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   7487篇
  免费   120篇
  国内免费   6篇
电工技术   73篇
综合类   4篇
化学工业   1090篇
金属工艺   113篇
机械仪表   207篇
建筑科学   233篇
矿业工程   33篇
能源动力   188篇
轻工业   523篇
水利工程   47篇
石油天然气   11篇
武器工业   2篇
无线电   639篇
一般工业技术   1172篇
冶金工业   2527篇
原子能技术   118篇
自动化技术   633篇
  2021年   64篇
  2020年   49篇
  2019年   52篇
  2018年   59篇
  2017年   69篇
  2016年   71篇
  2015年   59篇
  2014年   105篇
  2013年   236篇
  2012年   160篇
  2011年   254篇
  2010年   180篇
  2009年   185篇
  2008年   212篇
  2007年   207篇
  2006年   216篇
  2005年   152篇
  2004年   166篇
  2003年   156篇
  2002年   140篇
  2001年   144篇
  2000年   135篇
  1999年   176篇
  1998年   731篇
  1997年   400篇
  1996年   338篇
  1995年   199篇
  1994年   188篇
  1993年   217篇
  1992年   113篇
  1991年   112篇
  1990年   107篇
  1989年   112篇
  1988年   88篇
  1987年   95篇
  1986年   101篇
  1985年   103篇
  1984年   104篇
  1983年   85篇
  1982年   82篇
  1981年   114篇
  1980年   101篇
  1979年   93篇
  1978年   82篇
  1977年   110篇
  1976年   183篇
  1975年   76篇
  1974年   47篇
  1973年   68篇
  1972年   46篇
排序方式: 共有7613条查询结果,搜索用时 9 毫秒
991.
The MURCS association is traditionally regarded as a disorder limited to the female sex. It has been hypothesized that men displaying the combination of azoospermia, segmentation abnormalities of the cervicothoracic spine and renal anomalies may have a male analogue of MURCS. Here we describe a patient with non-obstructive azoospermia and Klippel-Feil anomaly type II and suggest that this may represent another case of 'MURCS in the male'.  相似文献   
992.
Williams  L.G. 《Software, IEEE》1994,11(1):51-60
Formal methods can reduce the ambiguity in specifications and provide a basis for verification later on-especially important for safety-critical systems. The author compares specifications in the software cost reduction method and in the Vienna Definition Method for a safety-critical system and identifies several key assessment issues: understandability, assessment criteria, and semantic capabilities  相似文献   
993.
It is well recognized within the pharmaceutical industry that high throughput screening is a valuable and rapid tool to identify novel chemical compounds that may lead to tomorrow''s drugs. High throughput screening involves testing as many chemical compounds as quickly as possible against a defined molecular or cellular ‘target’ (for example an enzyme) in the hope that interacting compounds may provide significant therapeutic benefits.At Wyeth-Ayerst Research, a Robotics and Automation Research Core Group has been established which serves as the in-house resource for high throughput screening. The robotics group has three missions: (1) develop and perform high throughput screens for customers in all therapeutic departments in the company; (2) educate customers in issues related to screen design; and (3) help customers to bring automated workstations into their laboratories. The mission, therefore, requires the effective use of automation, as well as building a strong collaboration with customers.The challenges that have been faced fall into two categories: technology limiting and customer relations. Technological challenges arise because it is necessary to develop and implement assays with very different formats and biochemical endpoints within extremely shortened time frames. The primary means to meet these challenges is with flexible robotics and flexible people. Challenges in the area of customer relations include setting realistic expectations, maintaining a sense of collaboration (and not merely service), educating investigators as to how to deal with the huge amount of data generated and seeking feedback. Effective and frequent communication, and an awareness of each individual''s perspective, are essential to provide the most appropriate service.  相似文献   
994.
