全文获取类型
收费全文 | 8647篇 |
免费 | 688篇 |
国内免费 | 177篇 |
专业分类
电工技术 | 68篇 |
综合类 | 588篇 |
化学工业 | 1641篇 |
金属工艺 | 253篇 |
机械仪表 | 119篇 |
建筑科学 | 631篇 |
矿业工程 | 240篇 |
能源动力 | 234篇 |
轻工业 | 4327篇 |
水利工程 | 136篇 |
石油天然气 | 422篇 |
武器工业 | 10篇 |
无线电 | 120篇 |
一般工业技术 | 267篇 |
冶金工业 | 267篇 |
原子能技术 | 37篇 |
自动化技术 | 152篇 |
出版年
2024年 | 44篇 |
2023年 | 144篇 |
2022年 | 266篇 |
2021年 | 356篇 |
2020年 | 335篇 |
2019年 | 319篇 |
2018年 | 292篇 |
2017年 | 348篇 |
2016年 | 299篇 |
2015年 | 342篇 |
2014年 | 429篇 |
2013年 | 519篇 |
2012年 | 649篇 |
2011年 | 623篇 |
2010年 | 466篇 |
2009年 | 451篇 |
2008年 | 431篇 |
2007年 | 526篇 |
2006年 | 449篇 |
2005年 | 400篇 |
2004年 | 336篇 |
2003年 | 269篇 |
2002年 | 271篇 |
2001年 | 159篇 |
2000年 | 157篇 |
1999年 | 104篇 |
1998年 | 84篇 |
1997年 | 70篇 |
1996年 | 69篇 |
1995年 | 36篇 |
1994年 | 38篇 |
1993年 | 45篇 |
1992年 | 23篇 |
1991年 | 17篇 |
1990年 | 19篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有9512条查询结果,搜索用时 15 毫秒
21.
微波消解-ICP-AES法测定菜油中P、S 总被引:2,自引:0,他引:2
采用微波加热,在高温高压下酸消解样品,运用电感耦合等离子体原子发射光谱法(ICP-AES)同时测定菜油中P、S。本法选用紫外区谱线P178.221nm、S180.669nm,避免了基体中存在的Fe、Zn、Al、Cu、Mn、Ca等元素的光谱干扰。实验通过用纯氮吹扫光谱仪光路的方法消减空气中氧对紫外线的吸收,获得了足够的灵敏度。该方法简便、快速,稳定可靠,P、S检出限分别为0.067、0.078μg/ml,RSD为1.35%~5.05%,回收率为89.0%~100.9%。 相似文献
22.
D. Bojinova R. Velkova Iv. Grancharov St. Zhelev 《Nutrient Cycling in Agroecosystems》1996,47(3):227-232
It is well known that the production of phosphoric fertilizers by traditional methods is connected with certain environmental problems, particularly related to use of acids during the decomposition of natural phosphates. A basic problem is also the fact that only 15 – 20% of the phosphorus contained in superphosphates is assimilated by plants.The development of methods to process natural phosphates without acid precipitation has potential advantages and in this respect biotechnological processing of natural phosphates in order to obtain organo-mineral fertilizers is very promising. The possibility of bioconverting the phosphorus of natural phosphates by usingAspergillus niger fungi through their deep incubation has been investigated. The investigations aim to achieve a high degree of P2O5 extraction from the phosphates with conversion from a non-utilizable to a utilizable form. The influence of the fungal strain, the kind of nutritive medium and the time of incubation of the process of biological mobilization of the phosphate rock is examined.It was established that the time of incubation, the kind of micro-organisms of theAspergillus niger group, as well as the kind of nutritive medium, influence significantly the process of bioconversion and the conversion of phosphorus from non-utilizable to water-soluble and utilizable for plants form. A maximum degree 90% of phosphorus extraction in the form of water-soluble and citrate-soluble has been reached for 10-day incubation. Physicochemical examinations have been carried out and they have proved that, as a result of the produced organic acids, a process of decomposition of the initial Tunisian phosphorite takes place. 相似文献
23.
光催化氧化后四环素的分解率与COD去除率之间关系的探讨 总被引:1,自引:0,他引:1
以粉状无机半导体(ZnO)为催化剂,探讨了水溶液中四环素经光催化氧化分解率和COD去除率之间的关系。实验表明,在本实验中四环素的分解率和COD去除率之间有较好的正相关性。当反庆系统中有足量的活性催化剂和足够的光照时间时,绝大部分四环素将被较彻底地氧化分解成CO2,这不仅有助于光催化反应机理的研究,助于今后在环保中的实际应用。 相似文献
24.
