首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   8552篇
  免费   562篇
  国内免费   27篇
电工技术   132篇
综合类   6篇
化学工业   1766篇
金属工艺   322篇
机械仪表   585篇
建筑科学   168篇
矿业工程   1篇
能源动力   370篇
轻工业   627篇
水利工程   30篇
石油天然气   11篇
无线电   1742篇
一般工业技术   1825篇
冶金工业   622篇
原子能技术   149篇
自动化技术   785篇
  2023年   103篇
  2022年   149篇
  2021年   274篇
  2020年   211篇
  2019年   181篇
  2018年   240篇
  2017年   267篇
  2016年   312篇
  2015年   223篇
  2014年   336篇
  2013年   541篇
  2012年   550篇
  2011年   668篇
  2010年   481篇
  2009年   500篇
  2008年   472篇
  2007年   369篇
  2006年   331篇
  2005年   303篇
  2004年   276篇
  2003年   236篇
  2002年   251篇
  2001年   211篇
  2000年   203篇
  1999年   197篇
  1998年   307篇
  1997年   182篇
  1996年   140篇
  1995年   94篇
  1994年   99篇
  1993年   79篇
  1992年   43篇
  1991年   55篇
  1990年   38篇
  1989年   32篇
  1988年   28篇
  1987年   29篇
  1986年   17篇
  1985年   13篇
  1984年   12篇
  1983年   14篇
  1982年   10篇
  1981年   14篇
  1980年   8篇
  1979年   6篇
  1977年   10篇
  1976年   10篇
  1975年   3篇
  1974年   5篇
  1971年   2篇
排序方式: 共有9141条查询结果,搜索用时 15 毫秒
181.
Dispatching rules are important to the performance of a manufacturing system. Selective applications of different priority rules at different processing stages in a multiple workstation manufacturing system have a positive impact on shop performance. This type of problem is a combinatorial dispatching decision. However, no dispatching rule can consistently produce better performance than all other rules under a variety of operating conditions and criteria. It is the purpose of this study to provide a robust solution for a dispatching decision that will have ‘good’ performance under different operating scenarios. In this paper a simulation case of a flow shop with multiple processors is proposed, specifically a multi-layer ceramic capacitor manufacturing system. Two multiple criteria decision-making methods – techniques for order preference by similarity to ideal solution (TOPSIS) and an analytic hierarchy process (AHP) – in combination with Taguchi orthogonal array are used to find the most suitable dispatching rule for every workstation. The results show that for 15 production scenarios and 4 criteria this combinatorial dispatching rule is robust, in the sense that it outperforms other commonly employed strategies.  相似文献   
182.
Abstract— A flexible fluorescent lamp that utilizes the same plasma discharge mode as in PDPs has been manufactured. The structure of the flexible lamp is simple and easy to manufacture. All‐plastic materials including plastic substrates, barrier ribs (spacers), and sealants for low‐temperature manufacturing processing have been adopted except for the phosphor and MgO thin film. The MgO thin films were coated on the plastic substrates as a protection layer against the plasma discharge. The adhesion and biaxial texture of MgO thin film deposited on the plastic substrates, poly‐ethyle‐nenaphthalate (PEN) and polycarbonate (PC), at low temperature (100–180°C) has been characterized. The MgO film on PEN shows good adhesion under a repeated bending test. The manufactured flexible lamp consists of two plastic substrates of about 3 in. on the diagonal, barrier rib (spacer), and external ITO electrodes. The Ne‐Xe (5%) gas mixture at 100–200 Torr was used for the discharge gas. A maximum surface luminance of about 100 cd/m2 was achieved for a 1 ‐kHz AC pulse.  相似文献   
183.
Probe design is one of the most important tasks in successful deoxyribonucleic acid microarray experiments. We propose a multiobjective evolutionary optimization method for oligonucleotide probe design based on the multiobjective nature of the probe design problem. The proposed multiobjective evolutionary approach has several distinguished features, compared with previous methods. First, the evolutionary approach can find better probe sets than existing simple filtering methods with fixed threshold values. Second, the multiobjective approach can easily incorporate the user's custom criteria or change the existing criteria. Third, our approach tries to optimize the combination of probes for the given set of genes, in contrast to other tools that independently search each gene for qualifying probes. Lastly, the multiobjective optimization method provides various sets of probe combinations, among which the user can choose, depending on the target application. The proposed method is implemented as a platform called EvoOligo and is available for service on the Web. We test the performance of EvoOligo by designing probe sets for 19 types of Human Papillomavirus and 52 genes in the Arabidopsis Calmodulin multigene family. The design results from EvoOligo are proven to be superior to those from well-known existing probe design tools, such as OligoArray and OligoWiz.  相似文献   
184.
