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   1894篇
  免费   63篇
  国内免费   6篇
电工技术   15篇
综合类   2篇
化学工业   316篇
金属工艺   15篇
机械仪表   23篇
建筑科学   39篇
矿业工程   3篇
能源动力   21篇
轻工业   157篇
水利工程   4篇
石油天然气   3篇
无线电   124篇
一般工业技术   177篇
冶金工业   958篇
原子能技术   8篇
自动化技术   98篇
  2023年   13篇
  2022年   41篇
  2021年   55篇
  2020年   23篇
  2019年   18篇
  2018年   46篇
  2017年   27篇
  2016年   23篇
  2015年   24篇
  2014年   33篇
  2013年   82篇
  2012年   53篇
  2011年   58篇
  2010年   49篇
  2009年   53篇
  2008年   53篇
  2007年   41篇
  2006年   34篇
  2005年   29篇
  2004年   29篇
  2003年   29篇
  2002年   21篇
  2001年   17篇
  2000年   10篇
  1999年   44篇
  1998年   251篇
  1997年   134篇
  1996年   103篇
  1995年   65篇
  1994年   63篇
  1993年   60篇
  1992年   19篇
  1991年   25篇
  1990年   24篇
  1989年   30篇
  1988年   31篇
  1987年   24篇
  1986年   12篇
  1985年   11篇
  1984年   7篇
  1983年   6篇
  1982年   13篇
  1981年   14篇
  1980年   12篇
  1979年   10篇
  1978年   11篇
  1977年   16篇
  1976年   68篇
  1975年   10篇
  1974年   9篇
排序方式: 共有1963条查询结果,搜索用时 15 毫秒
1.
Whole and sliced fresh mushrooms (Agaricus bisporus) were packaged with PVC wrap or two polyolefins (PD-941 and PD-961) films after coating with CaCl2 and chitosan. Package gas composition, color, weight loss and maturity were measured during storage at 12 °C and 80%RH. For PD-961, the highest in-package concentration occurred during the first day of storage regardless of treatments, while wrap and PD-941 showed varying degrees in-package concentration with different processes and coatings. The whiteness of whole mushrooms varied significantly with the type of coating, but not with the type of films. The extent of darkening was greater in coated whole mushrooms than in sliced ones. Weight loss occurred in all packages and varied from 3 (g/100 g) to about 7 (g/100 g) after 6 days of storage. Due to a lower permeability, PD-961 packages had the lowest weight loss. The type of packaging films significantly affected the maturity index, where PD-961 most effectively lowered maturity index for both whole and sliced mushrooms, thus extending the shelf-life. The type of coating did not appear to affect maturity index except for the wrap package where chitosan coating markedly lowered the maturity index of sliced mushrooms.  相似文献   
2.
This paper gives a first comparison of specific absorption rate (SAR) induced in a child-sized (CS) head and an adult head using a dual-band mobile phone. In the second study, the visible human head is considered and comparison of SAR induced in a CS or child-like (CL) head and an adult head using a dual-band mobile phone is given. All the peaks of average SAR over a mass of 10 and 1 g in the head and the power budget are determined in the two comparisons using the finite-difference time-domain method. The differences between the results for adult and CS or CL heads are given at 900 and 1800 MHz. No important differences are noted for the peak SAR averaged over 10 g (SAR10 g), between the two adult head models, as well as between the two child head models. The peak SAR10 g in the brain of the CS or CL head is slightly more significant than that for the adult one.  相似文献   
3.
We discovered that a food aversion could be conditioned in anesthetized sheep. Sheep were allowed to eat a familiar food (alfalfa-grain pellets) for 30 min, and 90 min later they were given either an intraruminal (IR) injection of water (C), an IR injection of LiCl (L), anesthesia followed by an IR injection of water (A), or anesthesia followed by an IR injection of LiCl (A+L). Induction of anesthesia was by an intravenous injection of pentobarbitone sodium, and maintenance of deep anesthesia was by halothane. Sheep were maintained in deep anesthesia for 2 h to ensure that the effects of LiCl on the acquisition of a food aversion, which occur within about 1 h, were completed before they awakened. When tested 5 days later, sheep that received LiCl (treatments L and A+L) consumed less alfalfa-grain pellets than sheep that did not receive LiCl (treatments C and A) (241 g vs. 306 g; p = 0.057). Intake of sheep that were anesthetized (treatments A and A+L) did not differ from that of sheep that were not anesthetized (treatments C and L) (295 g vs. 252 g; p = 0.183). Nor was there an interaction between LiCl and anesthesia (p = 0.423). Thus, we conclude that changes in preferences for foods caused by postingestive feedback occur automatically every time food is ingested (i.e., they are noncognitive), and the kind and amount of feedback is a function of the match between the food's chemical characteristics and its ability to meet the animal's current demands for nutrients.  相似文献   
4.
