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排序方式: 共有278条查询结果,搜索用时 31 毫秒
51.
Plastics have become an integral part of our contemporary life because of many desirable properties including durability and resistance to degradation. However, these non-degradable, petrochemicals-derived plastics accumulate in the environment at a rate of 25 million tons per year. Recently there is an interest in the development of a class of microbially produced bioplastics, e.g., polyhydroxyalkanoates (PHAs) which retain the desired physical and chemical properties of conventional synthetic plastics. Broader usage of biodegradable plastics in packaging and disposable products as a solution to the environmental problem would heavily depend on further reduction of costs and the discovery of novel biodegradable plastics with improved properties. In this paper, the microbial production of PHAs by activated sludge utilizing food industrial wastes is reported. The melting points of the products as well as the co-polymer composition of the products investigated by GC and NMR were compared. By use of activated sludge to convert the carbon source into PHAs not only environment-friendly bioplastics are produce, but also part of the problem of the disposal of municipal activated sludge is solved. The selection of food industrial waste as carbon resource can also further reduce the cost of production of PHAs. 相似文献
52.
Biologically-produced polymers, from microbial fermentation are naturally biodegradable and are potential environment-friendly substitutes for some synthetic plastics. However, broader applications are restricted by the high production costs and limitations in physical and mechanical properties. In this study, activated sludge bacteria in a conventional wastewater treatment system treating a wastewater that contained organic pollutants, were induced by nitrogen deficiency to accumulate intracellular storage polymers, which can be extracted as a low-cost source of biodegradable plastics. Chromatographic analysis of the extracted polymers revealed a composition of poly-hydroxyalkanoate and a number of related co-polymers. Alcaligene spp. in the activated sludge microbial consortium was identified as the main genus accumulated these polymers. When the C:N ratio was increased from 20 to 140, the specific polymer yield increased to a maximum of 0.39 g polymer/g dry cell while specific growth yield decreased to 0.26 g dry cell/g carbonaceous matter consumed. The highest overall polymer production yield of 0.11 g polymer/g carbonaceous matter consumed was achieved when the C:N ratio was maintained at a nitrogen-deficient level of 100. The specific polymer yield in the isolated Alcaligene spp. cells were as high as 0.7 g polymer/g dry cell mass. The composition of the co-polymers, and hence the physical and mechanical properties, could be controlled by manipulating the influent organic compositions. 相似文献
53.
Yan Q Zhao XS Teng JH Chua SJ 《Langmuir : the ACS journal of surfaces and colloids》2006,22(16):7001-7006
With planar photolithography and self-assembly techniques, multilayer colloidal crystals with a woodpile structure were fabricated. They represent a new kind of photonic crystals, that is, three-dimensional (3D) photonic crystals with a dual periodicity; one comes from the face-centered cubic (fcc) structure within the colloidal crystal strips and the other one results from the periodic arrangement of the colloidal crystal strips. 相似文献
54.
Z. B. Yan F. Duan T. N. Wong K. C. Toh K. F. Choo P. K. Chan Y. S. Chua L. W. Lee 《Heat and Mass Transfer》2013,49(7):985-990
An inclined spray chamber with four multiple nozzles to cool a 1 kW 6U electronic test card has been designed and tested in this study. The multiple inclined sprays can cover the same heated surface area as that with the multiple normal sprays but halve the volume of the spray chamber. The spray cooling system used R134a as a working fluid in a modified refrigeration cycle. It is observed that increasing mass flow rate and pressure drop across the nozzles improved the heat transfer coefficient with a maximum enhancement of 117 %, and reduced the maximum temperature difference at the heated surface from 13.8 to 8.4 °C in the inclined spray chamber with a heat flux of 5.25 W/cm2, while the heat transfer coefficient of the normal spray increased with a maximum enhancement of 215 % and the maximum temperature difference decreased from 10.8 to 5.4 °C under similar operating conditions. We conclude that the multiple inclined sprays could produce a higher heat transfer coefficient but with an increase in non-uniformity of the surface temperature compared with the multiple normal sprays. 相似文献
55.
Hongwei Gao Jinghua Teng Soo Jin Chua Ning Xiang 《Applied Physics A: Materials Science & Processing》2014,115(2):487-490
Coupling effect of surface plasmon (SP) with InGaAs/GaAs QW emission is demonstrated experimentally. The SP resonance is generated by disordered arrays of Au nanodisks on the InGaAs/GaAs QW surface. More than twofold enhancement in QW PL is observed. Theoretical simulations also indicated that the disordered arrays of Au structures enlarged the cone angle for which light can be radiated out. The larger angle enhances the PL intensity. 相似文献
56.
