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   593篇
  免费   3篇
  国内免费   1篇
电工技术   4篇
化学工业   31篇
金属工艺   1篇
机械仪表   2篇
建筑科学   1篇
能源动力   4篇
轻工业   43篇
水利工程   1篇
无线电   15篇
一般工业技术   24篇
冶金工业   447篇
原子能技术   2篇
自动化技术   22篇
  2023年   4篇
  2022年   2篇
  2021年   2篇
  2019年   3篇
  2015年   4篇
  2013年   2篇
  2012年   5篇
  2011年   14篇
  2010年   8篇
  2009年   13篇
  2008年   11篇
  2007年   5篇
  2006年   6篇
  2005年   7篇
  2004年   3篇
  2003年   9篇
  2002年   9篇
  2001年   4篇
  2000年   2篇
  1999年   12篇
  1998年   115篇
  1997年   80篇
  1996年   57篇
  1995年   25篇
  1994年   23篇
  1993年   25篇
  1992年   3篇
  1991年   6篇
  1990年   3篇
  1989年   3篇
  1987年   4篇
  1986年   2篇
  1985年   6篇
  1984年   6篇
  1983年   4篇
  1982年   13篇
  1981年   3篇
  1980年   6篇
  1977年   15篇
  1976年   34篇
  1975年   3篇
  1970年   2篇
  1945年   1篇
  1944年   2篇
  1943年   2篇
  1941年   3篇
  1940年   8篇
  1939年   7篇
  1938年   2篇
  1937年   2篇
排序方式: 共有597条查询结果,搜索用时 31 毫秒
1.
In this paper, we propose low-power designs for the synchronizer and channel estimator units of the Inner Receiver in wireless local area network systems. The objective of the work is the optimization, with respect to power, area, and latency, of both the signal processing algorithms themselves and their implementation. Novel circuit design strategies have been employed to realize optimal hardware and power efficient architectures for the fast Fourier transform, arc tangent computation unit, numerically controlled oscillator, and the decimation filters. The use of multiple clock domains and clock gating reduces the power consumption further. These blocks have been integrated into an experimental digital baseband processor for the IEEE 802.11a standard implemented in the 0.25mum- 5-metal layer BiCMOS technology from Institute for High Performance Microelectronics.  相似文献   
2.
The effects of arginine vasopressin (AVP) and oxytocin (OT) upon thyroid-stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3) release were studied in euthyroid rats. Intracerebroventricular (i.c.v.) infusion of AVP in doses of 0.5 ng or 5 ng led to significant increases in plasma levels of TSH as well as FT4 and FT3. The effects of OT injected i.c.v. in similar doses were not consistent (there was no parallel between the changes of respective hormones plasma levels). It may be concluded that vasopressin modulate the pituitary-thyroid system function; AVP is probably a physiological stimulator of TSH and thyroid hormones secretion.  相似文献   
3.
4.
5.
OBJECTIVE: The initially well-fixed implants of total hip replacement (THR) are in the long-term subject to aseptic loosening. Many cytokines can contribute to osteolysis due to osteoclast recruitment and/or activation. However, in this respect tumor necrosis factor-alpha (TNF-alpha) plays a pivotal role, because it upregulates interleukin-1 and 6 and granulocyte-macrophage colony stimulating factor. The aim of this study was to assess the eventual presence, cellular localization and extent of expression of TNF-alpha in the synovial-like membrane at the implant or at the cement to bone interface compared to control synovial membrane. METHODS: Twenty samples from the synovial-like membrane of the periprosthetic tissues were compared to control samples. TNF-alpha containing cells were visualized using an avidin-biotin-peroxidase complex (ABC) method and analyzed by light microscopy, double labelling and image analysis. RESULTS: TNF-alpha was found in the periprosthetic tissues in fibroblasts and vascular endothelial cells, but mainly in the macrophages was it found to coincide with areas containing implant-derived debris. TNF-alpha containing cells were more numerous in the synovial-like membrane in the interface tissue from the proximal stem area (2816 +/- 318 cells) than in the control synovial membrane (565 +/- 93 cells, p < 0.01). Interestingly, similarly high TNF-alpha expression (3452 +/- 582 cells) was also seen in the synovial-like membrane of the pseudocapsule. CONCLUSION: These findings suggest that the foreign body-type host reaction caused by THR is characterized by the high expression of TNF-alpha. Because such expression occurred in the interface tissue between the implant and surrounding bone, TNF-alpha, due to its pivotal direct and indirect role in the activation and recruitment of osteoclasts, may contribute to periprosthetic osteolysis and to the loosening of THR.  相似文献   
6.
