全文获取类型
收费全文 | 67024篇 |
免费 | 10086篇 |
国内免费 | 5437篇 |
专业分类
电工技术 | 7828篇 |
技术理论 | 2篇 |
综合类 | 7371篇 |
化学工业 | 6558篇 |
金属工艺 | 2641篇 |
机械仪表 | 6529篇 |
建筑科学 | 3267篇 |
矿业工程 | 2328篇 |
能源动力 | 3101篇 |
轻工业 | 4787篇 |
水利工程 | 1764篇 |
石油天然气 | 2850篇 |
武器工业 | 922篇 |
无线电 | 5732篇 |
一般工业技术 | 5742篇 |
冶金工业 | 1918篇 |
原子能技术 | 302篇 |
自动化技术 | 18905篇 |
出版年
2024年 | 252篇 |
2023年 | 1486篇 |
2022年 | 2736篇 |
2021年 | 2914篇 |
2020年 | 3134篇 |
2019年 | 2683篇 |
2018年 | 2394篇 |
2017年 | 3002篇 |
2016年 | 3311篇 |
2015年 | 3742篇 |
2014年 | 5202篇 |
2013年 | 4998篇 |
2012年 | 5956篇 |
2011年 | 6002篇 |
2010年 | 4182篇 |
2009年 | 4317篇 |
2008年 | 3821篇 |
2007年 | 4386篇 |
2006年 | 3637篇 |
2005年 | 2845篇 |
2004年 | 2280篇 |
2003年 | 1780篇 |
2002年 | 1466篇 |
2001年 | 1214篇 |
2000年 | 936篇 |
1999年 | 621篇 |
1998年 | 580篇 |
1997年 | 489篇 |
1996年 | 382篇 |
1995年 | 376篇 |
1994年 | 303篇 |
1993年 | 226篇 |
1992年 | 199篇 |
1991年 | 164篇 |
1990年 | 138篇 |
1989年 | 116篇 |
1988年 | 73篇 |
1987年 | 29篇 |
1986年 | 25篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 10篇 |
1980年 | 16篇 |
1979年 | 14篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1959年 | 5篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
41.
Traditional optimization methods, which take a specific order of modal frequency as the design constraint, could fail to obtain the desired solution because of modal substitution. An improved optimization model with continuous sizing variables is established to solve this problem, in which the minimum weight and a given local modal frequency are considered as the objective and the constraint. To capture accurately the expected mode of vibration, a local mode identification technique is proposed based on the strain energy ratio between the local area and the whole structure. With that scheme, an optimization system is developed, in which the local mode can be effectively identified and the constraint can be updated with it in the iteration process. Two numerical examples, of a reinforced plate and a satellite structure, are applied to illustrate the effectiveness and efficacy of the proposed method. 相似文献
42.
Ashok Mahajan Naazneen Surti Pooja Koladiya 《Drug development and industrial pharmacy》2018,44(3):463-471
The aim of the present study was to improve the dissolution and flow properties of lurasidone hydrochloride (LH) by solid dispersion adsorbate (SDA) technique. Solid dispersions (SDs) of LH were prepared by fusion method using Poloxamer P188. The melt dispersion was adsorbed onto the porous carrier Florite (calcium silicate). A 32 factorial design was employed to quantify the effect of two independent variables, namely ratio of carrier (Poloxamer 188) and LH in SD and ratio of adsorbent (Florite) to SD. SDA granules of LH were studied for flow properties and characterized using differential scanning calorimetry, scanning electron microscopy, and X-ray diffraction. Tablets of optimized composition of SDA granules (equivalent to 20?mg of drug) and plain tablets were prepared by direct compression method. The dissolution studies were carried out in Mcllvaine buffer (pH 3.8) as per USFDA guidelines and characterized for parameters such as percent dissolution efficiency, t50, and Q30. Tablets prepared from SDA granules showed almost four-fold increase in cumulative percentage drug release as compared to tablets prepared from plain LH. The value of dissolution efficiency was enhanced from 49.60% for plain tablets to 94.15% for SDA tablets. SDA granules did not show any change in drug release and X-ray diffraction pattern after storage at 40?°C/75% of RH for 3?months, which confirms that Florite prevented conversion of drug from amorphous form to crystalline form improving physical stability of the amorphous state of LH. 相似文献
43.
