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   684篇
  免费   47篇
  国内免费   5篇
电工技术   83篇
综合类   8篇
化学工业   187篇
金属工艺   17篇
机械仪表   21篇
建筑科学   19篇
矿业工程   6篇
能源动力   33篇
轻工业   48篇
水利工程   2篇
石油天然气   20篇
武器工业   6篇
无线电   72篇
一般工业技术   133篇
冶金工业   24篇
原子能技术   11篇
自动化技术   46篇
  2024年   5篇
  2023年   5篇
  2022年   15篇
  2021年   21篇
  2020年   10篇
  2019年   15篇
  2018年   13篇
  2017年   10篇
  2016年   18篇
  2015年   25篇
  2014年   30篇
  2013年   60篇
  2012年   33篇
  2011年   47篇
  2010年   39篇
  2009年   44篇
  2008年   36篇
  2007年   20篇
  2006年   32篇
  2005年   12篇
  2004年   17篇
  2003年   21篇
  2002年   24篇
  2001年   11篇
  2000年   12篇
  1999年   9篇
  1998年   18篇
  1997年   9篇
  1996年   12篇
  1995年   5篇
  1994年   17篇
  1993年   6篇
  1992年   4篇
  1991年   5篇
  1990年   9篇
  1989年   2篇
  1988年   6篇
  1987年   5篇
  1986年   7篇
  1985年   5篇
  1984年   6篇
  1983年   8篇
  1982年   6篇
  1981年   3篇
  1980年   2篇
  1979年   3篇
  1978年   3篇
  1977年   4篇
  1969年   2篇
  1967年   1篇
排序方式: 共有736条查询结果,搜索用时 16 毫秒
81.
Females of the solitary endoparasitoid Cotesia vestalis respond to a blend of volatile organic compounds (VOCs) released from plants infested with larvae of their host, the diamondback moth (Plutella xylostella), which is an important pest insect of cruciferous plants. We investigated the flight response of female parasitoids to the cruciferous plant Brassica rapa, using two-choice tests under laboratory conditions. The parasitoids were more attracted to plants that had been infested for at least 6 hr by the host larvae compared to intact plants, but they did not distinguish between plants infested for only 3 hr and intact plants. Although parasitoids preferred plants 1 and 2 days after herbivory (formerly infested plants) over intact plants they also preferred plants that had been infested for 24 hr over formerly infested plants. This suggests that parasitoids can distinguish between the VOC profiles of currently and formerly infested plants. We screened for differences in VOC emissions among the treatments and found that levels of benzyl cyanide and dimethyl trisulfide significantly decreased after removal of the host larvae, whereas terpenoids and their related compounds continued to be released at high levels. Benzyl cyanide and dimethyl trisulfide attracted parasitoids in a dose-dependent manner, whereas the other compounds were not attractive. These results suggest that nitrile and sulfide compounds temporarily released from plants under attack by host larvae are potentially more effective attractants for this parasitoid than other VOCs that are continuously released by host-damaged plants.  相似文献   
82.
Hong Gao  Junji Wakita  Shinji Ando 《Polymer》2010,51(14):3173-99
Novel hybrid films of fluorinated hyperbranched polyimide (HBPI) and zinc oxide (ZnO) were prepared via the in situ sol-gel polymerization technique, in which mono-ethanolamine (MEA) was used as the coupling agent between the termini of HBPI and the precursor of ZnO. The hybrid films were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) absorption, ultraviolet-visible (UV-vis) absorption, and fluorescent excitation/emission spectroscopy. The films, which originated from the colourless fluorinated HBPI structure and homogeneously dispersed ZnO nanoparticles, exhibited good optical transparency. Furthermore, two kinds of model compounds with and without ZnO and a HBPI film blended with ZnO microparticles were prepared to clarify the fluorescence mechanism in the pristine HBPI and in situ hybrid films. Efficient energy transfer from the ZnO nanoparticles to the aromatic HBPI main chains was observed in the in situ hybrid films, whereas energy transfer occurred only from the locally excited (LE) states to the charge-transfer (CT) state in the HBPI film. These facts demonstrate that the peripheral termini of HBPI are covalently bonded to ZnO particles via the MEA function, which operates as an effective pathway for energy transfer to give intense fluorescent emission.  相似文献   
83.
