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   246243篇
  免费   18600篇
  国内免费   9143篇
电工技术   12666篇
技术理论   24篇
综合类   14161篇
化学工业   42505篇
金属工艺   13460篇
机械仪表   14911篇
建筑科学   18561篇
矿业工程   7548篇
能源动力   6919篇
轻工业   15100篇
水利工程   3704篇
石油天然气   16671篇
武器工业   1648篇
无线电   26686篇
一般工业技术   30314篇
冶金工业   15804篇
原子能技术   2435篇
自动化技术   30869篇
  2024年   1006篇
  2023年   3952篇
  2022年   6769篇
  2021年   9544篇
  2020年   7408篇
  2019年   6364篇
  2018年   7142篇
  2017年   7916篇
  2016年   7220篇
  2015年   9271篇
  2014年   11752篇
  2013年   14321篇
  2012年   15044篇
  2011年   16541篇
  2010年   14177篇
  2009年   13492篇
  2008年   13195篇
  2007年   12596篇
  2006年   13033篇
  2005年   11330篇
  2004年   7739篇
  2003年   6655篇
  2002年   5877篇
  2001年   5177篇
  2000年   5748篇
  1999年   6781篇
  1998年   6154篇
  1997年   4924篇
  1996年   4573篇
  1995年   3782篇
  1994年   3078篇
  1993年   2229篇
  1992年   1718篇
  1991年   1379篇
  1990年   1068篇
  1989年   874篇
  1988年   660篇
  1987年   451篇
  1986年   391篇
  1985年   334篇
  1984年   271篇
  1983年   229篇
  1982年   213篇
  1981年   199篇
  1980年   155篇
  1979年   132篇
  1978年   113篇
  1977年   135篇
  1976年   172篇
  1975年   88篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
研究提出了超低硫燃料暂定战术技术指标,并规定了其润滑性要求。通过对基础油生产工艺研究、柴油润滑性添加剂研究及配方性能评定,成功研制了一种环保型超低硫燃料,满足外燃发动机(燃烧室高温高压)的使用要求。研制产品具有馏分窄、闪点高、氧化安定性好、低温性能优异、硫含量超低、润滑性能好等特点。燃料的低硫化是燃料发展的必然趋势。在我国开展低硫或超低硫环保型燃料研制,同时开展燃料润滑性添加剂的研制,具有重要意义。  相似文献   
912.
The synthesis and magnetostriction of PrxTb1-x.Fe2, PrxTb1-x Fe2BO2 and PrxTb1-x(Fe0.6Co0.4)2 alloys were investigated in this study. The addition of boron or cobalt atom in PrxTb1-xFe2 could effectively prevent the formation of non-cubic phases, and Pr concentration limit was successfully increased from 0.2 to 0.4. X-ray step scanning for the PrxTb1-xFe2BO2 and PrxTb1-x(Fe0.6Co0.4)2 alloys showed that PrFe2 possessed a large spontaneous magnetostriction λ1111.  相似文献   
913.
书法艺术是视觉艺术的一个独立门类,又是我国语言文字的记录手段,是我国文化的重要组成部分。从古至今,书法艺术经久不衰,具有浓厚的群众基础。在我国历史上涌现过许多著名书法家,如:王羲之、颜真卿、米芾、怀素等等,他们在中国文化史与艺术史上占有举足轻重的地位。这些书法家所流传下来的作品,无一不是我国民族的瑰宝。虽然这些书法原作大多已散失,但这些作品的碑刻,乃至后世摹品,仍散发着无穷魅力,  相似文献   
914.
