全文获取类型
收费全文 | 863篇 |
免费 | 30篇 |
国内免费 | 38篇 |
专业分类
化学 | 421篇 |
晶体学 | 3篇 |
力学 | 327篇 |
综合类 | 11篇 |
数学 | 25篇 |
物理学 | 144篇 |
出版年
2023年 | 39篇 |
2022年 | 26篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 15篇 |
2018年 | 22篇 |
2017年 | 27篇 |
2016年 | 20篇 |
2015年 | 42篇 |
2014年 | 32篇 |
2013年 | 49篇 |
2012年 | 29篇 |
2011年 | 47篇 |
2010年 | 40篇 |
2009年 | 59篇 |
2008年 | 42篇 |
2007年 | 54篇 |
2006年 | 45篇 |
2005年 | 43篇 |
2004年 | 26篇 |
2003年 | 41篇 |
2002年 | 24篇 |
2001年 | 30篇 |
2000年 | 27篇 |
1999年 | 24篇 |
1998年 | 29篇 |
1997年 | 15篇 |
1996年 | 12篇 |
1995年 | 14篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有931条查询结果,搜索用时 125 毫秒
81.
Some hydrodynamic aspects of 3-phase inverse fluidized bed 总被引:2,自引:0,他引:2
Krishna S.V.S.R. Bandaru D.V.S. Murthy K. Krishnaiah 《中国颗粒学报》2007,5(5):351-356
Hydrodynamics of 3-phase inverse fluidized bed is studied experimentally using low density particles for different liquid and gas velocities. The hydrodynamic characteristics studied include pressure drop, minimum liquid and gas fluidization velocities and phase holdups. The minimum liquid fluidization velocity determined using the bed pressure gradient, decreases with increase in gas velocity. The axial profiles of phase holdups shows that the liquid holdup increases along the bed height, whereas the solid holdup decreases down the bed. However, the gas holdup is almost uniform in the bed. 相似文献
82.
Qingru Chen Lubin Wei 《中国颗粒学报》2005,(2)
In China more than two-thirds of available coal reserves are in arid areas, where, to beneficiate the run-of-mine coal,there is not enough water resource required by conventional processing. Developing efficient dry beneficiation technology is of great significance for efficient coal utilization in China, notably the clean coal technology (CCT). The dry coal beneficiation technology with air-dense medium fluidized bed utilizes air-solid suspension as beneficiating medium whose density is consistent for beneficiation, similar in principle to the wet dense medium beneficiation using liquid-solid suspension as separating medium. The heavy portion in feedstock whose density is higher than the density of the fluidized bed will sink, whereas the lighter portion will float, thus stratifying the feed materials according to their density.In order to obtain efficient dry separation in air-dense medium fluidized bed, stable fluidization with well dispersed micro-bubbles must be achieved to ensure low viscosity and high fluidity. The pure buoyancy of beneficiation materials plays a main role in fluidized bed, and the displaced distribution effect should be restrained. The displaced distribution effects include viscosity displaced distribution effect and movement displaced distribution effect. The former is caused by viscosity of the fluidized bed. It decreases with increasing air flow velocity. Movement displaced distribution effect will be large when air flow rate is too low or too high. If medium particle size distribution and air flow are well controlled, both displaced distribution effects could be controlled effectively. A beneficiation displaced distribution model may be used to optimize beneficiation of feedstock with a wide particle size distribution and multiple components in the fluidized bed. The rheological characteristics of fluidized beds were studied using the falling sphere method. Experimental results indicated that the fluidized bed behaves as a Bingham fluid. The plastic viscosity and yield stress can be obtained by measurement of the terminal settling velocity of spheres and linear regression of the experimental data. Both plastic viscosity and yield stress increase with increasing size of the fluidized particles. The drag coefficient can be calculated with favorable agreement with experimental data.The first dry coal beneficiation plant with air-dense medium fluidized bed was established by CUMT with an output of 320000 t.a-1 and a probable error Ep value up to 0.05 was achieved. The plant was accepted by the Chinese government in June, 1994. Since then, new applications have been found including a 700000 t.a-1 dry coal beneficiation plant put up for commercial testing. To realize coal dry beneficiation of full size range of 300~0 mm, further research on dry coal beneficiation of different size fractions has been under way at the Mineral Processing Research Center of CUMT, leading to the following results:● Dry beneficiation technology with a vibrated air-dense medium fluidized bed for fine coal of size fraction 6~0.5 mm Ash content was reduced from 16.57% to 8.35%, with yield up to 80.20% and Ep value up to 0.065.● Coal dry beneficiation technology with a deep air-dense medium fluidized bed for >50 mm coal An Ep value up to 0.02 was achieved. This technology is of great value for waste removal from 300~50 mm large feedstock, especially for big surface mines in China.● Coal triboelectric cleaning technology for <1 mm pulverized Coal Coal is comminuted down to 320 mesh (0.043 mm) to fully liberate the embedded minerals, yielding an ultra-low ash coal (less than 2%). Currently a pilot system with triboelectric cleaning has successfully passed technical appraisal.● Three-product beneficiation technology with dual-density fluidized bedThis technology yields three products: clean coal, middling and tailing, with the following typical results: Ep value of 0.06~0.09 for the upper layer with a density of 1.5~1.54 g.cm-3 and Ep value of 0.09~0.11 for the lower layer with density of 1.84~1.9 g.cm-3. 相似文献
83.
