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   39116篇
  免费   2747篇
  国内免费   62篇
电工技术   253篇
综合类   128篇
化学工业   9626篇
金属工艺   697篇
机械仪表   786篇
建筑科学   1253篇
矿业工程   90篇
能源动力   1015篇
轻工业   7899篇
水利工程   397篇
石油天然气   243篇
武器工业   2篇
无线电   1664篇
一般工业技术   5893篇
冶金工业   6641篇
原子能技术   182篇
自动化技术   5156篇
  2024年   67篇
  2023年   364篇
  2022年   866篇
  2021年   1567篇
  2020年   1008篇
  2019年   1089篇
  2018年   1557篇
  2017年   1553篇
  2016年   1618篇
  2015年   1224篇
  2014年   1622篇
  2013年   3112篇
  2012年   2573篇
  2011年   2587篇
  2010年   2040篇
  2009年   1872篇
  2008年   1774篇
  2007年   1567篇
  2006年   1174篇
  2005年   954篇
  2004年   877篇
  2003年   864篇
  2002年   685篇
  2001年   524篇
  2000年   450篇
  1999年   493篇
  1998年   2176篇
  1997年   1405篇
  1996年   917篇
  1995年   517篇
  1994年   424篇
  1993年   406篇
  1992年   160篇
  1991年   113篇
  1990年   101篇
  1989年   111篇
  1988年   135篇
  1987年   126篇
  1986年   95篇
  1985年   106篇
  1984年   89篇
  1983年   61篇
  1982年   65篇
  1981年   82篇
  1980年   80篇
  1979年   49篇
  1978年   47篇
  1977年   120篇
  1976年   227篇
  1973年   50篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
91.
Gamma delta T-Cells represent a minor subpopulation of T-lymphocytes in man and their role in normal and diseased human skin is unknown. This article is a comprehensive review of T-lymphocytes bearing the gamma delta T-cell receptor in normal and pathological human skin. Firstly, we have documented the occurrence of gamma delta T-cells in normal skin and in a range of reactive and malignant skin conditions. We have then discussed the experimental findings regarding the repertoire used by gamma delta T-cells in normal human skin and in cutaneous disorders with an increased percentage of gamma delta T-cells.  相似文献   
92.
93.
94.
Comparative genomic hybridization (CGH) was used to detect copy number changes of DNA sequences in the Ewing family of tumours (ET). We analysed 20 samples from 17 patients. Fifteen tumours (75%) showed copy number changes. Gains of DNA sequences were much more frequent than losses, the majority of the gains affecting whole chromosomes or whole chromosome arms. Recurrent findings included copy number increases for chromosomes 8 (seven out of 20 samples; 35%), 1q (five samples; 25%) and 12 (five samples; 25%). The minimal common regions of these gains were the whole chromosomes 8 and 12, and 1q21-22. High-level amplifications affected 8q13-24, 1q and 1q21-22, each once. Southern blot analysis of the specimen with high-level amplification at 1q21-22 showed an amplification of FLG and SPRR3, both mapped to this region. All cases with a gain of chromosome 12 simultaneously showed a gain of chromosome 8. Comparison of CGH findings with cytogenetic analysis of the same tumours and previous cytogenetic reports of ET showed, in general, concordant results. In conclusion, our findings confirm that secondary changes, which may have prognostic significance in ET, are trisomy 8, trisomy 12 and a gain of DNA sequences in 1q.  相似文献   
95.
Motor vehicle accidents are the main cause of death and disability between 1 and 4 years of age. Since 1980 the Academy of Pediatrics has been promoting the correct use of car seats. The major reason that car seats are not fulfilling their full potential is their incorrect or lack of use. In order to evaluate parental knowledge about car seat use for children and their actual use in the population visiting HURRA, a survey was performed which demonstrated that only 57.6% of the parents interviewed had infant car seats and that only 83.3% of owners actually use it. As many as 94.4% had correct knowledge about car seat use, but the majority of correct information was not provided by the medical staff. The majority of parents use seat belts for their own protection but a significantly smaller percentage use car seats for their own children.  相似文献   
96.
97.
The complete nucleotide sequence (4,826 bp) of the cryptic plasmid pGA1 from Corynebacterium glutamicum was determined. DNA sequence analysis revealed four putative coding regions (open reading frame A [ORFA], ORFA2, ORFB, and ORFC). ORFC was identified as a rep gene coding for an initiator of plasmid replication (Rep) according to the high level of homology of its deduced amino acid sequence with the Rep proteins of plasmids pSR1 (from C. glutamicum) and pNG2 (from Corynebacterium diphtheriae). This function was confirmed by deletion mapping of the minimal replicon of pGA1 (1.7 kb) which contains only ORFC. Deletion derivatives of pGA1 devoid of ORFA exhibited significant decreases in the copy number in C. glutamicum cells and displayed segregational instability. Introduction of ORFA in trans into the cells harboring these deletion plasmids dramatically increased their copy number and segregational stability. The ORFA gene product thus positively influences plasmid copy number. This is the first report on such activity associated with a nonintegrating bacterial plasmid. The related plasmids pGA1, pSR1, and pNG2 lacking significant homology with any other plasmid seem to be representatives of a new group of plasmids replicating in the rolling-circle mode.  相似文献   
98.
99.
The neuronal cytoskeleton is one of the most profoundly altered organelles in late life neuro-degenerative disorders that are characterized by progressive impairments in cognitive abilities. The elucidation of the protein building blocks of these organelles as well as advances in understanding how these proteins become altered in Alzheimer's disease (AD) and other less common dementing illnesses, i.e., diffuse Lewy body disease (DLBD) or the Lewy body variant of AD (LBVAD), will provide insights into the molecular basis of these disorders. Within, we review evidence that normal adult human tau is abnormally phosphorylated and converted into the subunits of AD paired helical filaments (PHFs), and that Lewy bodies (LBs) represent accumulation of altered neurofilament (NF) triplet subunits. Although the precise biological consequences of PHF and LB formation in neurons is unknown, growing evidence suggests that the formation of PHFs and LBs from normal neuronal cytoskeletal proteins could have deleterious effects on neuronal function and survival. Finally, insights into the composition of PHFs and LBs could lead to the development of novel strategies for the timely and accurate diagnosis of AD, DLBD and the LBVAD.  相似文献   
100.
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