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   1088篇
  免费   4篇
化学工业   34篇
金属工艺   4篇
机械仪表   2篇
建筑科学   2篇
矿业工程   5篇
能源动力   6篇
轻工业   41篇
水利工程   1篇
无线电   27篇
一般工业技术   22篇
冶金工业   920篇
原子能技术   6篇
自动化技术   22篇
  2020年   2篇
  2019年   2篇
  2016年   3篇
  2013年   12篇
  2012年   5篇
  2011年   7篇
  2010年   2篇
  2009年   2篇
  2008年   6篇
  2007年   2篇
  2006年   9篇
  2005年   7篇
  2004年   7篇
  2003年   8篇
  2002年   6篇
  2001年   7篇
  1999年   27篇
  1998年   265篇
  1997年   137篇
  1996年   106篇
  1995年   64篇
  1994年   65篇
  1993年   63篇
  1992年   16篇
  1991年   10篇
  1990年   17篇
  1989年   20篇
  1988年   14篇
  1987年   19篇
  1986年   18篇
  1985年   14篇
  1983年   7篇
  1982年   6篇
  1981年   6篇
  1980年   8篇
  1979年   6篇
  1978年   5篇
  1977年   22篇
  1976年   66篇
  1975年   2篇
  1974年   1篇
  1973年   2篇
  1972年   1篇
  1971年   4篇
  1969年   2篇
  1968年   3篇
  1966年   1篇
  1965年   2篇
  1964年   1篇
  1955年   1篇
排序方式: 共有1092条查询结果,搜索用时 15 毫秒
1.
Continuously variable ferroelectric (BST on sapphire) phase shifters based on all-pass networks are presented. An all-pass network phase shifter consists of only lumped LC elements, and thus the total size of the phase shifter is kept to less than 2.2 mm /spl times/ 2.6 mm at 2.4 GHz. The tunability (C/sub max//C/sub min/) of a BST interdigital capacitor is over 2.9 with a bias voltage of 140 V. The phase shifter provides more than 121/spl deg/ phase shift with the maximum insertion loss of 1.8 dB and the worst case return loss of 12.5 dB from 2.4 GHz to 2.5 GHz. By cascading two identical phase shifters, more than 255/spl deg/ phase shift is obtained with the maximum insertion loss of 3.75 dB. The loss figure-of-merit of both the single- and double-section phase shifters is over 65/spl deg//dB from 2.4 GHz to 2.5 GHz.  相似文献   
2.
3.
4.
Health care exhibits a competitive dynamic today that increasingly resembles that in other service industries. Organizations are becoming larger to achieve scale economies and to increase market power. Vertical integration, whether through ownership or complex contracts, is also being pursued both to seek efficiencies and to improve the bargaining position of the organization. External forces that are driving these changes include more aggressive activities on the part of purchasers to contain their costs, developments in information technology, management innovation in other service industries, and advances in medical technology. Within the health care industry, there is a pattern of organizations taking the initiative to respond to these external forces--often in anticipation of them--and other organizations then responding to the pressures in turn placed on them. Although information on strategies is communicated rapidly throughout the country, what is attempted and what succeeds differs a great deal across communities. The nature of current health care institutions in the community, including the presence of large entities with extensive capital and strong management in a particular segment of the health system and the community's experience with managed care are important factors in the path that change takes.  相似文献   
5.
6.
Status of risk factors for dementia associated with stroke   总被引:1,自引:0,他引:1  
This study presents a brief investigation into sex differences of speakers in the voice onset time of English plosives that are stressed in both word-initial and prevocalic position. 72 short phrases were presented to 5 men (range 25 to 37 years, mean age 34.2 yr.) and five women speakers (range 28 to 38 years, mean 32.6 yr.). Analysis showed that the women as speakers had on average, longer voice onset time values than their male peers.  相似文献   
7.
Cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme in the bile acid biosynthetic pathway, is thought to be regulated by hydrophobic bile acids through negative feedback control. The role of cholesterol in the regulation of cholesterol 7 alpha-hydroxylase is more controversial, in part because of incomplete understanding of the relationship between the pathways of cholesterol synthesis and degradation. The main objective of this study was to define the interaction between these two pathways in an experimental model in which the supply of newly synthesized cholesterol was interrupted by sustained infusion of mevinolin (lovastatin), an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) or accelerated by a continuous infusion of mevalonate, a cholesterol precursor. The study was carried out in rats subjected to short-term bile fistula. In one set of experiments, rats were treated postoperatively with mevinolin (5 mg/kg loading dose followed by 2 mg/kg/hr infusion), mevalonate (180 mumol/hr infusion) or both for up to 96 hr. In a separate set of experiments, rats were infused intraduodenally with taurocholate (36 mumol/100 gm/hr for up to 96 hr). We determined cholesterol 7 alpha-hydroxylase- and HMG-CoA reductase specific activities at those time intervals, whereas bile acid synthesis rates were determined throughout the study. Compared with rats not subjected to surgery, rats with short-term biliary diversion had increases in cholesterol 7 alpha-hydroxylase activity of 259% and 827% at 48 and 96 hr, respectively. The increase in bile acid biosynthesis was less pronounced. Continuous infusion of mevinolin completely prevented increases in cholesterol 7 alpha-hydroxylase specific activity and bile acid biosynthesis at both time intervals.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
8.
Psoralens and sunlight have been used by the Egyptians and Indians for hundreds of years for treating vitiligo. The combination of oral psoralens and artificial ultraviolet A (PUVA) therapy was approved for managing severe psoriasis by the Food and Drug Administration in 1982. Since then, PUVA therapy has been an effective modality for treating many cutaneous conditions (psoriasis, atopic dermatitis, vitiligo, and mycosis fungoides). However, proper knowledge and administration of PUVA therapy are vital to treatment success and reducing side effects.  相似文献   
9.
10.
PURPOSE: To assess long-term survival following cladribine salvage treatment for previously treated patients with chronic lymphocytic leukemia. PATIENTS AND METHODS: Fifty-two patients aged 39-84 years with previously treated CLL received cladribine 0.12 mg/kg/day in 2-hour infusions for 5 days in monthly courses. Two-thirds were refractory to previous therapy, and 8 had prior fludarabine. RESULTS: Sixteen (31%) patients achieved complete response (CR) and 14 (27%) partial remission (PR) according to consensus criteria. Response correlated with clinical stage, number of previous treatment regimes, blood lymphocyte count, and lymphocyte halflife following the first cladribine course. Toxicity included pneumonia (n = 9), herpes zoster (n = 7), and septicemia (n = 2). Four patients in CR underwent high-dose chemotherapy with autologous blood stem cell support, and 2 remain in CR 48 and 60 months from start of cladribine, and 2 had relapse at 42 and 48 months, respectively. Median progression-free survival (Kaplan-Meier analysis) for CR patients was 23 months from start of cladribine treatment, and for PR patients 16 months. The projected overall survival was 80% at 3 years for CR patients, and the median survival 28 months for PR patients and 4 months for non-responding patients. CONCLUSIONS: Our previous finding of durable CRs from cladribine in advanced CLL is thus confirmed in a larger patient material, and follow-up indicate that long-term survival may be achieved.  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