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   440356篇
  免费   6016篇
  国内免费   1537篇
电工技术   8061篇
综合类   943篇
化学工业   63974篇
金属工艺   16947篇
机械仪表   14315篇
建筑科学   9150篇
矿业工程   2540篇
能源动力   11903篇
轻工业   30288篇
水利工程   4789篇
石油天然气   7964篇
武器工业   21篇
无线电   50924篇
一般工业技术   85986篇
冶金工业   92318篇
原子能技术   9350篇
自动化技术   38436篇
  2022年   2661篇
  2021年   3987篇
  2020年   2956篇
  2019年   3850篇
  2018年   6922篇
  2017年   7119篇
  2016年   7912篇
  2015年   5063篇
  2014年   7528篇
  2013年   20404篇
  2012年   13333篇
  2011年   17481篇
  2010年   12757篇
  2009年   14406篇
  2008年   14607篇
  2007年   14370篇
  2006年   12939篇
  2005年   14220篇
  2004年   12917篇
  2003年   12351篇
  2002年   10631篇
  2001年   10434篇
  2000年   9399篇
  1999年   10002篇
  1998年   29040篇
  1997年   19656篇
  1996年   14820篇
  1995年   10677篇
  1994年   9224篇
  1993年   9270篇
  1992年   6258篇
  1991年   5938篇
  1990年   5929篇
  1989年   5547篇
  1988年   5286篇
  1987年   4611篇
  1986年   4462篇
  1985年   4964篇
  1984年   4479篇
  1983年   4065篇
  1982年   3760篇
  1981年   3895篇
  1980年   3591篇
  1979年   3379篇
  1978年   3422篇
  1977年   4302篇
  1976年   6047篇
  1975年   2939篇
  1974年   2697篇
  1973年   2773篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
972.
Density results obtained on the same cable sample with a column and from ultrasonic measurements are reported. A calibration curve relating ultrasonic velocity and cable insulation density is given for PE and crosslinked PE (XLPE) cables. The limits and advantages of deducing density profiles of cable insulation using a focused, ultrasound beam rather than the more time-consuming column measurements are discussed  相似文献   
973.
The morphologic changes and signal intensity of the spinal cord on preoperative magnetic resonance images were correlated with postoperative outcomes in 74 patients undergoing decompressive cervical surgery for compressive myelopathy. The transverse area of the spinal cord on T1-weighted images at the level of maximum compression was closely correlated with the severity of myelopathy, duration of disease, and recovery rate as determined by the Japanese Orthopaedic Association score. In patients with ossification of the posterior longitudinal ligament or cervical spondylotic myelopathy, the increased intramedullary T2-weighted magnetic resonance imaging signal at the site of maximal cord compression and duration of disease significantly influenced the rate of recovery. A multiple regression equation was then developed with these three variables to predict surgical outcomes.  相似文献   
974.
975.
PURPOSE OF THE STUDY: To assess efficacy and safety of fluconazole in neonates with Candida fungemia. STUDY DESIGN: Multicenter prospective protocol of all fungemias appearing between January 1, 1993, and December 31, 1997, in four major university hospitals. RESULTS: Forty neonates, 28 of them with very low birth weight (<1500 g; 30.5 median gestation week), with documented Candida albicans fungemia were treated with intravenous fluconazole in a daily dosage of 6 mg/kg once daily for 6 to 48 days. Thirty-four received fluconazole as monotherapy and 6 received it in combination with amphotericin B. Thirty-two (80%) were cured; 4 of them relapsed despite at least 14 days of therapy, but they were ultimately cured without sequelae. Eight other neonates died, 4 because of fungal infection and 4 because of prematurity or hemorrhage or lung failure, with fungemia (20% overall and 10% attributable mortality). Two neonates had elevated liver enzymes during fluconazole therapy and 2 others had elevated serum creatinine during fluconazole monotherapy. In none of them did these abnormalities necessitate discontinuation of antifungal therapy. In 8 neonates fungal meningitis developed as a complication of fungemia. All but 3 fungemias were C. albicans; 3 were Candida parapsilosis. CONCLUSIONS: Fluconazole was safe and effective antifungal therapy even in complicated or Candida fungemia in neonates and in infants with very low birth weight.  相似文献   
976.
