全文获取类型
收费全文 | 199906篇 |
免费 | 2313篇 |
国内免费 | 613篇 |
专业分类
电工技术 | 3472篇 |
综合类 | 149篇 |
化学工业 | 29026篇 |
金属工艺 | 8054篇 |
机械仪表 | 6069篇 |
建筑科学 | 4820篇 |
矿业工程 | 1303篇 |
能源动力 | 5130篇 |
轻工业 | 17124篇 |
水利工程 | 2299篇 |
石油天然气 | 4040篇 |
武器工业 | 8篇 |
无线电 | 23095篇 |
一般工业技术 | 40036篇 |
冶金工业 | 37302篇 |
原子能技术 | 5086篇 |
自动化技术 | 15819篇 |
出版年
2021年 | 1608篇 |
2019年 | 1570篇 |
2018年 | 2578篇 |
2017年 | 2649篇 |
2016年 | 2777篇 |
2015年 | 1796篇 |
2014年 | 3075篇 |
2013年 | 8949篇 |
2012年 | 5057篇 |
2011年 | 7032篇 |
2010年 | 5595篇 |
2009年 | 6359篇 |
2008年 | 6452篇 |
2007年 | 6517篇 |
2006年 | 5585篇 |
2005年 | 5231篇 |
2004年 | 5015篇 |
2003年 | 4895篇 |
2002年 | 4534篇 |
2001年 | 4660篇 |
2000年 | 4583篇 |
1999年 | 4727篇 |
1998年 | 11411篇 |
1997年 | 8134篇 |
1996年 | 6418篇 |
1995年 | 4678篇 |
1994年 | 4276篇 |
1993年 | 4081篇 |
1992年 | 3229篇 |
1991年 | 3079篇 |
1990年 | 2871篇 |
1989年 | 2952篇 |
1988年 | 2827篇 |
1987年 | 2398篇 |
1986年 | 2313篇 |
1985年 | 2717篇 |
1984年 | 2505篇 |
1983年 | 2347篇 |
1982年 | 2091篇 |
1981年 | 2206篇 |
1980年 | 2030篇 |
1979年 | 2124篇 |
1978年 | 2120篇 |
1977年 | 2368篇 |
1976年 | 3189篇 |
1975年 | 1834篇 |
1974年 | 1762篇 |
1973年 | 1774篇 |
1972年 | 1443篇 |
1971年 | 1339篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
B. Dix und R. Marutzky 《Holz als Roh- und Werkstoff》1985,43(4):148
Ohne Zusammenfassung 相似文献
952.
This newsletter provides information on past and upcoming events related to the IEEE Computer Society's Test Technology Technical Council and the test community. 相似文献
953.
John D. Fitzsimons Bill Williston Georgina Williston Lisa Brown Abdel El-Shaarawi Lenore Vandenbyllaardt Dale Honeyfeld Don Tillitt Martha Wolgamood Scott B. Brown 《Journal of Great Lakes research》2007,33(1):93-103
Alewives (Alosa pseudoharengus), the major prey fish for Lake Ontario, contain thiaminase. They are associated with development of a thiamine deficiency in salmonines which greatly increases the potential for developing an early mortality syndrome (EMS). To assess the possible effects of thiamine deficiency on salmonine reproduction we measured egg thiamine concentrations for five species of Lake Ontario salmonines. From this we estimated the proportion of families susceptible to EMS based on whether they were below the ED20, the egg thiamine concentration associated with 20% mortality due to EMS. The ED20s were 1.52, 2.63, and 2.99 nmol/g egg for Chinook salmon (Oncorhynchus tshawytscha), lake trout (Salvelinus namaycush), and coho salmon (Oncorhynchus kisutch), respectively. Based on the proportion of fish having egg thiamine concentrations falling below the ED20, the risk of developing EMS in Lake Ontario was highest for lake trout, followed by coho (O. kisutch), and Chinook salmon, with the least risk for rainbow trout (O. mykiss). For lake trout from western Lake Ontario, mean egg thiamine concentration showed significant annual variability during 1994 to 2003, when the proportion of lake trout at risk of developing EMS based on ED20 ranged between 77 and 100%. Variation in the annual mean egg thiamine concentration for western Lake Ontario lake trout was positively related (p < 0.001, r2 = 0.94) with indices of annual adult alewife biomass. While suggesting the possible involvement of density-dependent changes in alewives, the changes are small relative to egg thiamine concentrations when alewife are not part of the diet and are of insufficient magnitude to allow for natural reproduction by lake trout. 相似文献
954.
