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   655篇
  免费   9篇
  国内免费   6篇
电工技术   28篇
综合类   1篇
化学工业   152篇
金属工艺   28篇
机械仪表   15篇
建筑科学   8篇
能源动力   28篇
轻工业   54篇
石油天然气   1篇
无线电   32篇
一般工业技术   181篇
冶金工业   79篇
原子能技术   19篇
自动化技术   44篇
  2022年   4篇
  2021年   7篇
  2020年   4篇
  2019年   3篇
  2018年   7篇
  2017年   5篇
  2016年   9篇
  2015年   7篇
  2014年   15篇
  2013年   30篇
  2012年   27篇
  2011年   46篇
  2010年   36篇
  2009年   31篇
  2008年   36篇
  2007年   29篇
  2006年   27篇
  2005年   21篇
  2004年   14篇
  2003年   19篇
  2002年   17篇
  2001年   8篇
  2000年   10篇
  1999年   17篇
  1998年   26篇
  1997年   28篇
  1996年   20篇
  1995年   7篇
  1994年   16篇
  1993年   13篇
  1992年   8篇
  1991年   8篇
  1990年   12篇
  1989年   7篇
  1988年   11篇
  1987年   7篇
  1986年   8篇
  1985年   10篇
  1982年   13篇
  1981年   3篇
  1980年   6篇
  1979年   3篇
  1978年   3篇
  1977年   6篇
  1976年   6篇
  1975年   4篇
  1974年   2篇
  1973年   5篇
  1967年   2篇
  1966年   2篇
排序方式: 共有670条查询结果,搜索用时 19 毫秒
21.
We have characterized the electronic structure of FeSe1−xTex for various x values using soft x-ray photoemission spectroscopy (SXPES), high-resolution photoemission spectroscopy (HRPES) and inverse photoemission spectroscopy (IPES). The SXPES valence band spectral shape shows that the 2 eV feature in FeSe, which was ascribed to the lower Hubbard band in previous theoretical studies, becomes less prominent with increasing x. HRPES exhibits systematic x dependence of the structure near the Fermi level (EF): its splitting near EF and filling of the pseudogap in FeSe. IPES shows two features, near EF and approximately 6 eV above EF; the former may be related to the Fe 3d states hybridized with chalcogenide p states, while the latter may consist of plane-wave-like and Se d components. In the incident electron energy dependence of IPES, the density of states near EF for FeSe and FeTe has the Fano lineshape characteristic of resonant behavior. These compounds exhibit different resonance profiles, which may reflect the differences in their electronic structures. By combining the PES and IPES data the on-site Coulomb energy was estimated at 3.5 eV for FeSe.  相似文献   
22.
Global warming and the problem of successfully incorporating environmental safeguards are promoting the need for a more power‐efficient motor. Therefore, as a driving source, permanent magnet synchronous motors (PMSMs) with concentrated winding are widely used in a variety of fields. However, a PMSM with a concentrated winding generates more vibration than one with a distributed winding because of the radial electromagnetic force. This paper describes the effect of a new skewed rotor on the characteristics of a concentrated winding PMSM. We investigated this effect by three‐dimensional finite element method (3D FEM) analysis and measurement. We also demonstrate that the proposed rotor is effective in reducing the radial electromagnetic force without decreasing motor efficiency. © 2014 Wiley Periodicals, Inc. Electr Eng Jpn, 187(2): 33–43, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22400  相似文献   
23.
24.
We demonstrate that domain structure of single-layer graphene grown by ambient pressure chemical vapor deposition is strongly dependent on the crystallinity of the Cu catalyst. Low energy electron microscopy analysis reveals that graphene grown using a Cu foil gives small and mis-oriented graphene domains with a number of domain boundaries. On the other hand, no apparent domain boundaries are observed in graphene grown over a heteroepitaxial Cu(111) film deposited on sapphire due to unified orientation of graphene hexagons. The difference in the domain structures is correlated with the difference in the crystal plane and grain structure of the Cu metal. The graphene film grown on the heteroepitaxial Cu film exhibits much higher carrier mobility than that grown on the Cu foil.  相似文献   
25.
Thermoplastic polyurethane fiber webs were prepared using a laser‐heated electrospinning process combined with air blowing. The effect of spinning conditions such as air flow rate and air temperature on fiber diameter and molecular weight was investigated. Although the average fiber diameter decreased with increased air flow rate at each air temperature, the diameter increased when the air flow rate was >15 NL min?1. In addition, the fiber was comparatively thicker with an increase in the air temperature. The variation in the fiber diameter tends to increase with the air flow rate, and a reduction in the molecular weight of the fiber by thermal degradation was suppressed. The thinnest and most uniform fiber with a diameter of 0.9 µm and a diameter coefficient variation of 15% was obtained at an air temperature of 25°C under an air flow rate of 15 NL min?1. This fiber also had a minimum of decreased molecular weight. POLYM. ENG. SCI., 54:2605–2609, 2014. © 2013 Society of Plastics Engineers  相似文献   
26.