OBJECTIVE: This study aimed to investigate the role of interleukin-12 (IL-12) and interleukin-10 (IL-10) in initiation and maintenance of intraocular inflammation. DESIGN: Case series. PARTICIPANTS: Aqueous humor and vitreous levels of IL-12 and IL-10 were measured in 22 patients with uveitis undergoing cataract surgery, paracentesis of the anterior chamber, and/or vitrectomy for diagnostic reasons, and in 4 patients with cataract only. INTERVENTION: Aqueous humor and vitreous levels of IL-12 and IL-10 were measured with specific enzyme-linked immunosorbent assays. MAIN OUTCOME MEASURES: Disease activity was correlated to IL-12 levels in the aqueous humor and the vitreous of patients with uveitis. RESULTS: Cytokine levels found in the anterior chamber and the vitreous are presented in picogram/milliliter (medium; range). The highest IL-12 levels were found in patients with active uveitis (108.5 pg/ml; 72-293 pg/ml). Interleukin-12 in patients with moderate uveitis or with their disease in remission was lower (32 pg/ml; 15-94 pg/ml) than in patients with active disease (P > 0.001) but higher than in the control group (10.5 pg/ml; 9-14 pg/ml). Interleukin-10 was detectable in only 3 of 22 patients with uveitis (12 pg/ml; 9-23 pg/ml). CONCLUSION: The authors found statistically significant differences of IL-12 levels in the various patient groups (active vs. inactive vs. control). These results support the idea that these uveitis cases represent type 1 (Th1)-T lymphocyte-mediated diseases in which IL-12 plays a pivotal role in the initiation and maintenance of the intraocular inflammation. The high levels of IL-12 in the vitreous and/or aqueous humor of the patients with uveitis suggest that susceptibility or resistance to ocular autoimmunity may be connected to a genetic predisposition to an elevated Th1 response.  相似文献   
977.
Spontaneous nasal tumors are rare in mice, and only one adenocarcinoma and two more primary neoplasms of the nose have been observed in our files of long-term feeding studies, which are composed of 3,419 male and 3,521 female CD-1 (Crl:CD-1 (ICR)BR) mice. This adenocarcinoma was a 1-cm-diameter mass observed grossly in the right nasal cavity of a 454-day-old, male CD-1 mouse from a treated group in a bioassay study conducted with 340 males and 340 females. The neoplastic epithelial cells affected the normal nasal architecture on the right side of the nose. Roughly, tumor neoplastic cells of the outer, lateral portion occurred as cuboidal to low columnar cells with basilarily located nuclei and eosinophilic cytoplasm. These cells were arranged in cylindrical profiles and frequently entrapped acini of the glands of the maxillary sinus. Neoplastic epithelial cells of the inner, medial portion appeared as serous acinar or ductular structures circumscribed by multiple lagers of myoepithelial-like cells. Staining failed to demonstrate mucous secretion. The site of origin of this neoplasm appeared to be the serous glands of the maxillary sinus. The adenocarcinoma was believed to be spontaneous.  相似文献   
978.
Bedo  S. Luthy  W. Weber  H.P. 《Electronics letters》1995,31(3):199-200
The saturation of the 2.71 μm laser output has been measured in erbium-doped ZBLAN singlemode fibres with Er3+ concentrations of 1000, 5000 and 10000 ppm mol. Limits of the single-mode-laser output are discussed  相似文献   
979.
A thorough functional analysis of the anorectal continence organ and the pelvic floor is a prerequisite for adequate treatment of incontinence. If conservative therapy has failed, corrective surgery on the basis of careful patient selection may well lead to improvement of continence. In our experience, plastic surgery of both the anterior levator ani muscle and the sphincter ani externus muscle is the treatment of choice for idiopathic incontinence.  相似文献   
980.
Results of chemical, x-ray phase, and petrographic investigations of slag are presented. It is established that slag from the production of aluminum alloys from secondary raw materials can be classified as a high-alumina refractory material (85–95% Al2O3 + SiO2, refractoriness 1670–1770°C). The refractory properties of the slag can be retained by magnetic separation. There is a practical possibility of using this slag in the production of refractories. Semidry pressing of a charge based on the slag can give a refractory of grade ShA in accordance with GOST 390-83.Translated from Ogneupory, No. 2, pp. 24 – 26, February, 1996.  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