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   203623篇
  免费   2461篇
  国内免费   652篇
电工技术   4175篇
综合类   127篇
化学工业   28047篇
金属工艺   7742篇
机械仪表   5844篇
建筑科学   4149篇
矿业工程   749篇
能源动力   4986篇
轻工业   14874篇
水利工程   1715篇
石油天然气   2848篇
武器工业   9篇
无线电   28204篇
一般工业技术   38756篇
冶金工业   45670篇
原子能技术   3617篇
自动化技术   15224篇
  2021年   1408篇
  2020年   1077篇
  2019年   1418篇
  2018年   2311篇
  2017年   2286篇
  2016年   2377篇
  2015年   1645篇
  2014年   2878篇
  2013年   8302篇
  2012年   4897篇
  2011年   6606篇
  2010年   5278篇
  2009年   6168篇
  2008年   6504篇
  2007年   6483篇
  2006年   5850篇
  2005年   5512篇
  2004年   5420篇
  2003年   5244篇
  2002年   5053篇
  2001年   5428篇
  2000年   5041篇
  1999年   5536篇
  1998年   15749篇
  1997年   10425篇
  1996年   8008篇
  1995年   5850篇
  1994年   5056篇
  1993年   5066篇
  1992年   3411篇
  1991年   3276篇
  1990年   3236篇
  1989年   3061篇
  1988年   2801篇
  1987年   2248篇
  1986年   2312篇
  1985年   2614篇
  1984年   2315篇
  1983年   2070篇
  1982年   1908篇
  1981年   2048篇
  1980年   1791篇
  1979年   1662篇
  1978年   1657篇
  1977年   2026篇
  1976年   2708篇
  1975年   1424篇
  1974年   1369篇
  1973年   1317篇
  1972年   1124篇
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
991.
In this paper, an indirect noninvasive method for measuring input impedance and the variations in the assembly of the interconnect and packaging between antenna and the integrated circuit (IC) effects of passive radio frequency identification (RFID) transponder (tags) antennas is presented. The analysis of different RFID tags is presented together with the experimental data.  相似文献   
992.
993.
Mechanical stimuli have been shown to enhance chondrogenesis on both animal and human chondrocytes cultured in vitro. Different mechanical stimuli act simultaneously in vivo in cartilage tissue and their effects have been extensively studied in vitro, although often in a separated manner. A new bioreactor is described where different mechanical stimuli, i.e. shear stress and hydrostatic pressure, can be combined in different ways to study the mechanobiology of tissue engineered cartilage. Shear stress is imposed on cells by forcing the culture medium through the scaffolds, whereas a high hydrostatic pressure up to 15 MPa is generated by pressurizing the culture medium. Fluid-dynamic experimental tests have been performed and successful validation of the bioreactor has been carried out by dynamic culture of tissue-engineered cartilage constructs. The bioreactor system allows the investigation of the combined effects of different mechanical stimuli on the development of engineered cartilage, as well as other possible three-dimensional tissue-engineered constructs.  相似文献   
994.
Model-based feedback control of vibration in flexible structures can be complicated by the possibility that interaction with an external body occurs. If not accounted for, instability or poor performance may result. In this paper, a method is proposed for achieving robust vibration control of flexible structures under contact. The method uses robust linear state feedback, coupled with a state estimation scheme utilizing contact force measurement. Uncertain contact characteristics are modelled by a sector-bounded non-linear function, such that state feedback gains can be synthesized using a matrix inequality formulation of the Popov stability criterion. A separation theorem is used to establish a robust H2 cost bound for the closed loop system. Experimental results from a multi-mode flexible structure testbed confirm that vibration attenuation and stability can be maintained over a broad range of contact characteristics, in terms of compliance and clearance.  相似文献   
995.
我非常钟爱办公用品商店的商业模式,就如同按下按钮那般简单。如果收益同按按钮一样简单,你能想象将会发生什么吗?现在就有这样一个例子:我们写(按钮),您接受(动),每个人都获取收益(这很简单)。标准其实就处于可盈利的按钮之间。我坚信ISA88第5部分标准的价值,如果可以得到广泛的应用,将意味着许多设施的盈  相似文献   
996.
