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   47272篇
  免费   1147篇
  国内免费   187篇
电工技术   579篇
综合类   634篇
化学工业   5464篇
金属工艺   751篇
机械仪表   1130篇
建筑科学   916篇
矿业工程   391篇
能源动力   605篇
轻工业   2466篇
水利工程   623篇
石油天然气   51篇
武器工业   4篇
无线电   2653篇
一般工业技术   4293篇
冶金工业   21721篇
原子能技术   246篇
自动化技术   6079篇
  2024年   63篇
  2023年   251篇
  2022年   212篇
  2021年   278篇
  2020年   107篇
  2019年   179篇
  2018年   600篇
  2017年   815篇
  2016年   1209篇
  2015年   919篇
  2014年   634篇
  2013年   690篇
  2012年   2410篇
  2011年   2782篇
  2010年   920篇
  2009年   1026篇
  2008年   833篇
  2007年   809篇
  2006年   746篇
  2005年   3492篇
  2004年   2685篇
  2003年   2148篇
  2002年   956篇
  2001年   812篇
  2000年   368篇
  1999年   702篇
  1998年   6274篇
  1997年   3894篇
  1996年   2571篇
  1995年   1509篇
  1994年   1117篇
  1993年   1119篇
  1992年   273篇
  1991年   325篇
  1990年   323篇
  1989年   291篇
  1988年   305篇
  1987年   235篇
  1986年   216篇
  1985年   174篇
  1984年   71篇
  1983年   85篇
  1982年   131篇
  1981年   178篇
  1980年   192篇
  1979年   60篇
  1978年   98篇
  1977年   615篇
  1976年   1325篇
  1975年   101篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Hemiballism is a rare hyperkinetic disorder which is characterized by irregular vigorous rotatory movements of the limbs of one side of the body. The disabling and exhausting movements with their high risk of severe injuries require an acute drug treatment. However, there are no common guidelines for the treatment of this disorder. Therefore we reviewed the available literature to establish a concept for a rational symptomatic drug treatment. Furthermore, own observations in 6 patients with hemiballism of different origins are reported.  相似文献   
92.
The bit error rate (BER) analysis of a direct-sequence code-division multiple-access (DS-CDMA) cellular system over a Rayleigh-fading channel often results in complicated expressions even though the Gaussian approximation is applied. A combined probability density function (pdf) approach for the forward link and a mean-method technique for the reverse link are proposed to significantly reduce the computational complexity. The simplified BER expressions are derived and yield accurate results  相似文献   
93.
94.
It was found, that To?pa Peat Preparation (TPP) administered to healthy volunteers in doses of 100-300 mg/day during 14 days evoked the stimulation of the phagocytic and bactericidal activity of the granulocytes. The dose of 600 mg/day causes only a transient and insignificant increase of phagocytic and bactericidal properties of the granulocytes.  相似文献   
95.
A total of 259 Gram-negative Porphyromonas-like rods isolated from subgingival plaque samples of 16 family-owned dogs with naturally occurring periodontitis were characterized phenotypically by biochemical reactions, metabolic end products and enzymatic activities (API-ZYMTM, RoscoTM). Four distinct groups were found. Group A isolates (63) were asaccharolytic, lipase negative, trypsin positive and produced phenylacetic acid (PAA) from peptone-yeast extract glucose broth. Unlike P. gingivalis strains they were catalase positive. Group B isolates (42) differed from those of group A by a positive lipase reaction and from those of group D by failing to ferment sugars. Group C isolates (88) were asaccharolytic and did not produce PAA. They were alpha-fucosidase, N-acetyl-beta-glucosaminidase (beta-NAG) and trypsin negative, resembling P. endodontalis, but unlike human isolates, they were catalase positive. Subgroup C.1 isolates (6) differed from those of parent group C by producing minor amounts of PAA, and subgroup C.2 isolates (12) were beta-NAG positive. Group D isolates (46) were weakly fermentative, lipase, catalase and trypsin positive, and produced PAA. They resembled the B (P.) salivosus type strain which, in our hands, fermented weakly glucose, lactose and mannose. Two isolates could not be assigned to any of the previous groups.  相似文献   
96.
The plasma membrane (PM) H(+)-ATPase has been proposed to play important transport and regulatory roles in plant physiology, including its participation in auxin-induced acidification in coleoptile segments. This enzyme is encoded by a family of genes differing in tissue distribution, regulation, and expression level. A major expressed isoform of the maize PM H(+)-ATPase (MHA2) has been characterized. RNA gel blot analysis indicated that MHA2 is expressed in all maize organs, with highest levels being in the roots. In situ hybridization of sections from maize seedlings indicated enriched expression of MHA2 in stomatal guard cells, phloem cells, and root epidermal cells. MHA2 mRNA was induced threefold when nonvascular parts of the coleoptile segments were treated with auxin. This induction correlates with auxin-triggered proton extrusion by the same part of the segments. The PM H(+)-ATPase in the vascular bundies does not contribute significantly to auxin-induced acidification, is not regulated by auxin, and masks the auxin effect in extracts of whole coleoptile segments. We conclude that auxin-induced acidification in coleoptile segments most often occurs in the nonvascular tissue and is mediated, at least in part, by increased levels of MHA2.  相似文献   
97.
98.
The interaction of human peripheral blood leukocytes with alpha 1-acid glycoprotein (AGP), its glycoforms as well as neoglyco-conjugates representing carbohydrate chains of AGP or its fragments was studied by flow cytometry. It was shown that the main target cells for AGP as well as for conjugates of its carbohydrate chains with polyacrylamide (PAA) are monocytes and polymorphonuclear leukocytes but not lymphocytes. The interaction of AGP with monocytes and granulocytes are mediated by its carbohydrate chains: the binding of AGP with cells was inhibited by AGP, AGP oligosaccharides as well as conjugates of oligosaccharides and its fragments with PAA. The data obtained show the existence of monocyte (and granulocyte) receptors which interact with complex type sialooligosaccharides of AGP.  相似文献   
99.
100.
Here we present a case of a patient with a massive ossification of annulus fibrosus and longitudinal ligament at the level C3-C4, C4-C5 and C5-C6, also called the Van Swaay bridge. One can observe a propulsion of the pharingeal tissue at the level of the massive Van Swaay bridge between C5 and C6 which caused pressure and dysphagia.  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