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   516篇
  免费   15篇
电工技术   4篇
化学工业   99篇
金属工艺   2篇
机械仪表   4篇
建筑科学   19篇
能源动力   13篇
轻工业   49篇
石油天然气   3篇
无线电   16篇
一般工业技术   59篇
冶金工业   191篇
原子能技术   2篇
自动化技术   70篇
  2023年   7篇
  2022年   10篇
  2021年   10篇
  2020年   7篇
  2019年   14篇
  2018年   6篇
  2017年   3篇
  2016年   3篇
  2015年   11篇
  2014年   11篇
  2013年   23篇
  2012年   18篇
  2011年   21篇
  2010年   21篇
  2009年   17篇
  2008年   18篇
  2007年   27篇
  2006年   15篇
  2005年   19篇
  2004年   16篇
  2003年   17篇
  2002年   15篇
  2001年   8篇
  2000年   7篇
  1999年   7篇
  1998年   13篇
  1997年   9篇
  1996年   14篇
  1995年   10篇
  1994年   10篇
  1993年   6篇
  1992年   5篇
  1991年   6篇
  1990年   10篇
  1989年   7篇
  1988年   6篇
  1987年   5篇
  1986年   5篇
  1985年   3篇
  1984年   6篇
  1983年   11篇
  1982年   9篇
  1981年   8篇
  1980年   5篇
  1979年   7篇
  1978年   3篇
  1977年   7篇
  1976年   6篇
  1962年   3篇
  1946年   2篇
排序方式: 共有531条查询结果,搜索用时 498 毫秒
101.
A technique to study nanowire growth processes on locally heated microcantilevers in situ in a transmission electron microscope has been developed. The in situ observations allow the characterization of the nucleation process of silicon wires, as well as the measurement of growth rates of individual nanowires and the ability to observe the formation of nanowire bridges between separate cantilevers to form a complete nanowire device. How well the nanowires can be nucleated controllably on typical cantilever sidewalls is examined, and the measurements of nanowire growth rates are used to calibrate the cantilever‐heater parameters used in finite‐element models of cantilever heating profiles, useful for optimization of the design of devices requiring local growth.  相似文献   
102.
Objective: Despite proven efficacy of cognitive behavioral therapy (CBT) for treating eating disorders with binge eating as the core symptom, few patients receive CBT in clinical practice. Our blended efficacy–effectiveness study sought to evaluate whether a manual-based guided self-help form of CBT (CBT-GSH), delivered in 8 sessions in a health maintenance organization setting over a 12-week period by master's-level interventionists, is more effective than treatment as usual (TAU). Method: In all, 123 individuals (mean age = 37.2; 91.9% female, 96.7% non-Hispanic White) were randomized, including 10.6% with bulimia nervosa (BN), 48% with binge eating disorder (BED), and 41.4% with recurrent binge eating in the absence of BN or BED. Baseline, posttreatment, and 6- and 12-month follow-up data were used in intent-to-treat analyses. Results: At 12-month follow-up, CBT-GSH resulted in greater abstinence from binge eating (64.2%) than TAU (44.6%; number needed to treat = 5), as measured by the Eating Disorder Examination (EDE). Secondary outcomes reflected greater improvements in the CBT-GSH group in dietary restraint (d = 0.30); eating, shape, and weight concern (ds = 0.54, 1.01, 0.49, respectively; measured by the EDE Questionnaire); depression (d = 0.56; Beck Depression Inventory); and social adjustment (d = 0.58; Work and Social Adjustment Scale), but not weight change. Conclusions: CBT-GSH is a viable first-line treatment option for the majority of patients with recurrent binge eating who do not meet diagnostic criteria for BN or anorexia nervosa. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
103.
Objective: Adoption of effective treatments for recurrent binge-eating disorders depends on the balance of costs and benefits. Using data from a recent randomized controlled trial, we conducted an incremental cost-effectiveness analysis (CEA) of a cognitive–behavioral therapy guided self-help intervention (CBT–GSH) to treat recurrent binge eating compared to treatment as usual (TAU). Method: Participants were 123 adult members of an HMO (mean age = 37.2 years, 91.9% female, 96.7% non-Hispanic White) who met criteria for eating disorders involving binge eating as measured by the Eating Disorder Examination (C. G. Fairburn & Z. Cooper, 1993). Participants were randomized either to treatment as usual (TAU) or to TAU plus CBT–GSH. The clinical outcomes were binge-free days and quality-adjusted life years (QALYs); total societal cost was estimated using costs to patients and the health plan and related costs. Results: Compared to those receiving TAU only, those who received TAU plus CBT–GSH experienced 25.2 more binge-free days and had lower total societal costs of $427 over 12 months following the intervention (incremental CEA ratio of ?$20.23 per binge-free day or ?$26,847 per QALY). Lower costs in the TAU plus CBT–GSH group were due to reduced use of TAU services in that group, resulting in lower net costs for the TAU plus CBT group despite the additional cost of CBT–GSH. Conclusions: Findings support CBT–GSH dissemination for recurrent binge-eating treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
