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排序方式: 共有108条查询结果,搜索用时 15 毫秒
91.
Let X be a complete Alexandrov space with curvature ≥1 and radius 〉 π/2. We prove that any connected, complete, and locally convex subset without boundary in X also has the radius 〉 π/2. 相似文献
92.
In order to provide cost-efficient and rapid protection against the key link failures dynamically, an intelligent p-cycle protection strategy based on network coding is proposed. Data units are combined from different links using network coding method at the on-cycle nodes, and then they are transmitted downstream for recovering data units lost due to failures. Under static traffic, an integer linear program (ILP) is formulated to provision the optimal p-cycles. Furthermore, according to the dynamic variation of the link importance degree, a heuristic cycle construction algorithm for generating, extending and contracting p-cycle is introduced to achieve intelligent and self-adaptive protection. The key of the proposed protection strategy is how to set the key link as a straddling link of the p-cycle as possible. The experiments demonstrate that the proposed strategy can guarantee instantaneous recovery of data units upon the failure of a key link with a low blocking rate and resource cost. 相似文献
93.
94.
Wang Kaiwu Shi Chenxu Li Zhongyang Liu Pengxiang Chen Zhiliang Xu Juan Bing Pibin Zhu Anfu Xu Degang Zhong Kai Yao Jianquan 《Optical Review》2023,30(2):199-207
Optical Review - We introduce an infrared laser generation scheme by cascaded difference frequency generation (CDFG) combined with optical parametric oscillator (OPO). An inventive infrared laser... 相似文献
95.
生物油酸酮类模化物与乙醇在HZSM-5上共裂化制备生物汽油 总被引:1,自引:0,他引:1
生物油酸类和酮类化合物具有较高的裂化活性,而使用分子蒸馏技术能将这些组分富集到蒸出馏分中,因此蒸出馏分相比原始生物油具有更好的裂化特性.为了模拟实际蒸出馏分的组成,本文将生物油模化物(羟基丙酮(HPO)、环戊酮和乙酸)进行配比混合,在固定床反应器上对其与乙醇的共裂化行为进行了研究,考察了不同反应温度和压力对混合反应物的转化率、粗汽油相的选择性和组成的影响.研究发现,当反应温度在340℃时,乙酸和乙醇的转化率分别仅为67.9%和74.4%,同时得到的油相产物中烃类含量仅为59.8%,并含有大量的含氧副产物.常压裂化同样生成了低品质的油相产物,同时油相选择性仅为10.8%.提高反应温度能促进反应物的转化,提高裂化过程中的脱氧效率,而提高反应压力对液体烃类的生成有明显的促进作用.在400℃和2MPa时,酸类和酮类都有良好的裂化表现,反应物接近完全转化,粗汽油相选择性达到31.5%,且全部由烃类组成,其中芳香烃含量高达91.5%.此外,反应后催化剂表征和稳定性测试结果表明,催化剂在较长时间反应后会失活,但通过催化剂再生能够很好地恢复催化剂活性. 相似文献
96.
Shurong Wang Xiujuan Guo Kaige Wang Zhongyang Luo 《Journal of Analytical and Applied Pyrolysis》2011,91(1):183-189
There has been much interest in the utilization of biomass-derived fuels as substitutes for fossil fuels in meeting renewable energy requirements to reduce CO2 emissions. In this study, the pyrolysis characteristics of biomass have been investigated using both a thermogravimetric analyzer coupled with a Fourier-transform infrared spectrometer (TG-FTIR) and an experimental pyrolyzer. Experiments have been conducted with the three major components of biomass, i.e. hemicellulose, cellulose, and lignin, and with four mixed biomass samples comprising different proportions of these. Product distributions in terms of char, bio-oil, and permanent gas are given, and the compositions of the bio-oil and gaseous products have been analysed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography (GC). The TG results show that the thermal decomposition of levoglucosan is extended over a wider temperature range according to the interaction of hemicellulose or lignin upon the pyrolysis of cellulose; the formation of 2-furfural and acetic acid is enhanced by the presence of cellulose and lignin in the range 350-500 °C; and the amount of phenol, 2,6-dimethoxy is enhanced by the integrated influence of cellulose and hemicellulose. The components do not act independently during pyrolysis; the experimental results have shown that the interaction of cellulose and hemicellulose strongly promotes the formation of 2, 5-diethoxytetrahydrofuran and inhibits the formation of altrose and levoglucosan, while the presence of cellulose enhances the formation of hemicellulose-derived acetic acid and 2-furfural. Pyrolysis characteristics of biomass cannot be predicted through its composition in the main components. 相似文献
97.
LIU Xueping ZHOU Zhenhua ZHANG Liangliang TAN Zhongyang SHEN Guoli YU Ruqin 《中国化学》2009,27(10):1855-1859
A simple and rapid colorimetric approach for the determination of adenosine has been developed via target inducing aptamer structure switching, thus leading to Au colloidal solution aggregation. In the absence of the analytes, the aptamer/gold nanoparticle (Au NP) solution remained well dispersed under a given high ionic strength condition in that the random‐coil aptamer was readily wrapped on the surface of the Au NPs, which resulted in the enhancement of the repulsive force between the nanoparticles due to the high negative charge density of DNA molecules. While in the presence of adenosine, target‐aptamer complexes were formed and the conformation of the aptamer was changed to a folded structure which disfavored its adsorption on the Au NP surface, thus leading to the reduction of the negative charge density on each Au NP and then the reduced degree of electrostatic repulsion between Au nanoparticles. As a result, the aggregation of the Au colloidal solution occurred. The changes of the absorption spectrum could be easily monitored by a UV‐Vis spectrophotometer. A linear correlation exists between the ratio of the absorbance of the system at 522 to 700 nm (A522 nm/A700 nm) and the concentration of adenosine between 100 nmol·L?1 and 10 µmol·L?1, with a detection limit of 51.5 nmol·L?1. 相似文献
98.
In this paper, by using the corrector method we give another proof of the quenched invariance principle for the random walk on the infinite random graph generated by a one-dimensional long-range percolation under the conditions that the connection probability p(1)=1 and the percolation exponent s>2. The key step of the proof is the construction of the corrector. We show that the corrector can be constructed under either s∈(2,3] or s>3, though the corresponding underlying measures may be different. As an application of the main result we get a new lower bound of the quenched diagonal transition probability for the random walk. 相似文献
99.
100.