全文获取类型
收费全文 | 11372篇 |
免费 | 1054篇 |
国内免费 | 280篇 |
专业分类
电工技术 | 353篇 |
技术理论 | 1篇 |
综合类 | 766篇 |
化学工业 | 1810篇 |
金属工艺 | 249篇 |
机械仪表 | 245篇 |
建筑科学 | 1050篇 |
矿业工程 | 186篇 |
能源动力 | 190篇 |
轻工业 | 5661篇 |
水利工程 | 139篇 |
石油天然气 | 356篇 |
武器工业 | 23篇 |
无线电 | 412篇 |
一般工业技术 | 525篇 |
冶金工业 | 209篇 |
原子能技术 | 38篇 |
自动化技术 | 493篇 |
出版年
2024年 | 94篇 |
2023年 | 187篇 |
2022年 | 448篇 |
2021年 | 472篇 |
2020年 | 549篇 |
2019年 | 424篇 |
2018年 | 385篇 |
2017年 | 422篇 |
2016年 | 454篇 |
2015年 | 527篇 |
2014年 | 634篇 |
2013年 | 649篇 |
2012年 | 866篇 |
2011年 | 787篇 |
2010年 | 569篇 |
2009年 | 537篇 |
2008年 | 407篇 |
2007年 | 645篇 |
2006年 | 579篇 |
2005年 | 518篇 |
2004年 | 430篇 |
2003年 | 438篇 |
2002年 | 327篇 |
2001年 | 252篇 |
2000年 | 261篇 |
1999年 | 163篇 |
1998年 | 126篇 |
1997年 | 100篇 |
1996年 | 82篇 |
1995年 | 66篇 |
1994年 | 51篇 |
1993年 | 52篇 |
1992年 | 51篇 |
1991年 | 24篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 23篇 |
1987年 | 16篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
直播稻田化学除草试验 总被引:1,自引:0,他引:1
直播稻田用不同药剂在播种后各一次化除或播种后两次化除都具有很好的除草效果。播后前期是化学除草的关键时期播后前期每667米^2用10%苄嘧黄隆15克+60%丁划胺60毫升,10%苄嘧黄隆15克+50%杀草丹150毫升,17.2%新幼禾葆240克或15.8%幼禾葆200克防铲均较好。 相似文献
92.
P.?N.?Mayamol T.?Samuel C.?Balachandran A.?Sundaresan C.?ArumughanEmail author 《Journal of the American Oil Chemists' Society》2004,81(4):407-413
Several pilot-scale trials reported in this paper, using palm stearin-rice bran oil (PS-RBO) blends, obviously did not contain
trans FA (TFA), whereas the commercial products were found to contain 18–27% TFA. The effects of processing conditions such as
rate of agitation, crystallization temperature, and composition of the blends on the crystal structure of shortenings were
studied. The products were evaluated for their physicochemical characteristics using DSC, X-ray diffraction (XRD), HPLC, and
FTIR techniques. The formulation containing 50% PS and 50% RBO showed melting and cooling characteristics similar to those
of hydrogenated commercial “vanaspati” samples. Analysis of the FA composition revealed that the formulated shortenings contained
15–19% C18∶2 PUFA. Tocopherol and tocotrienol contents of the experimental shortenings were in the range of 850–1000 ppm with oryzanol
content up to 0.6%. XRD studies demonstrated that the crystal form in the shortenings was predominantly the most stable β′
form, and there was less of the undesirable β form. 相似文献
93.
Germplasm with shorter duration than that of the currently grown varieties is being generated to maximize productivity of irrigated rice. However, short-duration varieties often produce yields lower than the medium- and long-duration varieties. Experiments were conducted during the 1980–82 dry and wet seasons to increase productivity through the use of very early-maturing rices and the improved management of nitrogen (N) fertilizers.Results over three years showed that IR58 and IR9729-67-3 (growth duration 100 ± 5 days) yield as well as or higher than IR36 although earlier maturing. They generally had a higher productivity (kg ha–1 day–1) than IR36 (110 ± 5 days).Three years' data suggest that the improved timing of broadcast applications of urea in split doses increased grain yield comparable with the basal incorporation of slow-release sulfur-coated urea (SCU) or deep point-placement of urea supergranules (USG).Results on elite breeding lines showed that the early-maturing IR9729-67-3 produced higher protein yield ha–1 than longer duration varieties such as IR8 and IR42 in the dry season. Furthermore, contrary to earlier results, single basal incorporation of slow-release SCU increased the protein yield of rice by 53 kg ha–1 and deep point-placement of USG by 43 kg ha–1 over split application of prilled urea. 相似文献
94.
