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   1333篇
  免费   62篇
  国内免费   3篇
电工技术   73篇
化学工业   416篇
金属工艺   34篇
机械仪表   27篇
建筑科学   19篇
矿业工程   2篇
能源动力   53篇
轻工业   151篇
水利工程   3篇
石油天然气   5篇
无线电   80篇
一般工业技术   284篇
冶金工业   65篇
原子能技术   36篇
自动化技术   150篇
  2023年   10篇
  2022年   22篇
  2021年   53篇
  2020年   15篇
  2019年   29篇
  2018年   29篇
  2017年   20篇
  2016年   40篇
  2015年   36篇
  2014年   43篇
  2013年   90篇
  2012年   75篇
  2011年   98篇
  2010年   70篇
  2009年   74篇
  2008年   85篇
  2007年   61篇
  2006年   66篇
  2005年   49篇
  2004年   39篇
  2003年   49篇
  2002年   45篇
  2001年   28篇
  2000年   25篇
  1999年   26篇
  1998年   32篇
  1997年   26篇
  1996年   21篇
  1995年   22篇
  1994年   13篇
  1993年   14篇
  1992年   15篇
  1991年   14篇
  1990年   5篇
  1989年   3篇
  1988年   7篇
  1987年   8篇
  1986年   3篇
  1985年   6篇
  1984年   11篇
  1983年   4篇
  1982年   5篇
  1981年   1篇
  1980年   3篇
  1979年   4篇
  1974年   1篇
  1972年   1篇
  1966年   1篇
  1964年   1篇
排序方式: 共有1398条查询结果,搜索用时 15 毫秒
81.
82.
The annual growth rings and bark pockets of a 250-year-old Japanese oak (Quercus crispula), collected from the Nikko National Park, Japan in 2000 AD, were analysed by ICP mass spectrometry. The annual rings, sampled in 5-year increments, recorded Pb concentrations from 0.01 to 0.1 mg kg(-1) and there was no significant change in concentration with time. In contrast, bark pocket samples dating from 1875 to the present showed a progressive increase in Pb concentration with time, from approximately 0.1 to 10 mg kg(-1). Shoots of epiphytic moss growing on the tree trunk contained 17 mg kg(-1) Pb. The bark pockets recorded historical increases in airborne Pb pollution accompanying the industrialisation of Japan, which was initiated by the opening of Japan's borders from 1854. This increase was not reflected by the annual rings. The 206Pb/207Pb isotope ratio of the bark pockets decreased from approximately 1.18 to 1.16 from 1964 to the present, indicating changes in the sources of Pb pollution. The 206Pb/207Pb isotope ratio of the moss shoots was similar to the current bark (1.16). The data showed bark pockets to be more effective than annual rings for recording historical change in airborne lead pollution.  相似文献   
83.
This paper presents calibration of the Vehicle Routing and scheduling Problems with Time Windows-Probabilistic (VRPTW-P) model which takes into account the uncertainty of travel times. Probe vehicle data of travel times were obtained from usual operation of pickup-delivery trucks in South Osaka area. The optimal solution of the VRPTW-P model resulted in reducing total cost, running times and CO2, NOx and Particle Materials (PM) emissions compared with the usual operation. This is attributed to better routing of VRPTW-P to choose more reliable roads. Therefore, VRPTW-P can contribute to establish efficient and environmentally friendly delivery systems in urban area.  相似文献   
84.
The rare earth manganite BaLn2Mn2O7 (Ln=rare earth element) has a Sr3Ti2O7-type layered perovskite structure with double-block oxygen octahedra belonging to the Ruddlesden-Popper-type homologous series AO(ABO3)2. In Pr-manganite, a novel phase transition was first observed in situ at 1040 K by a thermal transmission electron microscope. At 1040 K, reflections began to split along the c-direction in the selected area diffraction pattern. This indicates that a new phase appears in the original phase matrix; the c length of the new phase is 1.5% longer than that of the original phase. After about 5 min, the original phase disappears. No change in the crystal symmetry (space group I4/mmm) is observed above 1040 K.  相似文献   
85.
The application of superconductivity technology to electric power apparatus is very important from the viewpoint of energy saving. Especially, the superconducting generators using superconductors as the field windings have many merits compared with conventional generators. Super-GM has been researching and developing 70-MW-class model machines since FY 1988 for a scheduled period of eight years, aiming at a 200-MW-class superconducting generator. This paper describes the basic specifications and designs of 70-MW-class superconducting generators by Super-GM and also describes the propriety of these basic specifications and designs.  相似文献   
86.
