首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4960篇
  免费   375篇
  国内免费   278篇
电工技术   164篇
综合类   387篇
化学工业   210篇
金属工艺   136篇
机械仪表   269篇
建筑科学   791篇
矿业工程   427篇
能源动力   90篇
轻工业   349篇
水利工程   120篇
石油天然气   826篇
武器工业   38篇
无线电   203篇
一般工业技术   759篇
冶金工业   121篇
原子能技术   22篇
自动化技术   701篇
  2024年   16篇
  2023年   35篇
  2022年   113篇
  2021年   121篇
  2020年   134篇
  2019年   138篇
  2018年   101篇
  2017年   139篇
  2016年   185篇
  2015年   194篇
  2014年   301篇
  2013年   297篇
  2012年   362篇
  2011年   388篇
  2010年   271篇
  2009年   261篇
  2008年   272篇
  2007年   341篇
  2006年   308篇
  2005年   253篇
  2004年   205篇
  2003年   207篇
  2002年   174篇
  2001年   134篇
  2000年   139篇
  1999年   121篇
  1998年   91篇
  1997年   85篇
  1996年   58篇
  1995年   41篇
  1994年   40篇
  1993年   18篇
  1992年   13篇
  1991年   8篇
  1990年   11篇
  1989年   4篇
  1988年   4篇
  1987年   1篇
  1986年   3篇
  1985年   5篇
  1984年   3篇
  1983年   4篇
  1982年   3篇
  1981年   3篇
  1980年   5篇
  1979年   2篇
  1956年   1篇
排序方式: 共有5613条查询结果,搜索用时 15 毫秒
1.
洛钼集团矿山公司三道庄矿区由于历史原因,露天开采境界地下内存在的采空区已危及矿山公司的正常安全生产,阻碍了洛钼集团可持续发展。为解决这一重大问题,经过充分调研和多方论证,认为深孔一次爆破成井技术是解决此类采空区难题唯一的经济上合理、技术可行、安全可靠的手段与途径。深孔爆破成井实现与采空区顶板的贯通,使采空区边岩稳定,顶岩暴露面积缩小,确保了采空区的稳定;保证了台阶正常推进。  相似文献   
2.
For decades now, Douglas Crimp’s landmark 1980 essay ‘The Photographic Activity of Postmodernism’ has shaped our understanding of modernism’s aftermath, at least as it unfolded in North America and Western Europe. Less remembered, however, is the degree to which the procedures of disjunction, copying, appropriation, and outright theft that he highlighted were epitomised not just by contemporary photography, but by photomontage in particular. This article recovers the debates that led critics such as Crimp, Abigail Solomon-Godeau, Christopher Phillips, Benjamin Buchloh and others to turn to photomontage as one of their principal objects of concern in what became known as the postmodern critique of photography. Why was montage tasked to perform this critical function, particularly by people around the journal October who had not otherwise devoted the balance of their writing to photography’s history? The article suggests that these men and women, along with the contemporary artists they foregrounded, manifested what Mary Anne Doane has called a ‘desire for signification’, a reaction in the late 1970s against the mute theatricality of minimalist and conceptual art. Photomontage reintroduced representation to contemporary art and to the canon of art history. But unlike the reemerging illusionism in painting that also manifested this desire, montage guarded against an uncomplicated realism by highlighting and critiquing operations of representation in a manner that painting no longer could.  相似文献   
3.
就经典分水岭图像分割算法中存在的过分割问题,提出一种结合位图切割和区域合并的彩色图像分割算法。对原始彩色图像通过空域梯度算子求其梯度图像,并利用位图切割重建梯度图像;对新梯度图像进行分水岭预分割;对预分割图像基于异质性最小原则进行区域合并,并获得最终分割结果。相比于现有的同类方法,该算法引入位图切割,抑制噪声对分割结果的影响,在边缘模糊处分割准确,得到符合人类视觉的较小分割区域数目,同时在运行效率上提高。  相似文献   
4.
