全文获取类型
收费全文 | 380篇 |
免费 | 14篇 |
专业分类
化学 | 257篇 |
力学 | 2篇 |
数学 | 35篇 |
物理学 | 100篇 |
出版年
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 17篇 |
2014年 | 10篇 |
2013年 | 24篇 |
2012年 | 19篇 |
2011年 | 14篇 |
2010年 | 11篇 |
2009年 | 16篇 |
2008年 | 13篇 |
2007年 | 22篇 |
2006年 | 20篇 |
2005年 | 11篇 |
2004年 | 10篇 |
2003年 | 8篇 |
2001年 | 5篇 |
1999年 | 5篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1986年 | 3篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1965年 | 2篇 |
1963年 | 2篇 |
1956年 | 2篇 |
1935年 | 2篇 |
1928年 | 2篇 |
1927年 | 2篇 |
1920年 | 2篇 |
1910年 | 2篇 |
1907年 | 2篇 |
1889年 | 2篇 |
排序方式: 共有394条查询结果,搜索用时 31 毫秒
21.
22.
Lisa A. Bischoff Jarno Riefer Raphael Wirthensohn Tobias Bischof Rüdiger Bertermann Dr. Nikolai V. Ignat'ev Prof. Dr. Maik Finze 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(60):13615-13620
Salts of the tetrakis(pentafluoroethyl)aluminate anion [Al(C2F5)4]− were obtained from AlCl3 and LiC2F5. They were isolated with different counter-cations and characterized by NMR and vibrational spectroscopy and mass spectrometry. Degradation of the [Al(C2F5)4]− ion was found to proceed via 1,2-fluorine shifts and stepwise loss of CF(CF3) under formation of [(C2F5)4−nAlFn]− (n=1–4) as assessed by NMR spectroscopy and mass spectrometry and supported by results of DFT calculations. In addition, the [(C2F5)AlF3]− ion was structurally characterized. 相似文献
23.
Dr. Florian Rauch Peter Endres Dr. Alexandra Friedrich Dr. Daniel Sieh Dr. Martin Hähnel Dr. Ivo Krummenacher Prof. Dr. Holger Braunschweig Prof. Dr. Maik Finze Prof. Dr. Lei Ji Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(57):12951-12963
Using a new divergent approach, conjugated triarylborane dendrimers were synthesized up to the 2nd generation. The synthetic strategy consists of three steps: 1) functionalization, via iridium catalyzed C−H borylation; 2) activation, via fluorination of the generated boronate ester with K[HF2] or [N(nBu4)][HF2]; and 3) expansion, via reaction of the trifluoroborate salts with aryl Grignard reagents. The concept was also shown to be viable for a convergent approach. All but one of the conjugated borane dendrimers exhibit multiple, distinct and reversible reduction potentials, making them potentially interesting materials for applications in molecular accumulators. Based on their photophysical properties, the 1st generation dendrimers exhibit good conjugation over the whole system. However, the conjugation does not increase further upon expansion to the 2nd generation, but the molar extinction coefficients increase linearly with the number of triarylborane subunits, suggesting a potential application as photonic antennas. 相似文献
24.
Zhenguo Huang Suning Wang Rian D. Dewhurst Nikolai V. Ignat'ev Maik Finze Holger Braunschweig 《Angewandte Chemie (International ed. in English)》2020,59(23):8800-8816
Boron's unique position in the Periodic Table, that is, at the apex of the line separating metals and nonmetals, makes it highly versatile in chemical reactions and applications. Contemporary demand for renewable and clean energy as well as energy‐efficient products has seen boron playing key roles in energy‐related research, such as 1) activating and synthesizing energy‐rich small molecules, 2) storing chemical and electrical energy, and 3) converting electrical energy into light. These applications are fundamentally associated with boron's unique characteristics, such as its electron‐deficiency and the availability of an unoccupied p orbital, which allow the formation of a myriad of compounds with a wide range of chemical and physical properties. For example, boron's ability to achieve a full octet of electrons with four covalent bonds and a negative charge has led to the synthesis of a wide variety of borate anions of high chemical and electrochemical stability—in particular, weakly coordinating anions. This Review summarizes recent advances in the study of boron compounds for energy‐related processes and applications. 相似文献
25.
