全文获取类型
收费全文 | 3092篇 |
免费 | 89篇 |
国内免费 | 11篇 |
专业分类
化学 | 2039篇 |
晶体学 | 12篇 |
力学 | 89篇 |
数学 | 395篇 |
物理学 | 657篇 |
出版年
2024年 | 7篇 |
2023年 | 28篇 |
2022年 | 100篇 |
2021年 | 99篇 |
2020年 | 82篇 |
2019年 | 87篇 |
2018年 | 66篇 |
2017年 | 64篇 |
2016年 | 138篇 |
2015年 | 101篇 |
2014年 | 126篇 |
2013年 | 192篇 |
2012年 | 182篇 |
2011年 | 236篇 |
2010年 | 136篇 |
2009年 | 199篇 |
2008年 | 180篇 |
2007年 | 197篇 |
2006年 | 149篇 |
2005年 | 116篇 |
2004年 | 95篇 |
2003年 | 69篇 |
2002年 | 64篇 |
2001年 | 58篇 |
2000年 | 54篇 |
1999年 | 36篇 |
1998年 | 27篇 |
1997年 | 31篇 |
1996年 | 41篇 |
1995年 | 30篇 |
1994年 | 24篇 |
1993年 | 18篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1975年 | 9篇 |
1973年 | 4篇 |
1916年 | 3篇 |
排序方式: 共有3192条查询结果,搜索用时 15 毫秒
181.
Aurelian Luca Maria Sahagia Andrei Antohe Mihail-Răzvan Ioan Leonardo Şerbina Constantin Ivan 《Journal of Radioanalytical and Nuclear Chemistry》2017,311(2):1075-1079
In order to validate its original method for the radon gas activity standardization and to assure the international metrological traceability and equivalence, the Radionuclide Metrology Laboratory of IFIN-HH participated recently in the international comparison CCRI(II)-K2.Rn-222, organized by the International Committee for Weights and Measures—CIPM-CCRI(II)-Radionuclide Measurements. The radon gas sample received, the measurement equipment and the experimental procedures are described. Because the comparison is underway, the results are presented only as relative values to the liquid scintillator vial measurement result. The uncertainty budget of the measurements performed is provided. 相似文献
182.
Anise Akhundi Elisa I. García-López Giuseppe Marcì Aziz Habibi-Yangjeh Leonardo Palmisano 《Research on Chemical Intermediates》2017,43(9):5153-5168
Carbon nitride photocatalysts have been prepared by different methodologies, such as chemical ultrasonic irradiation (sonochemical treatment), hydrothermal and ball milling and thermoexfoliation, and have been used for the selective oxidation of 5-hydroxymethyl-2-furaldehyde (HMF) to form 2,5-furandicarboxyaldehyde (FDC) in water suspension both under UV and natural solar irradiation. The physico-chemical features of the photocatalysts have been studied by X-ray diffraction, infrared spectroscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, scanning electron microscopy, and specific surface area measurements. The results indicate that exfoliation of carbon nitrides can increase the conversion of HMF and the selectivity to FDC. In particular, samples exfoliated by both thermal and acidic ultrasonic irradiation treatments showed the best photocatalytic performance. 相似文献
183.
Dayana Borges Bittar Tiago Augusto Catelani Karina Nigoghossian Hernane da Silva Barud Sidney José Lima Ribeiro Leonardo Pezza 《Analytical letters》2017,50(5):829-841
A colorimetric method based on silver nanoparticles was developed for the determination of melamine in milk. Silver nanoparticles were synthesized without any stabilizer, using sodium borohydride as the reducing agent. Optimization of the variables for the formation of the nanoparticles was performed by factorial design, resulting in stable colloidal silver nanoparticles with a mean diameter of 14.0?±?2.7?nm. Spectrophotometric measurements performed at 475?nm showed a linear range from 0.033 to 1.50?mg?L?1 of melamine with limits of detection and quantification of 0.009 and 0.031?mg?L?1, respectively. The method provided highly sensitive determination of melamine in milk. 相似文献
184.
Magda Carvalho Henriques Maria Amparo F. Faustino Artur M. S. Silva Juliana Felgueiras Margarida Fardilha 《Journal of Coordination Chemistry》2017,70(14):2393-2408
The coordination of ruthenium(II) complexes to anionic oxygen-based donors are very rare. This study describes a simple, one-pot method for obtaining [ruthenium(II)(trithiacyclononane)(curcumin)(S-DMSO)]Cl (1) in 37% yield. The structural characterization of complex 1 by elemental analysis, FT-IR, 1-D and 2-D NMR, ESI+-MS as well as UV–vis and fluorescence spectroscopies are presented. The DNA-melting temperature (Tm) assay shows that salmon sperm DNA (smDNA) in the presence of complex 1 has a higher melting temperature, with ΔTm = 7.4 °C, while in the presence of curcumin the melting temperature remains unaltered. The in vitro cytotoxic activities of curcumin and complex 1 were investigated using the tumor human prostate cell line, PC-3, and the healthy cell line, PNT-2. Complex 1 is innocuous toward normal prostate epithelial cells and, whereas curcumin is toxic, with inhibition rates of ca. 35 and 65% at 50 and 80 μM, respectively. On the tumor cell line PC-3, complex 1 did not cause viability changes, whereas curcumin exhibited dose-dependent inhibition, with ca. 73% inhibition at the highest concentration tested, i.e. 80 μM. This study suggests that coordination with the trithiacyclononane ruthenium(II) scaffold stabilizes the photochemical properties of curcumin and strongly changes its biologic activity. 相似文献
185.
186.
A new apparatus for the extraction of organic compounds from sea water is described. With this apparatus it is possible to extract 54 standard compounds with high recovery percentages from 9 1 of sea water with 3 ml ofn-hexane. The analysis time (about 1 h) is appreciably lower than those of the extraction methods based on RP-18 and Carbopack-B adsorption (about 15 h). Furthermore, it is possible to analyze samples without filtration. An application of this method to the analysis of Tirreno sea water is reported. 相似文献
187.
R. Fausto L.A.E. Batista De Carvalho J.J.C. Teixeira-Dias 《Journal of computational chemistry》1992,13(7):799-809
The internal rotation in the HC(?X)YCH2CH3 (X, Y = O or S) series of molecules was studied by the ab initio SCF-MO method using 3-21G and 3-21G + d(ζ = 0.65S) basis sets. Energies and structures of several conformations of these molecules, determined by gradient geometry refinement, are reported and used to assess the effects of oxygen-by-sulphur substitution on molecular properties. The nature and relative importance of intramolecular interactions involving both the ? CH2CH3 and the HC(?X)Y (X, Y = O or S) fragments are also discussed. © 1992 by John Wiley & Sons, Inc. 相似文献
188.
189.
Rosa Maria Miró -Roig Helena Soares 《Proceedings of the American Mathematical Society》2008,136(11):3751-3757
A very long-standing problem in Algebraic Geometry is to determine the stability of exceptional vector bundles on smooth projective varieties. In this paper we address this problem and we prove that any exceptional vector bundle on a smooth complete intersection -fold of type with and is stable.
190.
We present a form of the Mean Value Theorem (MVT) for a continuous function f between metric spaces, connecting it with the possibility to choose the relation of f in a homeomorphic way. We also compare our formulation of the MVT with the classic one when the metric spaces are open subsets of Banach spaces. As a consequence, we derive a version of the Mean Value Propriety for measure spaces that also possesses a compatible metric structure. 相似文献