全文获取类型
收费全文 | 178095篇 |
免费 | 4970篇 |
国内免费 | 2094篇 |
学科分类
工业技术 | 185159篇 |
出版年
2021年 | 1894篇 |
2020年 | 1370篇 |
2019年 | 1651篇 |
2018年 | 1999篇 |
2017年 | 2019篇 |
2016年 | 2229篇 |
2015年 | 2185篇 |
2014年 | 3157篇 |
2013年 | 8154篇 |
2012年 | 4895篇 |
2011年 | 6523篇 |
2010年 | 5222篇 |
2009年 | 5700篇 |
2008年 | 6143篇 |
2007年 | 6368篇 |
2006年 | 5741篇 |
2005年 | 5324篇 |
2004年 | 4921篇 |
2003年 | 4877篇 |
2002年 | 5077篇 |
2001年 | 5016篇 |
2000年 | 4438篇 |
1999年 | 4316篇 |
1998年 | 7024篇 |
1997年 | 5605篇 |
1996年 | 4823篇 |
1995年 | 4008篇 |
1994年 | 3549篇 |
1993年 | 3339篇 |
1992年 | 2926篇 |
1991年 | 2786篇 |
1990年 | 2695篇 |
1989年 | 2669篇 |
1988年 | 2511篇 |
1987年 | 2203篇 |
1986年 | 2147篇 |
1985年 | 2571篇 |
1984年 | 2328篇 |
1983年 | 2202篇 |
1982年 | 2081篇 |
1981年 | 1999篇 |
1980年 | 1871篇 |
1979年 | 1883篇 |
1978年 | 1772篇 |
1977年 | 2086篇 |
1976年 | 2535篇 |
1975年 | 1542篇 |
1974年 | 1393篇 |
1973年 | 1434篇 |
1972年 | 1177篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
951.
Four reactive power meters, operating on different principles, were tested under nonsinusoidal conditions. Different definitions of the reactive power are discussed. Because the definition and meaning of the nonsinusoidal reactive power are still being actively debated, the readings of the tested meters were compared with four nonsinusoidal reactive powers and the first harmonic reactive power, to verify whether these readings can be interpreted as approximate measures of the different definitions. A digital instrument, programmed to measure each of these powers, was used as a reference 相似文献
952.
953.
954.
955.
Object boundary location by region and contour deformation 总被引:2,自引:0,他引:2
Chan F.H.Y. Lam F.K. Poon P.W.F. Zhu H. Chan K.H. 《Vision, Image and Signal Processing, IEE Proceedings -》1996,143(6):353-360
Many applications in image analysis need to distinguish an object from its surroundings. The `snake' method (Kass, 1987) is a well known method to solve such problems by locating the object boundary from an initial plan, but it has the limitation that the distance between the initial plan and the object boundary should be `very small'. The authors present a two-step method, which combines region and contour deformation, to locate the boundary of an object from a designated initial boundary plan. First, they propose a new deformable region model to represent an object, and use the model to locate the boundary of the object by region deformation. This step fills the gap between a fairly rough initial plan and the `snake' method. The resulting boundary is then used as the initial plan of a `snake' method to further refine the boundary. The results of the method are shown in simulated images and MRI images of brain tumour patients 相似文献
956.
M. Hamacher D. Trommer K. Li H. Schroeter-Janssen W. Rehbein H. Heidrich 《Photonics Technology Letters, IEEE》1996,8(1):75-77
An optimized integration process is reported requiring only three epitaxial growth steps for the fabrication of an OEIC encompassing a single-mode laser, a waveguide element, and fast photodiodes. The process was applied to the fabrication of a heterodyne receiver including a semi-insulating buried heterostructure (SIBH)-DFB-laser with an output power of 14 mW and a side-mode suppression ratio greater than 40 dB, a 3-dB coupler, and high-speed balanced photodiodes with a bandwidth of 9 GHz. The laser can also be used as a transmitter laser exhibiting a modulation bandwidth of 11 GHz. 相似文献
957.
958.
加脂是软革制造过程中最重要的工序。本文建立了一个加脂过程和加脂机理的模型。在该模型中,传统的完全依赖PH值的观察被扩展,结合了加脂剂与浴液间的相互作用的性能和传送提供润滑作用的中性油组分的乳化剂的作用,并扩展了乳化剂的角色。以这种方式引入的化学柔软作用对革的强度有积极的效果,而相比效应力柔软作用会降低革的强度。 相似文献
959.
M Linden W Maier M Achberger R Herr H Helmchen O Benkert 《Canadian Metallurgical Quarterly》1996,67(3):205-215
As part of an international study initiated by the World Health Organization (WHO) about psychological disorders in primary health care, patients in the Federal Republic of Germany were compared with patients in other European centres. Patients from Germany do not differ from other European patients in respect to sociodemographic variables or psychiatric disorders. The most frequent CIDI-based diagnoses recorded in patients attending general practices are current depressive episodes (8.6%), generalized anxiety disorders (8.5%), neurasthenia (7.5%), and alcohol dependence (6.3%). In 20.9% of the patients at least one psychiatric diagnosis based on ICD-10 was recorded. In Germany significantly lower global ratings of health status are given than in other European centres although there is no difference in diagnostic prevalence rates. The recognition rate, i.e. the agreement between the CIDI-based ICD-10 diagnoses and the recognition as a case by the physician, is 56.2%-60.2%. On the other hand, the CIDI detects 90% of the patients described as psychologically ill by the physicians if subthreshold cases are also counted, or 46.4% if only defined diagnoses are taken into account. There is a significant correlation between severity of the psychiatric disorder and disability in social functioning. In Mainz and in the other European countries the disability rate of patients with a well-defined disorder is between 67.0% and 72.7%, whereas in Berlin this relation is not as clear, because especially in East Berlin there is a higher rate of unemployment in view of the political situation. Drug treatment is prescribed for 16.1% of the patients in primary care for psychiatric disorders. Half the patients recognized by physicians as cases receive medication. In the rest of Europe patients receive significantly more tranquillizers than in Germany, where the use of herbal drugs is more wide spread. 相似文献
960.
LW Didenko IB Buchwalow W Schulze K Augsten M Susa E Unger 《Canadian Metallurgical Quarterly》1996,98(4):399-409
Heterotrimeric GTP-binding proteins (G-proteins) have been shown to play an important role in cellular signalling. However, G-protein involvement in the intracellular spreading of bacterial pathogens is still poorly understood. In this study, antibodies, that recognize G-protein alpha-subunits (anti-G alpha), were used to investigate the localization of G-proteins in the macrophage-like cell line P388D1 and E. coli, also in their L-forms, during phagocytosis. In E. coli, anti-G alpha-binding sites were detected preferably in the cell wall and septa of the whole bacterial forms as well as in the cytoplasm of L-forms. Western blotting of bacterial lysates demonstrated protein bands with positive immunoreaction to antibodies against Gs alpha, Gi alpha, and Gcommon alpha with a higher affinity to the antibody against Gs alpha. Immunoreaction with the anti-Gs alpha-antibody was markedly higher in pathogenic strains of E. coli. Because of the conserved structure in all GTP-binding proteins which seem to derive from a single primordial protein involved in signal transduction mechanisms, it is reasonable to assume that some anti-Ga-positive proteins in E. coli might be related to G-proteins of higher organisms. A putative candidate for bacterial G-proteins seems to be a 36 kDa protein. Enhancement in G-protein immunostaining in the cytoplasm of macrophages around the internalized bacteria testifies to the involvement of G-proteins in mediation of endocytosis responses of phagocytes. 相似文献