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   1736篇
  免费   14篇
  国内免费   1篇
电工技术   6篇
综合类   1篇
化学工业   68篇
金属工艺   36篇
机械仪表   12篇
建筑科学   19篇
矿业工程   5篇
能源动力   6篇
轻工业   89篇
水利工程   1篇
石油天然气   3篇
无线电   47篇
一般工业技术   116篇
冶金工业   1256篇
原子能技术   15篇
自动化技术   71篇
  2022年   5篇
  2018年   6篇
  2017年   7篇
  2016年   12篇
  2014年   14篇
  2013年   37篇
  2012年   24篇
  2011年   22篇
  2010年   12篇
  2009年   14篇
  2008年   13篇
  2007年   23篇
  2006年   22篇
  2005年   18篇
  2004年   14篇
  2003年   10篇
  2002年   18篇
  2001年   12篇
  2000年   6篇
  1999年   35篇
  1998年   350篇
  1997年   204篇
  1996年   131篇
  1995年   94篇
  1994年   83篇
  1993年   92篇
  1992年   22篇
  1991年   16篇
  1990年   30篇
  1989年   21篇
  1988年   18篇
  1987年   13篇
  1986年   9篇
  1985年   20篇
  1984年   14篇
  1983年   13篇
  1982年   14篇
  1981年   14篇
  1980年   22篇
  1979年   10篇
  1978年   18篇
  1977年   48篇
  1976年   102篇
  1975年   7篇
  1973年   10篇
  1971年   4篇
  1970年   5篇
  1969年   4篇
  1967年   5篇
  1955年   4篇
排序方式: 共有1751条查询结果,搜索用时 15 毫秒
991.
Behavior problems and family functioning were investigated in a sample of 10 adolescent girls with chronic fatigue syndrome (CFS), 10 matched healthy adolescent girls, and 10 adolescents with childhood cancer in remission. Based on the adolescent girls' reports, the CFS group had significantly higher scores than the cancer and healthy comparison adolescent girls on somatic complaints and also significantly higher scores than the cancer controls on internalizing symptoms and depression. Parent reports resulted in significantly higher scores in the CFS group than the adolescent girls from the healthy comparison groups on internalizing scores and somatic complaints. There were no significant differences on any family variables.  相似文献   
992.
TNF-alpha plays a pivotal role in the pathogenesis of septic shock. It exerts its effects by binding two cell surface receptors, designated TNF-R I and II, also referred to as the p55 and p75 receptors, respectively. TNF-Rs are transmembrane proteins, which on cleavage of their extracellular domains, result in the release of soluble fragments (sTNF-R). sTNF-R levels increase markedly during infection, and may serve to modulate TNF-alpha bioactivity. The mechanisms regulating this process are uncertain. To investigate this, we measured sTNF-R release in endotoxin-sensitive C3H/HeN and endotoxin-resistant C3H/HeJ mice given LPS or live Gram-negative bacteria. In C3H/HeN mice, there was a rapid early response during the first 4 h, and a second peak at 8 h, particularly noticeable in the case of the p75 receptor. Prior administration of neutralizing Abs to TNF-alpha or IFN-gamma had no effect on receptor shedding. Surprisingly, C3H/HeJ mice also responded to both bacterial challenge and to LPS by shedding sTNF-R; the magnitude and duration of the early response was not substantially different from C3H/HeN mice, although the second peak was absent. Peritoneal macrophages from C3H/HeN mice responded promptly (5 h) when stimulated with LPS in vitro, and by 22 h levels had increased five- to 10-fold. In contrast, cells from C3H/HeJ mice demonstrated only a very modest response at 22 h following maximal stimulation. The data suggest that there may be at least two separately regulated pathways that control sTNF-R shedding in these mice.  相似文献   
993.
