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   1035篇
  免费   41篇
  国内免费   2篇
电工技术   109篇
化学工业   280篇
金属工艺   20篇
机械仪表   29篇
建筑科学   12篇
能源动力   47篇
轻工业   77篇
水利工程   1篇
无线电   78篇
一般工业技术   173篇
冶金工业   152篇
原子能技术   32篇
自动化技术   68篇
  2023年   9篇
  2022年   14篇
  2021年   18篇
  2020年   11篇
  2019年   24篇
  2018年   9篇
  2017年   15篇
  2016年   34篇
  2015年   17篇
  2014年   28篇
  2013年   44篇
  2012年   44篇
  2011年   50篇
  2010年   46篇
  2009年   43篇
  2008年   58篇
  2007年   43篇
  2006年   45篇
  2005年   27篇
  2004年   31篇
  2003年   22篇
  2002年   32篇
  2001年   15篇
  2000年   15篇
  1999年   17篇
  1998年   81篇
  1997年   45篇
  1996年   34篇
  1995年   23篇
  1994年   25篇
  1993年   22篇
  1992年   15篇
  1991年   11篇
  1990年   9篇
  1989年   10篇
  1988年   11篇
  1987年   9篇
  1986年   7篇
  1985年   7篇
  1984年   4篇
  1983年   3篇
  1982年   3篇
  1981年   5篇
  1980年   8篇
  1979年   3篇
  1978年   7篇
  1977年   7篇
  1976年   3篇
  1974年   5篇
  1971年   3篇
排序方式: 共有1078条查询结果,搜索用时 15 毫秒
231.
A room temperature CW operation of Ga0.3In0.7As/GaInAsP/InP GRINSCH compressive strained MQW lasers with 30~60 nm wide wire active region was achieved. This device was fabricated by two-step LP-OMVPE growths on p-type InP substrate and wet chemical etching. Threshold current as low as 53 mA ( L=910 μm, Jth=2.9 kA/cm2) was obtained at RT-CW condition. The spontaneous emission peak and the lasing wavelength of strained MQW wire lasers exhibited approximately 20-meV blue shift from those of MQW film lasers cut out from the same wafer  相似文献   
232.
We propose a new cone-beam shift-variant filtered backprojection (FBP) method for non-planar orbit data acquisitions. The new method is exact, fast and stable to discretization errors. It is based on the hybrid FBP framework whose key feature is to combine the shift-variant filtering with the ramp filtering to produce the filtered projections. We show that an adequate combination of the two filterings allows us to minimize contributions of the time-consuming and numerically unstable shift-variant filtering. We demonstrate the performances of the new method by simulation studies. We also apply the new method to real x-ray data acquired from our experimental system of monochromatic computed tomography.  相似文献   
233.
Highly crystalline monoclinic scheelite BiVO4 powders are synthesized from aqueous Bi(NO3)3 and NH4VO3 solutions over a wide range of pH by a hydrothermal process. BiVO4 powders with various morphologies, surface textures, and grain shapes are selectively synthesized by adjusting the pH. The dependence of the Raman peak position and intensity on the synthesis conditions indicates that the symmetry distortions in the local structure of the synthesized BiVO4 are affected by the preparation conditions. These variations in the local structure result in the modification of the electronic structure of BiVO4, which results in a blue‐shift in the UV‐vis absorption spectrum of hydrothermally synthesized BiVO4 in comparison with a well‐crystallized sample prepared by homogeneous coprecipitation. The photocatalytic activities for O2 evolution from an aqueous AgNO3 solution under visible‐light irradiation are strongly dependent on the pH used in the synthesis. The differences in the photocatalytic activities between BiVO4 samples prepared under various conditions is attributed to the degree of structural distortion, leading to differences in the mobility of photogenerated holes formed in the valence band, which consists of Bi 6s and O 2p orbitals.  相似文献   
234.
235.
