全文获取类型
收费全文 | 129049篇 |
免费 | 10200篇 |
国内免费 | 4943篇 |
专业分类
电工技术 | 3599篇 |
技术理论 | 2篇 |
综合类 | 8077篇 |
化学工业 | 39956篇 |
金属工艺 | 5553篇 |
机械仪表 | 3520篇 |
建筑科学 | 4729篇 |
矿业工程 | 4378篇 |
能源动力 | 7200篇 |
轻工业 | 26235篇 |
水利工程 | 1641篇 |
石油天然气 | 9690篇 |
武器工业 | 708篇 |
无线电 | 5075篇 |
一般工业技术 | 8931篇 |
冶金工业 | 7487篇 |
原子能技术 | 1694篇 |
自动化技术 | 5717篇 |
出版年
2024年 | 508篇 |
2023年 | 1730篇 |
2022年 | 3563篇 |
2021年 | 4268篇 |
2020年 | 4359篇 |
2019年 | 3790篇 |
2018年 | 3414篇 |
2017年 | 4307篇 |
2016年 | 4468篇 |
2015年 | 4436篇 |
2014年 | 7365篇 |
2013年 | 8271篇 |
2012年 | 9377篇 |
2011年 | 9577篇 |
2010年 | 7133篇 |
2009年 | 6996篇 |
2008年 | 6108篇 |
2007年 | 7800篇 |
2006年 | 7146篇 |
2005年 | 6124篇 |
2004年 | 5267篇 |
2003年 | 4643篇 |
2002年 | 4064篇 |
2001年 | 3432篇 |
2000年 | 3010篇 |
1999年 | 2522篇 |
1998年 | 2019篇 |
1997年 | 1564篇 |
1996年 | 1393篇 |
1995年 | 1140篇 |
1994年 | 944篇 |
1993年 | 711篇 |
1992年 | 604篇 |
1991年 | 459篇 |
1990年 | 368篇 |
1989年 | 260篇 |
1988年 | 176篇 |
1987年 | 158篇 |
1986年 | 124篇 |
1985年 | 133篇 |
1984年 | 111篇 |
1983年 | 71篇 |
1982年 | 45篇 |
1981年 | 45篇 |
1980年 | 58篇 |
1979年 | 21篇 |
1978年 | 18篇 |
1977年 | 16篇 |
1975年 | 14篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
KeShun Liu Frank Orthoefer Edward A. Brown 《Journal of the American Oil Chemists' Society》1995,72(2):189-192
Ten soybean genotypes grown in 1992 with seed size ranging from 7.6 to 30.3 g/100 seeds and maturity group V or VI were selected
and tested for oil and protein content and for fatty acid composition. In these germplasm, protein varied from 39.5 to 50.2%,
oil, 16.3 to 21.6%, and protein plus oil, 59.7 to 67.5%. Percentages of individual fatty acids relative to total fatty acids
varied as follows: palmitic, 11.0 to 12.8; stearic, 3.2 to 4.7; oleic, 17.6 to 24.2; linoleic, 51.1 to 56.3 and linolenic,
6.9 to 10.0. Seed size showed no significant correlations with individual saturated fatty acids, protein or oil content. However,
significant correlations were found between seed size and individual unsaturated fatty acids: positive with oleic, and negative
with linoleic and linolenic. Oil and protein content were negatively correlated with each other. Among the major fatty acids,
only the unsaturated were significantly correlated with each other: negative between oleic and linoleic or linolenic, and
positive between linoleic and linolenic. A subsequent study with soybeans grown in 1993 generally confirmed these findings.
Variation in relative percentages of unsaturated fatty acids andr values for most pairs of relationships were even higher than those obtained from the 1992 crop.
Presented at the 85th AOCS Annual Meeting and Expo, Atlanta, Georgia, May 8–12, 1994. 相似文献
962.
