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   176932篇
  免费   2137篇
  国内免费   708篇
电工技术   3290篇
综合类   102篇
化学工业   27886篇
金属工艺   7783篇
机械仪表   5117篇
建筑科学   4410篇
矿业工程   876篇
能源动力   4679篇
轻工业   16372篇
水利工程   1703篇
石油天然气   3127篇
武器工业   2篇
无线电   19850篇
一般工业技术   33333篇
冶金工业   33116篇
原子能技术   4291篇
自动化技术   13840篇
  2021年   1313篇
  2019年   1247篇
  2018年   2108篇
  2017年   2081篇
  2016年   2191篇
  2015年   1571篇
  2014年   2720篇
  2013年   7782篇
  2012年   4553篇
  2011年   6376篇
  2010年   5039篇
  2009年   5883篇
  2008年   5861篇
  2007年   5836篇
  2006年   5010篇
  2005年   4681篇
  2004年   4472篇
  2003年   4144篇
  2002年   4101篇
  2001年   4125篇
  2000年   3922篇
  1999年   4054篇
  1998年   10383篇
  1997年   7389篇
  1996年   5654篇
  1995年   4281篇
  1994年   3617篇
  1993年   3564篇
  1992年   2604篇
  1991年   2537篇
  1990年   2416篇
  1989年   2435篇
  1988年   2376篇
  1987年   2126篇
  1986年   2066篇
  1985年   2368篇
  1984年   2185篇
  1983年   2012篇
  1982年   1880篇
  1981年   1944篇
  1980年   1796篇
  1979年   1816篇
  1978年   1776篇
  1977年   2108篇
  1976年   2687篇
  1975年   1557篇
  1974年   1549篇
  1973年   1607篇
  1972年   1350篇
  1971年   1262篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Dry red kidney beans were canned using two different pretreatments: soaking for 12 hr at 20°C, and vacuum hydration for 5 min followed by soaking for 2 hr at temperatures from 45-59.1°C. Samples were then packed, processed to commercial sterility, and tested for percentage of split beans after processing. Vacuum hydration pretreatments greatly decreased the incidence and severity of splitting in the canned product and accelerated water uptake while retaining the same moisture content after soaking as the conventional soak treatment. Vacuum-hydrated beans gained less moisture during retorting than conventionally treated samples.  相似文献   
992.
Aiming at producing high temperature structural ceramics, ultra-fine SiC powders were synthesized by the gas phase reaction of silicon tetrachloride with methane in a d.c. thermal plasma. The influence of parameters as the SiCl4 feeding rate, C/Si and H2/C molar ratios and internal pressure on the powder properties were investigated. The SiC powders were characterized by chemical analysis, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electronic microscopy. The experimental set-up allows the production of β-SiC powders at a rate of 200 g h−1 with particle size around 0.1 μm. The main impurities in the as-produced powder handled at ambient atmosphere are: oxygen (1.8–2.5%) and free carbon (3–4%). Interesting relationships were found between the SiCl4 feeding rate and the H2/C molar ratio and between the C/Si molar ratio and the internal pressure. The internal pressure plays a major role in controlling the particle size.  相似文献   
993.
Two experiments were conducted to compare methods of determining oxygen consumption by portal-drained viscera and to relate this consumption to total oxygen consumption by lactating dairy cows. Oxygen consumption was the product of portal blood flow (determined by dilution of dye infused into a mesenteric vein) and portal-arterial concentration differences of oxygen. In Experiment 1, portal-arterial concentrations of oxygen were determined in samples from three cows using equations based on blood pH, hemoglobin, partial pressure of carbon dioxide, and partial pressure of oxygen (method 1) or by direct oxygen determination with an oximeter (method 2). Overall, there were no differences in oxygen concentrations or oxygen consumption by portal-drained viscera between methods. In Experiment 2, oxygen consumption by portal-drained viscera (method 2) and total oxygen consumption were measured in two lactating cows. Oxygen consumption by portal-drained viscera accounted for 18% of total oxygen consumption.  相似文献   
994.
The structure function of a binary coherent system is approximated by using only a few of its minimal path sets and minimal cut sets. These two incomplete structure functions are represented as disjoint sums. The average of each is a lower and upper bound, respectively, for the system reliability. The usefulness of these bounds is demonstrated on example networks  相似文献   
995.
996.
997.
The effect of steam cooking (96 degrees C for 15 minutes) and drying at two temperatures, 70 degrees C and 110 degrees C, on nutritive value of mussel protein was studied. The measurements were carried out by nitrogen balance techniques in growing rats, and the nutritional parameters studied were: CD, BV and NPU. The crude digestibility (CD) values were: 87 +/- 1 and 82 +/- 1, and the biological values (BV), 80 +/- 1 and 74 +/- 1 for raw mussels, dried at 70 degrees C and at 110 degrees C respectively. This implies a significant decrease in the protein nutritive values of the mussel dried at a higher temperature. Cooking prior to drying significantly improved the digestibility and the biological value of the mussel's protein. In effect, improvement was so great, that the different drying temperatures did not affect the previously cooked product in a different way; therefore, the CD (94 +/- 1 and 94 +/- 1) and the BV (90 +/- 1 and 90 +/- 2) were the same for the mussel's protein, cooked and dried at 70 degrees C or at 110 degrees C.  相似文献   
998.
Lamb carcasses of > 22 kg weight were not adversely affected by spray washing, but carcasses of < 22 kg weight were affected to some extent. Characteristics of carcasses significantly affected included the appearance of the fat in the crutch region and on the back, and the degree of flaccidity and dampness of the abdominal region. These faults were alleviated somewhat during refrigerated storage and consequently the faults detected in the experiments were probably not of commercial significance since, under pilot market tests in Europe, buyers did not find any faults in spray washed carcasses.  相似文献   
999.
Alfalfa was harvested in large round bales or small square bales and storage and feeding losses were determined for different storage methods. Large bales were stored 1) in a barn; 2) outside in single rows and uncovered; 3) outside in two-high stacks and covered; and 4) outside in three-high stacks and covered. These bales were fed to dairy heifers with small square bales for comparison. Dry matter storage losses were 2% for large bales stored inside, 6% for large bales stored outside covered, and 15% for large bales stored outside uncovered. Feeding losses of large bales were 12% for stored inside, 25% for stored outside uncovered, and 13 to 15% for stored outside covered. Total losses for large round bales were 40% (stored outside uncovered), 20% (stored outside covered) and 15% (stored inside). Intake and gains were greatest for small bales (2.35 kg/100 kg body weight and .77 kg/d, respectively) and least for large bales (2.11 kg/100 kg body weight and .54 kg/d) stored outside uncovered.Rain penetrated 10 to 25 cm into uncovered bales stored outside. The resulting weathered hay, about 40% of the original bale dry weight, deteriorated. Heifers rummaged through this unpalatable material, and large feeding losses resulted. Storage and feeding losses of large round bales stored outside are economically important enough to warrant protection of bales.  相似文献   
1000.
The effects, during formation, of current density, charge capacity, and concentration and temperature of H2SO4 electrolyte on the capacity of tubular electrodes in lead/acid batteries have been studied. Electrode capacity was found to be maximum at a H2SO4 concentration of 1.05 sp. gr., a charge amount of 250% theoretical capacity, a current density of 0.44 A dm?2, and an electrolyte temperature of 40 °C. A study of the soaking process for tubular electrodes showed the electrode capacity to be maximum when the acid absorption was about 170 mg of H2SO4 per g of oxide. Finally, the discharge overpotential of tubular electrodes was analyzed by a galvanostatic transient method.  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