首页 | 官方网站   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   16182篇
  免费   1452篇
  国内免费   530篇
工业技术   18164篇
  2024年   88篇
  2023年   344篇
  2022年   590篇
  2021年   774篇
  2020年   598篇
  2019年   440篇
  2018年   482篇
  2017年   497篇
  2016年   510篇
  2015年   607篇
  2014年   802篇
  2013年   1046篇
  2012年   967篇
  2011年   1024篇
  2010年   838篇
  2009年   859篇
  2008年   885篇
  2007年   777篇
  2006年   652篇
  2005年   557篇
  2004年   466篇
  2003年   434篇
  2002年   376篇
  2001年   327篇
  2000年   303篇
  1999年   278篇
  1998年   532篇
  1997年   393篇
  1996年   275篇
  1995年   192篇
  1994年   166篇
  1993年   163篇
  1992年   99篇
  1991年   95篇
  1990年   86篇
  1989年   57篇
  1988年   60篇
  1987年   59篇
  1986年   63篇
  1985年   35篇
  1984年   40篇
  1983年   25篇
  1981年   42篇
  1980年   34篇
  1979年   24篇
  1978年   27篇
  1977年   41篇
  1976年   46篇
  1974年   12篇
  1971年   12篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
While current psychiatric taxonomies recognise a classification of amphetamine dependence, derived from the notion of an alcohol dependence syndrome, little research has validated that such a condition exists for this drug. Current amphetamine users (N = 331), were interviewed using the World Health Organization operationalisation of DSM-III-R substance dependence criteria, and a measure of the psychological components of dependence. Structural analyses indicated that a unidimensional dependence syndrome as assessed by DSM-III-R and DSM-IV criteria exists for amphetamine, and that physiological, psychological and behavioural indicators were all important in accounting for the variance in responses. It was demonstrated that the concept of a dependence syndrome is applicable to amphetamine, and that the inclusion of the amphetamine dependence syndrome in DSM-III-R and DSM-IV is valid.  相似文献   
72.
Room temperature synthesis of crystalline metal oxides   总被引:6,自引:0,他引:6  
Crystalline titanium dioxide powders have been synthesized as either rutile or anatase from aqueous solutions at low temperatures (T≤100°C) and atmospheric pressure. First, a sol is prepared by the hydrolysis of a titanium alkoxide in an acidic solution. The sol is subsequently heated at different rates to produce the different crystalline phases of titanium dioxide. Powder characterization was carried out using X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy. In general, the precipitate size was observed to be between 50 and 100 nm. Possible mechanisms involved in determining the crystal variants are discussed. This revised version was published online in November 2006 with corrections to the Cover Date.  相似文献   
73.
In 1994, the Eco-Vehicle Project was begun to develop an electric vehicle (EV) using a ground-up design approach that incorporates unique designs specific to an EV. The Eco-Vehicle will be a high-performance, but ultrasmall, battery-powered vehicle. New designs for the Eco-Vehicle include an in-wheel motor drive system, a hollow load floor which will house the batteries, and a new battery management system. The Eco-Vehicle may also utilize other advanced concepts suitable especially for EVs, including solar panels for battery charging and intelligent crash avoidance and guidance systems  相似文献   
74.
Ultrathin dielectric materials that provide high capacitance values are needed for 64- and 256-Mb stacked DRAMs. It is shown that capacitance values as high as 12.3 fF/μm2 can be obtained with ultrathin nitride-based layers deposited on rugged polysilicon storage electrodes. These films present the reliability and low leakage current levels required for 3.3-V applications. The nitride thickness, however, cannot be scaled much below 6 nm to avoid the oxidation-punchthrough mechanisms that appear when too-thin films are unable to withstand the reoxidation step  相似文献   
75.