25.
149 strains of bacteria, mostly brewery contaminants able to spoil wort or beer, and 12 brewing strains of yeast (8 ale and 4 lager strains) have been screened using a well-test assay for sensitivity to the food preservative, Nisin (E234), Nisin inhibited growth of 92% of the gram-positive strains, predominantly lactic acid bacteria of the genera Lactobacillus and Pediococcus. In contrast, all 32 gram-negative strains tested, except 3 Flavobacter strains, were Nisin-resistant; in addition none of the brewing yeasts showed Nisin-sensitivity. Therefore. Nisin has potential applications in preventing spoilage of worts or beers by lactic acid bacteria. 相似文献
26.
臭氧在食品加工用水处理工程上的应用 总被引:2,自引:0,他引:2
本文叙述了臭氧的一些特性 ,并以烟台某食品加工公司食品加工用水处理工程为例 ,介绍了臭氧的产生及应用情况 ,提供了处理前后水中各项指标的对照 相似文献
27.
《Drying Technology》2007,25(7):1193-1201
This work describes how probiotic bacteria can be dried at low temperature in two steps, combining spray drying and vacuum drying, in order to enhance their survival during storage. A sufficient number of dried probiotics survived storage for more than 3 months at 30°C, if an appropriate combination of protein and carbohydrate was selected as carrier and storage conditions were maintained optimal. The use of soy protein and maltodextrin or skim milk and arabic gum resulted in the best survival rates of probiotics during storage. No evident difference was found between different spray dryer configurations, although a cocurrent flow was preferred. 相似文献
28.
Kornl L. Kovcs Barna Fodor kos T. Kovcs Gyula Csandi Gergely Marti Judit Balogh Solmaz Arvani Gbor Rkhely 《International Journal of Hydrogen Energy》2002,27(11-12)
The purple (Sulphur) phototrophic bacterium, Thiocapsa roseopersicina BBS contains several [NiFe] hydrogenases, of which two are membrane bound. Mutant T. roseopersicina cells, carrying deletions in both gene clusters showed hydrogenase activity. This activity was located in the cytoplasm. The structural gene cluster hoxEFUYH was identified and sequenced. In addition, genes homologous to hupUV/hoxBC, the hydrogen sensing hydrogenase have been identified and sequenced.Regulation of hydrogenase biosynthesis was studied in detail for HydSL (renamed HynSL). A random mutagenesis system was optimised for T. roseopersicina. One of the mutations was in a gene similar to that coding for the HypF proteins in other organisms. Inactivation of the hypF gene resulted in a 60-fold increase in hydrogen evolution under nitrogen fixing conditions. In addition to hypF, the following accessory genes were identified: hydD, hupK, hypC1, hypC2, hypDE. Characterisation of the corresponding gene products and search for additional accessory genes are in progress. 相似文献
29.
We modeled nisin's anticlostridial activity and assessed the antagonistic or potentiating influences of food ingredients. The model systems contained yeast extract, proteose peptone, and glucose; were supplemented with protein (0.075, 0.75, 7.5% w/v), phospholipid (0.075, 0.75, 7.5% w/v), or soluble starch (5, 17.5, 30% w/v); and were adjusted to pH 5.5, 6.0, or 6.5. Samples inoculated with 104/mL spores were incubated at 15, 25, or 35°C. Statistical analysis developed an equation (r2= 0.76) that modeled the response and identified temperature as the most significant (α 0.001) variable. Nisin lost effectiveness with increasing temperature. Nisin concentration had significant positive and phospholipid negative, linear effects. Many interactive effects were significant (α 0.20). Nisin inhibited C. botulinum until its residual level dropped below a threshold, which decreased from 154 IU/mL at 35°C to 12 IU/mL at 15°C. 相似文献
30.
Of 100 gas-producing bacterial isolates, 65% were Gram-negative. Bacterial growth and gas production in commercial tofu was accompanied by acidification, and pH decreases as low as 5.2. Coliform bacteria constituted 15% of the total bacterial flora. Sporeformers and yeast counts remained < 103 CFU/mL. Pasteurization was effective in lowering the bacterial counts, and retarded gas production. The addition of lactic acid (reducing pH to 5.5) or lactic acid bacteria (2 × 107 CFU/g) to tofu helped reduce gas production by about 50%. Addition of both lactic acid and Lactobacillus plantarum stopped gas production in contaminated tofu. 相似文献