全文获取类型
收费全文 | 11194篇 |
免费 | 237篇 |
国内免费 | 11篇 |
专业分类
化学 | 6406篇 |
晶体学 | 144篇 |
力学 | 163篇 |
数学 | 1672篇 |
物理学 | 3057篇 |
出版年
2022年 | 84篇 |
2021年 | 100篇 |
2020年 | 129篇 |
2019年 | 141篇 |
2018年 | 187篇 |
2017年 | 210篇 |
2016年 | 300篇 |
2015年 | 287篇 |
2014年 | 303篇 |
2013年 | 637篇 |
2012年 | 468篇 |
2011年 | 608篇 |
2010年 | 413篇 |
2009年 | 357篇 |
2008年 | 523篇 |
2007年 | 413篇 |
2006年 | 440篇 |
2005年 | 314篇 |
2004年 | 318篇 |
2003年 | 257篇 |
2002年 | 254篇 |
2001年 | 185篇 |
2000年 | 202篇 |
1999年 | 181篇 |
1998年 | 131篇 |
1997年 | 111篇 |
1996年 | 147篇 |
1995年 | 132篇 |
1994年 | 137篇 |
1993年 | 126篇 |
1992年 | 117篇 |
1991年 | 102篇 |
1990年 | 112篇 |
1989年 | 101篇 |
1988年 | 82篇 |
1986年 | 90篇 |
1985年 | 134篇 |
1984年 | 133篇 |
1983年 | 109篇 |
1982年 | 125篇 |
1981年 | 105篇 |
1980年 | 107篇 |
1979年 | 99篇 |
1978年 | 115篇 |
1977年 | 105篇 |
1976年 | 128篇 |
1975年 | 109篇 |
1974年 | 89篇 |
1973年 | 82篇 |
1972年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Zuzana Cibulková Andrea Černá Peter Šimon Ján Uhlár Karol Kosár Peter Lehocký 《Journal of Thermal Analysis and Calorimetry》2012,108(2):415-419
The type of cooperation between antioxidants in the binary mixtures of four substituted diphenylamines and phenotiazine in
the stabilization of styrene-butadiene rubber has been tested. Thermooxidation of the samples has been studied by differential
scanning calorimetry under non-isothermal conditions. The protection factors of the individual stabilizers and their mixtures
were determined. The synergy factors were applied to asses the type of cooperation of antioxidants in the mixtures. From their
values it can be concluded that the type of cooperation depends on temperature. The highest synergistic effect has been observed
for the mixture of phenotiazine and [4-(1-methyl-1-phenyl-ethyl)-phenyl]-phenylamine. 相似文献
922.
Bartosz Mozgawa Dr. Filip Zasada Dr. Monika Fedyna Prof. Kinga Góra-Marek Dr. Edyta Tabor Dr. Kinga Mlekodaj Dr. Jiří Dědeček Prof. Zhen Zhao Dr. Piotr Pietrzyk Prof. Zbigniew Sojka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(68):17159-17180
NH3 temperature-programmed desorption (NH3-TPD) is frequently used for probing the nature of the active sites in CuSSZ-13 zeolite for selective catalytic reduction (SCR) of NOx. Herein, we propose an interpretation of NH3-TPD results, which takes into account the temperature-induced dynamics of NH3 interaction with the active centers. It is based on a comprehensive DFT/GGA+D and first-principles thermodynamic (FPT) modeling of NH3 adsorption on single Cu2+, Cu+, [CuOH]+ centers, dimeric [Cu-O-Cu]2+, [Cu-O22−-Cu]2 species, segregated CuO nanocrystals and Brønsted acid sites (BAS). Theoretical TPD profiles are compared with the experimental data measured for samples of various Si/Al ratios and distribution of Al within the zeolite framework. Copper reduction, its relocation, followed by the intrazeolite olation/oxolation processes, which are concomitant with NH3 desorption, were revealed by electron paramagnetic resonance (EPR) and IR. DFT/FPT results show that the peaks in the desorption profiles cannot be assigned univocally to the particular Cu and BAS centers, since the observed low-, medium- and high-temperature desorption bands have contributions coming from several species, which dynamically change their speciation and redox states during NH3-TPD experiment. Thus, a rigorous interpretation of the NH3-TPD profiles of CuSSZ-13 in terms of the strength and concentration of the active centers of a particular type is problematic. Nonetheless, useful connections for molecular interpretation of TPD profiles can be established between the individual component peaks and the corresponding ensembles of the adsorption centers. 相似文献
923.
Heavily n‐type doped and several nanometres thick In0.485Ga0.515P layers are necessary for various devices. We studied the delta‐doping of this ternary with tellurium; the layers were grown by metalorganic vapour phase epitaxy (MOVPE), and diethyltelluride was used as the precursor. A maximum Hall sheet concentration of 2.75 × 1013 cm–2 was achieved in our samples grown at 560 °C. The Te profiles were analyzed with secondary ion mass spectrometry (SIMS), and a very narrow spectrum with a full width at half maximum of 7.5 nm was measured. This value indicates that the memory effect, referred to in the literature, was practically eliminated with appropriate growth conditions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
924.
