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   2784篇
  免费   15篇
  国内免费   1篇
电工技术   2篇
综合类   6篇
化学工业   17篇
机械仪表   6篇
建筑科学   3篇
能源动力   16篇
轻工业   29篇
水利工程   1篇
无线电   15篇
一般工业技术   37篇
冶金工业   2657篇
原子能技术   2篇
自动化技术   9篇
  2024年   1篇
  2023年   7篇
  2022年   4篇
  2021年   11篇
  2020年   7篇
  2019年   7篇
  2018年   9篇
  2017年   5篇
  2016年   4篇
  2015年   2篇
  2014年   7篇
  2013年   11篇
  2012年   1篇
  2011年   5篇
  2010年   3篇
  2009年   4篇
  2008年   4篇
  2007年   3篇
  2006年   2篇
  2005年   3篇
  2004年   8篇
  2003年   9篇
  2002年   1篇
  2000年   2篇
  1999年   105篇
  1998年   870篇
  1997年   498篇
  1996年   332篇
  1995年   167篇
  1994年   138篇
  1993年   179篇
  1992年   12篇
  1991年   22篇
  1990年   27篇
  1989年   32篇
  1988年   17篇
  1987年   21篇
  1986年   20篇
  1985年   27篇
  1984年   1篇
  1983年   3篇
  1982年   14篇
  1981年   8篇
  1980年   29篇
  1979年   1篇
  1978年   5篇
  1977年   49篇
  1976年   99篇
  1975年   2篇
  1973年   2篇
排序方式: 共有2800条查询结果,搜索用时 15 毫秒
81.
82.
We investigated the nature of the effects of memory associations on alcohol use and abuse. First, we determined if effects of memory associations on drinking problems are mediated entirely through the frequency of alcohol consumption or, alternatively, if such effects are more direct. Second, personality traits were assessed to evaluate whether they were confounded with memory association in their effects or whether they might moderate the effects of memory associations on alcohol use and abuse. The results showed that memory association measures directly and independently predicted alcohol consumption; these measures indirectly predicted problems from drinking, including drunk driving. None of the assessed personality variables moderated the predictive effects of memory association. The results are consistent with the view that memory associations influence behavior through cognitive processes that are not affected by personality traits or by cognitions emanating from such traits.  相似文献   
83.
Tonsils have a privileged situation in the immune system in that they are in touch with the environment. Melatonin is a hormone that is influenced by the circadian environmental variations of dark-light and is a modulator of the immune system. We have studied a group of thirty five children with recurrent acute tonsillitis that were submitted for tonsillectomy. Tonsillar lymphocyte subsets were determined before and after culture through flow cytometry in a tonsillar mononuclear suspension. After the culture, the lymphocyte subsets of type B suffered a decrease that was restored in the presence of melatonin or phytohemaglutinin, and even increased above the values of the control when the culture was accomplished in the presence of both substances. This process was specific for B cells, no occurrence for T lymphocytes or natural killer cells. Melatonin is found in the crossroads of the interaction of the microorganisms, pollens or inert substances with the tonsillar lymphocytes in the production of the immune defences. Further study is required on tonsillar pathology to explain its physiopathology and its possible therapeutic role.  相似文献   
84.
We studied the effect of the nitric oxide synthase (NOS) inhibitor asymmetric dimethyl arginine (ADMA) and the inactive enantiomer N G-methyl-D-arginine (D-NMMA) on Pseudomonas aeruginosa infection of the respiratory mucosa in nasal turbinate organ cultures. We also investigated the effect of P. aeruginosa culture filtrate on the expression of inducible NOS (iNOS) messenger RNA (mRNA) by an epithelial cell line (A549). Organ cultures were preincubated with ADMA (0.1 to 4 x 10(-4) M) or D-NMMA (2 x 10(-4) M) for 30 min prior to bacterial infection. Infected organ cultures (8 h) had significantly (P <= 0.05) greater epithelial damage and fewer ciliated and unciliated cells than did control cultures. There was an increased level of nitrite in the medium feeding infected organ cultures as compared with control cultures. ADMA significantly (P <= 0.05) reduced both bacterially induced epithelial damage and loss of ciliated cells in a concentration-dependent manner. D-NMMA did not influence the effect of P. aeruginosa infection of the mucosa. ADMA, but not D-NMMA, significantly (P <= 0.04) reduced total bacterial numbers adherent to the respiratory mucosa. P. aeruginosa culture filtrates (24 h and 36 h) significantly (P = 0.02) increased iNOS with respect to glyceraldehyde-3-phosphate dehydrogenase mRNA expression. These results show that P. aeruginosa stimulates iNOS expression by a cell line and NO production by an organ culture. ADMA reduces mucosal damage and loss of ciliated cells, which suggests that NO may be a mediator of epithelial damage caused by P. aeruginosa.  相似文献   
85.
