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   50484篇
  免费   2567篇
  国内免费   156篇
电工技术   716篇
综合类   66篇
化学工业   10936篇
金属工艺   2163篇
机械仪表   3285篇
建筑科学   1120篇
矿业工程   25篇
能源动力   2160篇
轻工业   3944篇
水利工程   271篇
石油天然气   89篇
武器工业   2篇
无线电   7954篇
一般工业技术   10816篇
冶金工业   3900篇
原子能技术   670篇
自动化技术   5090篇
  2024年   50篇
  2023年   574篇
  2022年   878篇
  2021年   1494篇
  2020年   1085篇
  2019年   1183篇
  2018年   1452篇
  2017年   1439篇
  2016年   1781篇
  2015年   1326篇
  2014年   2129篇
  2013年   3048篇
  2012年   3323篇
  2011年   3960篇
  2010年   2870篇
  2009年   3004篇
  2008年   2857篇
  2007年   2232篇
  2006年   2069篇
  2005年   1764篇
  2004年   1599篇
  2003年   1545篇
  2002年   1350篇
  2001年   1147篇
  2000年   1018篇
  1999年   943篇
  1998年   1583篇
  1997年   1006篇
  1996年   818篇
  1995年   566篇
  1994年   464篇
  1993年   416篇
  1992年   295篇
  1991年   283篇
  1990年   261篇
  1989年   244篇
  1988年   205篇
  1987年   170篇
  1986年   120篇
  1985年   117篇
  1984年   93篇
  1983年   63篇
  1982年   40篇
  1981年   39篇
  1980年   30篇
  1979年   31篇
  1978年   30篇
  1977年   38篇
  1976年   61篇
  1973年   21篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
We propose a face detection method based on skin color likelihood via a boosting algorithm which emphasizes skin color information while deemphasizing non-skin color information. A stochastic model is adapted to compute the similarity between a color region and the skin color. Both Haar-like features and Local Binary Pattern (LBP) features are utilized to build a cascaded classifier. The boosted classifier is implemented based on skin color emphasis to localize the face region from a color image. Based on our experiments, the proposed method shows good tolerance to face pose variation and complex background with significant improvements over classical boosting-based classifiers in terms of total error rate performance.  相似文献   
92.
Summary The cyclopolymerization of 1,8-diethynylnaphthalene(DEN) and its copolymerization with diethyl dipropargylmalonate(DEDPM) were carried out by various transition metal catalysts. MoCl5-based catalyst was found to be very effective and gave almost a quantitative polymer yield. The resulting dark-brown homopolymer(PDEN) was partially soluble in chloroform, tetrahydrofuran, and dimethyl sulfoxide, whereas copolymer (1:1) with number avaerage molecular weight of 2.1x104 by GPC showed good solubility in those solvents. The structure of the polymers was analysed by IR, NMR, and UV-VIS spectroscopies. From the spectral and solubility data, it is proposed that cyclized products with the conjugated system are formed. Room temperature conductivities of the I2-doped homo and copolymer were found to be about 7.5x10-3 and 5.1x10-3 S/cm, respectively.  相似文献   
93.
Adsorption and desorption characteristics of the 2-methyl-4-chlorophenoxyacetic acid (MCPA) from aqueous solution onto the activated carbon (GAC, F-400) were studied. Adsorption equilibrium capacities of the MCPA increased with decreasing pH and temperature of the solution. Adsorption equilibrium of the MCPA could be represented by the Sips equation. The internal diffusion coefficients were determined by comparing the experimental concentration decay curves with those predicted from surface diffusion model and pore diffusion model. The adsorption model based on the linear driving force approximation (LDFA) was used for simulating the adsorption behavior of the MCPA in a fixed bed. Over ninety five percent desorption of the MCPA could be obtained using distilled water.  相似文献   
94.
Micron‐sized polymer particles were coated with layers of nickel compounds by plating electrolessly in the presence of aqueous solutions of nickel chloride, sodium hypophosphite, sodium citrate, and ammonium chloride at elevated temperature. The uniform functional polymer particle could be obtained by seeded polymerization. To investigate the effect of surface functionality on the conditions for nickel deposition, the polymer particle was functionalized with the thiol group. From morphological observation, it was found that the mode of nickel deposition was greatly dependent on the surface functionality of the polymer particle. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 420–424, 2003  相似文献   
95.
