全文获取类型
收费全文 | 41999篇 |
免费 | 2989篇 |
国内免费 | 1225篇 |
专业分类
电工技术 | 1625篇 |
综合类 | 1939篇 |
化学工业 | 8053篇 |
金属工艺 | 1730篇 |
机械仪表 | 2101篇 |
建筑科学 | 3318篇 |
矿业工程 | 646篇 |
能源动力 | 1271篇 |
轻工业 | 2452篇 |
水利工程 | 546篇 |
石油天然气 | 1839篇 |
武器工业 | 210篇 |
无线电 | 4813篇 |
一般工业技术 | 6650篇 |
冶金工业 | 2753篇 |
原子能技术 | 511篇 |
自动化技术 | 5756篇 |
出版年
2024年 | 110篇 |
2023年 | 575篇 |
2022年 | 928篇 |
2021年 | 1497篇 |
2020年 | 1124篇 |
2019年 | 966篇 |
2018年 | 1092篇 |
2017年 | 1184篇 |
2016年 | 1201篇 |
2015年 | 1404篇 |
2014年 | 1880篇 |
2013年 | 2409篇 |
2012年 | 2507篇 |
2011年 | 2747篇 |
2010年 | 2204篇 |
2009年 | 2202篇 |
2008年 | 2176篇 |
2007年 | 2141篇 |
2006年 | 2096篇 |
2005年 | 1851篇 |
2004年 | 1322篇 |
2003年 | 1188篇 |
2002年 | 1169篇 |
2001年 | 952篇 |
2000年 | 1022篇 |
1999年 | 1096篇 |
1998年 | 1158篇 |
1997年 | 937篇 |
1996年 | 884篇 |
1995年 | 722篇 |
1994年 | 572篇 |
1993年 | 545篇 |
1992年 | 364篇 |
1991年 | 278篇 |
1990年 | 280篇 |
1989年 | 198篇 |
1988年 | 174篇 |
1987年 | 132篇 |
1986年 | 107篇 |
1985年 | 94篇 |
1984年 | 82篇 |
1983年 | 63篇 |
1982年 | 59篇 |
1981年 | 46篇 |
1980年 | 42篇 |
1979年 | 29篇 |
1978年 | 35篇 |
1977年 | 34篇 |
1976年 | 72篇 |
1975年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Jonathan P. Belnoue Giang D. Nguyen Alexander M. Korsunsky 《International Journal of Fracture》2007,144(1):53-60
This paper presents a new 1-D non-local damage-plasticity deformation model for ductile materials. It uses the thermodynamic
framework described in Houlsby and Puzrin (2000) and holds, nevertheless, some similarities with Lemaitre’s (1971) approach.
A 1D finite element (FE) model of a bar fixed at one end and loaded in tension at the other end is introduced. This simple
model demonstrates how the approach can be implemented within the finite element framework, and that it is capable of capturing
both the pre-peak hardening and post-peak softening (generally responsible for models instability) due to damage-induced stiffness
and strength reduction characteristic of ductile materials. It is also shown that the approach has further advantages of achieving
some degree of mesh independence, and of being able to capture deformation size effects. Finally, it is illustrated how the
model permits the calculation of essential work of rupture (EWR), i.e. the specific energy per unit cross-sectional area that
is needed to cause tensile failure of a specimen. 相似文献
102.
Alexander Chroneos Nicholas J. Ashley Kaajal H. Desai John F. Maguire R. W. Grimes 《Journal of Materials Science》2007,42(6):2024-2029
The structures of a number of hydroxide and oxyhydroxide minerals have previously been reported without the hydrogen positions
explicitly defined. Here we use two atomic scale computer simulation techniques, one based on classical ionic potentials,
the other on density functional theory (DFT), to predict these positions. The aim is not only to provide data that can be
used as the basis for future experimental structure optimizations but also model parameters that can be used to predict complex
hydroxide structures. The efficacy of the approach is demonstrated through the comparison of predicted and experimental data
for minerals whose hydrogen positions are known. 相似文献
103.
Alexander Katsman Shalom Cohen Menachem Bamberger 《Journal of Materials Science》2007,42(16):6996-7003
This work deals with the development of Mg-based alloys with enhanced properties at elevated temperatures. This is achieved
by precipitation of binary phases such as MgZn2 and Mg2Sn during the aging of these alloys. The aim of the present work is to develop and calibrate a model for precipitation hardening
in Mg-based alloys, as different types of precipitates form simultaneously. The modified Langer-Schwartz approach, while taking
into account nucleation, growth and coarsening of the new phase precipitations, was used for the analysis of precipitates’
evolution and precipitation hardening during aging of Mg-based alloys. Two strengthening mechanisms associated with particle-dislocation
interaction (shearing and bypassing) were considered to be operating simultaneously due to particle size-distribution. Parameters
of the model, R
N
i and k
σ i
, were found by fitting of calculated densities and average sizes of precipitates with ones estimated from experiments. The
effective diffusion coefficients of phase formation processes, which determine the strengthening kinetics, were estimated
from the hardness maximum positions on the aging curves. 相似文献
104.
