全文获取类型
收费全文 | 1873篇 |
免费 | 107篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 14篇 |
综合类 | 1篇 |
化学工业 | 414篇 |
金属工艺 | 44篇 |
机械仪表 | 51篇 |
建筑科学 | 49篇 |
矿业工程 | 3篇 |
能源动力 | 83篇 |
轻工业 | 176篇 |
水利工程 | 11篇 |
石油天然气 | 19篇 |
无线电 | 178篇 |
一般工业技术 | 300篇 |
冶金工业 | 353篇 |
原子能技术 | 34篇 |
自动化技术 | 253篇 |
出版年
2024年 | 8篇 |
2023年 | 18篇 |
2022年 | 39篇 |
2021年 | 85篇 |
2020年 | 62篇 |
2019年 | 63篇 |
2018年 | 58篇 |
2017年 | 61篇 |
2016年 | 62篇 |
2015年 | 45篇 |
2014年 | 50篇 |
2013年 | 95篇 |
2012年 | 81篇 |
2011年 | 94篇 |
2010年 | 66篇 |
2009年 | 74篇 |
2008年 | 72篇 |
2007年 | 65篇 |
2006年 | 53篇 |
2005年 | 62篇 |
2004年 | 43篇 |
2003年 | 22篇 |
2002年 | 25篇 |
2001年 | 26篇 |
2000年 | 41篇 |
1999年 | 33篇 |
1998年 | 105篇 |
1997年 | 77篇 |
1996年 | 49篇 |
1995年 | 36篇 |
1994年 | 25篇 |
1993年 | 36篇 |
1992年 | 14篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1976年 | 17篇 |
1973年 | 6篇 |
1972年 | 6篇 |
1969年 | 6篇 |
排序方式: 共有1983条查询结果,搜索用时 31 毫秒
991.
992.
Interbasin Water Transfers: The Brazilian Experience and International Case Comparisons 总被引:1,自引:0,他引:1
José Geraldo Pena de Andrade Paulo Sergio Franco Barbosa Luiz Carlos Alves Souza Daniel Lucas Makino 《Water Resources Management》2011,25(8):1915-1934
This paper critically examines Brazil’s transbasin diversion experiences and two select, large-scale transbasin projects outside
of Brazil. Rather than simply compare Brazil’s experiences with international cases, the authors explore the historical context
of the projects, focusing on the water resources and environmental regulatory and institutional frameworks in place during
the initial proposals and how they influenced the projects’ development and completion rates. Huge investments, the lengthy
time span between the date of the initial project proposals and the start of construction, the need to garner public and political
support, and more recently, the need to fulfill national and regional environmental laws are major factors underlying heated
public debates about the proposed projects. After a broad discussion about the subject, the authors examine a recently approved
large-scale Brazilian project, the Sao Francisco river transbasin diversion. This river diversion project is considered crucial
to the economic development of Brazil’s semi-arid northeastern region. Despite the fact that this government-funded project
was debated for several decades among the various stakeholders, it was approved under Brazil’s newly formed water resources
regulatory and environmental framework, which enabled improvements in various key technical aspects of the project, and greater
involvement of various key social players. 相似文献
993.
Lucas Duffrène René Gy John E. Masnik John Kieffer Jay D. Bass 《Journal of the American Ceramic Society》1998,81(5):1278-1284
The high-frequency viscoelastic behavior of a soda-lime-silica glass has been investigated using the Brillouin scattering technique. The temperature dependence of instantaneous elastic constants and very short-time relaxation mechanisms have been measured in a temperature range between 100° and 1000°C. Variations in the elastic constants in the transition region are significant, and have to be taken into account for numerical computations of tempering and annealing of glasses. A complex thermorheological behavior is observed for very fast relaxation mechanisms in the transition range, whereas intermediate and slow relaxation mechanisms exhibit a simple thermorheological behavior. The viscoelastic behavior of this glass can be adequately represented by assuming a different thermorheological behavior in the alpha- and β-relaxation regimes. 相似文献
994.
We have shown previously that non-stationary signals recorded in a static multi-path environment can often be recovered by simultaneously decorrelating varying second order statistics. As typical sources are often moving, however, the multi-path channel is not static. We present here an on-line gradient algorithm with adaptive step size in the frequency domain based on second derivatives, which we refer to as multiple adaptive decorrelation (MAD). We compared the separation performance of the proposed algorithm to its off-line counterpart and to another decorrelation based on-line algorithm. 相似文献
995.