Facile structure determination of acylpolyamines, glutamatergic nerve blocker obtained from the venom of the Joro spider (Nephila clavata) was carried out with the use of micro-column LC/MS and high energy collision induced dissociation (CID) mass spectrometry. 6-hydroxyindole-3-acetyl was proposed previously as a putative partial structure, for the acyl moiety of hydroxyindole-type polyamines (NPTX-1 to -6). The NMR data obtained for NPTX-6, NPTX-687 and hydroxyindole-3-acetic acid which was released by acid hydrolysis of Nephila clavata crude venom extracts proved that the lipophilic head is the 4-hydroxyindole-3-acetic acid. Various hydroxyindole-3-acetyl polyamines were found in N. Clavata venom and characterized by mass spectrometry. As a result, type-E, a new class of generalized acylpolyamine structure was proposed in addition to the previously reported polyamine backbones type-A to -D.  相似文献   
87.
88.
We have previously identified and cloned a human gene, D40, that is preferentially expressed in testis among normal organs, while it is widely expressed in various human tumor cell lines and primary tumors derived from different organs. In this report, we have examined the expression and localization of this protein in human testis with an antibody specific to D40 protein. In Western analyses, the anti-D40 antibody recognized a major band with a molecular mass of 300 kDa and a minor band of 250 kDa. These bands were not observed in the testis lysates from patients with Sertoli-cell-only syndrome and with Kleinfelter syndrome, who lack germ cells of the testis, indicating that D40 protein is expressed in the germ cells of normal testis. Immunohistochemical studies have revealed that D40 protein is highly expressed in spermatocytes and in the pre-acrosome of round spermatids. In the acrosome, D40 protein expression is observed not inside but outside the acrosome membrane. This is consistent with the finding that the amino-acid sequence at the amino terminal of the D40 protein lacks a hydrophobic signal peptide that is required for proteins to translocate to the membrane. Expression of D40 protein is observed in the acrosome of ejaculated spermatozoa as well, although the level is low compared with that in the pre-acrosome of spermatids. These results suggest that D40 protein plays important roles in spermatogenesis, especially in the formation and maintenance of the acrosome.  相似文献   
89.
A simple method for analysis of fumonisin B1 (FB1) and fumonisin B2 (FB2) in beer and raw materials of beer using liquid chromatography-electrospray ionization tandem mass spectrometry (LC/MS/MS) was developed. Samples were prepared and purified by using solid-phase extraction columns (SAX). The LC separation was performed with an octadecylated silica column at a flow-rate of 0.2 mL/min, using a mobile phase consisting of water and acetonitrile. MS/MS was used in multiple reaction monitoring, employing electrospray ionization (ESI-MRM). Recoveries of spiked FB1 and FB2 from beer were 64% and 52%, respectively, at the level of 5 microg/kg. Recoveries of spiked FB1 and FB2 from malt, cornstarch, and corn grit, at the level of 50 microg/kg, were 87.9% and 86.4%, 89.5% and 87.9%, 86.6% and 81.1%, respectively. This method may have applications in quality assurance.  相似文献   
90.
A simple method for analysis of trichothecenes [Type A: diacetoxyscirpenol, neosolaniol, HT-2 toxin, and T-2 toxin, Type B: deoxynivalenol, nivalenol, fusarenon-X, 3-acetyldeoxynivalenol, 15-acetyldeoxynivarenol] in barley tea and beer using liquid chromatography tandem mass spectrometry (LC/MS/MS) was developed. Trichothecenes were extracted with ethyl acetate-methanol (19:1). The solvent was evaporated to dryness and the residue was dissolved in water-methanol (3:1) for injection into the LC/MS/MS. The LC separation was performed with an octadecylated silica column at a flow-rate of 0.2 mL/min, using a mobile phase consisting of water, methanol and acetonitrile. MS/MS was used in multiple reaction monitoring, employing electrospray ionization (ESI-MRM). The recoveries of trichothecenes from drinks at 1 microg/L (Type A) and 10 microg/L (Type B) were 52.5-115.2% (barley tea) and 68.1-127.5% (beer). Five barley tea and ten beer samples were analyzed by this method. Trichothecenes were not detected in them. This method may have applications in quality assurance.  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