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   4695篇
  免费   146篇
  国内免费   3篇
电工技术   36篇
综合类   14篇
化学工业   1066篇
金属工艺   62篇
机械仪表   41篇
建筑科学   184篇
矿业工程   4篇
能源动力   55篇
轻工业   321篇
水利工程   3篇
石油天然气   2篇
无线电   177篇
一般工业技术   679篇
冶金工业   1734篇
原子能技术   26篇
自动化技术   440篇
  2023年   40篇
  2022年   46篇
  2021年   73篇
  2020年   43篇
  2019年   61篇
  2018年   51篇
  2017年   50篇
  2016年   85篇
  2015年   88篇
  2014年   101篇
  2013年   165篇
  2012年   171篇
  2011年   206篇
  2010年   152篇
  2009年   165篇
  2008年   170篇
  2007年   155篇
  2006年   141篇
  2005年   129篇
  2004年   103篇
  2003年   78篇
  2002年   71篇
  2001年   61篇
  2000年   62篇
  1999年   115篇
  1998年   554篇
  1997年   324篇
  1996年   211篇
  1995年   142篇
  1994年   123篇
  1993年   123篇
  1992年   51篇
  1991年   61篇
  1990年   39篇
  1989年   54篇
  1988年   43篇
  1987年   42篇
  1986年   35篇
  1985年   34篇
  1984年   33篇
  1983年   18篇
  1982年   16篇
  1981年   32篇
  1980年   26篇
  1979年   21篇
  1978年   21篇
  1977年   39篇
  1976年   108篇
  1975年   23篇
  1974年   16篇
排序方式: 共有4844条查询结果,搜索用时 140 毫秒
151.
How can we measure subjective experiences or internal states? The rise of happiness as a variable of interest in policy decisions, for instance, necessitates appropriate methods for valid and practical measurements. This self-experimental work contributes to scientific development by analysing and evaluating three methods for recording stress: the experience sampling method with a smartphone, an adapted version of the day reconstruction method (DRM, a diary method) and an ubiquitous biophysical measure of the heart rate. All three methods yield significant treatment effects for eight “natural experiments” as stressors. Surprisingly, the DRM outperforms the other two methods in a simple factor analysis and appears to have no recall bias. Also reactivity has no substantial impact, and an applied researcher should minimise the complexity of the input (amount and type of questions, interface and integration) rather than reduce the number of prompts. Some evidence suggests a Likert-type scale should be preferred over a continuous one. This work also reflects upon the nature of single-subject research and the role of the experimenter.  相似文献   
152.
This article deals with the differences in the long-term durability and thermal stability under load of terrace deckings from various materials. The tested materials were deckings made of wood, thermally modified timber (TMT), and wood–polymer–composites (WPC). For the determination of the test temperatures for component testing according to EN 310, the surface temperatures of the decks during a normal hot summer day were measured. A cyclic test according to EN 321 was applied to all decking materials. Afterwards the component testing was repeated. All wooden samples reveal considerable cracks, some were twisted, and few were even broken. In particular regarding the optical appearance, wood decks show advantages against the TMT decks. Some WPC decks show very fine cracks on the face, which were additionally analyzed by means of X-ray computed tomography (CT). Except for the WPC deck with higher wood content, no WPC deck revealed significant changes after the cyclic test. The CT analysis was also suitable to find cracks inside the materials and illustrate them. Thus, the whole damage inside a sample could be characterized by calculating a kind of error pattern. No considerable cracks or failures could be observed on the WPC decks.  相似文献   
153.
Condensation of layered silicate precursors leads to new, all silica zeolite frameworks. In order to introduce catalytic functionality, boron has been substituted into the silicate layer of RUB-39 in a single step synthesis process. Condensation of the silicate layer to the zeolite framework of RUB-41, RRO framework structure type, preserved B as constituent of the material. Analysis of structural details obtained from Rietveld analysis of powder diffraction data, 11B and 29Si NMR experiments of the as synthesized precursor as well as of the zeolite condensation product, and crystal chemical reasoning indicates segregation of B on one specific T-site. This T-site is buried in the silicate anionic layer of the precursor shielding the additional negative charge introduced by the trivalent T-atom.  相似文献   
154.
The development and cultivation of genetically modified crops is still increasing globally. Food and feed imports from outside the European Union (EU) will subsequently require more effort from the responsible authorities in monitoring the compliance with effective labelling regulations. The aim of this study was the development of the GMOfinder, a database for collection and interpretation of information related to the screening for genetically modified organisms (GMOs). Different genetic elements (e.g. promoters, terminators, structural genes) are artificially introduced into plants to establish new genetic modifications. The introduced elements may vary between GMO events, depending on the intended trait(s). Screening for such inserted elements with (real-time) polymerase chain reaction is a common first step to analyse samples for the presence of any genetical modification. From the pattern of detectable and nondetectable elements, valuable conclusions about the identity of putative present GMO event(s) can be drawn with the GMOfinder. Information about selected genetic elements from the literature, applications for authorisation and other (web) sources were systematically integrated in a tabular matrix format. Special care was taken to additionally record the sources of the information, thus facilitating evaluation of screening results, and tracing of possible errors in the matrix. The GMOfinder accesses data from the element matrix with implemented algorithms and facilitates to interpret the outcome of screenings. Such a preselection helps to systematically narrow down the candidates for subsequent identification reactions. Optional display of events with potentially masked elements completes the included features.  相似文献   
155.
The objective of this paper is to provide a theoretical foundation for program extraction from inductive and coinductive proofs geared to practical applications. The novelties consist in the addition of inductive and coinductive definitions to a realizability interpretation for first-order proofs, a soundness proof for this system, and applications to the synthesis of non-trivial provably correct programs in the area of exact real number computation. We show that realizers, although per se untyped, can be assigned polymorphic recursive types and hence represent valid programs in a lazy functional programming language such as Haskell. Programs extracted from proofs using coinduction can be understood as perpetual processes producing infinite streams of data. Typical applications of such processes are computations in exact real arithmetic. As an example we show how to extract a program computing the average of two real numbers w.r.t. the binary signed digit representation.  相似文献   
156.
157.
The identification of plant-wide faults is a very important topic as it enables plant operators to decrease rejections or to increase the product quality. This paper shows a fault propagation approach for this field of interest based on time delay estimation. Due to the fact that the estimation of time delays in multiple-input single-output systems or nonlinear systems is either impossible or very difficult with known methods, a new method based on k nearest neighbor imputation was developed and is validated in this paper theoretically. The effectiveness of the identification algorithm is demonstrated on several simulations and on an industrial hydrocracker plant.  相似文献   
158.
159.
160.
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