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   16094篇
  免费   603篇
  国内免费   48篇
电工技术   173篇
综合类   26篇
化学工业   2908篇
金属工艺   319篇
机械仪表   303篇
建筑科学   948篇
矿业工程   57篇
能源动力   394篇
轻工业   1248篇
水利工程   176篇
石油天然气   55篇
武器工业   1篇
无线电   1200篇
一般工业技术   2694篇
冶金工业   3695篇
原子能技术   72篇
自动化技术   2476篇
  2023年   74篇
  2022年   150篇
  2021年   254篇
  2020年   173篇
  2019年   195篇
  2018年   287篇
  2017年   242篇
  2016年   354篇
  2015年   271篇
  2014年   431篇
  2013年   930篇
  2012年   709篇
  2011年   966篇
  2010年   751篇
  2009年   709篇
  2008年   824篇
  2007年   832篇
  2006年   701篇
  2005年   668篇
  2004年   567篇
  2003年   457篇
  2002年   541篇
  2001年   352篇
  2000年   334篇
  1999年   316篇
  1998年   514篇
  1997年   388篇
  1996年   303篇
  1995年   317篇
  1994年   274篇
  1993年   270篇
  1992年   207篇
  1991年   110篇
  1990年   203篇
  1989年   183篇
  1988年   166篇
  1987年   164篇
  1986年   128篇
  1985年   182篇
  1984年   175篇
  1983年   121篇
  1982年   106篇
  1981年   99篇
  1980年   75篇
  1979年   79篇
  1978年   65篇
  1977年   68篇
  1976年   107篇
  1974年   50篇
  1973年   44篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
Difficulty differentiating physiologic genu varum from early Blount's disease persists. Drennan's metaphyseal-diaphyseal (MD) angle remains the most consistently valuable radiographic parameter despite measurement error. Clinical risk factors also should be considered. All patients receiving orthoses for genu varum since 1985 were reviewed. The focus of the study was those patients with an MD angle of >16 degrees or between 9 and 16 degrees with a clinical risk factor for progression. Risk factors considered were ligamentous instability, obesity, asymmetry, and being female, black, or Hispanic. Thirty-eight patients with 60 tibiae were included. The success rate was 90%. Risk factors for failure (six cases) were instability, obesity, and delayed bracing. In cases with MD angles >16 degrees, the success rate was 86%. The results of orthotic treatment, restricted to patients meeting the stated parameters, represent improvement on the reported natural history.  相似文献   
962.
Business visualization applications   总被引:1,自引:0,他引:1  
Three-dimensional computer graphics can be extremely expressive. With the correct approach to a layout's visual design, people can quickly and easily comprehend large amounts of information. You can convey far more information in 3D than with 2D bar charts, or rows and columns of numbers. This article provides examples of information visualization applications in several industries, including the capital markets, retail banking, manufacturing, and consumer product goods. These examples help show what it means to put abstract information in 3D and what benefits result  相似文献   
963.
Explored how older adults recall the traits they possessed at an earlier age. It was hypothesized that older adults' recollections would be related to their theories about aging. In Study 1, a group of older Ss provided their theories concerning how various traits change with age. Another group of older Ss rated their current status on these traits and recalled the status they possessed at a younger age. In addition, a group of younger adults rated their current status on the same traits. On traits theorized to increase with age, older Ss recalled themselves as possessing lower levels at an earlier age than the younger group reported possessing. On traits theorized to decrease with age, older Ss recalled themselves as possessing higher levels at an earlier age than the younger group reported possessing. Study 2 indicated that this effect is obtained regardless of trait positivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
964.
OBJECTIVE: To determine the suitability of insurance claims information for use in clinical outcomes research in ischemic heart disease. DESIGN: Concordance study of two databases. SETTING: Tertiary care referral center. PATIENTS: A total of 12,937 consecutive patients hospitalized for cardiac catheterization for suspected ischemic heart disease between July 1985 and May 1990. INTERVENTIONS: Two-by-two tables were used to compute overall and kappa measures of agreement comparing clinical versus claims data for 12 important predictors of prognosis in patients with ischemic heart disease. MEASUREMENTS: Kappa statistics (agreement adjusted for chance agreement) were used to quantify agreement rates. RESULTS: Agreement rates between the clinical and claims databases ranged from 0.83 for the diagnosis of diabetes to 0.09 for the diagnosis of unstable angina (kappa values). Claims data failed to identify more than one half of the patients with prognostically important conditions, including mitral insufficiency, congestive heart failure, peripheral vascular disease, old myocardial infarction, hyperlipidemia, cerebrovascular disease, tobacco use, angina, and unstable angina, when compared with the clinical information system. CONCLUSIONS: Our results suggest that insurance claims data lack important diagnostic and prognostic information when compared with concurrently collected clinical data in the study of ischemic heart disease. Thus, insurance claims data are not as useful as clinical data for identifying clinically relevant patient groups and for adjusting for risk in outcome studies, such as analyses of hospital mortality.  相似文献   
965.
