全文获取类型
收费全文 | 2711篇 |
免费 | 116篇 |
国内免费 | 65篇 |
专业分类
电工技术 | 35篇 |
综合类 | 108篇 |
化学工业 | 1881篇 |
金属工艺 | 45篇 |
机械仪表 | 31篇 |
建筑科学 | 17篇 |
矿业工程 | 13篇 |
能源动力 | 40篇 |
轻工业 | 375篇 |
水利工程 | 1篇 |
石油天然气 | 155篇 |
武器工业 | 4篇 |
无线电 | 23篇 |
一般工业技术 | 124篇 |
冶金工业 | 6篇 |
原子能技术 | 3篇 |
自动化技术 | 31篇 |
出版年
2024年 | 6篇 |
2023年 | 33篇 |
2022年 | 29篇 |
2021年 | 48篇 |
2020年 | 57篇 |
2019年 | 43篇 |
2018年 | 37篇 |
2017年 | 47篇 |
2016年 | 48篇 |
2015年 | 65篇 |
2014年 | 145篇 |
2013年 | 170篇 |
2012年 | 188篇 |
2011年 | 163篇 |
2010年 | 141篇 |
2009年 | 135篇 |
2008年 | 128篇 |
2007年 | 169篇 |
2006年 | 161篇 |
2005年 | 122篇 |
2004年 | 123篇 |
2003年 | 127篇 |
2002年 | 101篇 |
2001年 | 81篇 |
2000年 | 71篇 |
1999年 | 72篇 |
1998年 | 56篇 |
1997年 | 39篇 |
1996年 | 40篇 |
1995年 | 44篇 |
1994年 | 39篇 |
1993年 | 16篇 |
1992年 | 23篇 |
1991年 | 11篇 |
1990年 | 22篇 |
1989年 | 14篇 |
1988年 | 17篇 |
1987年 | 28篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
排序方式: 共有2892条查询结果,搜索用时 15 毫秒
101.
102.
针对尿素振动筛振动大,严重影响设备及基础结构的安全使用等问题,分析其原因,并制定相应的改造措施。改造后,产品质量大幅度提升,振动大大降低,保证了设备及基础结构的安全、稳定、长周期运行。 相似文献
103.
104.
105.
106.
Large variation exists in the potassium content of dairy cow feeds and also within a feed type due to soil type and fertilization. Increased ration K concentration causes a subsequent increase in urinary volume and could be expected to also lower milk urea concentration. Six multiparous mid-lactation Swedish Red dairy cows, all fitted with rumen cannulas, were subjected to 3 different levels of K intake in a Latin square experiment with three 2-wk periods to evaluate the effects on concentrations of milk urea and rumen ammonia, urinary output, and drinking water intake. The treatments were achieved by K supplementation on top of a low-K basal ration fed at individual allowances fixed throughout the experiment. The basal ration, consumed at 20.2 kg of dry matter (DM)/d, provided 165 g of crude protein/kg of DM and consisted of grass silage, concentrates, and urea in the proportions 39.3:60.0:0.7 on a DM basis. Potassium bicarbonate supplementation was 0, 616, and 1,142 g/d, respectively, to give total ration K concentrations that were low (LO; 12 g/kg of DM), medium (MED; 23 g/kg of DM), or high (HI; 32 g/kg of DM). Production and composition of milk was not affected by treatment. A linear effect on milk urea concentration was detected, being 4.48, 4.18, and 3.77 mM for LO, MED, and HI, respectively, and a linear tendency for rumen ammonia concentration with 6.65, 6.51, and 5.84 mg of NH3-N/dL for LO, MED, and HI, respectively. Milk urea concentration peaked about 3 h after the rumen ammonia peak from the morning feeding, at a level 1.3 mM over the baseline. Urinary urea excretion declined linearly (105, 103, and 98 g of urea-N/d for LO, MED, and HI, respectively). Linear increases occurred in urinary output (0.058 ± 0.001 kg of urine/g of K intake; no intercept; coefficient of determination = 0.997) and drinking water intake (65.9 ± 2.02 + 0.069 ± 0.004 kg of water/g of K intake; coefficient of determination = 0.95). Urinary K concentration leveled off at 12.4 g/L. Urinary creatinine excretion was not affected by K addition, but allantoin excretion increased linearly by 27% from LO to HI, suggesting increased rumen microbial growth. Rumen pH, acetate proportion of total volatile fatty acids, and digestibility of DM, organic matter, and neutral detergent fiber increased linearly with increasing potassium intake. We concluded that increased ration K concentration lowers milk urea concentration with a magnitude significant for the interpretation of milk urea values, but other sources of variation, such as sampling time relative to feeding, may be even more important. 相似文献
107.
简述了剩余焦炉煤气综合利用的途径,分析了在不同结焦时间下的合成气量分配情况,针对由于结焦时间较长低负荷工况下出现合成气量不足的情况提出了解决措施,根据提出的解决措施制定了设想工艺方案,采用UGI炉气化技术工艺造气来解决合成气不足的问题较为现实,整体工艺方案的预计投资约1000万元。 相似文献
108.
Nitrogen‐based compounds can potentially be used as alternative non‐carbon or low‐carbon fuels. Nevertheless, the corrosion of construction materials at high temperatures and pressures in the presence of such fuel has not been reported yet. This work is focused on the corrosion of AISI Al 6061, 1005 carbon steel (CS), 304, 316L, 310 austenitic stainless steels (SS) and 680 nickel alloy in highly concentrated water solution of ammonium nitrate and urea (ANU). The corrosion at 50 °C and ambient pressure and at 350 °C and 20 bar was investigated to simulate storage and working conditions. Sodium chloride was added to the fuel (0–5 wt%) to simulate industrial fertilizers and accelerated corrosion environment. Heavy corrosion of CS was observed in ANU solution at 50 °C, while Al 6061, 304 and 316L SS showed high resistance both to uniform and pitting corrosion in ANU containing 1% of sodium chloride. Addition of 5% sodium chloride caused pitting of Al 6061 but had no influence on the corrosion of SS. Tests in ANU at 350 °C and 20 bar showed pitting on SS 304 and 316L and 680 nickel alloy. The highest corrosion resistance was found for SS 310 due to formation of stable oxide film on its surface. 相似文献
109.
在现有DCS控制系统的基础上,进行了初步增容改造的设想,对CO2压缩机和合成系统增加了部分新的控制手段和方法。 相似文献
110.
首次尝试以二苯甲烷二胺(MDA)、尿素和甲醇为原料直接合成二苯甲烷二氨基甲酸甲酯(MDC),分别考察了催化剂种类和反应条件对MDC合成反应的影响。结果表明:经400℃焙烧2h的γ-Al2O3对该反应具有较高的催化活性。适宜反应条件为:反应温度180℃,反应时间6h,反应初压1.2 MPa,n(MDA)∶n(尿素)∶n(甲醇)∶n(γ-Al2O3)=1∶3∶50∶0.1。在此条件下,MDA的转化率为81.7%,MDC的收率和选择性分别为26.3%和32.2%。采用液相色谱-质谱联用技术对MDC合成反应的反应路径进行了分析,认为促进中间产物4-氨基-4′-氨基甲酸甲酯二苯甲烷(MMC)向MDC转化是提高MDC选择性的关键。 相似文献