全文获取类型
收费全文 | 466篇 |
免费 | 3篇 |
学科分类
工业技术 | 469篇 |
出版年
2021年 | 2篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 17篇 |
2012年 | 8篇 |
2011年 | 10篇 |
2010年 | 3篇 |
2009年 | 5篇 |
2008年 | 15篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 11篇 |
2002年 | 3篇 |
2001年 | 11篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 44篇 |
1997年 | 29篇 |
1996年 | 19篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 2篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 15篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 8篇 |
1971年 | 3篇 |
1967年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有469条查询结果,搜索用时 140 毫秒
1.
Many problems consist in splitting a set of objects into different groups so that each group verifies some properties. In practice, a partitioning is often encoded by an array mapping each object to its group numbering. In fact, the group number of an object does not really matter, and one can simply rename each group to obtain a new encoding. That is what we call the symmetry of the search space in a partitioning problem. This property may be prejudicial for optimization methods such as evolutionary algorithms (EA) which require some diversity during the search. 相似文献
2.
This is a review of two electrical equivalent circuits for multi-element magnetostatic wave transducers. The two circuit models are identified as a transmission line and a two terminal model. Both models have been extended to all three principal MSW modes of propagation to the point where computer programs have been written to plot phase and amplitude response as measured by commercial network analyzers. A review is provided of the basic assumptions, similarities and differences, advantages and disadvantages, and limitations of the two models. The useful range of them covers many cases of practical interest in the one to twelve Ghz frequency range. 相似文献
3.
Carsten Carstensen Kerstin Weinberg 《International journal for numerical methods in engineering》2003,56(15):2313-2330
Adaptive algorithms are important tools for efficient finite‐element mesh design. In this paper, an error controlled adaptive mesh‐refining algorithm is proposed for a non‐conforming low‐order finite‐element method for the Reissner–Mindlin plate model. The algorithm is controlled by a reliable and efficient residual‐based a posteriori error estimate, which is robust with respect to the plate's thickness. Numerical evidence for this and the efficiency of the new algorithm is provided in the sense that non‐optimal convergence rates are optimally improved in our numerical experiments. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
4.
5.
6.
OBJECTIVES: A randomized trial was conducted to evaluate the effectiveness of a work-site health promotion program in reducing obesity and the prevalence of cigarette smoking. METHODS: Thirty-two work sites were randomized to treatment or no treatment for 2 years. Treatment consisted of health education classes combined with a payroll-based incentive system. Evaluation was based on cohort and cross-sectional surveys. RESULTS: Of 10,000 total employees in treatment work sites, 2041 and 270 participated in weight control and smoking cessation programs, respectively. Weight losses averaged 4.8 lbs, and 43% of smoking participants quit. Net 2-year reductions in smoking prevalence in treatment vs control work sites were 4.0% and 2.1% in cross-sectional and cohort surveys, respectively. No treatment effect was found for weight. Treatment effects for smoking prevalence and weight were both positively correlated with participation rates in the intervention programs (r = .45 for smoking and r = .55 for weight). CONCLUSIONS: This work-site health promotion program was effective in reducing smoking prevalence at a cost that is believed to make the investment worthwhile. 相似文献
7.
Mechanisms for the abnormal copper (Cu) accumulation in the liver of LEC rats were examined using primary cultured liver parenchymal cells prepared from mutant LEC rats and those from control LEA rats (original strain). The Cu and metallothionein (MT) mRNA levels in the liver of LEC rats were caused to decrease to the same levels as those of LEA rats by removing Cu in vivo selectively with tetrathiomolybdate. Cu was taken up by LEC rat cells to the same extent as LEA rat cells by exposure to low medium Cu and to a higher extent by exposure to high medium Cu, while the MT mRNA level in LEC rat cells increased dose-dependently at a much higher rate than that in LEA rats. MT mRNA levels in both cells were comparable by exposure to cadmium, zinc and dexamethasone. The results indicate that expression of MT mRNA is selectively enhanced by Cu in LEC cells despite the fact that uptake of Cu is comparable with normal cells. 相似文献
8.
Several off-the-shelf animation software packages provide extensive capabilities, obviating the need for studios to develop their own software, except for highly specialized effects and interfaces. These capabilities make it feasible for a university to educate students in animation production without years of software development. The author discusses The UTS School of Cinema-Television and The USC Computer Animation Laboratory in particular 相似文献
9.
AI Robles ML Rodriguez-Puebla AB Glick C Trempus L Hansen P Sicinski RW Tennant RA Weinberg SH Yuspa CJ Conti 《Canadian Metallurgical Quarterly》1998,12(16):2469-2474
Cyclin D1 is part of a cell cycle control node consistently deregulated in most human cancers. However, studies with cyclin D1-null mice indicate that it is dispensable for normal mouse development as well as cell growth in culture. Here, we provide evidence that ras-mediated tumorigenesis depends on signaling pathways that act preferentially through cyclin D1. Cyclin D1 expression and the activity of its associated kinase are up-regulated in keratinocytes in response to oncogenic ras. Furthermore, cyclin D1 deficiency results in up to an 80% decrease in the development of squamous tumors generated through either grafting of retroviral ras-transduced keratinocytes, phorbol ester treatment of ras transgenic mice, or two-stage carcinogenesis. 相似文献
10.
Karin Yaccato Alfred Hagemeyer Andreas Lesik Anthony Volpe Henry Weinberg 《Topics in Catalysis》2004,(1):127-132
High-throughput synthesis and screening methods have been developed for the discovery of highly active lead compounds for the selective catalytic reduction as well as direct decomposition of NO in the temperature range 200–300 °C. The discovery libraries for primary screening consisted of 16 × 16 catalyst arrays on 4in. square quartz wafers. Catalysts were prepared by robotic liquid dispensing techniques and screened for catalytic activity in Symyx' scanning mass spectrometer. The scanning mass spectrometer is a fast serial screening tool that uses flat wafer catalyst surfaces, local laser heating, a scanning/sniffing nozzle and a quadrupolar mass spectrometer to compare relative catalytic activities. The feed consisted of NO/NH3 mixtures with optional O2 cofeed and Kr as the internal standard in Ar carrier gas. QMS detection allowed for tracking of H2O, N2, NO, O2, N2O and Kr. Screening protocols for catalytic materials encompassed metal precursors and carriers for supported vanadia systems, extensive doping of V2O5/TiO2, and broad screening of mixed redox metal oxides and supported base and noble metal systems. More than 500 samples could be screened in a single day. Active hits (high NO consumption accompanied by corresponding N2 production) identified in discovery libraries were re-synthesized as focus libraries for lead confirmation and further optimization. These libraries used shallower compositional gradients, for example 56 points (compositions) per ternary, with four 56-point ternaries per 4in. wafer. Broad screening ternaries were generally 8 or 15 points. The focus libraries more clearly reveal the trends and provide guidelines for secondary screening and scale-up. High conversions were achieved in scanning mass spectrometer so the scalability risk is small for the short contact time reactions. 相似文献