全文获取类型
收费全文 | 367篇 |
免费 | 15篇 |
国内免费 | 21篇 |
专业分类
化学 | 166篇 |
晶体学 | 3篇 |
力学 | 24篇 |
综合类 | 1篇 |
数学 | 74篇 |
物理学 | 59篇 |
无线电 | 76篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 14篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 21篇 |
2015年 | 22篇 |
2014年 | 22篇 |
2013年 | 21篇 |
2012年 | 23篇 |
2011年 | 21篇 |
2010年 | 22篇 |
2009年 | 19篇 |
2008年 | 14篇 |
2007年 | 20篇 |
2006年 | 12篇 |
2005年 | 13篇 |
2004年 | 16篇 |
2003年 | 6篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 10篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1987年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有403条查询结果,搜索用时 250 毫秒
71.
Dalma Czett Katalin Bddi Veronika Nagy Anik Taktsy Jzsef Deli Paul Tone Gyrgy T. Balogh Anna Vincze Attila Agcs 《Molecules (Basel, Switzerland)》2022,27(15)
Carotenoid succinates were synthesized from hydroxy carotenoids and were coupled to a commercially available derivative of melatonin via amide bond for producing more powerful anti-oxidants and yet new hybrid lipophilic bifunctional molecules with additional therapeutic effects. The coupling reactions produced conjugates in acceptable to good yields. Succinylation increased the water solubility of the carotenoids, while the conjugation with melatonin resulted in more lipophilic derivatives. The conjugates showed self-assembly in aqueous medium and yielded relatively stable colloidal solutions in phosphate-buffered saline. Antioxidant behavior was measured with ABTS and the FRAP methods for the carotenoids, the carotenoid succinates, and the conjugates with melatonin. A strong dependence on the quality of the solvent was observed. TEAC values of the new derivatives in phosphate-buffered saline were found to be comparable to or higher than those of parent carotenoids, however, synergism was observed only in FRAP assays. 相似文献
72.
The purpose of this article is to characterize conformal vector fields with respect to the Sasaki metric tensor field on the
tangent bundle of a Riemannian manifold of dimension at least three. In particular, if the manifold in question is compact,
it is found that the only conformal vector fields are Killing vector fields. 相似文献
73.
Mehmet Cem Dikbaş 《International Journal of Electronics》2018,105(10):1716-1727
In this article, a new active building component with electronically tunable transresistive block, voltage difference transresistance amplifier, and its floating frequency dependent negative resistor simulator circuit application is presented. The simulator circuit is shown to operate using single active building block with two grounded passive components, to be electronically tunable over its value which is controlled by an independent current source, not to require any conditions of component matching and to have good sensitivity performance with respect to tracking errors. To examine functionality of the design, a CRD band-pass filter example is given.
Numerous simulation program with integrated circuit emphasis (SPICE) simulations are performed and depicted through the article to verify validity of the study. Taiwan semiconductor manufacturing company (TSMC) 0.18 µm complementary metal oxide semiconductor technology parameters are used through simulations. 相似文献
74.
Periodica Mathematica Hungarica - Let a, b be fixed positive integers such that $$2\not \mid {ab}$$ , $$\gcd (a,b)=1$$ and a is square-free, and let $$h(-a)$$ denote the class number of... 相似文献
75.
76.
Shasha Zhou Renyan Wang Junbo Han Deli Wang Huiqiao Li Lin Gan Tianyou Zhai 《Advanced functional materials》2019,29(3)
Two dimensional (2D) magnetic materials display enormous application potential in spintronic fields. However, most of currently reported magnetic materials are van der Waals layered structure that is easy to be isolated via exfoliation method. By contrast, the studies on non‐van der Waals ultrathin magnetic materials are rare, largely due to the difficulty in fabrication. Rhombohedral Cr2S3, an intensively studied antiferromagnetic transition metal chalcogenide with Neel temperature of ≈120 K, has a typical non‐van der Waals structure. Restricted by the strong covalent bonding in all the three dimensions of non‐van der Waals structure, the synthesis of ultrathin Cr2S3 single crystals is still a challenge that is not achieved yet. Besides, the study on the Raman modes of rhombohedral Cr2S3 is also absent. Herein, by employing space‐confined chemical vapor deposition strategy, ultrathin rhombohedral Cr2S3 single crystals with a thickness down to ≈2.5 nm for the first time are successfully grown. Moreover, a systematically investigation is also conducted on the Raman vibrations of ultrathin rhombohedral Cr2S3. With the aid of angle‐resolved polarized Raman technique, the Raman modes of rhombohedral Cr2S3 for the first time based on crystal symmetry and Raman selection rules are rationally assigned. 相似文献
77.
Summary The carotenoid compositions of four different, industrially-produced paprika pastes (Piros Arany delicacy; Piros Arany hot;
Vega delicacy; Vega hot) were investigated by HPLC, and compared with the composition of fresh red, tomato-shaped paprika
(Capsicum annuum var.lycopersice forme rubrum). In addition, two kinds of ground raw paprika (Er?s Pista; édes Anna) were also investigated. In total, 23 carotenoids have
been identified or tentatively identified, based on their UV-Vis spectra and co-chromatography with authentic samples.
Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001. 相似文献
78.
Beyrul Canbaz Cem Onem Fatma Aydogmus K. Gediz Akdeniz 《Chaos, solitons, and fractals》2012,45(2):188-191
Recently we have investigated the role of the coupling constant in the evolution of the two dimensional spinor-type instantons (Thirring Instantons [1]) in phase space [2] via Heisenberg ansatz. In this paper we study the stability of bifurcation points of the Thirring Instanton’s behaviours in phase space. 相似文献
79.
The practical application of adsorbents with the desired separation properties depends not only upon the adsorption characteristics of the material but also upon the mechanical properties of the packed bed. The packed bed, the vessel surrounding the bed and any internal structure that supports the bed are subjected to both static and cyclic loads during an adsorption process. In order to properly design the vessel and its internal structure, the bulk mechanical properties (most particularly the elastic properties) of the adsorbent bed must be known. The primary focus of this study was to determine the elastic properties of adsorbent beds packed with activated alumina, synthetic molecular sieve 13X or natural zeolite clinoptilolite. The bulk modulus of elasticity was found to be a linear function of applied stress for each of these materials in a range of stresses lower than the bulk crush strength. The Poisson’s ratio for the packed bed was also deduced from these results. 相似文献
80.
Motivated by an investigation of finding necessary and sufficient conditions for the Kolmogorov strong law of large numbers for the general Gini's mean difference, new versions of the classical Lévy, Ottaviani, and Hoffmann-J\ooTrgensen inequalities are obtained for a sequence of Banach space valued random variables. No geometric conditions are imposed on the Banach space. An application to the general Gini's mean difference in a Banach space setting is presented. 相似文献