现场地质预测与决策技术   总被引:1,自引:1,他引:0  
油气的生成、运移、分布、成藏、保存具有规律性,技术人员可以依据其规律性对地下地质情况进行推理、预测和决策。钻井过程的现场地质预测技术方法主要是外推法、因果法和直观法三大类。外推法是常用的预测方法,包含了岩性、沉积旋回、标志层、标准层、重矿物等岩石地层学对比方法和生物地层学方法及地球物理方法。现场地质预测与决策是通过确定预测目标、收集相关资料、进行对比分析、形成地质预测结果、拟定地质决策方案、方案优选、方案实施等环节来完成。该技术是现场地质监督的核心技术,在实践中取得显著成效。  相似文献   
915.
This paper is the result of a plenary discussion session held at the 11th European Conference on Mixing. Three perspectives on mixing research are explored: that of the industrialist, the equipment manufacturer, and the academic researcher. There was strong agreement that, while the one dimensional problems are reasonably well understood and many engineers thus perceive that mixing is simple, current practice actually requires us to address complex, multi‐dimensional problems with interactions between mixing, reaction, multi‐phase physics, surface phenomena, and transport phenomena. Understanding these multi‐scale, multi‐mechanism problems requires models which include interactions between the phenomena, and allow the effects of these interactions to emerge. Developing these models will require us to shift our perspective on mixing from one of equipment design to one of the mixing field as a fundamental physical mechanism.  相似文献   
916.
In the area of image retrieval from data bases and for copyright protection of large image collections there is a growing demand for unique but easily computable fingerprints for images. These fingerprints can be used to quickly identify every image within a larger set of possibly similar images. This paper introduces a novel method to automatically obtain such fingerprints from an image. It is based on a reinterpretation of an image as a Riemannian manifold. This representation is feasible for gray value images and color images. We discuss the use of the spectrum of eigenvalues of different variants of the Laplace operator as a fingerprint and show the usability of this approach in several use cases. Contrary to existing works in this area we do not only use the discrete Laplacian, but also with a particular emphasis the underlying continuous operator. This allows better results in comparing the resulting spectra and deeper insights in the problems arising. We show how the well known discrete Laplacian is related to the continuous Laplace-Beltrami operator. Furthermore, we introduce the new concept of solid height functions to overcome some potential limitations of the method.  相似文献   
917.
紫杉醇的全合成困难,许多工作还只能停留在实验室的模型化合物上。作者以思想实验方法提出了:先以D-A反应形成A环和C环,然后用两步形成B环,最后形成D环,以此完成紫杉醇母核的全合成。  相似文献   
918.
919.
Ilexonin A, a new drug in improving the blood circulation and microcirculation, is extracted from Ilicis pubescentis. The preventive and therapeutic effects of Ilexonin A on chemical salpingitis induced tubal obstruction (CSTO) with morphological and hemorheological change in rats was studied. Results showed that Ilexonin A was effective in treating (CSTO by oppositing the degeneration and necrosis of epithelium, inhibiting the hyperplasia of connective tissue, and reducing the infiltration of inflammatory cells. The improvement of morphology was more significant in treated groups than that in controls (P < 0.05-0.01). The indices concerning model rat's hemorheology were also analysed between treated groups and controls. It indicated that Ilexonin A could improve the viscosity of blood and aggregation of red blood cells. It is suggested Ilexonin A could promote the absorption of inflammatory substances as a result of improving hemorheology.  相似文献   
920.
OBJECTIVE: To analyze the levels of free carnitine and carnitine esters in the muscles of patients with inflammatory myopathies. METHODS: Six men and 7 women with inflammatory myopathy and 25 age-matched healthy controls were studied. Free carnitine and carnitine esters in muscle homogenates were measured by a radiochemical procedure. Muscle histochemical staining and measurement of respiratory chain enzyme activity were also performed. RESULTS: Eleven patients had muscle carnitine insufficiency. Five of them had subsarcolemmal oxidative accumulations, 5 had lipid droplets, and 4 had defects of the respiratory chain enzyme complexes. CONCLUSION: Abnormal distribution of muscle carnitine is present in patients with inflammatory myopathies and could impair muscle function. Coexistent mitochondrial dysfunction may contribute to carnitine insufficiency.  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