全文获取类型
收费全文 | 3480篇 |
免费 | 606篇 |
国内免费 | 110篇 |
专业分类
电工技术 | 187篇 |
技术理论 | 1篇 |
综合类 | 191篇 |
化学工业 | 1528篇 |
金属工艺 | 30篇 |
机械仪表 | 40篇 |
建筑科学 | 144篇 |
矿业工程 | 43篇 |
能源动力 | 1209篇 |
轻工业 | 381篇 |
水利工程 | 62篇 |
石油天然气 | 63篇 |
武器工业 | 1篇 |
无线电 | 43篇 |
一般工业技术 | 156篇 |
冶金工业 | 42篇 |
原子能技术 | 5篇 |
自动化技术 | 70篇 |
出版年
2024年 | 16篇 |
2023年 | 87篇 |
2022年 | 211篇 |
2021年 | 175篇 |
2020年 | 206篇 |
2019年 | 187篇 |
2018年 | 173篇 |
2017年 | 123篇 |
2016年 | 193篇 |
2015年 | 203篇 |
2014年 | 222篇 |
2013年 | 223篇 |
2012年 | 246篇 |
2011年 | 327篇 |
2010年 | 190篇 |
2009年 | 218篇 |
2008年 | 158篇 |
2007年 | 223篇 |
2006年 | 230篇 |
2005年 | 122篇 |
2004年 | 89篇 |
2003年 | 70篇 |
2002年 | 49篇 |
2001年 | 29篇 |
2000年 | 27篇 |
1999年 | 29篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 26篇 |
1995年 | 14篇 |
1994年 | 14篇 |
1993年 | 16篇 |
1992年 | 13篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1951年 | 8篇 |
排序方式: 共有4196条查询结果,搜索用时 15 毫秒
91.
92.
93.
【目的】为有效保护连香树资源、人工促进连香树群落天然更新和种群形成,探索林窗面积变化对幼苗生长及生物量分配的规律。【方法】以连香树幼苗为材料,通过设置2种林窗面积和林下环境,研究林窗面积对连香树幼苗生长及生物量分配的影响。【结果】不同处理连香树幼苗地径和高呈现极显著差异。小林窗下连香树幼苗高生长和地径生长最大,分别是大林窗和林下处理的108.15%、284.86%和109.13%、197.12%。连香树幼苗在不同处理下叶片形态性状、总生物量以及各营养器官生物量均达到显著水平(P<0.05),其总生物量大小依次为小林窗>大林窗>林下,小林窗单株总生物量分别比大林窗和林下增加134.14%和860.35%。【结论】连香树在幼苗期适宜在光照强度相对较弱的环境下生长,小林窗环境下连香树幼苗生长迅速,生物量分配均衡,苗木竞争力强,有利于幼苗天然更新。 相似文献
94.
95.
96.
Supercritical water gasification driven by solar energy is a promising way for clean utilization of biomass with high moisture content, but direct discharge of liquid residual causes energy waste and decreases energy efficiency. To reduce energy waste, a poly-generation system for hydrogen-rich gas production coupling heat supply and power generation based on supercritical water gasification of biomass driven by concentrated solar energy was established in this paper, which also provided a novel... 相似文献
97.
The efficient utilization of lignocellulosic biomass and the reduction of production cost are mandatory to attain a cost-effective lignocellulose-to-ethanol process. The selection of suitable pretreatment that allows an effective fractionation of biomass and the use of pretreated material at high-solid loadings on saccharification and fermentation (SSF) processes are considered promising strategies for that purpose. Eucalyptus globulus wood was fractionated by organosolv process at 200 °C for 69 min using 56% of glycerol-water. A 99% of cellulose remained in pretreated biomass and 65% of lignin was solubilized. Precipitated lignin was characterized for chemical composition and thermal behavior, showing similar features to commercial lignin. In order to produce lignocellulosic ethanol at high-gravity, a full factory design was carried to assess the liquid to solid ratio (3–9 g/g) and enzyme to solid ratio (8–16 FPU/g) on SSF of delignified Eucalyptus. High ethanol concentration (94 g/L) corresponding to 77% of conversion at 16FPU/g and LSR = 3 g/g using an industrial and thermotolerant Saccharomyces cerevisiae strain was successfully produced from pretreated biomass. Process integration of a suitable pretreatment, which allows for whole biomass valorization, with intensified saccharification-fermentation stages was shown to be feasible strategy for the co-production of high ethanol titers, oligosaccharides and lignin paving the way for cost-effective Eucalyptus biorefinery. 相似文献
98.