Kellen Cristina da Cruz Rodrigues Rodrigo Martins Pereira Guilherme Francisco Peruca Lucas Wesley Torres Barbosa Marcella Ramos SantAna Vitor Rosetto Muoz Ana Paula Morelli Fernando Moreira Simabuco Adelino Sanchez Ramos da Silva Dennys Esper Cintra Eduardo Rochete Ropelle Jos Rodrigo Pauli Leandro Pereira de Moura 《International journal of molecular sciences》2021,22(12)
Obesity is closely related to insulin resistance and type 2 diabetes genesis. The liver is a key organ to glucose homeostasis since insulin resistance in this organ increases hepatic glucose production (HGP) and fasting hyperglycemia. The protein-tyrosine phosphatase 1B (PTP1B) may dephosphorylate the IR and IRS, contributing to insulin resistance in this organ. Aerobic exercise is a great strategy to increase insulin action in the liver by reducing the PTP1B content. In contrast, no study has shown the direct effects of strength training on the hepatic metabolism of PTP1B. Therefore, this study aims to investigate the effects of short-term strength exercise (STSE) on hepatic insulin sensitivity and PTP1B content in obese mice, regardless of body weight change. To achieve this goal, obese Swiss mice were submitted to a strength exercise protocol lasting 15 days. The results showed that STSE increased Akt phosphorylation in the liver and enhanced the control of HGP during the pyruvate tolerance test. Furthermore, sedentary obese animals increased PTP1B content and decreased IRS-1/2 tyrosine phosphorylation; however, STSE was able to reverse this scenario. Therefore, we conclude that STSE is an important strategy to improve the hepatic insulin sensitivity and HGP by reducing the PTP1B content in the liver of obese mice, regardless of changes in body weight. 相似文献
996.
Lucas Ballard Daniel Lopresti Fabian Monrose 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2007,37(5):1107-1118
Biometric security is a topic of rapidly growing importance in the areas of user authentication and cryptographic key generation. In this paper, we describe our steps toward developing evaluation methodologies for behavioral biometrics that take into account threat models that have been largely ignored. We argue that the pervasive assumption that forgers are minimally motivated (or, even worse, naive) is too optimistic and even dangerous. Taking handwriting as a case in point, we show through a series of experiments that some users are significantly better forgers than others, that such forgers can be trained in a relatively straightforward fashion to pose an even greater threat, that certain users are easy targets for forgers, and that most humans are a relatively poor judge of handwriting authenticity, and hence, their unaided instincts cannot be trusted. Additionally, to overcome current labor-intensive hurdles in performing more accurate assessments of system security, we present a generative attack model based on concatenative synthesis that can provide a rapid indication of the security afforded by the system. We show that our generative attacks match or exceed the effectiveness of forgeries rendered by the skilled humans we have encountered. 相似文献
997.
A randomised multicentre study of human milk versus formula and later development in preterm infants
Whether breast milk influences later neurodevelopment has been explored in non-randomised studies, potentially confounded by social and demographic differences between feed groups. Here in a strictly randomised prospective multicentre trial, Bayley psychomotor and mental development indices (PDI and MDI) were assessed at 18 months postterm in survivors of 502 preterm infants assigned to receive, during their early weeks, mature donor breast milk or a preterm formula. These diets were compared as sole enteral feeds or as supplements to the mother's expressed breast milk. No differences in outcome at 18 months were seen between the two diet groups despite the low nutrient content of donor milk in relation to the preterm formula and to the estimated needs of preterm infants. These results contrast with those reported from our parallel two centre study that compared infants randomly assigned a standard term formula or the preterm formula during their early weeks; those fed standard formula, now regarded as nutritionally insufficient for preterm infants, were substantially disadvantaged in PDI and MDI at 18 months post-term. It is shown here that infants from that study fed solely on standard formula had significantly lower developmental scores at 18 months than those fed on donor breast milk in the present study; yet the standard formula had a higher nutrient content than the donor milk. Thus, donor milk feeding was associated with advantages for later development that may have offset any potentially deleterious effects of its low nutrient content for preterm infants. As these outcome advantages were not confounded by the social and educational biases usually associated with mothers' choice to breast feed, our data add significant support to the view that breast milk promotes neurodevelopment. 相似文献
998.
999.
1000.
The phosphorus grain boundary segregation kinetics during tempering at 680°C and aging at 500°C of 2.7Cr-0.7Mo-0.3V steels with phosphorus mass contents of 0.004, 0.014, and 0.027 % was investigated. To determine the grain boundary concentrations of phosphorus the Auger electron spectroscopy was used. Chemical compositions of carbide particles were determined by means of EDX/STEM. Xu Tingdong's and McLean's models of non-equilibrium and equilibrium segregations, respectively, were used to analyze experimental data. It was shown that a phosphorus grain boundary enrichment during tempering was mainly caused by non-equilibrium segregation. During aging the mechanism of the equilibrium grain boundary segregation was prevalent. Slow phosphorus segregation kinetics was observed in the experimental steels during aging. 相似文献