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   1943篇
  免费   8篇
  国内免费   3篇
电工技术   11篇
化学工业   61篇
金属工艺   18篇
机械仪表   14篇
建筑科学   19篇
矿业工程   1篇
能源动力   11篇
轻工业   80篇
水利工程   3篇
石油天然气   2篇
无线电   147篇
一般工业技术   73篇
冶金工业   1392篇
原子能技术   3篇
自动化技术   119篇
  2020年   4篇
  2018年   4篇
  2016年   5篇
  2015年   14篇
  2014年   7篇
  2013年   26篇
  2012年   17篇
  2011年   27篇
  2010年   16篇
  2009年   29篇
  2008年   28篇
  2007年   36篇
  2006年   32篇
  2005年   27篇
  2004年   30篇
  2003年   23篇
  2002年   25篇
  2001年   17篇
  2000年   26篇
  1999年   43篇
  1998年   383篇
  1997年   253篇
  1996年   163篇
  1995年   100篇
  1994年   84篇
  1993年   81篇
  1992年   18篇
  1991年   12篇
  1990年   27篇
  1989年   13篇
  1988年   21篇
  1987年   15篇
  1986年   15篇
  1985年   22篇
  1984年   10篇
  1983年   16篇
  1982年   15篇
  1981年   15篇
  1980年   16篇
  1979年   6篇
  1978年   14篇
  1977年   49篇
  1976年   99篇
  1975年   7篇
  1974年   7篇
  1973年   10篇
  1972年   6篇
  1971年   4篇
  1969年   5篇
  1961年   4篇
排序方式: 共有1954条查询结果,搜索用时 515 毫秒
141.
35 female and 27 male undergraduates completed the Personality Research Form, Eysenck Personality Inventory, and Self-Monitoring Scale. Ss were also assessed on posed emotional sending ability and on physical attractiveness. Ss were then videotaped while giving a spontaneous "explanation." Trained coders measured 5 separate nonverbal cue factors displayed by the Ss in the videotapes. Groups of untrained judges viewed the tapes and rated their impressions of the Ss on scales of likability, speaking effectiveness, and expressivity-confidence. Males who were nonverbally skilled and extraverted tended to display more outwardly focused and fluid expressive behaviors, and made more favorable impressions on judges, than did males who scored low on the measures of nonverbal skills and extraversion. Females who were nonverbally skilled displayed more facial expressiveness, which led to more favorable initial impressions. It is suggested that these sex differences may reflect basic differences in the acquisition and use of expressive nonverbal cues by males and females. (45 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
142.
143.
Tomato (Lycopersicon esculentum) plants synthesise nutrients, pigments and secondary metabolites. These include the green pigment chlorophyll, the yellow pigment β‐carotene, the red pigment lycopene and the colourless glycoalkaloid α‐tomatine. The levels of these compounds are strongly influenced by the maturity of the tomatoes. Widely consumed Japanese tomato varieties Momotaro, Momotaro‐T93 and First Memory at five different stages of ripeness, each harvested at 10, 20, 30, 40 and 50 days after flowering of the plants, were analysed for the contents of these compounds. Additionally, tomato clusters from different locations along the vine on the same plant were also evaluated. The results show that chlorophyll and tomatine concentrations decrease rapidly during the growth of the tomatoes. By contrast, β‐carotene and lycopene levels are low in immature and high in mature tomatoes. The location of the tomato clusters and tomato variety did not significantly affect these results. The possible usefulness of these results to optimise health‐promoting effects of tomatoes is discussed. © 2003 Society of Chemical Industry  相似文献   
144.
145.
146.
147.
Superplastic response in Al-Mg sheet alloys   总被引:1,自引:0,他引:1  
The ability to achieve large strains to failure coupled with extremely low flow stresses makes superplastic forming (SPF) an attractive option in the automotive industry for the manufacture of complex parts from aluminum (Al) sheet. However, a barrier to increased usage is the cost penalty associated with superplastic alloys, which are specially processed to have a small and stable grain size. In this article, high-temperature tensile tests are used to compare the superplastic performance of two different Al-Mg alloys that were specially processed for SPF with that of a conventionally processed Al-Mg alloy. The results of the tensile tests and optical microscopy are used to highlight the mechanisms that control deformation in each of these alloys under different test conditions. Failure in both types of materials was found to change from internal cavitation to external necking with increases in strain rate. The specially processed alloys experienced minimal grain growth or grain elongation during forming, and therefore it was assumed that deformation was controlled by grain boundary sliding. Contrary to this, the conventionally processed alloy experienced significant grain growth at the higher test temperatures, and hence it was concluded that deformation was at least partially controlled by some mechanism other than grain boundary sliding. The different deformation characteristics resulted in a different set of optimal forming conditions for the two types of materials. The SPF alloys displayed higher strains to failure at the slower strain rates and higher temperatures, while the conventionally processed alloy displayed higher strains to failure at the faster strain rates and lower temperatures.  相似文献   
148.
