全文获取类型
收费全文 | 80659篇 |
免费 | 12118篇 |
国内免费 | 6461篇 |
专业分类
电工技术 | 17916篇 |
技术理论 | 1篇 |
综合类 | 9757篇 |
化学工业 | 4602篇 |
金属工艺 | 2518篇 |
机械仪表 | 7155篇 |
建筑科学 | 12518篇 |
矿业工程 | 2797篇 |
能源动力 | 5779篇 |
轻工业 | 1225篇 |
水利工程 | 3214篇 |
石油天然气 | 2014篇 |
武器工业 | 1341篇 |
无线电 | 5139篇 |
一般工业技术 | 7309篇 |
冶金工业 | 1840篇 |
原子能技术 | 352篇 |
自动化技术 | 13761篇 |
出版年
2024年 | 519篇 |
2023年 | 1412篇 |
2022年 | 2708篇 |
2021年 | 2888篇 |
2020年 | 3179篇 |
2019年 | 2579篇 |
2018年 | 2521篇 |
2017年 | 3123篇 |
2016年 | 3563篇 |
2015年 | 3877篇 |
2014年 | 5729篇 |
2013年 | 5101篇 |
2012年 | 6853篇 |
2011年 | 7027篇 |
2010年 | 5200篇 |
2009年 | 5230篇 |
2008年 | 4893篇 |
2007年 | 5657篇 |
2006年 | 4831篇 |
2005年 | 3937篇 |
2004年 | 3102篇 |
2003年 | 2667篇 |
2002年 | 2147篇 |
2001年 | 1915篇 |
2000年 | 1659篇 |
1999年 | 1345篇 |
1998年 | 992篇 |
1997年 | 879篇 |
1996年 | 730篇 |
1995年 | 598篇 |
1994年 | 519篇 |
1993年 | 371篇 |
1992年 | 283篇 |
1991年 | 232篇 |
1990年 | 208篇 |
1989年 | 200篇 |
1988年 | 145篇 |
1987年 | 72篇 |
1986年 | 38篇 |
1985年 | 46篇 |
1984年 | 71篇 |
1983年 | 39篇 |
1982年 | 39篇 |
1981年 | 19篇 |
1980年 | 31篇 |
1979年 | 24篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1955年 | 5篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
TCP/IP网络的动态模型描述 总被引:2,自引:0,他引:2
拥塞现象成为TCP/IP网络发展面临的一个重要问题。因此,拥塞控制对TCP/IP网络的鲁棒性和稳定性具有重要作用。目前,网络拥塞控制策略主要包括两类:端到端的控制机制,如TCP拥塞控制算法;网络内部的主动队列管理(AQM)策略。但由于缺乏对网络系统动态特性的了解,这些拥塞控制策略大都基于专家经验,并没有建立完整的理论分析框架。为此,本文从数据流的角度出发,通过建立网络基本单元状态方程模型来实现IP网络系统的数学解析模型,然后用混杂系统来描述TCP带有拥塞控制策略的数据传输过程,建立了TCP/IP网络的动态模型,为网络系统中动态性能的分析、拥塞控制策略的设计奠定了基础。实验结果表明,该数学模型与NS仿真实验的结果相一致。 相似文献
82.
We study the stressed state of an inhomogeneous welded joint containing an interlayer of a more high-strength material under the action of tensile loads. It is assumed that the contact boundary has a cracklike defect. We deduce analytic dependences of the fracture load on the mechanical inhomogeneity of the joint, thickness of the interlayer, and depth of the defect. The maximum depth of the defect to which the joint is insensitive is established. The proposed theoretical results are innovative and agree with the experimental data obtained for specimens cut out from a pipe of 14KhGS steel. 相似文献
83.
