全文获取类型
收费全文 | 889篇 |
免费 | 12篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 1篇 |
综合类 | 31篇 |
化学工业 | 78篇 |
金属工艺 | 2篇 |
机械仪表 | 14篇 |
建筑科学 | 61篇 |
矿业工程 | 1篇 |
能源动力 | 2篇 |
轻工业 | 25篇 |
水利工程 | 10篇 |
无线电 | 3篇 |
一般工业技术 | 24篇 |
冶金工业 | 628篇 |
原子能技术 | 1篇 |
自动化技术 | 23篇 |
出版年
2023年 | 5篇 |
2022年 | 16篇 |
2021年 | 21篇 |
2020年 | 12篇 |
2019年 | 7篇 |
2018年 | 12篇 |
2017年 | 11篇 |
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 12篇 |
2013年 | 25篇 |
2012年 | 15篇 |
2011年 | 61篇 |
2010年 | 77篇 |
2009年 | 62篇 |
2008年 | 58篇 |
2007年 | 60篇 |
2006年 | 51篇 |
2005年 | 78篇 |
2004年 | 47篇 |
2003年 | 47篇 |
2002年 | 63篇 |
2001年 | 46篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 8篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 11篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1961年 | 2篇 |
1960年 | 2篇 |
1957年 | 1篇 |
1956年 | 4篇 |
1955年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有904条查询结果,搜索用时 15 毫秒
1.
胡振 《西安建筑科技大学学报(自然科学版)》2012,(1):90-96,108
针对公私合作(PPP)项目,以VFM效果作为政府收益的评价指标,分析控制权为连续变量的情况下投资、成本和收益等变量的取值,在此基础上构建控制权配置与VFM效果的相关关系模型,结果发现,VFM效果与项目公司拥有的控制权呈二次曲线关系,因此,二次项系数、一次项系数及对称轴位置影响VFM的单调性,进而决定着控制权的最佳配置.论文基于上述原理构建控制权配置的决策模型,并通过算例验证所得模型具有较强的适用性. 相似文献
2.
从媒体控制考察媒体工作者的性观念与性道德,围绕媒体工作者的双重身份——普通大众与媒体人,对媒体工作者进行实证调查,分析得出媒体工作者的性观念与性道德总体上趋于保守和规范,但仍存在偏离现象。 相似文献
3.
4.
Telecommunications in the US is undergoing a revolution. Corporations are attempting to leverage their competencies in the deregulated environment in order to enhance their competitive position. While the eventual results of this flurry of partnerships that has recently occurred are uncertain, there are certain trends that are becoming increasingly apparent. This paper represents an essay on the telecommunications industry (or its converging associated industries) and describes its history and evolving structure. Fifty-four partnerships are examined in an attempt to systematically examine an industry in transition. Key implications of these partnerships are also discussed. 相似文献
5.
6.
Effect of dietary supplementation of tiger nut (Cyperus esculentus l.) and walnut (Tetracarpidium conophorum müll. Arg.) on sexual behavior,hormonal level,and antioxidant status in male rats 下载免费PDF全文
7.
Stigma theory was used to examine the fears underlying the disclosure of a gay identity at work. Using a national sample of 534 gay, lesbian, and bisexual employees, this study examined the antecedents that affect the degree of disclosure of a gay identity at work and, for those who had not disclosed, the factors that influence their fears about full disclosure. Employees reported less fear and more disclosure when they worked in a group that was perceived as supportive and sharing their stigma. Perceptions of past experience with sexual orientation discrimination were related to increased fears but to greater disclosure. For those who had not fully disclosed their stigma, the fears associated with disclosure predicted job attitudes, psychological strain, work environment, and career outcomes. However, actual disclosure was unrelated to these variables. The utility of fear of disclosure for understanding processes underlying the disclosure of gay and other invisible stigmatized identities in the workplace is discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
8.
Schistosome adults attract each other in vitro and the attraction is chemically mediated. InSchistosoma mansoni adults, excretory-secretory (ES) products of worms of one sex attract worms of the opposite sex, and at least the lipophilic fraction is attractive. Intra- and interspecific attraction occurs inSchistosoma mansoni, S. japonicum, andS. haematobium adults. Current knowledge of schistosome behavior in vitro is reviewed. 相似文献
9.
Laboratory studies with live and frozen Maladera matrida female and male beetles showed that males were attracted to chemical substances emanating from the females at dusk. Beetles exhibited sexual activity (including mating) at dusk towards frozen females but not towards frozen males. Frozen females that had been extracted with methanol together with either hexane or dichloromethane or with a mixture of all three solvents did not elicit male sexual activity. Activity was fully restored when a concentrate of the extract was applied to the previously extracted frozen females. Males also responded with vigorous sexual activity to frozen males to which female extract had been applied. Deterrent chemicals appear to be absent from the male body. Males exposed to females that had been frozen during the morning displayed weak sexual activity, indicating that females lack active semiochemicals. Differences between dusk and morning extracts were found with respect to more than 20 compounds, some of which were present in much higher concentrations at dusk than in the morning, while others were not detected in the morning extract. The active component(s) of the short-range sex pheromone of female M. matrida is (are) presumably to be found among these compounds. 相似文献
10.
Mant J Brändli C Vereecken NJ Schulz CM Francke W Schiestl FP 《Journal of chemical ecology》2005,31(8):1765-1787
Male Colletes cunicularius bees pollinate the orchid, Ophrys exaltata, after being sexually deceived by the orchid’s odor-mimicry of the female bee’s sex pheromone. We detected biologically active volatiles of C. cunicularius by using gas chromatographic–electroantennographic detection (GC-EAD) with simultaneous flame ionization detection. After identification of the target compounds by coupled gas chromatography–mass spectrometry (GC-MS), we performed behavioral tests using synthetic blends of the active components. We detected 22 EAD active compounds in cuticular extracts of C. cunicularius females. Blends of straight chain, odd-numbered alkanes and (Z)-7-alkenes with 21–29 carbon atoms constituted the major biologically active compounds. Alkenes were the key compounds releasing mating behavior, especially those with (Z)-7 unsaturation. Comparison of patterns of bee volatiles with those of O. exaltata subsp. archipelagi revealed that all EAD-active compounds were also found in extracts of orchid labella. Previous studies of the mating behavior in C. cunicularius showed linalool to be an important attractant for patrolling males. We confirmed this with synthetic linalool but found that it rarely elicited copulatory behavior, in accordance with previous studies. A blend of active cuticular compounds with linalool elicited both attraction and copulation behavior in patrolling males. Thus, linalool appears to function as a long-range attractant, whereas cuticular hydrocarbons are necessary for inducing short-range mating behavior. 相似文献