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   12971篇
  免费   1642篇
  国内免费   673篇
电工技术   432篇
综合类   1024篇
化学工业   4075篇
金属工艺   628篇
机械仪表   524篇
建筑科学   1454篇
矿业工程   449篇
能源动力   207篇
轻工业   175篇
水利工程   233篇
石油天然气   1277篇
武器工业   40篇
无线电   1356篇
一般工业技术   1243篇
冶金工业   291篇
原子能技术   46篇
自动化技术   1832篇
  2024年   45篇
  2023年   132篇
  2022年   223篇
  2021年   380篇
  2020年   335篇
  2019年   312篇
  2018年   291篇
  2017年   396篇
  2016年   458篇
  2015年   493篇
  2014年   838篇
  2013年   825篇
  2012年   1007篇
  2011年   972篇
  2010年   753篇
  2009年   837篇
  2008年   781篇
  2007年   897篇
  2006年   834篇
  2005年   690篇
  2004年   615篇
  2003年   625篇
  2002年   501篇
  2001年   384篇
  2000年   320篇
  1999年   269篇
  1998年   233篇
  1997年   165篇
  1996年   127篇
  1995年   106篇
  1994年   97篇
  1993年   68篇
  1992年   52篇
  1991年   33篇
  1990年   33篇
  1989年   27篇
  1988年   21篇
  1987年   9篇
  1986年   11篇
  1985年   26篇
  1984年   23篇
  1983年   15篇
  1982年   22篇
  1981年   4篇
  1980年   1篇
排序方式: 共有10000条查询结果,搜索用时 718 毫秒
71.
碳化硅砖和碳化硅砖与普通碳砖复合侧块,在上世纪末期我国铝电解槽上开始推广应用。使用后各厂家普遍发现碳化硅砖及碳化硅砖与普通碳块复合侧块均出现不同程度的断裂、上抬和脱落现象,该文对断裂、上抬和脱落原因进行了分析,并提出了改进措施。  相似文献   
72.
Nuclear magnetic resonance (n.m.r.) studies of 19F nuclei in a 7030mol% random copolymer of vinylidene fluoride and trifluoroethylene were performed at 9.14 MHz and 20.0 MHz. The free induction decays (FIDs) were analysed in terms of two T2 components attributed to the amorphous and crystalline portions of the polymer. The changes in crystallinity as well as the effects of the ferroelectric transition were observed during cycles of heating and cooling between 20°C and 140°C. The crystalline component of the FID lengthens by a factor of 2 at 100°C on heating and decreases by this factor at 60°C on cooling, thus exhibiting the thermal hysteresis of this ferroelectric transition. The spin-lattice relaxation was also investigated. From measurements at 9.14 MHz the observed longitudinal relaxation time T1 appears to be dominated by the dynamics of the amorphous phase and exhibits no anomaly through the phase transition. However, from measurements at 20 MHz, well defined minima of T1 were observed, which are associated with the ferroelectric transition (especially after repeated annealing of the samples). Results are discussed in terms of the crystalline phase structure, which appears dynamically disordered above the ferroelectric phase transition. An analogy is considered with the plastic phase transitions encountered in molecular crystals.  相似文献   
73.
杜84断块超稠油开发中后期稳产对策研究   总被引:3,自引:1,他引:2  
对杜84断块超稠油生产中后期暴露的主要矛盾,即随着轮次升高,周期吞吐效果变差,井下技术状况日益变差。油层动用不均,汽窜加剧等问题进行了分析。并提出了相应的稳产对策-实施多井整体吞吐,大修复产,调剖等措施。现场应用证明,这些措施基本能够确保杜84断块超稠油中后期的稳产。  相似文献   
74.
Using the energy approach as the base, the criteria are developed for brittle rock failure in outcropping in the workings driven in the rock masses of different degree of disturbance. A method is presented for estimating the stability of workings under conditions of zonal disintegration.  相似文献   
75.
介绍砌块仿花岗岩挡土结构的特点和砌块形状,针对砌块挡土结构在我国刚开始应用,没有设计、施工规范的现状,依托可以借鉴的加筋挡土结构和浆砌块石挡土结构设计规范,提出了自锁式砌块加筋挡土结构设计中的地面荷载强度及土压力计算方法、砌块层间稳定验算方法、加筋长度和间距验算方法、挡土结构整体稳定验算方法和施工过程中需要注意的主要问题,为自锁式砌块加筋挡土结构设计人员提供了设计验算内容、验算方法和安全系数取值范围,为现场施工和监理人员提供参考,并为该类型的挡土结构推广应用提供技术支持。  相似文献   
76.
