全文获取类型
收费全文 | 675篇 |
免费 | 20篇 |
国内免费 | 1篇 |
专业分类
化学 | 404篇 |
晶体学 | 28篇 |
力学 | 4篇 |
数学 | 65篇 |
物理学 | 195篇 |
出版年
2023年 | 6篇 |
2022年 | 14篇 |
2021年 | 14篇 |
2020年 | 18篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 25篇 |
2015年 | 14篇 |
2014年 | 45篇 |
2013年 | 49篇 |
2012年 | 46篇 |
2011年 | 40篇 |
2010年 | 28篇 |
2009年 | 31篇 |
2008年 | 34篇 |
2007年 | 19篇 |
2006年 | 29篇 |
2005年 | 27篇 |
2004年 | 24篇 |
2003年 | 20篇 |
2002年 | 13篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 21篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 5篇 |
1936年 | 4篇 |
排序方式: 共有696条查询结果,搜索用时 15 毫秒
641.
Lyocell is a type of regenerated cellulose. Fibres spun from cellulose solution in N-methylmorpholine-N-oxide hydrate consist of crystalline cellulose II and amorphous cellulose. Lyocell fabrics were treated with aqueous sodium hydroxide solution (NaOH) to study the influence of alkali on optical and structural properties. It was observed that sodium hydroxide treatment causes the density, orientation and crystallinity of lyocell fibre to decrease with increasing sodium hydroxide concentration, a corresponding decrease in tensile strength is also observed. The greatest change in fibre properties occurs between 3.0 and 5.0 mol dm−3 NaOH. This is attributed to the onset of formation of Na-cellulose II at 3.0 mol dm−3 NaOH; a fully formed Na-cellulose II structure is expected above 6.8 mol dm−3 NaOH. Formation of Na-cellulose II causes plasticization of the lyocell fibres as both inter- and intra-molecular hydrogen bonds are broken by these higher sodium hydroxide concentrations. 相似文献
642.
Manashi Panda Chayan Das Chen-Hsiung Hung Sreebrata Goswami 《Journal of Chemical Sciences》2007,119(1):3-9
Reactions of IrCl3·xH2O with the ligands, 2-[(phenylamino)phenylazo]pyridine (HL1a) and 2-[(p-tolylamino)phenylazo]pyridine (HL1b) produce [Ir(L1)2]Cl (L1 = L1a, [1]Cl and L1 = L1b, [2]Cl) along with many unidentified products. The iridium complexes have been characterized by various techniques such as X-ray
crystallography, mass spectrometry, 1H and 13C NMR, cyclic voltammetry and absorption studies. The complex [1]ClO4 crystallises in triclinic space group. The crystallographic data have been determined. Notably, the Ir-N (azo) lengths are
short (av. 1·9875(4) ?) as compared to the remaining four Ir-N lengths (av. 2·052(5) ?). There is significant degree of ligand
backbone conjugation in the coordinated ligands, which result in shortening of the C-N lengths on the other side of the middle
phenyl ring and also in lengthening of the diazo (N=N) lengths. The complexes display multiple low energy transitions ranging
between 1010 and 450 nm. These are electro active and show three reversible redox responses in the potential range, +1·5 V
to −1·5 V. The cathodic potential responses are ascribed as ligand reductions, while the redox process at the anodic potential
occurs at a mixed metal-ligand (HOMO) orbital. 相似文献
643.
Isomeric cross-section ratios of evaporation residues formed in12C+93Nb and16O+89Y reactions were measured by recoil catcher technique followed by off-line γ-ray spectrometry in the beam energy range of
55.7–77.5 MeV for12C and 68–81 MeV for16O. The isomeric cross-section ratios were resolved into that for complete and incomplete fusion reactions. The angular momentum
of the intermediate nucleus formed in incomplete fusion was deduced from the isomeric cross-section ratio by considering the
statistical deexcitation of the incompletely fused composite nucleus. The data show that incomplete fusion is associated with
angular momenta slightly smaller than critical angular momentum for complete fusion, indicating the deeper interpenetration
of projectile and target nuclei than that in peripheral collisions. 相似文献
644.
