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   58374篇
  免费   3399篇
  国内免费   54篇
电工技术   392篇
综合类   54篇
化学工业   11183篇
金属工艺   1073篇
机械仪表   1073篇
建筑科学   1813篇
矿业工程   137篇
能源动力   1210篇
轻工业   8269篇
水利工程   573篇
石油天然气   254篇
武器工业   6篇
无线电   3181篇
一般工业技术   10007篇
冶金工业   14318篇
原子能技术   281篇
自动化技术   8003篇
  2023年   490篇
  2022年   589篇
  2021年   1375篇
  2020年   1118篇
  2019年   1106篇
  2018年   2151篇
  2017年   2088篇
  2016年   2210篇
  2015年   1628篇
  2014年   2082篇
  2013年   4091篇
  2012年   3388篇
  2011年   3171篇
  2010年   2583篇
  2009年   2357篇
  2008年   2603篇
  2007年   2341篇
  2006年   1718篇
  2005年   1405篇
  2004年   1374篇
  2003年   1221篇
  2002年   1067篇
  2001年   704篇
  2000年   693篇
  1999年   888篇
  1998年   4541篇
  1997年   2795篇
  1996年   1813篇
  1995年   1038篇
  1994年   882篇
  1993年   902篇
  1992年   315篇
  1991年   315篇
  1990年   309篇
  1989年   306篇
  1988年   283篇
  1987年   236篇
  1986年   251篇
  1985年   301篇
  1984年   236篇
  1983年   181篇
  1982年   210篇
  1981年   240篇
  1980年   209篇
  1979年   160篇
  1978年   147篇
  1977年   292篇
  1976年   591篇
  1975年   104篇
  1973年   96篇
排序方式: 共有10000条查询结果,搜索用时 937 毫秒
21.
Photonic Network Communications - Optical packet switching is a prominent technology proposing not only a reduction in the energy consumption by the elimination of numerous...  相似文献   
22.
23.
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   
24.
The Journal of Supercomputing - Infrastructure-as-a-service container-based virtualization is gaining interest as a platform for running distributed applications. With increasing scale of cloud...  相似文献   
25.
Upper Barremian – Lower Aptian inner platform “Urgonian” limestones in the Mont de Vaucluse region, SE France, consist of alternating metre-scale microporous and tight intervals. This paper focuses on the influence of structural deformation on the reservoir properties of the Urgonian limestone succession in a study area near the town of Rustrel. Petrographic, petrophysical and structural data were recovered from five fully-cored boreholes, from the walls of a 100 m long underground tunnel, and from a 50 m long transect at a nearby outcrop. The data allowed reservoir property variations in the Urgonian limestones to be studied from core to reservoir scale. Eleven Reservoir Rock Types (RRTs) were identified based on petrographic features (texture, grain size), reservoir properties (porosity, permeability), and the frequency of structural discontinuities such as fractures, faults and stylolites. Tight and microporous reservoir rock types were distinguished. Tight reservoir rock types were characterised by early cementation of intergranular pore spaces and by the presence of frequent structural discontinuities. By contrast microporous reservoir rock types contained preserved intragranular microporosity and matrix permeability, but had very few structural discontinuities. Observed vertical alternations of microporous and tight rock types are interpreted to have been controlled by the early diagenesis of the Urgonian carbonates. Deformation associated with regional-scale tectonic phases, including Albian – Cenomanian “Durancian” uplift (∼105 to 96 Ma) and Pyrenean compression (∼55 to 25 Ma), resulted in the modification of the initial petrophysical properties of the Urgonian limestones. An early diagenetic imprint conditioned both the intensity of structural deformations and the associated circulations of diagenetic and meteoric fluids. Evolution of the Reservoir Rock Types is therefore linked both to the depositional conditions and to subsequent phases of structural deformation.  相似文献   
26.
27.
28.
29.
30.
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