全文获取类型
收费全文 | 1937篇 |
免费 | 15篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 6篇 |
化学工业 | 77篇 |
金属工艺 | 6篇 |
机械仪表 | 6篇 |
建筑科学 | 17篇 |
矿业工程 | 1篇 |
能源动力 | 3篇 |
轻工业 | 74篇 |
水利工程 | 9篇 |
石油天然气 | 4篇 |
无线电 | 118篇 |
一般工业技术 | 65篇 |
冶金工业 | 1517篇 |
原子能技术 | 5篇 |
自动化技术 | 46篇 |
出版年
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2017年 | 4篇 |
2015年 | 12篇 |
2014年 | 9篇 |
2013年 | 19篇 |
2012年 | 14篇 |
2011年 | 25篇 |
2010年 | 20篇 |
2009年 | 14篇 |
2008年 | 16篇 |
2007年 | 21篇 |
2006年 | 14篇 |
2005年 | 19篇 |
2004年 | 22篇 |
2003年 | 13篇 |
2002年 | 17篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 60篇 |
1998年 | 447篇 |
1997年 | 274篇 |
1996年 | 179篇 |
1995年 | 94篇 |
1994年 | 77篇 |
1993年 | 99篇 |
1992年 | 17篇 |
1991年 | 23篇 |
1990年 | 18篇 |
1989年 | 21篇 |
1988年 | 29篇 |
1987年 | 24篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 20篇 |
1980年 | 17篇 |
1978年 | 10篇 |
1977年 | 59篇 |
1976年 | 87篇 |
1975年 | 10篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1966年 | 3篇 |
1955年 | 3篇 |
排序方式: 共有1954条查询结果,搜索用时 0 毫秒
11.
12.
13.
The frequency characteristics of a Salisbury screen radar absorber that incorporates a layer exhibiting both resistive and capacitive properties are considered. If the capacitance is fixed, the absorber thickness and hence weight may be reduced but at the expense of bandwidth. If the capacitance is variable then the absorber may be tuned via an external control signal. The practical limitations of both applications are discussed in relation to recent advances in conducting polymer materials 相似文献
14.
15.
The judged likelihood of a focal outcome should generally decrease as the list of alternative possibilities increases. For example, the likelihood that a runner will win a race goes down when 2 new entries are added to the field. However, 6 experiments demonstrate that the presence of implausible alternatives (duds) often increases the judged likelihood of a focal outcome. This dud-alternative effect was detected for judgments involving uncertainty about trivia facts and stochastic events. Nonnumeric likelihood measures and betting measures reliably detected the effect, but numeric likelihood measures did not. Time pressure increased the magnitude of the effect. The results were consistent with a contrast-effect account: The inclusion of duds increases the perceived strength of the evidence for the focal outcome, thereby affecting its judged likelihood. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
16.
Philosophical explanations of the phenomenon of akrasia have been used in this article to characterize some of the difficulties involved in successful behavior change. The theory of psychological reversals provides a framework for understanding various types of akratic behavior. In addition, empirical research on the temptations of persons trying to quit smoking has supported hypotheses generated by the theory. The theory suggests that resisting the temptation to engage in akratic behavior is a complex phenomenon. Different strategies are needed in different types of metamotivational states. Reversal theory provides a coherent system for understanding and predicting akratic behavior. It suggests possible interventions that would improve the probability of circumventing akrasia and that would improve behavior change efforts of nurses engaged in health-promotion and disease-prevention activities. 相似文献
17.