It is well recognized that performance changes over time. However, the effect of these changes on overall assessments of performance is largely unknown. In a laboratory experiment, we examined the influence of salient Gestalt characteristics of a dynamic performance profile on supervisory ratings. We manipulated performance trend (flat, linear-improving, linear-deteriorating, U-shaped, and ∩-shaped), performance variation (small, large), and performance mean (negative, zero, positive) within subjects and display format (graphic, tabular) between subjects. Participants received and evaluated information about the weekly performance of different employees over a simulated 26-week period. Results showed strong main effects on performance ratings of both performance mean and performance trend, as well as interactions with display format. Theoretical and practical implications of the results are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
84.
就我公司动力厂给水车间155kW水泵电机无功就地补偿的可行性及经济效益进行了分析和研究,对工厂用电如何节能降耗有一定的参考价值。 相似文献
85.
D. SHERMAN 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(1):32-40
Fracture experiments with silicon specimens in recent years have shown the need for a new approach to the analysis of rapidly propagating cracks in single crystals. Behaviour and phenomena have been revealed that fracture in these materials is rather different from the fracture of both amorphous and polycrystalline materials. We show that continuum mechanics is insufficient for analyzing crack propagation in single crystals since it is unable to consider atomistic‐scale phenomena. Accordingly, we describe basic phenomena associated with rapid crack propagation in silicon : (i) anisotropic velocity‐dependent R‐curve behaviour, as a key phenomenon dictating atomistic scale behaviour, (ii) crack deflection from one cleavage plane to another as a mesoscopic scale phenomenon in single‐crystal fracture, (iii) the Rayleigh surface wave speed as the limiting crack tip velocity is re‐examined, (vi) the lowest crack velocity in brittle crystals is examined, and finally (v) the interaction between crack path and preferred cleavage planes in single crystals is depicted. 相似文献
86.
An increasing amount of laser beam welded T‐joints (e.g. skin‐stringer) of aluminium alloys are now in use in advanced fuselage applications designed as ‘integral structures’ for weight and cost savings. It is known that weld joints generally show lower strength (undermatching) than base metal in both laser beam and friction stir welded joints of 6xxx series Al‐alloys. Damage tolerance considerations in terms of the residual strength of such joints require limit load solutions to be used in engineering fitness‐for‐service (FFS) analysis. The paper, therefore, provides an upper bound limit load solution in closed form for welded T‐joints (idealized) with strength undermatching and subject to a bending moment. In addition to the necessary requirements of the upper bound theorem, the kinematically admissible velocity field chosen leads to a stress field, which satisfies the equilibrium equations and some stress boundary conditions in the plastic zone. This is an advantage of the solution and, therefore, it is expected that the upper bound obtained is close to the exact limit load of such joints. 相似文献
87.
A method for constructing an approximation of the critical excitation that drives an elastoplastic system from rest to a target threshold at a specified time instant, referred to as the “suboptimal excitation,” is presented in this paper. It is based on the observations gained from study of the critical excitations in the companion paper. Essentially, for the usual case of interest where the failure time is not small compared to the natural period, the duration of the positive and negative pulses of the critical excitation are roughly equal to half of the natural period. This consideration allows for a simple intuitive approximation of the critical excitation. The amplitudes of the positive and negative pulses are obtained in closed forms using energy balance. Numerical investigations show that the critical excitations are well approximated by the suboptimal excitations. 相似文献
88.
已往库存论中的决策模型,它是把现实过程用数学的方法进行分析,得到决策值,但不能看到决策的过程,不能反映出现实生活中的不确定性、动态性。运用Delphi 7.0和SQL server 2000对销售过程进行了动态仿真,利用Newsboy模型的推广(S,s)订购策略来监控库存并做出决策,这样就体现出此过程的不确定性、动态性;且举出了一个仿真商品销售的实例,对其中的一些关键技术,如何仿真、算法的实现等进行了阐述。 相似文献
89.
90.
介绍了500W宽频带功率负载的设计及实验结果,并将研究成果扩展到10~1000W范围。负载主要技术指标:输入阻抗50Ω,频带宽度0~1000MHz,电压驻波比≤1.1.表面最高温升△t≤100℃。 相似文献