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   1124篇
  免费   29篇
  国内免费   5篇
电工技术   64篇
综合类   2篇
化学工业   293篇
金属工艺   44篇
机械仪表   37篇
建筑科学   14篇
能源动力   44篇
轻工业   62篇
水利工程   2篇
石油天然气   4篇
无线电   106篇
一般工业技术   168篇
冶金工业   206篇
原子能技术   48篇
自动化技术   64篇
  2023年   3篇
  2022年   6篇
  2021年   9篇
  2020年   7篇
  2018年   12篇
  2017年   11篇
  2016年   27篇
  2015年   24篇
  2014年   19篇
  2013年   44篇
  2012年   21篇
  2011年   52篇
  2010年   30篇
  2009年   39篇
  2008年   53篇
  2007年   40篇
  2006年   49篇
  2005年   29篇
  2004年   31篇
  2003年   60篇
  2002年   29篇
  2001年   31篇
  2000年   23篇
  1999年   25篇
  1998年   93篇
  1997年   50篇
  1996年   51篇
  1995年   23篇
  1994年   21篇
  1993年   26篇
  1992年   19篇
  1991年   11篇
  1990年   7篇
  1989年   7篇
  1988年   11篇
  1987年   13篇
  1986年   15篇
  1985年   15篇
  1984年   14篇
  1983年   9篇
  1982年   10篇
  1981年   14篇
  1980年   10篇
  1979年   10篇
  1978年   9篇
  1977年   13篇
  1976年   16篇
  1975年   3篇
  1974年   3篇
  1973年   5篇
排序方式: 共有1158条查询结果,搜索用时 15 毫秒
931.
932.
A mixed continuous culture system was made up as a model for bulking and flocculation phenomena of the activated sludge to study the effect of dissolved oxygen (DO) deficiency and the effect of high organic loading. The system consisted of a floc forming bacterium and a filamentous bacterium which were isolated from the activated sludge and were identified as Pseudomonas sp. and Sphaerotilus sp., respectively. Sphaerotilus sp. had potential to cause a filamentous bulking phenomenon on the activated sludge. It was observed that the filamentous microorganism showed three kinds of growth form, filamentous form, pellet form and dispersed form, and that the floc former showed two kinds of growth form, good floc form and dispersed form. In the model system, these changes of growth form of two microorganisms, which could be thought as the cause of settling characteristics changes, depended on the DO level and the dilution rate (as a substitution for organic loading). The DO level also influence the aggregative ability of each microorganism and the maximum oxygen uptake rate, QO2max, of filamentous microorganism. The proportions of both microorganisms in model system were inverted reversibly by the DO level or the dilution rate changes.  相似文献   
933.
In standard agency models, only performance‐based wages (monetary incentives) motivate an agent to work more. The present paper proposes a new agency model in which the principal makes an investment, in addition to the standard wage incentive, to raise non‐monetary utility. We clarify two problems according to the type of non‐monetary utility: the intrinsic motivation (IM) problem and the fringe benefits (FB) problem. The results of our analysis of both problems are as follows: (1) The results of the IM model and the FB model are similar regarding monetary payment. (2) Although IM is dependent on the attributes of a job and the worker, such as productivity or cost sensitivity, FB is not dependent on such factors.  相似文献   
934.
A novel specimen holder that enables in situ observation of crack-tip deformation and/or fracture under a controlled environment is developed for a high-voltage electron microscope (HVEM). A window-type environmental cell (EC) that incorporates a uniaxial straining apparatus is built into a side-entry-type single-tilt specimen holder. The gas control in EC, straining apparatus design, limited field of view for crack-tip observation, and specimen preparation for the specimen holder are presented in detail. Experimental results successfully demonstrate that the developed specimen holder is quite useful for the dynamic observation of crack-tip deformation and/or fracture subjected to a hostile environment, such as hydrogen gas.  相似文献   
935.
Flash lamp annealing (FLA) with millisecond-order pulse duration can crystallize microm-order-thick a-Si films on glass substrates through explosive crystallization (EC), and flash-lamp-crystallized (FLC) poly-Si films consist of densely-packed nanometer-sized fine grains. We investigate the impact of the hydrogen concentration and the defect density of precursor a-Si films on crystallization mechanism and the microstructures of FLC poly-Si films, by comparing chemical-vapor-deposited (CVD) and sputtered precursor a-Si films. Transmission electron microscopy (TEM) observation reveals that FLC poly-Si films with similar periodic microstructures are formed by the FLA of the two kinds of precursor films, meaning no significant influence of hydrogen atoms and defect density on crystallization mechanism. This high flexibility of the properties of precursor a-Si films would contribute to a wide process window to reproducibly form FLC poly-Si films with the particular periodic microstructures.  相似文献   
936.
