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   492300篇
  免费   10544篇
  国内免费   3491篇
电工技术   10816篇
技术理论   5篇
综合类   3926篇
化学工业   73079篇
金属工艺   20084篇
机械仪表   17501篇
建筑科学   12925篇
矿业工程   4290篇
能源动力   13540篇
轻工业   33914篇
水利工程   5651篇
石油天然气   11721篇
武器工业   417篇
无线电   56532篇
一般工业技术   92093篇
冶金工业   95117篇
原子能技术   9995篇
自动化技术   44729篇
  2022年   4271篇
  2021年   6256篇
  2020年   4618篇
  2019年   5278篇
  2018年   8545篇
  2017年   8860篇
  2016年   9458篇
  2015年   7115篇
  2014年   10178篇
  2013年   23435篇
  2012年   16568篇
  2011年   20998篇
  2010年   15899篇
  2009年   17212篇
  2008年   17370篇
  2007年   17041篇
  2006年   15751篇
  2005年   16623篇
  2004年   14404篇
  2003年   13650篇
  2002年   11870篇
  2001年   11410篇
  2000年   10573篇
  1999年   11445篇
  1998年   30144篇
  1997年   20623篇
  1996年   15783篇
  1995年   11533篇
  1994年   9904篇
  1993年   9722篇
  1992年   6622篇
  1991年   6232篇
  1990年   6158篇
  1989年   5737篇
  1988年   5453篇
  1987年   4719篇
  1986年   4553篇
  1985年   5018篇
  1984年   4532篇
  1983年   4097篇
  1982年   3790篇
  1981年   3922篇
  1980年   3606篇
  1979年   3387篇
  1978年   3427篇
  1977年   4307篇
  1976年   6055篇
  1975年   2941篇
  1974年   2699篇
  1973年   2776篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
71.
RCAS1 is a protein that participates in regulation of the tumor microenvironment and its immune responses, all in order to evade the immune system. The aim of this study was to analyze RCAS1 expression in urothelial bladder cancer cells (and in fibroblasts and macrophages of the tumor stroma) and its relationship with the histological pattern of malignancy. Eighty-three postcystectomy patients were enrolled. We analyzed the histological maturity (grade), progress (pT stage), tissue invasion type (TIT), nonclassic differentiation number (NDN), and the ability to metastasize (pN). The expression of RCAS1 protein was analyzed by immunohistochemistry. Indicators of histological malignancy were observed solely in association with the RCAS1 expression in cells in the border parts (BPs) of the tumor. Histological malignancy of the tumor, indicated by the pT and pN, and metastasis-free survival time, correlated significantly with RCAS1 expression in tumor neoplastic cells, whereas malignancy determined by grade, TIT, and NDN correlated with RCAS1 expression in fibroblasts and macrophages in the tumor microenvironment. These findings suggest that the increased RCAS1 expression depends on its cellular source and that RCAS1 expression itself is a component of various signaling pathways. The immune escape occurs within the tumor BPs, where the increase in the RCAS1 expression occurs within tumor cells and stromal cells in its microenvironment. We conclude that the histological pattern of tumor malignancy, indicated by grade, TIT, NDN, pT, and pN is a morphological indicator of immune escape.  相似文献   
72.
73.
74.
Fefelov  S. A.  Kazakova  L. P.  Bogoslovskiy  N. A.  Bylev  A. B.  Yakubov  A. O. 《Semiconductors》2020,54(4):450-453
Semiconductors - The current–voltage characteristics measured on Ge2Sb2Te5 thin films in the current mode are studied. The effect of multilevel recording is established when applying...  相似文献   
75.
Hussien  O. S.  Elamy  M. I. 《Strength of Materials》2020,52(3):470-479
Strength of Materials - The use of a damping system is one of the seismic protection systems that improve the seismic response of structures. The proposed methodology estimates the location (which...  相似文献   
76.
Powder Metallurgy and Metal Ceramics - The infiltration of aluminum melts into porous metal skeletons produced by powder metallurgy methods, including 3D printing, under a pressure gradient was...  相似文献   
77.
As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided.  相似文献   
78.
Yang  Xi  Gao  Ling  Guo  Qing  Li  Yongjiang  Ma  Yue  Yang  Ju  Gong  Changyang  Yi  Cheng 《Nano Research》2020,13(10):2579-2594

Over the past decade, numerous studies have attempted to enhance the effectiveness of radiotherapy (external beam radiotherapy and internal radioisotope therapy) for cancer treatment. However, the low radiation absorption coefficient and radiation resistance of tumors remain major critical challenges for radiotherapy in the clinic. With the development of nanomedicine, nanomaterials in combination with radiotherapy offer the possibility to improve the efficiency of radiotherapy in tumors. Nanomaterials act not only as radiosensitizers to enhance radiation energy, but also as nanocarriers to deliver therapeutic units in combating radiation resistance. In this review, we discuss opportunities for a synergistic cancer therapy by combining radiotherapy based on nanomaterials designed for chemotherapy, photodynamic therapy, photothermal therapy, gas therapy, genetic therapy, and immunotherapy. We highlight how nanomaterials can be utilized to amplify antitumor radiation responses and describe cooperative enhancement interactions among these synergistic therapies. Moreover, the potential challenges and future prospects of radio-based nanomedicine to maximize their synergistic efficiency for cancer treatment are identified.

  相似文献   
79.
Wireless Personal Communications - In the fusion experiment, sensitive radio frequency signal diagnostic instruments need to be protected against high power stray radiation coming from the Electron...  相似文献   
80.
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   
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