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   2709篇
  免费   41篇
  国内免费   5篇
电工技术   51篇
综合类   5篇
化学工业   214篇
金属工艺   9篇
机械仪表   40篇
建筑科学   106篇
矿业工程   1篇
能源动力   77篇
轻工业   54篇
水利工程   10篇
无线电   375篇
一般工业技术   255篇
冶金工业   1309篇
原子能技术   5篇
自动化技术   244篇
  2022年   18篇
  2021年   17篇
  2020年   14篇
  2019年   16篇
  2018年   9篇
  2017年   17篇
  2016年   25篇
  2015年   21篇
  2014年   31篇
  2013年   93篇
  2012年   44篇
  2011年   69篇
  2010年   56篇
  2009年   73篇
  2008年   49篇
  2007年   72篇
  2006年   70篇
  2005年   63篇
  2004年   48篇
  2003年   43篇
  2002年   47篇
  2001年   55篇
  2000年   41篇
  1999年   82篇
  1998年   377篇
  1997年   244篇
  1996年   186篇
  1995年   111篇
  1994年   98篇
  1993年   103篇
  1992年   39篇
  1991年   47篇
  1990年   35篇
  1989年   31篇
  1988年   44篇
  1987年   29篇
  1986年   34篇
  1985年   31篇
  1984年   14篇
  1983年   12篇
  1982年   11篇
  1981年   17篇
  1980年   29篇
  1979年   14篇
  1978年   18篇
  1977年   33篇
  1976年   76篇
  1975年   6篇
  1973年   9篇
  1972年   6篇
排序方式: 共有2755条查询结果,搜索用时 15 毫秒
81.
A novel serological test, IPAzyme Chlamydia (Savyon Diagnostics Ltd., Beer Sheva, Israel), was compared with an enzyme immunoassay (EIA) for the ability to detect serum immunoglobulin G and A antibodies in the diagnosis of acute chlamydial pelvic inflammatory disease. In comparison with cell culture, which is the "gold standard," IPAzyme Chlamydia and EIA exhibited sensitivities of 63 and 68% and specificities of 76 and 87%, respectively. Thus, IPAzyme Chlamydia offers no advantages over the EIA, and neither serological test can be recommended for the diagnosis of acute Chlamydia trachomatis infection. So far, conventional cell culture remains the most reliable diagnostic test for chlamydial pelvic inflammatory disease.  相似文献   
82.
In addition to a submuscular and subepithelial nerve plexus an infra-epithelial nerve-net also occurs in Notoplana acticola. It contains naked nerve cells which lie between the bases of epithelial cells. Individual neurites occur separately or in small tracts. Synapses contain clear spherical vesicles and are polarized. Post-synaptic neurites tend to be flat and ribbon-like. Rhabdite and mucus secreting cells in the epithelium have synapses associated with them. Neurites ending on the rhabdites appear to originate in the subepithelial plexus. The "sensory-free nerve endings" of earlier workers are reinterpreted as being motor terminals on epithelial secretory cells.  相似文献   
83.
Dealing with high-dimensional data has always been a major problem in many pattern recognition and machine learning applications. Trace ratio criterion is a criterion that can be applicable to many dimensionality reduction methods as it directly reflects Euclidean distance between data points of within or between classes. In this paper, we analyze the trace ratio problem and propose a new efficient algorithm to find the optimal solution. Based on the proposed algorithm, we are able to derive an orthogonal constrained semi-supervised learning framework. The new algorithm incorporates unlabeled data into training procedure so that it is able to preserve the discriminative structure as well as geometrical structure embedded in the original dataset. Under such a framework, many existing semi-supervised dimensionality reduction methods such as SDA, Lap-LDA, SSDR, SSMMC, can be improved using our proposed framework, which can also be used to formulate a corresponding kernel framework for handling nonlinear problems. Theoretical analysis indicates that there are certain relationships between linear and nonlinear methods. Finally, extensive simulations on synthetic dataset and real world dataset are presented to show the effectiveness of our algorithms. The results demonstrate that our proposed algorithm can achieve great superiority to other state-of-art algorithms.  相似文献   
84.
85.
C.Y. Tan  Y.Z. Zhou  J.S. Chen  S.Y. Chow  G.M. Chow   《Thin solid films》2006,510(1-2):286-291
Nanocluster beam technology combined with conventional sputtering was used to fabricate FePt–SiO2 nanocomposite films in this present work. The post-deposition annealing affected the final particle size and size distribution of FePt nanoclusters. The effects of both volume fraction of SiO2 matrix and annealing temperature on magnetic and microstructural properties were studied. Partial ordering, grain growth and agglomeration of FePt particles in FePt–SiO2 nanocomposite films occurred during annealing. A higher volume fraction of SiO2 matrix was effective in suppressing diffusion of atoms and magnetic exchange coupling of FePt grains. Excessive SiO2 however resulted in a lower degree of FePt ordering and thus lower coercivity.  相似文献   
86.
