全文获取类型
收费全文 | 945篇 |
免费 | 38篇 |
专业分类
电工技术 | 8篇 |
综合类 | 7篇 |
化学工业 | 187篇 |
金属工艺 | 79篇 |
机械仪表 | 14篇 |
建筑科学 | 58篇 |
矿业工程 | 1篇 |
能源动力 | 33篇 |
轻工业 | 77篇 |
水利工程 | 2篇 |
无线电 | 105篇 |
一般工业技术 | 168篇 |
冶金工业 | 111篇 |
原子能技术 | 5篇 |
自动化技术 | 128篇 |
出版年
2022年 | 4篇 |
2021年 | 10篇 |
2020年 | 14篇 |
2019年 | 5篇 |
2018年 | 17篇 |
2017年 | 13篇 |
2016年 | 17篇 |
2015年 | 22篇 |
2014年 | 23篇 |
2013年 | 51篇 |
2012年 | 53篇 |
2011年 | 66篇 |
2010年 | 48篇 |
2009年 | 56篇 |
2008年 | 64篇 |
2007年 | 42篇 |
2006年 | 45篇 |
2005年 | 39篇 |
2004年 | 42篇 |
2003年 | 25篇 |
2002年 | 23篇 |
2001年 | 17篇 |
2000年 | 24篇 |
1999年 | 19篇 |
1998年 | 24篇 |
1997年 | 20篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1978年 | 5篇 |
1977年 | 10篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1969年 | 2篇 |
1955年 | 4篇 |
排序方式: 共有983条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
An objective of the study was to identify leaf morphophysiological characteristics indicative of high aboveground woody biomass production of Salix clones growing in the vegetation filter of a wastewater purification system. It was hypothesized, that in these extra irrigated stands, the characteristics of photosynthesis are stronger determinants of the production than the characteristics of leaf water relations. The biomass production of the clones was correlated with numerous characteristics of leaf water relations and photosynthesis. Significant correlation was found between the biomass production and the following characteristics of top foliage leaves: daily decrease in water potential, stomatal conductance, stomatal sensitivity to increase in light intensity, and hydraulic conductance (positive); daily minimum and maximum water potentials, instantaneous water use efficiency, and stomatal sensitivity to decrease in leaf water potential (negative); maximum rate of photosynthetic electron transport, chlorophyll content, and the partitioning coefficient for leaf nitrogen into bioenergetics associated with electron transport (positive). In the most productive clones, the vertical gradient (through foliage) of values of almost all the characteristics was the smallest. The biomass correlated more strongly with the characteristics of photosynthesis light stage than with the characteristics of water relations. We conclude that the characteristics of photosynthesis light stage – high maximum rate of photosynthetic electron transport, high chlorophyll content, and also flat vertical gradient (through foliage) in values of the characteristics could be the strongest indicators of high biomass production of Salix clones growing in vegetation filter. 相似文献
75.
76.
Bert Fraser-Reid G. Anilkumar Latha G. Nair Lars Olsson Mercedes Garcia Martin Jacquitta K. Daniels 《Israel journal of chemistry》2000,40(3-4):255-262
The C1 and C2 stereocenters of α-glucosaminides can be prepared by establishing the stereocenters in either order. For the former, a C2-azido glucosyl donor is prepared first, and the restraining effect of a 4,6-O-benzylidene ring is used to induce α-coupling. For the latter, the C1 linkage is prepared first by use of an n-pentenyl-manno-1,2-orthoester donor which ensures (a) clean α-coupling and (b) a convenient C2-ester. The C2-ester is replaced with a triflate leaving group, and nucleophilic displacement is effected by use of a hypervalent silicon azide. 相似文献
77.
78.
Explored the impact of counselor age, level of intimacy of clients' presenting problems, and client marital status on perception of counselors and the counseling relationship with 48 married females (mean age 21.9 yrs) and 48 unmarried females (mean age 26.3 yrs). Ss viewed a series of 3 videotapes, which were counterbalanced for level of intimacy of client's presenting problems and depicted initial interviews between young female clients and either younger or older female counselors. After viewing each individual vignette, Ss completed a counselor rating form, a client satisfaction form, and manipulation checks for presenting problem intimacy and counselor age. Overall, differences in presenting problems and counselor age were perceived as intended. Ss' marital status was unrelated to any measures. Counselors were judged as most expert, attractive, and trustworthy when dealing with presenting problems that were least intimate. Ss anticipated greater satisfaction with younger rather than older counselors only for the least intimate presenting problem. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
79.
80.