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   4155篇
  免费   110篇
  国内免费   13篇
电工技术   217篇
综合类   5篇
化学工业   1013篇
金属工艺   154篇
机械仪表   83篇
建筑科学   84篇
能源动力   168篇
轻工业   341篇
水利工程   5篇
石油天然气   7篇
武器工业   2篇
无线电   304篇
一般工业技术   706篇
冶金工业   710篇
原子能技术   108篇
自动化技术   371篇
  2023年   12篇
  2022年   53篇
  2021年   82篇
  2020年   44篇
  2019年   45篇
  2018年   54篇
  2017年   59篇
  2016年   96篇
  2015年   51篇
  2014年   108篇
  2013年   199篇
  2012年   193篇
  2011年   210篇
  2010年   170篇
  2009年   195篇
  2008年   196篇
  2007年   173篇
  2006年   156篇
  2005年   141篇
  2004年   116篇
  2003年   107篇
  2002年   103篇
  2001年   78篇
  2000年   74篇
  1999年   80篇
  1998年   319篇
  1997年   172篇
  1996年   128篇
  1995年   85篇
  1994年   92篇
  1993年   101篇
  1992年   70篇
  1991年   45篇
  1990年   42篇
  1989年   45篇
  1988年   33篇
  1987年   31篇
  1986年   28篇
  1985年   42篇
  1984年   30篇
  1983年   24篇
  1982年   27篇
  1981年   28篇
  1980年   15篇
  1979年   16篇
  1978年   10篇
  1977年   25篇
  1976年   30篇
  1975年   8篇
  1972年   6篇
排序方式: 共有4278条查询结果,搜索用时 15 毫秒
51.
A phytoplankton model, which includes a carbon cycle combined with a constant current obtained by the computation of tidal currents, was applied to the coastal region (Hiroshima Bay, Japan). The transformation rate constants for the carbon cycle were experimentally evaluated.The seasonal variations of particulate and dissolved organic matter by the simulation model were reasonably consistent with the field data. Carbon concentration increased by primary production in the upper layer was approx. 10 times that augmented by loading of carbon from land at the shore in summer. Sinking plays an important role in the elimination of particulate organic matter. On the other hand, horizontal advection and turbulent diffusion are important factors for the diminution of dissolved organic matter.  相似文献   
52.
On the basis of structural information for the cyclic hexapeptide endothelin (ET) receptor antagonist, TAK-044, a series of thieno[2,3-d]pyrimidine-2,4-dione derivatives bearing a carboxyl group and aromatic rings that were important for receptor binding were designed, synthesized, and evaluated for ET receptor binding affinities and inhibitory activities against ET-induced vasoconstriction. Optimization of each substituent in the thieno[2,3-d]pyrimidine ring led to the discovery of a novel and potent nonpeptide ET receptor antagonist, 6-(4-methoxymethoxyphenyl)-5-methylsulfonylaminomethyl-1-(2- methylthiobenzyl)-2,4-dioxo-1,2,3,4-tetrahydrothieno[2,3-d]p yrimidine-3- acetic acid (32 g), which binded to human ETA and ETB receptor subtypes with affinities (IC50) of 7.6 and 100 nM, respectively. Compound 32 g effectively antagonized ET-induced vasoconstriction and the inhibitory effect mediated by the ETB receptor was more potent than that of bosentan, while the inhibitory effect mediated by the ETA receptor was slightly less potent than that of bosentan.  相似文献   
53.
54.
OBJECTIVE: To characterize the existence and role of transforming growth factor-beta (TGF-beta) in otitis media with effusion (OME). STUDY DESIGN: Retrospective. METHODS: The levels of two major TGF-beta isoforms, TGF-beta1 and TGF-beta2, in the middle ear effusions (MEEs) of 44 children were evaluated using enzyme-linked immunospecific assays (ELISAs). Forty-eight MEEs were separated into three clinically relevant groups (i.e., serous, mucoid, and purulent), and TGF-beta levels were correlated with clinical parameters of disease for these MEEs. RESULTS: Both TGF-beta1 and TGF-beta2 were present in the samples. Mean levels of TGF-beta1 (920.36 +/- 437.75 pg/mg total protein) were generally 100-fold greater than those of TGF-beta2 (9.65 +/- 11.19 pg/mg total protein). TGF-beta1 levels were elevated in association with a history of previous tympanostomy tube placements (TTPs) (P = .029) and mucoid effusions (P = .042). TGF-beta2 levels were elevated in association with a history of previous TTPs (P = .100) and chronic (i.e., serous or mucoid) effusions (P = .003). CONCLUSIONS: TGF-beta1 is present in the MEEs of children with OME. Furthermore, TGF-beta1 and TGF-beta2 levels were elevated differentially in the presence of chronic disease indicators in OME, suggesting that these isoforms may have differing roles in the inflammatory processes that characterize OME.  相似文献   
55.
It has been pointed out in recent years that the potential impacts of global warming has been becoming more and more serious because of the rapid increase of anthropogenic CO2 emission.

