imaging, as well as in fluorescence imaging-guided photodynamic therapy. They not only improve diagnosis accuracy but also provide an efficient theranostic platform to accelerate preclinical translation as well. In this short review, we divide AIE–PSs into three categories. Through the analysis of such classification and construction methods, it will be helpful for scientists to further develop various types of AIE–PSs with superior performance. 相似文献
78.
79.
《Comptes Rendus Chimie》2017,20(1):7-19
Me/Ti-PILC catalysts (Me: La, Se, Rb) were prepared with 60% in weight of Ti-species and 3% in weight of Me-secondary species added under ultrasounds. All materials were characterized by XRF, XPS, XRD, BET, HR-TEM/EDS, FEG-SEM and UV-vis. Three kinds of Ti-oxide nanoparticles were identified: (1) Ti-pillars within the clay layers, (2) rutile nanoflowers, and (3) anatase. In UV-vis spectra, no significant change in the band-gap was observed. In La and Se samples, small variations of the anatase XRD lines are associated with cationic diffusion after deposition of secondary species and calcination. An O1s XPS-peak (533.5 eV) is attributed to oxygen vacancies generated by this diffusion. Phosphate photo-removal in water was studied using phosphoric acid solution (75.97 g L−1). Dephosphatation is significantly improved in the presence of Me-species as La/Ti-PILC > Se/Ti-PILC > Rb/Ti-PILC > Ti-PILC. Partial dephosphatation by adsorption is possible in the dark but is strongly improved by UV irradiation. With a La catalyst and under UV irradiation, phosphates (6.6 × 10−3 mol L−1) were recovered in less than 70 min. Therefore, Me/Ti-PILC have a great potential as photocatalysts for the treatment of wastewaters and the recovery of phosphates. 相似文献
80.
Lorilee S.L. Arakaki Kenneth A. Schenkman Wayne A. Ciesielski Jeremy M. Shaver 《Analytica chimica acta》2013
We have developed a method to make real-time, continuous, noninvasive measurements of muscle oxygenation (Mox) from the surface of the skin. A key development was measurement in both the visible and near infrared (NIR) regions. Measurement of both oxygenated and deoxygenated myoglobin and hemoglobin resulted in a more accurate measurement of Mox than could be achieved with measurement of only the deoxygenated components, as in traditional near-infrared spectroscopy (NIRS). Using the second derivative with respect to wavelength reduced the effects of scattering on the spectra and also made oxygenated and deoxygenated forms more distinguishable from each other. Selecting spectral bands where oxygenated and deoxygenated forms absorb filtered out noise and spectral features unrelated to Mox. NIR and visible bands were scaled relative to each other in order to correct for errors introduced by normalization. Multivariate Curve Resolution (MCR) was used to estimate Mox from spectra within each data set collected from healthy subjects. A Locally Weighted Regression (LWR) model was built from calibration set spectra and associated Mox values from 20 subjects using 2562 spectra. LWR and Partial Least Squares (PLS) allow accurate measurement of Mox despite variations in skin pigment or fat layer thickness in different subjects. The method estimated Mox in five healthy subjects with an RMSE of 5.4%. 相似文献