The authors propose a method for the extraction of material parameter and thickness information from sub-100-μm thin samples using non-differential transmission terahertz time domain spectroscopy. The approach relies on an additional Fourier transform of the frequency dependent material parameters to a quasi space regime. In this quasi space, periodic Fabry-Perot oscillations from the frequency domain, which originate from multiple reflections inside the sample, correspond to discrete peaks. By iterative minimization of these peaks, the highly precise thickness information along with the refractive index and absorption coefficient of the sample can be determined. Experimental verification of the approach is also provided. 相似文献
26.
Seeing through fog is better with holography than with ordinary photography or human vision. This has to do with the Doppler effect, which is imparted on the light that is scattered by moving fog droplets. Experiments of this type are known since about ten years. So far, these experiments were always performed with off-axis holography, while we now propose to use on-axis holography. The new approach is better matched to the capabilities of the electronic components that are needed for hologram reconstruction in real-time. Advantages in resolution and dynamic range are predicted and verified experimentally. 相似文献
27.
The energy dependence of total cross sections for twenty-three two-body hypercharge-exchange reactions is studied. It is found that the planar reactions have in general a less steep fall-off with increasing energy than the non-planar reactions. Explanations of the difference in terms of kinematics and dynamics (baryon exchange and t-channel exchange effects) are discussed and found highly improbable. Implications of the effects observed are discussed. 相似文献
28.
It is possible to overcome the Abbe limit of resolution by a factor two. For this one needs the A PRIORI knowledge, that the object is not birefringent or dichroic. That is to say, the object acts identically on both of the independant polarization components of the incident light. Then already one polarization component would be enough to form an image as complete as it is permitted by the lens system and by the aperture. The other polarization component would produce an identical image. Hence the capacity of the other polarization component to carry information from the object plane to the image plane is vasted. This vaste can be avoided by means of a special set up, containing e.g. twoWollaston prism. The result is the doubling in resolution without any increase of the aperture. This has been confirmed experimentally both for coherent and incoherent illumination. 相似文献
29.
K. Pretzl G. Ambrosini R. Arsenescu C. Baglin H. P. Beck K. Borer A. Bussière K. Elsener Ph. Gorodetzky J. P. Guillaud P. Hess S. Kabana R. Klingenberg G. Lehmann T. Lindén K. D. Lohmann R. Mommsen U. Moser K. Pretzl J. Schacher R. Spiwoks F. Stoffel J. Tuominiemi M. Weber 《Acta Physica Hungarica A》2001,14(1-4):297-308
Besides the dedicated search for strangelets NA52 measures light (anti)particle and (anti)nuclei production over a wide range of rapidity. Compared to previous runs the statistics has been increased in the 1998 run by more than one order of magnitude for negatively charged objects at different spectrometer rigidities. Together with previous data taking at a rigidity of ?20 GeV/c we obtained $10^6 \bar p, 10^3 \bar d$ and two $\overline {^3 He} $ without centrality requirements. We measured nuclei and antinuclei (p, d, $\bar p,\bar d$ ) near midrapidity covering an impact parameter range of b ~ 2–12 fm. Our results strongly indicate that nuclei and antinuclei are mainly produced via the coalescence mechanism. However, the centrality dependence of the antibaryon to baryon ratios shows that antibaryons are diminished due to annihilation and breakup reactions in the hadron dense environment. The volume of the particle source extracted from coalescence models agrees with results from pion interferometry for an expanding source. The chemical and thermal freeze-out of nuclei and antinuclei appear to coincide with each other and with the thermal freeze-out of hadrons. 相似文献
30.
W. Lohmann 《Pramana》2007,69(6):1209-1214
An overview is given on the test-beam programs to perform detector and system studies for luminosity and energy measurements
and beam diagnostics for luminosity optimization.
相似文献