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   463篇
  免费   6篇
化学工业   91篇
金属工艺   8篇
机械仪表   3篇
建筑科学   14篇
能源动力   13篇
轻工业   26篇
水利工程   9篇
无线电   15篇
一般工业技术   62篇
冶金工业   165篇
自动化技术   63篇
  2024年   3篇
  2023年   2篇
  2022年   4篇
  2021年   6篇
  2020年   1篇
  2019年   4篇
  2018年   10篇
  2017年   2篇
  2016年   6篇
  2015年   2篇
  2014年   10篇
  2013年   17篇
  2012年   16篇
  2011年   28篇
  2010年   17篇
  2009年   29篇
  2008年   32篇
  2007年   28篇
  2006年   22篇
  2005年   21篇
  2004年   15篇
  2003年   13篇
  2002年   18篇
  2001年   13篇
  2000年   13篇
  1999年   15篇
  1998年   10篇
  1997年   12篇
  1996年   13篇
  1995年   9篇
  1994年   9篇
  1993年   15篇
  1992年   5篇
  1991年   2篇
  1990年   10篇
  1989年   6篇
  1988年   8篇
  1987年   6篇
  1986年   4篇
  1985年   5篇
  1984年   4篇
  1983年   1篇
  1982年   1篇
  1977年   1篇
  1976年   1篇
排序方式: 共有469条查询结果,搜索用时 31 毫秒
71.
With a Hunsdiecker–Barton iododecarboxylation strategy, we converted the carboxylate group of the oseltamivir precursor into exemplary phosphonate monoesters. In all cases, Ki values towards influenza virus sialidase remained in the sub‐nanomolar range. We have thus made valuable structural space available for the design of novel oseltamivir‐based tools for influenza virus research.

  相似文献   

72.
73.

Background

Although animal and human studies have demonstrated interactions between dietary choline and fetal alcohol spectrum disorders, dietary choline deficiency in pregnancy is common in the US and worldwide. We sought to develop and validate a quantitative food frequency questionnaire (QFFQ) to estimate usual daily choline intake in pregnant mothers.

Methods

A panel of nutrition experts developed a Choline-QFFQ food item list, including sources with high choline content and the most commonly consumed choline-containing foods in the target population. A data base for choline content of each item was compiled. For reliability and validity testing in a prospective longitudinal cohort, 123 heavy drinking Cape Coloured pregnant women and 83 abstaining/light-drinking controls were recruited at their first antenatal clinic visit. At 3 prenatal study visits, each gravida was interviewed about alcohol, smoking, and drug use, and administered a 24-hour recall interview and the Choline-QFFQ.

Results

Across all visits and assessments, > 78% of heavy drinkers and controls reported choline intake below the Dietary Reference Intakes adequate intake level (450 mg/day). Women reported a decrease in choline intake over time on the QFFQ. Reliability of the QFFQ across visits was good-to-acceptable for 2 of 4 group-level tests and 4 of 5 individual-level tests for both drinkers and controls. When compared with 24-hr recall data, validity of the QFFQ was good-to-acceptable for 3 of 4 individual-level tests and 3 of 5 group-level tests. For controls, validity was good-to-acceptable for all 4 individual-level tests and all 5 group-level tests.

