全文获取类型
收费全文 | 16094篇 |
免费 | 603篇 |
国内免费 | 48篇 |
专业分类
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 |
出版年
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.
R Arens B Wright J Elliott H Zhao PP Wang LW Brown T Namey P Kaplan 《Canadian Metallurgical Quarterly》1998,133(5):670-674
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.
Discordance of databases designed for claims payment versus clinical information systems. Implications for outcomes research 总被引:6,自引:0,他引:6
JG Jollis M Ancukiewicz ER DeLong DB Pryor LH Muhlbaier DB Mark 《Canadian Metallurgical Quarterly》1993,119(8):844-850
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.
PJ Morrison S Macphail D Williams G McCusker P McKeever C Wright NC Nevin 《Canadian Metallurgical Quarterly》1998,18(9):963-967
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.
Rudisill John R.; Hempy Paula E.; Eddy Mark F.; Zimmerman Gretchen L.; Rudisill Teresa L. 《Canadian Metallurgical Quarterly》1998,50(1):36
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.
PJ Simpson-Haidaris MA Courtney TW Wright R Goss A Harmsen F Gigliotti 《Canadian Metallurgical Quarterly》1998,66(9):4431-4439
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