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   38499篇
  免费   4263篇
  国内免费   955篇
电工技术   1810篇
综合类   2257篇
化学工业   12911篇
金属工艺   1217篇
机械仪表   1265篇
建筑科学   1975篇
矿业工程   484篇
能源动力   833篇
轻工业   4762篇
水利工程   569篇
石油天然气   761篇
武器工业   137篇
无线电   2402篇
一般工业技术   5006篇
冶金工业   1066篇
原子能技术   248篇
自动化技术   6014篇
  2024年   128篇
  2023年   945篇
  2022年   1357篇
  2021年   1851篇
  2020年   1572篇
  2019年   1321篇
  2018年   1417篇
  2017年   1376篇
  2016年   1461篇
  2015年   1868篇
  2014年   2321篇
  2013年   3002篇
  2012年   2765篇
  2011年   2874篇
  2010年   2730篇
  2009年   2768篇
  2008年   2151篇
  2007年   1986篇
  2006年   1540篇
  2005年   1198篇
  2004年   897篇
  2003年   714篇
  2002年   644篇
  2001年   389篇
  2000年   282篇
  1999年   265篇
  1998年   225篇
  1997年   191篇
  1996年   190篇
  1995年   184篇
  1994年   141篇
  1993年   188篇
  1992年   133篇
  1991年   119篇
  1990年   124篇
  1989年   128篇
  1988年   96篇
  1987年   122篇
  1986年   127篇
  1985年   115篇
  1984年   99篇
  1983年   123篇
  1982年   93篇
  1981年   123篇
  1980年   98篇
  1979年   80篇
  1976年   74篇
  1974年   71篇
  1973年   139篇
  1972年   80篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
In pretreatment tumor samples of EGFR-mutated non-small cell lung cancer (NSCLC) patients, EGFR-Thr790Met mutation has been detected in a variable prevalence by different ultrasensitive assays with controversial prognostic value. Furthermore, its detection in liquid biopsy (LB) samples remains challenging, being hampered by the shortage of circulating tumor DNA (ctDNA). Here, we describe the technical validation and clinical implications of a real-time PCR with peptide nucleic acid (PNA-Clamp) and digital droplet PCR (ddPCR) for EGFR-Thr790Met detection in diagnosis FFPE samples and in LB. Limit of blank (LOB) and limit of detection (LOD) were established by analyzing negative and low variant allele frequency (VAF) FFPE and LB specimens. In a cohort of 78 FFPE samples, both techniques showed an overall agreement (OA) of 94.20%. EGFR-Thr790Met was detected in 26.47% of cases and was associated with better progression-free survival (PFS) (16.83 ± 7.76 vs. 11.47 ± 1.83 months; p = 0.047). In LB, ddPCR was implemented in routine diagnostics under UNE-EN ISO 15189:2013 accreditation, increasing the detection rate of 32.43% by conventional methods up to 45.95%. During follow-up, ddPCR detected EGFR-Thr790Met up to 7 months before radiological progression. Extensively validated ultrasensitive assays might decipher the utility of pretreatment EGFR-Thr790Met and improve its detection rate in LB studies, even anticipating radiological progression.  相似文献   
162.
Endometrial cancer (EC) is the 4th most common neoplasm of the female genital tract, with 15–20% of patients being of high risk of recurrence which leads to a significant decrease in patient survival. Current therapeutic options for patients with EC are poor, being the combined therapy of carboplatin and paclitaxel the standard of care, with limited efficacy. Therefore, new therapeutic options and better monitoring tools are needed to improve the management of the disease. In the current case report, we showcase the value of liquid biopsy analyses in a microsatellite instability EC patient with initially good prognosis that however underwent rapid progression disease within 6 months post-surgery; through the study of plasma cfDNA/ctDNA dynamics to assess the tumour evolution during treatment, as well as the study of the uterine aspirate as a valuable sample that captures the intra-tumour heterogeneity that allows a comprehensive genomic profiling of the disease to identify potential therapeutic options. Furthermore, preclinical models were generated at the time of tumour progression to assess the efficacy of the identified targeted therapies.  相似文献   
163.