Pruning urban forests generates significant amounts of lignocellulosic biomass every year. The energy potential of this biomass is unclear. The aim of this research was direct analysis of the gross calorific value (GCV), elemental composition and moisture content of Morus alba L., Platanus hispanica Münchh. and Sophora japonica L. by means of laboratory equipment. This analysis allowed for further development of indirect GCV prediction models which are economically attractive and less time consuming to direct analysis. These models presented high coefficients of determination (R2 0.66–0.96). It has been determined that the species with highest mean GCV is S. japonica L. (19615.68 kJ/kg-dry sample) whereas the one with the lowest is the M. alba L. (18192.87 kJ/kg-dry sample). Elemental analysis showed highest carbon (48.22%), hydrogen (6.17%) and nitrogen (1.16%) content in S. japonica L. in dry samples. Sulfur was constant at the level 0.05% for all analyzed species. Also percentage of bark and wood density were determined. Mean percentage of bark was highest for P. hispanica Münchh. (13.05%) while wood density was highest for S. japonica L. (0.86 g cm−3). This way the research has proven that the biomass produced by pruning urban forests appears to be an interesting source of renewable energy. 相似文献
99.
Two different sugar yield definitions (cellulose-based and biomass-based) were used in reported studies investigating the relationship between biomass particle size and enzymatic hydrolysis sugar yield. It is noticed that these reported relationships are not consistent if sugar yield is defined differently. The literature does not contain any reports on the effects of sugar yield definition on the relationship between biomass particle size and enzymatic hydrolysis sugar yield. This paper presents a consistency mapping to show under what conditions the relationships are consistent (or inconsistent) when these two definitions are used. The application of this mapping is illustrated via an experimental study with poplar wood biomass on the relationship between biomass particle size and enzymatic hydrolysis sugar yield using both sugar yield definitions. The application of this mapping is also illustrated via data reported in the literature. Not limited to particle size, this mapping is applicable to investigations of the relationships between a variety of parameters (biomass type, pretreatment condition, etc.) and enzymatic hydrolysis sugar yield. 相似文献
100.
Yinglai Teng Elinor L. Scott Johan P. M. Sanders 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2012,87(10):1458-1465
BACKGROUND: Amino acids are promising feedstocks for the chemical industry due to their chemical functionality. They can be obtained by the hydrolysis of potentially inexpensive protein streams such as the byproduct of biofuel production. However, individual amino acids are required before they can be used for the further production of chemicals. Here, the separation of L‐aspartic acid (Asp) and L‐glutamic acid (Glu) mixture, which can be isolated from protein hydrolysis solutions at low pH or from electrodialysis of complex amino acid mixtures, was studied. RESULTS: Glu was converted into L‐pyroglutamic acid (pGlu) which can be separated from the mixture of Asp and Glu due to its higher solubility in water. The conversion was carried out under aqueous or melt conditions. Under aqueous conditions, the conversion was studied as a factor of time, temperature and the amount of Glu. The conversion was specific with high yield and not effected by Asp. After pGlu was separated from Asp and residual Glu by solubility difference, it can be transferred back to Glu through hydrolysis. CONCLUSION: The conversion of Glu to pGlu is specific and can be applied to separation Asp and Glu for their use in the production of bio‐based chemicals. Copyright © 2012 Society of Chemical Industry 相似文献