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   939722篇
  免费   12747篇
  国内免费   2142篇
电工技术   17065篇
综合类   861篇
化学工业   142724篇
金属工艺   38827篇
机械仪表   29458篇
建筑科学   22205篇
矿业工程   5824篇
能源动力   23988篇
轻工业   76572篇
水利工程   10640篇
石油天然气   19437篇
武器工业   64篇
无线电   102509篇
一般工业技术   187049篇
冶金工业   173663篇
原子能技术   20292篇
自动化技术   83433篇
  2021年   8360篇
  2020年   6158篇
  2019年   7889篇
  2018年   16740篇
  2017年   16841篇
  2016年   16265篇
  2015年   9567篇
  2014年   15669篇
  2013年   41575篇
  2012年   25457篇
  2011年   36844篇
  2010年   29979篇
  2009年   32543篇
  2008年   33265篇
  2007年   33850篇
  2006年   26096篇
  2005年   25189篇
  2004年   23669篇
  2003年   23251篇
  2002年   21835篇
  2001年   21188篇
  2000年   20077篇
  1999年   20594篇
  1998年   51182篇
  1997年   36464篇
  1996年   28184篇
  1995年   21312篇
  1994年   18895篇
  1993年   18512篇
  1992年   13723篇
  1991年   13017篇
  1990年   12875篇
  1989年   12466篇
  1988年   11833篇
  1987年   10636篇
  1986年   10384篇
  1985年   11690篇
  1984年   10688篇
  1983年   9918篇
  1982年   9141篇
  1981年   9288篇
  1980年   8847篇
  1979年   8793篇
  1978年   8610篇
  1977年   9937篇
  1976年   12878篇
  1975年   7597篇
  1974年   7222篇
  1973年   7381篇
  1972年   6179篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Currently, the efficient detection of fingerprints is essential for the crime investigations. Revealing fingerprints is commonly achieved with fluorescent organic compounds but they are not efficient for fingerprint detection on porous or reflective surfaces. In order to solve the problem of collecting fingerprints on porous/reflective surfaces, inorganic phosphors have been employed, since they have characteristics of variable color emission, afterglow, high chemical stability and nano-size, which allow the fingerprint detection on any porous or non-porous surfaces. Due to these last properties, this review presents a summary about the use of phosphorescent and fluorescent phosphors for the detection of latent fingerprints. First, we discussed the main physical and chemical characteristics of the fingerprints which permit their detection and collection from any surface. After this, we presented the main morphological, structural and luminescent properties of the phosphorescent and fluorescent phosphors that allow their use for fingerprint detection. Later, we demonstrated with pictures of fingerprints (with and without light emission from the phosphors deposited on them) that both, phosphorescent and fluorescent phosphors can be used to visualize fingerprints with high resolution and high contrast without interference of the background surface, which is ideal for its collection and registration in the Automated Fingerprint Identification System (AFIS). We believe that this review could be useful to understand how to select an appropriate phosphorescent or fluorescent material for fingerprint detection depending on the type of surface (porous or non-porous, reflective or not reflective) where the fingerprint is deposited.  相似文献   
32.
Cell surface and secreted proteins provide essential functions for multicellular life. They enter the endoplasmic reticulum (ER) lumen co-translationally, where they mature and fold into their complex three-dimensional structures. The ER is populated with a host of molecular chaperones, associated co-factors, and enzymes that assist and stabilize folded states. Together, they ensure that nascent proteins mature properly or, if this process fails, target them for degradation. BiP, the ER HSP70 chaperone, interacts with unfolded client proteins in a nucleotide-dependent manner, which is tightly regulated by eight DnaJ-type proteins and two nucleotide exchange factors (NEFs), SIL1 and GRP170. Loss of SIL1′s function is the leading cause of Marinesco-Sjögren syndrome (MSS), an autosomal recessive, multisystem disorder. The development of animal models has provided insights into SIL1′s functions and MSS-associated pathologies. This review provides an in-depth update on the current understanding of the molecular mechanisms underlying SIL1′s NEF activity and its role in maintaining ER homeostasis and normal physiology. A precise understanding of the underlying molecular mechanisms associated with the loss of SIL1 may allow for the development of new pharmacological approaches to treat MSS.  相似文献   
33.
