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   21197篇
  免费   1631篇
  国内免费   39篇
电工技术   138篇
综合类   116篇
化学工业   5550篇
金属工艺   459篇
机械仪表   384篇
建筑科学   749篇
矿业工程   59篇
能源动力   659篇
轻工业   5083篇
水利工程   200篇
石油天然气   170篇
武器工业   1篇
无线电   973篇
一般工业技术   3311篇
冶金工业   2024篇
原子能技术   117篇
自动化技术   2874篇
  2024年   39篇
  2023年   169篇
  2022年   376篇
  2021年   905篇
  2020年   567篇
  2019年   650篇
  2018年   816篇
  2017年   838篇
  2016年   865篇
  2015年   656篇
  2014年   979篇
  2013年   1804篇
  2012年   1462篇
  2011年   1584篇
  2010年   1200篇
  2009年   1137篇
  2008年   1034篇
  2007年   917篇
  2006年   741篇
  2005年   564篇
  2004年   507篇
  2003年   532篇
  2002年   445篇
  2001年   356篇
  2000年   293篇
  1999年   289篇
  1998年   798篇
  1997年   517篇
  1996年   370篇
  1995年   256篇
  1994年   210篇
  1993年   152篇
  1992年   82篇
  1991年   57篇
  1990年   55篇
  1989年   57篇
  1988年   63篇
  1987年   50篇
  1986年   35篇
  1985年   55篇
  1984年   44篇
  1983年   43篇
  1982年   38篇
  1981年   26篇
  1980年   42篇
  1979年   22篇
  1978年   20篇
  1977年   29篇
  1976年   53篇
  1973年   17篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
81.
82.
The solid phase crystallization kinetics of chemically vapour-deposited amorphous silicon films were studied by in situ X-ray diffraction. We determined the crystalline volume directly from the Bragg peak intensities at various times during isothermal annealing in the temperature range 578 °C < T < 658 °C. From these experiments we deduced that the crystallization was due to nucleation predominantly at the substrate-film interface followed by crystal growth perpendicular to this interface. The crystal growth rate was thermally activated with an activation energy Ev of 3.1 eV. A strong 〈111〉 preferred orientation of the growing polycrystal was observed and the grain size remained constant at about 60 nm. Evidence of stresses at the amorphous-crystalline interface during the early stages of crystallization was observed. A comparison with previous conductivity measurements is also carried out.  相似文献   
83.
84.
85.
Gut involvement in bladder tumours is low, even exceptional in the presence of surface, low-grade neoplasia. The authors explain their experience in the diagnosis and management of a patient treated endoscopically for a vesical surface tumour which subsequently exhibited peritoneal and gut metastatic seeding. The various mechanisms for gut dissemination of vesical neoplasias and the repercussion of their endoscopic management are discussed.  相似文献   
86.
The application of frozen and radiation sterilized allogenic bone grafts for reconstructions in orthopaedic operations is described. Analysis of results of treatment of 1125 patients was performed. It was found that use of preserved bone allows to reduce the extend and duration of surgery. Nearly total substitution of grafts may be seen in 3 to 8 months after surgery.  相似文献   
87.
88.
89.
Continuous intracameral infusions of a balanced salt solution (0.175 microliter min-1) have been reported to raise intraocular pressure (IOP) in anesthetized rats. Palm et al. (1995) previously reported that this effect was attenuated significantly by inclusion of arginine-vasopressin (AVP, 10 ng 0.175 microliter-1) in the infusate. This study used experimental and computer simulation methods to investigate factors underlying these changes in IOP. First, constant intracameral infusions of artificial cerebrospinal fluid (aCSF) at different fixed rates (0.049-0.35 microliter min-1) were used to estimate the outflow resistance. Secondly, IOP responses were measured during an 2 hr intracameral infusion of either aCSF or AVP that was the sum of a small constant component (0.05 microliter min-1) and a larger periodic component (0.25 microliter min-1, cycling for 4 min on, then 4 min off); the mean infusion rate was 0.175 microliter min-1. As shown previously for 0.175 microliter min-1 constant infusions, the periodic aCSF infusion induced a significant rise in IOP that was attenuated by AVP administration. Complex demodulation analysis and the estimated gain parameter of a second order transfer function fit to the periodic responses indicated that outflow resistance increased significantly during the infusions in both aCSF and AVP groups, but that the indices of resistance did not differ significantly between aCSF and AVP infused eyes. This finding implies that changes in outflow resistance do not explain the difference in IOP responses to intracameral aCSF and AVP. The two responses differed significantly, though, in damping factors, such that the aCSF responses were considerably more underdamped than the AVP responses. It is hypothesized that aCSF-induced increase in IOP reflects both (1) a small component reflecting increased outflow resistance and (2) a larger non-resistive component. Since the non-resistive component is insensitive to pretreatment with acetazolamide, it is suggested that the aCSF-induced elevation in IOP reflects primarily vascular perfusion changes that are reduced by local vasoconstrictor actions of AVP. The latter mechanism likely maintains vascular perfusion of the globe when intraocular hypertension develops.  相似文献   
90.
长25-29井在完井阶段通井过程中发生粘附卡钻事故,在处理卡钻过程中又发生卡套铣筒、井漏、溢流等事故及复杂情况。通过对井下情况的认真分析,采取先堵漏后循环再解卡的处理方案,顺利地解除了该次卡钻事故,大大地减少了经济损失。  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