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   2215篇
  免费   36篇
  国内免费   8篇
电工技术   10篇
综合类   16篇
化学工业   26篇
金属工艺   16篇
机械仪表   7篇
建筑科学   5篇
矿业工程   6篇
能源动力   1篇
轻工业   15篇
水利工程   8篇
石油天然气   4篇
无线电   14篇
一般工业技术   55篇
冶金工业   2059篇
自动化技术   17篇
  2024年   3篇
  2023年   4篇
  2022年   3篇
  2021年   7篇
  2020年   6篇
  2019年   5篇
  2018年   6篇
  2017年   2篇
  2015年   6篇
  2014年   7篇
  2013年   7篇
  2012年   12篇
  2011年   18篇
  2010年   13篇
  2009年   17篇
  2008年   15篇
  2007年   13篇
  2006年   5篇
  2005年   12篇
  2004年   2篇
  2003年   11篇
  2002年   8篇
  2001年   3篇
  2000年   2篇
  1999年   73篇
  1998年   631篇
  1997年   364篇
  1996年   234篇
  1995年   135篇
  1994年   121篇
  1993年   142篇
  1992年   13篇
  1991年   18篇
  1990年   9篇
  1989年   16篇
  1988年   27篇
  1987年   21篇
  1986年   15篇
  1985年   16篇
  1982年   8篇
  1981年   13篇
  1980年   21篇
  1978年   4篇
  1977年   62篇
  1976年   112篇
  1975年   7篇
  1967年   1篇
  1966年   2篇
  1955年   1篇
  1954年   1篇
排序方式: 共有2259条查询结果,搜索用时 0 毫秒
21.
22.
23.
Thoracoscopy provides a minimally invasive technique for the diagnosis and management of many posterior mediastinal masses. Benign neurogenic tumors, esophageal tumors, and bronchogenic cysts all can be approached using video-assisted thoracic surgical (VATS) techniques. Malignant lesions are still best approached via open thoracotomy. VATS techniques allow for less pain and dysfunction and can result in shortened hospital stays.  相似文献   
24.
25.
26.
Su Vida, Su Salud/Your Life, Your Health is a community program to increase participation in breast and cervical cancer screening. This program illustrates the diffusion of an innovative outreach strategy from a research environment to two local health departments. The program uses A Su Salud, the communication model in which positive role models are featured in the media, and community volunteers who give positive social reinforcement. Local health departments in Galveston and Corpus Christi, TX, were selected to implement the model because of excessive mortality rates in the region and the departments' adequate level of resources and commitment. Over an 18-month period, 54 stories of role models appeared in the media in Corpus Christi, and 60 appeared in Galveston. There were 490 volunteers active in Corpus Christi and 279 in Galveston. Of 365 inquiries to the Corpus Christi program, 35 percent were from the Mexican American target group of women ages 40-70. Of 1,457 women who contacted the Galveston program, 9 percent were from the African American target group ages 40-70. Local health departments are well-suited to participation in cancer control research applications because they have direct access to high-risk populations and have the authority to institutionalize effective interventions.  相似文献   
27.
Combinations of EDTA-Tris and two aminoglycoside antibiotics (amikacin and neomycin) were tested for synergistic activities against the microorganisms associated with otitis externa in dogs and for the solutions' stability over time. Synergistic activity was observed when EDTA-Tris plus amikacin and EDTA-Tris plus neomycin were tested against Staphylococcus intermedius, Proteus mirabilis, Pseudomonas aeruginosa, and Escherichia coli, but not against Candida albicans. Stability studies over a 3-month period indicated that the test solutions were stable at room temperature and that their antimicrobial activity was maintained.  相似文献   
28.
Recognition by integrin proteins on the cell surface regulates the adhesive interactions between cells and their surroundings. The structure of the 'I' domain that is found in some but not all integrins, has been determined. However, the only integrin ligands for which structures are known, namely fibronectin and VCAM-1, are recognized by integrins that lack I domains. The intercellular adhesion molecules ICAM-1, 2 and 3 are, like VCAM-1, members of the immunoglobulin superfamily (IgSF), but they are recognized by an I domain-containing integrin, lymphocyte-function-associated antigen 1 (LFA-1, or CD11a/CD18). Here we present the crystal structure of the extracellular region of ICAM-2. The glutamic acid residue at position 37 is critical for LFA-1 binding and is proposed to coordinate the Mg2+ ion in the I domain; this Glu 37 is surrounded by a relatively flat recognition surface and lies in a beta-strand, whereas the critical aspartic acid residue in VCAM-1 and fibronectin lie in protruding loops. This finding suggests that there are differences in the architecture of recognition sites between integrins that contain or lack I domains. A bend between domains 1 and 2 of ICAM-2 and a tripod-like arrangement of N-linked glycans in the membrane-proximal region of domain 2 may be important for presenting the recognition surface to LFA-1. A model of ICAM-1 based on the ICAM-2 structure provides a framework for understanding its recognition by pathogens.  相似文献   
29.
Because of concerns among veterans over Agent Orange exposure, the Department of Veterans Affairs (VA) has conducted a series of studies of specific cancers among Vietnam veterans. Lung cancer is the topic of investigation in this report. The VA's Patient Treatment File (PTF) was used to identify 329 Vietnam era veterans with a diagnosis of lung cancer made between 1983 and 1990. The PTF is a computerized hospitalized database of inpatient records, including patients' demographic data, and diagnoses. A record is created for each patient discharged from any one of the VA's Medical Centers. Variables abstracted from the military record include education, race, branch of service, Military Occupational Specialty Code, rank, and units served within Vietnam. Two hundred sixty-nine controls were randomly selected from the PTF file of men hospitalized for a reason other than cancer. A second control group numbering 111 patients with colon cancer was also selected from the PTF file. Data were also gathered on exposure to Agent Orange through the location of each individual ground troop veteran's unit in relation to an area sprayed and the time elapsed since that area was sprayed. The crude odds ratio between service in Vietnam and lung cancer was of borderline significance (odds ratio = 1.39 with 95% confidence interval = 1.01-1.92). The relationship disappeared when the confounder year of birth was considered. We conclude from these data that there is no evidence of increased risk in lung cancer associated with service in Vietnam at this time.  相似文献   
30.
Germline mutations in the presenilin 1 (PS1) gene apparently account for the majority of early-onset, familial Alzheimer's disease (AD). Using a mutation-screening strategy (denaturing gradient gel electrophoresis; DGGE), we analyzed a large family with early onset AD and seizures. The patients in this family showed a novel missense mutation in exon 5 of the PS1 gene (A to T change in codon 120, altering glutamine to aspartic acid). This novel mutation is located within the second hydrophilic domain of the molecule, a region not particularly involved in previously described germline mutations, and is of unknown biological significance. These results also demonstrate that DGGE can be used effectively to screen for mutations within this gene.  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