Journal of Inorganic and Organometallic Polymers and Materials - In this work, a borosilicate glass sample (5SiO2–45B2O3–20Na2O–25CaO–5Ag2O) was added to nano-sized...  相似文献   
34.
Automation and Remote Control - We consider multicriteria minimax optimization problems with criteria in the form of the maxima of functionals given by the induced norms of linear operators taking...  相似文献   
35.
The G protein-coupled receptor GPR183/EBI2, which is activated by oxysterols, is a therapeutic target for inflammatory and metabolic diseases where both antagonists and agonists are of potential interest. Using the piperazine diamide core of the known GPR183 antagonist (E)-3-(4-bromophenyl)-1-(4-(4-methoxybenzoyl)piperazin-1-yl)prop-2-en-1-one (NIBR189) as starting point, we identified and sourced 79 structurally related compounds that were commercially available. In vitro screening of this compound collection using a Ca2+ mobilization assay resulted in the identification of 10 compounds with agonist properties. To enable establishment of initial structure-activity relationship trends, these were supplemented with five in-house compounds, two of which were also shown to be GPR183 agonists. Taken together, our findings suggest that the agonist activity of this compound series is dictated by the substitution pattern of one of the two distal phenyl rings, which functions as a molecular efficacy-switch.  相似文献   
36.
Fire spread and growth on real‐scale four cushion mock‐ups of residential upholstered furniture (RUF) were investigated with the goal of identifying whether changes in five classes of materials (barrier, flexible polyurethane foam, polyester fiber wrap, upholstery fabric, and sewing thread), referred to as factors, resulted in statistically significant changes in burning behavior. A fractional factorial experimental design plus practical considerations yielded a test matrix with 20 material combinations. Experiments were repeated a minimum of two times. Measurements included fire spread rates derived from video recordings and heat release rates (HRRs). A total of 13 experimental parameters (3 based on the videos and 10 on the HRR results), referred to as responses, characterized the measurements. Statistical analyses based on Main Effects Plots (main effects) and Block Plots (main effects and factor interactions) were used. The results showed that three of the factors resulted in statistically significant effects on varying numbers of the 13 responses. The Barrier and Fabric factors had the strongest main effects with roughly comparable magnitudes. Foam was statistically significant for fewer of the responses and its overall strength was weaker than for Barrier and Fabric. No statistically significant main effects were identified for Wrap or Thread. Multiple two‐term interactions between factors were identified as being statistically significant. The Barrier*Fabric interaction resulted in the highest number of and strongest statistically significant effects. The existence of two‐term interactions means that it will be necessary to consider their effects in approaches designed to predict the burning behavior of RUF.  相似文献   
37.
Theoretical Foundations of Chemical Engineering - Using gas–liquid chromatography, the activity coefficients upon the infinite dilution of the components of the reaction mixture for obtaining...  相似文献   
38.
Ceria-based solid solutions are important materials for high- and medium-temperature electrochemical applications. However, the stabilities of both binary and ternary ceria-based solid solutions are insufficient at elevated temperatures, which limits their application as solid electrolytes or SOFC cathodes. Data on the high-temperature stability of ceria-based ceramics are unavailable in the literature. In the present study, we report a thermodynamic stability investigation of Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions. The thermal prehistories of binary and ternary systems were investigated using STA, XRD, and ESCA techniques. The vaporization processes were investigated in the temperature range of 1577–2227°С via the Knudsen effusion mass spectrometry technique. Using data on the component activity in solid-phase thermodynamic properties of Y2O3-CeO2 solid solutions, which is represented as the Gibbs energy, the excess Gibbs energy was calculated as a function of the ceria mol. %. It was shown that the reduction of Ce4+ to Ce3+ in Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions corresponds to less-negative Gibbs energy compared to ZrO2-CeO2 solid solutions.  相似文献   
39.
Theoretical Foundations of Chemical Engineering - The main approaches to developing a reactor block for the hydrodesulfurization of diesel fuels are considered taking into account the reactivity of...  相似文献   
40.
Journal of Signal Processing Systems - Convolutional Neural Networks (CNNs) have improved several computer vision applications, like object detection and classification, when compared to other...  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