全文获取类型
收费全文 | 29980篇 |
免费 | 3591篇 |
国内免费 | 2960篇 |
专业分类
电工技术 | 2002篇 |
技术理论 | 1篇 |
综合类 | 3815篇 |
化学工业 | 3237篇 |
金属工艺 | 3261篇 |
机械仪表 | 1888篇 |
建筑科学 | 724篇 |
矿业工程 | 499篇 |
能源动力 | 573篇 |
轻工业 | 849篇 |
水利工程 | 206篇 |
石油天然气 | 442篇 |
武器工业 | 355篇 |
无线电 | 3684篇 |
一般工业技术 | 5437篇 |
冶金工业 | 950篇 |
原子能技术 | 237篇 |
自动化技术 | 8371篇 |
出版年
2024年 | 107篇 |
2023年 | 484篇 |
2022年 | 781篇 |
2021年 | 958篇 |
2020年 | 968篇 |
2019年 | 992篇 |
2018年 | 902篇 |
2017年 | 1171篇 |
2016年 | 1208篇 |
2015年 | 1381篇 |
2014年 | 1817篇 |
2013年 | 2134篇 |
2012年 | 2117篇 |
2011年 | 2203篇 |
2010年 | 1754篇 |
2009年 | 2002篇 |
2008年 | 1766篇 |
2007年 | 2064篇 |
2006年 | 1738篇 |
2005年 | 1511篇 |
2004年 | 1271篇 |
2003年 | 1077篇 |
2002年 | 906篇 |
2001年 | 851篇 |
2000年 | 726篇 |
1999年 | 588篇 |
1998年 | 480篇 |
1997年 | 447篇 |
1996年 | 369篇 |
1995年 | 355篇 |
1994年 | 305篇 |
1993年 | 236篇 |
1992年 | 195篇 |
1991年 | 149篇 |
1990年 | 131篇 |
1989年 | 94篇 |
1988年 | 73篇 |
1987年 | 45篇 |
1986年 | 26篇 |
1985年 | 24篇 |
1984年 | 22篇 |
1983年 | 24篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
1Introduction Reconstructivesurgeryisoneofthehottestre searchedsubjectsthatdealingwithbonedefects.Thetra ditionalmethodisimplantationoffreshautograftbonebe causeofitsnon immunoreactiveproperty.Butautologousbonewasnotabundantinsomecases.Sowefoundbeta trica… 相似文献
22.
The formation of aluminum matrix composites fabricated by exothermic dispersion reaction in A1-TiO2-B2O3 system was investigated. The thermal analysis results show that the reactions are spontaneous and exothermic. The Gibbs free energy of α-Al2O3 is the lowest among all the combustion products, followed by TiB2 and Al3Ti. It is noted that when the B2O3/TiO2 mole ratio is below 1, the reaction products are composed of particle-like α-Al2O3, TiB2 and rod-like Al3Ti. The α-Al2O3 crystallites, resulting from the reaction between A1 and TiO2 or B2O3, are segregated at the grain boundaries due to a lower wettability with the matrix. SEM micrographs show that rod-like Al3Ti phase distributes uniformly in the matrix. When the BEO3/TiO2 mole ratio is around 1, the Al3Ti phase almost disappears in the composites, and the distribution of α-Al2O3 particulates is improved evidently. 相似文献
23.
Jiang Minhong Gu Zhengfei Cheng Gang 《中国稀土学报(英文版)》2005,23(6):723-723
Polymer matrix RE-Fe giant magnetostrictire composite (GMPC) was prepared using bonding and magnetic field forming technique, and magnetostriction of samples was measured for different compressive stress. The experimental results show thai there is certain compressive effect in GMPC. And the influence of compressive stress on magnetostriction of sample was investigated. It offers essential reference for application and device design of GMPC. 相似文献
24.
Average consensus in networks of dynamic agents with switching topologies and multiple time-varying delays 总被引:5,自引:0,他引:5
In this paper, we discuss average consensus problem in undirected networks of dynamic agents with fixed and switching topologies as well as multiple time-varying communication delays. By employing a linear matrix inequality method, we prove that all the nodes in the network achieve average consensus asymptotically for appropriate communication delays if the network topology is connected. Particularly, several feasible linear matrix inequalities are established to determine the maximal allowable upper bound of time-varying communication delays. Numerical examples are given to demonstrate the effectiveness and the sharpness of the theoretical results. 相似文献
25.
