全文获取类型
收费全文 | 245篇 |
免费 | 5篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 17篇 |
金属工艺 | 4篇 |
机械仪表 | 4篇 |
建筑科学 | 8篇 |
能源动力 | 3篇 |
轻工业 | 12篇 |
无线电 | 64篇 |
一般工业技术 | 29篇 |
冶金工业 | 83篇 |
原子能技术 | 1篇 |
自动化技术 | 21篇 |
出版年
2023年 | 2篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2016年 | 2篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 8篇 |
2011年 | 2篇 |
2010年 | 5篇 |
2009年 | 8篇 |
2007年 | 5篇 |
2006年 | 6篇 |
2005年 | 3篇 |
2004年 | 8篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 23篇 |
1997年 | 10篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 8篇 |
1975年 | 2篇 |
1972年 | 3篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1969年 | 3篇 |
1968年 | 5篇 |
1967年 | 3篇 |
1966年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有250条查询结果,搜索用时 11 毫秒
1.
Hagness S.C. Taflove A. Bridges J.E. 《IEEE transactions on bio-medical engineering》1998,45(12):1470-1479
A novel focused active microwave system is investigated for detecting tumors in the breast. In contrast to X-ray and ultrasound modalities, the method reviewed here exploits the breast-tissue physical properties unique to the microwave spectrum, namely, the translucent nature of normal breast tissues and the high dielectric contrast between malignant tumors and surrounding lesion-free normal breast tissues. The system uses a pulsed confocal technique and time-gating to enhance the detection of tumors while suppressing the effects of tissue heterogeneity and absorption. Using published data for the dielectric properties of normal breast tissues and malignant tumors, the authors have conducted a two-dimensional (2-D) finite-difference time-domain (FDTD) computational electromagnetics analysis of the system. The FDTD simulations showed that tumors as small as 2 mm in diameter could be robustly detected in the presence of the background clutter generated by the heterogeneity of the surrounding normal tissue. Lateral spatial resolution of the tumor location was found to be about 0.5 cm 相似文献
2.
3.
4.
Here we describe a novel, hand-held reference point indentation (RPI), instrument that is designed for clinical measurements of bone material properties in living patients. This instrument differs from previous RPI instruments in that it requires neither a reference probe nor removal of the periosteum that covers the bone, thus significantly simplifying its use in patient testing. After describing the instrument, we discuss five guidelines for optimal and reproducible results. These are: (1) the angle between the normal to the surface and the axis of the instrument should be less than 10°, (2) the compression of the main spring to trigger the device must be performed slowly (>1 s), (3) the probe tip should be sharper than 10 μm; however, a normalized parameter with a calibration phantom can correct for dull tips up to a 100 μm radius, (4) the ambient room temperature should be between 4?°C and 37 °C, and (5) the effective mass of the bone or material under test must exceed 1 kg, or if under 1 kg, the specimen should be securely anchored in a fixation device with sufficient mass (which is not a requirement of previous RPI instruments). Our experience is that a person can be trained with these guidelines in about 5 min and thereafter obtain accurate and reproducible results. The portability, ease of use, and minimal training make this instrument suitable to measure bone material properties in a clinical setting. 相似文献
5.
Linoleic and arachidonic acids, labeled with14C and injected intratesticularly, were used to study with time the interconversion of polyunsaturated fatty acids in rat testis
and their incorporation into the major lipid classes. With both substrates14C activity was readily incorporated into longer chain, more highly unsaturated fatty acids. After the injection of 1-14C-linoleic acid the major portion of the14C was found in palmitic, linoleic, 8,11,14-eicosatrienoic, 5,8,11,14-eicosatetraenoic, 7,10,13,16-docosatetraenoic and 4,7,10,13,16-docosapentaenoic
acids. Hydrogenation of the total fatty acids isolated from rat testes after intratesticular injection of 1-14C-linoleate revealed that the polyenoic acids hydrogenating to lignoceric acid (previously characterized as 9,12,15,18-tetracosatetraenoate
and 6,9,12,15,18-tetracosapentaenoate) had a relatively high specific activity. After the injection of 1-14C-arachidonate significant14C activity was found in palmitate, 7,10,13,16-docosatetraenoate, 4,7,10,13,16-docosapentaenoate, 9,12,15,18-tetracosatetraenoate
and 6,9,12,15,18-tetracosapentaenoate. The biosynthesis of the ω6 polyunsaturated fatty acids in rat testis is discussed in relation to these data. Investigation of the distribution of label
in the complex lipid fractions demonstrated the majority of the14C activity to be present in phosphatides and triglycerides after injection of either of these14C substrates with only small quantities being present as nonesterified acids. At the time periods studied the polyenoic acids
of triglycerides had a higher specific activity than the corresponding acids of phosphatides with the exception of linoleate.
Presented in part at the Meeting of the American Institute of Nutrition, Atlantic City, April 1968 and at the AOCS Meeting
in New York, April 1969. These data were taken from a thesis submitted by R. B. Bridges in partial fulfillment of the requirements
for the Ph.D. degree, Vanderbilt University. 相似文献
6.
