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   2821篇
  免费   45篇
  国内免费   8篇
电工技术   25篇
综合类   2篇
化学工业   142篇
金属工艺   22篇
机械仪表   18篇
建筑科学   60篇
矿业工程   4篇
能源动力   31篇
轻工业   47篇
水利工程   1篇
石油天然气   5篇
无线电   168篇
一般工业技术   140篇
冶金工业   2077篇
原子能技术   11篇
自动化技术   121篇
  2023年   4篇
  2022年   4篇
  2021年   14篇
  2020年   11篇
  2019年   18篇
  2018年   11篇
  2017年   12篇
  2016年   25篇
  2015年   19篇
  2014年   27篇
  2013年   46篇
  2012年   39篇
  2011年   53篇
  2010年   38篇
  2009年   42篇
  2008年   26篇
  2007年   47篇
  2006年   34篇
  2005年   43篇
  2004年   32篇
  2003年   37篇
  2002年   30篇
  2001年   15篇
  2000年   16篇
  1999年   94篇
  1998年   757篇
  1997年   415篇
  1996年   254篇
  1995年   139篇
  1994年   125篇
  1993年   123篇
  1992年   23篇
  1991年   25篇
  1990年   12篇
  1989年   22篇
  1988年   13篇
  1987年   19篇
  1986年   12篇
  1985年   22篇
  1984年   5篇
  1983年   4篇
  1982年   4篇
  1981年   11篇
  1980年   15篇
  1979年   4篇
  1977年   36篇
  1976年   70篇
  1975年   8篇
  1972年   3篇
  1971年   4篇
排序方式: 共有2874条查询结果,搜索用时 15 毫秒
81.
Analysis of Bence Jones proteinuria by high resolution two-dimensional electrophoresis (2-DE) and immunoblotting reveals a complex pattern of light chain (LC) isoforms corresponding to the free monoclonal Bence Jones protein and its fragments. Replica blotting gives duplicate blots for LC typing (lambda, chi) and, under the conditions employed, leaves sufficient protein for Coomassie Blue staining of the urinary protein profile and pIIMr determination of the LC isoforms. Carrier ampholytes (CAs, in our "simplified" 2-DE system) and immobilised pH gradients (IPGs, in the Multiphor 2-DE system) give similar LC isoform patterns. Artifacts, including cone-like distortions and trailing "piggyback" spots, are visualised with both 2-DE systems. IPGs are advantageous as they allow reproducible detection of strongly basic LC isoforms by isoelectric focusing (under equilibrium conditions) without recourse to CA nonequilibrium pH gradient electrophoresis.  相似文献   
82.
A variety of dosing schedules have been reported for the hyperventilation method of broncho-provocation testing. To evaluate the effect of challenge technique on the bronchoconstrictive response, we had 16 subjects perform eucapnic voluntary hyperventilation (EVH) with dry, room temperature gas using four different dosing schedules. The hyperventilation challenge dosages included the following: (1) a target minute ventilation (VE) of 20 x FEV1 for 6 min; (2) a target VE of 15 x FEV1 for 12 min; (3) an interrupted challenge with a target VE of 30 x FEV1 for 2 min repeated 3 times; and (4) a target VE of 30 x FEV1 for 6 min. Challenges 2, 3, and 4 gave identical absolute ventilatory challenges (identical factor FEV1 x minutes) but at different VE dosages or time. Challenges 1 and 4 were of identical length, but different target VE. The mean postchallenge fall in FEV1 was 16.6 +/- 10.9%, 11.0 +/- 8.1%, 19.6 +/- 9.9%, and 26.7 +/- 11.3% for challenges 1, 2, 3, and 4, respectively. The response to an identical EVH challenge (FEV1 x 30 for 6 min) was reproducible when performed on separate days. We conclude that the challenge technique used for hyperventilation testing will have a significant impact on the bronchoconstrictive response and must be taken into account when interpreting study results. Tests may be quantitatively comparable over a narrow range of challenge time and VE. We recommend that a 6-min uninterrupted EVH challenge using dry, room temperature gas at a target VE of 30 x FEV1 be adopted as the "standard" challenge.  相似文献   
83.
84.
We sought to compare self-assessment of preoperative anxiety levels and selection of worst fears by surgical patients with the assessments made by the anesthesia and surgery residents providing intraoperative care for those patients. One hundred inpatients at a Veterans Affairs hospital (Group 1) and 45 patients at a University hospital (Group 2) were asked to complete a brief questionnaire; the residents were asked to complete the same questionnaire. Group 1 results showed that median patient visual analog scale (VAS) scores were lower for anxiety about anesthesia compared to surgery (16 vs 22, P < or = 0.05). Anesthesia resident VAS scores were higher than patient or surgery resident scores. Neither type of resident was able to predict their individual patient's VAS score (Kendall's tau). The fear chosen with the greatest incidence by Group 1 patients and residents was "whether surgery would work". A significant number of residents (34%, anesthesia or surgery, P < or = 0.05) matched their patient's fear choice. Residents commonly chose fears related to their specialty (e.g., anesthesia residents chose anesthesia-related fears more often than surgery residents, 50% vs 28%, P < or = 0.001). In Group 2, residents demonstrated an improved ability to predict patient scores. For instance, both surgery and anesthesia residents were able to predict individual University patient VAS scores (P < or = 0.01). The fear chosen with the greatest frequency by Group 2 patients was "pain after the operation". Sixty percent of anesthesia residents matched their patients' fear choice (P < or = 0.001). This study indicates a variable ability of anesthesia and surgery residents to predict patient anxiety and fear which may be due, in part, to difficulty in understanding a Veterans Affairs hospital patient population.  相似文献   
