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   260461篇
  免费   3213篇
  国内免费   824篇
电工技术   5133篇
综合类   330篇
化学工业   37417篇
金属工艺   10256篇
机械仪表   8489篇
建筑科学   6114篇
矿业工程   1076篇
能源动力   6399篇
轻工业   22904篇
水利工程   2562篇
石油天然气   3910篇
武器工业   68篇
无线电   34743篇
一般工业技术   50133篇
冶金工业   46533篇
原子能技术   5418篇
自动化技术   23013篇
  2021年   2092篇
  2019年   2049篇
  2018年   3489篇
  2017年   3545篇
  2016年   3751篇
  2015年   2332篇
  2014年   4068篇
  2013年   11305篇
  2012年   6593篇
  2011年   8900篇
  2010年   6996篇
  2009年   7860篇
  2008年   8686篇
  2007年   8621篇
  2006年   7809篇
  2005年   7144篇
  2004年   6891篇
  2003年   6735篇
  2002年   6374篇
  2001年   6471篇
  2000年   6172篇
  1999年   6255篇
  1998年   14243篇
  1997年   10272篇
  1996年   8112篇
  1995年   6411篇
  1994年   5710篇
  1993年   5582篇
  1992年   4553篇
  1991年   4216篇
  1990年   4048篇
  1989年   3779篇
  1988年   3624篇
  1987年   3170篇
  1986年   3066篇
  1985年   3610篇
  1984年   3382篇
  1983年   3031篇
  1982年   2851篇
  1981年   2951篇
  1980年   2761篇
  1979年   2649篇
  1978年   2500篇
  1977年   2946篇
  1976年   3556篇
  1975年   2317篇
  1974年   2312篇
  1973年   2319篇
  1972年   1849篇
  1971年   1745篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Zusammenfassung der Untersuchungsergebnisse Nach dem Ergebnis dieser Unterschung kann als festgestellt gelten, daß durch den Befall mit Fusarium roseum bezw. Gibberella Saubinetii die Stärke der befallenen Gerste in einer atypischen Weise korrodiert wird. Die Art dieser Korrodierung unterscheidet sich wesentlich, sowohl von der Korrodierung im keimenden Korn, als auch von der bei starkem Schimmelpilzbefall beobachteten Korrodierung. Die Ursache für die atypische Korrodierung kann in einem örtlichen Nährstoffentzug durch die Pilzhyphen angenommen werden (lokale Frementbildung). Da solche atypisch korrodierte Stärke in den von Fusarium roseum befallenen Teilen eines Kornes immer angetroffen wird, kann diese Veränderung zur Diagnose des Pilzes im Schrot und Mehl mit herangezogen werden.bedeutet mit Abbildungen.  相似文献   
92.
Industry widely uses rotary valves and blow tanks for the pneumatic conveying of products, each having their pros and cons depending on the specific application. This article shows the differing results obtained when low-velocity conveying a product through a common pipeline using both a drop-through rotary valve and a bottom-discharge blow tank feeder. A number of issues arise in the rotary valve system, the main one being rotary valve air leakage. A blow tank system, on the other hand, does not leak, as it is an enclosed system. The experimental results show dramatic differences in product throughput. Further exploration leads to a novel modification being made to the rotary valve system in an attempt to increase its capacity. The result of this modification shows a slight increase in output tonnage, but still significantly less than that obtained from the blow tank.  相似文献   
93.
Thermal treatment applied in association with a biological system allows for a significant reduction in excess sludge production (approximately 50%). In general, heat treatment is described as a sludge disintegration technique. This paper offers a thorough study on the impact of heat treatment, at temperatures below 100 degrees C, on the solubilisation of the sludge COD and its biodegradability. Discontinuous heating experiments were performed on activated and digested sludge. At all temperatures tested the released COD for digested sludge was systematically higher than that for activated sludge (15 and 40%, respectively, at 95 degrees C for 40 min of contact time). For the first 30 min, a 1st order kinetic, with respect to the residual COD, was systematically found. In the range of 40-95 degrees C, digested sludge had a lower activation energy than activated sludge (26 kcal/mol compared to 70-160 kcal/mol). COD solubilisation is thus more positively influenced by temperature in the case of activated sludge. This may be due to the significant difference in the ratio of protein/carbohydrate in digested and activated sludge (1-5 and 0.2-0.7, respectively). The increase in the COD/TKN ratio in the solubilised fraction after thermal treatment of activated sludge suggests a preferential solubilisation of proteins over carbohydrates. Respirometric tests performed on the solubilised COD showed that whatever the sludge origin, only 40-50% of released COD is biodegradable at a conventional hydraulic retention time (i.e., 24 h). Hence, heat treatment would act more through organic matter solubilisation rather than by a biodegradability increase.  相似文献   
94.
An algorithm was obtained for restoration of a continuous process from a finite number of its equispaced discrete samples. The necessary and sufficient sampling conditions were formulated.  相似文献   
95.
Guest Editors' Introduction: Overview of Sensor Networks   总被引:4,自引:0,他引:4  
Culler  D. Estrin  D. Srivastava  M. 《Computer》2004,37(8):41-49
Wireless sensor networks could advance many scientific pursuits while providing a vehicle for enhancing various forms of productivity, including manufacturing, agriculture, construction, and transportation.  相似文献   
96.
A cylinder having a length less than 0.707 of its diameter will float with its axis vertical while one of length exceeding one diameter floats with its axis horizontal. This transition range was investigated and under certain circumstances, two stable positions of the cylinder axis were found in each quadrant of rotation. Details of behaviour in the transition range were attributed to the edges of the square-ended cylinder.  相似文献   
97.
Formaldehyde is used in ruminant feeding for different purposes including the protection of dietary proteins from ruminal degradation. The formaldehyde content of milk of goats fed various levels of formaldehyde-treated soybean oil-meal has been determined by using a sensitive HPLC method. Results showed a significant linear correlation between ingested formaldehyde and formaldehyde concentration in milk. About 0.02% of ingested formaldehyde was excreted in milk, as free formaldehyde.  相似文献   
98.
The main purpose of this study was to evaluate the performance of the electrochemical oxidation process as a post-treatment for the effluents of a bench-scale UASB reactor treating simulated wastewater from an unbleached pulp plant. The oxidation process was performed using a single compartment cell with two plates as electrodes. The anode was made of Ti/Ru0.3Ti0.7O2 and the cathode of stainless steel. The following variables were evaluated: current density (75, 150 and 225 mA cm(-2)) and recirculation flow rate in the electrochemical cell (0.22, 0.45 and 0.90 L h(-1)). The increase in current density from 75 to 225 mA cm(-2) did not increased the color removal efficiency for the tested flow rates, 0.22, 0.45 and 0.90 L h(-1), however the energy consumption increased significantly. The results indicated the technical feasibility of the electrochemical treatment as post-treatment for UASB reactors treating wastewaters from pulp and paper plants.  相似文献   
99.
Suppose that an equilibrium is asymptotically stable when external inputs vanish. Then, every bounded trajectory which corresponds to a control which approaches zero and which lies in the domain of attraction of the unforced system, must also converge to the equilibrium. This "well-known" but hard-to-cite fact is proved and slightly generalized here.  相似文献   
100.
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