Why Phenolic Acids Are Unlikely Primary Allelochemicals in Rice 总被引:21,自引:0,他引:21
Olofsdotter M Rebulanan M Madrid A Dali W Navarez D Olk DC 《Journal of chemical ecology》2002,28(1):229-242
Allelopathy in rice (Oryza sativa, L.) effective against weeds has been found in about 3.5% of tested rice germplasm in both laboratory and field experimentation. However, the allelochemicals responsible for growth inhibition of rice-associated weeds have not yet been identified. In the literature, phenolic acids are often mentioned as putative allelochemicals. If phenolic acids commonly reach growth inhibitory concentrations in rice ecosystems, it must be expected that the degree of tolerance to phenolic acids will vary among traditional rice cultivars or plant species adapted to rice environments having inherently different phenolic acid concentrations. Phenolic acids concentrations are normally greater in submerged than in aerobic soils. A dose–response study, however, showed that seedlings of rice cultivars adapted to submerged anaerobic soils did not have higher level of tolerance against p-hydroxybenzoic acid than did seedlings of varieties adapted to aerobic upland soils. Moreover, traditional rice cultivars had no greater tolerance than did improved cultivars that were recently bred for traits other than tolerance of phenolic acids. Similarly, there were no differences in tolerance of p-hydroxybenzoic acid between two Echinochloa weed species adapted to either anaerobic or aerobic growth conditions. Thus, neither the rice cultivars nor weed species had evolved different tolerance levels against the phenolic acid. However, all rice cultivars had significantly greater tolerance of p-hydroxybenzoic acid than did either weed species. In a second experiment, the rates at which rice plants released phenolic acids into solution cultures were measured for at least one month, the time period of greatest allelopathic activity following planting under field conditions. The maximum release rate of phenolic acids during the first month of growth was approximately 10 g/plant/day. At a conventional plant density, the release rate of phenolic acids would be approximately 1 mg/m2day. This order of release rate cannot provide concentrations remotely close to phytotoxic levels determined for these rice cultivars and weed species. The results presented in this paper do not preclude the possibility that phenolic acids might be one component in a mixture of chemicals that, when present simultaneously, are allelopathic. 相似文献
95.
R. Venkitaswamy S. Subramanian V. Veerabadran 《Nutrient Cycling in Agroecosystems》1991,28(3):315-321
The growth of weeds and their subsequent reduction of rice yield as affected by N source neem cake coated urea (NCU), dicyandiamide coated urea (DCU), rock phosphate coated urea (RPCU), urea supergranules (USG) and prilled urea (PU) was studied on a clay loam soil at Coimbatore, India. Experiments were conducted in northeast monsoon (NEM) 1981, summer 1982, and southwest monsoon (SWM) 1982 seasons.The crop was associated with eleven weed species, and the dominant weeds wereEchinochloa crus-galli, Cyperus difformis andMarsilea quadrifolia. The weed flora varied between seasons. Deep placement of USG reduced the dry weight of weeds in NEM and summer seasons at 60, 90 and 120 Kg N ha–1 whereas it increased the dry weight at 60 and 90 but not 120 Kg N ha–1 in SWM season. The dry weight of weeds decreased with increased N rates for all N sources during NEM and summer seasons. In SWM season, dry weight of weeds increased with increased N rates for all N sources except USG. The grain yield of rice was drastically reduced with the deep placement of USG at 60 but not 120 Kg N ha–1 in SWM season. The differential effect of the N sources between seasons was due to the change of the weed flora. Dominance ofE. crus-galli during SWM season had greater influence on weed dry weight and grain yield of rice.Nitrogen uptake by weeds was frequently greater in unfertilized plots, particularly in NEM and summer seasons. In SWM season, the apparent fertilizer N recovery by weeds was high for USG. It decreased from 53% for 60 Kg USG-N ha–1 to 4% for 120 Kg USG-N ha–1.Contribution from the part of Ph.D. work of the first author at Department of Agronomy, Tamil Nadu Agricultural University, Coimbatore-641 003, Tamil Nadu, India. 相似文献
96.
97.
移动智能终端操作系统技术的逐步成熟,致使应用服务快速从互联网产业向移动互联网领域进行迁移.文章首先介绍了全球移动互联网应用生态的发展概况,总结了移动互联网应用产业要素的变化,最后对移动互联网应用产业发展现状及趋势进行了分析. 相似文献
98.
A. Proctor C. Adhikari G. D. Blyholder 《Journal of the American Oil Chemists' Society》1995,72(3):331-335
Fourier transform infrared spectroscopy was used to investigate the adsorption of oleic acid (OA) onto dry rice hull ash (RHA)
silica. Adsorption partially occurred by surface hydrogen bonding of the carboxylic acid. There was also formation of carboxylate
ions by reaction of OA with residual potassium oxide. These ions were strongly bound by the ash. Isopropanol inhibited OA
adsorption by H-bonding and encouraged desorption of H-bonded OA, but without itself being significantly bound. RHA with 40%
moisture also adsorbed a small amount of OA by H-bonding and reacted with OA to form and adsorb carboxylate ions. 相似文献
99.
本文介绍了用一种再结晶技术制造高炖、超细Al_2O_3粉体的新方法。 将硫酸铝铵溶液(AA)滴入碳酸氢铵溶液(AHC),经过反应合成一种新的含铝化合物,碳酸氢铝铵(AACH),然后在高温下煅烧,生成超细Al_2O_3粉体。另外还采用了X射线,红外光谱,DTA,以及TEM等手段,研究了反应温度、浓度、PH值和老化条件等对生成物AACH和Al_2O_3的影响。 相似文献
100.