104.
This study examined the association of sociodemographic characteristics and smoking behaviors (i.e., cigarette, cigar, and waterpipe) with nicotine product harm perception in college freshmen. Students were asked to compare the perceived harmfulness of 11 nicotine-delivering products with that of a regular cigarette. Data were from a cross-sectional Internet survey conducted during the spring 2004 semester at a private university (N = 411). Binomial logistic regression was used to determine the association between sociodemographic and behavioral factors with nicotine product harm perception. A statistically significant association was found between nicotine product harm perception and sex, race, income, citizenship, and smoking behavior (p< or =.05). Regarding the three medicinal nicotine replacement therapies, 19.6% of respondents incorrectly perceived the nicotine patch to be as harmful as or more harmful than a regular cigarette; corresponding values were 24.1% for nicotine gum and 52.9% for nicotine inhaler. Respondents incorrectly perceived the following smoked tobacco products to be less harmful than regular cigarettes: ultra-light cigarettes (40.4%), waterpipe (37%), light cigarettes (35.2%), cigarillos (17.4%), and cigars (16.9%). Regarding smokeless nicotine products, 89.3% of respondents incorrectly perceived dip and chew to be as harmful as or more harmful than regular cigarettes; corresponding values were 36.2% for nicotine lollipops and 35.2% for nicotine water. Our findings reveal misperceptions about nicotine product harmfulness and underscore the importance of developing a science base to inform policies and educate consumers about these products.  相似文献   
105.
Three groups of 15 female pigs were fed diets containing 0.8%, 1.1%, or 1.8% linoleic acid from 20 to 35 kg followed by 1.0%, 1.2% or 1.4% linoleic acid respectively from 35 kg to slaughter at 85 kg live-weight. Pigs grew at similar rates on all three diets and had similar proportions of carcass fat. The mean proportions of linoleic acid in the backfat lipids were 8.6%, 11.0%, and 13.9% respectively as the amount of the diet increased. There was a significant correlation between the concentration of linoleic acid in the inner backfat lipid and P2 backfat thickness for those animals on the high and medium linoleic acid diets but not for those on the low diet. Backfat from pigs fed the high linoleic acid diet was softer than that from the other two groups of pigs which could not be distinguished using the subjective finger probe method. Using a mechanical probe backfat consistency was distinguished between all three groups and was inversely correlated (r=?0.775, P<0.001) with the concentration of linoleic acid in the lipid. However, none of the pigs had fat which was too soft for bacon production based on either consistency data or linoleic acid content. If 15% linoleic acid is taken to be the maximum acceptable in bacon, then extrapolation of the regression of linoleic acid concentration on backfat thickness suggested that only the 1.4% linoleic acid diet is likely to result in unacceptably soft fat as pigs become leaner. However, this high concentration, although frequently present in current feeds, is not necessary since it is twice that recommended for normal growth and development of pigs.  相似文献   
106.
In a commercial process for the production of moisture-enhanced pork, boneless pork loins were conveyed through a recirculating injection apparatus, and brine (sodium phosphate, sodium chloride, and lemon juice solids) was pumped into the meat through banks of needles inserted automatically into the upper surfaces of cuts. Brine samples were collected at intervals during the production process and analyzed to determine the total plate count and the numbers of lactic acid bacteria, pseudomonads, Brochothrix thermosphacta, and Enterobacteriaceae. Listeria monocytogenes numbers in the brine were determined using a PCR with primers for the hemolysin gene in combination with a most probable numbers determination. Maximum numbers of bacteria (log CFU/ml) recovered from the brine after 2.5 h of recirculation were as follows: total plate count, 4.50; lactic acid bacteria, 2.99; pseudomonads, 3.95; B. thermosphacta, 2.79; and enterics, 3.01. There was an increase in the number of L. monocytogenes in the recirculating brine with time, reaching a maximum of 2.34 log CFU/100 ml after 2.5 h of moisture-enhanced pork production. Thus, recirculating brines can harbor large populations of spoilage bacteria and L. monocytogenes and are an important source of contamination for moisture-enhanced pork.  相似文献   
107.

