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   620007篇
  免费   8565篇
  国内免费   2472篇
电工技术   11201篇
综合类   848篇
化学工业   92522篇
金属工艺   22844篇
机械仪表   18070篇
建筑科学   16132篇
矿业工程   2320篇
能源动力   16071篇
轻工业   57985篇
水利工程   5748篇
石油天然气   7373篇
武器工业   56篇
无线电   77543篇
一般工业技术   118650篇
冶金工业   115834篇
原子能技术   11856篇
自动化技术   55991篇
  2021年   4389篇
  2019年   4092篇
  2018年   6713篇
  2017年   6856篇
  2016年   7314篇
  2015年   5381篇
  2014年   9015篇
  2013年   28189篇
  2012年   15302篇
  2011年   21752篇
  2010年   16798篇
  2009年   19229篇
  2008年   20338篇
  2007年   20700篇
  2006年   18265篇
  2005年   16943篇
  2004年   16693篇
  2003年   16254篇
  2002年   15685篇
  2001年   15701篇
  2000年   14771篇
  1999年   15486篇
  1998年   36222篇
  1997年   26258篇
  1996年   20374篇
  1995年   15909篇
  1994年   14113篇
  1993年   13838篇
  1992年   10226篇
  1991年   9821篇
  1990年   9371篇
  1989年   9078篇
  1988年   8597篇
  1987年   7508篇
  1986年   7502篇
  1985年   8803篇
  1984年   8201篇
  1983年   7277篇
  1982年   6831篇
  1981年   6831篇
  1980年   6563篇
  1979年   6327篇
  1978年   6054篇
  1977年   7084篇
  1976年   9519篇
  1975年   5148篇
  1974年   4971篇
  1973年   4894篇
  1972年   4054篇
  1971年   3545篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
The proliferating need for sustainability intervention in food grain transportation planning is anchoring the attention of researchers in the interests of stakeholders and environment at large. Uncertainty associated with food grain supply further intensifies the problem steering the need for designing robust, cost-efficient and sustainable models. In line with this, this paper aims to develop a robust and sustainable intermodal transportation model to facilitate single type of food grain commodity shipments while considering procurement uncertainty, greenhouse gas emissions, and intentional hub disruption. The problem is designed as a mixed integer non-linear robust optimisation model on a hub and spoke network for evaluating near optimal shipment quantity, route selection and hub location decisions. The robust optimisation approach considers minimisation of total relative regret associated with total cost subject to several real-time constraints. A version of Particle Swarm Optimisation with Differential Evolution is proposed to tackle the resulting NP-hard problem. The model is tested with two other state-of the art meta-heuristics for small, medium, and large datasets subject to different procurement scenarios inspired from real time food grain operations in Indian context. Finally, the solution is evaluated with respect to total cost, model and solution robustness for all instances.  相似文献   
3.
4.
5.
6.

Stability constants and formation enthalpies of supramolecular complexes of crown ethers and their cyclic and acyclic analogues are determined on the basis of experimental data obtained by different physicochemical methods in the terms of a general approach developed and implemented in the ChemEqui software package. The established regularities of variation of stability of complexes are discussed as dependent on the ligand structure, nature of the cation, solvent, and anion. The applicability of the suggested method of determining complexation selectivity is shown for multicomponent equilibria in solutions.

  相似文献   
7.
Lobster krill (Munida genus) represents an under‐valued crustacean frequently caught on European fishing banks. In this work, its sensory, microbiological and biochemical qualities were evaluated during chilled storage. Additionally, the effects of a prestorage antimelanosic treatment consisting of soaking in sodium metabisulphite (SMB) solutions at two different concentrations (0.25% and 0.75%) were also studied. SMB prestorage treatment provided lobster specimens that still exhibited acceptable sensory quality after 10 days of storage, while control specimens were unacceptable at that time. SMB treatment also resulted in a significant (P < 0.05) inhibition of microbial growth, mainly of Enterobacteriaceae, psychrotrophes and proteolytic bacteria. Low lipid oxidation levels were observed for all batches; however, a significantly higher (P < 0.05) retention of polyunsaturated fatty acids was found in SMB‐treated lobster, especially in the 0.75% SMB batch. The results presented here open the way to the potential commercialisation of currently under‐utilised lobster krill as a chilled product.  相似文献   
8.
9.
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