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   10286篇
  免费   782篇
  国内免费   178篇
电工技术   556篇
综合类   240篇
化学工业   1681篇
金属工艺   336篇
机械仪表   577篇
建筑科学   730篇
矿业工程   339篇
能源动力   284篇
轻工业   651篇
水利工程   124篇
石油天然气   449篇
武器工业   31篇
无线电   813篇
一般工业技术   1139篇
冶金工业   2073篇
原子能技术   34篇
自动化技术   1189篇
  2024年   53篇
  2023年   201篇
  2022年   285篇
  2021年   453篇
  2020年   344篇
  2019年   332篇
  2018年   395篇
  2017年   398篇
  2016年   314篇
  2015年   415篇
  2014年   596篇
  2013年   700篇
  2012年   775篇
  2011年   779篇
  2010年   675篇
  2009年   553篇
  2008年   512篇
  2007年   447篇
  2006年   483篇
  2005年   360篇
  2004年   165篇
  2003年   126篇
  2002年   64篇
  2001年   26篇
  2000年   23篇
  1999年   66篇
  1998年   526篇
  1997年   292篇
  1996年   228篇
  1995年   111篇
  1994年   99篇
  1993年   105篇
  1992年   11篇
  1991年   31篇
  1990年   33篇
  1989年   23篇
  1988年   37篇
  1987年   22篇
  1986年   24篇
  1985年   15篇
  1983年   3篇
  1982年   10篇
  1981年   12篇
  1980年   11篇
  1979年   2篇
  1978年   3篇
  1977年   36篇
  1976年   71篇
  1966年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
雷电具有强烈的破坏作用,因此,需要设置防雷装置。防雷装置需要定期进行检查和维护,才能够发挥保护作用。因此,应对各类防雷保护装置进行定期维护和检查,从而保证系统正常可靠的工作。  相似文献   
992.
993.
OBJECTIVE: The purpose of this study is to determine the efficacy of initial trabeculotomy in the patient with aniridic glaucoma. DESIGN: Clinical charts were reviewed. PARTICIPANTS: Twenty-nine eyes of 16 patients with aniridia were studied. INTERVENTION: Glaucoma surgery was performed. As an initial procedure, trabeculotomy was performed in 12 eyes, other surgery was performed in 17 eyes (trabeculectomy, 5; goniotomy, 5; other, 7). MAIN OUTCOME MEASURES: Success was defined as an intraocular pressure (IOP) of 21 mmHg or lower, and no further surgery was performed. RESULTS: Ten (83%) of 12 eyes obtained IOP control after first (6 eyes) or second (4 eyes) trabeculotomy with a mean follow-up period of 9.5 years. Five eyes maintained visual acuity of 20/40 to 20/200. No serious complications were found after trabeculotomy. Three (18%) of 17 eyes were controlled with the first glaucoma surgery other than trabeculotomy (goniotomy, trabeculectomy, trabeculectomy combined with trabeculotomy, and Molteno implant). Good IOP control was obtained in 8 (47%) of 17 eyes after several surgeries with a mean follow-up period of 10.4 years. Four of 17 eyes became phthisical. CONCLUSION: This study suggests that trabeculotomy is the preferred initial operation for uncontrolled glaucoma with aniridia.  相似文献   
994.
995.
吕强 《华中建筑》2008,26(5):53-56
随着北京奥运会的临近和全民健身运动的推广,全国各地均在进行不同程度的体育场馆新建、改建、扩建工程,体育建筑设计也逐渐进入更深入的专业化设计领域。该文基于体育场馆的空间特点,简要介绍了一些体育场馆内部常用声学材料的特点及使用。  相似文献   
996.
粒子群优化算法的原理较易理解,所需参数较少而易于实现,但在具体问题中仍存在如收敛性不稳定等不足。基于收缩因子改进的粒子群算法可以保证算法的收敛性,同时使得速度的限制放松。结合新安江模型参数的特点,将其应用于该模型参数的率定.并编程实现检验分析。实例应用结果表明,该优化算法可得到较为稳定的模型参数.提高模型在洪水预报中的效率。  相似文献   
997.
BACKGROUND: Adynamic bone disease (ABD) has been described in the current dialysis population to have an unexpectedly high prevalence. Moreover, it is clearly more prevalent in CAPD patients, compared to haemodialysis patients. Recently we demonstrated that both a low (< or = 27 U/1) level of bone alkaline phosphatase (BAP) as determined by an optimized agarose gel electrophoretic technique and a low (< or = 150 pg/ml ) level of iPTH are good markers of ABD with sensitivities of 78.1% and 80.6% and specificities of 86.4% and 76.2% respectively. METHODS: In this study (n = 212), the prevalence of ABD in the European CAPD population was evaluated by means of these biochemical markers. Clinical data on the patients included were recorded at the moment of blood sampling. In patients under CAPD treatment for longer than 9 months, we calculated an index of calcium exposure through PD fluid. RESULTS: In this population with a low exposure to aluminium, the prevalence of ABD as indicated by either a low level of BAP or PTH was 43%. The following risk factors could be identified: advanced age, shorter time on renal replacement therapy, male gender, and high calcium content of PD fluid. The index of calcium exposure was significantly higher in the patients with low BAP and low iPTH levels compared to those with either BAP > or = 27 U/1 or iPTH > 150 pg/ml. The latter finding gives further support to the hypothesis that a high calcium load administered to renal failure patients may lead to 'oversuppressed' parathyroids in ABD. In a subgroup of patients with a high level of BAP associated with a low iPTH level a profile previously shown to be associated in the presence of aluminium overload, significantly higher serum aluminium levels were noted. suggesting that even in patients with low exposure to aluminium, this element still can affect bone metabolism. CONCLUSION: A high prevalence of ABD--as diagnosed by biochemical markers--was observed in the European CAPD population. A number of risk factors could be put forward. The aetiology and pathogenesis of this type of renal osteodystrophy remain to be elucidated, but appear, however, to be multifactorial.  相似文献   
998.
Patients with craniocervical mandibular (TMD) disorders can present with tinnitus as a primary or secondary complaint. The embryology and functional anatomy of the middle ear, temporomandibular joint, muscles of mastication and associated tendons, ligaments, blood vessels, nerves and lymphatics was found to be helpful in establishing etiologic concepts which relate tinnitus to these temporomandibular disorders. In addition to etiologic concepts, treatment modalities are described. The authors relate their experiences as well as those of others with different patient populations.  相似文献   
999.
为保证复杂探井的顺利钻进,更好地保护油气层,在钻前进行地层3项压力(地层孔隙压力、坍塌压力和破裂压力)剖面的预测非常重要.利用邻井测井资料、钻井工程资料对大港油田南大港潜山构造带歧南9X1、歧南9X2等井,在钻前进行了地层3项压力预测.根据该地区进入油气层段前地层坍塌压力较高,而进入油气层后地层坍塌压力下降,同时油层孔隙压力较低的实际情况,采用了一套与传统井身结构设计完全不同的设计方式,虽然增加了一定的套管成本,却保证了钻井施工的顺利进行,有效保护了油气层,与邻井相比,产量大幅度提高.  相似文献   
1000.
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