Polyisobutylene succinic anhydride-urea/polyamines (PIBSA) copolymers were synthesized as potential antioxidants and detergent dispersant agents for lubricating oils samples (SAE-30). Homogeneity, thermal stability and dispersancy of the solutions were determined. Fully soluble oil compounds that are thermally stable up to 250 °C were achieved. The oxidation stability of lube oil samples in the presence of four designed PIBSA additives (varying in the number of amine groups) was determined for a time period of up to 72 hours. The dependence of the additive efficiency on its concentration was studied to achieve maximum stability. Some PIBSA additives at concentration 3.0 · 104 ppm exhibit the best results. Dispersivity values were measured at predetermined oxidation times. The results proved reliable dispersion capability as the nitrogen content of the additive is increased, i.e. the increase in the basic character of the additive leads to the increase in the neutralization capability. Moreover, the designed PIBSA additives retain their efficiency after long oxidation times, confirming their role as multifunctional nitrogen containing polymeric additive. Electronic Publication  相似文献   
77.
Poly(vinylbenzyltrimethylammonium chloride)‐graft‐cotton cellulose, an anion‐exchange matrix, was synthesized by a mutual radiation‐induced grafting technique with a 60Co γ‐radiation source. The grafted matrix was characterized by grafting yield estimation, elemental analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. The grafting yield decreased with the increase in the dose rate. However, the grafting yield and nitrogen content of grafted samples increased almost linearly with an increase in the total irradiation dose. To evaluate the performance of the grafted anion‐exchange matrix, the protein adsorption and elution behavior were investigated in a continuous column process under various experimental conditions, with bovine serum albumin used as a model protein. The binding and elution behavior of the anion‐exchange matrix depended on different experimental parameters, such as the grafting yield, ionic strength, pH of the medium, and amount of protein loaded. From a breakthrough curve, the equilibrium binding capacity and elution percentage of the grafted anion‐exchange matrix were estimated to be 40 mg/g and 94%, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5512–5521, 2006  相似文献   
78.
NUMERICAL SIMULATION OF TIP-CLEARANCE FLOW IN CASCADE   总被引:1,自引:1,他引:0  
1 . INTRODUCTIONTip clearanceflowsoccurinvariousengineer ingapplicationssuchasaxial flow pumpsandduct edpropellers .Theinertialforcesactinguponthefluidinthenarrow gapbetweenbladetipandthesurroundingwallaresufficientto generateatipleakagevortexonthesuctions…  相似文献   
79.
随着苏丹1/2/4区块的深入开发,为了加快开发主力油层,提高原油产量,降低钻井成本,GNPOC在此区块布置水平井开发任务。所开发的区域主要分布于Heglig,Munga,Simbir,Bamboo区块,油层所在是Zaqar和Bentiue地层。此层位具有高渗透,地层温度高,易塌、气窜等复杂问题,尤其是Heglig和Munga地区井壁坍塌严重。为此,根据地质资料、井身结构和对水平井注水泥的技术要求,科学合理设计施工工艺,优选出适合此地区固井施工的冲洗液和隔离液,特别是经过努力实践,开发出了新型膨胀水泥浆体系,此体系具有高强度、低失水、无析水、防气窜之功效。结合使用哈里伯顿CPT—Y4大功率固井车,精确计量和自动密度控制,该体系水泥浆目前已在7口水平井施工中得以应用,均为优质井。现正在被大量使用,此体系的开发,解决了该固井技术难题,创造了中国固井在海外首次水平井作业一次成功的历史记录,具有较高的经济和社会效益。  相似文献   
80.
刘炳官 《特种油气藏》2006,13(1):68-70,74
在总结复杂小断块油田CO2吞吐系列配套技术的基础上,分别从油藏规模、物性、能量等角度剖析了71口吞吐井的实施效果,分析了影响CO2吞吐效果的关键参数,得出了注入量、注入压力、返排速度、吞吐周期等工艺技术参数的取值范围和标准,对提高采收率具有重要意义。  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