全文获取类型
收费全文 | 254223篇 |
免费 | 31685篇 |
国内免费 | 21709篇 |
专业分类
电工技术 | 22949篇 |
技术理论 | 19篇 |
综合类 | 30544篇 |
化学工业 | 22252篇 |
金属工艺 | 13397篇 |
机械仪表 | 21757篇 |
建筑科学 | 23295篇 |
矿业工程 | 11373篇 |
能源动力 | 12481篇 |
轻工业 | 7410篇 |
水利工程 | 12864篇 |
石油天然气 | 13443篇 |
武器工业 | 6238篇 |
无线电 | 20324篇 |
一般工业技术 | 21880篇 |
冶金工业 | 10199篇 |
原子能技术 | 2914篇 |
自动化技术 | 54278篇 |
出版年
2024年 | 1333篇 |
2023年 | 3813篇 |
2022年 | 7368篇 |
2021年 | 8385篇 |
2020年 | 9017篇 |
2019年 | 7433篇 |
2018年 | 7183篇 |
2017年 | 9065篇 |
2016年 | 10575篇 |
2015年 | 11328篇 |
2014年 | 16113篇 |
2013年 | 16200篇 |
2012年 | 19388篇 |
2011年 | 20877篇 |
2010年 | 15794篇 |
2009年 | 16134篇 |
2008年 | 15692篇 |
2007年 | 18522篇 |
2006年 | 16116篇 |
2005年 | 13733篇 |
2004年 | 11260篇 |
2003年 | 9565篇 |
2002年 | 7642篇 |
2001年 | 6306篇 |
2000年 | 5339篇 |
1999年 | 4183篇 |
1998年 | 3370篇 |
1997年 | 2849篇 |
1996年 | 2568篇 |
1995年 | 2228篇 |
1994年 | 1821篇 |
1993年 | 1266篇 |
1992年 | 1069篇 |
1991年 | 834篇 |
1990年 | 671篇 |
1989年 | 581篇 |
1988年 | 382篇 |
1987年 | 234篇 |
1986年 | 221篇 |
1985年 | 209篇 |
1984年 | 184篇 |
1983年 | 131篇 |
1982年 | 104篇 |
1981年 | 93篇 |
1980年 | 84篇 |
1979年 | 79篇 |
1978年 | 30篇 |
1977年 | 24篇 |
1959年 | 38篇 |
1951年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
T.L. Phillips 《Polymer》2005,46(24):11035-11050
Results are presented from atomistic molecular dynamics simulations of the mobile pseudo-hexagonal phase of polyethylene, which occurs under conditions of elevated pressure and temperature. Three different types of model are considered, all of which employ periodic boundary conditions. The first model consists of n-alkane sequences (48×-C24H48-) that are bonded across the simulation box boundaries to produce chains that are effectively infinite in extent. On heating, at high pressure, this system displays a rotator phase, in which the chains retain an all-trans conformation, and rotate as semi-rigid units. A second model, consisting of finite n-alkanes (48×C24H50) displays the same behaviour at low temperatures, but at high temperature and pressure forms a conformationally disordered rotator phase, characterised by a large proportion of gauche defects and a significant lattice expansion. The final model considered contains long n-alkanes (24×C102H206) which contain jog defects and each pass twice through the simulation box. This model forms a conformationally disordered rotator phase at high temperature and ambient pressure. The behaviour of the three models, in terms of the variations in chain conformation and rotational and translational dynamics, are compared. The conformationally disordered phases provide useful representations of the experimentally observed mobile phase. 相似文献
82.
A feasibility analysis methodology adopted from reactive distillation is applied to membrane reactors. A model is formulated to depict the reactive liquid phase composition on the retentate side of a continuous type membrane reactor. The effects of both the chemical reaction kinetics and the membrane mass transfer kinetics on the feasible products are elucidated by means of retentate phase diagrams and bifurcation analysis. The proposed method can be applied to various membrane processes, independent of the specific structure of the membrane. Two quaternary reaction systems are considered to illustrate the methodology. In the first hypothetical system, it is shown how selective membranes can influence the sequence of effective volatilities which in turn affects the feasible products of the system. In the second example of practical importance, i.e. the heterogeneously catalysed synthesis of propyl acetate coupled with permeation through a porous polycarbonate membrane, the dusty gas model is applied to describe the component fluxes through the membrane. For the latter reaction system, the existence of reactive arheotrope is demonstrated. Arheotropes represent mass transfer controlled feasible products of membrane separation process. 相似文献
83.
84.