In rats, the phosphorothionate insecticide parathion exhibits greater toxicity than chlorpyrifos, while in catfish the toxicities are reversed. The in vitro inhibition of brain acetylcholinesterase (AChE) by the active metabolites of the insecticides and the rates at which these inhibitor-enzyme complexes undergo reactivation/ aging were investigated in both species. Rat AChE was more sensitive to inhibition than catfish AChE as demonstrated by greater bimolecular rate constants (ki) in rats than in catfish. In both species, chlorpyrifos-oxon yielded higher ki's than paraoxon. The higher association constant (KA) of chlorpyrifos-oxon than paraoxon in both species and the lack of significant differences in the phosphorylation constants (kp) suggest that association of the inhibitor with AChE is the principal factor in the different potencies between these two inhibitors. In catfish, the ki of chlorpyrifos-oxon was 22-fold greater than that of paraoxon, while in rats it was 9-fold greater, suggesting that target site sensitivity is an important factor in the higher toxicity of chlorpyrifos to catfish but not in the higher toxicity of parathion to rats. No spontaneous reactivation of phosphorylated catfish AChE occurred and there were no differences in the first oder aging constants (ka) between compounds. For phosphorylated rat AChE, there were no differences in the first order reactivation constants (kr) but the ka for chlorpyrifos-oxon was significantly greater than that for paraoxon. This difference suggests that the steric positioning of the diethyl phosphate in the esteratic site is not the same between the two compounds, leading to differences in aging. 相似文献
18.
AA Sazanov LA Alekseevich AL Sazanova AF Smirnov 《Canadian Metallurgical Quarterly》1996,32(7):869-878
Various molecular methods are now used to map the chicken genome, including chromosome scraping, flow cytofluorimetry, zonal centrifugation, construction of chromosome-specific libraries, genetic analysis with polymorphic DNA markers, and in situ hybridization. Two main drawbacks are characteristic of existing maps of chicken chromosomes. First, classic genetic maps (i.e., linkage groups of genes for morphological, physiological, and biochemical characters), physical maps of chromosomes, and new genetic maps constructed on the basis of polymorphic DNA markers (RFLP, RAPD, VNTR, SSR, and CR1-PCR) do not coordinate with one another. Second, a relatively low number of genes is present in classic genetic maps and physical chromosome maps. Application of cytogenetic methods to chromosome mapping in birds is limited because of some specific features characteristic of the organization of avian genomes. For the same reason, studying the location and expression of avian genes is very important. Since mammalian and avian genomes differ in structure, revealing their possible common functional characteristics will provide for a better understanding of the general mechanisms that control biologically important characters in higher animals. 相似文献
19.
Don Chambers 《Journal of Automated Methods and Management in Chemistry》1994,16(4):135-137
It is generally believed that successful robot users have dedicated
centralized robotic groups. While such a generalization holds some
merit historically, the availability of newer more user-friendly robots
and workstations in recent years and a more computer-literate work
force today is changing the way that automation can be managed.
Decentralization recognizes robots and workstations as additional
tools for all analysts, not a select few. Such an approach initiates
involvement and education of more staff with respect to automation.
This further ushers the development of automated methods instead
of the automation of manually-developed methods. Decentralization
also provides local control of resources to address the priorities of
a specific functional group within the department. Both a vision of
the future, as well as a look at the past, should be considered when
determining how to manage robotic and other means of automation.
This paper discusses decentralized management of robots as
currently applied and envisioned in a large pharmaceutical
analytical R & D department. 相似文献
20.
Resistance-modifying agents (RMAs) such as Verapamil have been proved to be effective in reversing multi-drug resistance (MDR) in many in vitro assays. In this study we have investigated the efficacy of Dex-Verapamil, the R-isomer of Verapamil, as a chemosensitizer in a murine leukemia cell line (P388) and in its resistant counterpart (P388/Dx) expressing a typical MDR phenotype. We have examined in vivo the effect of the co-administration of Dex-Verapamil and Doxorubicin in mice transplanted with P388 or P388/Dx cells. Mice treated with the combination of Doxorubicin plus RMA had a significant increase in survival rate as compared to controls; however, the effect was modest. On the contrary, in vitro Dex-Verapamil can enhance Doxorubicin cytotoxicity in P388/Dx cells with a much greater effect depending on the treatment scheme used, by increasing the intracellular content of drug. Taken together our data indicate that Dex-Verapamil can indeed increase the sensitivity to Doxorubicin in resistant cells, but the limited efficacy shown in vivo demonstrates that this phenomenon is strongly dependent on the treatment scheme used and on the maintenance of constantly elevated serum levels. 相似文献