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   509篇
  免费   17篇
  国内免费   6篇
电工技术   22篇
化学工业   157篇
金属工艺   12篇
机械仪表   7篇
建筑科学   12篇
能源动力   33篇
轻工业   25篇
水利工程   1篇
无线电   31篇
一般工业技术   91篇
冶金工业   72篇
原子能技术   14篇
自动化技术   55篇
  2024年   1篇
  2023年   6篇
  2022年   25篇
  2021年   35篇
  2020年   14篇
  2019年   12篇
  2018年   21篇
  2017年   14篇
  2016年   19篇
  2015年   14篇
  2014年   22篇
  2013年   33篇
  2012年   25篇
  2011年   41篇
  2010年   20篇
  2009年   21篇
  2008年   26篇
  2007年   18篇
  2006年   22篇
  2005年   18篇
  2004年   15篇
  2003年   12篇
  2002年   6篇
  2001年   9篇
  2000年   3篇
  1999年   11篇
  1998年   17篇
  1997年   11篇
  1996年   6篇
  1995年   7篇
  1994年   4篇
  1993年   7篇
  1992年   3篇
  1991年   2篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1987年   1篇
  1985年   2篇
  1981年   1篇
  1980年   1篇
  1976年   2篇
  1968年   1篇
  1966年   1篇
排序方式: 共有532条查询结果,搜索用时 15 毫秒
51.
Pulmonary fibrosis is a progressive and fatal disorder characterized by dysregulated repair after recurrent injury. Destruction of the lung architecture with excess extracellular matrix deposition induces respiratory failure with hypoxia and progressive dyspnea. The impact of hypoxia on pulmonary endothelial cells during pulmonary fibrogenesis is unclear. Using a magnetic-activated cell sorting system, pulmonary endothelial cells were isolated from a mouse model of pulmonary fibrosis induced by intratracheally administered bleomycin. When endothelial cells were exposed to hypoxic conditions, a hypoxia-inducible factor (HIF)-2α protein was detected in CD31- and α-smooth muscle actin (SMA)-positive cells. Levels of plasminogen activator inhibitor 1, von Willebrand factor, and matrix metalloproteinase 12 were increased in endothelial cells isolated from bleomycin-treated mice exposed to hypoxic conditions. When endothelial cells were cultured under hypoxic conditions, levels of fibrotic mediators, transforming growth factor-β and connective tissue growth factor, were elevated only in endothelial cells from bleomycin-treated and not from saline-treated lungs. The increased expression of α-SMA and mesenchymal markers and collagen production in bleomycin- or hypoxia-stimulated endothelial cells were further elevated in endothelial cells from bleomycin-treated mouse lungs cultured under hypoxic conditions. Exposure to hypoxia damaged endothelial cells and enhanced fibrogenesis-related damage in bleomycin-treated pulmonary endothelial cells.  相似文献   
52.
Cancer stem cells (CSCs) contribute to the drug resistance, recurrence, and metastasis of breast cancers. Recently, we demonstrated that HER2 overexpression increases mammosphere formation via the activation of aryl hydrocarbon receptor (AHR). In this study, the objective was to identify the mechanism underlying mammosphere maintenance mediated by HER2 signaling-activated AHR. We compared the chromatin structure of AHR-knockout (AHRKO) HER2-overexpressing MCF-7 (HER2-5) cells with that of wild-type HER2-5 cells; subsequently, we identified TP63, a stemness factor, as a potential target gene of AHR. ΔNp63 mRNA and protein levels were higher in HER2-5 cells than in HER2-5/AHRKO cells. Activation of HER2/HER3 signaling by heregulin treatment increased ΔNp63 mRNA levels, and its induction was decreased by AHR knockdown in HER2-5 cells. The results of the chromatin immunoprecipitation assay revealed an interaction between AHR and the intronic region of TP63, which encodes ΔNp63. A luciferase reporter gene assay with the intronic region of TP63 showed that AHR expression increased reporter activity. Collectively, our findings suggest that HER2-activated AHR upregulates ΔNp63 expression and that this signaling cascade is involved in CSC maintenance in HER2-expressing breast cancers.  相似文献   
53.
