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   3250篇
  免费   30篇
  国内免费   2篇
电工技术   93篇
化学工业   359篇
金属工艺   1569篇
机械仪表   31篇
建筑科学   20篇
矿业工程   1篇
能源动力   52篇
轻工业   76篇
水利工程   2篇
石油天然气   1篇
无线电   258篇
一般工业技术   267篇
冶金工业   423篇
原子能技术   43篇
自动化技术   87篇
  2023年   6篇
  2022年   14篇
  2021年   15篇
  2020年   14篇
  2019年   9篇
  2018年   16篇
  2017年   13篇
  2016年   28篇
  2015年   11篇
  2014年   32篇
  2013年   110篇
  2012年   86篇
  2011年   89篇
  2010年   54篇
  2009年   95篇
  2008年   108篇
  2007年   101篇
  2006年   91篇
  2005年   80篇
  2004年   70篇
  2003年   105篇
  2002年   123篇
  2001年   130篇
  2000年   101篇
  1999年   121篇
  1998年   242篇
  1997年   209篇
  1996年   157篇
  1995年   100篇
  1994年   105篇
  1993年   161篇
  1992年   152篇
  1991年   137篇
  1990年   51篇
  1989年   38篇
  1988年   38篇
  1987年   30篇
  1986年   38篇
  1985年   35篇
  1984年   41篇
  1983年   23篇
  1982年   14篇
  1981年   17篇
  1980年   14篇
  1979年   14篇
  1978年   9篇
  1976年   15篇
  1975年   3篇
  1974年   4篇
  1973年   5篇
排序方式: 共有3282条查询结果,搜索用时 328 毫秒
11.
This correspondence proposes an explicit construction of codes achieving capacity for arbitrary discrete memoryless channels. The proposed code is obtained by concatenating variable inner codes and an algebraic geometry code. Further, we clarify that the proposed code achieves the error exponent obtained by Forney for concatenated codes  相似文献   
12.
The incidence of Campylobacter jejuni and Campylobacter coli in broiler farms was 33.9% (19/56). C. jejuni-positive flocks accounted for 20.0% (17/85) and C. coli-positive ones was 4.7% (4/85). There were 14 patterns (fla type) of restriction fragment length polymorphism (RFLP) of flagellin A gene among these 22 strains of C. jejuni and C. coli including the standard strain C. jejuni ATCC 33560. Different fla types of Campylobacter were isolated from broilers in different growing cycles on the same farms. Four strains of C. jejuni were isolated from four breeder farms and four fla types of C. jejuni were detected from their progenies reared on growing farms. Three fla types of C. jejuni detected from the progenies were different from those of each breeder. Also, the other three fla types of C. jejuni were detected from different progenies of each growing farm during the next growing cycle. These findings indicate that the RFLP analysis may contribute to epidemiological studies of C. jejuni and C. coli contamination of broilers and suggest the risk of contamination with different types of Campylobacter in every growing cycle of broilers on the farm even on the same farm. They also supported that there was little likeliness of the vertical transmission of C. jejuni and C. coli from breeders to broilers.  相似文献   
13.
14.
15.
Malignant human gliomas are the most common forms of primary tumors in the central nerve system. Due to their location and invasive nature, treatment so far has been mainly palliative. Thus, understanding the molecular detail of tumor transformation and progression is crucial for developing effective therapeutic strategy for this fetal tumor. Among the genetic alternations found in these tumors, p53 inactivation and PDGF/PDGFR activation represent the early events, and the loss of chromosome 10 and gene amplification and rearrangement of EGFR represent the late events. Studies with both glioma cell lines and primary tumor tissues have strongly suggested that TGF-alpha and EGFR function as an important autocrine loop in supporting proliferation of human glioma, especially in high grade glioma, since elevated TGF-alpha expression is also found in these high grade tumors. Furthermore, down regulation of the expression of TGF-alpha by antisense constructs has been shown to inhibit several types of human tumor cell growth including glioma. Other means of therapeutic approaches using this autocrine loop as a target also include the use of monoclonal antibodies and their cytotoxic conjugated. Considerable understanding of the EGFR-mediated signal transduction pathways has become available recently, which including GRB2/mSOS1 mediated MAP kinase activation; JAK/STATs pathway; PLC-gamma pathway. However, much work still needs to be done before a specific component of these pathways can be applied for effective control of tumor growth in the clinic.  相似文献   
16.
17.
18.
19.
In order to produce highly concentrated bioethanol by pervaporation using an ethanol‐permselective silicalite membrane, techniques to suppress adsorption of succinic acid, which is a chief by‐product of ethanol fermentation and causes the deterioration in pervaporation performance, onto the silicalite crystals was investigated. The amount adsorbed increased as the pH of the aqueous succinic acid solution decreased. The pervaporation performance also decreased with decreasing pH when the ternary mixtures of ethanol/water/succinic acid were separated. Using silicalite membranes individually coated with two types of silicone rubber, pervaporation performance was significantly improved in the pH range of 5 to 7, when compared with that of non‐coated silicalite membranes in ternary mixtures of ethanol/water/succinic acid. Moreover, when using a silicalite membrane double‐coated with the two types of silicone rubber, pervaporation performance was stabilized at lower pH values. In the separation of bioethanol by pervaporation using the double‐coated silicalite membrane, removal of accumulated substances having an ultraviolet absorption maximum at approximately 260 nm from the fermentation broth proved to be vital for efficient pervaporation. Copyright © 2005 Society of Chemical Industry  相似文献   
20.
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