全文获取类型
收费全文 | 2616篇 |
免费 | 68篇 |
国内免费 | 2篇 |
学科分类
工业技术 | 2686篇 |
出版年
2022年 | 25篇 |
2021年 | 43篇 |
2020年 | 28篇 |
2019年 | 41篇 |
2018年 | 33篇 |
2017年 | 40篇 |
2016年 | 33篇 |
2015年 | 30篇 |
2014年 | 64篇 |
2013年 | 132篇 |
2012年 | 86篇 |
2011年 | 118篇 |
2010年 | 96篇 |
2009年 | 72篇 |
2008年 | 91篇 |
2007年 | 91篇 |
2006年 | 61篇 |
2005年 | 69篇 |
2004年 | 61篇 |
2003年 | 38篇 |
2002年 | 54篇 |
2001年 | 55篇 |
2000年 | 39篇 |
1999年 | 56篇 |
1998年 | 196篇 |
1997年 | 116篇 |
1996年 | 78篇 |
1995年 | 48篇 |
1994年 | 42篇 |
1993年 | 59篇 |
1992年 | 36篇 |
1991年 | 38篇 |
1990年 | 35篇 |
1989年 | 33篇 |
1988年 | 36篇 |
1987年 | 30篇 |
1986年 | 33篇 |
1985年 | 29篇 |
1984年 | 41篇 |
1983年 | 29篇 |
1982年 | 21篇 |
1981年 | 35篇 |
1980年 | 14篇 |
1979年 | 24篇 |
1978年 | 24篇 |
1977年 | 30篇 |
1976年 | 49篇 |
1975年 | 20篇 |
1974年 | 21篇 |
1973年 | 18篇 |
排序方式: 共有2686条查询结果,搜索用时 31 毫秒
101.
Molly K. Reif Jennifer M. Wozencraft Lauren M. Dunkin Charlene S. Sylvester Christopher L. Macon 《Journal of Great Lakes research》2013
The U.S. Army Corps of Engineers (USACE) Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBTCX) collected its first airborne coastal mapping data on the Great Lakes in 1995. Since then, the JALBTCX has collected nearly 5 billion elevation and depth measurements and created over 2000 geographic information system (GIS) products for the shorelines of the Great Lakes. With improvements in airborne coastal mapping technology and the introduction of regional management for the USACE, surveys expanded into the regional scale, multi-sensor National Coastal Mapping Program (NCMP). The NCMP was initiated in 2004 to produce recurrent, regional, high-resolution light detection and ranging (lidar) elevation data and hyperspectral and aerial imagery to support regional sediment management, regulatory functions, flood damage reduction, asset management, emergency operations, and environmental stewardship. The JALBTCX is a collaboration among the USACE, the U.S. Naval Oceanographic Office (NAVOCEANO), and the National Oceanic and Atmospheric Administration (NOAA). The partners have worked together on airborne coastal mapping and charting since the late 1980s with the goal of advancing airborne lidar bathymetry and associated technologies. The collaboration has fielded three generations of airborne sensors and has transferred this technology to the commercial sector, supporting an expanding market for bathymetric lidar. The purpose of this paper is to provide an overview of the history of USACE survey efforts in the Great Lakes (1995–2012), an in-depth review of the resulting imagery and lidar data products, and new information product developments and applications to support environmental and coastal engineering throughout the Great Lakes region. 相似文献
102.
In this study, the authors examined parent-adolescent cortisol associations in 45 families with adolescent children (24 girls; M age = 15.78 years, SD = 1.44 years). Family members’ salivary cortisol levels were measured seven times a day on 2 typical weekdays. Family members provided reports of demographic and health variables, and adolescents rated parent-child relationship characteristics. After accounting for the effects of time of day and relevant demographic and health control variables on cortisol levels, hierarchical linear models indicated the presence of significant covariation over time in mother-adolescent cortisol (i.e., physiological synchrony). Furthermore, moderating tests revealed that mother-adolescent cortisol synchrony was strengthened among dyads characterized by mothers and adolescents spending more time together, and in families rated higher on levels of parent-youth shared activities and parental monitoring or supervision. Analysis of momentary characteristics indicated that maternal presence at the time of cortisol sampling lowered adolescent cortisol levels but did not account for mother-adolescent cortisol synchrony. Within-family physiological synchrony was amplified in momentary contexts of elevated maternal negative affect and elevated adolescent negative affect. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
S.P. Marshall S. Taylor C.R. Stone T.J. Davies R.F. Cracknell 《Combustion and Flame》2011,(10):1920-1932
The laminar burning velocity is a fundamental property of a fuel that affects many aspects of its combustion behaviour. Experimental values are required to validate kinetic simulations, and also to provide input for models of flashback, minimum ignition energy and turbulent combustion.A constant volume vessel (rated at 3.4 MPa) in conjunction with a multi-zone model was used to calculate burning velocity from pressure and schlieren data, allowing the user to select data uncorrupted by heat transfer or cellularity. Using the pressure rise data allows measurements to be derived for much higher pressures and temperatures than when the constant pressure data are used. A 12 term correlation for burning velocity was fitted to the data.n-Heptane, iso-octane, toluene, ethylbenzene and ethanol were tested over a wide range of initial pressures (50, 100, 200 and 400 kPa), temperatures (310, 380 and 450 K) and equivalence ratios (0.7–1.4), along with tests using combustion residuals at mole fractions of up to 0.3. The results compared favourably with the limited data already published, especially at high pressures. Conditions at the onset of cellularity are given for iso-octane. 相似文献
104.
