全文获取类型
收费全文 | 292篇 |
免费 | 3篇 |
专业分类
化学 | 248篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 12篇 |
物理学 | 32篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 8篇 |
2013年 | 23篇 |
2012年 | 7篇 |
2011年 | 10篇 |
2010年 | 6篇 |
2009年 | 8篇 |
2008年 | 22篇 |
2007年 | 22篇 |
2006年 | 16篇 |
2005年 | 21篇 |
2004年 | 15篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 12篇 |
1994年 | 14篇 |
1993年 | 5篇 |
1991年 | 5篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1963年 | 1篇 |
1960年 | 2篇 |
1957年 | 1篇 |
1912年 | 1篇 |
1908年 | 1篇 |
排序方式: 共有295条查询结果,搜索用时 421 毫秒
91.
Giovanni Zin 《Annali di Matematica Pura ed Applicata》1963,62(1):351-383
Sunto Si estende dapprima allo spazio euclideo a quattro dimensioni e poi allo spazio-tempo pseudoeuclideo la particolare classe
di funzioni tensoriali di un vettore che, in una memoria precedente dello stesso autore, era stata considerata limitatamente
allo spazio euclideo tridimensionale. Tali tensori godono della proprietà che al mutare del sistema di riferimento le espressioni
analitiche delle nuove componenti del tensore, scritte rispetto alle nuove componenti del vettore, conservano l'invarianza
formale. L'analisi di tali funzioni tensoriali mette in evidenza che le espressioni analitiche delle loro componenti risultano
indeterminate a meno di un piccolo numero di funzioni del solo modulo del vettore, chiamate funzioni di distanza (f. d. d.).
Dall' attuale analisi risulta che il numero delle f. d. d. atte ad individuare un tensore dello stesso ordine diminuisce con
l aumentare del numero delle dimensioni dello spazio. Così per il tenore del 20 ordine si hanno tre funzioni di distanza nell' S3 e due nell' S4. Per il tensore del 30 ordine si hanno 7 f. d. d. nell' S3 e 5 nell' S4. Il tensore ql, m, n emisimmetrico negli indici l ed n è individuato nello spazio-tempo da una sola f. d. d.
Nell' ultima parte della memoria si cerca un' interpretazione dell' elettromagnetismo di Maxwell-Lorentz mediante le dette
funzioni tensoriali nello spazio-tempo. Si compone il detto tensore emisimmetríco ql, m, n con il tetraelemento di linea oraria percorsa da una carica puntiforme in moto e si integra lungo la linea oraria. Il detto
tensore ql, m, n è funzione, appartenente alla classe in considerazione, del tetrasegmento che unisce il punto-evento in cui si trova la carica
con il punto-evento in cui si vuole calcolare il campo elettromagnetico da essa generato. Scegliendo opportunamente l' unica
f. d. d. che individua ql, m, n è possibile ottenere il tensore elettromagnetico generato dalla carica.
Si riesce così ad isolare l' aspetto geometrico dell' elettromagnetismo di Maxwell-Lorentz dall'aspetto analitico, che consiste
nella particolare f. d. d. del tensore elettromagnetico ql, m, n. 相似文献
92.
93.
94.
95.
Thin binary blends of poly(styrene‐b‐methyl methacrylate) (PS‐PMMA) block copolymers in films where the lamellar thickness of one domain is controlled while preserving the thickness of the other domain were demonstrated without microphase separation. One of the block copolymers used here was short and symmetric, and the other was long and asymmetric; the molecular weights of the PMMA block chains in the constituents were similar. A random copolymer brush was introduced and film thickness and composition of brush were adjusted to induce perpendicular orientation in thin film. As the blend composition of the long asymmetric block copolymer increased, the PS lamellar thickness increased from 15.8 to 25.1 nm, whereas the PMMA lamellar thickness remained constant at approximately 14 nm (the thickness decreased slightly from 14.0 to 13.3 nm). The domain spacing behavior in thin film was consistent in the bulk. These results were compared with the Birshtein, Zhulina, and Lyatskaya model and the theories for pure block copolymers in the strong segregation limit and in the intermediate segregation regime. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1393–1399 相似文献
96.
