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   1624篇
  免费   31篇
  国内免费   5篇
电工技术   22篇
综合类   1篇
化学工业   279篇
金属工艺   31篇
机械仪表   23篇
建筑科学   50篇
矿业工程   5篇
能源动力   36篇
轻工业   196篇
水利工程   9篇
石油天然气   40篇
无线电   124篇
一般工业技术   180篇
冶金工业   383篇
原子能技术   21篇
自动化技术   260篇
  2023年   7篇
  2022年   13篇
  2021年   21篇
  2020年   12篇
  2019年   13篇
  2018年   24篇
  2017年   25篇
  2016年   34篇
  2015年   20篇
  2014年   30篇
  2013年   101篇
  2012年   64篇
  2011年   87篇
  2010年   50篇
  2009年   56篇
  2008年   66篇
  2007年   60篇
  2006年   50篇
  2005年   47篇
  2004年   31篇
  2003年   25篇
  2002年   37篇
  2001年   25篇
  2000年   34篇
  1999年   34篇
  1998年   135篇
  1997年   85篇
  1996年   54篇
  1995年   46篇
  1994年   35篇
  1993年   26篇
  1992年   13篇
  1991年   10篇
  1990年   11篇
  1989年   17篇
  1988年   22篇
  1987年   17篇
  1986年   14篇
  1985年   15篇
  1984年   14篇
  1983年   12篇
  1982年   8篇
  1981年   17篇
  1980年   14篇
  1979年   23篇
  1978年   8篇
  1977年   19篇
  1976年   20篇
  1974年   7篇
  1973年   13篇
排序方式: 共有1660条查询结果,搜索用时 15 毫秒
91.
一个简单的监控线路连接的交流负载供电所用的时间(如图1).可以转换成标准单线协议所用时间的计数值.当给交流负载供电时,光隔离器以交流线路频率向单线计数器DS2423 IC的输入端提供脉冲.  相似文献   
92.
Segmentation of vertebral contours is an essential task in the design of imaging biomarkers for osteoporosis based on vertebra shape or texture. In this paper, we propose a novel automatic segmentation technique which can optionally be constrained by the user. The proposed technique solves the segmentation problem in a hierarchical manner. In the first phase, a coarse estimate of the overall spine alignment and the vertebra locations is computed using a sampling scheme. These samples are used to initialize a second phase of active shape model search, under a nonlinear model of vertebra appearance. The search is constrained by a conditional shape model, based on the variability of the coarse spine location estimates. In supplement, we describe an approach for manual initialization of the segmentation procedure as a simple set of constraints on the fully automatic technique. The technique is evaluated on a data base of 157 manually annotated lumbar radiographs, resulting in a final mean point-to-contour error of $0.81~\pm ~0.98$  mm for automatic segmentation. The results outperform the previous work in automatic vertebra segmentation in terms of both segmentation accuracy and failure rate, offering a both automatic and semi-automatic approach in one unifying framework.  相似文献   
93.
This paper considers the problem of simultaneously stabilizing a finite collection of linear time-varying systems via a stable linear time-varying controller. The class of controllers proposed in this paper are linear, time varying and infinite dimensional. However, the computer implementation of these controllers would not be computationally more demanding than the computer implementation of a finite-dimensional linear time-varying controller.  相似文献   
94.
A robust incoherent quantum control scheme via projective measurements plus unitary transformations is proposed for driving a qubit system from an unknown initial mixed state to an arbitrary target pure state. This scheme consists of two main steps: projective measurement on the initial mixed state and optimal control between two pure states. The first step projects the initial state into an eigenstate of the qubit system by projective measurement and guarantees that the proposed scheme is robust to different initial mixed states. The second step finds a set of suitable optimal controls to drive the qubit system from the conditional eigenstate to the target pure state. The connection between the two steps is accomplished by a switching strategy. To accomplish the second step, two approaches are presented in detail. These approaches are time-optimal transition with unbounded control and bang-bang control with minimal switches. The minimal time and minimal number of switches in these approaches can be calculated by simple analytical expressions. The proposed approaches provide two relatively straightforward optimal design methods.  相似文献   
95.
Software organizations face challenges in managing and sustaining their measurement programs over time. The complexity of measurement programs increase with exploding number of goals and metrics to collect. At the same time, organizations usually have limited budget and resources for metrics collection. It has been recognized for quite a while that there is the need for prioritizing goals, which then ought to drive the selection of metrics. On the other hand, the dynamic nature of the organizations requires measurement programs to adapt to the changes in the stakeholders, their goals, information needs and priorities. Therefore, it is crucial for organizations to use structured approaches that provide transparency, traceability and guidance in choosing an optimum set of metrics that would address the highest priority information needs considering limited resources. This paper proposes a decision support framework for metrics selection (DSFMS) which is built upon the widely used Goal Question Metric (GQM) approach. The core of the framework includes an iterative goal-based metrics selection process incorporating decision making mechanisms in metrics selection, a pre-defined Attributes/Metrics Repository, and a Traceability Model among GQM elements. We also discuss alternative prioritization and optimization techniques for organizations to tailor the framework according to their needs. The evaluation of the GQM-DSFMS framework was done through a case study in a CMMI Level 3 software company.  相似文献   
96.
This paper is concerned with the decentralized stabilization problem for a class of uncertain large-scale systems with Markovian jump parameters. The controllers use local subsystem states and neighboring mode information to generate local control inputs. A sufficient condition involving rank constrained linear matrix inequalities is proposed for the design of such controllers. A numerical example is given to illustrate the developed theory.  相似文献   
97.
In this paper we recall general methodologies we developed for observation and identification in non-linear systems theory, and we show how they can be applied to real practical problems.

