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   18849篇
  免费   440篇
  国内免费   17篇
电工技术   233篇
综合类   14篇
化学工业   2599篇
金属工艺   229篇
机械仪表   335篇
建筑科学   892篇
矿业工程   42篇
能源动力   452篇
轻工业   1944篇
水利工程   263篇
石油天然气   28篇
无线电   1719篇
一般工业技术   2382篇
冶金工业   5393篇
原子能技术   142篇
自动化技术   2639篇
  2023年   68篇
  2022年   152篇
  2021年   266篇
  2020年   138篇
  2019年   200篇
  2018年   266篇
  2017年   246篇
  2016年   271篇
  2015年   251篇
  2014年   387篇
  2013年   657篇
  2012年   676篇
  2011年   916篇
  2010年   635篇
  2009年   664篇
  2008年   699篇
  2007年   674篇
  2006年   567篇
  2005年   553篇
  2004年   506篇
  2003年   469篇
  2002年   428篇
  2001年   345篇
  2000年   320篇
  1999年   439篇
  1998年   1940篇
  1997年   1178篇
  1996年   797篇
  1995年   483篇
  1994年   467篇
  1993年   462篇
  1992年   204篇
  1991年   202篇
  1990年   195篇
  1989年   192篇
  1988年   200篇
  1987年   129篇
  1986年   134篇
  1985年   183篇
  1984年   141篇
  1983年   100篇
  1982年   107篇
  1981年   111篇
  1980年   84篇
  1979年   92篇
  1978年   79篇
  1977年   133篇
  1976年   147篇
  1975年   76篇
  1974年   71篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Forty-seven patients with cancer of the lower half of the oral cavity underwent primary restoration of mandibular continuity with a threaded wire after "en bloc" resection. The overall 3 years tolerance rate of the wire calculated according to the actuarial method is 0.29. Preoperative radiotherapy and inclusion of the wire into silastic reduced tolerance of the prosthesis. The occurrence of an oral fistula required removal of the wire.  相似文献   
92.
The feasibility of anaerobic ammonium oxidation (anammox) process to treat wastewaters containing antibiotics and heavy metals (such as the liquid fraction of the anaerobically digested swine manure) was studied in this work. The specific anammox activity (SAA) was evaluated by means of manometric batch tests. The effects of oxytetracycline, sulfathiazole, copper and zinc were studied. The experimental data of the short-term assays were fitted with an inhibition model to identify the half maximal inhibitory concentration (IC(50)). After 24 h exposures, IC(50)-values equal to 1.9, 3.9, 650 and 1,100 mg L(-1) were identified for copper, zinc, sulfathiazole and tetracycline respectively. The effect of prolonged exposure (14 days) to oxytetracycline and sulfathiazole was studied by means of repeated batch-assays. Anabolism and catabolism reactions were active during the inhibition tests indicating that anammox bacteria could grow even in the extreme conditions tested. Considering the average concentrations expected in swine wastewaters, the inhibitors studied do not seem to represent a problem for the application of the anammox process. However, in order to verify the effect of these compounds on the growth of anammox bacteria, continuous culture experiments could be conducted.  相似文献   
93.
Due to changes in the Dutch flood management paradigm, governance practices have been shifting from technocratic and state-oriented towards more collaborative governance approaches in which many governmental actors, together with private and societal actors, search out integral solutions. This shift has had an impact on how water management is legitimized. This paper evaluates two water governance processes that reflect the new management paradigm in different ways, and analyzes how these changing paradigms influence the democratic legitimacy of water governance. It is concluded that the extent to which the new paradigm is implemented influences the way in which democratic legitimacy is organized. It is also shown that new forms of democratic legitimacy do not replace existing ones but rather contribute to hybrid and contextualized forms of legitimacy.  相似文献   
94.
This work aims to model the optimal control of dike heights. The control problem leads to so-called Hamilton-Jacobi-Bellman (HJB) variational inequalities, where the dike-increase and reinforcement times act as input quantities to the control problem. The HJB equations are solved numerically with an Essentially Non-Oscillatory (ENO) method. The ENO methodology is originally intended for hyperbolic conservation laws and is extended to deal with diffusion-type problems in this work. The method is applied to the dike optimisation of an island, for both deterministic and stochastic models for the economic growth.  相似文献   
95.
A behavioural pseudometric is often defined as the least fixed point of a monotone function F on a complete lattice of 1-bounded pseudometrics. According to Tarski?s fixed point theorem, this least fixed point can be obtained by (possibly transfinite) iteration of F, starting from the least element ⊥ of the lattice. The smallest ordinal α such that Fα()=Fα+1() is known as the closure ordinal of F. We prove that if F is also continuous with respect to the sup-norm, then its closure ordinal is ω. We also show that our result gives rise to simpler and modular proofs that the closure ordinal is ω.  相似文献   
96.
97.
This paper proposes a novel method for preference relaxation in online product search, which enables consumers to make quality choices without suffering from the commonly experienced information overload. In online shopping scenarios that involve multi-attribute choice tasks, it can be difficult for consumers to process the vast amounts of information available and to make satisfactory buying decisions. In such situations consumers are likely to eliminate potentially good choices early on, using hard-constraint filtering tools. Our approach uses edge sets to identify the alternatives on the soft boundary and the principle of alternative domination to suppress the alternatives on this boundary that are irrelevant. We demonstrate how our approach outperforms existing methods for product search in a set of simulations using two sets of 2650 car advertisements and 1813 digital cameras gathered from a popular online store.  相似文献   
98.
In this paper we present a machine learning framework to analyze moving object trajectories from maritime vessels. Within this framework we perform the tasks of clustering, classification and outlier detection with vessel trajectory data. First, we apply a piecewise linear segmentation method to the trajectories to compress them. We adapt an existing technique to better retain stop and move information and show the better performance of our method with experimental results. Second, we use a similarity based approach to perform the clustering, classification and outlier detection tasks using kernel methods. We present experiments that investigate different alignment kernels and the effect of piecewise linear segmentation in the three different tasks. The experimental results show that compression does not negatively impact task performance and greatly reduces computation time for the alignment kernels. Finally, the alignment kernels allow for easy integration of geographical domain knowledge. In experiments we show that this added domain knowledge enhances performance in the clustering and classification tasks.  相似文献   
99.
The threshold gradient for perception of a linear change in luminance with time has been measured as a function of the stimulus duration. These data are compared with the "De Lange" curves representing the flicker sensitivity measured with intermittent presentation of the stimulus as a function of the stimulus duration. For this purpose it is necessary to take into account the fact that a linear luminance gradient, being a relatively low-frequency signal, is affected less by the low-pass filter supposedly situated in the visual system than by a sinusoidal signal (flicker) of the same duration.  相似文献   
100.
Software release management is the process through which software is made available to and obtained by its users. Until now, this process has been relatively straightforward. However, the emergence of component‐based software is complicating software release management. Increasingly, software is constructed via the assembly of pre‐existing, independently produced, and independently released components. Both developers and users of such software are affected by these complications. Developers need to accurately document the complex and changing dependencies among the components constituting the software. Users must be involved in locating, retrieving, and assembling components in order to appropriately bring the software into their particular environment. In this paper, we introduce the problem of release management for component‐based software and discuss SRM, a prototype software release management tool we have developed that supports both developers and users in the software release management process. Copyright © 2002 John Wiley & Sons, Ltd.  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