全文获取类型
收费全文 | 622948篇 |
免费 | 7144篇 |
国内免费 | 1925篇 |
专业分类
电工技术 | 11388篇 |
综合类 | 464篇 |
化学工业 | 94392篇 |
金属工艺 | 25068篇 |
机械仪表 | 19589篇 |
建筑科学 | 14006篇 |
矿业工程 | 3583篇 |
能源动力 | 16718篇 |
轻工业 | 49272篇 |
水利工程 | 6652篇 |
石油天然气 | 12855篇 |
武器工业 | 28篇 |
无线电 | 72317篇 |
一般工业技术 | 124835篇 |
冶金工业 | 115844篇 |
原子能技术 | 14214篇 |
自动化技术 | 50792篇 |
出版年
2021年 | 5349篇 |
2020年 | 4123篇 |
2019年 | 5181篇 |
2018年 | 8950篇 |
2017年 | 8878篇 |
2016年 | 9596篇 |
2015年 | 6086篇 |
2014年 | 10089篇 |
2013年 | 29066篇 |
2012年 | 16204篇 |
2011年 | 21993篇 |
2010年 | 17622篇 |
2009年 | 20054篇 |
2008年 | 20554篇 |
2007年 | 20231篇 |
2006年 | 18032篇 |
2005年 | 16408篇 |
2004年 | 15470篇 |
2003年 | 15313篇 |
2002年 | 14743篇 |
2001年 | 14552篇 |
2000年 | 13725篇 |
1999年 | 14183篇 |
1998年 | 35741篇 |
1997年 | 25316篇 |
1996年 | 19537篇 |
1995年 | 14648篇 |
1994年 | 13018篇 |
1993年 | 12908篇 |
1992年 | 9509篇 |
1991年 | 9072篇 |
1990年 | 8977篇 |
1989年 | 8701篇 |
1988年 | 8430篇 |
1987年 | 7205篇 |
1986年 | 7170篇 |
1985年 | 8132篇 |
1984年 | 7576篇 |
1983年 | 6899篇 |
1982年 | 6446篇 |
1981年 | 6565篇 |
1980年 | 6176篇 |
1979年 | 6027篇 |
1978年 | 6151篇 |
1977年 | 7016篇 |
1976年 | 9049篇 |
1975年 | 5399篇 |
1974年 | 5070篇 |
1973年 | 5204篇 |
1972年 | 4426篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The whole history of failure of a rectangular panel with two symmetrical notches and a central crack subjected to a progressively increasing tension load normal to the crack plane is studied. The material of the panel exhibits substantial plastic deformation prior to fracture. An elastic-plastic analysis of the plate is first performed based on finite elements. The results of stress analysis are coupled with the strain energy density theory to determine the critical load for crack initiation and the history of stable crack growth up to the point of instability. At instability the crack runs fast through the elastic material bypassing the plastic zone near the plate boundary. The crack deviates from its initial direction and is curved even though the plate is subjected to opening-mode loading. Results for crack trajectories are given for various initial crack lengths and notch radii of the plate.Presented at Fourth Greek National Congress on Mechanics, 26–29 June 1995, held at Xanthi, Greece. 相似文献
992.
A Colli M Cocciolo C Riva L Marcassoli M Pirola P Di Gregorio G Buccino 《Canadian Metallurgical Quarterly》1993,72(3):677-682
BACKGROUND: Ascites in patients with hepatocellular carcinoma (HCC) is a poorly characterized subgroup of malignancy-related ascites. Not only the underlying liver disease, but also the tumor growth and spread contributes to the ascites formation. The authors differentiated ascites in HCC from other types of ascites. METHODS: The authors analyzed the ascitic fluid of 185 consecutive patients (89 liver cirrhosis, 33 HCC, 31 peritoneal carcinomatosis, 22 liver metastases, 10 spontaneous bacterial peritonitis). RESULTS: Each subgroup showed a typical pattern. Compared with the cirrhotic patients, those with HCC showed a higher frequency of positive cytologic findings (4 of 33 versus 0/89, P < 0.004), elevated fibronectin concentration (10/33 versus 8/89, P < 0.004), and elevated polymorphonuclear cell count (10/33 versus 5/89 P < 0.004). CONCLUSIONS: A significant number of patients with ascites and HCC patients showed signs of peritoneal infiltration with positive cytologic findings and increased concentration of fibronectin. Moreover, neutrocytic ascites without signs of superinfection is relatively common (30%). 相似文献
993.
994.
G Bioque D Vargas O Bulbena J Roselló-Catafau Gelpi E 《Canadian Metallurgical Quarterly》1993,38(1-2):38-43
N-phenyllinoleamide (NPLA) has been detected as extraneous compound in adulterated cooking oils associated with a unique epidemic disease known as the Toxic Oil Syndrome (TOS). In this communication we report on the action of NPLA on the endogenous cyclooxygenase and lipoxygenase arachidonate metabolism. Results show that mouse peritoneal macrophages (MPM) exposed to 1 mM NPLA for 2 h undergo significant increases of 6-keto prostaglandin F1a, prostaglandin E2, leukotriene B4, 12- and 15-hydroxyeicosatetraenoic acids. MPM prelabelled with 3H-AA showed an enhanced release when exposed to NPLA. Thus, it is concluded that NPLA potentiates AA release from cell membrane phospholipids and the subsequent cyclooxygenase and lipoxygenase oxidative metabolism of this precursor to various eicosanoids. This is in agreement with the implication of peroxidative process mediated by fatty acids anilides in TOS. 相似文献
995.
996.
997.
S Clark 《Canadian Metallurgical Quarterly》1995,179(6):209-213
The elucidation of the chemical structure of lpriflavone was carried out by ultraviolet absorption spectrophotometric, infrared spectroscopic, 1H and 13C nuclear magnetic resonance spectroscopic, low and high resolution EI mass spectrometric, thermoanalytical, elemental analytical and X-ray diffraction methods. The results unambigously verify the structure of Ipriflavone. 相似文献
998.
999.
An extensive Markov process, which considers both the coding redundancy and the intersample redundancy, is presented to measure the entropy value of an ECG signal more accurately. It utilizes the intersample correlations by predicting the incoming n samples based on the previous m samples which constitute an extensive Markov process state. Theories of the extensive Markov process and conventional n repeated applications of m-th order Markov process are studied first. After that, they are realized for ECG exact coding. Results show that a better performance can be achieved by the authors' system. The average code length for the extensive Markov system on the second difference signals was 2.512 b/sample, while the average Huffman code length for the second difference signals was 3.326 b/sample 相似文献
1000.
Harame D.L. Comfort J.H. Cressler J.D. Crabbe E.F. Sun J.Y.-C. Meyerson B.S. Tice T. 《Electron Devices, IEEE Transactions on》1995,42(3):455-468
A detailed review of SiGe epitaxial base technology is presented, which chronicles the progression of research from materials deposition through device and integration demonstrations, culminating in the first SiGe integrated circuit application. In part I of this paper, the requirements and processes for high-quality SiGe film preparation are discussed, with emphasis on fundamental principles. A detailed overview of SiGe HBT device design and implications for circuit applications is then presented 相似文献