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   165240篇
  免费   13220篇
  国内免费   7541篇
电工技术   8912篇
技术理论   11篇
综合类   13355篇
化学工业   27230篇
金属工艺   7941篇
机械仪表   6854篇
建筑科学   17968篇
矿业工程   3253篇
能源动力   4242篇
轻工业   12737篇
水利工程   3808篇
石油天然气   5831篇
武器工业   1197篇
无线电   12807篇
一般工业技术   21220篇
冶金工业   5566篇
原子能技术   2809篇
自动化技术   30260篇
  2024年   506篇
  2023年   1704篇
  2022年   4711篇
  2021年   5064篇
  2020年   3563篇
  2019年   3256篇
  2018年   3512篇
  2017年   4222篇
  2016年   5886篇
  2015年   7079篇
  2014年   9918篇
  2013年   10901篇
  2012年   8485篇
  2011年   8747篇
  2010年   7213篇
  2009年   8735篇
  2008年   8574篇
  2007年   10243篇
  2006年   9795篇
  2005年   8131篇
  2004年   6278篇
  2003年   5980篇
  2002年   5519篇
  2001年   4176篇
  2000年   4357篇
  1999年   3727篇
  1998年   3039篇
  1997年   2834篇
  1996年   2957篇
  1995年   2985篇
  1994年   2734篇
  1993年   1679篇
  1992年   1670篇
  1991年   1197篇
  1990年   910篇
  1989年   797篇
  1988年   718篇
  1987年   447篇
  1986年   287篇
  1985年   459篇
  1984年   495篇
  1983年   490篇
  1982年   379篇
  1981年   446篇
  1980年   316篇
  1979年   136篇
  1978年   125篇
  1977年   81篇
  1975年   60篇
  1962年   65篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
鄂尔多斯盆地三叠系延长组层序地层与生储盖组合特征   总被引:14,自引:2,他引:12  
鄂尔多斯盆地三叠系延长组地层层序划分方案较多。在V ail经典层序地层学理论指导下,综合利用露头、岩芯、钻井、地震和古生物等资料,通过古水深分析和层序界面的识别与划分,认为将鄂尔多斯盆地三叠系延长组划分为7个三级层序更为合理,指出层序4水进体系域(生)+层序5低位体系域(储)+层序5水进体系域(盖)和层序4水进体系域(生)+层序4低位体系域(储)+层序4水进体系域(盖)是相对较佳的2套生储盖组合,并指出了鄂尔多斯盆地延长组最主要的2套生储盖勘探目的层。  相似文献   
172.
深层及非生物成烃的催化机制   总被引:8,自引:1,他引:7  
讨论了非生物成因烃的可能生成机制。通过对比分析,探讨了在地质条件下碳、氢经历费-托合成和由过渡金属催化产生烃的可能机制。  相似文献   
173.
本文首先介绍了VoIP的原理、相关协议.然后介绍了VoIP业务在HFC网络应用的业务环境和体系结构。并对其中的功能实体进行描述和说明。最后介绍一个具体的业务实例。  相似文献   
174.
Formation of cobalt sulfide hollow nanocrystals through a mechanism similar to the Kirkendall Effect has been investigated in detail. It is found that performing the reaction at > 120 °C leads to fast formation of a single void inside each shell, whereas at room temperature multiple voids are formed within each shell, which can be attributed to strongly temperature‐dependent diffusivities for vacancies. The void formation process is dominated by outward diffusion of cobalt cations; still, the occurrence of significant inward transport of sulfur anions can be inferred as the final voids are smaller in diameter than the original cobalt nanocrystals. Comparison of volume distributions for initial and final nanostructures indicates excess apparent volume in shells, implying significant porosity and/or a defective structure. Indirect evidence for fracture of shells during growth at lower temperatures was observed in shell‐size statistics and transmission electron microscopy images of as‐grown shells. An idealized model of the diffusional process imposes two minimal requirements on material parameters for shell growth to be obtainable within a specific synthetic system.  相似文献   
175.
We report a general template strategy for rational fabrication of a new class of nanostructured materials consisting of multicore shell particles. Our approach is demonstrated by encapsulating Au or Pt nanoparticles in silica shells. Other superstructures of these hollow shells, like dimers, trimers, and tetramers can also be formed by nanoparticle‐mediated self‐assembly. We have also used the as‐prepared multicore Au–silica hollow particles to perform the first studies of Ostwald ripening in confined microspace, in which chloride was found to be an efficient mediating ligand. After treatment with aqua regia, Au–Cl complex is formed inside the shell, and is found to be very active under in situ transmission electron microscopy observations while confined in a microcell. This aspect of the work is expected to motivate further in situ studies of confined crystal growth.  相似文献   
176.
浅析医药包装   总被引:2,自引:0,他引:2  
董翠芳  邓开发 《包装工程》2003,24(4):133-134
随着市场经济的深入,医药包装正成为我国经济发展的朝阳产业,文中意在介绍先进的医药包装材料。分析其应用情况及发展趋势和动态。  相似文献   
177.
运动会新闻发布系统的设计与实现   总被引:2,自引:0,他引:2  
针对运动会比赛期间随时需要方便、快捷、高效地更新大量新闻的需求 ,研制和开发一套运动会新闻发布系统。利用微软最新推出的asp .net动态网页开发工具 ,采用web分布式三层设计模型设计实现了一套操作简单、功能完善、具有通用性的运动会新闻发布系统  相似文献   
178.
This study was undertaken to develop a modified atmosphere package to control microbial growth in ready‐to‐eat (RTE) products stored at ambient temperature. Ethanol and/or limonene associated with modified atmosphere (CO2 : O2 : N2 = 30% : 5% : 65%) was used to inhibit the growth of total air‐borne microorganisms and Escherichia coli in RTE products stored at 25°C. The results indicated that 0.05% ethanol vapour in the headspace was effective to inhibit the growth of air‐borne microorganisms and E. coli at 25°C for 72 h in a model study, and the effectiveness was related to ethanol content. Both 73 ppm limonene and 0.05% ethanol vapour enhanced the bacteriostatic effect of modified atmosphere in RTE sushi roll products, and no off‐flavour was detected using this formulated gas; however, no significant inhibitory effect was observed for RTE cold noodle products. This study concludes that combinations of carbon dioxide, ethanol or limonene vapours are effective to inhibit microbial growth in RTE food at ambient temperature, and the outcome may be due to the hurdle effect. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
179.
An efficient algorithm is presented for numerically evaluating a self-consistent field theoretic (SCFT) model of block copolymer structure. This algorithm is implemented on a distributed memory parallel cluster in order to solve the SCFT equations on large computational grids. Simulation results are presented for a two-component molten mixture of a symmetric ABA triblock copolymer with an A homopolymer. These results illustrate a case in which simulating a large system is required to resolve features with a wide range of length scales.  相似文献   
180.
We demonstrate that alkali-halide salts, particularly potassium bromide, can reduce the photothermal emission (PTE) from single walled carbon nanotubes (SWNT). PTE is a prominent spectral feature in Raman spectroscopy when a near infrared laser is used to analyze a dark colored sample. We subsequently show that trapping salts inside SWNT and coating SWNT with the salt has a more pronounced impact on not only reducing PTE, but also enhancing the intensity of the Raman spectral features. The effect, which we have called nanotube enhanced Raman spectroscopy (NERS), has differences and similarities to the widely studied surface enhanced Raman spectroscopy (SERS).  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