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   835篇
  免费   49篇
  国内免费   5篇
电工技术   105篇
综合类   8篇
化学工业   211篇
金属工艺   19篇
机械仪表   26篇
建筑科学   22篇
矿业工程   6篇
能源动力   33篇
轻工业   56篇
水利工程   2篇
石油天然气   20篇
武器工业   6篇
无线电   77篇
一般工业技术   158篇
冶金工业   75篇
原子能技术   15篇
自动化技术   50篇
  2024年   5篇
  2023年   5篇
  2022年   18篇
  2021年   24篇
  2020年   10篇
  2019年   18篇
  2018年   14篇
  2017年   13篇
  2016年   20篇
  2015年   27篇
  2014年   34篇
  2013年   63篇
  2012年   39篇
  2011年   52篇
  2010年   41篇
  2009年   47篇
  2008年   43篇
  2007年   25篇
  2006年   34篇
  2005年   20篇
  2004年   21篇
  2003年   23篇
  2002年   25篇
  2001年   11篇
  2000年   12篇
  1999年   11篇
  1998年   28篇
  1997年   23篇
  1996年   20篇
  1995年   10篇
  1994年   24篇
  1993年   15篇
  1992年   8篇
  1991年   7篇
  1990年   10篇
  1988年   6篇
  1987年   4篇
  1986年   8篇
  1985年   5篇
  1984年   7篇
  1983年   11篇
  1982年   10篇
  1981年   5篇
  1980年   2篇
  1979年   6篇
  1978年   3篇
  1977年   5篇
  1976年   6篇
  1975年   3篇
  1969年   2篇
排序方式: 共有889条查询结果,搜索用时 0 毫秒
161.
This paper, based on research by the Japan National Land Policy Institute (NaLPI), describes various forms of urban underground space use and the proper use of underground space. The paper discusses images that people working above-ground and below-ground hold about underground space, as measured by their responses to a questionnaire survey; and suggests ways to alleviate concerns people have about underground spaces (e.g., related to health, fear of being underground, and safety).  相似文献   
162.
本文基于Fourier变换提出了场图像的等高线插值法,使场图像恢复为帧图像。通过单方向指定灰度最小波动方法寻找场图像的等高线,将等高线灰度值Fourier变换后插值,插值后的场图像与实际帧图像比较,并与一些其它插值法比较,结果很理想。  相似文献   
163.
Aphytis yanonensis De Bach & Rosen, a parasitic wasp of the arrowhead scale,Unaspis yanonensis (Kuwana), was introduced to Japan to controlU. yanonensis. A. yanonensis recognizes a host insect by antennal contact and deposits eggs on the insect body underneath the scale. Ovipositional behavior is induced by perceiving the cuticular wax of the host insect,U. yanonensis, and other coccoids. Chemical composition of the cuticular wax was analyzed and oviposition stimulants were isolated following a bioassay usingA. yanonensis.  相似文献   
164.
This paper presents the results of analyses of the effectiveness of a superconducting fault current limiter (SFCL) to stabilize the synchronous generators, suppress turbine shaft torque oscillations, and limit the fault current in a two‐machine infinite bus system. In this study, the system model with two SFCLs having shunt resistance installed at each generator terminal was used taking 3LG (three lines to ground) fault at 12 fault points into account. These analyses were performed using EMTP/ATP. It is found that the use of SFCL with a shunt resistance value of 1.1 pu is most effective for all fault points for the stabilization of synchronous generators, the suppression of turbine shaft torque oscillations, and the limitation of fault current. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(3): 44–53, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10272  相似文献   
165.
The New South Wales Department of Corrective Services has introduced a number of suicide prevention measures in order to deal with the problem of inmate suicides. This article describes the measures. The article also shows that the characteristics of the incarcerated population differ greatly from those in the community. Findings from the self-harm database 1991-1995 show that, nevertheless, there are some unique characteristics of the group of self-harmers and fatal self-harmers. These findings are discussed in relation to the preventive measures that are introduced in the NSW correctional centers.  相似文献   
166.
Human prostatic carcinoma frequently metastasizes to bone tissue and activates bone metabolism, especially bone formation, at the site of metastasis. It has been reported that an extract of prostatic carcinoma and conditioned medium (CM) of a human prostatic carcinoma cell line, PC-3, established from a bone metastastic lesion, stimulate osteoblastic cell proliferation. However, there is little information about the effect of PC-3 CM on the differentiation of osteoblastic cells. In this study, we investigated the effect of PC-3 CM on the differentiation of two types of osteoblastic cells, primary fetal rat calvaria (RC) cells containing many undifferentiated osteoprogenitor cells, and ROS 17/2.8, a well-differentiated rat osteosarcoma cell line. PC-3 CM inhibited bone nodule formation and the activity of alkaline phosphatase (ALPase), an osteoblastic marker enzyme, on days 7, 14, and 21 (RC cells) or 3, 6, and 9 (ROS 17/2.8 cells) in a dose-dependent manner (5-30% CM). However, the CM did not affect cell proliferation or cell viability. PC-3 CM was found to markedly block the gene expression of ALPase and osteocalcin (OCN) mRNAs but had no effect on the mRNA expression of osteopontin (OPN), the latter two being noncollagenous proteins related to bone matrix mineralization. These findings suggest that PC-3 CM contains a factor that inhibits osteoblastic cell differentiation and that this factor may be involved in the process of bone metastasis from prostatic carcinoma.  相似文献   
167.