本文以引信电子安全系统(ESA)为应用背景,应用美国ADI公司生产的新型单片机ADμ C812,设计并实现了为ESA模拟产生各种环境信号,并能够同时对ESA的工作状态进行实时检测的一款实用设备--多功能测试仪,为ESA的进一步研制和开发应用奠定了一定的基础. 相似文献
105.
106.
Alexander E. Meyerovich 《Journal of Low Temperature Physics》2004,134(1-2):163-168
Similarities between alkali gases in optical lattices with non-integer occupation of the lattice sites and quantum crystals are explored. The analogy with the vacancy liquid provides an agternative explanation to the Mott transition for the recent experiment on the phase transition in the lattice. The vacancy liquid can undergo BEC with T c within experimental reach. Direct and vacancy-assisted mechanisms of the band motion for hyperfine impurities are discussed. The presence of vacancies can resugt in the spatial decomposition of the system into pure hyperfine components. Below BEC for the vacancies, the impurity component resembles 3He in 3He-Hell mixtures. 相似文献
107.
Weiming Shen S.Y.T. Lang Lihui Wang 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》2005,35(3):371-381
Global competition is driving manufacturing companies to change the way they do business. New kinds of shop floor control systems need to be implemented for these companies to respond quickly to changing shop floor environments and customer demands. This paper presents a new concept called iShopFloor-an intelligent shop floor based on the Internet, web, and agent technologies. It focuses on the implementation of distributed intelligence in the manufacturing shop floor. The proposed approach provides the framework for components of a complex control system to work together as a whole rather than as a disjoint set. It encompasses both information architecture and integration methodologies. The paper introduces the basic concept of iShopFloor, a generic system architecture, and system components. It also describes the implementation of eXtensible Markup Language message services in iShopFloor and the application of intelligent agents to distributed manufacturing scheduling. A prototype environment is presented, and some implementation issues are discussed. 相似文献
108.
Alexander Tessler 《International journal for numerical methods in engineering》1991,31(5):1027-1030
A variational higher-order theory for bending and stretching of linearly elastic orthotropic beams including the deformations due to transverse shearing and stretching of the transverse normal fibre is presented. The theory assumes a linear distribution for the longitudinal displacement and a parabolic variation of the transverse displacement across the thickness. Additionally, independent expansions are introduced for the through-thickness displacement gradients with the requirement of a least-square compatibility for the transverse strains and the satisfaction of exact stress boundary conditions at the top/bottom beam surfaces. The theory is shown to be well suited for finite element development requiring simple C0- and C?1- continuous displacement interpolation fields. To demonstrate the computational utility of the theory, a simple two-node stretching-bending finite element is formulated. The analytic and finite element results are obtained for a simple bending problem for which an exact elasticity solution is available. It is shown that the inclusion of the transverse normal deformation in the present theory enables improved displacement, strain and stress predictions, particularly, in the analysis of deep beams. 相似文献
109.
Fernando J. Muzzio Marcos Llusa Christopher L. Goodridge Nhat-Hang Duong Elizabeth Shen 《Powder Technology》2008,186(3):247-254
This paper investigates the effects of processing and equipment parameters of a ribbon blender (i.e. loading method of lubricant, fill level, blade speed and blade design) on magnesium stearate homogeneity. A core sampling technique is used to obtain at least one hundred samples per sampling event, which are extracted throughout the blender and yield a thorough characterization of the entire bed. The results presented here can be used as a guideline to develop appropriate blending processes and characterization protocols for ribbon blenders. 相似文献
110.
采用氨吸附-程序升温脱附(NH3-TPD)、低温N2吸附(BET)、压汞法以及加氢精制活性评价等技术,探索SiO2-Al2O3载体在制备过程中孔结构和表面性质的变化。实验结果表明,采用特殊扩孔剂制备载体,当焙烧温度为700℃时,平均孔径可达到17.3nm,其中孔径大于20nm的孔占总孔体积的13.2%;同时载体表面上的中、强酸中心也全部丧失,均为弱酸中心。采用该载体制备的MoNiP/SiO2-Al2O3石蜡加氢精制催化剂,在MoO3用量减少了约1/4的情况下,比目前工业上使用的催化剂具有更高的脱金属能力和加氢精制活性。 相似文献