A synthetic method of azaspirocyclohexadienones has been developed through copper-catalyzed aerobic spirocyclization of biaryl-N-H-imines prepared by the reaction of biarylcarbonitriles and Grignard reagents. 相似文献
57.
Wan Kamarul Zaman Wan Safwani Suzana Makpol Somasundaram Sathapan Kien Hui Chua 《Applied biochemistry and biotechnology》2012,166(8):2101-2113
Human adipose-derived stem cells (ASCs) have generated a great deal of excitement in regenerative medicine. However, their safety and efficacy issue remain a major concern especially after long-term in vitro expansion. The aim of this study was to investigate the fundamental changes of ASCs in long-term culture by studying the morphological feature, growth kinetic, surface marker expressions, expression level of the senescence-associated genes, cell cycle distribution and ß-galactosidase activity. Human ASCs were harvested from lipoaspirate obtained from 6 patients. All the parameters mentioned above were measured at P5, P10, P15 and P20. Data were subjected to one-way analysis of variance with a Tukey post hoc test to determine significance difference (P?0.05). The data showed that growth of ASCs reduced in long-term culture and the ß-galactosidase activity was significantly increased at later passage (P20). The morphology of ASCs in long-term culture showed the manifestation of senescent feature at P15 and P20. Significant alteration in the senescence-associated genes expression levels was observed in MMP1, p21, Rb and Cyclin D1 at P15 and P20. Significant increase in CD45 and HLA DR DQ DP surface marker was observed at P20. While cell cycle analysis showed significant decrease in percentage of ASCs at S and G2/M phase at later passage (P15). Our data showed ASCs cultured beyond P10 favours the senescence pathway and its clinical usage in cell-based therapy may be limited. 相似文献
58.
The functionalization of graphene with dichlorocarbene has been successfully attained based on a conventional method for the generation of dichlorocarbenes. The obtained material was fully characterized using high resolution X-ray photoelectron spectroscopy, transmission electron microscopy, infrared and Raman spectroscopies. 相似文献
59.
The detection of TNT and related nitroaromatic compounds in seawater is of great interest. Electrochemical techniques can be applied for detection purposes since nitroaromatic compounds contain easily reducible nitro groups. In this study, we investigate the performance of thermally reduced graphenes prepared by three different oxidative methods: Hummers, Staudenmaier and Hofmann methods with consequent thermal exfoliation. The Hofmann method‐based graphene was found to exhibit the highest sensitivity in detecting TNT electrochemically. Extended study on the detection of TNT in seawater using the graphene material provided significant improvements in the detection sensitivity. These findings will have profound impacts on the detection of nitroaromatic explosives in seawater. 相似文献
60.
Wong Mui F. Chua Hong Lo Waihung Leung Chu K. Yu Peter H. F. 《Applied biochemistry and biotechnology》2001,91(1-9):447-457
Studies were conducted toinvestigate the removal and recovery of copper (II) ions from aqueous solutions by Micrococcus sp., which was isolated from a local activated sludge process. The equilibrium of copper biosorption followed the Langmuir
isotherm model very well with a maximum biosorption capacity (qmax) of 36.5 mg of Cu2+/gofdry cell at pH 5.0 and 52.1 mg of Cu2+/g of dry cell at pH 6.0. Cells harvested at exponential growth phase and stationary phase showed similar biosorption characteristics
for copper, Copper uptake by cells was negligible at pH 2.0 and then increased rapidly with increasing pH un til 6.0. In multim
etal systems, Micrococcus sp. exhibited a preferential biosorption order: Cu−Pb>Ni−Zn. There is virtually no interference with copper uptake by Micrococcus sp. from solutions bearing high concentrations of Cl−, SO
4
2−
, and NO3/− (0–500 mg/L). Sulfuric acid (0.05 M) was the most efficient desorption medium, recovering >90% of the initial
copper sorbed. The copper capacity of Micrococcus sp. remained unchanged after five successive sorption and desorption cycles. Immobilization of Micrococcus sp. in 2% calcium alginate and 10% polyacrylamide gel beads increased copper uptake by 61%. Biomass of Micrococcus sp. may be applicable to the development of potentially cost-effective biosorbent for removing and recovering copper from
effluents. 相似文献