The reinforced suspension preheater (RSP) process for the production of portland cement comprises a suspension preheater equipped with precalcining vessels designated as swirl burner and swirl calciner. The process has been demonstrated through the operation of a 235 metric ton per day plant. The swirl burner and swirl calciner provide effective heat transfer and permit control of temperature to obtain raw meal decarbonation of 85-90 percent. Data are presented describing sulfur absorption at various stages of the process. Nitrogen oxide emissions are limited due to the low temperature maintained in the swirl calciner. Excellent cement quality has been obtained.  相似文献   
937.
MYC is a major oncogene that plays an important role in cell proliferation in human cancers. Therefore, the mechanism behind MYC regulation is a viable therapeutic target for the treatment of cancer. Comprehensive and efficient screening of MYC regulators is needed, and we had previously established a promoter screening system using fluorescent proteins and the CRISPR library. For the efficient identification of candidate genes, a database was used, for which mRNA expression was correlated with MYC using datasets featuring “Similar” and “Not exactly similar” contexts. INTS14 and ERI2 were identified using datasets featuring the “Similar” context group, and INTS14 and ERI2 were capable of enhancing MYC promoter activity. In further database analysis of human cancers, a higher expression of MYC mRNA was observed in the INTS14 mRNA high-expressing prostate and liver cancers. The knockdown of INTS14 in prostate cell lines resulted in decreased MYC mRNA and protein expression and also induced G0/1 arrest. This study confirmed that CRISPR screening combined with context-matched database screening is effective in identifying genes that regulate the MYC promoter. This method can be applied to other genes and is expected to be useful in identifying the regulators of other proto-oncogenes.  相似文献   
938.
Complex phenomena such as phase transitions and heat transfers in multiphase, multicomponent flows were modeled in the fluid-dynamics portion of SIMMER-III, which was developed to appropriately assess core disruptive accidents (CDAs) in liquid–metal fast reactors (LMFRs). A new multicomponent vaporization/condensation (V/C) model was developed and introduced to SIMMER-III by the authors. In the present study, a new series of multi-bubble condensation experiments was performed to demonstrate that SIMMER-III with the present V/C model is practically applicable to multicomponent, multiphase flow systems with phase transition. In the experiments, bubble diameters and void fractions were quantified from visualization images using original image-processing techniques. Comparing SIMMER-III predictions with experimental data, it was confirmed that SIMMER-III with the proposed V/C model could suitably represent the effects of noncondensable components on the condensation process in multi-bubble systems. This work has improved the reliability of SIMMER-III with regard to multicomponent phase-transition phenomena.  相似文献   
939.
Glass milling is discussed with influences of tool inclination on brittle fracture. Cutting tests are performed to observe surfaces in the up-cut and the down-cut processes with a ball end mill inclined in the feed direction of the cutter. Brittle fracture occurs in the down-cut process at high feed rates. Then the machined surfaces in cutting with the ball end mills tilted in the vertical plane with respect to the feed direction are associated with those of the up-cut and the down-cut processes. The cutting forces are also measured to discuss brittle fracture with the change of the undeformed chip thickness. The scratches on the surface finished with the tilted ball end mill are shown in an analytical model with a notched edge shape. The maximum feed rates at which brittle fracture does not occur are shown with the tool inclination in the cutting tests.  相似文献   
940.
Proanthocyanidins (PAs) or condensed tannins are a major group of phenolic compounds in the leaves of birch trees and many other woody and herbaceous plants. These compounds constitute a significant allocation of carbon in leaves and are involved in plant responses to environmental stress factors, such as pathogens or herbivores. In some plants, PA concentrations are affected by atmospheric carbon dioxide (CO2) and ozone (O3) levels that may influence, for example, species fitness, community structure, or ecosystem nutrient cycling. Therefore, a study on the quantitative response of PAs to elevated concentrations of carbon dioxide (CO2) and ozone (O3) was undertaken in seedlings of Betula platyphylla, Betula ermanii, and Fagus crenata. Seedlings were exposed to ambient or elevated O3 and CO2 levels during two growing seasons in the Kanto district in Japan. Ten open-top chambers were used for five different treatments with two replicates: filtered air (FA), ambient air (ambient O3, 43 ppb; ambient CO2, 377 ppm), elevated O3 (1.5 × ambient O3, 66 ppb), elevated CO2 (1.5 × ambient CO2, 544 ppm), and elevated O3 and CO2 combined. In addition, seedlings growing in natural conditions outside of chambers were studied. Leaf samples were analyzed for total PA concentrations by butanol–HCl assay and for polymeric PA concentrations by normal-phase high-performance liquid chromatography. Total PA concentrations in leaves of all species were similarly affected by different treatments. They were significantly higher in seedlings treated with elevated CO2 and O3 combined, and in seedlings growing outside chambers compared with the FA controls. F. crenata contained only traces of polymeric PAs, but significant species × treatment interaction was observed in the polymeric PA concentrations in B. ermanii and B. platyphylla. In B. platyphylla, leaves treated with elevated CO2 + O3 differed significantly from all other treatments. It was suggested that the strongest effect of elevated CO2 and O3 combined on leaf PA contents resulted from the additive effect of these environmental factors on phenolic biosynthesis.  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