To perform assembly tasks requiring compliant manipulation, the robot must follow a motion trajectory and exert an appropriate force profile while making compliant contact with a dynamic environment. For this purpose, a generalized impedance in the task space consisting of a second-order function relating the motion errors and interaction force errors is introduced such that the contact force can be commanded and controlled. With generalized impedance control, the robot can behave with a desired dynamic characteristic when it interacts with the environment. To ensure the success of the assembly, a strategy during task planning which takes into consideration the interrelation between motion and force trajectories as well as contact compliance is introduced. The generalized impedance control method is applied to the prismatic joint of a selective compliance assembly robot arm (SCARA) robot for inserting a printed circuit board (PCB) into an edge connector socket. Depending on the progress of the parts joining operation, various amount of interaction forces are generated which have to be accommodated. It is demonstrated that an assembly strategy which consists of a sequence of carefully planned target impedance can enable the task to be executed in a desirable manner. The effectiveness of this approach is illustrated through experiments by comparing the results with those obtained using a well-established position control scheme as well as the original impedance control method  相似文献   
76.
1. A case of poisoning due to the raw root tuber of a Chinese medicinal plant, Alocasia macrorrhiza is presented. 2. The patient developed neurological (severe pain and numbness in the perioral area and throat) and gastrointestinal (nausea, vomiting, abdominal pain) symptoms immediately after eating the root tuber. 3. A macrorrhiza has properties and morphology very similar to another medical plant. A. odora. The root tuber of the latter is known to contain a neurotoxin sapotoxin.  相似文献   
77.
A new analytical model to eliminate redundant discrete cosine transform (DCT) and quantisation (Q) computations in block-based video encoders is proposed. The dynamic ranges of the quantised DCT coefficients are analysed, then a threshold scheme is derived to determine whether the DCT and Q computations can be skipped without video quality degradation. In addition, fast DCT/inverse DCT (IDCT) algorithms are presented to implement the proposed analytical model. The proposed analytical model is compared with other comparable analytical models reported in the literature. Both the theoretical analysis and experimental results demonstrate that the proposed analytical model can greatly reduce the computational complexity of video encoding without any performance degradation and outperforms other analytical models  相似文献   
78.
Total variation blind deconvolution   总被引:54,自引:0,他引:54  
We present a blind deconvolution algorithm based on the total variational (TV) minimization method proposed by Acar and Vogel (1994). The motivation for regularizing with the TV norm is that it is extremely effective for recovering edges of images as well as some blurring functions, e.g., motion blur and out-of-focus blur. An alternating minimization (AM) implicit iterative scheme is devised to recover the image and simultaneously identify the point spread function (PSF). Numerical results indicate that the iterative scheme is quite robust, converges very fast (especially for discontinuous blur), and both the image and the PSF can be recovered under the presence of high noise level. Finally, we remark that PSFs without sharp edges, e.g., Gaussian blur, can also be identified through the TV approach.  相似文献   
79.
孟宪珩  郑航 《钢铁钒钛》1998,19(3):51-53,58
利用生产实践数据,分析了铁水中Si+Ti含理对炼铁焦比、产量、生铁S以及提钒时的钒回收率、钒渣品位、白灰消耗等工序指标的影响,提出了适合于承钢铁水的Si+Ti含量。  相似文献   
80.
A real-time planning algorithm for obstacle avoidance of redundant robots   总被引:3,自引:0,他引:3  
A computationally efficient, obstacle avoidance algorithm for redundant robots is presented in this paper. This algorithm incorporates the neural networks and pseudodistance function D p in the framework of resolved motion rate control. Thus, it is well suited for real-time implementation. Robot arm kinematic control is carried out by the Hopfield network. The connection weights of the network can be determined from the current value of Jacobian matrix at each sampling time, and joint velocity commands can be generated from the outputs of the network. The obstacle avoidance task is achieved by formulating the performance criterion as D p>d min (d min represents the minimal distance between the redundant robot and obstacles). Its calculation is only related to some vertices which are used to model the robot and obstacles, and the computational times are nearly linear in the total number of vertices. Several simulation cases for a four-link planar manipulator are given to prove that the proposed collision-free trajectory planning scheme is efficient and practical.  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-23

京公网安备 11010802026262号