Soil incubation studies were undertaken in controlled environment cabinets at 15°C to investigate the effect of increasing application rates of calcium ammonium nitrate (CAN) on net nitrification in two grassland soils. Granular CAN was applied to the surface of freshly collected, moist soil, at a rate equivalent to 0, 100, 200, 400, 800 and 1600µg NH
4
+
-N and NO
3
-
-N per gram of oven dry soil. In half the treatments finely ground CaCO3 was incorporated into the moist soil to raise the starting pH. Changes in soil mineral N and pH were measured at weekly intervals up to six-weeks. The most probable number (MPN) technique was used to enumerate the NH
4
+
-N and NO
2
-
-N oxidizers at the beginning and end of the incubation.At low rates of CAN application there was considerable NH
4
+
-N oxidation to NO
3
-
-N during the incubation of both soils. Lime stimulated this N transformation. At high application rates (i.e. 800 and 1600 ppm) there was little change in NH
4
+
-N or NO
3
-
-N on either soil during the 6 week incubation, in the presence or absence of lime. The rate of NO
3
-
-N produced peaked at 5.6 and 3.8 mg NO
3
-
-N kg–1 d–1 on soil 1 and 2 respectively, in the presence of lime. Above a level of 400 ppm CAN (equivalent to 38 kg N ha–1) the rate of NO
3
-
-N produced decreased. The higher rate of net nitrification in soil 1 compared with soil 2 was probably due to a higher number of nitrifying bacteria. Although high rates of CAN decreased the nitrifying activity of both soils there was little difference between treatments in the actual numbers of NH
4
+
-N and NO
2
-
-N oxidizers determined by the MPN technique.The results showed that the rate of granular CAN applied to the soil surface can influence the local activity of nitrifying bacteria and subsequent N transformations. At application rates of CAN generally used agriculturally for grass production, it is likely that net nitrification of the NH
4
+
-N in the fertilizer granule will be inhibited. 相似文献
963.
摘要:为解决常规聚合物无法满足超高温深井酸化压裂的技术要求,本文分别以丙烯酰胺(AM) 甲基丙烯酰氧乙基三甲基氯化铵(DMC)、AM DMC SMA(十八烷基甲基丙烯酸酯)为原料,通过自由基聚合制备出两种耐酸聚合物SY-1和SY-2,并对其结构进行表征及性能测试。结果表明:SY-2红外谱图中720 cm-1为—(CH2)n—的弯曲振动吸收峰,单体成功接枝到聚丙烯酰胺分子链上;热重分析表明,SY-1升温至600℃失重比为98%,SY-2失重比86%,热稳定性得到改善;质量分数为20%盐酸中,SY-2质量分数0.8%:180℃,170s-1流变性能测试,SY-2剪切终点黏度56mPa?s,90℃、120℃、150℃剪切1h,黏度为83.6mPa?s、43.5mPa?s、27.8mPa?s,剪切稳定性分别为85.66%、74.45%、52.01%; 180℃、3MPa条件下,静态酸岩反应速率为8.94?10-5(g/cm2?s),较常规SY-1反应速率1.69?10-4(g/cm2?s)减小一个量级。且与缓蚀剂、铁离子稳定剂配伍性良好,克服高温酸化压裂技术的应用瓶颈。 相似文献
964.
David W. L. Ma Catherine J. Field M. T. Clandinin 《Journal of the American Oil Chemists' Society》2002,79(8):755-758
CLA refers to a group of geometrical and positional isomers of linoleic acid. CLA has been shown to have potentially beneficial
effects on cancer, atherosclerosis, and body metabolism in animals. Mixtures containing equal amounts of these isomers are
commonly used in many research studies because of their greater availability and lower cost relative to pure isomers. This
has hindered progress in elucidating the biological properties of specific isomers and their relevance in animal and human
biology. A method was developed that offers a compromise between cost and utility to make available enriched mixtures of either
the Δ9c,11t- or Δ10t,12c-18:2 isomers for use in a wide range of experimental applications. A countercurrent approach was developed to separate the
Δ9c,11t- and Δ10t,12c-18:2 isomers from an equal mixture of these two isomers by urea complexation. After three successive rounds of complexation
using an equal amount of CLA and urea, a fraction enriched in Δ9c,11t-18:2 containing 42.5 and 17.4% of Δ9c,11t-and Δ10t,12c-18:2, respectively, was recovered. After a single round of complexation using 2.5 g urea/g CLA, a fraction enriched in Δ10t,12c-18:2 was recovered containing 29.7 and 69.1% of Δ9c,11t- and Δ10t,12c-18:2, respectively. 相似文献
965.