OBJECTIVES: This ecologic study assessed whether there was a change in health status in Alaska in the winter of 1992-93 after the introduction of MTBE in gasoline. Methyl tertiary butyl ether(MTBE) is used as a fuel oxygenate in the United States and in Europe. In the winter of 1992-93 MTBE was added to gasoline in the cities of Fairbanks and Anchorage, Alaska. The program was discontinued in Fairbanks in December, 1992, but continued in Anchorage until February 28, 1993. METHODS: Outpatient visits for state employees and dependents (n = approximately 28,000) living in Alaska were compared over three winters by analyzing health insurance claims. RESULTS: Odds ratios were calculated. The odds ratios indicated that the winter of 92-93 was not statistically different from previous winters in numbers of claims for upper respiratory illness, bronchitis, headache, or asthma in either Anchorage or Fairbanks. CONCLUSION: There was no increase in claims for respiratory illness in either city after introduction of MTBE.  相似文献   
86.
The use of a model to appraise arboviral epizootics is described, and examples are given which demonstrated long-distance wind-dispersal of the biting-midge vector Culicoides brevitarsis from the same endemic source. Vector abundance is characterised by peaks and troughs of abundance, the patterns of which vary between localities and annually. Short term climatic effects can change rapidly the age structure of a population, thus increasing the number of midges that can transmit a virus and profoundly influencing the probabilities of viral transmission. The population dynamics of vector and viral foci are complex, if not chaotic.  相似文献   
87.
The age-related induction of inducible nitric synthase (iNOS) and apoptotic cell death in spiral ganglion cells (SGCs) of ddy strain mice were studied with immunohistochemical method and TdT-mediated dUTP-biotin nick end labeling (TUNEL), respectively. A large amount of iNOS was expressed in SGCs of 18- to 24-month-old mice, but not in those of the mice less than 12 months of age. Moreover, these mice were accompanied by a great rise in auditory brainstem response threshold as well as a great decrease in the number of SGCs that seemed to be due to preceding cell death of the cells. However, we were unable to find apoptotic TUNEL-positive cells in the spiral ganglions. This was assumed to be due to a very short clearance time of the dead cell bodies of less than one hour. As has been known, NO produced by iNOS can implicate in causes for either protection of cells from peroxidation and cell death. In the present study, therefore, the steep augmentation of iNOS in the SGCs of senescent mice implies that the iNOS initially induced to protect SGCs from the cytotoxicity of cellular peroxidation eventually contribute to the cell death of SGCs themselves.  相似文献   
88.
INTRODUCTION: This study looks at the degree of satisfaction colostomy patients feel in regards to their perception of the health care that they receive, whether they think that their physicians care could improve and the level of the medical staffs professional experience. METHOD AND MATERIAL: The study was performed in the Area Hospitalaria de Valme (Sevilla). With a population of 350,000 possible patients of which 215 have an ostomy, 55 of these took part in the study. 215 questionnaires were mailed to the ostomy patients with paid return mail enclosed. The survey was based on Lickerts attitude scale and had six items to respond to, using an evaluation of zero to five. This method is sufficiently valid and has been used in other studies such as project CORCH. RESULTS: First, averages were obtained for all items and variables. Second, a patient profile was obtained regarding sex and age. Third, a correlation of the three study variables was compared against variables of a global index of satisfaction. DISCUSSION: In contrast with the global index, the satisfaction of the patients in the study is very high (3.93 out of a possible 5). 45% of these patients perceive that the medical treatment that they receive could improve but that the professional experience of the medical staff is acceptable (62%).  相似文献   
89.
A simple spectrophotometric assay for the determination of cefepime and L-arginine in injections is described. Since zero-order spectra showed considerable overlap, second-derivative spectrophotometry was used to enhance the spectral details. A linear relationship between second-derivative amplitude and concentration of each compound was found. Beer's law was obeyed up to 50 and 22 micrograms ml-1 of cefepime and arginine, respectively, in the second-derivative mode. Detection limits were 0.31 and 0.58 micrograms ml-1 for cefepime and arginine, respectively. The method, which is rapid, simple and does not require any separation step, has been successfully applied to the assay of commercial injections containing cefepime and arginine.  相似文献   
90.
The remarkable ability of the body to maintain balance is the result of central nervous system integration of sophisticated inputs from the vestibular, visual, and somatosensory systems. Strategies by patients with balance dysfunction are aphysiologic when their performance is relatively better on more difficult conditions of sensory conflict than on easier ones. Twenty-two aphysiologic patterns on computerized dynamic posturography were compared with age-matched normal and vestibular patterns. The aphysiologic group performed significantly better than the patients in the vestibular dysfunction group on the most difficult subtests of computerized dynamic posturography, conditions 5 and 6, yet significantly poorer on the easier subtests, conditions 1 through 4. In addition, patients in the aphysiologic group tended to show greater intertrial variability compared with patients in both normal and vestibular system dysfunction groups. A stepwise linear discriminant analysis was used to determine a set of conditions that had significant value in discriminating between the three patient groups. Case studies are presented to further illustrate the clinical usefulness of computerized dynamic posturography testing in the evaluation of patients suspected of having a functional component to their on-feet balance problems.  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