Conclusions

To our knowledge, this is the first quantitative choline food frequency screening questionnaire to be developed and validated for use with both heavy and non-drinking pregnant women and the first to be used in the Cape Coloured community in South Africa. Given the high prevalence of inadequate choline intake and the growing evidence that maternal choline supplementation can mitigate some of the adverse effects of prenatal alcohol exposure, this tool may be useful for both research and future clinical outreach programs.
  相似文献   
74.
Relations between marital aggression (psychological and physical) and children's health were examined. Children's emotional insecurity was assessed as a mediator of these relations, with distinctions made between marital aggression against mothers and fathers and ethnicity (African American or European American), socioeconomic status, and child gender examined as moderators of effects. Participants were 251 community-recruited families, with multiple reporters of each construct. Aggression against either parent yielded similar effects for children. Children's emotional insecurity mediated the relation between marital aggression and children's internalizing, externalizing, and posttraumatic stress disorder symptoms. No differences were found in these pathways for African American and European American families or as a function of socioeconomic status or child gender. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
75.
This study examined nonsuicidal self-injury (NSSI) in a community sample of young adolescent girls. Potential moderators of the relationships between different types of distress (internal and interpersonal) and particular functions of NSSI (emotion-regulation and interpersonal) were explored. Participants included 94 girls (49% Hispanic; 25% African American) ages 10-14 years who completed questionnaires regarding self-injurious behavior and other constructs of interest. Fifty-six percent of girls (n = 53) reported engaging in NSSI during their lifetime, including 36% (n = 34) in the past year. Internal distress (depressive symptoms) was associated with engaging in NSSI for emotion-regulation functions, and rumination moderated the relationship between depressive symptoms and engaging in NSSI for automatic positive reinforcement. Interpersonal distress (peer victimization) was associated with engaging in NSSI for social reinforcement, and quality of peer communication moderated this relationship. The clinical implications of these findings include designing preventions that address the particular contexts of self-injurious behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
76.
Planar circularly polarized microstrip antenna with a single feed   总被引:4,自引:0,他引:4  
A novel circularly polarized (CP) microstrip antenna is introduced. The antenna is fed with a single coaxial probe and the structure is planar. The CP bandwidth is much larger than available single-probe microstrip antennas and the CP radiation quality is excellent over the entire upper hemisphere  相似文献   
77.
As an internship applicant, do you know what internship agencies look for to select or exclude you from further consideration? In a survey, the authors examined exclusion and inclusion criteria used at 402 internship sites accredited by the American Psychological Association (APA). The 249 respondents (62%) rated fit between applicant goals and site opportunities as the most important inclusion criteria. Four exclusion criteria (lack of completion of orals, lack of APA status of doctoral program, poor fit between applicant goals and site opportunities, and incomplete doctoral course work) were most commonly used to eliminate applicants from consideration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
78.
This paper studies the approximation of the partitioned multiobjective risk method's (PMRM) extreme event risk function for time-to-failure models. The analytic expression of the approximation for the extreme event risk function is derived through the use of the statistics of extremes for the case where the underlying distribution is of an extreme-value type III for minima. This analytic expression provides an effective theoretical tool for understanding the behavior of conditional expected values for time-to-failure models for a large class of distribution functions used in reliability. The results are confirmed for example problems of exponential and uniform distributions.  相似文献   
79.
Electronic commerce is inevitable and will reshape our lives, but before true electronic commerce environments can be realized, it will be necessary to secure your enterprise against outside attacks on its electronic information and provide controls for authorized access to that information. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   
80.
Hemodialysis (HD) catheter dysfunction compromises HD adequacy and increases the cost of patient care. Repeated administration of alteplase in HD catheters typically produces only short-term benefits. The purpose of this study was to design, implement, and evaluate the efficacy of an experimental alteplase algorithm to manage HD catheter dysfunction. This was a two-part prospective nonrandomized study. Baseline data of alteplase use and catheter exchange were collected during part 1 of the study. Part 2 consisted of the alteplase algorithm implementation and repeat collection of catheter data. Rates of alteplase use and catheter exchange per 1000 catheter-days were the primary and secondary outcomes of the study. One hundred and seventy-two catheters in 131 patients were followed prospectively during the course of the study. The adjusted relative rate (RR) of alteplase use showed no significant difference between both parts of the study, adjusted RR: 1.10, 95% confidence interval (CI) (0.73-1.65). Similarly, catheter exchange rates were not significantly different over the duration of the study (1.12 vs. 1.03 per 1000 catheter-days). However, waiting time for catheter exchange increased from 20.36 ± 14 days in part 1 to 38.42 ± 28 days in part 2 (P < 0.05). The alteplase algorithm did not significantly reduce alteplase use. This may be partially explained by repeated use of alteplase in part 2, due to longer waiting times for catheter exchange procedures.  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