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   324470篇
  免费   5302篇
  国内免费   716篇
电工技术   6272篇
综合类   568篇
化学工业   49549篇
金属工艺   10561篇
机械仪表   9119篇
建筑科学   8342篇
矿业工程   901篇
能源动力   8821篇
轻工业   34115篇
水利工程   2711篇
石油天然气   3730篇
武器工业   10篇
无线电   40381篇
一般工业技术   60910篇
冶金工业   60186篇
原子能技术   5531篇
自动化技术   28781篇
  2021年   2634篇
  2020年   2006篇
  2019年   2529篇
  2018年   4286篇
  2017年   4095篇
  2016年   4214篇
  2015年   3056篇
  2014年   5093篇
  2013年   15520篇
  2012年   8365篇
  2011年   10920篇
  2010年   8607篇
  2009年   9768篇
  2008年   10265篇
  2007年   10201篇
  2006年   8909篇
  2005年   8189篇
  2004年   8088篇
  2003年   7781篇
  2002年   7578篇
  2001年   7707篇
  2000年   7358篇
  1999年   7746篇
  1998年   18779篇
  1997年   13579篇
  1996年   10571篇
  1995年   8128篇
  1994年   7412篇
  1993年   7136篇
  1992年   5361篇
  1991年   5135篇
  1990年   5000篇
  1989年   4852篇
  1988年   4740篇
  1987年   3942篇
  1986年   4062篇
  1985年   4785篇
  1984年   4314篇
  1983年   4051篇
  1982年   3650篇
  1981年   3812篇
  1980年   3498篇
  1979年   3438篇
  1978年   3246篇
  1977年   3900篇
  1976年   5009篇
  1975年   2791篇
  1974年   2675篇
  1973年   2685篇
  1972年   2221篇
排序方式: 共有10000条查询结果,搜索用时 671 毫秒
31.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations.  相似文献   
32.
Polymer Bulletin - In this study, we synthesized a new ion-imprinted polymer (IIP) based on introduction of amidoxime groups in acrylonitrile, complexation with Cd2+ ions and polymerization with...  相似文献   
33.
A hybrid sorbent material for removal of hydrogen sulfide from air was developed. The material is based on activated carbon and iron compounds obtained from waste iron(II) sulfate(VI) heptahydrate. The iron salt is deposited on the carbonaceous support and subjected to oxidation (Fe2+ to Fe3+) using atmospheric oxygen under alkaline conditions. An effect of H2O2 addition to the process on the composition of the resultant material was also examined. X-ray diffraction (XRD) analyses confirmed easy conversion of waste FeSO4·7H2O to iron oxides Fe3O4 and FeOOH. The activated carbon supporting iron oxides revealed a higher efficiency in H2S elimination from air compared to the commercial activated carbon, without any modification.  相似文献   
34.
Urbano  Cristóbal  Ardanuy  Jordi 《Scientometrics》2020,124(1):575-602
Scientometrics - The interdisciplinary nature of library and information science (LIS) research has been highlighted for some time now. The term “interdisciplinary” is used primarily in...  相似文献   
35.
36.
37.
RCAS1 is a protein that participates in regulation of the tumor microenvironment and its immune responses, all in order to evade the immune system. The aim of this study was to analyze RCAS1 expression in urothelial bladder cancer cells (and in fibroblasts and macrophages of the tumor stroma) and its relationship with the histological pattern of malignancy. Eighty-three postcystectomy patients were enrolled. We analyzed the histological maturity (grade), progress (pT stage), tissue invasion type (TIT), nonclassic differentiation number (NDN), and the ability to metastasize (pN). The expression of RCAS1 protein was analyzed by immunohistochemistry. Indicators of histological malignancy were observed solely in association with the RCAS1 expression in cells in the border parts (BPs) of the tumor. Histological malignancy of the tumor, indicated by the pT and pN, and metastasis-free survival time, correlated significantly with RCAS1 expression in tumor neoplastic cells, whereas malignancy determined by grade, TIT, and NDN correlated with RCAS1 expression in fibroblasts and macrophages in the tumor microenvironment. These findings suggest that the increased RCAS1 expression depends on its cellular source and that RCAS1 expression itself is a component of various signaling pathways. The immune escape occurs within the tumor BPs, where the increase in the RCAS1 expression occurs within tumor cells and stromal cells in its microenvironment. We conclude that the histological pattern of tumor malignancy, indicated by grade, TIT, NDN, pT, and pN is a morphological indicator of immune escape.  相似文献   
38.
39.
Metallurgical and Materials Transactions A - The influence of the chemical composition on the crystallization process, amorphous phase formation, and the anticorrosion properties of Al-Zr-Ni-Fe-Y...  相似文献   
40.
ABSTRACT

This paper deals with asymptotic stabilisation of a class of nonlinear input-delayed systems via dynamic output feedback in the presence of disturbances. The proposed strategy has the structure of an observer-based control law, in which the observer estimates and predicts both the plant state and the external disturbance. A nominal delay value is assumed to be known and stability conditions in terms of linear matrix inequalities are derived for fast-varying delay uncertainties. Asymptotic stability is achieved if the disturbance or the time delay is constant. The controller design problem is also addressed and a numerical example with an unstable system is provided to illustrate the usefulness of the proposed strategy.  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