A 16 Mb embedded DRAM macro in a fully CMOS logic compatible 90 nm process with a low noise core architecture and a high-accuracy post-fabrication tuning scheme has been developed. Based on the proposed techniques, 61% improvement of the sensing accuracy is realized. Even with the smallest 5 fF/cell capacitance, a 322 MHz random-cycle access while 32 ms data retention time which contributes to save the data retention power down to 60 /spl mu/W are achieved.  相似文献   
54.
Auer-rod-like bodies were found in plasma cells from a 74-year-old man with plasma cell dyscrasia. These bodies exhibited red purple staining by May-Giemsa staining and were indistinguishable from Auer bodies often found in acute myeloid leukemia. These bodies, however, failed to stain with peroxidase and showed acid phosphatase positivity. Bone marrow examinations were performed three times at the sternum or iliac crest. The proportions of plasma cells were 4.4%, 3.4% and 3.8%. The Auer-rod-like bodies were found in 0.05% (2/3824), 0.07% (4/6883) and 0.08% (2/2656) of the plasma cells.  相似文献   
55.
56.
Hardware implementation aspects of sophisticated speech codecs are addressed. The major points discussed are approaches to implementation of the sophisticated speech codecs, requirements for DSP (digital signal-processing) implementation of the codecs, such as the type of arithmetic processing and the necessity of bit-level specifications, and codec implementation and DSP programming techniques for three specific coding algorithms: 32-kb/s ADPCM (adaptive digital pulse code modulation), 64-kb/s (7 kHz) SB (subband)-ADPCM, and 16-kb/s APC-AB (adaptive predictive coding with adaptive but allocation) codecs  相似文献   
57.
The development of a microprocessor-controlled 96/48 DSI terminal is described. The terminal is intended for domestic use, and is designed so as to maximize compatibility with existing digital carrier systems, it merges four T1 signals into two T1 compatible bit streams for transmission. The terminal is given sufficient excess capacity to accommodate voiceband data, while retaining toll-grade transmission quality for speech. Implementation approaches and considerations in both calculated and measured system characteristics are described.  相似文献   
58.
This paper describes the use of computational fluid dynamics for the calculation of the flow resistance through computer-generated models resembling silica monoliths. This study was undertaken to determine the effect of skeleton heterogeneity on the flow resistance and, more precisely, to test the hypothesis that increased skeleton heterogeneity decreases the flow resistance. To evaluate the proposed model, 24 real silica monoliths have been prepared using the same method, covering a wide range of skeleton sizes (2.2 microm < d(s) < 8 microm) and porosities (0.47 < epsilon < 0.66). The permeability of these monoliths was determined by pressure drop measurements, and structural information was obtained by image analysis of laser scanning confocal microscopy-generated 3D images of the skeleton structure. The results indicate that the presence of preferential flow paths due to an increased heterogeneity of the flow through pore space reduces the flow resistance of monolithic media. It is also shown that the pore size is hence a much better suited scaling dimension than the skeleton size to reduce the permeability of monolithic columns.  相似文献   
59.
Adherent natural soils on fiber surfaces have been studied with the scanning electron microscope. The soils on the fiber surface resemble oily soil.  相似文献   
60.
An immunohistological investigation using anti-thyroid peroxidase (PO) and JT-95 (JT) antibodies was conducted on surgical specimens of papillary carcinoma (n = 12), follicular carcinoma (n = 8), follicular adenoma with prominent papillary structure (n = 12), follicular adenoma (n = 8) and adenomatous goiter (n = 8). In benign lesions, follicle-forming and papillae-forming epithelia showed positive staining with anti-PO antibody. In 26 of 28 benign lesions, PO-positive areas covered 50% or more of the cut surface area of the lesions. However in carcinomas, PO-positive areas were non-existent (13/20) or only focal (7/20) and the papillae did not stain. The incidence of JT-positive cases was higher in papillary carcinomas (12/12) than in other lesions (13/36). JT-positive areas were much wider than PO-positive areas in papillary carcinomas, whereas in benign lesions, PO-positive areas were wider than or at least roughly equal to, JT-positive areas. Follicular carcinomas did not stain or stained only focally with these antibodies. In conclusion, these two antibodies seem useful in differentiating benign from malignant follicular cell tumors.  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