全文获取类型
收费全文 | 500篇 |
免费 | 6篇 |
国内免费 | 11篇 |
专业分类
化学 | 342篇 |
晶体学 | 1篇 |
力学 | 32篇 |
综合类 | 11篇 |
数学 | 43篇 |
物理学 | 88篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 22篇 |
2021年 | 19篇 |
2020年 | 16篇 |
2019年 | 13篇 |
2018年 | 17篇 |
2017年 | 9篇 |
2016年 | 18篇 |
2015年 | 14篇 |
2014年 | 16篇 |
2013年 | 41篇 |
2012年 | 38篇 |
2011年 | 33篇 |
2010年 | 20篇 |
2009年 | 19篇 |
2008年 | 23篇 |
2007年 | 33篇 |
2006年 | 20篇 |
2005年 | 21篇 |
2004年 | 6篇 |
2003年 | 18篇 |
2002年 | 29篇 |
2001年 | 6篇 |
2000年 | 1篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 1篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有517条查询结果,搜索用时 15 毫秒
71.
Dark transient capacitance measurements have been used to investigate the deeplevel content of red GaP LEDs. Thermal emission rate data is obtained and the 0.75 eV “killer” centre is identified from the signature. 相似文献
72.
Summary The magnetic susceptibilities of certain vanadium pentoxide systems supported by kieselgur have been determined in the temperature
interval 30° to 400° C. The plot of reciprocal susceptibility against temperature for all the systems studied indicates sudden
deflections at temperatures which are about 150° lower than those of optimum catalytic activity. It has been suggested that
these points may mark the temperatures of commencement of structural changes which may be responsible for the activity of
these catalysts.
Zusammenfassung Die magnetische Susceptibilit?t gewisser Vanadium-Pentoxyd-Systeme mit Kieselgur als Tr?ger wurden im Temperaturintervall zwischen 30 und 400° C bestimmt. Die Auftragung der reziproken Susceptibilit?t gegen die Temperatur zeigt für alle untersuchten Systeme pl?tzliche Knicke bei Temperaturen, die etwa 150° niedriger liegen als die optimale katalytische Aktivit?t. Es wird vermutet, da? diese Knickpunkte die Temperaturen des Beginns von Struktur?nderungen zeigen, die für die Aktivit?t dieser Katalysatoren verantwortlich sind.相似文献
73.
We have studied the photoinduced trans/cis isomerization of the protonated form of p-hydroxycinnamic thiophenyl ester, a model chromophore of the photoactive yellow protein (PYP), in crystalline phase, by both fluorescence and infrared spectroscopies. The conversion from trans to cis configuration is revealed by a shift of the fluorescence peak and by inspection of the infrared maker bands. The crystal packing apparently stabilizes the cis photoproduct, suggesting different environmental effects from the solvent molecules for this model chromophore in liquid solutions or from the amino acid residues for the PYP chromophore. 相似文献
74.
Four new carbamates (RZ1–RZ4) were synthesized from different amine moieties through reported methods. The reaction was monitored using thin layer chromatography and characterization was done using m.p., fourier‐transform infrared spectroscopy (FTIR), and X‐ray diffraction (XRD) techniques. Density functional theory (DFT) studies were carried out using Gaussian 09 software to compare the theoretical and practical parameters of the synthesized compounds. Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were also drawn to calculate the energy difference between orbitals. In‐vitro enzyme inhibition potential against acetylcholine esterase (AChE), butyrylcholine esterase (BChE), and protease was checked through standard protocols that suggested moderate inhibition against selected enzymes. Docking studies were also carried out, which depicted that these compounds have ability to bind on the active site of AChE and BChE. 相似文献
75.
Andrew Care Helena Nevalainen Peter L. Bergquist Anwar Sunna 《Applied biochemistry and biotechnology》2014,173(8):2225-2240
An inorganic-binding peptide sequence with high affinity to silica-containing materials was fused to a glycoside hydrolase GH26 mannanase, ManA, from the extremely thermophilic bacterium Dictyoglomus thermophilum. The resulting recombinant enzyme produced in Escherichia coli, ManA-Linker, displayed high binding affinity towards synthetic zeolite while retaining its catalytic activity at 80 °C. ManA-Linker was able to bind to the zeolite at different pH levels, indicating a true pH-independent binding. However, complete degradation of the peptide linker was observed when the recombinant ManA-Linker was exposed to the supernatant from the filamentous fungus Trichoderma reesei. This degradation was caused by extracellular proteinases produced by T. reesei during its growth phase. Several derivatives of ManA-Linker were designed and expressed in E. coli. All the derivatives carrying a single sequence of the linker were still susceptible to T. reesei proteinase degradation. Complete substitution of the linker sequence by (GGGGS)16 resulted in a proteinase-resistant ManA derivative, ManA-Linker-(GGGGS)16, which was able to bind to zeolite in a pH-dependent manner. 相似文献
76.
77.
Polysulfides as biologically active ingredients of garlic 总被引:2,自引:0,他引:2
Garlic has long been considered as a natural remedy against a range of human illnesses, including various bacterial, viral and fungal infections. This kind of antibiotic activity of garlic has mostly been associated with the thiosulfinate allicin. Even so, recent studies have pointed towards a significant biological activity of trisulfides and tetrasulfides found in various Allium species, including a wide range of antibiotic properties and the ability of polysulfides to cause the death of certain cancer cells. The chemistry underlying the biological activity of these polysulfides is currently emerging. It seems to include a combination of several distinct transformations, such as oxidation reactions, superoxide radical and peroxide generation, decomposition with release of highly electrophilic S(x) species, inhibition of metalloenzymes, disturbance of metal homeostasis and membrane integrity and interference with different cellular signalling pathways. Further research in this area is required to provide a better understanding of polysulfide reactions within a biochemical context. This knowledge may ultimately form the basis for the development of 'green' antibiotics, fungicides and possibly anticancer agents with dramatically reduced side effects in humans. 相似文献
78.
79.
80.
A. Jeyabharathi M. N. Ponnuswamy S. Nanjundan Hoong‐Kun Fun Suchada Chantrapromma Anwar Usman Ibrahim Abdul Razak 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(1):o26-o28
Chalcones (α,β‐unsaturated ketones) are effective antitumour agents. It has been proved that having halogen or methoxy groups substituted in various positions of the phenyl ring enhances the activity of chalcones many times. The title compounds, C21H20O5 and C19H15BrO3, respectively, were chosen for crystallographic study in order to determine their structures and conformations. In both compounds, the keto group is in the s‐cis conformation and is almost planar. There are weak intramolecular interactions in both structures. 相似文献