In an attempt to diagnose ventricular mural thrombi complicating acute myocardial infarction (AMI), 80 patients have been given 100 muCi 125I-labelled fibrinogen after admission to a CCU. Precordial radioactivity was recorded for the following 6 days over four sites corresponding to chest leads CR1-CR4. A sustained rise in radioactivity of at least 15% of initial recordings was classed as type A pattern, a minor rise or flattened response as type B pattern and a rapid decrease as type C pattern; 28% showed a type A, 19% a type B and 54% a type C pattern. There was no significant difference between the groups in incidence of pericardial friction rub but when patients with suspected pericarditis (as evidenced by characteristic pains) were added, pericarditis was significantly overrepresented in the type A group. Smaller infarctions (SGOT less than 100 U/1) were significantly more common in patients with a type C decay pattern. No differences were noted between the groups as regards type and site of the infarction. A sustained rise in precordial radioactivity after an AMI may be an indication of mural thrombosis but the influence of other factors secondary to an infarction, e.g. pericarditis, cannot be determined at present.  相似文献   
994.
995.
We previously reported (1) that tracheobronchial secretions of patients in hemorrhagic shock contained significantly more iron laden histiocytes than secretions of matched controls and demonstrated by histiologic studies in rats bled to hemorrhagic shock that these animals' lungs contained significantly more iron laden histiocytes than those of a control group. Two explanations appeared plausible: 1) abnormal hemoglobin breakdown products of systemic hypoperfusion during shock (2, 3, 5) may have accumulated in the pulmonary circulation where they were phagocytozed by pulmonary histiocytes, or 2) circulating iron laden histiocytes may have been arrested in the lung, which is well known to act as a filter during low-flow states (4). The present study reports on assay of bronchial secretions of 12 open-heart surgery patients under cardiopulmonary bypass from specimens obtained 1) immediately after onset of anesthesia; 2) during; and 3) after termination of cardiopulmonary bypass. The percentage of iron laden histiocytes rose from 15.6+/-6.0 after intubation, to 49.6+/-6.8 after 1 hour on bypass with occluded pulmonary arteries (p less than 0.0025), remaining close to the latter value after pulmonary circulation was restored. Hypoperfusion, accumulation of metabolites, or falling pH at the tissue level are probable explanations for these findings.  相似文献   
996.
Electron microscope studies on Necturus maculosus oocytes ranging in size from 1.1-1.5 mm in diameter indicate the primary proteinaceous yolk to arise within structures referred to in other amphibian oocytes as yolk precursor sacs or bodies. The origin of these yolk precursor sacs appears to result from the activity of the Golgi complexes which form multivesicular and granular-vesicular bodies, the limiting membrane of which is at times incomplete. During differentiation, the yolk precursor sacs contain small vesicles similar in size to Golgi vesicles, larger vesicles similar to vesicular elements of the agranular endoplasmic reticulum and, on occasion, a portion of a mitochondrion. The interior of these sacs becomes granular, perhaps by a dissolution of the components just described, and soon becomes organized into a crystalline configuration. In oocytes 2.0-2.5 mm in diameter, an extensive micropinocytotic activity begins, continues throughout vitellogenesis, and constitutes the primary mechanism for the formation of secondary yolk protein. Numerous coated and smooth-surfaced vesicles, as well as electron-dense and electronlucent ones, fuse in the cortical ooplasm to form progressively larger yolk platelets.  相似文献   
997.
A short review of the prevalence of ischaemic heart disease in South African Whites is given, and primary prevention, which entails an alteration in life style, is emphasised. The role of increased physical activity in primary prevention is discussed. Any programme to increase the fitness status of a population based on activities that must be performed outside the daily routine, willhave limited impact. The possible role of cycling is discussed and it is shown that ordinary cycling to work probably causes sufficient stimulation of the cardiovascular system to produce an acceptable standard of physical fitness.  相似文献   
998.
Sear  J.F. Carpenter  R. 《Electronics letters》1975,11(22):532-533
A noise-cancelling communication microphone using a piezoelectric plastic as the transducer element has been developed. The bimorph structure adopted in conjunction with an impedance matching preamplifier circuit and suitable acoustic design provides an adequate, stable output at low impedance, with an acceptable frequency response. The susceptibility of the microphone to electromagnetic fields is low.  相似文献   
999.
Aberrant tissue bands and craniofacial defects   总被引:1,自引:0,他引:1  
A report of 8 cases of craniofacial anomalies and aberrant tissue bands has been presented. Analyses of the pedigrees, pregnancy histories and chromosome analyses were unrevealing. This syndrome appears to be a sporadic disorder and it is important to delineate it further from other syndromes for which recurrence risks are known.  相似文献   
1000.
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