系统地研究了用空气——乙炔火焰原子吸收光谱分析法测定高纯石英粉中钙的最佳条件,建立了14%的乙醇作为增感剂,在2%盐酸介质中,0.4% LaCl3溶液作为释放剂,用塞曼火焰原子吸收法测定的可行性方案,探讨了共存元素对钙的干扰及其消除。方法操作简便快速,干扰少,方法相对标准偏差小于3%,适用于日常分析石英粉中的杂质。 相似文献
966.
铬盐清洁生产中铬渣的综合利用 总被引:6,自引:0,他引:6
利用二氧化碳与液相氧化铬盐清洁生产工艺所产生的铬渣反应 ,得到碳酸氢镁溶液和富铁渣。碳酸氢镁溶液经加热分解得到轻质碳酸镁产品 ,富铁渣可以作为水泥行业原料铁精矿的替代品 ,最终实现了铬铁矿资源的充分利用和铬盐生产的零排放。 相似文献
967.
Electrodiffusion diagnostics of the flow and mass transfer inside a network of crossing minichannels
F. Huchet J. Comiti J. Tihon A. Montillet P. Legentilhomme 《Journal of Applied Electrochemistry》2007,37(1):49-55
The global mass transfer and the local flow structure inside a set of crossing minichannels were characterized using the electrodiffusion
method. The individual square-cross channel sections (a = 1.5 mm in sides) intersect at right-angles in order to form the flow cell. An array of 39 circular platinum electrodes
(0.25 mm in diameter) was flush-mounted into the wall of the flow cell to investigate the wall shear rate at different locations.
This array of small sensors allowed characterization of longitudinal and lateral variations in wall shear rate across the
flow cell, flow distribution at the inlet and outlet sections, transition between laminar and turbulent flow regimes, and
flow behaviour at the channel crossings. The results of global wall mass transfer measurements demonstrated that, from a mass
transfer point of view, the flow cell exhibits similar behaviour to a porous medium. 相似文献
968.
F. Bianchi S. Cantagallo G. Consolati M. Laporta M. Pegoraro G. Tieghi L. Zanderighi 《应用聚合物科学杂志》2002,86(3):559-571
Four production steps, extrusion, blowing, stabilization, and finishing, are involved in the manufacture of biorented nylon 6 films. The films obtained after each step were studied by wide‐angle diffraction X‐rays, IR analysis, and density measurements. Orientation in the amorphous phase was evaluated by thermal retraction. Free volume was investigated by positron annihilation spectroscopy. Mechanical properties were tested by tensile tests, and permeability was tested with isopiestic permeameters. Quenching, after extrusion, generated an unstable γ crystalline phase and an amorphous phase. Blowing transformed the unstable γ phase into the thermodynamically stable α phase and increased the chain orientation; stabilization increased α phase crystals, favored hydrogen bond formation and, therefore, the mechanical properties, leaving unchanged the chain orientation; the final treatment increased the mechanical properties. The film permeabilities to O2, N2, and CO2 were practically unchanged after each production step; this result may be explained by considering that the nanoholes, present in the films and responsible for the diffusion inside the polymer, maintained practically constant their radius, whereas their number concentration decreased slowly after thermomechanical treatments. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 559–571, 2002 相似文献
969.
970.