首页 | 官方网站   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   541414篇
  免费   9228篇
  国内免费   1558篇
工业技术   552200篇
  2021年   5391篇
  2020年   3937篇
  2019年   4948篇
  2018年   8505篇
  2017年   8226篇
  2016年   8666篇
  2015年   6219篇
  2014年   9994篇
  2013年   25444篇
  2012年   15664篇
  2011年   21164篇
  2010年   16699篇
  2009年   18539篇
  2008年   19021篇
  2007年   18634篇
  2006年   16174篇
  2005年   14725篇
  2004年   13958篇
  2003年   13698篇
  2002年   12928篇
  2001年   13035篇
  2000年   12063篇
  1999年   12845篇
  1998年   33912篇
  1997年   23608篇
  1996年   17950篇
  1995年   13343篇
  1994年   11538篇
  1993年   11122篇
  1992年   7912篇
  1991年   7419篇
  1990年   7283篇
  1989年   6975篇
  1988年   6466篇
  1987年   5753篇
  1986年   5665篇
  1985年   6325篇
  1984年   5964篇
  1983年   5216篇
  1982年   4904篇
  1981年   5022篇
  1980年   4768篇
  1979年   4642篇
  1978年   4427篇
  1977年   5416篇
  1976年   7239篇
  1975年   3810篇
  1974年   3566篇
  1973年   3708篇
  1972年   2983篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Sustainable and efficient food supply chain has become an essential component of one’s life. The model proposed in this paper is deeply linked to people's quality of life as a result of which there is a large incentive to fulfil customer demands through it. This proposed model can enhance food quality by making the best possible food quality accessible to customers, construct a sustainable logistics system considering its environmental impact and ensure the customer demand to be fulfilled as fast as possible. In this paper, an extended model is examined that builds a unified planning problem for efficient food logistics operations where four important objectives are viewed: minimising the total expense of the system, maximising the average food quality along with the minimisation of the amount of CO2 emissions in transportation along with production and total weighted delivery lead time minimisation. A four objective mixed integer linear programming model for intelligent food logistics system is developed in the paper. The optimisation of the formulated mathematical model is proposed using a modified multi-objective particle swarm optimisation algorithm with multiple social structures: MO-GLNPSO (Multi-Objective Global Local Near-Neighbour Particle Swarm Optimisation). Computational results of a case study on a given dataset as well as on multiple small, medium and large-scale datasets followed by sensitivity analysis show the potency and effectiveness of the introduced method. Lastly, there has been a scope for future study displayed which would lead to the further progress of these types of models.  相似文献   
82.
83.
84.
Programming and Computer Software - Image segmentation using a hierarchical sequence of piecewise constant approximations that minimally differ from the original image in terms of the total squared...  相似文献   
85.
86.
87.
88.
基于香豆素类化合物在化妆品中的使用情况及其对人体健康的危害,采用C18色谱柱作为分析柱,通过优化试验条件建立了一种可准确、简便测定化妆品中多种香豆素类化合物的高效液相色谱法。试验结果表明,7种香豆素类化合物的保留时间和峰面积的相对标准偏差分别小于0.1%和2%,且检出限均低于40μg/L;通过样品加标试验,得到7种目标化合物的回收率为80%~94%。所建立方法具有快速、简便、准确、灵敏的特点,是测定化妆品中多种香豆素类化合物的有效方法。  相似文献   
89.
90.
The diagnosis and treatment of prostate cancer (PCa) is a major health-care concern worldwide. This cancer can manifest itself in many distinct forms and the transition from clinically indolent PCa to the more invasive aggressive form remains poorly understood. It is now universally accepted that glycan expression patterns change with the cellular modifications that accompany the onset of tumorigenesis. The aim of this study was to investigate if differential glycosylation patterns could distinguish between indolent, significant, and aggressive PCa. Whole serum N-glycan profiling was carried out on 117 prostate cancer patients’ serum using our automated, high-throughput analysis platform for glycan-profiling which utilizes ultra-performance liquid chromatography (UPLC) to obtain high resolution separation of N-linked glycans released from the serum glycoproteins. We observed increases in hybrid, oligomannose, and biantennary digalactosylated monosialylated glycans (M5A1G1S1, M8, and A2G2S1), bisecting glycans (A2B, A2(6)BG1) and monoantennary glycans (A1), and decreases in triantennary trigalactosylated trisialylated glycans with and without core fucose (A3G3S3 and FA3G3S3) with PCa progression from indolent through significant and aggressive disease. These changes give us an insight into the disease pathogenesis and identify potential biomarkers for monitoring the PCa progression, however these need further confirmation studies.  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-23

京公网安备 11010802026262号