Akiyoshi Wakatani 《Parallel Computing》2004,30(12):1345-1359
It is hard to implement the ADI method in an efficient way on distributed-memory parallel computers. We propose “P-scheme” which parallelizes a tridiagonal linear system of equations for the ADI method, but its effectiveness is limited to the cases where the problem size is large enough mainly because of the communication cost of the propagation phase of the scheme.
In order to overcome this difficulty, we propose an improved version of the P-scheme with “message vectorization” which aggregates several communication messages into one and alleviates the communication cost. Also we evaluate the effectiveness of message vectorization for the ADI method and show that the improved version of the P-scheme works well even for smaller problems and linear and super-linear speedups can be achieved for 8194 × 8194 and 16,386 × 16,386 problems, respectively. 相似文献
26.
27.
YOSHIHARU KARIYA TADATOMO SUGA 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(5):413-419
This paper details the deformation mechanism and low‐cycle fatigue life of eutectic solder alloys at high temperature (around 0.8Tm). Grain boundary sliding generally nucleates a wedge‐type cavity that reduces the low‐cycle fatigue life of metals. In this study, grain boundary sliding has promoted intergranular failure contributing to the reduction in fatigue life of Sn–Ag–Cu alloy. However, grain boundary sliding has exerted no deleterious effects on fatigue resistance of eutectic Pb–Sn and Bi–Sn alloys. The phase boundary sliding with very fine microstructure induces exceptional ductility in these alloys leading to superior low‐cycle fatigue endurance for theses eutectic Pb–Sn and Bi–Sn alloys. 相似文献
28.
The effect of particle distribution on damage formation in particulate reinforced metal matrix composites deformed in compression 总被引:1,自引:0,他引:1
P.B. Prangnell S.J. Barnes S.M. Roberts P.J. Withers 《Materials Science and Engineering: A》1996,220(1-2):41-56
Image analysis results are reported on the generation of damage in particulate reinforced metal matrix composites during compressive deformation. The technique allows the automated collection of data on the incidence of particle fracture and void formation in the matrix as a function of important microstructural parameters such as local particle volume fraction and particle size. There is a strong relationship between damage and the local volume fraction of the reinforcement proving that damage formation is accentuated in regions of particle clustering. With the SiC reinforced materials examined, there was observed to be a change in dominance of damage mechanism from particle fracture at low local volume fractions to void formation in the matrix within strongly clustered regions. The results are compared with finite element (FE) modelling of the compressive deformation of clustered particles using a simple cluster of equi-spaced particles. The FE results suggest that plastic flow is generally inhibited in clustered regions. In certain highly clustered configurations shielding is such that flow does not occur in the heart of the cluster even at high levels of average plastic strain. The modelling suggests that the change in dominance of damage mechanism is related to the dramatic increase in tensile hydrostatic stresses in the matrix with higher levels of particle clustering. 相似文献
29.
The partial oxidation of methanol to formaldehyde was studied over YBa2Cu3O7-x catalyst in a flow reactor. The structural change of YBa2Cu3O7-x before and after the reaction was measured by means of XRD and iodometric titration method. The catalytic characteristics
of YBa2Cu3O7-x for the partial oxidation of methanol to formaldehyde was due to copper ions. It was found that Cu+2 was responsible for the higher selectivity for formaldehyde. 相似文献
30.
The general mixed μ problem has been shown to be NP hard, so that the exact solution of the general problem is computationally intractable, except for small problems. In this paper we consider not the general problem, but a particular special case of this problem, the rank one mixed μ problem. We show that for this case the mixed μ problem is equivalent to its upper bound (which is convex), and it can in fact be computed easily (and exactly). This special case is shown to be equivalent to the so-called ‘affine parameter variation’ problem (for a polynomial with perturbed coefficients) which has been examined in detail in the literature, and for which several celebrated ‘Kharitonov-type’ results have been proven. 相似文献