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   34432篇
  免费   872篇
  国内免费   45篇
电工技术   413篇
综合类   30篇
化学工业   7366篇
金属工艺   713篇
机械仪表   636篇
建筑科学   1562篇
矿业工程   184篇
能源动力   916篇
轻工业   2366篇
水利工程   388篇
石油天然气   367篇
武器工业   2篇
无线电   2257篇
一般工业技术   5313篇
冶金工业   7859篇
原子能技术   294篇
自动化技术   4683篇
  2022年   261篇
  2021年   412篇
  2020年   338篇
  2019年   420篇
  2018年   463篇
  2017年   482篇
  2016年   567篇
  2015年   451篇
  2014年   683篇
  2013年   2040篇
  2012年   1181篇
  2011年   1557篇
  2010年   1149篇
  2009年   1185篇
  2008年   1420篇
  2007年   1485篇
  2006年   1310篇
  2005年   1184篇
  2004年   997篇
  2003年   952篇
  2002年   943篇
  2001年   599篇
  2000年   587篇
  1999年   597篇
  1998年   703篇
  1997年   637篇
  1996年   620篇
  1995年   603篇
  1994年   554篇
  1993年   655篇
  1992年   558篇
  1991年   410篇
  1990年   474篇
  1989年   494篇
  1988年   431篇
  1987年   461篇
  1986年   477篇
  1985年   543篇
  1984年   517篇
  1983年   488篇
  1982年   405篇
  1981年   439篇
  1980年   414篇
  1979年   434篇
  1978年   401篇
  1977年   362篇
  1976年   344篇
  1975年   364篇
  1974年   299篇
  1973年   306篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
We present a fully automatic arm and hand tracker that detects joint positions over continuous sign language video sequences of more than an hour in length. To achieve this, we make contributions in four areas: (i) we show that the overlaid signer can be separated from the background TV broadcast using co-segmentation over all frames with a layered model; (ii) we show that joint positions (shoulders, elbows, wrists) can be predicted per-frame using a random forest regressor given only this segmentation and a colour model; (iii) we show that the random forest can be trained from an existing semi-automatic, but computationally expensive, tracker; and, (iv) introduce an evaluator to assess whether the predicted joint positions are correct for each frame. The method is applied to 20 signing footage videos with changing background, challenging imaging conditions, and for different signers. Our framework outperforms the state-of-the-art long term tracker by Buehler et al. (International Journal of Computer Vision 95:180–197, 2011), does not require the manual annotation of that work, and, after automatic initialisation, performs tracking in real-time. We also achieve superior joint localisation results to those obtained using the pose estimation method of Yang and Ramanan  (Proceedings of the IEEE conference on computer vision and pattern recognition, 2011).  相似文献   
83.
Policy flight simulators are designed for the purpose of exploring alternative management policies at levels ranging from individual organizations to national strategy. This article focuses on how such simulators are developed and on the nature of how people interact with these simulators. These interactions almost always involve groups of people rather than individuals, often with different stakeholders in conflict about priorities and courses of action. The ways in which these interactions are framed and conducted are discussed, as well as the nature of typical results.  相似文献   
84.
Byrdwell WC 《Lipids》2001,36(4):327-346
Atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) has proven to be a very valuable technique for analysis of lipids from a variety of classes. This instrumental method readily produces useful ions with gentle fragmentation from large neutral molecules such as triacylglycerols and carotenoids, which are often difficult to analyze using other techniques. Molecules that are easily ionized, such as phospholipids, produce molecular ions and diagnostically useful fragment ions that are complementary to those produced by methods such as electrospray ionization MS with collision-induced dissociation. The simplicity and versatility of APCI-MS make it an ideal tool for use in solving hitherto very difficult analytical problems.  相似文献   
85.
The stepwise HBr titration method for the cyclopropenoid analysis of cottonseed oils is subject to serious inaccuracies when applied to samples containing higher cyclopropenoid concentrations, particularly if they contain appreciable amounts of alumina-adsorbable materials. A modification of the method is described which eliminates these sources of error. Its validity has been established by the analysis of a wide range of synthetic compositions including compositions containing massive amounts of interfering HBr-reactive substances and other alumina-adsorbable materials. The method with further modification can be used to analyze glycerides with the same high degree of accuracy. Presented at the AOCS Meeting in Houston, April 1965. So. Utiliz. Res. Dev. Div., ARS, USDA.  相似文献   
86.
The classical game theoretic resolutions to Selten’s Chain Store game are unsatisfactory; they either alter the game to avoid the paradox or struggle to organize the existing experimental data. This paper applies co-evolutionary algorithms to the Chain Store game and demonstrates that the resulting system’s dynamics are neither intuitively paradoxical nor contradicted by the existing experimental data. Specifically, some parameterizations of evolutionary algorithms promote genetic drift. Such drift can lead the system to transition among the game’s various Nash Equilibria. This has implications for policy makers as well as for computational modelers.  相似文献   
87.
Chlorination of a low molecular weight polystyrene in the α position was studied by following changes in the infrared spectrum, glass transition temperature, and molecular weights of the polymer. The logarithm of the absorbance ratio at 2920 and 1500 cm?1 as a function of mole per cent chlorination was linear. The glass transition temperatures, determined by use of a differential scanning calorimeter (DSC), were found to obey an equation developed by Dyvik for copolymers. The molecular weight of the chlorinated polystyrene decreased as a function of chlorination.  相似文献   
88.
A new method for the numerical solution of a stagewise process is presented. The method consists of total linearization of all the equations in the distillation process, using the method of quasi-linearization. The resulting equations form a block-band matrix which can be readily solved by a method developed by the author. The method used for obtaining convergence is presented. The method has been tested for both binary and multi-component systems. The method has been compared with the Amundson-Pontinen method for a five component mixture. The method gives more rapid convergence. Numerical experiments indicate that the vapor and liquid flow rates are more stringent requirements than the bubble point.  相似文献   
89.
Protein, total phospholipid, phosphatidyl cholines and phosphatidyl choline fractions from liver mitochondria and microsomes of female rats were analyzed after treatment with CCl4 (0.3 ml of CCl4 suspended in corn oil) or ethionine (50 mg in 0.9% saline) or after feeding a choline deficient, low protein diet for seven days. Phosphatidyl cholines were separated into four fractions differing in the degree of fatty acid unsaturation. Over 50% of total phosphatidyl choline phosphorus was present in fraction 3 of liver mitochondria and microsomes. The major fatty acid in fraction 1 was docosahexaenoic acid. Fraction 4 contains oleic and linoleic acids. Arachidonic acid occurs in fraction 2 and 3. Ethionine decreased the amount of microsomal protein and phosphatidyl choline fraction 1 of mitochondria. Microsomal protein was decreased by CCl4. The choline deficient, low protein diet caused a decrease in mitochondrial and microsomal phospholipids. The amount of the mitochondrial phosphatidyl choline decreased. Corn oil increased the level of phosphatidyl choline fraction 3. Choline deficiency decreased the amount of phosphatidyl choline fraction 3, increased fraction 4 of mitochondria and microsomes and increased fraction 1 of microsomes.  相似文献   
90.
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