全文获取类型
收费全文 | 3254篇 |
免费 | 96篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 32篇 |
综合类 | 2篇 |
化学工业 | 448篇 |
金属工艺 | 106篇 |
机械仪表 | 51篇 |
建筑科学 | 137篇 |
矿业工程 | 12篇 |
能源动力 | 65篇 |
轻工业 | 374篇 |
水利工程 | 41篇 |
石油天然气 | 10篇 |
无线电 | 198篇 |
一般工业技术 | 419篇 |
冶金工业 | 1147篇 |
原子能技术 | 41篇 |
自动化技术 | 268篇 |
出版年
2023年 | 9篇 |
2022年 | 45篇 |
2021年 | 49篇 |
2020年 | 39篇 |
2019年 | 49篇 |
2018年 | 51篇 |
2017年 | 45篇 |
2016年 | 50篇 |
2015年 | 51篇 |
2014年 | 55篇 |
2013年 | 137篇 |
2012年 | 104篇 |
2011年 | 158篇 |
2010年 | 128篇 |
2009年 | 139篇 |
2008年 | 158篇 |
2007年 | 117篇 |
2006年 | 118篇 |
2005年 | 107篇 |
2004年 | 88篇 |
2003年 | 77篇 |
2002年 | 95篇 |
2001年 | 61篇 |
2000年 | 72篇 |
1999年 | 59篇 |
1998年 | 257篇 |
1997年 | 158篇 |
1996年 | 94篇 |
1995年 | 68篇 |
1994年 | 70篇 |
1993年 | 65篇 |
1992年 | 39篇 |
1991年 | 32篇 |
1990年 | 46篇 |
1989年 | 27篇 |
1988年 | 26篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 26篇 |
1984年 | 26篇 |
1983年 | 21篇 |
1982年 | 12篇 |
1981年 | 24篇 |
1980年 | 28篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1977年 | 42篇 |
1976年 | 55篇 |
1973年 | 9篇 |
1972年 | 12篇 |
排序方式: 共有3351条查询结果,搜索用时 15 毫秒
1.
Puneet Parmar Nicolas Lopez-Villalobos John T. Tobin Eoin Murphy Frank Buckley Shane V. Crowley Alan L. Kelly Laurence Shalloo 《International Journal of Food Science & Technology》2021,56(5):2415-2422
The objective of this study was to determine the effect of temperature on whole milk density measured at four different temperatures: 5, 10, 15, and 20 °C. A total of ninety-three individual milk samples were collected from morning milking of thirty-two Holstein Friesian dairy cows, of national average genetic merit, once every two weeks over a period of 4 weeks and were assessed by Fourier transform infrared spectroscopy for milk composition analysis. Density of the milk was evaluated using two different analytical methods: a portable density meter DMA35 and a standard desktop model DMA4500M (Anton Paar GmbH, UK). Milk density was analysed with a linear mixed model with the fixed effects of sampling period, temperature and analysis method; triple interaction of sampling period x analysis method x temperature; and the random effect of cow to account for repeated measures. The effect of temperature on milk density (ρ) was also evaluated including temperature (t) as covariate with linear and quadratic effects within each analytic method. The regression equation describing the curvature and density–temperature relationship for the DMA35 instrument was ρ = 1.0338−0.00017T−0.0000122T2 (R2 = 0.64), while it was ρ = 1.0334 + 0.000057T−0.00001T2 (R2 = 0.61) for DMA4500 instrument. The mean density determined with DMA4500 at 5 °C was 1.0334 g cm−3, with corresponding figures of 1.0330, 1.0320 and 1.0305 g cm−3 at 10, 15 and 20 °C, respectively. The milk density values obtained in this study at specific temperatures will help to address any bias in weight–volume calculations and thus may also improve the financial and operational control for the dairy processors in Ireland and internationally. 相似文献
2.
3.
Matthew O'Sullivan Daire
hUallachin Patrícia Oliveira Antunes Eleanor Jennings Mary Kelly‐Quinn 《河流研究与利用》2019,35(2):146-158
Cattle access to streams has been linked globally with degradation of stream water quality, driven largely by bank erosion and resultant instream, fine sediment deposition. The majority of evidence on such effects is however based in arid and semiarid regions of the United States and Australia, with few studies relating to cool temperate climates such as Northwest Europe. In this study, “Quorer” resuspendable sediment samples were taken from riffle geomorphic units upstream (control) and at two points downstream (pressure and recovery) of cattle access points in headwater streams in agricultural catchments in Ireland to assess levels of deposited stream sediment. Samples were taken in April/May (2016) prior to the grazing season and in October (2016) at the end of the grazing season. Sites in good‐high ecological status catchments and less than good ecological status catchments were included in the study. Higher levels of sediment were found downstream of cattle access points in both good‐high status and less than good status catchments; however, the impacts of access points were spatially confined to, in most cases, the area immediately downstream of the point of access. There was a strong correlation between deposited sediment mass and organic matter (OM) mass, with levels of OM increasing linearly with deposited sediment mass. Levels of measured sediment were negatively correlated with riparian habitat health (measured using a qualitative habitat assessment). The results of this study highlight the need for measures to prevent cattle access to headwater streams where access points can be many in order to manage local habitat quality and downstream water quality issues. 相似文献
4.
5.