OBJECTIVE: To study the influence of continuous administration of heparin on platelet function in intensive care patients. DESIGN: Prospective, serial investigation. SETTING: Clinical investigation on a surgical and neurosurgical intensive care unit in a university hospital. PATIENTS: The study included 45 patients: 15 postoperative with patients sepsis (Acute Physiology and Chronic Health Evaluation II score between 15 and 25), 15 trauma patients (Injury Severity Score 15 to 25), and 15 neurosurgical patients. INTERVENTIONS: Management of the patients was carried out according to the guidelines for modern intensive care therapy. Sepsis and trauma patients received standard (unfractionated) heparin continuously [aim: an activated partial thromboplastin time (aPTT) approximately 2.0 times normal value; sepsis-heparin and trauma-heparin patients], whereas neurosurgical patients received no heparin (neurosurgical patients). MEASUREMENTS AND RESULTS: From arterial blood samples, platelet aggregation was measured by the turbidimetric method. Platelet aggregation was induced by adenosine diphosphate (ADP; 2.0 mumol/l), collagen (10 micrograms/ml), and epinephrine (25 mumol/l). Measurements were carried out on the day of diagnosis of sepsis or 12 h after hemodynamic stabilization (trauma and neurosurgery patients) (baseline) and during the next 5 days at 12.00 noon. Standard coagulation parameters [platelet count and fibrinogen and antithrombin III (AT III) plasma concentrations] were also monitored. Heparin 4-10 U/kg per h (mean dose: approximately 500 U/h) was necessary to reach an aPTT of about 2.0 times normal. Platelet count was highest in the neurosurgical patients, but it did not decrease after heparin administration to the trauma and sepsis patients. AT III and fibrinogen plasma levels were similar in the three groups of patients. In the sepsis group, platelet aggregation variables decreased significantly (e.g., epinephrine-induced maximum platelet aggregation:-45 relative % from baseline value). Platelet function recovered during the study and even exceeded baseline values (e.g., ADP-induced maximum platelet aggregation: +42.5 relative % from baseline value). Continuous heparinization did not blunt this increase of platelet aggregation variables. In the heparinized trauma patients, platelet aggregation variables remained almost stable and were no different to platelet aggregation data in the untreated neurosurgical patients. CONCLUSIONS: Continuous administration of heparin with an average dose of approximately 500 U/h did not negatively influence platelet function in the trauma patients. Recovery from reduced platelet function in the sepsis group was not affected by continuous heparinization. Thus, continuous heparinization with this dose appears to be safe with regard to platelet function in the intensive care patient.  相似文献   
149.
This document represents the recommendations of a panel of Spanish experts on antibiotic use and resistance. In a Task Force, under the auspices of the Spanish Ministry of Health and Consumer Affairs that took place in 1994 in Madrid, the members were gravely concerned about the national increase in antibiotic resistance. They analysed the development, evolution and spread of antibiotic resistance among community-acquired human bacterial pathogens in Spain, its relation with antibiotic consumption, and they proposed future surveillance strategies for monitoring the patterns of antibiotic use and consumption. Success will require a collective action among the producers (pharmaceutical industry), prescribers (doctors, veterinarians), dispensers (pharmacists), and consumers (patients). Two similar documents have been recently published by the American Society of Microbiology and the World Health Organization showing the global concern about this topic.  相似文献   
150.
Epidemiological research during the past 40 years has demonstrated with increasing clarity that amphibole asbestos fibres--crocidolite, amosite and tremolite--are more carcinogenic than chrysotile. A smaller number of well-controlled studies using lung burden analyses, while adding to the specificity of this conclusion, have shown that amphibole fibres also differ from chrysotile in being far more durable and biopersistent in lung tissue. Analyses of mesothelioma and lung cancer in a large cohort of Canadian chrysotile miners and millers have recently shown that the low-level presence of fibrous tremolite in these mines, rather than the chrysotile, may well be responsible. The high risk of lung cancer, but not of mesothelioma, in the chrysotile textile industry remains anomalous and cannot be explained in this way. These various findings are directly relevant to the choice of the experimental methods which should be used for screening man-made fibres for industrial use. Although it is clear that biopersistence is a major determinant of cancer risk in animals, and perhaps also in man, other factors affecting the biological activity of mineral fibres may also be important.  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