New climate change scenarios for the Netherlands. 总被引:4,自引:0,他引:4
B van den Hurk A K Tank G Lenderink A van Ulden G J van Oldenborgh C Katsman H van den Brink F Keller J Bessembinder G Burgers G Komen W Hazeleger S Drijfhout 《Water science and technology》2007,56(4):27-33
A new set of climate change scenarios for 2050 for the Netherlands was produced recently. The scenarios span a wide range of possible future climate conditions, and include climate variables that are of interest to a broad user community. The scenario values are constructed by combining output from an ensemble of recent General Climate Model (GCM) simulations, Regional Climate Model (RCM) output, meteorological observations and a touch of expert judgment. For temperature, precipitation, potential evaporation and wind four scenarios are constructed, encompassing ranges of both global mean temperature rise in 2050 and the strength of the response of the dominant atmospheric circulation in the area of interest to global warming. For this particular area, wintertime precipitation is seen to increase between 3.5 and 7% per degree global warming, but mean summertime precipitation shows opposite signs depending on the assumed response of the circulation regime. Annual maximum daily mean wind speed shows small changes compared to the observed (natural) variability of this variable. Sea level rise in the North Sea in 2100 ranges between 35 and 85 cm. Preliminary assessment of the impact of the new scenarios on water management and coastal defence policies indicate that particularly dry summer scenarios and increased intensity of extreme daily precipitation deserves additional attention in the near future. 相似文献
955.
956.
Experiment 1 was to test effect of three ratios of energy to protein in complete mixed diets for 36 lactating cows in three, 28-d periods. Energy was varied with cottonseed hulls, pelleted ground corrugated boxes, and a mixture of the two. Crude protein was varied with soybean meal to give energy:crude protein of 5.7, 5.0, and 4.6 for each energy amount. Cottonseed meal was compared with soybean meal in corrugated box diets. Feed intake was much higher with cottonseed hulls, and appreciable feedlot bloat resulted from pelleted ground corrugated box diets. Data adjusted to equal feed intake showed significant effect of energy to crude protein ratio on milk yield and improved digestion of organic matter with soybean meal vs. cottonseed meal. Experiment 2 tested the hypothesis that lactating cows consuming high-protein alfalfa may benefit from supplemental protein. Diets were 50% forage. Six diets were 14 or 18% crude protein in three ratios of alfalfa hay to corn silage (0:100, 50:50, 100:0). Additional corn silage diets were to compare: 14 versus 18% protein from distiller's dried grains with solubles only and with .5 or .9% urea (four diets); two 14% protein diets compared .6% added potassium chloride with or without .5% urea. Thirty-six Holstein cows in early lactation received one of the 12 diets in each of three 28-d periods. Distiller's grains with solubles markedly depressed milk yield (2.2 kg/d) and milk protein (.22%); heat damage of distiller's grains was evident. Protein interacted with alfalfa so gain in milk from 18 versus 14% increased from .55 to 1.36 to 2.66 kg/d as alfalfa changed from 0 to 50 to 100%. Thus, crude protein of alfalfa was not as effective as that from soybean meal in supporting milk yield. 相似文献
957.
Multilayer calculations by conventional matrix methods for dielectricum/noble metal/dielectricum systems on glass have been performed. The aim has been to maximize the integrated parameters for solar transmission, Tsol, and transmission of visible light, Teye We have found that Ag is superior for maximizing the transmittance over the narrow visible wavelength range owing to the low internal absorptance. When solar energy transmission is considered multilayers based on Au are the best choice for metal film thicknesses above 15 nm. For thinner films, Ag is still to be preferred. 相似文献
958.
959.
Bombay duck muscle β-glucuronidase purified 4200-fold had molecular weight of 160,000 as estimated by gel filtration on Sephadex G-200. The glycoprotein enzyme exhibited dimeric structure on SDS-PAGE and had a pI of 5.0. The enzyme was optimally active at pH 5.2 when phenolphthalein β-D-glucuronide was used as the substrate while with p-nitrophenyl glucuronide the pH optimum was 4.6. Saccharo-1,4-lactone was a potent competitive inhibitor of the enzyme. Heavy metalic ions such as Hg2+, Cd2+ and Ag+ also proved to be inhibitory to the enzyme. Radiation inactivation of the enzyme could be protected in the presence of mercaptoethanol. Sodium chloride activated the enzyme while sodium tripolyphosphate inhibited it. 相似文献
960.
Amjad B. Soulaka William R. Morrison 《Journal of the science of food and agriculture》1985,36(8):709-718
Starches isolated from 23 bread wheats (Triticum aestivum) and 26 durum wheats (T. durum) contained 26.3-30.6% (mean 29.1%) total amylose, 19.3–25.1% (mean 22.9%) apparent amylose and 783–1144mg 100g?1 (mean 977 mg 100g?1) lysophos-pholipids. Gelatinisation temperatures were 57.3–64.9°C (mean 61.8°C) and enthalpies 6.4–11.8 Jg?1 (mean 9.7Jg?1) in excess water, measured by differential scanning calorimetry. There were no correlations between any of these parameters. Starch granule size distributions were determined with a Coulter Counter and 100–channel analyser. A-granule mean volumes were 1235–2585μm3 (av. 1778), modal volumes 863–1804μm3 (av. 1264), mean diameters 13.9–16.0μm (av. 13.99), and specific surface areas 0.236–0.302m2g?1. B-granule mean volumes were 35.4–100.4μm3 (av. 55.9), modal volumes 16.5–54.5μm3 (av. 27.7), mean diameters 3.66–5.07μm (av. 4.09), and specific surface areas 0.684–0.920m2g?1. The B-granule contents of the starches were 12.8–34.6% (av. 27.3) by weight (sedimentation method) and 13.0–37.3% (av. 24.0) by volume (Coulter method), the latter being the more accurate method. 相似文献