Mrinal Sinha M. Maitra Goswami D. Mal T. R. Middya S. Tarafdar Udayan De Sandip Kumar Chaudhuri D. Das 《Ionics》2008,14(4):323-327
Irradiation affects the structures of materials at different scales, thus changing physical and chemical properties. We study
here the effect of gamma irradiation at different doses on the polymer electrolyte PEO-NH4ClO4. Optical micrographs show cracks in the irradiated samples and impedance spectroscopy measurements indicate reduced ion-conductivity
at room temperature but slight enhancement at higher temperature. At high frequencies, the real part of the admittance shows
a power-law variation; the exponent, which is a measure of self-similarity of the structure, is reduced on irradiation. The
overall results point to a more disordered structure at higher radiation doses. 相似文献
645.
646.
This paper analyzes a finite-buffer multiserver bulk-service queueing system in which the interarrival and service times are, respectively, arbitrarily and exponentially distributed. Using the supplementary variable and the imbedded Markov chain techniques, we obtain the queue-length distributions at prearrival and arbitrary epochs. We also present Laplace–Stiltjes transform of the actual waiting-time distribution in the queue. Finally, several performance measures and a variety of numerical results in the form of tables and graphs are discussed. 相似文献
647.
The fission track registration efficiency (K
wet) of the Garware polyester track (GPF) detector in solution has been determined with respect to the Lexan detector whose K
wet is very well known in the literature. The K
wet is found to be (1.2 ± 0.1) 10−3 cm. The track registration efficiency of the GPF detector in solution is better than the efficiencies of other nuclear track
detectors reported in the literature. This implies that the threshold energies for track registration are different for different
detectors and that GPF detector has a lower threshold-energy value. The effects of gamma irradiation in the dose range of
5–51 Mrad on the fission track registration efficiency (K
wet) of this track detector from the solution medium are also investigated. The results show that the K
wet values for the gamma-irradiated detectors in the above dose range in 2M HNO3 solution medium decreases by ∼7–15%. The changes induced in the gamma-irradiated detectors as a function of gamma dose have
also been studied by bulk-etch rate measurements. 相似文献
648.
Radon exhalation rates were studied using LR-115 (II) nuclear track detectors in and around the Makum coalfield, which has
significant geological features. Exhalation rates (mass and surface) from coal and soil samples were studied with reference
to the geological features. The mass and surface exhalation rates from coal samples ranged from 6.1–16.2 mBq/kg/h and 201.6–535.7
mBq/m2/h, respectively. The mass and surface exhalation rates from the soil samples collected from the Margherita Thrust area of
the coalfield and the coalfield area lying in between the Margherita Thrust and Disang Thrust of the coalfield were found
to be 10.7 mBq/kg/h and 354.2 mBq/m2/h, and 9.5 mBq/kg/h and 314.2 mBq/m2/h, respectively. 相似文献
649.
In an attempt to find minimal scenarios we study the implications of Dirac and Majorana mass matrices with texture zeros within the type I seesaw mechanism. For the Dirac mass matrices we consider 5 zero textures which we show to be the most minimal form that can successfully account for low energy phenomenology if the Majorana mass matrices are chosen minimal as well. For those, we consider both diagonal and even more minimal non-diagonal forms. The latter can be motivated e.g. by simple U(1) flavour symmetries and have two degenerate eigenvalues. We classify the allowed textures and discuss the ramifications for leptogenesis and lepton flavour violation. 相似文献
650.
Chirantan Gayen Upashi Goswami Kasturi Gogoi Srestha Basu Anumita Paul 《Chemphyschem》2019,20(7):953-958
Herein, we report the construction of intracellular logic operations using luminescent histidine stabilized gold nanoclusters (His Au NCs). The luminescence intensity of His Au NCs was found to be significantly enhanced following interaction with zinc ions, owing to “Crystallization induced emission enhancement”. Further, the luminescence intensity of His Au NCs was found to be effectively quenched in presence of sulphide ions, owing to transformation of emissive His Au NCs to non-emissive gold nanoparticles. Thus, the collective and individual effects of zinc ions and sulphide ions causing significant variation in the luminescence intensity of His Au NCs, were used as input parameters for construction of intracellular logic operations such as Tri state buffer, “on-off” switch and INHIBIT gate within mammalian cells. 相似文献