In this paper we propose an algorithm for structure learning in predictive expert systems based on a probabilistic network representation. The idea is to have the simplest structure (minimum number of links) with acceptable predictive capability. The algorithm starts by building a tree structure based on measuring mutual information between pairs of variables, and then it adds links as necessary to obtain certain predictive performance. We have applied this method for ozone prediction in México City, where the ozone level is used as a global indicator for the air quality in different parts of the city. It is important to predict the ozone level a day, or at least several hours in advance, to reduce the health hazards and industrial losses that occur when the ozone reaches emergency levels. We obtained as a first approximation a tree-structured dependency model for predicting ozone in one part of the city. We observe that even with only three parameters, its estimations are acceptable.A causal network representation and the structure learning techniques produced some very interesting results for the ozone prediction problem. Firstly, we got some insight into the dependence structure of the phenomena. Secondly, we got an indication of which are the important and not so important variables for ozone forecasting. Taking this into account, the measurement and computational costs for ozone prediction could be reduced. And thirdly, we have obtained satisfactory short term ozone predictions based on a small set of the most important parameters.  相似文献   
164.
分析了常见的几种分层分布式密钥管理方案,并且在前人的基础上提出了一种新的基于分层分布式结构的组播密钥管理构想,介绍了这种方案的基本思想。通过实验分析比较了这种方案与前人方案的不同点及相同点,以及各自的优缺点。  相似文献   
165.
The following paper demonstrates that programmed sequential graph grammars can be used in a systematic proceeding to specify the changes of high level intermediate data structures arising in a programming support environment, in which all tools work in an incremental and syntax-driven mode. In this paper we lay stress upon the way to get the specification rather than on the result of this process. Therefore, we give here some approach to “specification engineering” using graph grammars. This approach is influenced by the syntactical definition of the underlying language for Programming in the Small, the module concept etc. to be supported on one side but also by the idea of the user interface.  相似文献   
166.
李娟  余芬  郭瑞松 《电源技术》2008,32(1):27-29
采用固相法制备了BaCe0.5-xZr0.5-xYb2xO3-δ(2x=0.1,0.15,0.2,0.25)固体电解质。X射线衍射(XRD)谱图分析结果表明,材料为立方钙钛矿结构。利用直流四探针法测定不同温度和不同气氛下材料的电导率,BaCe0.5-xZr0.5-x-Yb2xO3-δ的电导率与氧空位以及固溶度有关。在空气气氛下材料以电子空穴和氧离子电导为主,而在氢气气氛下,表现为质子导体。当2x=0.2时,在湿氢气气氛下于950℃的电导率为3.6×10-3S/cm。  相似文献   
167.
长期以来,我国高职英语教育培养目标为基于国内中小企业的实际应用型人才.相较普通本科专业英语重基础而言,学生的英语综合素质低,理论基础不扎实,已经严重影响到高职英语专业学生的就业竞争力.如何提高高职英语学生的语言能力成为高专英语教育的一个关键问题.拟从英语教育的四个基本能力--听、说、读、写方面探讨,试图探索出适合高专英语语言教育的新途径.  相似文献   
168.
169.
A novel method which can detect the possible handoffs for mobile nodes is proposed in this article. The method can be deployed on mobile nodes. So when a possible handoff occurs, mobile nodes can detect and take some necessary actions in time. In this study, the method is also used to optimize the transmission mechanism of Q-TCP. Moreover, the simulation results show that Q-TCP can provide better quality of service (QoS) for mobile nodes when they are moving among different agents.  相似文献   
170.
提出了一种基于Labview语言的实时数据采集及处理系统设计方案,介绍了光纤光栅温度传感波长解调原理,应用Labview语言编写了程序,实现对数据的处理和显示,试验结果表明:该系统能够有效利用计算机实现信号的处理,满足FBG传感器实时数据采集和处理的要求,获得了0.3℃温度测量精度和0.1 ℃分辨率.  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