全文获取类型
收费全文 | 2261篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 15篇 |
化学工业 | 105篇 |
金属工艺 | 6篇 |
机械仪表 | 6篇 |
建筑科学 | 9篇 |
矿业工程 | 2篇 |
能源动力 | 8篇 |
轻工业 | 37篇 |
水利工程 | 3篇 |
石油天然气 | 1篇 |
武器工业 | 2篇 |
无线电 | 82篇 |
一般工业技术 | 66篇 |
冶金工业 | 1896篇 |
原子能技术 | 2篇 |
自动化技术 | 37篇 |
出版年
2023年 | 4篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 12篇 |
2012年 | 9篇 |
2011年 | 16篇 |
2010年 | 26篇 |
2009年 | 23篇 |
2008年 | 16篇 |
2007年 | 23篇 |
2006年 | 17篇 |
2005年 | 15篇 |
2004年 | 15篇 |
2003年 | 17篇 |
2002年 | 6篇 |
2001年 | 12篇 |
2000年 | 10篇 |
1999年 | 56篇 |
1998年 | 628篇 |
1997年 | 329篇 |
1996年 | 243篇 |
1995年 | 114篇 |
1994年 | 109篇 |
1993年 | 115篇 |
1992年 | 19篇 |
1991年 | 31篇 |
1990年 | 31篇 |
1989年 | 46篇 |
1988年 | 31篇 |
1987年 | 21篇 |
1986年 | 28篇 |
1985年 | 37篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 19篇 |
1978年 | 3篇 |
1977年 | 35篇 |
1976年 | 76篇 |
1975年 | 4篇 |
1955年 | 3篇 |
1914年 | 1篇 |
1905年 | 1篇 |
排序方式: 共有2277条查询结果,搜索用时 15 毫秒
991.
Hypochlorous (HOCl) and hypobromous (HOBr) acids are strong oxidants derived from myeloperoxidase and eosinophil peroxidase, the major antimicrobial enzymes of neutrophils and eosinophils, respectively. These oxidants are highly reactive with a wide range of biomolecules. At physiological pH, both HOCl and HOBr react readily with amines to form haloamines and with the unsaturated bonds of fatty acids to form halohydrins. We have investigated which of these reactions occur with phosphatidylethanolamine (PE), the predominant phospholipid of Escherichia coli. The formation of haloamines was determined by TLC and colorimetrically and the formation of halohydrins was determined by TLC and GC-MS. With HOCl, chloramines were much the preferred product and chlorohydrins were formed in substantial amounts only when HOCl was in excess of the amount required to convert the amine to the dichloramine. With HOBr at all concentrations, bromamines and bromohydrins were formed concurrently, indicating a greater relative reactivity with unsaturated fatty acids than with HOCl. The bromamine derivatives of PE, and other primary amines, were found to be more reactive than the equivalent chloramines, and were able to brominate the unsaturated bonds of fatty acids. Bromohydrins (formed directly or through the action of bromamines) may, therefore, be suitable biomarkers for the production of HOBr in vivo. 相似文献
992.
Several studies have shown that insulin resistance and hyperinsulinemia are associated with many metabolic disorders predisposing to coronary heart disease (CHD). This syndrome has been termed syndrome X. However, it is not completely known whether these relationships are still present in the elderly, or whether other factors such as age, gender, and body fat distribution modulate them. Therefore, we investigated the relationship between fasting plasma insulin, total and regional adiposity, fasting plasma glucose and lipids, plasma plasminogen activator inhibitor-1 (PAI-1), fibrinogen, and coagulation factor VII in a sample of 100 healthy free-living octogenarians-nonagenarians (52 men and 48 women) who were disability-free according to the Katz index. By univariate analysis, fasting insulin correlated positively with all anthropometric measures except the waist to hip ratio (WHR) in women. There was a positive correlation between fasting insulin and fasting glucose (r=.40, P < .01), plasma triglycerides ([TGs] r=.21, P < .05), and PAI-1 levels (r=.33, P < .01), whereas a negative relation was found with high-density lipoprotein cholesterol (HDL-C) and apolipoprotein, A-I (apo A-I) levels (r=-.22 and =-.24, respectively, P < .05). These relationships were weaker and less significant in women. In pooled data, stepwise multiple regression analysis showed an independent relationship of both the body mass index (BMI) and fasting insulin level with TGs (R2=.14), while gender and fasting insulin were the best predictors of HDL-C variance (R2=.17). Furthermore, fasting insulin was the only variable independently related to PAI-1 (R2=.12). Our findings support the existence of a metabolic syndrome even in very old age by showing that high insulin levels are related to various metabolic and hemostatic disorders. 相似文献
993.
