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   200篇
  免费   5篇
电工技术   18篇
化学工业   55篇
金属工艺   6篇
机械仪表   10篇
建筑科学   26篇
矿业工程   2篇
能源动力   4篇
轻工业   6篇
石油天然气   2篇
无线电   13篇
一般工业技术   20篇
冶金工业   21篇
原子能技术   1篇
自动化技术   21篇
  2022年   2篇
  2021年   5篇
  2020年   2篇
  2019年   22篇
  2018年   4篇
  2017年   5篇
  2016年   3篇
  2015年   3篇
  2014年   3篇
  2013年   14篇
  2012年   2篇
  2011年   6篇
  2009年   2篇
  2008年   2篇
  2006年   6篇
  2005年   3篇
  2004年   4篇
  2003年   5篇
  2001年   5篇
  2000年   3篇
  1998年   3篇
  1996年   3篇
  1995年   3篇
  1994年   2篇
  1993年   2篇
  1992年   2篇
  1991年   5篇
  1988年   3篇
  1987年   2篇
  1986年   4篇
  1984年   3篇
  1983年   2篇
  1982年   3篇
  1981年   6篇
  1980年   3篇
  1979年   2篇
  1978年   4篇
  1977年   4篇
  1976年   3篇
  1975年   4篇
  1974年   4篇
  1973年   4篇
  1968年   4篇
  1967年   2篇
  1955年   2篇
  1930年   3篇
  1924年   2篇
  1921年   1篇
  1920年   1篇
  1919年   2篇
排序方式: 共有205条查询结果,搜索用时 0 毫秒
31.
A simple synthetic route is developed to achieve gold functionalized radial mesoporous silica nanoparticles (Au‐MsNP) synthesized by a one step procedure fully compatible with basic conditions required for the preparation of monodispersed nanospheres. In a second step, Au‐MsNP particles have been coated with phospholipid bilayers in order to design an advanced biofunctional platform with the gold metallic nanoparticles previously grown into the pore channels and responsible for a plasmonic activity relevant for biosensing. The size of Au‐MsNP is checked by dynamic light scattering while zeta potential measurements reflect their surface charge. The particle morphology is characterized by transmission and scanning electron microscopy and the Si/Au ratios are obtained from energy dispersive X‐ray analysis. The textural properties of Au‐MsNP, specific surface area and pore size, are determined from N2 adsorption. The supported bilayers are achieved from vesicles of different phospholipids incubated with Au‐MsNP particles. The coating efficiency is investigated by zeta potential and cryo‐ transmission electron microscopy. The plasmonic activities of bare Au‐MsNP particles and coated lipid bilayer Au‐MsNP platform are evidenced for two model systems: direct adsorption of bovine serum albumin and molecular recognition events between avidin molecules and biotin receptors integrated in the supported lipid bilayer.  相似文献   
32.

Background

This study sets out to identify risk factors for post-traumatic stress disorder (PTSD) after a road traffic accident with a view to improving prevention.

Methods

The study used a prospective cohort of road traffic accident casualties. All subjects over 15 years of age were recruited in the course of an interview conducted while they were receiving care in a hospital of the Rhône area administrative département. Six months after their accident, they answered a self-administered postal questionnaire that included the Post-traumatic Check-List Scale (PCLS) in order to evaluate PTSD. Multivariate logistic regression analysis was conducted to compare those subjects with a PCLS score of 44 or over with those with a lower score, in order to identify factors that might be associated with PTSD.

Results

592 subjects (out of 1168) returned the 6-month questionnaire and 541 completed the PCLS test. One hundred subjects had a PCLS score ≥44, suggesting PTSD, and 441 subjects did not. The factors associated with PTSD were initial injury severity, post-traumatic amnesia, the feeling of not being responsible for their accident and persistent pain 6 months after it. A lower odds-ratio was associated with users of two-wheel than four-wheel motor vehicles (OR = 0.4; 0.2–0.9).

Conclusion

Besides predictive factors for PTSD (injury severity, post-traumatic amnesia and the feeling of not being responsible for their accident), our study suggested a reduced risk of PTSD among two-wheel motor vehicle users.  相似文献   
33.
Biological cells are complex in both morphological and biochemical structure. The effects of cellular fine structure on light scattered from cells are studied by employing a three-dimensional code named AETHER which solves the full set of Maxwell equations by using the finite-difference time-domain method. It is shown that changes in cellular fine structure can cause significant changes in the scattered light pattern over particular scattering angles. These changes potentially provide the possibility for distinguishability of cellular intrastructures. The effects that features of different intrastructure have on scattered light are discussed from the viewpoint of diagnosing cellular fine structure. Finally, we discuss scattered light patterns for lymphocyte-like cells and basophil-like cells.  相似文献   
34.
Changes in projects are common and may be deleterious or beneficial—whether you see a change as a conflict or a valuable lesson depends only on your prospective. Project changes affect the cost, the scheduling, and the duration of projects, both directly and indirectly. Despite many articles and much discussion in practice and academic literature, there is a lack of information about systematic approaches to manage project change. This paper introduces a comprehensive project change management system that is founded on five principles: (1) promote a balanced change culture; (2) recognize change; (3) evaluate change; (4) implement change; and (5) continuously improve from lessons learned. By applying this project change management system, project participants can minimize deleterious change and promote beneficial change.  相似文献   
35.
    