We examined whether heart rate (HR) could be used to estimate energy expenditure (EE) in cattle. Six Hereford heifers (345 +/- 10.8 kg BW) 12 mo of age were implanted with HR radio transmitters and maintained in individual pens under the following treatments: 1) shade or sun exposure, 2) high- or low-energy diet, and 3) feeding in morning or afternoon. The HR of animals was measured every .5 h during 3 mo; measurements of oxygen consumption and HR were made simultaneously in the morning and in the afternoon while animals were resting and exercising. Average daily HR (52 +/- 4 beats/min) and average daily EE (380 +/- 9 kJ/kg(.75)) in animals on the low-energy diet were less than values in animals on the high-energy diet (94 +/- 4 beats/min and 653 +/- 9 kJ/ kg(.75), respectively). For each animal and within each diet, linear regressions best described the relationship between HR and EE in resting animals, whereas quadratic regressions best described this relationship for exercising animals. The quadratic equation for the exercising animals could also be used for resting animals. In addition, a constant value of EE per heart beat (EE pulse) for each individual resting animal was found and gave accurate estimations. This method was convenient because 1) no exercise equipment was needed to generate the regression equations and 2) EE pulse was less affected by diet than was EE estimated by regression equations. We conclude that HR, a relatively easy measurement, can be useful and accurate in estimating EE. To increase the accuracy of the estimation of EE by HR, the relationship of HR to EE should be established for each animal. In addition, the nutritional regimen for the animal in which EE is estimated should be used for the animal in establishing the relationship.  相似文献   
966.
967.
In this article, we review unsupervised neural network learning procedures which can be applied to the task of preprocessing raw data to extract useful features for subsequent classification. The learning algorithms reviewed here are grouped into three sections: information-preserving methods, density estimation methods, and feature extraction methods. Each of these major sections concludes with a discussion of successful applications of the methods to real-world problems.The first author is supported by research grants from the James S. McDonnell Foundation (grant #93–95) and the Natural Sciences and Engineering Research Council of Canada. For part of this work, the second author was supported by a Temporary Lectureship from the Academic Initiative of the University of London, and by a grant (GR/J38987) from the Science and Engineering Research Council (SERC) of the UK.  相似文献   
968.
Congenital atresia of the larynx is a rare abnormality. We describe three cases where prenatal diagnosis during the second trimester showed massive abdominal fetal ascites and at post-mortem, laryngeal atresia was identified in two cases, and severe laryngeal stenosis in the third. All were associated with pulmonary hyperplasia. No additional abnormalities were found in other systems. Overdistended lung tissue and ascites are resultant from aberrant laryngeal growth; laryngeal anomalies are a cause of isolated fetal ascites. The association of ascites and voluminous lungs should arouse suspicion of laryngeal atresia and should be an indication for careful pathological study of the fetal larynx.  相似文献   
969.
Outlines a psychological procedure aimed at improving the working relationship between a newly hired executive and the executive's reporting official. The "Executive Fit Rehearsal" (EFR) attempts to systematically engage the executive and reporting official in a dialogue designed to anticipate and overcome problems resulting from individual differences in personality, expectations, work styles, and communication patterns. The procedure supports consensus and mutual understanding. To assess the effectiveness of the procedure, evaluation forms were mailed to participants of 15 consecutive Executive Fit sessions. Ss' reactions to the EFR indicate that the process facilitated adjustment to the work setting and improved communications. Comments from subordinates were more uniformly positive, suggesting that the process may be most helpful for new employees. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
970.
Pneumocystis carinii is an important pulmonary pathogen responsible for morbidity and mortality in patients with AIDS. The acute-phase response (APR), the primary mechanism used by the body to restore homeostasis following infection, is characterized by increased levels of circulating fibrinogen (FBG). Although the liver is the primary site of increased FBG synthesis during the APR, we unexpectedly discovered that FBG is synthesized and secreted by lung alveolar epithelial cells in vitro during an inflammatory stimulus. Therefore, we sought to determine whether lung epithelial cells produce FBG in vivo using animal models of P. carinii pneumonia (PCP). Inflammation was noted by an influx of macrophages to P. carinii-infected alveoli. Northern hybridization revealed that gamma-FBG mRNA increased two- to fivefold in P. carinii-infected lung tissue, while RNA in situ hybridization demonstrated increased levels of gamma-FBG mRNA in the lung epithelium. Immunoelectron microscopy detected lung epithelial cell-specific production of FBG, suggesting induction of a localized inflammatory response resembling the APR. A systemic APR was confirmed by a two- to fivefold upregulation of the levels of hepatic gamma-FBG mRNA in animals with PCP, resulting in a corresponding increase in levels of FBG in plasma. Furthermore, immunoelectron microscopy revealed the presence of FBG at the junction of cell membranes of trophic forms of P. carinii organisms aggregated along the alveolar epithelium. These results implicate FBG in the pathogenesis of PCP in a manner similar to that of the adhesive glycoproteins fibronectin and vitronectin, which are known to participate in intra-alveolar aggregation of organisms and adherence of P. carinii to the lung epithelium.  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