Objective

To identify the level of effort state tobacco control programmes and partners have expended on interventions recommended by the community guide and how those efforts have changed over time between 1999 and 2004.

Design

Longitudinal study.

Setting

United States.

Participants

State tobacco control partners, including the state health department, voluntary agencies and tobacco control coalitions.

Main outcome measure

We used the Strength of Tobacco Control survey responses in 1999, 2002 and 2004 to calculate the mean proportion of state tobacco control partners working on recommended interventions and subsequently analysed changes in effort over time.

Results

The proportion of state tobacco control partners working to promote clean indoor air legislation remained at more than 70% in all three years. The proportion working to increase taxes on tobacco rose significantly between 1999 and 2002 (from 54% to 70%), and those working to reduce patient costs for tobacco cessation treatments never exceeded 31% in any year. Use of mass media targeting youths decreased significantly in all years (from 40% to 32% to 26%), and the proportion of state tobacco control partners participating in a quitline has increased steadily and significantly in all years (from 24% to 36% to 41%). The level of effort in each area varied widely between states and over time.

Conclusions

State tobacco control partners are implementing evidence based interventions, but more focus is needed on the tobacco cessation and mass media campaign components of comprehensive tobacco control programmes.  相似文献   
108.
The effects of transition metals in either catalyzing or inhibiting oil oxidation in the liquid phase have been extensively reported in the literature. However, little attention has been paid to the surface films formed as by-products of these reactions. In this paper, the authors investigated surface films for the important case of copper-containing additives influencing the oxidation of oil that contacts a steel surface. Copper naphthenate in solution was found to inhibit oil oxidation and to form copper-containing precipitates and deposits on the steel surface. The surface films formed were characterized by X-ray photoelectron spectroscopy, Auger spectroscopy and scanning electron microscopy. The precipitates showed a unique morphology of spherical particles several microns in diameter. A high level of copper naphthenate was found to prevent corrosion of the steel surface.  相似文献   
109.
Doubts have been raised on whether the car industry will manage to reach the goal set by the Voluntary Agreement with the European Commission, unless tougher measures are taken to reduce CO2 emissions. Taking a stance from the concept of downsizing, we study the historical development of two strategies: first, shifting the market toward smaller cars, market downsizing; second, a technical downsizing, i.e., technical improvements that have enabled a reduction of engine size. We focus on the Swedish new car market from 1975 to 2002. Analysis is done by combining sales statistics with databases over car model parameters. The development of the top and bottom 10% and 20% of the car market of various parameters points to an increased differentiation of the market; still, the market share of small models remains low. We identify the potential for downsizing created by increase of maximum specific torque and power and conclude that these have enabled the cylinder volume to stabilize around 2 l. Increase in engine size has also partly been dampened by the utilization of supercharging. The potential savings of fuel use presented by the introduction of a sixth gear in manual gearboxes have not materialized since gearshifts have not systematically been used to lower engine speed. We conclude that there are few signs of a downsizing in the Swedish new car fleet. From a market perspective, larger cars are still dominant and the technical potentials to reduce engine size have not been harnessed.
Frances SpreiEmail:
  相似文献   
110.
Studies have consistently shown a spatial memory bias such that a target location is remembered toward the prototypical location of the region to which the target belongs, indicating a blending between the target’s specific information and the generic information of its region. The authors investigated whether people retain a veridical representation of a target location after a delay by determining the locus of the blending (during encoding, delay, or retrieval). To examine accessibility to the original target location, they used a recognition task, which is less demanding than the traditional reproduction procedure. The results showed that participants were able to recognize the original position of a target over their own biased recalled position after both a short (1,500 ms) and a longer (5,000 ms) delay. These findings reveal that spatial memories can be undistorted despite distorted recall responses. Results are discussed in terms of J. Huttenlocher, L. V. Hedges, and S. Duncan’s (1991) category adjustment model. (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