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   2165篇
  免费   32篇
  国内免费   4篇
电工技术   7篇
综合类   2篇
化学工业   100篇
金属工艺   9篇
机械仪表   20篇
建筑科学   4篇
能源动力   34篇
轻工业   74篇
水利工程   5篇
石油天然气   1篇
无线电   67篇
一般工业技术   120篇
冶金工业   1654篇
原子能技术   6篇
自动化技术   98篇
  2023年   4篇
  2022年   12篇
  2021年   26篇
  2020年   15篇
  2019年   16篇
  2018年   20篇
  2017年   22篇
  2016年   25篇
  2015年   19篇
  2014年   18篇
  2013年   41篇
  2012年   25篇
  2011年   17篇
  2010年   16篇
  2009年   25篇
  2008年   33篇
  2007年   26篇
  2006年   19篇
  2005年   9篇
  2004年   5篇
  2003年   10篇
  2002年   7篇
  2001年   5篇
  2000年   14篇
  1999年   50篇
  1998年   471篇
  1997年   284篇
  1996年   186篇
  1995年   115篇
  1994年   105篇
  1993年   114篇
  1992年   16篇
  1991年   36篇
  1990年   20篇
  1989年   20篇
  1988年   21篇
  1987年   30篇
  1986年   23篇
  1985年   31篇
  1984年   8篇
  1983年   10篇
  1982年   8篇
  1981年   17篇
  1980年   22篇
  1979年   3篇
  1978年   7篇
  1977年   44篇
  1976年   117篇
  1975年   3篇
  1972年   3篇
排序方式: 共有2201条查询结果,搜索用时 15 毫秒
261.
Adherence with inhaled beta-agonists and corticosteroids in 24 asthmatic children was tracked over 3 months utilizing the metered-dose inhaler chronolog (MDIC). Patients seldom took all of their medications as prescribed, and failed to take any inhaled corticosteroid doses on a median of 41.8% of days or inhaled beta-agonists on 28.1% of days despite prescribed daily use. Medication nonadherence was correlated with lower levels of asthma knowledge (Asthma Knowledge Questionnaire) and family dysfunction (Family Assessment Device), but not child behavior disorder (Child Behavior Checklist). Patients tended to dramatically over-report medication use. Improved identification of the markers of nonadherence can directly facilitate more efficient targeting of behavioral interventions, resulting in improved adherence, better illness control, and less requirement of urgent medication intervention.  相似文献   
262.
263.
BACKGROUND: The influence of diet in asthma control remains unclear. However, there is likely to be a wide gap between patient perceptions and the probable actual role. Some 20-60% of people with asthma report food as a trigger factor while approximately 2.5% react to double-blind placebo-controlled challenges. The aim of this study was to determine: the frequency, type and sources of dietary advice being offered to patients, the prevalence of dietary modification, whether dietary changes were perceived to be of benefit and the type and sources of food/beverage reactions that people perceive they have experienced. METHOD: A self-administered 'food and asthma' questionnaire was developed and mailed to 156 consecutive Alfred Hospital Asthma and Allergy Clinic patients registered on a computer database. RESULTS: The completed questionnaire response rate was 86.5%. Dietary advice had been offered to 47% of respondents while 61% had tried to modify their diet. Dietary restriction was the most common dietary modification. Where dietary restriction had occurred 79% of respondents perceived that this had improved their asthma control. A doctor was the most common source of dietary advice. Seventy-three per cent reported that food induced asthma. CONCLUSION: We confirmed that patients with asthma perceived diet to be important in their asthma control and that dietary modification is common despite its lack of objective basis. The influence of diet and asthma requires more research, evaluation and clinical attention.  相似文献   
264.
When nasoseptal dislocation or deviation contributes to nasal obstruction or external deformity, successful nasal surgery should include septal restructuring, maintenance or restoration of adequate nasal support, and stabilization of the reconstructed elements.  相似文献   
265.