The efficacy of corticosteroids in asthma has been recognized over 40 years ago. Since that time, the advent of inhaled forms has further improved the therapeutic of these drugs which are now recognized as the fundamental treatment for asthma, and described in detail by national and international consensus. Based on a large body of literature, it can now be recommended to prescribe inhaled corticosteroids for symptomatic asthma patients. Long-term treatment is required and dosage not exceeding 1000 micrograms/d (beclometasone dipropionate equivalent) in adults are safe. Differences in the pharmacological characteristics of the various systematic and inhaled corticosteroids can be used to adapt treatment and administration route to each patient and achieve good patient compliance with optimal therapeutic efficacy.  相似文献   
7.
BACKGROUND: While monotherapy has significant limitations in bipolar disorder, few published data addressing alternatives exist. Treatment algorithms have been proposed, but none have undergone empirical evaluation. This study provides a systematic prospective, open evaluation of the effectiveness and tolerability of a treatment algorithm for patients with histories of mania. METHOD: Twenty-eight symptomatic outpatients from a public mental health facility who were diagnosed as having either bipolar I or schizoaffective illness, bipolar type, entered the study. Minimum blood levels of lithium and divalproex sodium were defined. Medications were pushed to predetermined levels (as tolerated) before proceeding to the next algorithm step. Clinical symptoms were assessed monthly using the Brief Psychiatric Rating Scale (BPRS, 27 item) and Clinical Global Impressions scale. RESULTS: Pretreatment and posttreatment clinical symptoms were compared. Over 50% of patients attained 30% improvement from baseline BPRS after 4 months. Thirty-six percent of patients (N = 10) became mood stable, 46% (N = 13) remained mood unstable, and 18% (N = 5) dropped out before completing the algorithm. Although patients who finished the algorithm were taking more medication, either dosage and/or drugs, somatic complaints did not increase. CONCLUSION: The potential benefit of a defined treatment algorithm was demonstrated for these complex and persistently ill patients. Despite long treatment histories, patients improved with more frequent visits and addition of medication(s). A randomized controlled trial comparing a similar treatment algorithm with treatment-as-usual is warranted.  相似文献   
8.
This paper examines the effects of exposure to mass media messages promoting family planning on the reproductive behaviour of married women in Nigeria using cross-sectional data. Longitudinal data are also used to ensure that exposure to media messages pre-dates the indicators of reproductive behaviour. Cross-sectional analysis suggests that: (1) contraceptive use and intention are positively associated with exposure to mass media messages, and (2) women who are exposed to media messages are more likely to desire fewer children than those who are not exposed to such messages. Similarly, analysis of the longitudinal data shows that exposure to mass media messages is a significant predictor of contraceptive use. Thus, exposure to mass media messages about family planning may be a powerful tool for influencing reproductive behaviour in Nigeria.  相似文献   
9.
Among optical isomers of 3,7-dimethylpentadecan-2-ol (diprionol) acetate or propionate tested as synthetic attractants, the 2S, 3S, and 7S isomers were most effective in attracting the males ofNeodiprion sertifer in the field. The 2S, 3S, and 7R isomers showed weak activity, but the other optical isomers were not attractive. Capillary GC analysis showed that the natural pheromone from body extracts of females was identical with the synthetic acetate of diprionol in its GC behavior. However, the natural pheromone was about 100-fold stronger than the most purified synthetic acetate of 2S,3S,7S-diprionol in the field. As a result of various isomer combination studies, it was found that the acetate of 2S,3R,7R-diprionol, when added to 2S,3S,7S-diprionol preparation at a low concentration, increased the catch by the latter. It was therefore concluded that the above combination of the optical isomers could account for the major sex attractancy in this species.  相似文献   
10.
Ultrasonic based bolt preload evaluation is commonly performed using the mono-wave method. This method works by measuring the time of flight of longitudinal waves. Here, a reference measurement in the unloaded condition is necessary for each bolt. In this publication the longitudinal wave is complemented by another type of ultrasonic wave - the transverse wave. This method does not require a reference measurement in the unloaded condition for each bolt. Moreover, an analytic method for determining the bolt-specific K-value is introduced, which is needed for the ultrasonic bolt preload determination. The analytically calculated K-values are compared with experimental K-values from tensile tests. The influence of material, bolt property class and surface protection system were determined with cylindrical specimens. In component tests, the bolt preload was evaluated using the bi-wave method, a possible influence of the bolt assembly method was investigated and the results were interpreted regarding their accuracy.  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