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   40995篇
  免费   2018篇
  国内免费   36篇
电工技术   277篇
综合类   29篇
化学工业   7430篇
金属工艺   725篇
机械仪表   766篇
建筑科学   1268篇
矿业工程   74篇
能源动力   785篇
轻工业   5461篇
水利工程   380篇
石油天然气   170篇
武器工业   4篇
无线电   2297篇
一般工业技术   7192篇
冶金工业   10508篇
原子能技术   197篇
自动化技术   5486篇
  2023年   351篇
  2022年   345篇
  2021年   894篇
  2020年   744篇
  2019年   687篇
  2018年   1518篇
  2017年   1525篇
  2016年   1561篇
  2015年   1120篇
  2014年   1407篇
  2013年   2748篇
  2012年   2385篇
  2011年   2200篇
  2010年   1747篇
  2009年   1539篇
  2008年   1801篇
  2007年   1566篇
  2006年   1165篇
  2005年   968篇
  2004年   912篇
  2003年   813篇
  2002年   721篇
  2001年   462篇
  2000年   465篇
  1999年   614篇
  1998年   3368篇
  1997年   2012篇
  1996年   1299篇
  1995年   758篇
  1994年   651篇
  1993年   640篇
  1992年   212篇
  1991年   224篇
  1990年   221篇
  1989年   214篇
  1988年   193篇
  1987年   169篇
  1986年   182篇
  1985年   215篇
  1984年   184篇
  1983年   134篇
  1982年   164篇
  1981年   173篇
  1980年   153篇
  1979年   129篇
  1978年   124篇
  1977年   200篇
  1976年   419篇
  1975年   88篇
  1973年   83篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Glyconanoparticles which present carbohydrate and amino groups motifs at their surface were produced. These particles were highly stable and soluble in aqueous solutions. The presence of the carbohydrate groups also allowed the inclusion of more strongly binding groups, without affecting solubility. The binding of a model DNA, plasmid by these nanoparticles was studied by atomic force microscopy, transmission electron microscopy, and gel electrophoresis. Significant differences between the nanoparticles based on their affinities for the DNA were found, with implications for their potential use as nonviral gene delivery agents.  相似文献   
72.
73.
Polycrystalline magnesium films were deposited under ultrahigh vacuum by thermal evaporation onto a cooled silica substrate. During the growth process of a film a number of lattice defects are incorporated. It was found that the defect density decreases with increasing thickness. An annealing study of the electrical resistance and defect density in magnesium films was made. The results were interpreted on the basis of Vand's theory. The function F0 expressing the law of distribution of the decay energies exhibited a maximum. For thick films there was no appreciable variation in the activation energy with thickness. In this case the evaluated activation energy E was found to be about 0.35 eV. For very thin films this energy decreases with increasing thickness.  相似文献   
74.
 In this paper, a new approach for powder cold compaction simulations is presented. A density-dependent plastic model within the framework of finite strain multiplicative hyperelastoplasticity is used to describe the highly nonlinear material behaviour; the Coulomb dry friction model is used to capture friction effects at die-powder contact; and an Arbitrary Lagrangian–Eulerian (ALE) formulation is used to avoid the (usual) excessive distortion of Lagrangian meshes caused by large mass fluxes. Several representative examples, involving structured and unstructured meshes are simulated. The results obtained agree with the experimental data and other numerical results reported in the literature. It is shown that, contrary to other Lagrangian and adaptive h-remeshing approaches recently reported for this type of problems, the present approach verifies the mass conservation principle with very low relative errors (less than 1% in all ALE examples and exactly in the pure Lagrangian examples). Moreover, thanks to the use of an ALE formulation and in contrast with other simulations, the presented density distributions do not present spurious oscillations. Received: 20 March 2002 / Accepted: 15 October 2002 The partial financial support of the Ministerio de Ciencia y Tecnología (grant number DPI 2001-2204) is gratefully acknowledged.  相似文献   
75.
76.
Presents results of 3 studies on the psychometric properties of the LP-ABC (M. Loranger and M. Pépin, 1993), a French-language instrument for assessing general functioning in adults with mental retardation. The studies involved a total of 299 male and female Canadian adults with mental retardation. Results confirm the internal consistency, construct validity, criterion validity, discriminant validity, interrater reliability, and test–retest reliability of the LP-ABC. (English abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
77.
78.
BACKGROUND: Locally advanced thyroid cancer invading the tracheal cartilage represents a difficult treatment dilemma during thyroidectomy. METHODS: A retrospective chart review was performed to determine the results of laryngotracheal resection or tracheal cartilage shave with adjuvant radiotherapy in patients with locally advanced thyroid cancer invading the upper airway. RESULTS: Of 597 patients undergoing thyroidectomy for thyroid cancer, 40 were found to have laryngotracheal invasion. Thirty-five patients with superficial invasion underwent cartilage shave procedures with adjuvant radiotherapy; five with full-thickness invasion underwent radical resection, including tracheal sleeve resection (n = 3) or total laryngectomy (n = 2). Histologic subtypes included papillary (n = 32), follicular (n = 2), Hurthle cell (n = 1), medullary (n = 3), and anaplastic (n = 2). Of the cartilage shave group, 25 are currently alive with no evidence of disease at a mean follow-up of 81 months (range 1-290). Six developed isolated local/regional recurrence and were managed with total laryngectomy (n = 1), tracheal resection (n = 1), cervical lymphadenectomy (n = 1), or repeat radiotherapy (n = 3). All six patients remain free of disease at a mean follow-up of 5 years. Of those who underwent initial laryngotracheal resection, four remain free of disease at a mean follow-up of 5 years. The rates of 10-year disease-free survival and overall survival for all patients were 47.9% (95% confidence interval [CI] 24.8, 71.0) and 83.9% (95% CI 70.3, 97.5), respectively. CONCLUSIONS: These data suggest that adequate management of thyroid cancer with laryngotracheal invasion can be achieved with a more conservative surgical approach and adjuvant radiotherapy, reserving more radical resections for extensive primary lesions or locally recurrent disease.  相似文献   
79.
80.
INTRODUCTION AND DEVELOPMENT: Multiple sclerosis (ME) is an inflammatory disease of the myelin of the central nervous system, the origin of which is still unknown. Genetic, infectious, immunological and environmental factors have all been blamed, but none of these factors on their own can explain the whole spectrum of this disease. Of the environmental factors, fat in the diet has given rise to most discussion. At the present time, it is known that polyunsaturated essential fatty acids form a part of biological membranes. A relationship has been found between the dietary fat consumed and the plasma levels and cell membrane content. CONCLUSIONS: The possible immuno-modulation function of these fatty acids justify rigorous evaluation of this hypothesis.  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