Mechanisms involved in the renal uptake of inorganic mercury were studied in rats administered a nontoxic 0.5 mumol/kg intravenous dose of inorganic mercury with or without 2.0 mumol/kg cysteine, homocysteine, or N-acetylcysteine. The renal disposition of mercury was studied 1 h after treatment in normal rats and rats that had undergone bilateral ureteral ligation. In addition, the disposition of mercury (including the urinary and fecal excretion of mercury) was evaluated 24 h after treatment. In normal rats, coadministering inorganic mercury plus cysteine or homocysteine caused a significant increase in the renal uptake of mercury 1 h after treatment. The enhanced renal uptake of mercury was due to increased uptake of mercury in the renal outer stripe of the outer medulla and/or renal cortex. Ureteral ligation caused reductions in the renal uptake of mercury in all groups except for the one treated with inorganic mercury plus N-acetylcysteine. Thus, it appears that virtually all of the mercury taken up by the kidneys of the normal rats treated with inorganic mercury plus N-acetylcysteine occurred at the basolateral membrane. Urinary excretory data also support this notion, in that the rate of excretion of inorganic mercury was greatest in the rats treated with inorganic mercury plus N-acetylcysteine. Our data also indicate that uptake of inorganic mercury in the kidneys of rats treated with inorganic mercury plus cysteine occurred equally at both luminal and basolateral membranes. In addition, the renal uptake of mercury in rats treated with inorganic mercury plus homocysteine occurred predominantly at the basolateral membrane with some component of luminal uptake. The findings of the present study confirm that there are at least two distinct mechanisms involved in the renal uptake of inorganic mercury, with one mechanism located on the luminal membrane and the other located on the basolateral membrane. Our findings also show that cysteine and homologs of cysteine, when coadministered with inorganic mercury, greatly influence the magnitude and/or site of uptake of mercuric ions in the kidney.  相似文献   
266.
The subendothelial accumulation of macrophage-derived foam cells is one of the hallmarks of atherosclerosis. The recruitment of monocytes to the intima requires the interaction of locally produced chemokines with specific cell surface receptors, including the receptor (CCR2) for monocyte chemoattractant protein-1 (MCP-1). We have previously reported that monocyte CCR2 gene expression and function are effectively downregulated by proinflammatory cytokines. In this study we identified low density lipoprotein (LDL) as a positive regulator of CCR2 expression. Monocyte CCR2 expression was dramatically increased in hypercholesterolemic patients compared with normocholesterolemic controls. Similarly, incubation of human THP-1 monocytes with LDL induced a rapid increase in CCR2 mRNA and protein. By 24 hours the number of cell surface receptors was doubled, causing a 3-fold increase in the chemotactic response to MCP-1. The increase in CCR2 expression and chemotaxis was promoted by native LDL but not by oxidized LDL. Oxidized LDL rapidly downregulated CCR2 expression, whereas reductively methylated LDL, which does not bind to the LDL receptor, had only modest effects on CCR2 expression. A neutralizing anti-LDL receptor antibody prevented the effect of LDL, suggesting that binding and internalization of LDL were essential for CCR2 upregulation. The induction of CCR2 expression appeared to be mediated by LDL-derived cholesterol, because cells treated with free cholesterol also showed increased CCR2 expression. These data suggest that elevated plasma LDL levels in conditions such as hypercholesterolemia enhance monocyte CCR2 expression and chemotactic response and potentially contribute to increased monocyte recruitment to the vessel wall in chronic inflammation and atherogenesis.  相似文献   
267.
Staphylococcal enterotoxins A and C1 (SEA or SEC1) bound to major histocompatibility-I (MHCI) molecules with high affinity (binding constants ranging from 1.1 microM to 79 nM). SEA and SEC1 directly bound MHCI molecules that had been captured by monoclonal antibodies specific for H-2Kk, H-2Dk, or both. In addition, MHCI-specific antibodies inhibited the binding of SEC1 to LM929 cells and SEA competitively inhibited SEC1 binding; indicating that the superantigens bound to MHCI on the cell surface. The affinity and number of superantigen binding sites differed depending on whether MHCI was expressed in the membrane of LM929 cells or whether it was captured. These data support the hypothesis that MHCI molecules can serve as superantigen receptors.  相似文献   
268.