O. Lyutakov J. Tůma I. Huttel V. Prajzler J. Siegel V. Švorčík 《Applied physics. B, Lasers and optics》2013,110(4):539-549
Proposed work develops method of polymer surface patterning, suggested in our laboratory. Surface structures with different symmetry and shape are prepared on PMMA and photoresist (Su-8) surface. For surface modification, periodic laser scanning from confocal microscope was used. For optical response improvement meso tetraphenylporphyrine was added either in the polymer bulk or on the top of pristine polymer by vacuum evaporation method. Applications of vacuum deposition methods allow increasing applicability of the technique and preparation of more complex structure. Parameters of the created structures were studied with the aim to better understand the driving forces of the surface modification. Application of prepared structures in photonics as diffraction grating or light coupling elements is also given. 相似文献
925.
Zdeněk Slanina 《光谱学快报》2013,46(10):1965-1973
Abstract ClONO2 is treated ab initio by the second order M?ller-Plesset perturbation approach with the 6-31G? basis set. The minimum-energy structure is planar (Cs symmetry) while in the activated complex for internal rotation around the NO bond the Cl atom exhibits torsion by 90° but the structure has the Cs symmetry, too. For both structures harmonic vibrational frequencies and IR intensities are calculated. The agreement with available observed data from matrix isolation is very good. The MP2 frequencies are mostly somewhat lower comparing to related SCF values. The energetics is also evaluated in the MP4 fourth order perturbation treatment. The best value found for the barrier of internal rotation is 31 kJ/mol, i.e. significantly low. 相似文献
926.
The interior C γ, γ/2-regularity for the first gradient with respect to the space variables of a weak solution to a class of nonlinear second order parabolic systems is proven under the assumption that oscillations of coefficients are controlled by the ellipticity constant. 相似文献
927.
A simple method has been developed for the determination of arsenic and antimony in environmental samples by solid sampling electrothermal atomic absorption spectrometry, which was validated using certified reference materials of soils (S-VM — Soil Eutric Cambisol; S-MS — Soil Orthic Luvisols; S-SP — Soil Rendzina), sewage sludge (WT-L; WT-M) and sediments (NIES2; GBW07906). The analytical procedure combines solid sampling with utilization of a matrix modifier admixture containing 5 µg of W and 5 µg of Mg. The tungsten in the admixture serves to stabilize the solid matrix during atomisation, which results in dramatically reduced non-specific absorption compared with the conventional palladium modifier. Magnesium was efficient in reducing the accumulation of the matrix residue on the platform. An alternative resonance line of 197.2 nm for arsenic and 206.8 nm for Sb was used in order to eliminate the spectral interferences caused by aluminum compounds, and silicon and iron compounds, respectively. Under optimized experimental conditions, the effective in situ analyte/matrix separation was achieved so that the use of aqueous standards for calibration became possible. With the modifier, a 3 SD detection limit of 0.5 µg g−1 As and 0.1 µg g−1 Sb and 10 SD quantification limit of 1.7 µg g−1As and 0.3 µg g−1 Sb and a characteristic mass of 65 pg As and 53 pg Sb were obtained. For all the matrices under scrutiny, a good agreement with certified values was achieved with RSD values less than 10%. 相似文献
928.
Jaroslav Kahovec Frantisek Lednický 《Journal of Macromolecular Science: Physics》2013,52(3-4):vii-viii
929.
Binomial coefficients are used in many fields such as computational and applied mathematics, statistics and probability, theoretical physics and chemistry. For accurate numerical results, the correct calculation of these coefficients is very important. We present some new recurrence relationships and numerical methods for the evaluation of binomial coefficients for negative integers. For this purpose, we give some comparisons of the outputs for different computer programming languages in case of negative integers, and also we wrote two new algorithms for computations. 相似文献
930.
Lucia Dančová Igor Bodík Andrea Blšťáková Zuzana Jakubčová Miloslav Drtil 《Chemical Papers》2008,62(5):451-457
Possibilities of membrane technology and the use of membrane processes in wastewater treatment were investigated. The main
focus was the monitoring of the starting phase of a domestic wastewater treatment plant. Experimental part of the study was
realized at the municipal wastewater treatment plant (WWTP) Devínska Nová Ves — Bratislava during the period from February
2005 to September 2006. The system was stable without any external chemical treatment of the membrane modules and the permeate
quality was very high. Observed decrease of COD and BOD5 values ranged between 91 % and 98 %. The process of nitrification was very successful considering its high efficiency (>
95 %).
Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May
2007. 相似文献