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   42396篇
  免费   2495篇
  国内免费   46篇
电工技术   340篇
综合类   25篇
化学工业   8989篇
金属工艺   808篇
机械仪表   841篇
建筑科学   1277篇
矿业工程   84篇
能源动力   955篇
轻工业   6874篇
水利工程   394篇
石油天然气   149篇
武器工业   5篇
无线电   1700篇
一般工业技术   6961篇
冶金工业   9324篇
原子能技术   187篇
自动化技术   6024篇
  2024年   87篇
  2023年   355篇
  2022年   693篇
  2021年   1154篇
  2020年   835篇
  2019年   984篇
  2018年   1663篇
  2017年   1601篇
  2016年   1684篇
  2015年   1257篇
  2014年   1554篇
  2013年   3067篇
  2012年   2453篇
  2011年   2431篇
  2010年   1905篇
  2009年   1756篇
  2008年   1682篇
  2007年   1573篇
  2006年   1115篇
  2005年   969篇
  2004年   863篇
  2003年   764篇
  2002年   742篇
  2001年   561篇
  2000年   534篇
  1999年   576篇
  1998年   2902篇
  1997年   1936篇
  1996年   1258篇
  1995年   751篇
  1994年   584篇
  1993年   664篇
  1992年   242篇
  1991年   254篇
  1990年   196篇
  1989年   192篇
  1988年   194篇
  1987年   168篇
  1986年   150篇
  1985年   174篇
  1984年   144篇
  1983年   119篇
  1982年   159篇
  1981年   179篇
  1980年   188篇
  1979年   88篇
  1978年   96篇
  1977年   313篇
  1976年   685篇
  1973年   79篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
There are evidence indicating that endoscopic retrograde cholangiopancreatography with sphincterotomy (ERCP+S) reduces the rate of complications in patients with severe acute biliary pancreatitis (ABP). The aim of this study was to analyze our experience in the treatment of severe ABP with ERCP+S and compare the evolution of the patients treated early (3 days or less following admission) with those treated late (after the 3rd day). A retrospective review of the clinical histories of the 16 patients with severe ABP treated with ERCP+S over the last two years is presented, analyzing their clinical features on admission and evolution. Biliary stones or biliary sludge was observed in 11 cases (69%). Nine patients had undergone early, and 7 late, ERCP+S. The patients of the latter group presented a greater number of complications during evolution than the former group (43% vs 0%; p = 0.025). The mortality of the patients of the late ERCP+S was also greater although without statistical significance (28.6% vs 0%; p = 0.15). No complication secondary to ERCP+S was detected. These findings confirm the fact that ERCP+S performed early in severe ABP significantly reduces the number of complications and is associated with a lower mortality.  相似文献   
103.
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   
104.
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   
105.
Immunofluorescence microscopic observations indicated that a monoclonal antibody, Vmp 18, raised against the peptide 199-208 of murine interleukin 1 alpha, cross-reacted with an antigenic determinant of Drosophila thorax muscles. Immunoelectron microscopic analysis showed that the gold particles were mainly localized in the Z-line which is the attachment site of thin filaments from adjacent sarcomeres. On the contrary, the antibody failed to mark the Z-line in vertebrate skeletal muscle. A Western blot of total protein extract from Drosophila thorax muscles bound a protein of 43 kDa. Our observations suggest that the Vmp 18 antibody could contribute to clarify the composition of the Z-line in insect's flight muscles.  相似文献   
106.
107.
A cross-sectional study was performed to obtain risk factors for hepatitis B disease, HBsAg carriers and immunised personnel, among 2470 workers in a general hospital in Madrid, Spain. The data obtained were analyzed with multiple logistic regression to obtain beta coefficients for variables. The results of the analysis show that being a nurse or being regularly exposed to blood are the most important risk factors for hepatitis B acquisition. The length of time working at the same job activity was also a risk factor. The resulting beta coefficients allow the construction for a hepatitis non-immunised, HBsAg carrier and immunised HBV status, which can select subjects for a hepatitis B vaccination program.  相似文献   
108.
Generation of Technology-Independent Retargetable Analog Blocks   总被引:1,自引:0,他引:1  
This paper introduces a complete methodology for retargeting of analog cells to different sets of specifications. This methodology is technology-independent, thus allowing the migration, from one technology to another, of the circuit under retargeting. Careful integration of the device sizing and layout generation tasks via the incorporation of layout constraints during the sizing process allows to generate fully functional designs in a few minutes. The methodology is illustrated via the retargeting of a fully-differential Miller-compensated two-stage operational amplifier for a new set of specifications and two different technological processes.An erratum to this article can be found at  相似文献   
109.
This paper introduces a methodology for symbolic pole/zero extraction based on the formulation of the time-constant matrix of the circuits. This methodology incorporates approximation techniques specifically devoted to achieve an optimum trade-off between accuracy and complexity of the symbolic root expressions. The capability to efficiently handle even large circuits will be demonstrated through several practical circuits.  相似文献   
110.
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