全文获取类型
收费全文 | 31203篇 |
免费 | 2340篇 |
国内免费 | 1267篇 |
专业分类
电工技术 | 2098篇 |
技术理论 | 6篇 |
综合类 | 2401篇 |
化学工业 | 1935篇 |
金属工艺 | 294篇 |
机械仪表 | 1110篇 |
建筑科学 | 6734篇 |
矿业工程 | 2602篇 |
能源动力 | 891篇 |
轻工业 | 4257篇 |
水利工程 | 2749篇 |
石油天然气 | 1323篇 |
武器工业 | 343篇 |
无线电 | 995篇 |
一般工业技术 | 2238篇 |
冶金工业 | 1067篇 |
原子能技术 | 978篇 |
自动化技术 | 2789篇 |
出版年
2024年 | 141篇 |
2023年 | 389篇 |
2022年 | 888篇 |
2021年 | 1116篇 |
2020年 | 1102篇 |
2019年 | 774篇 |
2018年 | 780篇 |
2017年 | 883篇 |
2016年 | 1066篇 |
2015年 | 1115篇 |
2014年 | 2787篇 |
2013年 | 2044篇 |
2012年 | 2767篇 |
2011年 | 2520篇 |
2010年 | 2014篇 |
2009年 | 1895篇 |
2008年 | 1791篇 |
2007年 | 2157篇 |
2006年 | 1828篇 |
2005年 | 1424篇 |
2004年 | 1155篇 |
2003年 | 1029篇 |
2002年 | 768篇 |
2001年 | 557篇 |
2000年 | 431篇 |
1999年 | 316篇 |
1998年 | 212篇 |
1997年 | 185篇 |
1996年 | 121篇 |
1995年 | 112篇 |
1994年 | 87篇 |
1993年 | 82篇 |
1992年 | 48篇 |
1991年 | 36篇 |
1990年 | 28篇 |
1989年 | 34篇 |
1988年 | 32篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1985年 | 19篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1959年 | 6篇 |
1955年 | 2篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Well-planted and maintained landscaping can help reduce driving stress, provide better visual quality, and decrease over speeding, thus improving roadway safety. Florida Department of Transportation (FDOT) Standard Index (SI-546) is one of the more demanding standards in the U.S. for landscaping design criteria at highway medians near intersections. The purposes of this study were to (1) empirically evaluate the safety results of SI-546 at unsignalized intersections and (2) quantify the impacts of geometrics, traffic, and landscaping design features on total crashes and injury plus fatal crashes. The studied unsignalized intersections were divided into (1) those without median trees near intersections, (2) those with median trees near intersections that were compliant with SI-546, and (3) those with median trees near intersections that were non-compliant with SI-546. A total of 72 intersections were selected, for which five-year crash data from 2006–2010 were collected.The sites that were compliant with SI-546 showed the best safety performance in terms of the lowest crash counts and crash rates. Four crash predictive models—two for total crashes and two for injury crashes—were developed. The results indicated that improperly planted and maintained median trees near highway intersections can increase the total number of crashes and injury plus fatal crashes at a 90% confidence level; no significant difference could be found in crash rates between sites that were compliant with SI-546 and sites without trees. All other conditions remaining the same, an intersection with trees that was not compliant with SI-546 had 63% more crashes and almost doubled injury plus fatal crashes than those at intersections without trees. The study indicates that appropriate landscaping in highway medians near intersections can be an engineering technology that not only improves roadway environmental quality but also maintains intersection safety. 相似文献
992.
蒸汽发生器制造过程中对管板进行深孔钻时,发生管板孔桥超差。管板二次侧的3个管孔C165-R59、C167-R59、C168-R58不能满足设计要求,管板一次侧的这些管孔满足设计要求。针对该不符合项,核审评单位联合蒸汽发生器制造单位和设计单位,从管板的强度、管板孔桥超差不符合项对流致振动的影响、堵管后的传热管应力分析、传热管堵管的压差对孔桥强度的影响、孔桥超差导致的传热管接触磨损等角度进行了结构安全性分析。分析结果表明,目前的堵管方案合理可行,但需加强在役阶段的跟踪检查,以保证修复的可靠性和质量。 相似文献
993.