CC Piazza GP Hanley WW Fisher JM Ruyter CS Gulotta 《Canadian Metallurgical Quarterly》1998,19(5):395-407
The results of functional analyses suggested that the destructive behavior of two individuals was sensitive to escape and attention as reinforcement. In an instructional context, we evaluated the effects of reinforcing compliance with functional reinforcers when destructive behavior produced a break. For one participant we also evaluated the effects of reinforcing compliance with functional reinforcers when destructive behavior produced no differential consequence (escape extinction). We hypothesized that destructive behavior failed to decrease in an instructional context when compliance resulted in a break because presentation of a break evoked attention-maintained destructive behavior. The results of a reinforcer assessment supported this hypothesis by demonstrating that demands functioned as positive reinforcement when no alternative activities were available. These results are discussed in terms of the importance of establishing operations in determining the appetitive or aversive properties of stimuli when destructive behavior is multiply controlled. 相似文献
994.
995.
Rahmatian F. Jaeger N.A.F. James R. Berolo E. 《Photonics Technology Letters, IEEE》1998,10(5):675-677
A wide-band electrooptic polarization converter has been fabricated using slow-wave coplanar-strip electrodes on an AlGaAs-GaAs substrate. Microwave characteristics of the electrode have been measured up to 40 GHz. The microwave loss and the microwave index at 40 GHz are 0.4 Np/cm and 3.4, respectively. The optical measurements were done up to 20 GHz; a flat frequency response was observed 相似文献
996.
Day hospital and residential addiction treatment: Randomized and nonrandomized managed care clients.
Witbrodt Jane; Bond Jason; Kaskutas Lee Ann; Weisner Constance; Jaeger Gary; Pating David; Moore Charles 《Canadian Metallurgical Quarterly》2007,75(6):947
Male and female managed care clients randomized to day hospital (n=154) or community residential treatment (n=139) were compared on substance use outcomes at 6 and 12 months. To address possible bias in naturalistic studies, outcomes were also examined for clients who self-selected day hospital (n=321) and for clients excluded from randomization and directed to residential treatment because of high environmental risk (n=82). American Society of Addiction Medicine criteria defined study and randomization eligibility. More than 50% of followed clients reported past-30-day abstinence at follow-ups (unadjusted rates, not significant between groups). Despite differing baseline severities, randomized, self-selecting, and directed clients displayed similar abstinence outcomes in multivariate longitudinal models. Index treatment days and 12-step attendance were associated with abstinence (p 相似文献
997.
998.
Staffing the operating room requires a different approach than staffing inpatient units. Of course, there are similarities, namely: assuring safe, cost-effective care; dealing with fluctuating workloads; using various types of caregivers; and maximizing and maintaining resources in a responsible manner. However, many differences also exist. This article details the fundamental requirements for determining operating room staffing. 相似文献
999.
BACKGROUND: Despite a nationwide surplus of cardiac transplantation programs, the number of United States armed forces veterans who receive heart transplants has declined over the past several years. This study reviews the efficacy of a partnership between a Veterans Affairs hospital and a university hospital in maximizing the access of veterans to the limited donor heart supply. METHODS: As part of a contract-based sharing agreement between the University of Wisconsin Hospital and the William S. Middleton Memorial Veterans Affairs Hospital, 25 veterans underwent orthotopic heart transplantation between October 1993 and April 1995. Care of the patients was provided at the Veterans Affairs Hospital. The transplantation operations were performed at the University of Wisconsin Hospital, and all patients were transferred back to the Veterans Affairs Hospital 5 to 7 days afterward. All patients were men (mean age, 52.1 +/- 2.1 years) and were referred from Veterans Affairs hospitals in nine different states. RESULTS: During the 19-month period, the average length of hospital stay for pretransplantation evaluation was 7.0 +/- 0.7 days (range, 2 to 15 days). Average status I waiting time was 26.9 +/- 3.3 days (range, 5 to 54 days); the average waiting time for status II was 115.1 +/- 16 days (range, 15 to 242 days). Posttransplantation length of stay at the Veterans Affairs Hospital was 22 +/- 1.8 days (range, 11 to 41 days). Only 1 patient (4%) experienced a lethal postoperative complication. Ten patients (40%) exhibited graft rejection within the first month after transplantation, requiring treatment with augmented immunosuppressive therapy (steroids, orally in 2 patients and intravenously in 8). The overall 30-day mortality rate was 4% (1 patient). The cause of death was acute grade 4 graft rejection 3 weeks after transplantation. Overall patient survival was 96%. CONCLUSIONS: A partnership between a Veterans Affairs hospital and a university hospital committed to transplantation can increase Veterans Affairs cardiac transplantation activity, with excellent 30-day mortality and early survival results. 相似文献
1000.