Carl Thodesen Khaldoun Shatanawi Serji Amirkhanian William Bridges 《Construction and Building Materials》2009,23(5):1922-1927
This paper describes the development of an empirical model which may be used for predicting the G*/sin δ for neat and crumb rubber modified (CRM) binders. The model was developed using 36 unique CRM binder combinations, crumb rubber concentrations were varied at 5% intervals between 5% and 20%. The effects of crumb rubber particle size on model accuracy were also studied, ultimately a model was produced with the capability of predicting G*/sin δ values over a range of temperatures and crumb rubber concentrations. By definition, the upper limit of the performance grade is dependent on the G*/sin δ value; therefore, the relationship was also considered in terms of high end failure temperature.The rubber coefficient for G*/sin δ (Rcg) was identified as an important parameter in the estimation of G*/sin δ in addition to the CRM. This term is a quantitative representation of the increase typically witnessed in G*/sin δ values with the addition of CRM. Ambient ground CRM exhibited higher Rcg values than cryogenically ground particles. Additionally, 95% confidence intervals were generated for the predictive model, thus providing a range of accuracy for the model. The resulting confidence intervals were approximately ±1300 Pa, these confidence intervals were seen to capture 92.6% of the 462 data points used. Findings from this research suggest that the differences between cryogenic and ambient CRM binder are accurately described using the Rcg, furthermore binder properties may be predicted using an empirical equation. 相似文献
7.
Nephew Benjamin C.; Bridges Robert S.; Lovelock Dennis F.; Byrnes Elizabeth M. 《Canadian Metallurgical Quarterly》2009,123(5):949
Although it has often been speculated that prior reproductive experience improves subsequent maternal care, few studies have examined specific changes in behavior during a 1st versus 2nd lactation. During lactation, mothers display heightened aggression toward male intruders, purportedly to protect vulnerable young. In the current study, maternal aggression was examined in primiparous and age-matched multiparous females on postpartum days 5 (PPD5) and PPD15. Expression of oxytocin, oxytocin receptor, arginine vasopressin, arginine vasopressin V1a receptors, and corticotrophin-releasing hormone mRNA was measured following aggression testing at both time points using real-time quantitative PCR in brain regions previously implicated in the regulation of maternal aggression. Multiparity significantly enhanced maternal aggression on PPD5 but not on PPD15. In addition, this increased aggression was associated with region- and gene-specific changes in mRNA expression. These findings indicate that reproductive experience enhances maternal aggression, an effect that may be mediated by region-specific alterations in neuropeptidergic activity. The adaptations observed in multiparous females provide an innate model for the study of neuroplasticity in the regulation of aggression. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
8.
This paper addresses interactions among foraging behavior, habitat preferences, site characteristics, and spatial distribution of contaminants in developing PCB exposure estimates for winter flounder at a hypothetical open water dredged material disposal site in the coastal waters of New York and New Jersey (NY-NJ). The implications of these interactions for human health risk estimates for local recreational anglers who fish for and eat flounder are described. The models implemented in this study include a spatial submodel to account for spatial and temporal characteristics of fish exposures and a probabilistic adaptation of the Gobas bioaccumulation model that accounts for temporal variation in concentrations of hydrophobic contaminants in sediment and water. We estimated the geographic distribution of a winter flounder subpopulation offshore of NY-NJ based on species biology and its vulnerability to local recreational fishing, the foraging area of individual fish, and their migration patterns. We incorporated these parameters and an estimate of differential attraction to a management site into a spatially explicit model to assess the range of exposures within the population. The output of this modeling effort, flounder PCB tissue concentrations, provided exposure point concentrations for an estimate of human health risk through ingestion of locally caught flounder. The risks obtained for the spatially nonexplicit case are as much as 1 order of magnitude higher than those obtained with explicit consideration of spatial and temporal characteristics of winter flounder foraging and seasonal migration. This practice of "defaulting" to extremely conservative estimates for exposure parameters in the face of uncertainty ill serves the decision-making process for management of contaminated sediments in general and specifically for disposal of dredged materials. Consideration of realistic spatial and temporal scales in food chain models can help support sediment management decisions by providing a quantitative expression of the confidence in risk estimates. 相似文献
9.
Lendenmann H. Schrimpf R.D. Bridges A.D. 《Semiconductor Manufacturing, IEEE Transactions on》1991,4(3):213-218
A test structure for the measurement of electrostatic discharge (ESD) pulses using a floating gate transistor is presented. It was found that ESD pulses of a wide range of magnitudes can cause a shift in the threshold voltage of such a floating gate transistor. The change in device characteristics was quantified by measuring the drain current. For a given geometry, the response was proportional to the magnitude of the ESD event for a particular range of voltages. This particular range of sensitivity also scales linearly with the capacitance ratio of the devices studied. Numerical simulation of a simple model of the device leads to sufficiently accurate results for the design of a specific sensitivity if the processing parameters are considered. The lowest sensitivity determined was 60 V 相似文献
10.
Results are given for the beam distortion suffered by low order Gaussian-Laguerre modes propagating through a saturable laser amplifier. Both uniform and Bessel small-signal gain distributions are considered. Beam narrowing caused by saturable loss is also treated. 相似文献