Xuefei Guo Woo Hyoung Lee Noe Alvarez Vesselin N. Shanov William R. Heineman 《Electroanalysis》2013,25(7):1599-1604
Carbon nanotubes (CNTs) have attracted intense interest due to their excellent properties, such as increased electrode surface area, fast electron transfer rate, significant mechanical strength and good chemical stability. CNT threads, spun from shorter CNTs, inherit the advantages of CNTs, while avoiding the potential toxicity caused by individual CNTs. In this work, microelectrodes based on CNT threads were used to detect trace zinc by anodic stripping voltammetry with an estimated detection limit of 1.4 nM without mercury or bismuth films. CNT threads showed promise for measuring trace metals in small sample volumes without stirring such as encountered in some in vivo and in vitro applications. 相似文献
97.
A simple fabrication approach for achieving nanoparticle patterns based on a room temperature chemically driven strategy is reported. Suitably engineered colloidal luminescent nanocrystals (NCs) (4 and 6 nm in diameter), namely organic capped and silica-coated negatively charged CdSe@ZnS NCs, have been selectively assembled onto defined domains in a binary hydrophobic/hydrophilic chemical pattern, purposely fabricated by combining microcontact printing and wet chemistry procedures. The goal of the work has been to investigate the experimental parameters governing the assembly process at molecular level, in order to elucidate factors regulating interactions at the interfaces. For this purpose, specific sets of conditions, namely substrate patterns and NCs with distinct surface functionalization, have been prepared and tested using different NC dispersing solvents. The NC assembly has been demonstrated driven by non-covalent forces, namely Van der Waals or electrostatic interactions occurring at the NC/substrate interface. The overall study has provided a comprehensive understanding of the role of solvent and molecular chemistry at interfaces in NC assembling. The obtained results can be valuable to set up reliable procedures for developing reproducible patterning protocols potentially useful for the fabrication of NC-based devices. 相似文献
98.
This work studies the amount of gaseous and particle emissions and deposits on heat exchanger surfaces in a boiler firedwith commercially available pellets and with pellets primed with magnesium oxide and magnesium hydroxide.The combustionexperiments were performed on a residential boiler of 20 kW.Substrates placed in the heat exchanger was analysed with SEM-EDX-mapping to evaluate the chemical composition of the deposits.The results show that particle emissions(PM 2.5)using the additivesincreased by about 50%and the mass of the deposits in the flue gas heat exchanger(excluding loose fly ash)increased by about25%compared to the combustion of pellets without additives.The amount of additives was found to be eight times higher than theamount of the main alkali metals potassium(K)and sodium(Na)which leads to the assumption that the additives were overdosedand therefore caused the problems reported.The SEM analysis of the substrates placed in the flue gas heat exchanger indicate that thedeposits of sodium(Na),potassium(K),chlorine(Cl)and sulphur(S)decrease using the additives.If this was due to theexpected chemical reactions or due to the loose fly ash covering the substrates after the test,could not be determined in this study. 相似文献
99.
Chong-Kwang Lee Jae-Hoon Kim E-Joon Choi Wang-Cheol Zin Liang-Chy Chien 《Liquid crystals》2013,40(12):1749-1754
A new banana-shaped achiral compound, 1,3-phenylene bis[4-(3-fluoro-4-n-octyloxyphenyliminomethyl)benzoate] (PBFOB) was synthesized and its antiferroelectric liquid crystallinity determined. The PBFOB was characterized by differential scanning calorimetry, X-ray diffractometry in the small and wide angle regions, and polarizing optical microscopy; its polarization and antiferroelectric properties were also investigated. The presence of a lateral fluoro-substituent in the banana-shaped achiral molecules containing a Schiff's base mesogen induced a decrease in melting temperature and formation of the switchable smectic B2 phase in the melt. The spontaneous polarization for PBFOB was about 250 nC cm-2 and the polarization of this phase switched on the reversal of an applied electric field. 相似文献
100.
Lin Z Ramezani H Eichelkraut T Kottos T Cao H Christodoulides DN 《Physical review letters》2011,106(21):213901
Parity-time (PT) symmetric periodic structures, near the spontaneous PT-symmetry breaking point, can act as unidirectional invisible media. In this regime, the reflection from one end is diminished while it is enhanced from the other. Furthermore, the transmission coefficient and phase are indistinguishable from those expected in the absence of a grating. The phenomenon is robust even in the presence of Kerr nonlinearities, and it can also effectively suppress optical bistabilities. 相似文献