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   1790篇
  免费   60篇
  国内免费   4篇
电工技术   31篇
综合类   2篇
化学工业   260篇
金属工艺   25篇
机械仪表   62篇
建筑科学   93篇
矿业工程   6篇
能源动力   77篇
轻工业   117篇
水利工程   25篇
石油天然气   12篇
无线电   144篇
一般工业技术   312篇
冶金工业   394篇
原子能技术   4篇
自动化技术   290篇
  2023年   9篇
  2021年   21篇
  2020年   16篇
  2019年   32篇
  2018年   29篇
  2017年   30篇
  2016年   40篇
  2015年   27篇
  2014年   43篇
  2013年   135篇
  2012年   75篇
  2011年   100篇
  2010年   100篇
  2009年   80篇
  2008年   86篇
  2007年   91篇
  2006年   93篇
  2005年   86篇
  2004年   52篇
  2003年   51篇
  2002年   41篇
  2001年   26篇
  2000年   22篇
  1999年   30篇
  1998年   41篇
  1997年   40篇
  1996年   27篇
  1995年   24篇
  1994年   20篇
  1993年   25篇
  1992年   24篇
  1991年   9篇
  1990年   21篇
  1989年   20篇
  1988年   20篇
  1987年   15篇
  1986年   16篇
  1985年   23篇
  1984年   25篇
  1983年   21篇
  1982年   9篇
  1981年   15篇
  1980年   10篇
  1979年   12篇
  1978年   8篇
  1977年   11篇
  1976年   11篇
  1975年   16篇
  1970年   8篇
  1969年   8篇
排序方式: 共有1854条查询结果,搜索用时 15 毫秒
11.
Examined the impact of increasing the percentage of hires (above the T. A. Cleary [1968] fair-hiring level) from minority groups with demonstrated lower average job performance. Increased minority hiring resulted in only a small performance loss, even when minority hiring exceeded the minority applicant representation. However, when minorities were hired at a rate equal to or greater than their applicant representation, the expected performance loss among the hired minorities was much greater than performance loss across all hires. More important, the discrepancy in performance between majority and minority hires increased as minority hiring increased. With minority hiring above the level of minority applicant representation, this discrepancy exceeded the population difference in performance between the 2 groups. These findings suggest additional considerations when raising minority hiring above minority applicant representation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
12.
The basic structural units of the genome are nucleotides. A single nucleotide polymorphism (SNP) is a mutation at a single nucleotide position. This paper discusses several major problems in SNP data analysis and review some existing solutions in this work. Generally speaking, a rich set of SNP analysis problems are cast in the signal processing framework. Our objective is to offer a state-of-the art review on this topic from a signal processing viewpoint so that researchers in the signal processing field can grasp the important domain knowledge to overcome the barrier between the two fields  相似文献   
13.
The supply and return piping of passive solar domestic hot water systems (SDHWS) is typically exposed to ambient weather conditions, and damaging pipe freeze is a major concern. This paper presents a pipe-freeze model that accounts for hot water draws and uses 30 years of actual weather data. The simulation results are cast in terms of pipe-freeze probabilities. Using contour maps of the continental United States, the pipe-freeze probabilities for residential, commercial, and seasonal passive SDHWS are presented for various pipe and insulation geometries.  相似文献   
14.
Summary The polymerization of 1-hexyne, 3,3-dimethyl-1-butyne, 2-hexyne and 1-chloro-1-hexyne by using metal halide based initiators was studied. By analogy with ionic ring opening polymerization systems, living acetylene polymerizations resulted when backbiting and interchain reactions were suppressed, i.e., ktr, kt=0. Large acetylenic substituents suppress the formation of cis-cisoidal propagating chains and subsequently eliminate backbiting reactions and also propagating carbene interchain reactions. Possible explanations for differences in polymer dispersities which result under different reaction conditions were also provided.  相似文献   
15.
The Revised Memory and Behavior Problems Checklist (RMBPC), a 24-item, caregiver-report measure of observable behavioral problems in dementia patients, provides 1 total score and 3 subscale scores for S problems (memory-related, depression, and disruptive behaviors) and parallel scores for caregiver reaction. Data were obtained from 201 geriatric Ss and their caregivers. Factor analysis confirmed 3 1st-order factors, consistent with subscales just named, and 1 general factor of behavioral disturbance. Overall scale reliability was good, with alphas of .84 for S behavior and .90 for caregiver reaction. Subscale alphas ranged from .67 to .89. Validity was confirmed through comparison of RMBPC scores with well-established indexes of depression, cognitive impairment, and caregiver burden. The RMBPC is recommended as a reliable and valid tool for the clinical and empirical assessment of behavior problems in dementia Ss. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
16.
The mechanofusion process, a dry particle coating route, has been successfully applied to coat iron particles with alumina. The high-temperature oxidation resistance of Fe and coated Fe particles has been comparatively investigated in air in the temperature range 350°–900°C. The activation energy calculations demonstrate that, in the temperature range 350°–420°C, the oxidation mechanisms are the same for both particles. Scanning electron microscopy and energy-dispersive spectroscopy analyses show that oxidation products are mainly formed at the iron/alumina interface at low temperatures or at the alumina/gas interface at high temperatures. It is shown that, depending on the temperature range, two different oxidation mechanisms are predominant.  相似文献   
17.
18.
用电化学方法在不锈钢基体上沉积多晶Cu2O薄膜并用X射线衍射和扫描电进行了分析研究了溶液温度对薄膜相组成、晶粒尺寸和择优取向的影响,当溶液的PH=9,温度低于50℃时得到的是Cu2O/Cu复相薄膜,纯Cu2O薄膜可在溶液温度高于50℃时获得,纯Cu2O薄膜具有(100)择优取向,实验发现薄膜的晶粒尺寸随溶液温度的增加从0.12μm增加到0.65μm。  相似文献   
19.
BACKGROUND: The authors described unusual pathologic features in a left frontal lobe malignant glioma in a 31/2-year-old boy. The pathology was similar in the initial excision and two subsequent recurrences at 9 and 11 months and at autopsy, when extensive subarachnoid spread was noted. METHODS: The tumor was studied by conventional histology, immunohistochemistry, flow cytometry, transmission electron microscopy (TEM), immune electron microscopy (IEM), and cytogenetic and Southern blot analysis. RESULTS: The tumor revealed two different histologic patterns. One component showed large cells with eosinophilic cytoplasm, vesicular nuclei with prominent nucleoli, eosinophilic perinuclear inclusions, and immunoreactivity for glial fibrillary acidic protein (GFAP) and vimentin. The other component consisted of undifferentiated cells with hyperchromatic nuclei and scanty cytoplasm. By TEM, the perinuclear aggregates were composed of tubuloreticular inclusions, which were also observed in endothelial cells within the tumor vasculature. By IEM, the intermediate filaments in the tumor cell cytoplasm were decorated with GFAP. Flow cytometric results revealed a marked increase in the S-phase (48%), whereas cytogenetic analysis of short-term cultures showed an abnormal karyotype containing marker chromosomes and double minutes. In the second resection, additional karyotypic abnormalities were noted, including 1p- and several additional markers. The first and second resections showed MYCN amplification by Southern Blot analysis in the 60- to 80-fold range. CONCLUSIONS: This tumor presents unique histologic, ultrastructural, and cytogenetic findings as well as MYCN amplification that is notable for a pediatric malignant glioma. Tubuloreticular inclusions were a prominent feature in this tumor, which again is unique for a glioma.  相似文献   
20.
Knowledge and Information Systems - Developing effective and efficient data stream classifiers is challenging for the machine learning community because of the dynamic nature of data streams. As a...  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