全文获取类型
收费全文 | 25642篇 |
免费 | 2224篇 |
国内免费 | 959篇 |
专业分类
电工技术 | 1338篇 |
技术理论 | 5篇 |
综合类 | 1446篇 |
化学工业 | 4662篇 |
金属工艺 | 1680篇 |
机械仪表 | 1522篇 |
建筑科学 | 1956篇 |
矿业工程 | 709篇 |
能源动力 | 844篇 |
轻工业 | 1854篇 |
水利工程 | 410篇 |
石油天然气 | 1738篇 |
武器工业 | 158篇 |
无线电 | 2568篇 |
一般工业技术 | 3181篇 |
冶金工业 | 1394篇 |
原子能技术 | 273篇 |
自动化技术 | 3087篇 |
出版年
2024年 | 165篇 |
2023年 | 578篇 |
2022年 | 953篇 |
2021年 | 1226篇 |
2020年 | 966篇 |
2019年 | 783篇 |
2018年 | 904篇 |
2017年 | 923篇 |
2016年 | 784篇 |
2015年 | 1074篇 |
2014年 | 1236篇 |
2013年 | 1644篇 |
2012年 | 1593篇 |
2011年 | 1661篇 |
2010年 | 1437篇 |
2009年 | 1357篇 |
2008年 | 1304篇 |
2007年 | 1248篇 |
2006年 | 1311篇 |
2005年 | 1139篇 |
2004年 | 698篇 |
2003年 | 648篇 |
2002年 | 593篇 |
2001年 | 481篇 |
2000年 | 550篇 |
1999年 | 665篇 |
1998年 | 563篇 |
1997年 | 418篇 |
1996年 | 407篇 |
1995年 | 339篇 |
1994年 | 280篇 |
1993年 | 192篇 |
1992年 | 156篇 |
1991年 | 110篇 |
1990年 | 90篇 |
1989年 | 53篇 |
1988年 | 66篇 |
1987年 | 42篇 |
1986年 | 30篇 |
1985年 | 32篇 |
1984年 | 29篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1974年 | 3篇 |
1959年 | 3篇 |
1958年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
13.
万家寨引黄工程北干线系统输水损失,是关乎输水运行成本和水资源有效利用的重要问题之一。由于各类建筑物施工方法,材料及工艺的差异。其输水损失差异较大,计算方法和计算参数各不相同,文章在对各类建筑物进行输水损失计算的基础上,分析了不同类型建筑物的输水损失特点,提出了减少水量损失的建议和设想。 相似文献
14.
Aimin Xiang Zhongjie Du Qinghua Zeng Chen Zhang Hangquan Li 《Polymer International》2005,54(10):1366-1370
This paper presents recent efforts on the preparation of flexible polyhedral particles via concentrated emulsion templating polymerization in which the hydrophilic monomer (acrylamide) and hydrophobic monomer (butyl acrylate) are polymerized simultaneously in the continuous and dispersed phase, respectively. Such templating polymerization has been enhanced in our systems owing to the introduction of acrylamide monomer and their higher polymerization rate in continuous phase as compared with butyl acrylate in dispersed phase. Diffusion between the different phases was also inhibited. Furthermore, the stability of the concentrated emulsion and the molecular weight of the produced poly(butyl acrylate) were found to be significantly affected by the amount of redox initiator. The morphology of the particles could be controlled by varying the volume fraction of the dispersed phase and the polyhedral particles were achieved at higher volume fraction. Copyright © 2005 Society of Chemical Industry 相似文献
15.
The effects of key parameters on the preparation and regeneration of protoplast from the β-carotene-producing fungus Blakeslea trispora were discussed in this paper, including the combination of various enzymes, mycelial age, digesting time and temperature,
pH value, osmotic stabilizers, pretreatment, culture medium and culture method. Under the condition of mixed enzymes in osmotic
stabilizer (0.6 M NaCl) combined with 2% lysozyme, 3% cellulase and 3% snailase, the highest protoplast yield, as high as
7.48×106 protoplasts/mL, was obtained when mycelial age was 60 h at pH 5.0–6.0 with digesting for 14–16 h at 28 °C. After
purification of the obtained protoplasts, they were regenerated in PDA regenerative medium using bilayer plate culture method.
To validate the usability of the protoplasts, a novel plasmid with green fluorescent protein (GFP) was used in transformation
for easy visual observation. The results showed that the protoplasts prepared by the optimized method were active and applicable
in further gene manipulation experiments.
This work was presented at 13
th
YABEC symposium held at Seoul, Korea, October 20–22, 2007. 相似文献
16.
L. M. Du Plessis J. B. M. De Villiers W. H. Van Der Walt 《Journal of the American Oil Chemists' Society》1985,62(4):748-752
Fatty acid esters, high in linoleic acid, were prepared and stored for long-term engine tests. Storage tests with these esters were undertaken to obtain more information on optimal storage requirements and general stability characteristics. Samples were kept at three temperature levels (20 C, 30 C and fluctuating around 50 C) for a 90-day period and were removed at regular intervals for chemical and physical analysis. The influence of air, temperature, light, TBHQ and contact with mild steel was evaluated by comparing the free fatty acid, peroxide, anisidine, ultraviolet absorption, viscosity and induction periods. A statistical model was used to evaluate the data and to reduce the large number of data points to comparable curves. Storage of esters in contact with air, especially at a temperature above 30 C, resulted in significant increases in peroxide, ultraviolet absorption, free fatty acid, viscosity and anisidine values. Exclusion of air retarded oxidation at all temperature levels. A direct relationship between viscosity increases and oxidation parameters was evident. Exposure to light caused a small increase in the oxidation parameters of esters stored at the highest temperature level. Addition of TBHQ prevented oxidation of samples stored under moderate conditions. Under unfavorable storage conditions the anti-oxidant was no longer effective. Mild steel had very little effect on the oxidation parameters. Only the anisidine values of samples stored at the highest temperature level were slightly increased. Methyl esters performed slightly better than ethyl esters during the storage test. The following practical guidelines for storage of fatty acid ester fuels are: (i) airtight containers should be used; (ii) the storage temperature should be <30 C; (iii) mild steel (rust free) containers may be used, and (iv) TBHQ has a beneficial effect on oxidation stability. 相似文献
17.
用宏观断口分析、化学检验、力学性能测定、低倍检查、金相组织及夹杂物评定鉴别、受力分析及强度寿命定量估算的方法,对人字轮被动齿轴端断裂失效原因进行分析,并提出改进措施。 相似文献
18.
Ming Dai Yu Zhang Yiman Hua Wansun Ni Gonghuan Du 《Electronics letters》1998,34(10):951-953
By active-passive-decomposition synchronisation, the application of the one-way coupled ring map lattice hyperchaotic system in secure digital speech communication is demonstrated. Synchronisation guarantees strong security and recovery without error 相似文献
19.
20.