全文获取类型
收费全文 | 2324篇 |
免费 | 62篇 |
国内免费 | 9篇 |
专业分类
化学 | 1804篇 |
晶体学 | 38篇 |
力学 | 23篇 |
数学 | 134篇 |
物理学 | 396篇 |
出版年
2021年 | 19篇 |
2020年 | 13篇 |
2019年 | 24篇 |
2018年 | 16篇 |
2016年 | 28篇 |
2015年 | 29篇 |
2014年 | 38篇 |
2013年 | 91篇 |
2012年 | 95篇 |
2011年 | 107篇 |
2010年 | 70篇 |
2009年 | 55篇 |
2008年 | 103篇 |
2007年 | 133篇 |
2006年 | 148篇 |
2005年 | 156篇 |
2004年 | 115篇 |
2003年 | 97篇 |
2002年 | 104篇 |
2001年 | 31篇 |
2000年 | 37篇 |
1999年 | 32篇 |
1998年 | 31篇 |
1997年 | 28篇 |
1996年 | 38篇 |
1995年 | 26篇 |
1994年 | 20篇 |
1993年 | 28篇 |
1992年 | 22篇 |
1991年 | 15篇 |
1990年 | 18篇 |
1989年 | 16篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 24篇 |
1985年 | 42篇 |
1984年 | 43篇 |
1983年 | 31篇 |
1982年 | 37篇 |
1981年 | 34篇 |
1980年 | 28篇 |
1979年 | 36篇 |
1978年 | 36篇 |
1977年 | 34篇 |
1976年 | 41篇 |
1975年 | 29篇 |
1974年 | 29篇 |
1973年 | 31篇 |
1972年 | 15篇 |
1971年 | 11篇 |
排序方式: 共有2395条查询结果,搜索用时 15 毫秒
1.
By extracting combinatorial structures in well-solved nonlinear combinatorial optimization problems, Murota (1996,1998) introduced the concepts of M-convexity and L-convexity to functions defined over the integer lattice. Recently, Murota–Shioura (2000, 2001) extended these concepts to polyhedral convex functions and quadratic functions in continuous variables. In this paper, we consider a further extension to more general convex functions defined over the real space, and provide a proof for the conjugacy relationship between general M-convex and L-convex functions.Mathematics Subject Classification (1991): 90C10, 90C25, 90C27, 90C35This work is supported by Grant-in-Aid of the Ministry of Education, Culture, Sports, Science and Technology of Japan 相似文献
2.
3.
We report on the simultaneous generation of phase-conjugate signals by degenerate four-wave mixing (DFWM) and holographic processes using a nanosecond pulse and a CW lasers in polyvinyl alcohol (PVA) films doped with four kinds of saturable absorbing dyes. For the pulse laser, of the four kinds of dye-doped PVA films, the erythrosine B-doped PVA and uranine doped-PVA films generate PC signals only by the DFWM process, while the other dye-doped PVA films generate PC signals simultaneously by not only the DFWM process but also the holographic process. Especially, the safranin T-doped PVA film generates strong PC signals by the holographic process. In contrast, all of the dye-doped PVA films generate the two types of PC signals for the CW laser. The fading of dye molecules is found to result in the generation of the holographic component of PC signals which governs the temporal behavior of the total PC signals. 相似文献
4.
We demonstrate the potential of femtosecond two-color pulse interferometry for in vitro optical glucose monitoring, by dispersion of the group refractive index in a glucose solution sample with respect to a red-color
light and a blue-color light. By comparison with femtosecond one-color pulse interferometry, the basic performance of the
present system with regard to sensitivity, quantitativeness, and tolerance to surrounding disturbances, is evaluated. The
resulting accuracy and precision of glucose determination are 77 and 118mg/dl for 10-mm-sample-thickness, respectively. This
near-common-path configuration of the two-color pulse light provides good stability to fluctuations of sample temperature,
which is important in clinical applications. Considering the performance of femtosecond two-color pulse interferometry as
an optical glucose sensor, a suitable measurement site for in vivo optical glucose monitoring is discussed. 相似文献
5.
A cyanine dye, 2-[7-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-1,3,5-heptatrienyl]-1,3,3-trimethyl-3H-indolium iodide (NK-125), is doped in 4-cyano-4'-pentylbiphenyl (5 CB), and the mixture is sandwiched between two pieces of rubbed glass plates. The third-order nonlinear optical properties of the oriented NK-125-SCB layers are measured by the resonant femtosecond degenerate four-wave mixing (DFWM) technique at 760 nm. The third-order nonlinear optical susceptibility of one of the present samples is 5.5×10^-8 esu. The slow DFWM response of the NK-125-SCB layers due to a population grating is accelerated by the increasing laser power because of amplified spontaneous emission (ASE). On the other hand, we do not observe a similar phenomenon for NK-125- polyethylene glycol (PEG-400). Oriented NK-125 molecules in nematic liquid crystals must have very high ASE efficiency. Hence the population grating in a DFWM signal disappears within about 4 ps. It is expected that NK-125-SCB can be used as a material for very fast all-optical switching. 相似文献
6.
7.
Abstract— Irradiation of near-UV light in the presence of FeCl3 caused oxidation of adenosine with concomitant reduction of Fe(III) under either aerobic or anaerobic atmosphere. Major photoproducts were adenine and adenosine-5'-aldehyde, showing that oxidation took place mostly at the ribose moiety of adenosine. Detailed study showed that the reaction proceeded by the light absorption due to Fe(III) at 300-350 nm. 相似文献
8.
9.
Tsunehisa Hirashita Yousuke Hayashi Kazuma Mitsui Shuki Araki 《Tetrahedron letters》2004,45(16):3225-3228
Vinyl and methylindium ate complexes (indates) were prepared and both the tendency of immigration and regioselectivity toward cinnamyl bromide were investigated. The vinyl group was more preferably transferred than the Me group, giving a regioisomeric mixture of SN2 and SN2′ products. The ratio of SN2/SN2′ selectivity can be controlled by solvents; in the presence of polar solvents, such as N-butylpyrrolidone (NBP) and THF, the SN2′ product was mainly obtained, whereas the SN2 product was selectively prepared in solutions containing hexane. The vinylindium compound, generated by the reaction of allylic-type diindium reagents with imine, was also converted to the corresponding vinyl indate, which was allowed to react with allyl chloride to give a three-component coupling product. 相似文献
10.