DH Kang CL Coe DO McCarthy NN Jarjour EA Kelly RR Rodriguez WW Busse 《Canadian Metallurgical Quarterly》1997,17(8):481-487
T cell cytokines play an important role in mediating airway inflammation in asthma. The predominance of a Th2 cytokine profile, particularly interleukin (IL)-4 and IL-5, is associated with the pathogenesis and course of asthma. The aim of this study was to test the hypothesis that a stressful life event alters the pattern of cytokine release in asthmatic individuals. Thirteen healthy controls and 21 asthmatic adolescents gave blood samples three times over a semester: midsemester, during the week of final examinations, and 2-3 weeks after examinations. Interferon-gamma (IFN-gamma), IL-2, IL-4, and IL-5 were measured from supernatants of cells stimulated with PHA/PMA for 24 h. Cells from asthmatic subjects released significantly more IL-5 during the examination and postexamination periods, whereas cells from healthy controls released significantly more IL-2 during the midsemester and examination periods, thereby indicating a bias for a Th2-like pattern in asthmatics and a Th1-like pattern in healthy controls. IL-4 and IL-5 production showed a marked decrease during and after examinations in healthy controls, whereas this decline was absent in asthmatics. The ratios of IFN-gamma:IL-4 and IFN-gamma:IL-5 also revealed significant changes in the profile of cytokine release across the semester. These results indicate differential cytokine responses in asthmatics that may become pronounced during periods of cellular activation. 相似文献
6.
Negative thermal expansion of laminates 总被引:1,自引:0,他引:1
Measurements have been carried out on the in-plane and through the thickness thermal expansion coefficients of glass polypropylene fibre composites of 50% volume fraction between room temperature and 120°C. Only in the temperature range 20° to 75°C are reproducible results obtained. It is confirmed that in-plane negative values may be obtained in specific directions. The physical reason for this and its connection with the necessary appearance of a large Poisson ratio is pointed out. The expansivity of the matrix material depends strongly on temperature. Very good agreement between the experimental values and those predicted from the properties of the two constituents is found provided that the value for the expansivity of the polyoropylene is that within the temperature range considered. It is shown that the polypropylene matrix does not provide a matrix which is stable enough in its properties to enable the system to yield consistent negative values of expansivity. An alternative system is proposed and a single experiment confirms that a negative value of the thermal expansivity of as large as –50 × 10–6 K–1 may be obtained. 相似文献
7.
Wilcox Sara; Evenson Kelly R.; Aragaki Aaron; Wassertheil-Smoller Sylvia; Mouton Charles P.; Loevinger Barbara Lee 《Canadian Metallurgical Quarterly》2003,22(5):513
This study examined whether widowhood was associated with physical and mental health, health behaviors, and health outcomes using a cross-sectional (N=72,247) and prospective (N=55,724) design in women aged 50-79 years participating in the Women's Health Initiative observational study (85.4% White). At baseline, married women reported better physical and mental health and generally better health behaviors than widowed women. Whereas women who remained married over the 3-year period showed stability in mental health, recent widows experienced marked impairments and longer term widows showed stability or slight improvements. Both groups of widows reported more unintentional weight loss over the 3-year period. Changes in physical health and health behaviors were inconsistent, with generally small effect sizes. Findings underscore the resilience of older women and their capacity to reestablish connections, but point to the need for services that strengthen social support among women who have difficulty during this transition. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
8.
William E. Kelly 《Canadian Metallurgical Quarterly》2007,133(3):181-187
Certification has been common for technicians for many years but specialty certification is rapidly becoming important to engineering practitioners in addition to or as a substitute for licensure in some fields. Certification and accreditation are closely related but there are also important differences. International standards now exist for accreditation of certification programs and could provide the basis for mutual recognition of specialty certification worldwide. ASCE should seek international accreditation of its specialty certification programs and play an appropriate role in defining international standards related to specialty certification and assessment of conformity to those standards. 相似文献
9.
Integrating principles from a variety of theory has led to the development of a conceptual framework for reengineering in a clinical care delivery setting to improve the value of services provided to the customer. A conceptual framework involving the identification of three high level core processes to reengineer can provide clarity and focus for clinicians to begin directing reengineering efforts. Those core processes are: clinical management of the patient's medical needs, patient operational processes to support the clinical processes, and administrative decision-making processes to support the implementation of the clinical and operational processes. Improvement in any one of these areas has the potential to increase value, but the concurrent targeting of these core processes for reengineering has provided a synergy that has accelerated the achievement of the desired outcomes in the area of surgical services. 相似文献
10.
Kelly Jeffrey A.; Murphy Debra A.; Sikkema Kathleen J.; Kalichman Seth C. 《Canadian Metallurgical Quarterly》1993,48(10):1023
Behavior change remains the only means for primary prevention of HIV disease. Psychology should take a leading role in efforts to curtail the epidemic, but has not contributed to HIV prevention at a level proportionate to the urgency of the crisis. The authors propose an updated agenda for behavioral research on AIDS-HIV prevention implementing accelerated community trials of promising behavior change models, conducting trials of community-level interventions on a large scale and focused on populations most vulnerable to HIV infections, establishing partnerships between HIV research and community service organizations, integrating efforts from across psychology disciplines to advance and refine HIV prevention interventions, and mobilizing interdisciplinary HIV prevention resources and communication mechanisms to rapidly translate research findings to community and public policy arenas. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献