This paper investigates 3D image reconstruction from truncated cone-beam (CB) projections acquired with a helical vertex path. First, we show that a rigorous derivation of Grangeat's formula for truncated projections leads to a small additional term compared with previously published similar formulations. This correction term is called the boundary term. Next, this result is used to develop a CB filtered-backprojection (FBP) algorithm for truncated helical projections. This new algorithm only requires the CB projections to be measured within the region that is bounded, in the detector, by the projections of the upper and lower turns of the helix. Finally, simulations with mathematical phantoms demonstrate that: (i) the boundary term is necessary to obtain high-quality imaging of low-contrast structures and (ii) good image quality is obtained even with large values of the pitch of the helix.  相似文献   
236.
To reinforce cytotoxic activity and the targeting ability of lymphokine-activated killer cells with a T-cell phenotype (T-LAK) for adoptive immunotherapy against human bile duct carcinoma (BDC), staphylococcal enterotoxin A (SEA) was conjugated chemically with MUSE11 monoclonal antibody (MUSE11 mAb), directed to the MUC1 antigen, using N-succinimidyl 3-(2-pyridyldithio) propionate and 2-iminothiolane HCl. Both SEA-conjugated MUSE11 mAb (SEA-MUSE11) and the F(ab')2 of MUSE11 mAb (SEA-F(ab')2) showed significant enhancement of T-LAK cell tumor neutralization for MUC1 positive-target tumor cells, even with a concentration of 0.01 microg/ml at an E:T ratio of 5:1 in vitro. In this in vitro test, MUC1-positive BDC cells were observed to attach to surrounding T-LAK cells in the presence of SEA-MUSE11 or SEA-F(ab')2. Remarkable tumor growth inhibition was observed in BDC-grafted severe combined immunodeficient mice to which 2 x 10(7) T-LAK cells preincubated with 2 microg of SEA-MUSE11 or SEA-F(ab')2, together with recombinant interleukin 2 (500 IU), were administered i.v. for 4 consecutive days, when tumor size was 5 mm in diameter. These results point to a promising adoptive immunotherapy for patients with BDC.  相似文献   
237.
238.
A 52-year-old woman was admitted to our hospital because of repeated episodes of pneumonia in the middle lobe. She had also experienced coughing during meals. The history and chest CT findings suggested the presence of a bronchoesophageal fistula. An upper GI series revealed a fistula between an esophageal diverticulum and the superior segment bronchus of the right lower lobe. Fiberoptic bronchoscopy done immediately after the upper GI series revealed barium sulfate leaking from the superior segment bronchus of the right lower lobe into the middle lobe bronchus. These findings indicated that the repeated pneumonia in the middle lobe was caused by a congenital bronchoesophageal fistula. Examination of the resected fistula showed that it was a Braimbridge type I bronchoesophageal fistula. Although of at least 49 cases of congenital bronchoesophageal fistulas with esophageal diverticula have been reported in the Japanese medical literature, we know of no previous case in which such a fistula was associated with middle-lobe pneumonia.  相似文献   
239.
We recorded frontal, central and parietal somatosensory evoked potentials (SEPs) to median nerve stimulation in 20 patients with Huntington's disease (HD) and in a group of normal controls. Two stimulus repetition rates, 1 Hz and 5 Hz, were employed. In HD patients the early cortical potentials (latency range 20-30 ms) at all 3 recording locations were replaced by a widespread, broadly configured N20-25 deflection, while later potentials at 40-80 ms did not significantly differ from those of normals. In contrast to the early P22, P27 and N30 potentials in normals, the N20-25 potential in the patients was not significantly modified by changing the stimulus repetition rate. At 40-80 ms the stimulus rate effects were similar in the patients and normals. The results show that early pre- and postcentral SEPs are both pathological in HD, while later frontal and parietal components can be totally preserved. The early N20-25 in HD is possibly a subcortical potential, seen due to unmasking in the absence of early cortical deflections.  相似文献   
240.
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