84.
Xiangyang Zhou David Weise Shankar Mahalingam 《Proceedings of the Combustion Institute》2005,30(2):2287-2294
An extensive experimental and numerical study was completed to analyze the marginal burning behavior of live chaparral shrub fuels that grow in the mountains of southern California. Laboratory fire spread experiments were carried out to determine the effects of wind, slope, moisture content, and fuel characteristics on marginal burning in fuel beds of common chaparral species. Four species (Manzanita sp., Ceanothus sp., Quercus sp., and Arctostaphylos sp.), two wind velocities (0 and 2 m/s), two fuel bed depths (20 and 40 cm), and three slope percents (0%, 40%, or 70%) were used. Oven-dry moisture content M of fine fuels (<6.25 mm diameter) ranged from 29% to 105%. Sixty-five of 115 fires successfully propagated the length (2.0 m) of the elevated fuel bed. A previously derived empirical marginal burning criterion was assessed, and a suitable modification was proposed for live chaparral fuels. Based on the experimental data, a stepwise logistic regression model was developed to predict the probability of successful fire spread. This procedure resulted in the selection of wind speed, slope percent, fuel loading, fuel moisture content, and relative humidity as the primary variables. It correctly classified 96% of 115 fires. Finally, a multidimensional numerical model for vegetation fire spread using a porous media sub-model was developed to simulate the laboratory fires. Results are used to analyze the internal heat transfer and combustion processes that determine fire spread success in shrub fuel bed. 相似文献
85.
The effect of calcination temperature on the activity and some properties of low temperature water gas shift reaction catalysts
has been investigated. The activities of catalysts have been determined using a fixed bed catalytic reactor. The following
results may be deduced from the present study. 1. The catalysts' total surface area decreased with increasing calcination
temperature, presumably due to the partial sintering of the catalysts particles. 2. The presence of an amorphous CuO phase
within the structure of some catalysts may be related to the desirable conditions prevailing during synthesis of the latter.
3. Observation of a similar trend between the increase in copper crystallite particle size and enhancement of catalyst activities
with increasing calcination temperature demonstrates the important contribution made by the copper crystallite phase to the
overall activities of water gas shift reaction catalysts.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
86.
87.
Muhammad M. R. Qureshi Chao Zhu Chao-Hsin Lin Liang-Shih Fan 《中国颗粒学报》2006,4(3):147-152
A three-dimensional simulation study is performed for investigating the hydrodynamic behaviors of a cross-flow liquid nitrogen spray injected into an air-fluidized catalytic cracking (FCC) riser of rectangular cross-section. Rectangular nozzles with a fixed aspect ratio but different fan angles are used for the spray feeding. While our numerical simulation reveals a generic three-phase flow structure with strong three-phase interactions under rapid vaporization of sprays, this paper tends to focus on the study of the effect of nozzle fan angle on the spray coverage as well as vapor flux distribution by spray vaporization inside the riser flow. The gas-solid (air-FCC) flow is simulated using the multi-fluid method while the evaporating sprays (liquid nitrogen) are calculated using the Lagrangian trajectory method, with a strong two-way coupling between the Eulerian gas-solid flow and the Lagrangian trajectories of spray. Our simulation shows that the spray coverage is basically dominated by the spray fan angle. The spray fan angle has a very minor effect on spray penetration. The spray vaporization flux per unit area of spray coverage is highly non-linearly distributed along the spray penetration. The convection of gas-solid flow in a riser leads to a significant downward deviation of vapor generated by droplet vaporization, causing a strong recirculating wake region in the immediate downstream area of the spray. 相似文献
88.
David N. Thompson Peter G. Shaw Jeffrey A. Lacey 《Applied biochemistry and biotechnology》2003,105(1-3):205-218
Silica and alkali metals in wheat straw limit its use for bioenergy and gasification. Slag deposits occur via the eutectic
melting of SiO2 with K2O, trapping chlorides at surfaces and causing corrosion. A minimum melting point of 950°C is desirable, corresponding to an
SiO2:K2O weight ratio of about 3:1. Mild chemical treatments were used to reduce Si, K, and Cl, while varying temperature, concentration,
% solids, and time. Dilute acid was more effective at removing K and Cl, while dilute alkali was more effective for Si. Reduction
of minerals in this manner may prove economical for increasing utilization of the straw for combustion or gasification. 相似文献
89.
90.
生物质洁净能源研究中的流化床动力学模型 总被引:1,自引:0,他引:1
分别对最小流化床、鼓泡流化床和腾涌流化床及相应的全混模型、鼓泡模型、气泡汇集模型等加以综述 ,分析其优缺点 ,并在此基础上提出动力学模拟研究的新思路 .根据流化床内在的本质———流化态的不同 ,将流化床分为最小流化床、鼓泡流化床和腾涌流化床三种 .总结了前人针对各种流化床提出的全混模型、鼓泡模型、气泡汇集模型等思想 ,建议今后可以在以下几个方面进行深入研究 :⑴使得模型更有普适性 .⑵由于气泡有效直径尚不能在理论上求得 ,可以在理想气泡直径变化公式的基础上 ,加入非线性化学的计算 .⑶确定不同情况下的参数 ,使得工作更有延续性 ,也使得模型更加具有生命力 .⑷从高压的角度去进行模型的计算 ,并得到相应的试验数据支持 . 相似文献