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   6699篇
  免费   235篇
  国内免费   11篇
电工技术   37篇
综合类   4篇
化学工业   831篇
金属工艺   179篇
机械仪表   198篇
建筑科学   65篇
矿业工程   4篇
能源动力   172篇
轻工业   319篇
水利工程   5篇
石油天然气   10篇
无线电   528篇
一般工业技术   726篇
冶金工业   3472篇
原子能技术   38篇
自动化技术   357篇
  2024年   5篇
  2023年   59篇
  2022年   81篇
  2021年   123篇
  2020年   92篇
  2019年   89篇
  2018年   127篇
  2017年   118篇
  2016年   130篇
  2015年   89篇
  2014年   144篇
  2013年   196篇
  2012年   256篇
  2011年   309篇
  2010年   198篇
  2009年   185篇
  2008年   164篇
  2007年   136篇
  2006年   128篇
  2005年   104篇
  2004年   100篇
  2003年   100篇
  2002年   95篇
  2001年   69篇
  2000年   65篇
  1999年   162篇
  1998年   1045篇
  1997年   635篇
  1996年   416篇
  1995年   273篇
  1994年   190篇
  1993年   237篇
  1992年   47篇
  1991年   72篇
  1990年   57篇
  1989年   73篇
  1988年   71篇
  1987年   56篇
  1986年   45篇
  1985年   46篇
  1984年   12篇
  1983年   10篇
  1982年   25篇
  1981年   21篇
  1980年   26篇
  1979年   6篇
  1978年   7篇
  1977年   99篇
  1976年   137篇
  1975年   7篇
排序方式: 共有6945条查询结果,搜索用时 15 毫秒
61.
62.
The STERRAD 100 sterilization system (Johnson & Johnson Medical Ltd) uses low temperature hydrogen peroxide gas plasma for sterilization of heat labile equipment. The efficacy of the machine was tested by contaminating a standard set of instruments with different organisms and using a filtration method to assess recovery of organisms from the wash fluids of instruments post-sterilization. Experiments were performed under clean (the organism only) and dirty (organism mixed with egg protein) conditions. A parallel study conducted using a 3M STERIVAC ethylene oxide sterilizer could not be completed owing to closure of the ethylene oxide plant. For sterilization of instruments with long and narrow lumens, hydrogen peroxide adaptors are necessary. The STERRAD 100 sterilizer can achieve effective sterilization of heat labile instruments with a reduction of 6 log10 cfu/mL of organisms tested. This method has the advantages over ethylene oxide sterilization of safety, ease of maintenance and no requirement for aeration time.  相似文献   
63.
Numerous studies have confirmed the distinct biological behavior of two subsets of prostate cancer diagnosed incidentally after either transurethral resection (TURP) or open prostatectomy for presumed benign prostatic hyperplasia (BPH). Focal, low-grade lesions are associated with a low risk for clinical progression and are designated as stage T1a or A1. These cases have traditionally been managed conservatively with close clinical observation. In contrast, multifocal, high-volume, or high-grade tumors are associated with a more aggressive clinical course and are designated as stage T1b or A2. Early definitive intervention is usually advocated for these latter patients. Therefore, accurate pathological assignment to either stage T1a or T1b is crucial for selection of appropriate management options. A variety of methods for staging patients with incidentally detected prostate cancer have been proposed, including detailed histological analysis, repeat TURP or transurethral biopsy, serial prostate-specific antigen (PSA) analysis, and imaging with either transrectal ultrasound (TRUS) or magnetic resonance (MRI) techniques. This article critically examines the clinical utility of these staging modalities for patients with incidentally detected prostate cancer.  相似文献   
64.
65.
Dysphonic voices are often analyzed using automated voice analysis software. However, the reliability of acoustic measures obtained from these programs remains unknown, particularly when they are applied to pathological voices. This study compared perturbation measures from CSpeech, Computerized Speech Laboratory, SoundScope, and a hand marking voice analysis system. Sustained vowels from 29 male and 21 female speakers with mild to severe dysphonia were digitized, and fundamental frequency (F0), jitter, shimmer, and harmonics- or signal-to-noise ratios were computed. Commercially available acoustical analysis programs agreed well, but not perfectly, in their measures of F0. Measures of perturbation in the various analysis packages use different algorithms, provide results in different units, and often yield values for voices that violate the assumption of quasi-periodicity. As a result, poor rank order correlations between programs using similar measures of perturbation were noted. Because measures of aperiodicity apparently cannot be reliably applied to voices that are even mildly aperiodic, we question their utility in quantifying vocal quality, especially in pathological voices.  相似文献   
66.
Modeling molecular interactions in signalling networks is important from various perspectives such as predicting side effects of drugs, explaining unusual cellular behavior and drug and therapy design. Various formal languages have been proposed for representing and reasoning about molecular interactions. The interactions are modeled as triggered events in most of the approaches. The triggering of events is assumed to be immediate: once an interaction is triggered, it should occur immediately. Although working well for engineering systems, this assumption poses a serious problem in modeling biological systems. Our knowledge about biological systems is inherently incomplete, thus molecular interactions are constantly elaborated and refined at different granularity of abstraction. The model of immediate triggers can not consistently deal with this refinement. In this paper we propose an action language to address this problem. We show that the language allows for refinements of biological knowledge, although at a higher cost in terms of complexity.   相似文献   
67.
68.
A new furostanol saponin was isolated from the mesocarp of Balanites aegyptiaca fruits and identified as 26-O-beta-D-glucopyranosyl-(25R)-furost-5-ene-3,22,26-triol 3-O-[[alpha-L-rhamnopyranosyl-(1-->2)]-[beta-D-xylopyranosyl-(1-->2)]-be ta- D-xylopyranosyl-(1-->2)]-beta-D-xylopyranoside (balanitesin).  相似文献   
69.
70.
Sixty-six supine portable chest radiographs done on the day of bronchoscopy in 62 critical care unit patients suspected of having pneumonia were examined in a blinded fashion by two radiologists. Quantitative culture results obtained from protected brush catheter (PBC) specimens were compared with chest radiograph scores. For one observer, the sensitivity of the chest radiograph for predicting the presence of positive culture results was 0.60, specificity was 0.29, overall agreement was 0.41, positive predictive value was 0.34, and negative predictive value was 0.55. For the second observer, the values were as follows: sensitivity, 0.64; specificity, 0.27; overall agreement, 0.41; positive predictive value, 0.35; and negative predictive value, 0.55. The kappa statistic was calculated at 0.27 indicating marginal interobserver reproducibility. We conclude the portable chest radiograph in the critical care setting is not accurate in predicting the presence of pneumonia when the diagnosis is based on quantitative cultures obtained from protected brush catheter specimens.  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