全文获取类型
收费全文 | 12578篇 |
免费 | 1228篇 |
国内免费 | 234篇 |
专业分类
电工技术 | 250篇 |
综合类 | 617篇 |
化学工业 | 1832篇 |
金属工艺 | 66篇 |
机械仪表 | 112篇 |
建筑科学 | 165篇 |
矿业工程 | 50篇 |
能源动力 | 779篇 |
轻工业 | 9348篇 |
水利工程 | 28篇 |
石油天然气 | 123篇 |
武器工业 | 14篇 |
无线电 | 72篇 |
一般工业技术 | 176篇 |
冶金工业 | 61篇 |
原子能技术 | 12篇 |
自动化技术 | 335篇 |
出版年
2024年 | 100篇 |
2023年 | 229篇 |
2022年 | 498篇 |
2021年 | 518篇 |
2020年 | 615篇 |
2019年 | 580篇 |
2018年 | 476篇 |
2017年 | 478篇 |
2016年 | 485篇 |
2015年 | 544篇 |
2014年 | 620篇 |
2013年 | 737篇 |
2012年 | 1029篇 |
2011年 | 956篇 |
2010年 | 564篇 |
2009年 | 550篇 |
2008年 | 497篇 |
2007年 | 752篇 |
2006年 | 727篇 |
2005年 | 567篇 |
2004年 | 447篇 |
2003年 | 370篇 |
2002年 | 331篇 |
2001年 | 198篇 |
2000年 | 172篇 |
1999年 | 164篇 |
1998年 | 123篇 |
1997年 | 127篇 |
1996年 | 73篇 |
1995年 | 57篇 |
1994年 | 63篇 |
1993年 | 67篇 |
1992年 | 75篇 |
1991年 | 31篇 |
1990年 | 32篇 |
1989年 | 25篇 |
1988年 | 22篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 14篇 |
1974年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Sachiyuki Hasegawa Kazuyuki Shimizu Takeshi Kobayashi Masakazu Matsubara 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(1):33-42
Repeated batch operation using two fermentors (RBTF) to penicillin fermentation was demonstrated by computer simulation to improve productivity. Three operation modes were compared: chemostat, repeated batch operation using a single fermentor (RBSF) and RBTF; in each case account was made of the lag period before growth. The simulated fermentor performances were assessed on the basis of the penicillin productivity and concentration; the simulation was based on published batch fermentation data. It was shown that RBTF was superior to RBSF and chemostat. The advantage of RBTF increased as the lag period became greater. 相似文献
22.
温度是影响黄原胶发酵的重要因素之一。为了优化黄原胶发酵过程的温度控制,在5 L通气式搅拌发酵罐中,非溶氧限制的条件下,对恒温黄原胶发酵过程进行了研究。结果显示,发酵温度为28℃时,在发酵稳定期有较高的菌体浓度,所得黄原胶的丙酮酸含量与表观粘度较高,但有较长的发酵周期。而发酵温度为33℃时,有较短的发酵周期,在发酵稳定期有较高的比产胶速率,但所得黄原胶的丙酮酸含量与表观粘度较低。实验测定了控制黄原胶发酵生长期温度为28℃,稳定期温度为33℃的发酵过程数据。结果表明,与恒温发酵过程相比,通过温度的分段控制可以缩短发酵周期,提高产胶浓度及改善胶的品质,分段控温是黄原胶发酵的一种方便有效的调节手段。 相似文献
23.
24.
The steady-state performance of a two-stage recycle fermenter with two different types (I and II) of configurations for staging was investigated numerically for the continuous production of lactic acid. In Type I the bleed broth withdrawn from the first stage is supplied to the second fermenter, and in Type II both filtrate and bleed broth from the first stage are introduced to the second stage. Using four different kinetic models taken from the literature, the effects of operating parameters on the overall lactic acid productivities and the overall substrate conversions are examined. At moderate conversions, productivities for Type I operation are found to be higher than those for Type II and for the single-stage system. In the case of high conversions close to complete consumption, Type II operation is more efficient than the Type I and single-stage systems. For 99% conversion and 40 kg m-3 substrate feed concentration, productivities for Type II are predicted to be 14-74% higher compared to those for the single-stage system at the same bleed ratios. 相似文献
25.
高温季节食醋生产中影响酒精发酵的因素及改进措施 总被引:2,自引:0,他引:2
该文以镇江香醋生产为例,分析了高温季节食醋生产过程中影响酒精发酵的因素,并提出了改进措施。 相似文献
26.
Fernanda R C Damasceno Denise M G Freire Magali C Cammarota 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):730-738
BACKGROUND: The application of lipase‐rich enzyme pools (such as the crude solid enzymatic preparation (SEP) obtained from Penicillium restrictum solid‐state fermentation of agro‐industrial wastes) to activated sludge systems may be an effective strategy for preventing various operational problems. The continuous addition of SEP to the treatment system can become cost‐prohibitive when in situ production and/or storage are factored in. The application of SEP to high‐fat wastewater treatment would only be justified as an emergency measure, such as a sudden increase in the fat content of the bioreactor influent. Therefore, the primary objective of this work was to investigate the efficiency of a crude SEP during fat shock loads, simulated through the periodic addition of dairy industry waste containing high fat concentrations to the feed stock of an activated sludge system, operated in continuous mode. RESULTS: The test bioreactor exhibited a higher average chemical oxygen demand (COD) removal efficiency than the control bioreactor (83% for control and 90% for test) and the fat accumulation in the biological flocs of the test bioreactor was 3.2 times lower than that in the control bioreactor. Turbidity was also lower in the effluent of the test bioreactor (123 and 66 FTU in control and test, respectively) and it had a shorter recovery time between shock loads, especially when the interval between loads was shorter than one month (biweekly and weekly shock loads). CONCLUSION: The addition of SEP during fat overloads in the reactor feed maintained efficient COD removal in the test bioreactor for 270 days without any operational problems. Copyright © 2008 Society of Chemical Industry 相似文献
27.
28.
城市生活垃圾能源利用探讨 总被引:7,自引:0,他引:7
报道了城市有机废弃物转化为能源的几种途径。在管式反应器内甘蔗渣裂解气化制煤气以及在高压釜内湿式裂解气化制煤气液体产品,可得到中值煤气。也研究了甘蔗渣二步法糖化和糖发酵,当PH为3.6,酵母浓度为1.33%,乙醇产率可达理论值的64.86%。 相似文献
29.
Second-law-based thermodynamic analysis of two-stage and mechanical-subcooling refrigeration cycles 总被引:1,自引:0,他引:1
Thermodynamic analysis of HFC-134a vapor-compression refrigeration cycles is investigated by both the first and second laws of thermodynamics. Second-law analysis is carried out for both two-stage and mechanical-subcooling refrigeration cycles. The analysis is performed on each of the system components to determine their individual contribution to the overall system irreversible losses. It is found that most of the losses are due to a low compressor efficiency. Irreversibilities of expansion valves and condenser are also significant. In addition, it is shown that the optimum inter-stage pressure for two-stage and mechanical-subcooling refrigeration systems is very close to the saturation pressure corresponding to the arithmetic mean of the refrigerant condensation and evaporation temperatures. These results are compared with the existing practice in the industry. Furthermore, theoretical results of a two-stage refrigeration system performance are also compared with experimental values for a CFC-22 system. 相似文献
30.
对KCl与NaCl在低盐固态酱油发酵中的应用进行了比较研究。结果表明:用KCl代替NaCl,KCl的浓度要高于NaCl才能抑制发酵期间杂茵的污染,且使用KCl的发酵效果比NaCl要好。 相似文献