Japan's annual CO2 emissions (fiscal 1994) amounted to 343 million tons of carbon. Although CO2 emissions caused by fossil-fuel power generation accounted for 29.4% of total, on a sector basis, those directly from the energy conversion sector accounted for only 7.7%. Most CO2 emissions (21.7% of total) resulted from electric power use in the industrial, commercial and domestic sectors. Thus, the reduction of CO2 emissions caused by the use of electricity is a nationwide subject.

Understanding that both supply side and demand side approaches are necessary, Kansai Electric has been deploying “New ERA Strategy” as a comprehensive strategy to seek a potential for CO2 reduction more broadly and deeply. Among a number of action items are the promotion of nuclear power generation, and improvement of overall energy efficiency, besides such demand side measures as leveling off the peak load.

The effectiveness of action items of the New ERA Strategy was evaluated in terms of CO2 reduction. As a result, estimated CO2 reduction related to nuclear power amounted to 88% of the total for fiscal 1995 in comparison with 1990, and that expected in 2000 is 84%. These results reconfirm that nuclear power is always the key to practical CO2 reduction at present and in the future.

Comparison with candidate technology alternatives revealed that photovoltaic power generation needed 7 times greater rated capacity and 280 times larger area than nuclear power, so it is not realistic as a central power station alternative. The comparison also clarified that if wind power stations were constructed at all feasible sites in the Kansai region, they would not be a viable alternative to a single nuclear unit from CO2 reduction viewpoint.  相似文献   

56.
Two special cases of the bilateral 2-D polynomial matrix equationDU +VN=C whenC=I andC=I with being a -stable 2-D polynomial, which are related respectively to deadbeat and asymptotic control problems of 2-D systems, are first considered. By generalizing the concepts of factor coprimeness, zero coprimeness and zero skew primeness in the 2-D polynomial ring to the ring of causal -stable 2-D rational functions, a constructive solution of these two problems mentioned is proposed. Based on these results, we derive a solvability condition for the bilateral equiation whereC is a general 2-D polynomial matrix. The general solutions are investigated as well.  相似文献   
57.
Projected image on a screen is not always vivid enough when it is projected in a bright room. We generally have to choose either vivid image in a dark room or dull image in a bright room. We have suggested a new projection system which can realize high contrast image projection in a bright room. It is consisted of electronic paper screen, projector, and light‐emitting diode room light. The electronic paper (e‐Paper) screen alternates its whole surface white/black with 120 Hz. Room lights are controlled with the same frequency of 120 Hz with the opposite phase as that of the e‐Paper screen. We have confirmed that our new system has achieved higher contrast than the conventional projection system and also enough readability of paper documents in the room simultaneously. We have thus confirmed that our new system can bring an ideal condition, for audience, which can realize a vivid image projection in a bright room.  相似文献   
58.
We have successfully developed a quarter‐wave retardation film (QWF) for wide viewing angle 3D liquid crystal displays (3D‐LCDs) that provides high luminance, low crosstalk, low color change, and low head‐tilt‐angle dependency. It was found that the out‐of‐plane retardation (Rth) of the QWF in the LCD needs to be close to 0 nm in order to improve the 3D display properties at an off‐axis position and that the in‐plane retardation (Re) needs to be adjusted from 120 to 130 nm to achieve low color change with head tilting. We adopted a coating process for making our QWF because of its potential for retardation control. 3D‐LCDs with this QWF whose Rth was nearly zero had high performance and allowed off‐axis other than on‐axis.  相似文献   
59.
Cognitive model of team cooperation in en-route air traffic control   总被引:1,自引:1,他引:0  
Since controller teams are in charge of en-route air traffic control, team cooperation is a key issue for good control performance. We conducted ethnographic field observation at the Tokyo Area Control Center and then analyzed the obtained data to develop a cognitive model of team cooperation in en-route air traffic control. We segmented conversational records, behavioral records, and so on by control unit, and then clarified relations between the segments and identified expert knowledge and judgment behind them. Cognitive processes of controller teams were reconstructed based on a concept of distributed cognition. The analysis revealed that the mutual belief model is applicable to team cooperation processes, the role assignment of tasks within a controller team is implicit and that control plans are implemented smoothly once team situation awareness has been established. A cognitive model of controllers?? team cooperation has been constructed based on these findings.  相似文献   
60.
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