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   182725篇
  免费   24899篇
  国内免费   18938篇
电工技术   16102篇
技术理论   10篇
综合类   26077篇
化学工业   13387篇
金属工艺   5185篇
机械仪表   12936篇
建筑科学   16733篇
矿业工程   5341篇
能源动力   7085篇
轻工业   6806篇
水利工程   9751篇
石油天然气   8185篇
武器工业   2627篇
无线电   18069篇
一般工业技术   17509篇
冶金工业   5547篇
原子能技术   1851篇
自动化技术   53361篇
  2024年   985篇
  2023年   2776篇
  2022年   5166篇
  2021年   5867篇
  2020年   6441篇
  2019年   5713篇
  2018年   5526篇
  2017年   6813篇
  2016年   7766篇
  2015年   7987篇
  2014年   10825篇
  2013年   12044篇
  2012年   13293篇
  2011年   14147篇
  2010年   11195篇
  2009年   11701篇
  2008年   11893篇
  2007年   13560篇
  2006年   11763篇
  2005年   10366篇
  2004年   8445篇
  2003年   7289篇
  2002年   5826篇
  2001年   4943篇
  2000年   4350篇
  1999年   3398篇
  1998年   2835篇
  1997年   2421篇
  1996年   2196篇
  1995年   1912篇
  1994年   1574篇
  1993年   1132篇
  1992年   972篇
  1991年   763篇
  1990年   640篇
  1989年   525篇
  1988年   335篇
  1987年   204篇
  1986年   145篇
  1985年   138篇
  1984年   143篇
  1983年   85篇
  1982年   103篇
  1981年   55篇
  1980年   76篇
  1979年   67篇
  1978年   33篇
  1977年   22篇
  1959年   20篇
  1951年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
In this present work, Ca-alginate-biochar adsorbent has been synthesized, characterized and tested its effectiveness in the removal of aqueous phase Zn2+ metal. The removal efficiency was studied under various physicochemical process parameters. External mass transfer model, intraparticle diffusion model and pseudo-first-order and pseudo-second-order models were used to fit the experimental Zn2+ adoption kinetic results and to identify the mechanism of adsorption. The desorption studies indicate the possibilities of ion-exchange and physical–chemical adsorption of Zn2+. The adsorption was best described by Langmuir isotherm model. Thermodynamic parameters suggested that the adsorption process becomes spontaneous, endothermic and irreversible in nature.  相似文献   
92.
M-learning is characterized as a powerful element of learning and education for facilitating the learning experiences. With enhanced and rapid advancements in technologies of ICTs (Information and Communication Technologies) and mobile, numerous innovative services and applications are being developed. Therefore, it becomes significant to investigate the factors influencing the intentions of m-learning to be used among the students of higher education institution. This study examines the “Technology Acceptance Model” (TAM), “Theory of Reasoned Action” (TRA) and “Unified Theory of Acceptance and Use of Technology” (UTAUT). The study is based on a survey being conducted across diverse groups of students, belonging to different communities and universities. The survey questionnaire was utilized for collecting the relevant data from 250 respondents. The results analyzed yields the impact that the proposed model of m-learning is comprehensive to study in the institutions of higher education.  相似文献   
93.
为了系统地评价胸腺五肽作为辅助药物治疗各种肺癌的疗效及其对机体免疫功能的影响,利用电子检索收集有关胸腺五肽联合放疗或化疗方案治疗肺癌的临床随机对照试验文献,对符合纳入标准的文献,采用RevMan5.3 软件进行系统评价。最终共纳入文献 9 篇,总样本量 784 例。Meta 分析结果表明,胸腺五肽作为辅助药物治疗各种肺癌提高总有效率的差异无统计学意义[OR = 1.44, 95%CI(0.99, 2.10), P =0.06 > 0.05]。在对免疫功能的影响方面,胸腺五肽的使用显著增高外周血中的 CD3+ 细胞水平[OR = 5.88, 95% CI(2.34, 9.42), P =0.001],CD4+ 细胞水平也显著上升[OR =8.32, 95%CI(5.22, 11.42), P < 0.00001] , CD4+ /CD8+比值也有明显的提高[OR = 0.38, 95% CI(0.18, 0.59), P=0.0002],但 CD8+ 细胞水平的差异无统计学意义[OR =-3.12, 95% CI ( -9.02, 2.79), P >0.05]。总的来说,本研究在一定程度上反映了在辅助治疗肺癌方面,胸腺五肽能显著提高外周血中的 CD3+ 细胞水平、CD4+ 细胞水平、CD4+/CD8+ 比值。而对于治疗的有效率、CD8+ 细胞水平,差异无统计学意义。  相似文献   
94.