《Food Control》2014
Aflatoxins are common contaminants of staple crops, such as corn and groundnuts, and a significant cause of concern for food safety and public health in developing countries. Aflatoxin B1 (AFB1) has been implicated in the etiology of acute and chronic disease in humans and animals, including growth stunting, liver cancer and death. Cost effective and culturally acceptable intervention strategies for the reduction of dietary AFB1 exposure are of critical need in populations at high risk for aflatoxicosis. Fermented gruels consisting of cornmeal are a common source for such exposure and are consumed by both children and adults in many countries with a history of frequent, high-level aflatoxin exposure. One proposed method to reduce aflatoxins in the diet is to include a selective enterosorbent, Uniform Particle Size NovaSil (UPSN), as a food additive in contaminated foods. For UPSN to be effective in this capacity, it must be stable in complex, acidic mixtures that are often exposed to heat during the process of fermented gruel preparation. Therefore, the objective of the present study was to test the ability of UPSN to sorb aflatoxin while common cooking conditions were applied. The influence of fermentation, heat treatment, acidity, and processing time were investigated with and without UPSN. Analyses were performed using the field-practical Vicam assay with HPLC verification of trends. Our findings demonstrated that UPSN significantly reduced aflatoxin levels (47–100%) in cornmeal, regardless of processing conditions. Upon comparison of each element tested, time appeared to be the primary factor influencing UPSN efficacy. The greatest decreases in AFB1 were reported in samples allowed to incubate (with or without fermentation) for 72 h. This data suggests that addition of UPSN to staple corn ingredients likely to contain aflatoxins would be a sustainable approach to reduce exposure. 相似文献
994.
《Journal of Nuclear Science and Technology》2013,50(11):824-835
Massive ingress of air into the core of a high-temperature gas cooled reactor is among the accidents with a low occurrence frequency, but there are still gaps in understanding with respect to its consequences. In the present paper, massive air ingress combined with a delayed start of the afterheat removal system is investigated and compared to air ingress, accidents with normal operation of the afterheat removal procedure. A computer programme REACT/THERMIX used for these accident analyses is described. For a high-temperature gas cooled reactor with a pebble bed core, it is shown that massive air ingress has no real safety endangering consequences even if the operation of the afterheat removal system is delayed by 6 h. 相似文献
995.
分析了广西小型水库工程存在的年久失修,分布分散,资金、人才缺乏,责权利不清等共性问题,并提出了相应的资金、人才和管护模式等对策。 相似文献
996.
997.
本文对建筑施工企业安全管理问题进行了研究,并制定了相应的对策来解决这些问题,希望能为广大的建筑施工企业管理者提供一些参考。 相似文献
998.
999.
This paper explores the similarities and differences between bicycle and motorcycle crashes with other motor vehicles. If similar treatments can be effective for both bicycle and motorcycle crashes, then greater benefits in terms of crash costs saved may be possible for the same investment in treatments. To reduce the biases associated with under-reporting of these crashes to police, property damage and minor injury crashes were excluded. The most common crash type for both bicycles (31.1%) and motorcycles (24.5%) was intersection from adjacent approaches. Drivers of other vehicles were coded most at fault in the majority of two-unit bicycle (57.0%) and motorcycle crashes (62.7%). The crash types, patterns of fault and factors affecting fault were generally similar for bicycle and motorcycle crashes. This confirms the need to combat the factors contributing to failure of other drivers to yield right of way to two-wheelers, and suggest that some of these actions should prove beneficial to the safety of both motorized and non-motorized two-wheelers. In contrast, child bicyclists were more often at fault, particularly in crashes involving a vehicle leaving the driveway or footpath. The greater reporting of violations by riders and drivers in motorcycle crashes also deserves further investigation. 相似文献
1000.
For safety issues related to the storage of gases (e.g. hydrogen) under high pressure, it is necessary to determine how the gas is released in the case of failure. In particular, there exist limited quantitative information on the near-field properties of gas jets, which are important for establishing proper decay laws in the far-field. Simulations of the near-field of highly underexpanded (high pressure) gas jets have been performed using Finite-Volume solver of the CAST3M code and validated using several sources available in the literature. The numerical model solves the 3D Compressible Multi-Component Navier–Stokes equations directly without relying on the compressibility-corrected turbulence models. It provides sufficiently fair mean predictions both in the case of one-component air–air and two-component helium-air releases. Possible initial conditions for the far-field simulations are suggested in terms of distance from the source, as well as the turbulence characteristics and gas-dynamic parameters at this location. In addition, these results are used to evaluate several notional nozzle concepts in order to determine the one physically consistent. 相似文献