全文获取类型
收费全文 | 10604篇 |
免费 | 1029篇 |
国内免费 | 694篇 |
专业分类
电工技术 | 375篇 |
技术理论 | 8篇 |
综合类 | 653篇 |
化学工业 | 1921篇 |
金属工艺 | 286篇 |
机械仪表 | 244篇 |
建筑科学 | 854篇 |
矿业工程 | 395篇 |
能源动力 | 830篇 |
轻工业 | 343篇 |
水利工程 | 814篇 |
石油天然气 | 188篇 |
武器工业 | 30篇 |
无线电 | 1627篇 |
一般工业技术 | 1901篇 |
冶金工业 | 435篇 |
原子能技术 | 519篇 |
自动化技术 | 904篇 |
出版年
2024年 | 14篇 |
2023年 | 178篇 |
2022年 | 210篇 |
2021年 | 434篇 |
2020年 | 373篇 |
2019年 | 325篇 |
2018年 | 292篇 |
2017年 | 402篇 |
2016年 | 422篇 |
2015年 | 353篇 |
2014年 | 630篇 |
2013年 | 866篇 |
2012年 | 625篇 |
2011年 | 752篇 |
2010年 | 590篇 |
2009年 | 632篇 |
2008年 | 598篇 |
2007年 | 612篇 |
2006年 | 568篇 |
2005年 | 446篇 |
2004年 | 428篇 |
2003年 | 356篇 |
2002年 | 341篇 |
2001年 | 290篇 |
2000年 | 210篇 |
1999年 | 149篇 |
1998年 | 150篇 |
1997年 | 161篇 |
1996年 | 107篇 |
1995年 | 108篇 |
1994年 | 108篇 |
1993年 | 94篇 |
1992年 | 72篇 |
1991年 | 54篇 |
1990年 | 46篇 |
1989年 | 75篇 |
1988年 | 44篇 |
1987年 | 26篇 |
1986年 | 28篇 |
1985年 | 34篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1974年 | 4篇 |
1959年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
101.
102.
A numerical study of the transport phenomena arising in a single-screw extruder channel is carried out. A non-Newtonian fluid
is considered, using a power law model for the variable viscosity. Chemical reaction kinetics are also included. Finite difference
computations are carried out to solve the governing set of partial differential equations for the velocity, temperature and
species concentration fields, over a wide range of governing parameters for the case of a tapered screw channel.
The numerical treatment for this combined heat and mass transfer problem is outlined. A marching procedure in the down-channel
direction is adopted and the validity of the scheme for practical problems discussed. For large viscous dissipation, the material
heats up considerably due to the prevailing shear field, affecting the viscosity significantly, and results in large changes
in the pressure development at the end of the channel. The rate of reaction controls the mass diffusion rate which in turn
affects viscosity and the flow significantly. The dimensionless throughput,q
v
, is one of the most important parameters in the numerical solution. The dimensionless pressure variation is very sensitive
toq
v
, and orders of magnitude changes are possible for small variations inq
v
. Schemes for dealing with other important effects such as back flow, heat transfer by conduction in the barrel, and the effect
of the die are also outlined.
A list of symbols is given at the end of the paper
This is publication No. F-10544-4-91 of the New Jersey Agricultural Experiment Station supported by State Funds and the Center
for Advanced Food Technology (CAFT). The Center for Advanced Food Technology is a New Jersey Commission on Science and Technology Center. This work was also
supported in part by the US Army Research Office. 相似文献
103.
The condition of the surfaces is of crucial importance for the deuterium permeation through materials. In this work a study of the surface constants for the adsorption (σk1) and release (σk2) of deuterium under different surface conditions on the martensitic steel DIN 1.4914 (MANET) has been carried out. The growth of an oxide surface layer (Cr2O3) of about 25–30 nm in a MANET sample, heat treated in an oxidizing environment, compared to the bare MANET that have a ‘natural' oxide of about 5 nm has provoked a reduction of both the permeation rate and the recombination coefficient (about 3 orders of magnitude). In addition, the permeation governing process has changed from diffusion-limited to surface-limited. The measurements of the permeation rate of deuterium were performed by a gas-phase permeation technique over the temperature range 574–746 K and for deuterium driving pressures in the range from 3 to 105 Pa. 相似文献
104.
The decomposition of NO and of N2O over a CuZSM-5 zeolite and a Fe-mordenite, respectively, has been studied using tracer techniques. The results demonstrate the high mobility of the lattice oxygen ions in self-diffusion. They afford a possible explanation for the problem of how two extralattice oxygens located at positions remote from each other may combine to form the O2 molecules which are spontaneously desorbed in these redox reactions. They show that a portion of the lattice oxygen mixes into the O2 released on decomposition. The data also show that N18O and N2
18O undergo exchange with the catalyst oxygen under reaction conditions.On leave from Central Research Institute for Chemistry, Hungarian Academy of Sciences, H-1525 Budapest, Hungary. 相似文献
105.