An engineered variant of the yeast Pichia pastoris was used to produce the potential malaria vaccine D1M1. This paper describes the implementation of an expanded bed adsorption chromatography step into a sequential cultivation process of the yeast in order to link protein expression, cell release, and product capture of the secreted protein in a fully automated plant. The process is operated with a semi-continuous strategy for an integrated production. Process improvements have been achieved using design of experiments. Resulting purities of product achieved up to 87% with recoveries of 51% in a single downstream operation. Furthermore, a multivariate analysis of historical batch data was used to develop a golden batch model for process monitoring.  相似文献   
95.
96.
The eutectic 80Au/20Sn solder alloy is widely used in high power electronics and optoelectronics packaging. In this study, low cycle fatigue behavior of a eutectic 80Au/20Sn solder alloy is reported. The 80Au/20Sn solder shows a quasi-static fracture characteristic at high strain rates, and then gradually transforms from a transgranular fracture (dominated by fatigue damage) to intergranular fracture (dominated by creep damage) at low strain rates with increasing temperature. Coffin-Manson and Morrow models are proposed to evaluate the low cycle fatigue behavior of the 80Au/20Sn solder. Besides, the 80Au/20Sn solder has enhanced fatigue resistance compared to the 63Sn/37Pb solder.  相似文献   
97.
Metamerism phenomenon can be used in illuminant detection to ensure the accuracy of light source. A method based on Long‐, Middle‐, Short‐ wavelength cones(LMS) weighting algorithm to evaluate metamerism degree is proposed. The chromatic relationship between the degree of metamerism mismatch and the light source is studied. Herein, the consistency between the metameric indices (MIs) and CIE1976 L*a*b* color difference ranking is analyzed by SRCC, KRCC, PLCC and RMSE. A statistically sampling method to obtain practical LMS cone fundamentals to evaluate metamerism degree is employed. The analysis results obtained show that the method based on LMS weighting algorithm has good evaluation ability and stability in simulation experiments and statistically sampling experiments, which are in line with visual characteristics of human. Proposed method meets the requirements of selecting metameric pairs used in light source detection. The analysis results have certain guiding significance.  相似文献   
98.
In reliability analysis, the stress-strength model is often used to describe the life of a component which has a random strength (X) and is subjected to a random stress (Y). In this paper, we considered the problem of estimating the reliability R=P [Y<X] when the distributions of both stress and strength are independent and follow exponentiated Pareto distribution. The maximum likelihood estimator of the stress strength reliability is calculated under simple random sample, ranked set sampling and median ranked set sampling methods. Four different reliability estimators under median ranked set sampling are derived. Two estimators are obtained when both strength and stress have an odd or an even set size. The two other estimators are obtained when the strength has an odd size and the stress has an even set size and vice versa. The performances of the suggested estimators are compared with their competitors under simple random sample via a simulation study. The simulation study revealed that the stress strength reliability estimates based on ranked set sampling and median ranked set sampling are more efficient than their competitors via simple random sample. In general, the stress strength reliability estimates based on median ranked set sampling are smaller than the corresponding estimates under ranked set sampling and simple random sample methods.  相似文献   
99.
Wireless Body Area Networks (WBANs) are envisaged to play crucial role in psychological, medical and non-medical applications. This paper presents iM-SIMPLE; a reliable, and power efficient routing protocol with high throughput for WBAN. We deploy sensor nodes on human body to measure the physiological parameters such as blood pressure, temperature, glucose, lactic acid, EMG, acceleration, pressure, and position. Data from sensors is forwarded to intermediate node, from where it is transmitted to sink. An end user can access the required information available at sink via internet. To minimize energy consumption of the network, we utilize multi-hop mode of communication. A cost function is introduced to select the forwarder; node with high residual energy and least distance to sink has minimum cost function value and is selected. Residual energy parameter balances the energy consumption among the sensor nodes, and least distance improves packet delivery to sink because of reduced less path loss. We formulate the minimum energy consumption and high throughput problems as an Integer Linear Program. In order to support mobility, we also consider two body postures. Simulation results confirm the performance advantage of iM-SIMPLE compared to contemporary schemes in terms of maximizing stability period and throughput of the network.  相似文献   
100.
This paper examines what influences trust in mobile social commerce environment. Drawing on trust-based acceptance model (i.e. cognitive and emotional trust) and online review features (i.e. profile photo, linguistic style, and reported experience), we examine how these factors affect trust in mobile social commerce. Hypotheses were tested using survey data. The results of our model showed that there are significant influences of profile photo, reported experience, cognitive, and emotional trust towards trust in ms-commerce. This work contributes to existing literature by examining the roles of previous trust in mobile payments and online reviews on trust in mobile social commerce.  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