Parallel Multipopulation Differential Evolutionary Particle Swarm Optimization for Voltage and Reactive Power Control 下载免费PDF全文
This paper presents parallel multipopulation differential evolutionary particle swarm optimization (DEEPSO) for voltage and reactive power control (VQC). The problem can be formulated as a mixed integer nonlinear optimization problem and various evolutionary computation techniques have been applied to the problem including PSO, differential evolution (DE), and DEEPSO. Since VQC is one of the online controls, speed‐up of computation is required. Moreover, there is still room for improvement in solution quality. This paper applies parallel multipopulation DEEPSO in order to speed up the calculation and improve solution quality. The proposed method is applied to IEEE 30, 57, and 118 bus systems. The results indicate that the proposed method can realize fast computation and minimize more active power losses than the conventional evolutionary computation techniques. 相似文献
44.
Change in the color of heat‐treated,vacuum‐packed broccoli stems and florets during storage: effects of process conditions and modeling by an artificial neural network 下载免费PDF全文
45.
46.
47.
为了避免和减轻由过大隔震层位移引起的损害,对基础隔震框架结构装设调频液柱阻尼器(tuned liquid column damper,简称TLCD)后混合系统的减振效果进行研究。建立了单层和多层混合控制系统在地震作用下的运动方程,采用TLCD-结构体系转化为调频质量阻尼器(tuned mass damper,简称TMD)-结构体系的等效方法,利用TMD参数优化公式,得到单个TLCD初始设计参数,并采用状态空间方程得到多个TLCD最优设计参数。通过对某8层基础隔震结构进行模拟,证明了该理论设计方法的合理性。该混合结构不仅可以减小隔震层位移和加速度,而且对上部结构位移和加速度反应都能更有效的控制。 相似文献
48.
The inlet/outlet is an important part of a water conveyance system in a pumped storage power station (PSPS). Its hydraulic characteristics are directly related to the operation and economic benefit of the PSPS. Frequent changes between inflow and outflow operations pose significant challenges in the design of the inlet/outlet diffusion segment shape. In this study, an effective optimization method, including three-dimensional parametric modelling, computational fluid dynamics and a genetic algorithm, is introduced and coupled to the design of the diffusion segment shape. The hydraulic characteristics of bi-directional flow, including the head loss, velocity uneven distribution and uneven discharge distribution, are selected as the objective function in the optimization method. Using this method, the recommended shape of the inlet/outlet is studied and its hydraulic characteristics are discussed. The results indicate that the optimized inlet/outlet has better performance. 相似文献
49.
针对未考虑正偏心正交车铣切削层几何形状而导致难以全面反映正交车铣切削层几何形状变化规律的问题,基于正交车铣运动规律,在不考虑动力学影响的情况下,对切削层的形成过程进行了静态分析。建立的正偏心正交车铣切削层几何形状的解析模型涉及铣刀侧刃和底刃的切入/切出角度、切削厚度和切削深度。通过试验验证了该解析模型的正确性,并分析了切削参数对铣刀切削层的影响。研究结果为正偏心正交车铣切削层几何形状的变化提供了定量的分析依据,为切削力和颤振的研究提供了理论指导。 相似文献
50.
针对管道布局、最大允许能耗给定条件下快速热循环注塑成形(RHCM)注塑模具型腔表面快速均匀加热的问题,提出以单根加热棒热流密度为设计变量,以模具型腔表面升温效率和温度分布均匀性为目标,结合有限元模拟、响应面设计以及多目标粒子群优化技术来优化RHCM模具电加热系统。与优化前相比,加热系统优化后,模具型腔表面最大温差降低63.4%,加热系统总能耗降低9%。对比了不同注塑成形工艺条件下成形的平板塑件表面质量,结果表明,相对传统注塑成形(CIM)工艺,RHCM工艺将制品表面粗糙度Ra从320 nm降低到118 nm,并有效抑制了制品表面熔接痕、缩痕等缺陷;发现制品表面粗糙度与型腔表面对应点温度成负相关,说明优化后的型腔表面温度分布更有利于提升制品表面质量。 相似文献