In the mammalian brain, kynurenine aminotransferase (KAT) is pivotal to the synthesis of kynurenic acid, a preferential antagonist at the strychnine-insensitive NMDA-glycine site. As NMDA receptors are involved in autonomic function, we have examined the immunohistochemical localization of KAT in the medulla and spinal cord of the rat. KAT immunoreactivity (KAT-li) was found throughout these areas, in both glia and neurons. Unlike the mainly astrocytic localization in forebrain structures, KAT-li was predominantly neuronal, notably in areas important for blood pressure and heart rate regulation: ventral medulla, nucleus ambiguus, nucleus of the solitary tract and intramediolateral cell column of the spinal cord. The presence of KAT in these nuclei supports a neuromodulatory role for kynurenic acid in NMDA-mediated autonomic function.  相似文献   
168.
The authors previously reported that transforming growth factor beta1 (TGF-beta1) induces apoptosis in McA-RH7777 (7777) and McA-RH8994 (8994) rat hepatoma cell lines. Although these cell lines exhibit different responses to glucocorticoid treatment in various cellular functions and gene expression, dexamethasone (DEX) inhibited spontaneous and TGF-beta1-induced apoptosis in both. Analysis of analogous hormones in TGF-beta1-induced apoptosis in 8994 cells suggested the inhibitory effect to be glucocorticoid-specific. By cell-cycle analysis and DNA fragmentation assay using sodium butyrate, a G1-arrest-inducing reagent, regulation of apoptosis by TGF-beta1 and DEX was shown independent of the cell cycle. For elucidation of the mechanisms of anti-apoptotic action of DEX, the effects of various chemical probes on this apoptosis model were examined, and various reagents known to exhibit anti-apoptotic activity in other experimental systems were found to be ineffective. The effect of TGF-beta1 and DEX on cellular amounts of several apoptosis-related proteins, members of the Bcl-2 family, Bcl-2, Bcl-xL, Bcl-xS, Bad, and Bax was also examined. DEX drastically increased Bcl-xL in both cell lines irrespective of the presence of TGF-beta1. Bcl-2 and Bcl-xS proteins were not detected, and Bax and Bad content did not change by treatment with TGF-beta1 or DEX. Progesterone (Prog), a partial antagonist for glucocorticoid receptor, inhibited the effects of DEX on apoptosis and Bcl-xL expression in 8994 cells. Thus, Bcl-xL induction by DEX would appear closely associated with its inhibitory effect on spontaneous and TGF-beta1-induced apoptosis in the hepatoma cell lines.  相似文献   
169.
The effects of methionine on hepatocarcinogenesis induced by coadministration of a choline-deficient L-amino acid-defined (CDAA) diet and ethionine were examined. F344 male rats were divided into 4 experimental groups. Groups 1 and 2 received the CDAA diet and a choline-supplemented L-amino acid-defined (CSAA)++ diet, respectively. Group 3 received the CDAA diet containing 0.05% ethionine, and group 4 the CDAA diet containing 0.05% ethionine and 0.47% methionine. Animals were killed after 12 weeks of treatment. Histologically, the CDAA diet induced intracellular fat accumulation and foci. In contrast, ethionine caused not only foci, but also hyperplastic nodules, cholangiofibrosis and the proliferation of oval cells without such fat accumulation. Methionine abolished the development of all of the liver lesions induced by coadministration of the CDAA diet and ethionine. To investigate the effects of methionine on induction of c-myc and c-Ha-ras expression, as well as generation of 8-hydroxyguanine (8-OHGua) and 2-thiobarbituric acid-reacting substances (TBARS), by coadministration of the CDAA diet and ethionine, subgroups of 3 to 5 animals were killed at 2, 4, 8, or 11 days after the beginning of the experiment. Coadministration of the CDAA diet and ethionine markedly enhanced the level of expression of c-myc and c-Ha-ras, 8-OHGua formation and TBARS generation as compared with the CDAA or CSAA diet within 11 days, and methionine blocks these actions. These results indicate that addition of methionine prevents the induction of c-myc and c-Ha-ras expression, 8-OHGua formation and TBARS generation, as well as hepatocellular lesions, by coadministration of the CDAA diet and ethionine in rats, and suggest a possible involvement of oxidative stress and gene expression in hepatocarcinogenesis by these agents.  相似文献   
170.
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