Drunk drivers are a menace to themselves and to other road users, as drunk driving significantly increases the risk of involvement in road accidents and the probability of severe or fatal injuries. Although injuries and fatalities related to road accidents have decreased in recent decades, the prevalence of drunk driving among drivers killed in road accidents has remained stable, at around 25% or more during the past 10 years. Understanding drunk driving, and in particular, recidivism, is essential for designing effective countermeasures, and accordingly, the present study aims at identifying the differences between non-drunk drivers, drunk driving non-recidivists and drunk driving recidivists with respect to their demographic and socio-economic characteristics, road accident involvement and other traffic and non-traffic-related law violations. This study is based on register-data from Statistics Denmark and includes information from 2008 to 2012 for the entire population, aged 18 or older, of Denmark. The results from univariate and multivariate statistical analyses reveal a five year prevalence of 17% for drunk driving recidivism, and a significant relation between recidivism and the drunk drivers’ gender, age, income, education, receipt of an early retirement pension, household type, and residential area. Moreover, recidivists are found to have a higher involvement in alcohol-related road accidents, as well as other traffic and, in particular, non-traffic-related offences. These findings indicate that drunk driving recidivism is more likely to occur among persons who are in situations of socio-economic disadvantage and marginalisation. Thus, to increase their effectiveness, preventive measures aiming to reduce drunk driving should also address issues related to the general life situations of the drunk driving recidivists that contribute to an increased risk of drunk driving recidivism.  相似文献   
5.
The 2011 AASHTO Roadside Design Guide (RDG) contains perhaps the most widely used procedure for choosing an appropriate length of need (LON) for roadside barriers. However, this procedure has several limitations. The procedure uses a highly simplified model of vehicle departure, and the procedure does not allow designers to specify an explicit level of protection. A new procedure for choosing LON that addresses these limitations is presented in this paper. This new procedure is based on recent, real-world road departure trajectories and uses this departure data in a more realistic way. The new procedure also allows LON to be specified for a precisely known level of protection – a level which can be based on number of crashes, injury outcomes or even estimated crash cost – while still remaining straightforward and quick to use like the 2011 RDG procedure.  相似文献   
6.
ObjectiveTraffic collisions yield a substantial rate of morbidity and injury among child-pedestrians. We explored the formation of an innovative hazard perception training intervention – Child-pedestrians Anticipate and Act Hazard Perception Training (CA2HPT). Training was based upon enhancing participants’ ability to anticipate potential hazards by exposing them to an array of traffic scenes viewed from different angles.MethodTwenty-four 7–9-year-olds have participated. Trainees underwent a 40-min intervention of observing typical residential traffic scenarios in a simulated dome projection environment while engaging in a hazard detection task. Trainees were encouraged to note differences between the scenarios presented to them from separate angles (a pedestrian's point-of-view and a higher perspective angle). Next, trainees and control group members were required to perform crossing decision tasks.ResultsTrainees were found to be more aware of potential hazards related to restricted field of view relative to control.ConclusionsChild pedestrians are responsive to training and actively detecting materialized hazards may enrich child-pedestrians’ ability to cross roads.  相似文献   
7.
Simulating the psychological experience of human vision,a road extraction model based on the format tower is proposed to extract the road in the high resolution remote sensing image from the perspective of morphology.Firstly,based on the spectral and texture information,the suspected road targets are extracted by using segmentation technology.Then these targets are classified according to their reliability and extract the road targets for each category.Finally,three types of identified road information are verified and merged,and the continuous smooth road extraction results are obtained.Experiments on real high resolution images show that the results are consistent with the visual perception of the human eye,and the overall classification accuracy is higher,indicating that the algorithm is effective and feasible and has good use value.  相似文献   
8.
李永胜 《石油仪器》2006,20(5):35-36
目前油田相当一部分产液井产液量相对较低,井下含水率高。这些特点给油井找水工作增加了很大难度,必然要求测试仪器具有适用于高含水率、低产液量的特点。取样式环空找水组合测井仪与常规过流式仪器相比,有着独特的优势,测量含水时不受井筒内流体的流速和抽油机冲程波动的影响。仪器含水测量精度可达到±5%以内,极大地提高了含水参数资料录取的准确性,对油田动态监测具有重要意义。  相似文献   
9.
沥青混合料的使用性能与试验方法对保证和提高沥青路面的修建质量非常重要。在使用荷载、自然因素对沥青路面作用分析的基础上,对沥青混合料的温度稳定性、耐久性、抗滑性及施工的和易性等方面进行了系统的分析探讨,提出了相关的性能要求与试验评价方法。  相似文献   
10.
This article introduces a special section on the use of taxometrics to examine the categorical versus the dimensional structure of various forms of psychopathology. Paving the way into the special section, this introduction briefly describes 3 taxometric methods--mean above minus below a sliding cut (MAMBAC), maximum covariation (MAXCOV), and maximum eigenvalue (MAXEIG)--and discusses possible threats to statistical conclusion validity that often emerge when such techniques are applied in psychopathology research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号