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   24057篇
  免费   1910篇
  国内免费   1711篇
电工技术   421篇
技术理论   1篇
综合类   2088篇
化学工业   3976篇
金属工艺   2428篇
机械仪表   1263篇
建筑科学   1459篇
矿业工程   984篇
能源动力   664篇
轻工业   2779篇
水利工程   585篇
石油天然气   828篇
武器工业   232篇
无线电   1724篇
一般工业技术   5225篇
冶金工业   1357篇
原子能技术   197篇
自动化技术   1467篇
  2024年   83篇
  2023年   365篇
  2022年   770篇
  2021年   865篇
  2020年   786篇
  2019年   730篇
  2018年   627篇
  2017年   782篇
  2016年   847篇
  2015年   875篇
  2014年   1286篇
  2013年   1432篇
  2012年   1386篇
  2011年   1787篇
  2010年   1386篇
  2009年   1413篇
  2008年   1310篇
  2007年   1433篇
  2006年   1288篇
  2005年   1146篇
  2004年   1027篇
  2003年   850篇
  2002年   749篇
  2001年   612篇
  2000年   604篇
  1999年   430篇
  1998年   414篇
  1997年   360篇
  1996年   292篇
  1995年   236篇
  1994年   221篇
  1993年   180篇
  1992年   191篇
  1991年   177篇
  1990年   148篇
  1989年   106篇
  1988年   92篇
  1987年   50篇
  1986年   45篇
  1985年   48篇
  1984年   65篇
  1983年   32篇
  1982年   28篇
  1981年   23篇
  1980年   12篇
  1979年   10篇
  1977年   13篇
  1976年   10篇
  1975年   8篇
  1974年   10篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
通过借鉴中医学整体观和生命观的相关理论,从认识城市有机体的生命属性入手,发现并提炼能够产生和传递城市运营所需各种能量的生命要素:廊道和功能体。阐释了其多层级、多性质和多形态的特点,提出了功能体有动力、廊道成系统、敏感点有活力的疏通策略,旨在促进城市各种能量的有机循环,从而维护城市的健康与安全,提高城市生活的效率与质量。  相似文献   
2.
Pleurotus eryngii, the second largest industrial cultivation mushroom in China, is usually cultivated on substrates mainly consisting of sawdust and corncob. In this study, experiments were performed to determine the effects of different carbon sources and C/N values on nonvolatile taste components of P. eryngii. The effects of different carbon sources on nonvolatile taste components levels revealed that sawdust was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while corncob was beneficial to high contents of carbohydrate, polysaccharides and trehalose. At the similar C/N values, relatively higher sawdust content was beneficial to umami amino acid production, while relatively higher corncob content was beneficial to high contents of carbohydrate, polysaccharides and mannitol. Higher C/N value was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while lower C/N value was beneficial to high contents of carbohydrate, polysaccharides and trehalose. These results provided information for P. eryngii fruit body industrial cultivation to obtain specific nonvolatile taste components with high levels.  相似文献   
3.
4.
In this work, ZnO nanostructures are electrodeposited on a transparent conducting glass from chloride baths. The influence of H2O2 concentration on the electrochemical characteristics has been studied using cyclic voltammetry (CV) and chronoamperometry (CA) techniques. From the analysis of the current transients on the basis of the Scharifker–Hills model, it is found that nucleation mechanism is progressive with a typical three-dimensional (3D) nucleation and growth process; independently with the concentration of H2O2. However, the nucleation rate of the ZnO changes with the increase of H2O2 concentration. The Mott–Schottky measurements demonstrate an n-type semiconductor character for all samples with a carrier density varying between 5.14×1018 cm−3 and 1.47×1018 cm−3. Scanning electron microscopy (SEM) observations show arrays of vertically aligned ZnO nanorods (NRs) with good homogeneity. The X-ray diffraction (XRD) patterns show that the ZnO deposited crystallises according to a hexagonal Würtzite-type structure and with the c-axis perpendicular to the electrode surface. The directional growth along (002) crystallographic plane is very important for deposits obtained at 5 and 7 mM of H2O2. The high optical properties of the ZnO NRs with a low density of deep defects was checked by UV–vis transmittance analyses, the band gap energy of films varies between 3.23 and 3.31 eV with transparency around 80–90%.  相似文献   
5.
The non-equiatomic FeCoNiAlSi alloy is prepared by the Bridgman solidification (BS) technique at different withdrawal velocities (V = 30, 100, and 200 μm/s). Various characterization techniques have been used to study the microstructure and crystal orientation. The morphological evolutions accompanying the crystal growth of the alloy prepared at different withdrawal velocities are nearly the same, from equiaxed grains to columnar crystals. The transition of coercivity is closely related to the local microstructure, while the saturation magnetization changes little at different sites. The coercivity can be significantly reduced from the equiaxed grain area to the columnar crystal area when the applied magnetic field direction is parallel to the crystal growth direction, no matter what is the withdrawal velocity. In addition, the alloy possesses magnetic anisotropy when the applied magnetic field is in different directions.  相似文献   
6.
Fatigue crack growth behaviour of Ti–6Al–2Zr–1.5Mo–1.5V (VT-20 a near-α Ti alloy) was studied in lamellar, bimodal and acicular microstructural conditions. Fatigue crack growth tests at both increasing and decreasing stress intensity factor range values were performed at ambient temperature and a loading ratio of 0.3 using compact tension samples. Lamellar and acicular microstructures showed lower fatigue crack growth rates as compared to the bimodal microstructure due to the tortuous nature of cracks in the former and the cleavage of primary α in the latter. The threshold stress intensity factor range was highest for acicular microstructure.  相似文献   
7.
8.
9.
The effect of enzymatic hydrolysis of proteins in milk using neutrase on the growth of the probiotic strain Bifidobacterium bifidus was evaluated by estimation of microbial growth, acidity, viscosity and flavour production. A significant increase in the growth of B bifidus was observed in neutrase‐hydrolysed milk. The setting time of bifidus‐cultured milk was advanced by about 12 h at 5% degree of hydrolysis. Enzymatic hydrolysis of proteins prior to cultivation also significantly increased the viscosity of the product. An approximately 60% increase in viscosity of the product was observed in neutrase‐hydrolysed milk. Production of steam‐volatile monocarbonyls as an indication of development of flavour was also higher in neutrase‐hydrolysed milk. The concentration of steam‐volatile monocarbonyls was 2.47 µmol per 100 ml in neutrase‐hydrolysed milk but only 1.84 µmol per 100 ml in control milk at the setting point of the curd. © 2002 Society of Chemical Industry  相似文献   
10.
1 INTRODUCTIONParticlesreinforcedtitaniumalloymatrixcomposites(TMCp)havewideapplicationfieldsfortheirattractivehighspecificstreng  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