85.
The inherent key escrow problem is one of the main reasons for the slow adoption of identity-based cryptography. The existing solution for mitigating the key escrow problem is by adopting multiple Private Key Generators (PKGs). Recently, there was a proposal that attempted to reduce the trust of the PKG by allowing a malicious PKG to be caught if he reveals the user’s identity-based private key illegally. Nonetheless, the proposal does not consider that the PKG can simply decrypt the ciphertext instead of revealing the private key itself (in the case of identity-based encryption schemes). The aim of this paper is to present an escrow-free identity-based signature (IBS) scheme, in which the malicious PKG will be caught if it releases a signature on behalf of the user but signed by itself. We present a formal model to capture such a scheme and provide a concrete construction.  相似文献   
86.
The intersecting path is an important tool path generation method. This paper proposes an approach for the quart-parametric interpolation of intersecting paths. The objective of our approach is that the intersecting paths for surface machining can be directly interpolated within the computer numerical control (CNC) system. This enables the CNC interpolator to process the intersecting paths without geometric approximation as in existing approaches and take into consideration any specific feedrate profiles and further machining dynamical issues along the path.The interpolation of the intersection of two general parametric surfaces is transferred into interpolation of its projection curves and the time trajectories of four parameters along the intersecting curves are obtained. Our strategy is to carry out the quart-parametric interpolation based on the projection interpolation. The feedrate control method is developed, and then the interpolation algorithms for two projection curves are proposed. An error reduction scheme is presented to alleviate point deviation from the drive parametric surface. Simulations of quart-parametric interpolation have been carried out to verify the effectiveness of the proposed algorithm.  相似文献   
87.
Incremental linear discriminant analysis for face recognition.   总被引:3,自引:0,他引:3  
Dimensionality reduction methods have been successfully employed for face recognition. Among the various dimensionality reduction algorithms, linear (Fisher) discriminant analysis (LDA) is one of the popular supervised dimensionality reduction methods, and many LDA-based face recognition algorithms/systems have been reported in the last decade. However, the LDA-based face recognition systems suffer from the scalability problem. To overcome this limitation, an incremental approach is a natural solution. The main difficulty in developing the incremental LDA (ILDA) is to handle the inverse of the within-class scatter matrix. In this paper, based on the generalized singular value decomposition LDA (LDA/GSVD), we develop a new ILDA algorithm called GSVD-ILDA. Different from the existing techniques in which the new projection matrix is found in a restricted subspace, the proposed GSVD-ILDA determines the projection matrix in full space. Extensive experiments are performed to compare the proposed GSVD-ILDA with the LDA/GSVD as well as the existing ILDA methods using the face recognition technology face database and the Carneggie Mellon University Pose, Illumination, and Expression face database. Experimental results show that the proposed GSVD-ILDA algorithm gives the same performance as the LDA/GSVD with much smaller computational complexity. The experimental results also show that the proposed GSVD-ILDA gives better classification performance than the other recently proposed ILDA algorithms.  相似文献   
88.
In this paper, we study the bandwidth allocation problem for serving video requests in a mobile real-time video player system. One of the main issues to maintain the quality of services (QoS) in mobile video playback is to ensure sufficient number of video frames available at the client side while a video is being played. However, due to the limited bandwidth of a mobile network and variable workload streaming video, this is not easy to achieve in practice. In addition, the communication link between mobile clients and a video server is subject to frequent errors and temporary disconnection. In this paper, we propose to use the notion of buffered bandwidth in addition to the network bandwidth to support real-time playback of videos at mobile clients. Based on this, we designed a bandwidth allocation scheme called Cooperative Pre-Fetching (CP) in which the amount of bandwidth to be allocated to serve a video request depends on the current buffer level of the video at the client relative to the target buffer level of the client. In determining the target buffer level, we consider the errors in communication to the client as well as the other clients who are concurrently served by the system. The buffered video frames at the clients are then used to minimize the impact of error in communications on the overall QoS of video playbacks in the whole system.
Kam-Yiu Lam (Corresponding author)Email:
  相似文献   
89.
Fault-based test suite prioritization for specification-based testing   总被引:1,自引:0,他引:1  

