全文获取类型
收费全文 | 470097篇 |
免费 | 6387篇 |
国内免费 | 1689篇 |
专业分类
电工技术 | 8627篇 |
综合类 | 519篇 |
化学工业 | 68742篇 |
金属工艺 | 16987篇 |
机械仪表 | 14376篇 |
建筑科学 | 11884篇 |
矿业工程 | 1555篇 |
能源动力 | 12498篇 |
轻工业 | 46049篇 |
水利工程 | 4292篇 |
石油天然气 | 5606篇 |
武器工业 | 73篇 |
无线电 | 61163篇 |
一般工业技术 | 87681篇 |
冶金工业 | 87066篇 |
原子能技术 | 7974篇 |
自动化技术 | 43081篇 |
出版年
2021年 | 3532篇 |
2020年 | 2704篇 |
2019年 | 3450篇 |
2018年 | 5580篇 |
2017年 | 5674篇 |
2016年 | 6140篇 |
2015年 | 4156篇 |
2014年 | 7095篇 |
2013年 | 21511篇 |
2012年 | 12170篇 |
2011年 | 16938篇 |
2010年 | 13230篇 |
2009年 | 14902篇 |
2008年 | 16010篇 |
2007年 | 15942篇 |
2006年 | 14558篇 |
2005年 | 13210篇 |
2004年 | 12801篇 |
2003年 | 12483篇 |
2002年 | 11844篇 |
2001年 | 12115篇 |
2000年 | 11196篇 |
1999年 | 11872篇 |
1998年 | 28049篇 |
1997年 | 19876篇 |
1996年 | 15319篇 |
1995年 | 11822篇 |
1994年 | 10439篇 |
1993年 | 10228篇 |
1992年 | 7746篇 |
1991年 | 7286篇 |
1990年 | 6942篇 |
1989年 | 6519篇 |
1988年 | 6311篇 |
1987年 | 5376篇 |
1986年 | 5128篇 |
1985年 | 6250篇 |
1984年 | 5689篇 |
1983年 | 5176篇 |
1982年 | 4835篇 |
1981年 | 4946篇 |
1980年 | 4615篇 |
1979年 | 4365篇 |
1978年 | 4071篇 |
1977年 | 4809篇 |
1976年 | 5948篇 |
1975年 | 3648篇 |
1974年 | 3523篇 |
1973年 | 3598篇 |
1972年 | 2793篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
981.
982.
J. C. W. Davenport D. J. Smith 《Fatigue & Fracture of Engineering Materials & Structures》1993,16(10):1125-1133
A test apparatus has been developed to study the fracture behaviour of engineering materials subjected to superimposed tensile and shear (Mode I and II) loads using a single edge notch specimen. Stress intensity factors were calculated using finite element analysis. Test results for PMMA are reported. Results from circumferentially notched round bar specimens, subjected to combined tension and torsion (Mode I and III) loading are also reported. The Mode I/II results are consistent with the mixed mode fracture response of a wide range of brittle materials, although there is some evidence of non-linear behaviour. The fracture behaviour for superimposed Modes I and III indicates the strong influence of non-linear deformation which causes the mixed mode toughness to be dependent on the sequence and type of loading. 相似文献
983.
984.
985.
C Biddle 《Canadian Metallurgical Quarterly》1993,61(2):170-4; quiz 175
Mechanical ventilation has become commonplace in critical care environments and a number of improvements designed to improve the interface between patient and machine are finding their way into the operating room as well. Strategies which are discussed include differential lung ventilation, inspiratory pause, inverse ratio ventilation, mandatory minute volume, pressure support ventilation, and airway pressure release ventilation. These strategies are discussed individually in terms of both their theoretical and clinical utility. A user-friendly classification of ventilatory approaches based on the rate of breathing is also provided as is treatment of the issue of the cardiovascular effects of positive end-expiratory pressure. Conditions which increase ventilatory demand in mechanically ventilated patients are reviewed, as these require consideration when caring for the patient receiving mechanical ventilation. While conventional positive pressure approaches are suitable for the majority of patients who present for anesthesia and surgery, patients with significant pulmonary dysfunction should be availed the newer approaches to management when possible. This will only become feasible when practitioners recognize the importance and application of these approaches and urge their introduction into operating room based equipment. 相似文献
986.
987.
PJ Kelly CT McDonald GO Neill C Thomas J Niles G Rordorf 《Canadian Metallurgical Quarterly》1998,50(4):1157-1160
Idiopathic thrombotic thrombocytopenic purpura (TTP) is frequently complicated by microinfarcts in cerebral cortex and subcortical white matter. We describe two sisters who suffered massive hemispheric infarction due to thrombosis of the middle cerebral artery main stem during exacerbations of TTP. Acute TTP may be associated with intraluminal thrombosis of large-diameter arteries in addition to arterioles and capillaries. 相似文献
988.
The relationship between office size and noise level is one of the most significant, yet least investigated, factors affecting software productivity. According to Tom DeMarco and Tim Lister (1992), US programmers with more than 80 square feet of private, noise-free office space consistently outperform programmers who occupy two- or three-person cubicles. The result was the Santa Teresa Programming Laboratory in San Jose, California, which opened in 1978. The author discusses some requirements of an optimal programming office environment. He considers the effectiveness of home working 相似文献
989.
990.
INTRODUCTION: Previous work has shown that parents prefer to be present when their children undergo common invasive procedures, although physicians are ambivalent about parental presence. PURPOSE: To determine the effect of a parent-focused intervention on the pain and performance of the procedure, anxiety of parents and clinicians, and parental satisfaction with care. POPULATION: Children younger than 3 years old undergoing venipuncture, intravenous cannulation, or uretheral catheterization. SETTING: Pediatric emergency department of Boston City Hospital. DESIGN: Randomized controlled trial with three groups; parents present and given instructions on how to help their children; parents present, but no instructions given; and parents not present. INTERVENTION: The parents were instructed to touch, talk to, and maintain eye contact during the procedure. RESULTS: A total of 431 parents was randomized to the intervention (N = 153), present (N = 147), and not present (N = 131) groups. The groups were equivalent with respect to measured sociodemographic variables and parents' previous experience in the pediatric emergency department. No differences emerged with respect to pain (3-point scale measured by parent and clinician, and analysis of cry); performance of the procedure (number of attempts, completion of procedure by first clinician, time); clinician anxiety; or parental satisfaction with care. Parents who were present were more likely to rate the pain of the children as extreme/severe (52%) in comparison to clinicians (15%, kappa .07, poor agreement) and were significantly less anxious than parents who were not present. CONCLUSION: Overall, the intervention was not effective in reducing the pain of routine procedures. Parental presence did not negatively affect performance of the procedure or increase clinician anxiety. Parents who were present were less anxious than those who were not present. CLINICAL IMPLICATION: In general, parents have indicated that they want to be present when their children undergo procedures. The results of this study challenge the traditional belief that parental presence negatively affects our ability to successfully complete procedures. We should encourage parents who want to be present to stay during procedures. 相似文献