Video servers are essential in video‐on‐demand and other multimedia applications. In this paper, we present our high‐performance clustered CBR video server, Odyssey. Odyssey is a server connecting PCs with switched Ethernet. It provides efficient support for normal play and interactive browsing functions such as fast‐forward and fast‐backward. We designed a set of algorithms for scheduling, synchronization and admission control, which results in a high utilization of resources. Odyssey is able to deliver a large number of video streams. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
87.
An enzyme-linked immunosorbent assay (ELISA) for Neospora caninum antibodies was automated with a robotic workstation, the Beckman Coulter Biomek 2000, to screen 200 bovine sera. Comparing these results with manually run ELISA data, a 95.92% agreement (K = 0.9592) between the two assays was obtained. The automated assay was specific and sensitive with excellent positive and negative predictive values. The results were repeatable and reproducible. The automation flexibility was high and the operation complexity was minimal. High-throughput screening (HTS) for bovine antibodies to Neospora caninum was achieved. The assay was developed according to the internationally recognized ISO17025 standard requirements.  相似文献   
88.
This paper identifies managers who require ethics training in using IT at work. The identification of these managers is mainly based on studying the impact of their individual characteristics on a set of seven ethical issues and attitudes, which translated into IT ethical scenarios. This paper proposes a canonical model by treating individual characteristics of managers as predictor variables and considering information describing their beliefs on those seven ethical issues and attitudes as explained variables. A questionnaire survey was used for data collection and 249 managers participated in this study. The results show that the significant explained variables are based on a combination of six ethical events of accountability, conflict of interest, disclosure, personal conduct, protection of privacy, and social responsibility. The significant predictor variables are based on a combination of four individual characteristics of age, educational level, organizational level, and working experience. Discussion on the implication of the results and recommendations for remedial action are also provided in this paper.  相似文献   
89.
The coordination of multi-robots is required in many scenarios for efficiency and task completion. Combined with teleoperation capabilities, coordinating robots provide a powerful tool. Add to this the Internet and now it is possible for multi-experts at multi-remote sites to control multi-robots in a coordinated fashion. For this to be feasible there are several hurdles to be crossed including Internet type delays, uncertainties in the environment and uncertainties in the object manipulated. In addition, there is a need to measure and control the quality of tele-coordination. To this end, the measure of force sensed by each robot is suggested and justified as a coordination index. It was proven that if n robots are event-transparent and event-synchronous then they can be teleoperated under random delay conditions to coordinate to any index value, which is feasible under no delay conditions. The design procedure that ensures a system can satisfy a small coordination index was presented and analyzed.In addition, the design and analysis of event-synchronous systems using Petri Nets is detailed. The Petri Net design methodology is presented for both event-synchronous single operator single robot teleoperation systems and event-synchronous multi-operator multi-robot teleoperation systems.The theory developed was tested by bilaterally tele-coordinating two mobile manipulators via the Internet. The experimental results confirmed the theoretical results presented.  相似文献   
90.
Recent progress in silicon carbide (SiC) material has made it feasible to build power devices of reasonable current density. This paper presents results including a comparison with state-of-the-art silicon diodes. Switching losses for two silicon diodes (a fast diode, 600 V, 50 A, 60 ns Trr), an ultrafast silicon diode (600 V, 50 A, 23 ns Trr), and a 4H-SiC diode (600 V, 50 A) are compared. The effect of diode reverse recovery on the turn-on losses of a fast insulated gate bipolar transistor (IGBT) are studied both at room temperature and at 150 /spl deg/C. At room temperature, SiC diodes allow a reduction of IGBT turn-on losses by 25% compared to ultrafast silicon diodes and by 70% compared to fast silicon diodes. At 150 /spl deg/C junction temperature, SiC diodes allow turn-on loss reductions of 35% and 85% compared to ultrafast and fast silicon diodes, respectively. The silicon and SiC diodes are used in a boost converter with the IGBT to assess the overall effect of SiC diodes on the converter characteristics. Efficiency measurements at light load (100 W) and full load (500 W) are reported. Although SiC diodes exhibit very low switching losses, their high conduction losses due to the high forward drop dominate the overall losses, hence reducing the overall efficiency. Since this is an ongoing development, it is expected that future prototypes will have improved forward characteristics.  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