Context

Existing test suite prioritization techniques usually rely on code coverage information or historical execution data that serve as indicators for estimating the fault-detecting ability of test cases. Such indicators are primarily empirical in nature and not theoretically driven; hence, they do not necessarily provide sound estimates. Also, these techniques are not applicable when the source code is not available or when the software is tested for the first time.

Objective

We propose and develop the novel notion of fault-based prioritization of test cases which directly utilizes the theoretical knowledge of their fault-detecting ability and the relationships among the test cases and the faults in the prescribed fault model, based on which the test cases are generated.

Method

We demonstrate our approach of fault-based prioritization by applying it to the testing of the implementation of logical expressions against their specifications. We then validate our proposal by an empirical study that evaluates the effectiveness of prioritization techniques using two different metrics.

Results

A theoretically guided fault-based prioritization technique generally outperforms other techniques under study, as assessed by two different metrics. Our empirical results also show that the technique helps to reveal all target faults by executing only about 72% of the prioritized test suite, thereby reducing the effort required in testing.

Conclusions

The fault-based prioritization approach is not only applicable to the instance empirically validated in this paper, but should also be adaptable to other fault-based testing strategies. We also envisage new research directions to be opened up by our work.  相似文献   
90.
In recent years, industrial plants have been utilizing more electric motors as drivers because of their high efficiency and reliability and lower maintenance costs. Electrified continuous process plants are using electric motors for both primary and standby drives. When these standby motors are not operating during normal plant runs, their windings collect moisture. Moisture attacks insulation and causes insulation failure. A breakdown of motor insulation may occur when a standby motor is suddenly energized to take the place of the primary motor. When it is not in operation, directly heating the motor winding with a low voltage system, coupled with automatic control, will guard the motor from moisture attack and extend its service life. The experience with low voltage heating of motor windings as described by M. H. Yuen in his article [1] has proved its effectiveness. However, conventional relays, timers, contactors, etc., were utilized in the circuits.  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