全文获取类型
收费全文 | 123523篇 |
免费 | 11819篇 |
国内免费 | 7620篇 |
专业分类
电工技术 | 9005篇 |
技术理论 | 8篇 |
综合类 | 9578篇 |
化学工业 | 18211篇 |
金属工艺 | 8036篇 |
机械仪表 | 8433篇 |
建筑科学 | 9964篇 |
矿业工程 | 3942篇 |
能源动力 | 3858篇 |
轻工业 | 8637篇 |
水利工程 | 2935篇 |
石油天然气 | 6334篇 |
武器工业 | 1432篇 |
无线电 | 14524篇 |
一般工业技术 | 13281篇 |
冶金工业 | 5173篇 |
原子能技术 | 1764篇 |
自动化技术 | 17847篇 |
出版年
2024年 | 554篇 |
2023年 | 1767篇 |
2022年 | 3372篇 |
2021年 | 4881篇 |
2020年 | 3686篇 |
2019年 | 3089篇 |
2018年 | 3372篇 |
2017年 | 3877篇 |
2016年 | 3579篇 |
2015年 | 5174篇 |
2014年 | 6543篇 |
2013年 | 7787篇 |
2012年 | 8926篇 |
2011年 | 9776篇 |
2010年 | 9088篇 |
2009年 | 8689篇 |
2008年 | 8706篇 |
2007年 | 8416篇 |
2006年 | 8005篇 |
2005年 | 6449篇 |
2004年 | 4630篇 |
2003年 | 3845篇 |
2002年 | 3710篇 |
2001年 | 3125篇 |
2000年 | 2619篇 |
1999年 | 2139篇 |
1998年 | 1418篇 |
1997年 | 1151篇 |
1996年 | 997篇 |
1995年 | 831篇 |
1994年 | 659篇 |
1993年 | 486篇 |
1992年 | 356篇 |
1991年 | 266篇 |
1990年 | 205篇 |
1989年 | 159篇 |
1988年 | 130篇 |
1987年 | 97篇 |
1986年 | 83篇 |
1985年 | 52篇 |
1984年 | 48篇 |
1983年 | 41篇 |
1982年 | 29篇 |
1981年 | 28篇 |
1980年 | 27篇 |
1979年 | 17篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1959年 | 19篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
交流,共享,流动——现代大空间办公模式的优劣与对策 总被引:1,自引:0,他引:1
讨论了现代办公空间设计出现的新要求,通过办公空间演变趋势的探讨,归纳为若干大空间办公模式,并分析、比较其空间性质及特点,以及采用开放式办公布局的优势、不足及解决对策. 相似文献
12.
"橄榄型"社会阶层结构范式论 总被引:1,自引:0,他引:1
拥有一个"橄榄型"社会阶层结构,社会就会减少动荡,保持社会的相对稳定与和谐.现阶段培育"橄榄型"的社会阶层结构,是构建社会主义和谐社会的重要基础. 相似文献
13.
针对烧结厂烧结电除尘灰的工况特性,介绍了输送烧结电除尘灰的正压气力输灰系统的特点、组成,还对在调试和试运行过程中遇到的故障进行了分析并制订了解决措施。 相似文献
14.
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.
以三维软件进行车轮造型,用CAD软件建立固有频率分析数学模型,对车轮固有频率进行分析和处理.结合其他试验的分析,对车轮进行优化设计. 相似文献
17.
根据在农村通自来水工程实践中积累的经验,提出并较好地解决了农村供水工程的评价标准,设计供水时间的确定,输配水管网设计中的优化等问题,对建好、管好和用好农村自来水工程具有一定的帮助作用. 相似文献
18.
19.
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
20.
In this paper, we investigate the problem of determining the optimal bandwidth allocation for a Dynamic Bandwidth Allocation Scheme (DBAS). The objective is to minimize the total amount of bandwidth required to satisfy the Quality of Service (QoS) requirements of all traffic streams. It is shown that when the performance functions satisfy a certain number of conditions, there exists a unique optimal bandwidth allocation such that, for each traffic stream, either its QoS is just satisfied or its QoS is over-satisfied and it is allocated zero bandwidth. Such an allocation is said to be efficient. It is also shown that there exists a unique efficient allocation in the entire feasible region. An iterative algorithm is developed to compute the efficient allocation employing its special properties. Numerical examples are presented to demonstrate how the algorithm works. Future extensions of this work are also discussed.Partially supported by NSERC of Canada through grants OGP14020 and STRIN-200. 相似文献