The growth and metastasis of solid tumors is dependent on angiogenesis. The vascular endothelial growth factor (VEGF) and its cell surface receptor in human KDR (kinase domain containing receptor or VEGFR-2) have particular interest because of their importance in angiogenesis. The development of novel inhibitors of VEGFR-2 would be helpful to check the growth of tumors. Quantitative structure activity relationship (QSAR) analyses used to understand the structural factors affecting inhibitory potency of thiazole-substituted pyrazolone derivatives. Several pharmacophore-based models indicated the importance of steric, hydrophobic and hydrogen bond acceptor groups to inhibitory activity. The comparative molecular field analyses (CoMFA) and comparative molecular similarity indices analyses (CoMSIA) based 3D-QSAR models were derived using pharmacophore-based alignment. Both CoMFA (q2 = 0.70, r2 = 0.97 and ) and CoMSIA (q2 = 0.54, r2 = 0.82 and ) gave reasonable results. The molecular docking (receptor-guided technique) with a recently reported receptor structure (PDB = 1YWN) were performed. The docked alignment was subsequently used for 3D-QSAR (CoMFA; q2 = 0.56, r2 = 0.97, , CoMSIA; q2 = 0.58 r2 = 0.91, ). The overall both studies were indicated, steric, electrostatic and hydrogen bond acceptor effects contribute to the inhibitory activity. CoMFA and CoMSIA models suggested that a positive bulk with hydrophobic effect is desirable around position 4 and 5 and hydrogen bond acceptor groups around pyrazolones ring will be helpful.  相似文献   
185.
The paper proposes a multibody dynamic simulation to numerically evaluate the generated axial force (GAF) and plunging resistant force (PRF) practically related to the shudder and idling vibration of an automobile. A numerical analysis of the drive shaft coupling of a ball joint (BJ) and two plunging type joints, a tripod joint (TJ), and a very low axial force tripod joint (VTJ), are conducted using the commercial program DAFUL. User-defined subroutines of a friction model illustrating the contacted parts of the outboard and inboard joint are subsequently developed to overcome the numerical instability and improve the solution performance. The Coulomb friction effect is applied to describe the contact models of the lubricated parts in the rolling and sliding mechanisms. The numerical results, in accordance with the joint articulation angle variation, are validated with experimentation. The offset between spider and housing is demonstrated to be the critical role in producing the third order component of the axial force that potentially causes the noise and vibration in the vehicle. The VTJ shows an excellent behavior for the shudder when compared with the TJ. In addition, a flexible nonlinear contact analysis coupled with multibody dynamics is also performed to show the dynamic strength characteristics of the rollers, housing, and spider.  相似文献   
186.
The fairness (or TCP-friendliness) of recent high-speed TCP proposals for high bandwidth-delay product networks is generally poor. We believe that the lack of TCP-friendliness of high-speed TCP proposals stems from their ineffectiveness in detecting competing TCP flows. We suggest a competition detection mechanism for a single TCP flow to detect the presence of competing TCP flows. We propose a new TCP, called Adaptive TCP (A-TCP) to demonstrate the usefulness of the competition detection mechanism. A-TCP uses the competition detection mechanism to control its aggressiveness: If it does not detect competing flows, a single A-TCP flow increases its sending rate aggressively in order to highly utilize the network. Otherwise, it behaves like a standard TCP flow to fairly share network resources with competing flows. We implemented A-TCP as part of Linux as well as in ns-2. Experimental results show that A-TCP achieves better fairness than existing high-speed TCP proposals when they compete against standard TCP in simple topology networks.  相似文献   
187.
In this paper, we proposed a multi-objective Pareto based particle swarm optimization (MOPPSO) to minimize the architectural complexity and maximize the classification accuracy of a polynomial neural network (PNN). To support this, we provide an extensive review of the literature on multi-objective particle swarm optimization and PNN. Classification using PNN can be considered as a multi-objective problem rather than as a single objective one. Measures like classification accuracy and architectural complexity used for evaluating PNN based classification can be thought of as two different conflicting criterions. Using these two metrics as the criteria of classification problem, the proposed MOPPSO technique attempts to find out a set of non-dominated solutions with less complex PNN architecture and high classification accuracy. An extensive experimental study has been carried out to compare the importance and effectiveness of the proposed method with the chosen state-of-the-art multi-objective particle swarm optimization (MOPSO) algorithm using several benchmark datasets. A comprehensive bibliography is included for further enhancement of this area.  相似文献   
188.
This communication describes novel 3-D manipulations of objects using an acoustically excited oscillating bubble deposited on a hydrophobic rod tip. The oscillating bubble captures various millimeter- and micron-sized neighboring objects including glass and polystyrene beads (~100 μm), fish egg, and live water flea (~1 mm). The captured objects are carried in a 3-D space by traversing the bubble tip, and released at desired positions by simply turning off the oscillation. Carrying performance is characterized along with high-speed imaging of oscillating bubbles by varying the frequency and amplitude of the acoustic excitation and the carrying speed. The higher the oscillation amplitude, the higher the carrying efficiency. The maximum carrying speed is measured at over 3 mm/s. This method is effective with a low-level acoustic excitation (bubble oscillation amplitude relative to the diameter ≤5%), possibly providing a cost-effective, soft-contact manipulating tool for handling biological objects.  相似文献   
189.
Cho SY  Lee CH  Oh SY  Chung CM 《Ultramicroscopy》2008,108(10):1220-1223
Nanoporous polyimide films were prepared from triblock copolyimides. A thermally labile polymer, poly(propylene glycol), was incorporated into polyimides based on 4,4-(hexafluoroisopropylidene)diphthalic anhydride to obtain triblock copolyimides. Nanofoams were formed by thermolysis of the labile block. The thermal properties of the copolymers were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The nanopores were characterized by scanning electron microscopy (SEM).  相似文献   
190.
In the design process of gratings, the grating layout design is the most important activity influencing manufacturing cost. In the grating layout design, the key to saving manufacturing cost is to find a design with a minimal number of cutting operations. This paper presents an application of the A* algorithm in grating layout design. The design problem is represented as the space search problem of design alternatives. A* explores the feasible alternatives within the space, until an optimal solution is obtained.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号