全文获取类型
收费全文 | 96722篇 |
免费 | 9011篇 |
国内免费 | 5277篇 |
专业分类
电工技术 | 7694篇 |
技术理论 | 6篇 |
综合类 | 9876篇 |
化学工业 | 9119篇 |
金属工艺 | 4257篇 |
机械仪表 | 5892篇 |
建筑科学 | 18480篇 |
矿业工程 | 4563篇 |
能源动力 | 2917篇 |
轻工业 | 5835篇 |
水利工程 | 5187篇 |
石油天然气 | 5909篇 |
武器工业 | 1529篇 |
无线电 | 6331篇 |
一般工业技术 | 8124篇 |
冶金工业 | 4544篇 |
原子能技术 | 973篇 |
自动化技术 | 9774篇 |
出版年
2024年 | 312篇 |
2023年 | 1159篇 |
2022年 | 2296篇 |
2021年 | 2869篇 |
2020年 | 2956篇 |
2019年 | 2425篇 |
2018年 | 2239篇 |
2017年 | 2869篇 |
2016年 | 3257篇 |
2015年 | 3532篇 |
2014年 | 5851篇 |
2013年 | 5360篇 |
2012年 | 7047篇 |
2011年 | 7390篇 |
2010年 | 5635篇 |
2009年 | 5828篇 |
2008年 | 5263篇 |
2007年 | 6528篇 |
2006年 | 5965篇 |
2005年 | 5262篇 |
2004年 | 4404篇 |
2003年 | 3830篇 |
2002年 | 3269篇 |
2001年 | 2783篇 |
2000年 | 2276篇 |
1999年 | 1850篇 |
1998年 | 1431篇 |
1997年 | 1155篇 |
1996年 | 1090篇 |
1995年 | 944篇 |
1994年 | 710篇 |
1993年 | 554篇 |
1992年 | 459篇 |
1991年 | 292篇 |
1990年 | 309篇 |
1989年 | 252篇 |
1988年 | 185篇 |
1987年 | 139篇 |
1986年 | 101篇 |
1985年 | 82篇 |
1984年 | 71篇 |
1983年 | 36篇 |
1981年 | 52篇 |
1980年 | 92篇 |
1979年 | 76篇 |
1965年 | 32篇 |
1964年 | 36篇 |
1959年 | 34篇 |
1956年 | 30篇 |
1955年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
71.
论文比较详细地阐述了涉密网主机系统所面临的安全隐患,提出了涉密网主机安全防护所要解决的几个技术问题,并就可能实现的技术方法进行了探讨和比较。 相似文献
72.
Fatigue crack propagation of multiple coplanar cracks with the coupled extended finite element/fast marching method 总被引:1,自引:0,他引:1
A numerical technique for modeling fatigue crack propagation of multiple coplanar cracks is presented. The proposed method couples the extended finite element method (X-FEM) [Int. J. Numer. Meth. Engng. 48 (11) (2000) 1549] to the fast marching method (FMM) [Level Set Methods & Fast Marching Methods: Evolving Interfaces in Computational Geometry, Fluid Mechanics, Computer Vision, and Materials Science, Cambridge University Press, Cambridge, UK, 1999]. The entire crack geometry, including one or more cracks, is represented by a single signed distance (level set) function. Merging of distinct cracks is handled naturally by the FMM with no collision detection or mesh reconstruction required. The FMM in conjunction with the Paris crack growth law is used to advance the crack front. In the X-FEM, a discontinuous function and the two-dimensional asymptotic crack-tip displacement fields are added to the finite element approximation to account for the crack using the notion of partition of unity [Comput. Meth. Appl. Mech. Engng. 139 (1996) 289]. This enables the domain to be modeled by a single fixed finite element mesh with no explicit meshing of the crack surfaces. In an earlier study [Engng. Fract. Mech. 70 (1) (2003) 29], the methodology, algorithm, and implementation for three-dimensional crack propagation of single cracks was introduced. In this paper, simulations for multiple planar cracks are presented, with crack merging and fatigue growth carried out without any user-intervention or remeshing. 相似文献
73.
74.
分析了试井技术的发展趋势,对有限元分析技术及其发展作了较为全面的介绍,重点阐述了利用有限元技术进行三维建模的方法和步骤,尤其是对复杂的非对称边界和非均质油藏的建模方法和技巧进行了深入探讨。利用数值试井技术,石油工程师可以方便准确地对复杂油藏和边界进行建模,试井的模拟过程和油藏任意位置的压力瞬间变化都可以通过图形和颜色的变化显示出来,解释的精度和速度都得到了大大地提高。 相似文献
75.
The present work deals with the modelling of damage behaviour for sheet moulding compound (SMC) composite materials using a finite element analysis package. Specifically, a comparison is made between the results obtained experimentally for a three-point bending test, and those obtained from numerical simulation using a material model already implemented. The simulation has been performed for the material models available within the PAM-CRASH software. The simulation results are compared and validated with respect to experimentation. 相似文献
76.
This review article is devoted to the materials containing niobium, which have been discovered or developed in the past few years and exhibit the potential application in heterogeneous catalysis. Niobium oxides and mixed oxides as well as sulfides, nitrides (oxynitrides), carbides (oxycarbides), and phosphates are considered. Among the catalytic processes in which Nb-containing materials were tested, liquid and gas phase oxidation is described in details, and the role of niobium in the prevention of the catalyst from SO2 poisoning is mentioned. 相似文献
77.
78.
电子产品研制阶段可靠性增长试验研究 总被引:1,自引:0,他引:1
结合工程实际经验,深入讨论了可靠性增长过程及实现途径,在保持试验条件和改进过程不变的条件下,实施了对具体型号电子产品的可靠性增长试验,达到了预期的可靠性增长目标,并且利用可靠性增长试验的数学模型(AMSAA模型)来评估产品的可靠性增长,对开展可靠性增长与可靠性增长试验工作具有重要的实际意义. 相似文献
79.
The problem of operating freeze drying of pharmaceutical products in vials placed in trays of a freeze dryer to remove free water (in frozen state) at a minimum time was formulated as an optimal control problem. Two different types of freeze dryer designs were considered. In type I freeze dryer design, upper and lower plate temperatures were controlled together, while in type II freeze dryer design, upper and lower plate temperatures were controlled independently. The heat input to the material being dried and the drying chamber pressure were considered as control variables. Constraints were placed on the system state variables by the melting and scorch temperatures during primary drying stage. Necessary conditions of optimality for the primary drying stage of freeze drying process in vials are derived and presented. Furthermore, an approach for constructing the optimal control policies that would minimize the drying time for the primary drying stage was given. In order to analyze optimal control policy for the primary drying stage of the freeze-drying process in vials, a rigorous multi-dimensional unsteady state mathematical model was used. The theoretical approach presented in this work was applied in the freeze drying of skim milk. Significant reductions in the drying times of primary drying stage of freeze drying process in vials were obtained, as compared to the drying times obtained from conventional operational policies. 相似文献
80.
介绍了堆石料与基岩面的现场直剪试验方法,6个组次的直剪试验结果表明,堆石料与基岩面的抗剪强度指标随基岩面坚硬度的增大而增加,并随基岩面粗糙度的加大而加大。 相似文献