Hirshfeld-Becker Dina R.; Masek Bruce; Henin Aude; Blakely Lauren Raezer; Pollock-Wurman Rachel A.; McQuade Julia; DePetrillo Lillian; Briesch Jacquelyn; Ollendick Thomas H.; Rosenbaum Jerrold F.; Biederman Joseph 《Canadian Metallurgical Quarterly》2010,78(4):498
Objective: To examine the efficacy of a developmentally appropriate parent–child cognitive behavioral therapy (CBT) protocol for anxiety disorders in children ages 4–7 years. Method: Design: Randomized wait-list controlled trial. Conduct: Sixty-four children (53% female, mean age 5.4 years, 80% European American) with anxiety disorders were randomized to a parent–child CBT intervention (n = 34) or a 6-month wait-list condition (n = 30). Children were assessed by interviewers blind to treatment assignment, using structured diagnostic interviews with parents, laboratory assessments of behavioral inhibition, and parent questionnaires. Analysis: Chi-square analyses of outcome rates and linear and ordinal regression of repeated measures, examining time by intervention interactions. Results: The response rate (much or very much improved on the Clinical Global Impression Scale for Anxiety) among 57 completers was 69% versus 32% (CBT vs. controls), p 相似文献
105.
A. Aguilar-Arevalo M. Blecher D.A. Bryman J. Comfort J. Doornbos L. Doria A. Hussein N. Ito S. Kettell L. Kurchaninov C. Malbrunot G.M. Marshall T. Numao R. Poutissou A. Sher B. Walker K. Yamada 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2009,609(2-3):102-105
An extension of the TRIUMF M13 low-energy pion channel designed to suppress positrons based on an energy-loss technique is described. A source of beam channel momentum calibration from the decay π+→e+ν is also described. 相似文献
106.
A practical localization technology for underground drift networks—such as those excavated in the practice of underground mining—has yet to become commercially available. This paper focuses on the problem of mapping GPS‐deprived underground environments with the eventual goal of using these maps for navigation. Recent industry‐directed work in the creation of a landmark‐bounded occupancy grid mapping tool that combines odometry, scanning laser data, and sporadically placed passive RFID tags is described. Unlike other work, the suggested approach holds the philosophy that precise localization of the actual landmark locations is not necessary; rather, landmarks serve as a global means for partitioning the map. Successful field experiments were conducted in two underground environments, with the results used to conduct a basic analysis of the described method. © 2012 Wiley Periodicals, Inc. 相似文献
107.
Abstract Strategic management was introduced as a critical component of Australian local government reform during the 1990s. In addition to encouraging efficiency and effectiveness of operation, it was also intended to promote participatory democracy within local authorities. The paper explores the extent to which this objective has been achieved through an analysis of twenty‐five New South Wales municipalities. Discussion concludes that while strategic management has enhanced community involvement in local governance, it cannot be a substitute for traditional democratic processes. 相似文献
108.
Rachel E. Brimelow Nicholas P. West Lauren T. Williams Allan W. Cripps 《Critical reviews in food science and nutrition》2017,57(8):1593-1602
Obesity is a strong predictive factor in the development of chronic disease and has now superseded undernutrition as a major public health issue. Chronic inflammation is one mechanism thought to link excess body weight with disease. Increasingly, the gut and its extensive population of commensal microflora are recognized as playing an important role in the development of obesity-related chronic inflammation. Obesity and a high fat diet are associated with altered commensal microbial communities and increased intestinal permeability which contributes to systemic inflammation as a result of the translocation of lipopolysaccharide into the circulation and metabolic endotoxemia. Various milk proteins are showing promise in the prevention and treatment of obesity and chronic low-grade inflammation via reductions in visceral fat, neutralization of bacteria at the mucosa and reduced intestinal permeability. In this review, we focus on evidence supporting the potential antiobesogenic and anti-inflammatory effects of bovine whey-derived lactoferrin and immunoglobulins. 相似文献
109.
Researchers and practitioners have long utilized a variety of penetrometers to investigate the snowpack. Identifying definitive relationships between penetrometer-derived microstructural information and stability has been challenging. The purpose of this study is two-fold: 1. We propose a simple field test to establish relationships between load and penetrometer-derived microstructural estimates, 2. We utilize the SnowMicroPen (SMP) to quantify changes in weak layer residual strength and microstructural dimension associated with an artificial loading event. Our dataset is from Moonlight Basin, Montana and includes three modified loaded-column tests, each paired with 5 SMP profiles. Depth hoar comprised the targeted weak layer. Results indicate that loading caused the residual strength and rupture frequency to decrease significantly. Much like a compression test at a micro-scale, the force required for the SMP to rupture individual structures as well as the micro-scale strength decreased significantly when the slab stress was increased by artificially adding blocks of snow. A decrease in observed rupture frequency within the weak layer (or an increase in the distance between ruptured structures) also occurred after the loading event, probably because some structures within the weak layer had already failed or were so close to failing that the penetrometer could not detect their rupture. Due in part to the large difference in loads, microstructural differences between the natural and loaded columns were significant enough that only one profile would have been necessary to determine a significant difference in residual strength. Artificial removal of slab stress resulted in greater rupture forces and larger microstructures, likely due to elastic rebound. 相似文献
110.