一维河网非恒定流及悬沙数学模型的节点控制方法 总被引:19,自引:1,他引:18
本文的一维河网非恒定流及悬沙数学模型,是根据以一维圣维南方程组,悬沙非平衡输运方程及水位、含沙量节点控制法而建立。首先,利用单一河流有限差分方程组转换形式和节点处质量、能量守恒性,写出所有节点的水位控制方程组。求解此不规则稀疏矩阵方程组得到得有节点的水位,再由单一河流非恒定流的求解方法可获得所有单一河流的断面水位和流量。基于水注的节点水位控制法,本文提出了节点悬沙控制法。假设节点处冲刷或淤积较小,所有节点的含沙量控制方程组可通过输沙量守恒方程用矩阵形式写出。求解此不规则稀疏矩阵方程组,得到所有节点处的含沙量。所有单一河流断面处的含沙量通过单一河流悬沙输运的求解方法获得。本文介绍的模型适用于各种河网类型。作为检验,该模型成功地应用于珠江三角洲流域河网水流及悬沙的数值计算。 相似文献
106.
一度流超饱和输沙法是考虑了超饱和输沙特点的泥沙沉降计算方法.沉沙池内水流挟沙力是一定水力和床沙组成条件下水流挟带床沙质的能力.从已建沉沙池沉降标准、池内设计水流水力以及床沙组成条件来看,沉沙池运行前期、中期水流挟沙力一般都很小.用一度流趋饱和输沙法计算沉沙池沉降率时可不考虑水流换沙力的影响.均匀流条件下,用不考虑挟沙力和考虑挟沙力的一度流超饱和输沙法分别计算沉沙池的沉降率,二者相对误差取决于挟沙力与进口含沙量之比,该比值小于0.2时,相对误差小于20%.沉沙池内挟沙力与进口含沙量之比小于0.2时,用一度流趋饱和输沙法计算沉沙池的沉降率,可不考虑水流挟沙力的影响. 相似文献
107.
针对750m^3高炉铁水生产富余状况,制订了富余铁水向铸铁机铸铁的调送方案,通过创新思维、系统挖潜、优化资源配置等措施的实施,保证了750m^3高炉的正常生产,取得了良好效果。 相似文献
108.
Dmitry Beletsky Doran M. Mason David J. Schwab Edward S. Rutherford John Janssen David F. Clapp John M. Dettmers 《Journal of Great Lakes research》2007,33(4):842-866
Potential for large-scale physical transport processes to affect recruitment of Lake Michigan yellow perch (Perca flavescens) was studied by examining the variation in larval distribution, growth rate, and settlement during June–August 1998–2003 using a 3D particle transport model linked with an individual-based bioenergetics growth model. In all years, virtual larvae were released nearshore in southwestern Lake Michigan, a known and important spawning region for yellow perch. For any given year, the same circulation pattern and water temperature either promoted or reduced yellow perch settlement depending on the consumption rates and settlement size chosen in the growth model. Increased consumption increased the number of settled larvae and expanded the total area where larvae settled, whereas increased settlement size reduced the number of settled larvae and reduced the overall settlement area. Interannual variability in circulation patterns and water temperature also resulted in contrasting larval settlement rates, settlement locations, and size of settlement areas between years. Model predictions were most consistent with field observations of age-0 yellow perch from Illinois and Michigan waters when settlement was assumed to occur at 50 mm. Moreover, our model suggests that larvae originating from southwestern Lake Michigan can recruit anywhere within the southern basin and even in the northern basin. Future model improvement will require information on the relative contribution of various sectors to the larval pool, their distribution with reference to the hydrodynamic landscape, the feeding and growth of yellow perch during their pelagic phase, and the size at transition to demersal stage. 相似文献
109.
A three-dimensional (3D), two-phase, isothermal model of direct methanol fuel cells (DMFCs) was employed to investigate effects of electron transport through the backing layer and the land in bipolar plates. It was found that the electronic resistance of the backing layer, affected by backing layer electronic conductivity, backing layer thickness and flow channel width, played a relatively important role in determining the current density distribution and cell performance. In order to ignore the electron transport effect on the average current density, the minimum electronic conductivity of the backing layer has to be 1000 S m−1, with the relative error in the average current density less than 5%, under the given conditions. 相似文献
110.