This paper proposes a novel grading method of apples, in an automated grading device that uses convolutional neural networks to extract the size, color, texture, and roundness of an apple. The developed machine learning method uses the ability of learning representative features by means of a convolutional neural network (CNN), to determine suitable features of apples for the grading process. This information is fed into a one-to-one classifier that uses a support vector machine (SVM), instead of the softmax output layer of the CNN. In this manner, Yantai apples with similar shapes and low discrimination are graded using four different approaches. The fusion model using both CNN and SVM classifiers is much more accurate than the simple k-nearest neighbor (KNN), SVM, and CNN model when used separately for grading, and the learning ability and the generalization ability of the model is correspondingly increased by the combined method. Grading tests are carried out using the automated grading device that is developed in the present work. It is verified that the actual effect of apple grading using the combined CNN-SVM model is fast and accurate, which greatly reduces the manpower and labor costs of manual grading, and has important commercial prospects.  相似文献   
36.
以十二烷基磺酸钠为例,考察了利用电位滴定方法分析ASP三元复合驱采出液中表面活性剂浓度时,pH值、盐度、聚合物含量、石油酸皂浓度等因素对分析结果的影响,研究出因石油酸皂和聚合物的存在导致结果偏高的消除方法,并对方法的检出限进行研究。该方法为ASP三元驱中十二烷基磺酸钠类阴离子表面活性剂浓度的分析提供了参考。  相似文献   
37.
    
In constrained motion control of a robot, the interaction force is an important variable, which directly describes the state of interaction. It is required in a number of algorithms for interaction control. Desirably, the interaction force has to be measured by force sensors. However, there are inherent limitations with force sensors, such as the cost, sensing noise, limited bandwidth, and the difficulty of physical location at the required place, which is dynamic. In the present paper, the interaction force is estimated by using high order sliding mode observers. An adaptive version of a high order sliding mode observer is developed to robustly reconstruct the interaction force. Experimental results are given to show the effectiveness of the developed algorithms.  相似文献   
38.
为了提高超宽带雷达生命信号检测准确率,提出了一种改进型YOLOV3检测算法。考虑到超宽带雷达探测的人体呼吸信号成像后宽高相差较大,采用多尺度训练时网络对宽高的敏感程度不一样,因此在设计损失函数时,对宽高损失给予不同的权重系数。为了提高网络通道以及空间特征表达能力,使得网络能够扩大对目标特征区域的感知范围,因此将通道注意力与空间注意力结构(CBAM)嵌入到YOLOV3基础网络Darknet53的每个shortcut层,得到CBAM-YOLOV3网络结构。对比改进前后的算法。实验结果表明,改进后的算法在IoU阈值为0.5时,mAP为98.09%,提升3.90%,在阈值为0.75时,mAP为76.49%,提升16.48%。  相似文献   
39.
Study of the equilibrium phase behavior of systems containing water, triolein and secondary alcohol ethoxylates showed that a D or microemulsion phase, which solubilized significant amounts of triolein, formed at temperatures as low as 25°C when the surfactant was a suitable mixture of TERGITOL 15-S-3 and 15-S-5 (Union Carbide, Charleston, WV) with average ethylene oxide numbers of 3 and 5, respectively. In previous work with pure C12 linear ethoxylates and triolein, the D phase had formed only at temperatures above about 55°C. Based on the earlier studies, formation of the D phase would be expected to improve soil removal from synthetic fabrics by a solubilization-emulsification mechanism. When sufficient oleyl alcohol was mixed with triolein, the D phase was observed at 25°C with Tergitol 15-S-5 alone. Observation of dynamic behavior in this system for triolein-oleyl alcohol drops injected into surfactant-water mixtures revealed that intermediate phases frequently formed near the drop surfaces and that considerable spontaneous emulsification of triolein occurred for appropriate drop compositions. Experiments with drops initially attached to individual polyester fibers confirmed that little oil remained on the fibers when emulsification was extensive. This mechanism involving spontaneous emulsification provides a means for soil removal different from that found previously in other systems, where the soil was solubilized into an intermediate phase, and this phase was emulsified by externally imposed agitation.  相似文献   
40.
Recent satellite image processing developments have provided the means to calculate evapotranspiration (ET) as a residual of the surface energy balance to produce ET “maps.” These ET maps (i.e., images) provide the means to quantify ET on a field by field basis in terms of both the rate and spatial distribution. The ET images show a progression of ET during the year or growing season as well as its spatial distribution. The mapping evapotranspiration at high resolution with internalized calibration (METRIC) is a satellite-based image-processing procedure for calculating ET. METRIC has been applied with high resolution Landsat images in southern Idaho, southern California, and New Mexico to quantify monthly and seasonal ET for water rights accounting, operation of ground water models, and determination of crop coefficient populations and mean curves for common crops. Comparisons between ET by METRIC, ET measured by lysimeter, and ET predicted using traditional methods have been made on a daily and monthly basis for a variety of crop types and land uses. Error in estimated growing season ET was 4% for irrigated meadow in the Bear River basin of Idaho and 1% for an irrigated sugar beet crop near Kimberly, Id. Standard deviation of error for time periods represented by each satellite image averaged about 13 to 20% in both applications. The results indicate that METRIC and similar methods such as SEBAL hold substantial promise as efficient, accurate, and inexpensive procedures to estimate actual evaporation fluxes from irrigated lands throughout growing seasons.  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