Members of the bacterial genus Bdellovibrio include strains that are free-living whereas others are known to invade and parasitize larger Gram-negative bacteria. The bacterium can synthesize several sphingophospholipid compounds including those with phosphoryl bonds as well as phosphonyl bonds. In the present study, the dominant sphingophosphonolipid component was isolated by column chromatography, and the long-chain bases, fatty acids, and polar head groups were identified by thin-layer and gas-liquid chromatographic procedures. The definitive structural identity of the sphingolipid was established by nuclear magnetic resonance and mass spectrometry of hydrolysis products and the intact compound. The compound was identified as N-2′-hydroxypentadecanoyl-2-amino-3,4-dihydroxyheptadecan-1-phosphono-(1-hydroxy-2-aminoethane).  相似文献   
27.
Olivine lithium manganese phosphate (LiMnPO4) becomes research focus because of its high energy density and improved thermal stability. However, its application in lithium ion batteries suffers severely from poor electrochemical activity due to low conductivity and structural instability upon the charge and discharge process. By applying a high-energy ball-milling method we succeed in improving the capacity delivery and rate capability. LiMnPO4 materials ball-milled without or with acetylene black are able to deliver a high capacity of 135 and 127 mAh g−1, respectively, more than 50% greater than the pristine one. Particularly, the latter also shows an improved discharge plateau and stable cyclability. High-energy synchrotron radiation X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, laser particle analysis, and galvanostatic charge and discharge are employed to understand the effect of ball-milling on the LiMnPO4 material.  相似文献   
28.
Aberrant expression of microRNAs (miRNAs) is involved in the development and progression of various types of cancers. In this study, we investigated the role of miR-331-3p in cell proliferation and the expression of keratinocyte differentiation markers of uterine cervical cancer cells. Moreover, we evaluated whether neuropilin 2 (NRP2) are putative target molecules that regulate the human papillomavirus (HPV) related oncoproteins E6 and E7. Cell proliferation in the human cervical cancer cell lines SKG-II, HCS-2, and HeLa was assessed using the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) assay. Cellular apoptosis was measured using the TdT-mediated dUTP nick end labeling (TUNEL) and Annexin V assays. Quantitative RT-PCR was used to measure the messenger RNA (mRNA) expression of the NRP2, E6, E7, p63, and involucrin (IVL) genes. A functional assay for cell growth was performed using cell cycle analyses. Overexpression of miR-331-3p inhibited cell proliferation, and induced G2/M phase arrest and apoptosis in SKG-II, HCS-2 and HeLa cells. The luciferase reporter assay of the NRP2 3′-untranslated region revealed the direct regulation of NRP2 by miR-331-3p. Gene expression analyses using quantitative RT-PCR in SKG-II, HCS-2, and HeLa cells overexpressing miR-331-3p or suppressing NRP2 revealed down-regulation of E6, E7, and p63 mRNA and up-regulation of IVL mRNA. Moreover, miR-331-3p overexpression was suppressed NRP2 expression in protein level. We showed that miR-331-3p and NRP2 were key effectors of cell proliferation by regulating the cell cycle, apoptosis. NRP-2 also regulates the expression of E6/E7 and keratinocyte differentiation markers. Our findings suggest that miR-331-3p has an important role in regulating cervical cancer cell proliferation, and that miR-331-3p may contribute to keratinocyte differentiation through NRP2 suppression. miR-331-3p and NRP2 may contribute to anti-cancer effects.  相似文献   
29.
The 36K protein attached at the 5′ end of the linear DNA plasmid pGKL2 from the yeast Kluyveromyces lactis was first purified and characterized. The terminal protein was purified from cells (1 kg wet weight) by ammonium sulphate precipitation and two rounds of centrifugation to equilibrium in CsCl gradients. The pGKL2 was present only in the post-microsomal supernatant. Approximately 10 mg of the purified pGKL2 was recovered and digested with DNase I. The terminal protein (final ca. 0·8 mg) was homogeneous by electrophoresis and we determined the N-terminal amino acid sequence up to ten residues, showing that it existed in the cryptic N-terminal domain of pGKL2-ORF2 (DNA polymerase) sequence.  相似文献   
30.
We investigated the relationship between dietary highly hydrogenated soybean oil (HSO) and cholesterol transport in rats. In the first study, to examine the effects of cholesterol transport of different concentrations of HSO in dietary oil, rats were given one of the three diets containing 0, 25, or 50% HSO in dietary oil with cholesterol (5 g/kg diet) or a diet without HSO and cholesterol for 22 d. Feeding the high concentration of HSO prevented the increase in plasma total cholesterol, hepatic total lipids, and cholesterol and the decrease in high-density lipoprotein-cholesterol, which were caused by dietary cholesterol. Moreover, HSO increased the fecal excretion, fecal lipids, and steroids in a dose-dependent manner. In the second study, to examine the effects on cholesterol transport of redistribution of stearic acid in the triacylglycerol species contained in HSO, rats were given one of the six diets containing HSO (distearoylmonoacylglycerol and tristearoylglycerol)-rich, monostearoylglycerol-rich, or palmitic acid-rich oil with/without cholesterol (5 g/kg diet), for 30 d. Whereas the accumulation of cholesterol in the body was reduced, cholesterol excretion was enhanced effectively in rats given the HSO-rich diet compared with rats given the monostearoylglycerol-rich diet. These results suggested that not only the high concentration of stearic acid but also its uneven distribution in HSO-triacylglycerol contributed to the reduction in intestinal cholesterol absorption in rats.  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