The current BLS Annual Survey of Occupational Illnesses and Injuries and several recent analyses of factors affecting missed worktime in occupational back injuries rely on ANSI-based injury codes derived from injury narratives to classify occupational injuries and estimate incidence and outcome. No population-based studies of the concordance between back injury codes and clinical diagnoses have been reported. Back injury cases were identified in two large work-injured populations totaling almost 80,000 cases in the states of Michigan and Minnesota. In both populations, cases had been coded by the single nature-of-injury and part-of-body-injured codes assigned by an ANSI-based injury-coding system and by as many as four (Michigan) or three (Minnesota) clinical diagnoses according to the International Classification of Diseases-Clinical Modification, 9th Revision. Concordance was measured by the sensitivity and predictive value positive (PVP, aka PV+ or PPA) of the injury coding scheme for related diagnostic groups. We also used an algorithm based on the limited clinical information available to corroborate the diagnosis of displaced/herniated disc for cases that underwent spinal surgery. Cases identified by the algorithm were then used to obtain a lower bound estimate of the fraction with disc injury. The injury coding scheme had PVPs of 82.9-90.1% and overall sensitivities of 69.7-75.9%. Sensitivities for individual diagnostic groups show that their distribution in ANSI-coded injury groups is skewed slightly toward cases with sprain and disc displacement/herniation, but these shifts are modest. The lower bound estimate of the fraction of cases with disc displacement/herniation in a population of cases with back injuries producing at least 1 day of missed worktime is 5.8%. The demographic comparisons indicate that, as the time between injury and cohort ascertainment increases during the first 8 days of missed worktime following injury, the proportion of younger workers in an injury cohort decreases. The relationship between increasing age and increasing missed worktime disability, reported in various outcome studies, is also present during the first few days following injury. The use of ANSI injury codes underestimates the contribution of back injuries to missed worktime because 24-30% of cases are missed by the ANSI coding system. However, the distribution of diagnostic groups in the injury-coded groups approximates that observed with all diagnosed cases and supports the use of such data to study outcome. Our estimate, and one from Quebec, suggest that disc displacement/herniation occurs more frequently in the subset of occupational back injuries compared to the set of back injuries from all sources.  相似文献   
5.
Low molecular weight heparins are a group of drugs that have only recently been introduced in clinical practice. The are widely used for prophylaxis in thromboembolic disease and are being employed increasingly to treat established venous thrombosis. One way in which these drugs are often used is for prophylaxis in the perioperative period for patients at high risk of developing venous thromboembolism, and the anesthesiologist must therefore be familiar with the main aspects of this application. We review pharmacological characteristics of these drugs as well as the literature on low molecular weight heparins, stressing points of main interest to the anesthesiologist and intensive care recovery unit specialist, namely adverse effects (mainly bleeding) and the implications that use of low molecular weight heparin will have on choice of anesthetic (in particular the dilemma of whether to use local/regional anesthesia).  相似文献   
6.
7.
8.
9.
BACKGROUND: There is no empirical data available on attitudes concerning AIDS and habits towards HIV infected patients of physicians in general or private practice. In this study results of a self-evaluation are presented. METHODS: 178 physicians working with out-patients in different medical fields were randomly selected for a cross sectional study and interviewed using a standardised questionnaire. RESULTS: 89% think that they are sufficiently informed about AIDS (in the USA 20%). They regarded the risk of infection to be lower than the Anglo-American physicians. They believed there is a lack of interchange of information between colleagues regarding the degree of infectiousness of referred patients. A third of the physicians fear that other patients will go elsewhere if they find out that their physician is treating AIDS patients. 54% would hold special clinic sessions for HIV-patients outside the normal schedule for practice times. 89% believed that HIV patients were partly to blame for their illness. CONCLUSIONS: Although the physicians recognise the problem of HIV-infection, they partly deny the real necessities and facts. A reason for this could be the emotions underlying the general attitude to everything pertaining to HIV-disease. Attitudes to HIV-disease and the dealing with it in daily practice must be considered on the basis of individual emotional motives.  相似文献   
10.
This paper reviews the pathogenesis of Mycobacterium bovis infection in cattle, focusing on aspects relating to the host rather than the organism. A broad concept of pathogenesis has been considered and information is presented on sources and routes of infection, as well as the immune responses and pathology. In addition, data is presented on the excretion of M. bovis from tuberculous cattle.  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