A personalized service in the ubiquitous environment is to provide services or items, which reflect personal tastes, attitudes, and contexts. It is impossible to reflect the context information generated in u-healthcare environments due to the existing recommendation system performing the recommendation using the information directly input by users and application usage record only. This study develops a context-aware model using the context information provided by the context information model. The study applies it to the extraction of the missing value in a collaborative filtering process. The context-aware model reflects the information that selects items by users according to the appropriate context using the C-HMM and provides it to users. The solution of the missing value in the preference significantly affects the recommendation accuracy in a preference based item supply method. Thus, this study developed a new collaborative filtering for ubiquitous environments by reflecting the missing preference value and reflecting it to the collaborative filtering using the context-aware model. Also, the validity of this method will be evaluated by applying it to menu services in u-healthcare services.  相似文献   
96.
Ceramic beams are induced in situ to form complex shapes at elevated temperature without the application of an external stress. This process has been demonstrated for thin alumina substrates coated with a layer of magnesia. The internal strain causing the substrates to deform at elevated temperature arises as a consequence of strain mismatch accompanying the penetration of the coating into the substrate. The magnitude of the deformation depends on the amount of coating applied, on the thickness of the substrate, on the density of the substrate, and on the temperature. During exposure of the beams to elevated temperature, the magnesia coating reacts with the alumina substrate to form the spinel phase; the resulting volume change accompanying the phase transformation is likely the predominant driving force for deformation.  相似文献   
97.
Three-dimensionally ordered long-range macroporous carbon structures were prepared using commercially available phenolic resin by utilizing sacrificial colloidal silica crystalline arrays as templates that were subsequently removed by HF etching after pyrolysis in an argon atmosphere. SEM, TEM, and BET were employed to characterize the morphology and the surface area of the porous carbon structures. The pore size (150–1000 nm) and BET surface area, which reflect pore volume (298.6 m2/g (1.32 cm3/g) ∼ 93.7 m2/g (0.12 cm3/g)), of the macroporous carbon structures produced were approximately proportional to the size (150–1000 nm) of the sacrificial silica sphere templates used (annealing temp. 550°C). The achieved 550 nm porous carbon structures were examined to function as potential catalyst carriers and were successfully impregnated with Ag or Pt-Ru on their inner walls after borohydride reduction at room temperature. In addition, porous carbon patterns were fabricated using the ‘micromolding in capillary’ technique, which has potential applications in the microreaction technology.  相似文献   
98.
This study is to investigate the factors influencing the alcohol production byKluyveromyces fragilis using the juice of Jerusalem Artichoke tubers. The cell growth rate and ethanol production rate were stimulated by aeration and by the addition of unsaturated fatty acids and the cell mass production and the ethanol production were substantially improved. It was found that oxygen and unsaturated fatty acids added played a decisive role on the increase of alcohol tolerance of yeast.  相似文献   
99.
Summary New biodegradable hydrophobic polyurethane (PU)/hydrophilic poly (ethylene glycol) diacrylate (PEGDA) IPN was simultaneously synthesized with changing the molecular weight of PEGDA to investigate the effect of crosslinking density on the degree of phase separation. PU was modified using biodegradable poly(-caprolactone)diol and the hydroxy group of PEG was substituted to crosslinkable acrylate group having double bond, which induce photo-polymerization. The sturucture of PEGDA was confirmed by NMR. Because the reaction rate of PEGDA was faster than that of PU, the continuous matrix of the micro-separated PU/PEGDA IPNs having amphiphilic character was made of hydrophilic PEGDA-rich phase. All IPNs have sea-island morphology resulting from the suppressed phase separation. The effect of the degree of phase separation on blood compatibility was investigated.  相似文献   
100.
The oxidation behavior of a sintered aluminum nitride containing 3 wt% Y2O3 as a sintering aid was investigated. Samples were exposed to air at elevated temperatures for times up to 100 h. The weights of the samples were continuously monitored during exposure at various temperatures and humidity levels. The effects of oxidation on room-temperature flexural strength were also determined, and correlated to the observed weight changes of the samples. At temperatures 1200°C, linear weight gains were observed. However, at temperatures above 1200°C, the weight gains became parabolic with respect to exposure time. The oxidation rates were significantly increased by water vapor in the air. The oxidation products were found by X-ray analysis to be a mixture of Al2O3 and 5A12O3·3Y2O3. The oxide layer formed on the surface was severely cracked because of the thermal expansion mismatch between the oxide layer and the substrate. The cracks initiated in the oxide layer and propagated into the substrate, resulting in severe reduction in the room-temperature flexural strength of the material. When exposed to ambient air for more than 50 h at temperatures greater than 1100°C, the strengths of the samples decreased to less than half that of the as-received material.  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