We synthesized new polymers with both photocrosslinkability and biocompatibility by a random copolymerization of 4‐(4‐methoxycinnamoyl)phenyl methacrylate and 2‐methacryloyloxyethyl phosphorylcholine. These polymers were used as prepolymers to make a hydrogel by photoirradiation. Gelation began with 5 s of photoirradiation and reached an equilibrium state after 360 s of photoirradiation. The absorption maximum at 347 nm, attributed to the cinnamoyl group, disappeared with the photoirradiation time. That is, dimerization between cinnamoyl groups in the polymer proceeded and formed a hydrogel. The equilibrium water concentration of the hydrogels was more than 90%. Moreover, we succeeded in making a microshape hydrogel on glass by photoirradiation through a photomask. The window shape of the photomask was transferred to the hydrogel that was formed. We concluded that these photocrosslinkable polymers could be useful in preparing microfluidic devices for separating or immobilizing biomolecules and cells. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 44–50, 2007  相似文献   
84.
A novel dimer of an inositol glycoside was isolated from the mycelial extracts of Streptomyces sp. AJ 9463. Its structure was assigned as a disulfide of 2-(N-acetyl-L-cysteinyl)amido-2-deoxy-alpha-D-glucopyranosyl-(1-->1)-1D- myo- inositol (1).  相似文献   
85.
86.
For the diffusion-controlled adsorption, the expression of dynamic surface adsorption P(t) was ob- tained by solving the diffusion equation. Two cases, i.e. the short and long time limits, were mainly discussed in this paper. From the measured dynamic surface tension of aqueous surfactant sodium dodecyl sulfate (SDS) solutions at 25 ℃, the adsorption kinetics of SDS at air/solution interface was studied. It was proved that for both of the short and long time limits, the adsorption process of SDS was controlled by diffusion.  相似文献   
87.
Since the formation of helium bubbles degrades swelling property and thermal conductivity of minor actinide-containing mixed oxide (MA-MOX) fuel, it is essential to understand the conditions of the bubble formation. In order to examine the dependence of vacancy concentration on morphology of helium bubbles, helium was infused into (Zr,Fe)O2?x. The oxygen vacancy concentration was controlled by addition of solute Fe3+ into ZrO2. Helium was infused by hot isostatic pressing. The helium-infused specimens were observed by field emission scanning electron microscopy (FE-SEM) and field emission transmission electron microscopy (FE-TEM). In addition, X-ray fluorescence, X-ray diffraction analysis, conversion electron yield–X-ray absorption near-edge structure and FE-SEM/EDX (energy dispersive X-ray) analyses were also made to interpret the results of microstructure observations. As a result of the helium infusion treatment, numerous 0.5–10 nm bubbles were observed and its number density clearly depended on oxygen vacancy concentration. On the other hand, sizes of the helium nano-bubbles in all specimens were almost constant.  相似文献   
88.
We developed high-efficiency multi-photon emission (MPE) blue phosphorescent OLEDs with external quantum efficiency exceeding 40% at 100 cd m−2. In these MPE devices, we used a blue phosphorescent emitter, FIrpic and pyridine-containing electron-transporters, B3PyPB and B3PyMPM, B4PyMPM. We also used a well-known electron-transporter, BCP for comparison. We used a combination of TAPC/MoO3/Al/Liq layers as the charge-generation layer unit. An optimized MPE device showed an extremely high current efficiency of over 90 cd A−1 and a high power efficiency of over 40 lm W−1 at 100 cd m−2 without any outcoupling enhancement.  相似文献   
89.
A biomolecular interactive analysis with antibody-antigen and aptamer-protein was evaluated on Au-over layers deposited on the BioDVD surface. BioDVD consists of multilayered structures with Au layer on the top and it detects analytes by monitoring the changes in reflected light intensity due to analyte adsorption to the sensor surface, on which functional biomolecules are immobilized to bind specifically to the analytes. The BioDVD sensing instrument is based on a commercial digital versatile disc system, which allows the instrument to be small and inexpensive. The BioDVD platform can be fabricated utilizing mass production techniques with additional functional phase change layers that can serve both to enhance sensitivity by optimization of the interferometric cavity optical properties and also as a possible medium for the storage of test related information.  相似文献   
90.
A new photochromic compound, S1 , containing a trans-cis photoisomerizable unit and a mercury detecting chemosensor unit, has been designed and synthesized. S1 displayed dramatic selectivity for mercury ions over other ions, through fluorescence intensity measurement. In addition, in the photostationary state, a colorimetric response to mercury ions was also achieved. The fluorescence turn-off of S1 by mercury ions was defined as the first check, while mercury-induced colorimetric variation in the photostationary state was set as the second check. Thus, a double-check mercury chemosensor can be achieved.  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