A bioassay was used to measure erythropoietin (EPO) concentrations in calves with haemorrhagic anaemia due to blood loss and in calves with anaemia due to Trypanosoma congolense infection. The bioactivity of EPO was measured in the assay by its stimulatory effect on 125I-deoxyuridine incorporation in spleen cells from phenylhydrazine-treated mice. Erythropoietin concentrations in blood-volume-depleted calves were elevated 6 h after blood loss, maximal (1225 mU/ml) at 33 h and below detection limits at 72 h. Reticulocytes (0.05 +/- 0.1%) appeared in blood by 72 h, peaked at 120 h and disappeared from the circulation by 7 days after bleeding. The packed cell volume (PCV) started increasing at 120 h and reached near pre-bleeding values by 14 days. In T. congolense-infected calves, parasites were first detected in the peripheral blood 12 days post-infection (dpi). Parasitaemia peaked (5 x 10(5) trypanosomes/ml of blood) at 15-18 dpi and, thereafter, several waves of parasitaemia were observed, but the peaks gradually diminished. Undiluted plasma from T. congolense-infected calves suppressed 125I-deoxyuridine incorporation into spleen cells from 13 dpi onwards. The suppressive effect of plasma was partly negated by five-fold dilution, which made possible the detection of increased EPO concentrations during the acute and chronic stages of the anaemia. The highest EPO peaks, reaching 2300 mU/ml in one calf, were detected during the chronic stage of the infection. At 15-39 dpi, there was a transient bone-marrow erythropoietic response characterized by an increase in mean corpuscular volume and a decrease in mean corpuscular haemoglobin concentration but with few reticulocytes (0.4%). However, from 76 dpi onwards, this response waned despite low PCV and elevated EPO concentrations. These results suggest that there is an ineffective erythroid response in the face of elevated EPO concentrations during bovine trypanosomiasis. The negative effect of plasma and serum from trypanosome-infected calves on the in-vitro bioactivity of EPO suggests the presence of inhibitory factors.  相似文献   
995.
The versatility of electronic portal imaging devices (EPIDs) is best demonstrated by their ability to perform novel megavoltage imaging protocols, which are still pertinent to good radiotherapy practice. This paper examines two such techniques: composite and realtime imaging. Our EPID can be programmed to acquire and manipulate images very easily, allowing images from segmented treatment protocols to be mixed and displayed, giving a composite image of the effective treatment result. Its use for verifying the efficacy of spinal shielding using a segmented, offset collimator technique is described. By acquiring images very quickly, realtime imaging sequences can be obtained and used to analyse anatomical movement within a single treatment field. The technique is employed here to investigate movement in radical lung, breast, abdomen, pelvis and thyroid treatments. Our results show that the protocol is vital for treatment sites involving the lungs; changes up to 5 mm have been observed in the maximum lung depth for breast treatments, and displacements up to 16 mm for radical lung treatments. It is also useful in other anatomical sites for ensuring that no movement occurs.  相似文献   
996.
997.
998.
Anesthesiologists should approach the airway carefully in the patient with a diagnosis of head and neck carcinoma, particularly if the patient has had previous surgery and reconstruction. Patients with head and neck carcinoma may be difficult intubations due to altered anatomy from the tumor or fibrotic changes because of radiation therapy. Our patient had had pharyngectomy and reconstruction with a pectoralis major skin flap. The patient returned to the operating suite for wide-excision pharyngectomy and had acute airway obstruction after induction of general anesthesia. The pectoralis flap had necrosed, pulling away from the pharyngeal wall and obstructing the patient's glottic opening.  相似文献   
999.
1000.
Creatine, a natural nutrient found in animal foods, is alleged to be an effective nutritional ergogenic aid to enhance sport or exercise performance. Research suggests that oral creatine monohydrate supplementation may increase total muscle creatine [TCr], including both free creatine [FCr] and phosphocreatine [PCr]. Some, but not all, studies suggest that creatine supplementation may enhance performance in high-intensity, short-term exercise tasks that are dependent primarily on PCr (i.e., < 30 seconds), particularly laboratory tests involving repeated exercise bouts with limited recovery time between repetitions; additional corroborative research is needed regarding its ergogenic potential in actual field exercise performance tasks dependent on PCr. Creatine supplementation has not consistently been shown to enhance performance in exercise tasks dependent on anaerobic glycolysis, but additional laboratory and field research is merited. Additionally, creatine supplementation has not been shown to enhance performance in exercise tasks dependent on aerobic glycolysis, but additional research is warranted, particularly on the effect of chronic supplementation as an aid to training for improvement in competitive performance. Short-term creatine supplementation appears to increase body mass in males, although the initial increase is most likely water. Chronic creatine supplementation, in conjunction with physical training involving resistance exercise, may increase lean body mass. However, confirmatory research data are needed. Creatine supplementation up to 8 weeks has not been associated with major health risks, but the safety of more prolonged creatine supplementation has not been established. Creatine is currently legal and its use by athletes is not construed as doping.  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