全文获取类型
收费全文 | 724篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 144篇 |
金属工艺 | 15篇 |
机械仪表 | 3篇 |
建筑科学 | 25篇 |
能源动力 | 21篇 |
轻工业 | 69篇 |
水利工程 | 3篇 |
无线电 | 79篇 |
一般工业技术 | 79篇 |
冶金工业 | 206篇 |
原子能技术 | 3篇 |
自动化技术 | 87篇 |
出版年
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2014年 | 7篇 |
2013年 | 15篇 |
2012年 | 13篇 |
2011年 | 25篇 |
2010年 | 21篇 |
2009年 | 18篇 |
2008年 | 39篇 |
2007年 | 26篇 |
2006年 | 18篇 |
2005年 | 25篇 |
2004年 | 20篇 |
2003年 | 16篇 |
2002年 | 17篇 |
2001年 | 14篇 |
2000年 | 25篇 |
1999年 | 22篇 |
1998年 | 69篇 |
1997年 | 40篇 |
1996年 | 25篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 21篇 |
1992年 | 10篇 |
1991年 | 17篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 18篇 |
1975年 | 5篇 |
1973年 | 3篇 |
1968年 | 3篇 |
1966年 | 4篇 |
1965年 | 3篇 |
排序方式: 共有739条查询结果,搜索用时 31 毫秒
61.
Universal Portfolios With and Without Transaction Costs 总被引:1,自引:0,他引:1
A constant rebalanced portfolio is an investment strategy which keeps the same distribution of wealth among a set of stocks from period to period. Recently there has been work on on-line investment strategies that are competitive with the best constant rebalanced portfolio determined in hindsight (Cover, 1991, 1996; Helmbold et al., 1996; Cover & Ordentlich, 1996a, 1996b; Ordentlich & Cover, 1996). For the universal algorithm of Cover (Cover, 1991),we provide a simple analysis which naturallyextends to the case of a fixed percentage transaction cost (commission ), answering a question raised in (Cover, 1991; Helmbold et al., 1996; Cover & Ordentlich, 1996a, 1996b; Ordentlich & Cover, 1996; Cover, 1996). In addition, we present a simple randomized implementation that is significantly faster in practice. We conclude by explaining how these algorithms can be applied to other problems, such as combining the predictions of statistical language models, where the resulting guarantees are more striking. 相似文献
62.
In this note the studies begun in Blum and Suttmeier (1999) on adaptive finite element discretisations for nonlinear problems
described by variational inequalities are continued. Similar to the concept proposed, e.g., in Becker and Rannacher (1996)
for variational equalities, weighted a posteriori estimates for controlling arbitrary functionals of the discretisation error are constructed by using a duality argument.
Numerical results for the obstacle problem demonstrate the derived error bounds to be reliable and, used for an adaptive grid
refinement strategy, to produce economical meshes.
Received September 6, 1999; revised February 8, 2000 相似文献
63.
This study explored the adoption of preemployment drug testing by 360 organizations. Survival models were developed that included internal organizational and labor market factors hypothesized to affect the likelihood of adoption of drug testing. Also considered was another set of variables that included social and political variables based on institutional theory. An event history analysis using Cox regressions indicated that both internal organizational and environmental variables predicted adoption of drug testing. Results indicate that the higher the proportion of drug testers in the worksite's industry, the more likely it would be to adopt drug testing. Also, the extent to which an organization uses an internal labor market, voluntary turnover rate, and the extent to which management perceives drugs to be a problem were related to likelihood of adoption of drug testing. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
64.
Standard linear diversity combining techniques are not effective in combating fading in the presence of non-Gaussian noise. An adaptive spatial diversity receiver is developed for wireless communication channels with slow, flat fading and additive non-Gaussian noise. The noise is modeled as a mixture of Gaussian distributions and the expectation-maximization (EM) algorithm is used to derive estimates for the model parameters. The transmitted signals are detected using a likelihood ratio test based on the parameter estimates. The new adaptive receiver converges rapidly, its bit error rate performance is very close to optimum when relatively short training sequences are used, and it appears to be relatively insensitive to mismatch between the noise model and the actual noise distribution. Simulation results are included that illustrate various aspects of the adaptive receiver performance 相似文献
65.
A new method is proposed to quantify the local dislocation spacings on sections displaying the intersections of dislocation
lines. The method was applied to dislocation structures in single crystals of CaF2 introduced by deformation at elevated temperature and made visible by etch pits. The method yields the frequency distributions
and the spatial distributions of dislocation spacings. For cellular dislocation structures the method provides a quantitative
and objective characterization in terms of frequency distribution of dislocation spacings in cell boundaries and cell interiors
and of cell size. 相似文献
66.
67.
68.
Simulations of continuous-time systems are frequently used by designers of signal processing and communication systems. Windowed finite-impulse response models are often used in these simulations to model continuous-time linear filters. We investigate the performance of some common windows with respect to waveform fidelity, which is a primary goal in waveform simulation, and we also obtain the form of optimum windows for this criterion. Our results indicate that the rectangular window is generally a practical and reasonably good choice for waveform simulation 相似文献
69.
The relation of the physiological releases of growth hormone-releasing hormone (GHRH) and growth hormone (GH) into the circulation in various conditions was investigated using a sensitive and specific radioimmunoassay for plasma GHRH. The mean fasting plasma level of immunoreactive (IR)-GHRH in 72 normal adults was 10.3 +/- 0.5 (mean +/- SEM) pg/ml and there was no significant sex difference in the level. The concentrations of IR-GHRH in plasma from the umbilical artery and umbilical vein were 107.3 +/- 20.5 pg/ml and 33.6 +/- 3.8 pg/ml, respectively, and a marked arterio-venous gradient was observed in all 12 individuals examined. The plasma level of IR-GHRH in the maternal vein was significantly lower than that in the cord blood, but was similar to that in non-pregnant women. In normal adults, although there was no apparent fluctuation in the level of plasma IR-GHRH or of plasma GH during bed rest, a significant increase of plasma IR-GHRH was detected followed by, or synchronized with the surge of plasma GH after oral administration of L-dopa. In contrast, on L-arginine infusion, no proportional elevation of plasma IR-GHRH with increase in plasma GH was observed. During and after intravenous infusion of somatostatin, the circulating IR-GHRH level did not increase, but on stopping the infusion there was an immediate and marked rebound surge of GH. We conclude that 1) the elevated IR-GHRH in the cord blood plasma originates from the fetus and may have a primary role in enhancing secretion of GH which promotes growth in early human life, and 2) the participations of GHRH in the mechanisms of GH secretion seen after administrations of L-dopa, L-arginine and somatostatin are different. 相似文献
70.
This paper presents an overview of research in expert systems and artificial intelligence as they relate to software engineering. The paper begins with a review of current thinking regarding the software process. This is followed by a discussion of artificial intelligence (AI) and the paradigms it uses. Six current projects are described: three are concerned with programming in the large and three with programming in the small. These six projects provide a representative sample of the AI research now underway in the software engineering domain. The paper concludes with some observations regarding when and how the concepts represented by these projects will be available for application to operational projects. 相似文献