数据包络分析模型及其应用研究 总被引:1,自引:1,他引:0
郑明贵 《南方冶金学院学报》2004,25(4):62-66
通过对传统的C^2R模型进行研究并加以改进,建立了C2RHZ模型,利用有色金属矿采选业1993-2001年科技创新的相关数据进行了计算分析。说明了C^2RHZ模型的应用价值. 相似文献
85.
A comparative study of numerical solutions to non-linear discrete crack modelling of concrete beams involving sharp snap-back 总被引:1,自引:0,他引:1
Numerical problems are often encountered in modelling crack propagation in concrete beams using non-linear finite element (FE) analysis, especially when sharp snap-back behaviour in load-displacement relations occurs. This paper firstly identifies 16 arc-length control based numerical strategies based on extensive literature review. They are then used to carefully model the structural behaviour of a four-point single notched shear beam using discrete crack modelling approach in which cracks are represented by interface elements with bilinear softening constitutive laws. Based on extensive FE analyses, detailed comparisons of the merits and demerits of these numerical algorithms are then made. The results indicate that the effectiveness and efficiency of different algorithms may vary considerably from one to another, with the local arc-length based procedures in conjunction with tangential stiffness strategy and reversible unloading model being the most robust. 相似文献
86.
Dongchang Sun Liyong Tong 《International journal for numerical methods in engineering》2004,60(11):1911-1932
A novel finite element model is presented for static and dynamic analysis of composite plates integrated with a laminated piezoelectric layer, a host laminated composite plate and an adhesive layer between them. A new adhesive element is developed which includes both peel and shear effects in the adhesive layer based on first‐order shear deformation plate theory. The thin adhesive layer between the piezoelectric layer and the host plate is modelled by assuming that it carries constant shear and peel strains throughout its thickness. In addition, a weighted static shape control scheme for finding the optimal voltage distribution for static shape control is given. By selecting different weighting matrices, a variety of items such as displacements, slopes, curvatures, strains and even generalized forces, can be included in finding the optimal actuating voltage for static shape control. The present model is validated by comparing with those results available in the literature. The numerical results show that the weighted linear least method can give a satisfactory voltage distribution to best match the desired shape. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
87.
介绍了Multisim8的仿真功能的特点,并通过实例说明了用Multisim8进行仿真分析的具体方法,简单介绍了如何设置参数和进行仿真操作。 相似文献
88.
Specific interactions in blends containing Chitosan and functionalized polymers. Molecular dynamics simulations 总被引:2,自引:0,他引:2
Chitosan (CS)/poly(vinyl alcohol) (PVA) and Chitosan/poly(2-hydroxyethyl methacrylate) (P2HEM) blends have been studied through molecular dynamic simulations. In a previous work it was found miscibility between these polymers and it was attributed to hydrogen bonding formation. However, the experimental information obtained was not enough to know which of the interacting groups of Chitosan, i.e. -CH2OH or -NH2, are responsible of the interaction. Therefore, we have performed molecular dynamics simulation runs of 1 ns in order to calculate radial distribution functions (RDF) for the groups tentatively involved in the interaction. The results are correlated with our previous experimental data. This way, we have obtained a more precise conclusive information about the interactions involved as function of the blends composition. For low compositions of PVA and P2HEM the interaction is predominantly with the hydroxymethyl groups of CS while as the composition of PVA and P2HEM increases, the interaction with the amine groups increases. 相似文献
89.
Bedich ika Helena Bendov Ivan Macha
《Chemical Engineering and Processing: Process Intensification》2005,44(12):1312-1319
A procedure has been proposed for the estimation of the terminal falling velocity of non-spherical particles moving in a Carreau model fluid in the transition flow region. The procedure is based on a modification of the relationship formerly developed for the fall of spherical particles including the particle dynamic shape factor. The suitability of the proposed procedure has been confirmed by good agreement between experimental and calculated terminal falling velocity data. In the experiments, the terminal falling velocity of short cylinders and rectangular prisms in polymer solutions of different measure of shear thinning and elasticity has been measured. 相似文献
90.
基于Protel DXP的电路仿真设计 总被引:6,自引:0,他引:6
Protel DXP是集所有设计工具于一身的电子设计自动化(EDA)软件.文中运用其内嵌的仿真器叙述了分压式偏置电路放大器的仿真设计过程,设计过程简单、方便.在电子线路理论教学过程中引入电路设计仿真环节在不同情况下对电路进行实时分析,不仅可以提高学生的学习兴趣,而且能够在较短时间内加深学生对理论知识的理解;在工程设计过程中利用仿真工具对电路进行即时测试,可以缩短设计周期,提高设计效率. 相似文献