In a previous paper, we introduced a filter which is intermediate between the extended Kalman filter in its standard version and its high-gain version, and we applied it to certain observation problems. But we were missing some important cases. Here, we show how to treat these cases.

We also apply the same technique in the context of our identifiability theory.

As non-academic illustrations, we treat a problem of observation and a problem of identification, for a fluid catalytic cracker (FCC). This FCC unit is one of the most crucial from an economic point of view for the petroleum industry.  相似文献   
98.
To investigate the outcome of Graves' thyrotoxicosis after antithyroid drug management, data from 81 patients, treated in Chang Gung Memorial Hospital at Taipei and Linkou from October 1981 to March 1990, were analyzed. The gender ratio of female to male was 59:22. The mean age of onset was 33.1 +/- 10.5(15-60) year-old. All the patients were treated with antithyroid drug (Thionamide group) for a duration of 11 to 63 months (mean +/- SD = 28.1 +/- 9.8 months). Forty of 81 patients (49.4%) were remained remission after up to 2 years of follow-up. Those patients relapse usually occurred within 2 years after discontinuation of treatment (34/41), and only one exceptional case relapsed after 3 years. Three conditions affected the relapse rate. Patients with larger goiter (grade II-III) and shorter duration of treatment (< 23 months) had a higher relapse rate than those-with smaller goiter (grade O-I) [29/46 vs. 12/35; chi 2 = 6.576, p = 0.010; p = 0.015 in stepwise logistic regression (LR)] and longer duration of treatment (> or = 23 months) (15/20 vs. 26/61; chi 2 = 6.316, p = 0.012; p = 0.020 in LR). Patients with higher pre-treated serum triiodothyronine (T3) level (T3 > or = 300 ng/dl) had a higher relapse rate than those with lower T3 level (T3 < 300 ng/dl) in univariate analysis (30/50 vs. 11/31, chi 2 = 4.601, p = 0.032), but no significant difference by LR (P = 0.094). Other clinical parameters including age, sex, past history, family history, thyroxine (T4) level, T3/T4 ratio, thyroid autoantibodies, staging of ophthalmopathy, responsiveness to thyrotropin-releasing hormone stimulation test at the end of treatment, and whether combined treatment with thyroxine had no significant difference between the relapse and remission groups. These data suggest: (a) patients with larger goiter (grade II-III had higher relapse rate; (b) most of the recurrent thyrotoxicosis patients relapsed within two years after drug withdrawal; (c) continuing treatment for more than twenty-three months produces better outcome; (d) patients with Graves' thyrotoxicosis should be followed up for at least three years after withdrawal of antithyroid drug.  相似文献   
99.
Jean-Paul Gaspoz 《电信纪事》1995,50(7-8):667-675
This paper describes the specification of a bandwidth management system for ATM-based virtual private networks (vpn). Such a system allows a vpn customer to dynamically modify the bandwidth allocated to vpn connections. The analysis process focuses on the service management information model and interfaces required to provide that service to the customer. The specification work is performed according to a second generation object-oriented development method called Fusion. The vpn service and management architectures as well as the different actors involved are also described in detail.  相似文献   
100.
A method is proposed, for low-temperature geothermal systems, for calculating the aquifer temperature and relative proportions of mixed thermal and shallow groundwaters from carbonate-evaporite environments. The fluid is assumed to be in chemical equilibrium with anhydrite and chalcedony in the aquifer, and mixed with diluted waters during its ascent. An attempt has been made to establish a relationship between reservoir temperature, the aqueous sulfate and silica contents of the mixed fluid, the proportion of the thermal end-member and the temperature of the adiabatic mixture. The method calculates mineral solubilities in the field context, calibrated on representative thermal springs. The method also considers the effects of conductive cooling.  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