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   46479篇
  免费   1325篇
  国内免费   202篇
电工技术   499篇
综合类   30篇
化学工业   7466篇
金属工艺   1155篇
机械仪表   792篇
建筑科学   2019篇
矿业工程   114篇
能源动力   1091篇
轻工业   2906篇
水利工程   451篇
石油天然气   125篇
武器工业   5篇
无线电   2794篇
一般工业技术   6251篇
冶金工业   6724篇
原子能技术   389篇
自动化技术   15195篇
  2023年   215篇
  2022年   440篇
  2021年   686篇
  2020年   465篇
  2019年   630篇
  2018年   787篇
  2017年   699篇
  2016年   837篇
  2015年   762篇
  2014年   1246篇
  2013年   2542篇
  2012年   2434篇
  2011年   5120篇
  2010年   2772篇
  2009年   2533篇
  2008年   2461篇
  2007年   2352篇
  2006年   2030篇
  2005年   2002篇
  2004年   1687篇
  2003年   1694篇
  2002年   1323篇
  2001年   709篇
  2000年   558篇
  1999年   623篇
  1998年   694篇
  1997年   604篇
  1996年   580篇
  1995年   583篇
  1994年   538篇
  1993年   518篇
  1992年   508篇
  1991年   300篇
  1990年   431篇
  1989年   397篇
  1988年   328篇
  1987年   362篇
  1986年   321篇
  1985年   427篇
  1984年   456篇
  1983年   329篇
  1982年   301篇
  1981年   289篇
  1980年   269篇
  1979年   271篇
  1978年   249篇
  1977年   229篇
  1976年   209篇
  1975年   197篇
  1974年   173篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
971.
972.
973.
(S)-;(+)-4-Methyl-3-heptanone is the principal component in the secretion from the mandibular glands of unmated and mated males and females ofAtta sexdens rubropilosa. In mated and unmated females, it is essentially the only component in the glandular secretion. In unmated males up to 50% of the secretion is a mixture of (3S, 4S)- and (3R, 4S)-4-methyl-3-heptanol. After mating, the amount of alcohol in the males decreases markedly.  相似文献   
974.
Describing multi‐component adsorption is fundamental to using sorption in any chemical separation. 50 years ago, Myers and Prausnitz made a seminal contribution to characterization and prediction of multi‐component adsorption by introducing Ideal Adsorbed Solution Theory (IAST). Here, we give an overview of IAST, highlighting its continued role as a benchmark method in describing adsorption using illustrative examples from a variety of experimental and molecular modeling studies. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2757–2762, 2015  相似文献   
975.
976.
Genomic DNA is under constant assault by endogenous and exogenous DNA damaging agents. DNA breakage can represent a major threat to genome integrity but can also be necessary for genome function. Here we present approaches to map DNA double-strand breaks (DSBs) and single-strand breaks (SSBs) at the genome-wide scale by two methods called DSB- and SSB-Seq, respectively. We tested these methods in human colon cancer cells and validated the results using the Topoisomerase II (Top2)-poisoning agent etoposide (ETO). Our results show that the combination of ETO treatment with break-mapping techniques is a powerful method to elaborate the pattern of Top2 enzymatic activity across the genome.  相似文献   
977.
The mammalian target of rapamycin (mTOR) signaling pathway is hyperactive in liver, adipose and skeletal muscle tissues of obese rodents. Alpha‐lipoic acid (αLA) has been well accepted as a weight‐loss treatment, though there are limited studies on its effect on mTOR signaling in high‐fat fed, obese rodents. Therefore, the goal of this study was to determine mTOR signaling and oxidative protein alterations in skeletal muscle of high‐fat fed, obese rats after αLA supplementation. Phosphorylation of the mTOR substrate, eukaryotic initiation factor (eIF) 4E‐binding protein 1 (4E‐BP1) and eIF4B were significantly reduced (p < 0.05) in muscle from αLA supplemented rats. Activation of AMP‐activated protein kinase (AMPK), an mTOR inhibitory kinase, was higher (p < 0.05) in the αLA group. Protein expression of markers of oxidative metabolism, acetyl CoA carboxylase (ACC), cytochrome c oxidase IV (COX IV), peroxisome proliferator‐activated receptor (PPAR), and PPAR gamma coactivator 1‐alpha (PGC‐1α) were significantly higher (p < 0.05) after αLA supplementation compared to non‐supplemented group. Our findings show that αLA supplementation limits the negative ramifications of consuming a high fat diet on skeletal muscle markers of oxidative metabolism and mTORC1 signaling.  相似文献   
978.
This paper describes the reaction of the simplest isocyanate, isocyanic acid, conveniently generated in situ from sodium cyanate, with nucleophilic carboxylate and amino residues in polyamide fibres. Changing the pH conditions greatly affects the outcome of these reactions: under acidic conditions the carboxylate residues are selectively carbamoylated, whereas under neutral conditions both residues are carbamoylated. Such modifications greatly change the dyeing behaviour of the treated substrates. The carboxylate carbamoylation reaction leads to the formation of amides rather than the carbamoylcarboxylate, which is a reactive intermediate.  相似文献   
979.
Candidatus Liberibacter solanacearum (CLso) is an unculturable bacterium vectored by the tomato potato psyllid (TPP) Bactericera cockerelli and has been associated with Zebra chip disease in potato and with other economically relevant symptoms observed in solanaceous crops. By altering their host and vector’s biological system, pathogens are able to induce changes that benefit them by increasing their transmission rate. Understanding these changes can enable better targeting of mechanisms to control pathogen outbreaks. Here, we explored how the CLso infectious status affects the volatile organic compounds (VOCs) of the tomato plant, and whether the CLso infectious status of TPP influences host plant settlement. These chemical and behavioral changes can ultimately affect the rate of encounter between the host and the vector. Results from headspace volatile collection of tomato plants showed that CLso infected tomato plants emitted a qualitatively and quantitatively different blend of VOCs compared to sham-infected plants. By a factorial experiment, we showed that CLso negative (CLso-) TPP preferred to settle 70 % more often on infected tomato plants, while CLso positive (CLso+) TPP were found 68 % more often on sham-infected tomato plants. These results provide new evidence in favor of both host and vector manipulation by CLso.  相似文献   
980.
W(CO)6 and H2O2 were used in an atomic layer deposition (ALD)‐like process to grow thin WOx films onto TiO2 powders in a fluidized bed reactor. Carbonyl precursors are not widely used in this application, so that deviations from an ideal ALD process, previously not examined with W(CO)6, were identified. The resulting WOx films were a result of both ALD‐like and chemical vapor deposition‐based growth modes. A chemical reaction mechanism incorporating a combination of these two growth modes was inferred. As the move to expand the range of ALD precursors meets with the desire to scale up these processes, the simultaneous appearance of both these growth modes is likely to become more and more common, and so understanding the interaction of these two types of surface reactions is key to progress in the field. The films were observed to inhibit the anatase‐to‐rutile phase transformation in the TiO2 powders upon high temperature annealing, while crystallization of the amorphous WO3 was also not observed. Changes in the local bonding within the WO3 were observed and associated with changes in the structural nature of the film and its interface to the substrate. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1278–1286, 2014  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