最近有些读者朋友问:现在微软为什么这么霸道,连显示器都要通过它的认证,没有通过Windows Vista认证的液晶显示器会有什么不同吗?液晶显示器和Windows Vista操作系统之间到底有什么必要的联系呢?通过Windows Vista认证的显示器又有什么好处呢?针对上述种种疑问,今天我们将为大家一一解答。  相似文献   
997.
We present precise measurements of in-plane thermal conductivity for superconducting single crystals of YBa2Cu3O7?x (YBCO) withT c =92 and 60 K, Bi2Sr2CaCu2O8 (BSCCO), and of Zn-doped YBCO. Magnetization and thermal conductivity data obtained with the same 90-K YBCO crystal demonstrate a close relationship between the magnetic thermal resistivity and the internal magnetic fieldB in a superconductor in the mixed state. For all superconductors studied here, the magnetic thermal resistivity is a sublinear function of magnetic field. The origins of the nonlinearity are discussed. Angular dependences of the magnetic thermal resistivity have been shown to depart from the anisotropic 3D superconductor model and are in quantitative agreement with a quasi-2D model. Implications for spatial modulation of the order parameter are made.  相似文献   
998.
In clinical trials in advanced urogenital cancer with metastasis there are cases showing a poor clinical response and poor prognosis. The cure of advanced urogenital cancer still remains a major problem in management. The present paper is a summary of 8 articles presented at the symposium on "Management of advanced urogenital cancer: Treatment of metastasis" in the 43th Annual Meeting of Center Section of Japanese Urological Association in November, 1993. The present status, problems and future conception of treatment modalities for advanced urogenital cancer were discussed.  相似文献   
999.
The points of this presentation are reform of the theory relating to "Dysplasia and Carcinogenesis" and the cytological methods. In 1976, Meisels and Fortin reported that dysplasia is the disease caused by Human papilloma virus (HPV), and surprisingly, intermediate cells infected by HPV possessed the ability of proliferation and mitosis, resulting in binucleation and multinucleation. In cytology, dysplasia is thought to be delivered from basal cells and abnormal cells are differentiated from lower layer to upper layer, the grade of dysplasia is judged from the level of cell-differentiation. In histology, however, differentiated cells are thought to be normal cells from the histological definition. Therefore, the histological theory cannot explain the fact that the appearance of the abnormal cells from the all layers in cytology of the mild dysplasia. This discrepancy can be understood well if we think it is caused by HPV infection. HPV (ds-DNA) can only proliferate using cellular factors. And as keratinocytes is important with relating to this proliferation, HPV affects human intermediate layer and upper layer. In HPV-infected cells, HPV-E6 protein and E7 protein can bind the products of p53 and pRB, suppressor genes, respectively. These lead to degradation of these proteins' function, acceleration of cell proliferation, and abnormality of cell-cycle time. Our fundamental theory of dyskaryosis is based on these findings. Mild dysplasia is transferred from intermediate layer to upper layer and vanish after cell maturation. Immortalization, transformation, and gene alteration are important factors for carcinogenesis. The deletion of chromosome 3p is one of the most important genetic changes during carcinogenesis. On the basis of carcinogenesis theory described above, the cytological findings of HPV-infected cells are classified into three steps.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
1000.
The fundamentals of multi-step braiding for the fabrication of three-dimensional fibre preforms for composites have been studied. To facilitate the understanding of the complex multi-step braiding processes, a computer simulation algorithm has been developed. The simulation acts as a tool to allow the identification of individual yarn paths, number and location of yarn groups, and braid geometry. It was found that individual control of the rows and columns of yarn carriers on a Cartesian braiding bed allows for the fabrication of advanced multi-step braids; the micro-structural possibilities of three-dimensional braids are thus greatly extended. Some basic relationships of the braiding parameters have been identified. It has been concluded that the traditional four-step and two-step braidings are special cases of multi-step braidings. To verify the feasibility of the structures, experimental investigations have also been carried out. Innovative braid architectures have been designed and fabricated using a prototype multi-step braiding machine.  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