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   256905篇
  免费   2060篇
  国内免费   303篇
电工技术   4276篇
综合类   112篇
化学工业   42006篇
金属工艺   15295篇
机械仪表   10246篇
建筑科学   4434篇
矿业工程   3769篇
能源动力   4403篇
轻工业   10524篇
水利工程   4183篇
石油天然气   13161篇
武器工业   32篇
无线电   21185篇
一般工业技术   64156篇
冶金工业   32571篇
原子能技术   11215篇
自动化技术   17700篇
  2021年   3359篇
  2019年   3103篇
  2018年   5903篇
  2017年   6046篇
  2016年   6418篇
  2015年   3281篇
  2014年   5673篇
  2013年   10657篇
  2012年   7681篇
  2011年   9363篇
  2010年   7569篇
  2009年   8340篇
  2008年   8394篇
  2007年   8059篇
  2006年   6524篇
  2005年   5711篇
  2004年   5600篇
  2003年   5398篇
  2002年   5246篇
  2001年   5008篇
  2000年   5000篇
  1999年   4326篇
  1998年   7292篇
  1997年   5938篇
  1996年   4490篇
  1995年   3729篇
  1994年   3473篇
  1993年   3671篇
  1992年   3254篇
  1991年   3381篇
  1990年   3507篇
  1989年   3409篇
  1988年   3312篇
  1987年   3287篇
  1986年   3183篇
  1985年   3356篇
  1984年   3301篇
  1983年   3187篇
  1982年   3018篇
  1981年   3066篇
  1980年   3099篇
  1979年   3279篇
  1978年   3508篇
  1977年   3481篇
  1976年   3941篇
  1975年   3224篇
  1974年   3309篇
  1973年   3354篇
  1972年   3001篇
  1971年   2764篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.

Hydropower energy generation depends on the available water resources. Therefore, planning and operation of the water resource systems are paramount tasks for energy management. Since reservoirs are one of the important components of water resources systems, extracting optimal operating policies for proper management of energy generated from these systems is an imperative step. Optimizing reservoir system operation (ORSO) is a non-linear, large-scale, and non-convex problem with a large number of constraints and decision variables. To solve ORSO problem effectively, a robust diversity-based, sine-cosine algorithm (RDB-SCA) is developed in the present study by introducing several strategies to balance the global exploration and local exploitation ability and to achieve accurate and reliable solutions. An efficient linear operation rule is coupled with the RDB-SCA to maximize the energy generation. The proposed method is then applied to a real-world, multi-reservoir system to extract optimal operational policies and, consequently, maximize the energy production. It is shown that the RDB-SCA is able to generate 24, 14, and 6% more energy than the original SCA, respectively for 2-, 3-, and 4-reservoir systems. The present findings are useful to suggest guidelines for efficient operation of hydropower multi-reservoir systems. This paper is supported by https://imanahmadianfar.com/codes.

  相似文献   
2.
This paper proposes a reading of the cultural and social aspects associated with sundry notions of territory through Spanish photography at the end of the twentieth century and the beginning of the twenty-first. An analysis of a series of case studies reveals a new awareness of the common space through the concept of trace, being understood beyond the material imprint, as it falls under the influence of the cultural aspects that clarify the account of the conflict and consciousness of the suburbs and peripheries. Contemporary ruins arising from unbridled urban growth, or the invisible wounds associated with certain places, converge in a series of images that have their own tradition in the conceptual experiments of the 70s and the aesthetics of the “non-site” displayed in the 90s. As background, the economic and political avatars of recent years in Spain – also linked to a global crisis – are manifested in a series of photographic musings whose images portray the scenarios of a premature ruin linked to property speculation and the traces of a collective memory.  相似文献   
3.
Abstract

In the present work, we compare the structure and transport properties of carbon nanohorns (CNHs) synthesized by arc evaporation of graphite alone and with the addition of some portion of toluene. The materials have been investigated using transmission electron microscopy, Raman and infrared spectroscopies, thermogravimetric and BET analyses. The addition of a small amount of toluene during the evaporation of graphitic rod increases the length of CNHs, affects their hierarchical arrangement in aggregates and results in surface functionalization. All these features significantly enhance the conductivity of CNHs obtained with toluene additive in comparison with the pristine CNHs.  相似文献   
4.
5.
6.
The gel-forming ability of myofibrillar protein (MP) is highly correlated with the characteristics of emulsified meat products. Incorporation of Agaricus bisporus (Ab) powder into MP gels may enhance its gel properties to facilitate the development of a novel and safe meat product. Therefore, this study investigated the effects of Ab powder on gel strength, water holding capacity (WHC), texture, rheological behaviour, LF-NMR spin–spin relaxation (T2), microstructure and protein secondary structure of the MP gel system. The results indicated that the gel strength, WHC, G' value and G" value were significantly improved when the addition of Ab powder increased from 0% to 6% (P < 0.05). Meanwhile, the T2 relaxation time was shortened, and free water was transformed into immobilised water. The texture of the gel was improved when 1%–4% Ab powder was added compared to the control. Furthermore, Ab filled in the gel network and promoted the unfolding of MP α-helix and the formation of MP β-sheet during the thermal denaturation of MP, leading to a dense aggregated network structure. The study suggested that Ab could be a promising ingredient in improving chicken MP's gel properties and developing fat-reduced meat products.  相似文献   
7.
8.
9.
Search for conditions of conservation of fast ionic transport (FIT) in nanosystems of advanced superionic conductors (ASIC)[1-4] and synthesis of new types of device thin-film heterostructures on this basis is a fundamental scientific problem. ASICs (α-AgI, solid electrolytes of the family RbAg4I5, etc. ) are crystals with a record high level of ionic conductivity and a low value of activation energy E~0. 1 eV.  相似文献   
10.
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