The energy conserving corrinoid containing MtrA-H complex from Methanobacterium thermoautotrophicum is composed of eight different subunits of which MtrA harbors the corrinoid prosthetic group, the corrinoid being bound in the base-off/His-on configuration. Based on sequence comparisons it was recently proposed that His35 of MtrA is the active site histidine. We report here that His84 rather than His35 is the axial ligand to the cobamide in MtrA.  相似文献   
269.
The CD5 antigen is a T-cell associated marker that is also usually expressed by two B-cell neoplasms, chronic lymphocytic leukemia/small lymphocytic lymphoma and mantle cell lymphoma. We observed CD5 antigen expression in a subset of cases of intravascular large B-cell lymphoma (IVLBL), and we report here five cases. The patients, two men and three women, ranged in age from 59 to 81 years. Biopsy specimens were obtained from kidney, lung, bone marrow, abdominal wall, and neck, the latter involving a lymphangioma. All of the cases had histologic features typical of IVLBL, with large and atypical lymphoid cells located predominantly within blood vessels. Immunohistochemical studies performed using routinely fixed, paraffin-embedded tissue sections showed that the neoplastic cells were B cells, positive for the CD20 antigen and negative for the CD3 or CD43 antigens. All cases were also positive for the CD5 antigen. One case had an immunoglobulin heavy chain gene rearrangement shown by using a polymerase chain reaction method. The finding of CD5 antigen expression in a subset of IVLBL cases adds to other evidence in the literature suggesting that IVLBL is a heterogeneous entity. We considered the possibility that these cases were related to or represented unusual histologic forms of transformation from either chronic lymphocytic leukemia/small lymphocytic lymphoma or mantle cell lymphoma. All of the cases, however, were negative for the CD23 antigen and cyclin D1 (bcl-1) protein, which is evidence against this interpretation. The biologic significance of CD5 antigen expression in cases of IVLBL is uncertain. These neoplasms might arise from a separate lineage of CD5-positive B cells or from a specific, early stage of B-cell differentiation. Alternatively, some investigators have suggested that CD5 antigen expression by B cells is a marker of activation.  相似文献   
270.
BACKGROUND: Autosomal dominant, nonsyndromic, hereditary hearing impairment in a large Costa Rican kindred is caused by a mutation in the human homolog of the Drosophila diaphanous gene. OBJECTIVE: To further characterize the phenotype of DFNA1 with comprehensive audiovestibular evaluation and computed tomography of the temporal bone. PATIENTS: One affected child and 2 affected adults of the Costa Rican kindred who harbor a mutation in the diaphanous gene. SETTING: Medical Center at the University of California, San Francisco. INTERVENTION: Otologic and neuro-otologic examination; pure tone audiometry, speech audiometry, and immitance testing; auditory evoked potentials, electrocochleography, and otoacoustic emissions; electronystagmography and vestibular autorotation tests; and computed tomography of the temporal bone. RESULTS: The youngest subject, an 8-year-old boy, had a mild hearing loss, intact stapedial reflexes, otoacoustic emissions at high frequencies, normal auditory evoked potentials, and electrocochleographic findings consistent with endolymphatic hydrops. The two adults had severe to profound bilateral sensorineural hearing impairment. Electronystagmography disclosed normal vestibular function. Computed tomography demonstrated normal external, middle, and inner ear structures. CONCLUSIONS: These results suggest that the early low-frequency hearing loss in this family is associated with endolymphatic hydrops. Elucidation of the role of the diaphanous gene in hearing will therefore lead to a better understanding of the mechanism of endolymphatic hydrops.  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