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   26593篇
  免费   2319篇
  国内免费   1037篇
电工技术   1552篇
技术理论   1篇
综合类   1546篇
化学工业   4560篇
金属工艺   1543篇
机械仪表   1543篇
建筑科学   2132篇
矿业工程   779篇
能源动力   782篇
轻工业   1907篇
水利工程   485篇
石油天然气   1294篇
武器工业   208篇
无线电   2953篇
一般工业技术   3429篇
冶金工业   1209篇
原子能技术   360篇
自动化技术   3666篇
  2024年   141篇
  2023年   536篇
  2022年   904篇
  2021年   1246篇
  2020年   980篇
  2019年   770篇
  2018年   815篇
  2017年   1008篇
  2016年   865篇
  2015年   1102篇
  2014年   1305篇
  2013年   1603篇
  2012年   1642篇
  2011年   1803篇
  2010年   1505篇
  2009年   1427篇
  2008年   1361篇
  2007年   1258篇
  2006年   1235篇
  2005年   1206篇
  2004年   759篇
  2003年   662篇
  2002年   587篇
  2001年   497篇
  2000年   529篇
  1999年   630篇
  1998年   592篇
  1997年   468篇
  1996年   510篇
  1995年   417篇
  1994年   351篇
  1993年   267篇
  1992年   207篇
  1991年   173篇
  1990年   124篇
  1989年   103篇
  1988年   99篇
  1987年   66篇
  1986年   46篇
  1985年   35篇
  1984年   32篇
  1983年   15篇
  1982年   12篇
  1981年   12篇
  1980年   10篇
  1979年   9篇
  1978年   4篇
  1976年   5篇
  1972年   3篇
  1959年   3篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
11.
对二阶A型Cooper变换进行增强,放宽可用性条件,并证明了其正确性,最后举例说明其应用。  相似文献   
12.
米塔尔钢铁集团的全球并购发展战略   总被引:2,自引:0,他引:2  
概述了米塔尔的并购经过和并购特点,着重探讨了米塔尔的管理模式、人员情况、钢铁厂布局、生产经营、主要战略伙伴、研发机构及其生产、采购与销售策略。系统地分析了米塔尔在中国的发展,指出米塔尔在全球钢铁业整合中处于领先地位,米塔尔来中国投资看中的是中国的原料和市场,且运作步伐明显加快,会对中国钢铁企业构成很大的威胁。  相似文献   
13.
Satellite scatterometer winds over the northwestern Pacific were analyzed with the vector empirical orthogonal function (VEOF) method. The Hilbert-Huang transform (HHT), a newly developed non-linear and non-stationary time series data processing method, was also employed in the analysis. A combination of European Remote Sensing Satellite (ERS) −1/2 scatterometer, NASA Scatterometer (NSCAT) and NASA's Quick Scatterometer (QuikSCAT) winds covering the period from January 1992 to April 2000 and the area of 0-50°N, 100-148°E constitutes the baseline for this study. The results indicate that annual cycles dominate the two leading VEOF modes. The first VEOF shows the East Asian monsoon features and the second represents a spring-autumn oscillation. We removed the annual signal from the data set and calculated the interannual VEOFs. The first interannual VEOF represents the interannual variability existing in the spring-autumn oscillation. The temporal mode is correlated with the Southern Oscillation Index (SOI), but has a half-year lag with respect to the SOI. The spatial mode of the first interannual VEOF reflects the response of the tropical and extratropical winds to ENSO events. The second interannual VEOF is another ENSO related mode, and the temporal VEOF mode is correlated with the SOI with a correlation coefficient of 0.78, revealing the wind variability over mid-latitudes, which is associated with ENSO events. Further analysis indicated that the wind variability over the coast of East Asia represents anomalies of a Hadley cell. The quasi-biennial oscillation (QBO) was found in the temporal mode, indicating and verifying that the QBO in the wind fields is related to ENSO events. The third VEOF shows the interannaul variability in the winter-summer mode and displays the interannual variability of the East Asian monsoon. The three leading interannual VEOFs are statistically meaningful as confirmed by a significance test.  相似文献   
14.
Strategies to increase CdTe solar-cell voltage   总被引:1,自引:0,他引:1  
James Sites  Jun Pan 《Thin solid films》2007,515(15):6099-6102
There is a significant difference in performance between today's highest efficiency of CdTe solar cells and single-crystal cells of comparable band gap. The largest contribution to this difference is the voltage, where the values for the best CdTe cells are about 230 mV below the best GaAs cells when an appropriate adjustment is made for band gap. CdTe voltage and fill-factor are currently compromised by low recombination lifetime (near 1 ns), low hole density (near 1014 cm− 3), and in some cases an excessive back-contact barrier. Numerical simulation is used to evaluate how combinations of lifetime, carrier density, back electron reflection, and interfacial properties affect voltage and cell performance. Two different strategies for improving voltage and performance are explored.  相似文献   
15.
Atomic structures of crystallographic shear planes (CSPs) in nanocrystalline thin films of semiconductor SnO2 were investigated by high-resolution electron microscopy. The films were prepared by electron beam evaporation in high vacuum (10–6 torr) and followed by annealing in synthetic air at 700 °C for 1–2 H. CSPs with the displacement vector of [1/2 0 1/2] were observed in the planes parallel to (¯101), (110) and (¯3¯21). Most of the CPSs were found to terminate or interact with each other within SnO2 crystallites. Partial dislocations exist at terminal places of CSPs or along intersecting lines of CSPs. CSP steps were also observed. Structural models of these defects have been proposed. Based on analysis of experimental data, it has been suggested that the Sn/O ratio at CSPs which are not parallel to their displacement vector, at cores of partial dislocations and at CSP steps, is higher than that of the perfect structure, that is, these defects are able to provide extra free electrons with the films.  相似文献   
16.
17.
We studied 722 reexcision scars of benign and malignant lesions (except melanocytic lesions) excised over a 24-month period. The formalin-fixed, paraffin-embedded tissue sections were examined histologically and immunohistochemically. The histological features of melanocytic hyperplasia were present in 59 cases (8%), 56 from the sun-exposed skin of the face and neck and three from the trunk [p < 0.00001]. The most common sites were the nose and lower eyelids, but the forehead was also frequently involved. Of the 59 patients, 41 were women (p < 0.0001). Basal cell carcinoma was the most frequent original lesion in both sexes (80%). No melanocytic hyperplasia was found in 663 cases (298 on the trunk and extremities and 365 on the head and neck). We have seen this reaction pattern following reexcision of melanocytic lesions as well. Thus, interpreting reexcision margins when lentigo maligna or similar lesions are reexcised may be fraught with difficulty. It is important for pathologists and dermatopathologists to recognize this phenomenon because histologically the presence of increased numbers of large melanocytes could be misinterpreted as melanoma in situ.  相似文献   
18.
振动对火箭炮密集度影响研究   总被引:2,自引:0,他引:2  
潘宏侠  赵剡 《兵工学报》1993,14(4):17-22
  相似文献   
19.
Xie Huimin  Pan Shaochuan 《Strain》1993,29(4):139-140
The use of thin film grids coated on surfaces is described in relation to the determination of deformations in doubly curved shells. The technique is called the coating film moiré interference method and employs a laser holographic approach.  相似文献   
20.
本文提出一种从军用地图中提取铁路、道路的半自动方法和自动恢复显示其在地图中标识方式的算法,从而进一步实现地图图形显示系统的多层次结构。  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