全文获取类型
收费全文 | 2442篇 |
免费 | 76篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 23篇 |
综合类 | 11篇 |
化学工业 | 314篇 |
金属工艺 | 44篇 |
机械仪表 | 103篇 |
建筑科学 | 42篇 |
矿业工程 | 10篇 |
能源动力 | 53篇 |
轻工业 | 94篇 |
水利工程 | 5篇 |
石油天然气 | 15篇 |
无线电 | 214篇 |
一般工业技术 | 266篇 |
冶金工业 | 1121篇 |
原子能技术 | 15篇 |
自动化技术 | 201篇 |
出版年
2023年 | 18篇 |
2022年 | 24篇 |
2021年 | 39篇 |
2020年 | 28篇 |
2019年 | 30篇 |
2018年 | 39篇 |
2017年 | 40篇 |
2016年 | 36篇 |
2015年 | 31篇 |
2014年 | 50篇 |
2013年 | 116篇 |
2012年 | 67篇 |
2011年 | 99篇 |
2010年 | 78篇 |
2009年 | 86篇 |
2008年 | 78篇 |
2007年 | 75篇 |
2006年 | 51篇 |
2005年 | 57篇 |
2004年 | 44篇 |
2003年 | 40篇 |
2002年 | 43篇 |
2001年 | 26篇 |
2000年 | 25篇 |
1999年 | 54篇 |
1998年 | 325篇 |
1997年 | 209篇 |
1996年 | 146篇 |
1995年 | 98篇 |
1994年 | 68篇 |
1993年 | 68篇 |
1992年 | 12篇 |
1991年 | 32篇 |
1990年 | 22篇 |
1989年 | 29篇 |
1988年 | 38篇 |
1987年 | 19篇 |
1986年 | 23篇 |
1985年 | 18篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 17篇 |
1979年 | 5篇 |
1978年 | 10篇 |
1977年 | 17篇 |
1976年 | 42篇 |
1975年 | 5篇 |
1973年 | 8篇 |
排序方式: 共有2531条查询结果,搜索用时 15 毫秒
41.
K. Kumagai S. Ikeda J. Jiang M. S. Lin C. C. Lai H. C. Ku 《Journal of Low Temperature Physics》1996,105(5-6):1641-1646
195Pt-,139La- and11B-NMR have been investigated in quaternary RM2B2C (R=Y, La, Th and M=Ni, Pd, Pt). The electric quadrupole frequency of139La changes more than 5 times in magnitude from M=Ni to Pt, indicating that the hybridization of La-5d and d-electrons of M-element changes largely. The analysis of11B and139La spectra shows also the large change of the magnetic anisotropy with R and M element, i.e., II c>II ab in LaNi2B2C, but II c>II ab YNi2B2C.The data of T1T and K of195Pt and11B are consistent with the band effects and with no evidence of strong antiferromagnetic correlation effects. 相似文献
42.
43.
We present a view of the neuromechanical regulation of breathing and causes of breathing instability during sleep. First, we would expect transient increases in upper airway resistance to be a major cause of transient hypopnea. This occurs in sleep because a hypotonic upper airway is more susceptible to narrowing and because the immediate excitatory increase in respiratory motor output in response to increased loads is absent in non-REM sleep. Secondly, sleep predisposes to an increased occurrence of ventilatory "overshoots", in part because abruptly changing sleep states cause transient changes in upper airway resistance and in the gain of the respiratory controller. Following these ventilatory overshoots, breathing stability will be maintained if excitatory short-term potentiation is the prevailing influence. On the other hand, apnea and hypopnea will occur if inhibitory mechanisms dominate following the ventilatory overshoot. These inhibitory mechanisms include: a) hypocapnia-if transient, will inhibit carotid chemoreceptors and cause hypopnea, but if prolonged will inhibit medullary chemoreceptors and cause apnea; b) a persistent inhibitory effect from lung stretch; c) baroreceptor stimulation, from a transient rise in systemic blood pressure immediately following termination of apnea or hypopnea may partially suppress the accompanying hyperpnea; d) depression of central respiratory motor output via prolonged brain hypoxia. Once apneas are initiated, reinitiation of inspiration is delayed even though excitatory stimuli have risen well above their apneic thresholds, and these prolonged apneas are commonly accompanied by tonic EMG activation of expiratory muscles of the chest wall and upper airway. 相似文献
44.
In this paper we study a class of CQ Horn functions introduced in Boros et al. (Ann Math Artif Intell 57(3–4):249–291, 2010). We prove that given a CQ Horn function f, the maximal number of pairwise disjoint essential sets of implicates of f equals the minimum number of clauses in a CNF representing f. In other words, we prove that the maximum number of pairwise disjoint essential sets of implicates of f constitutes a tight lower bound on the size (the number of clauses) of any CNF representation of f. 相似文献
45.
Recently, Wang et al. showed that two new verifier-free remote user password authentication schemes, Ku-Chen's scheme and Yoon et al.'s scheme, are vulnerable to an off-line password guessing attack, a forgery attack, and a denial-of-service attack, and then proposed an improved scheme for the real application in resource-limited environments. Unfortunately, we find that Wang et al.'s scheme is still vulnerable to an impersonation attack and an off-line password guessing attack. In addition, Wang et al.'s scheme is not easily reparable and is unable to provide perfect forward secrecy. Finally, we propose an improved scheme with better security strength. 相似文献
46.
Fan Zhang Robert Hager Seung-Hoe Ku Choong-Seock Chang Stephen C. Jardin Nathaniel M. Ferraro E. Seegyoung Seol Eisung Yoon Mark S. Shephard 《Engineering with Computers》2016,32(2):285-293
XGC1 and M3D-C 1 are two fusion plasma simulation codes being developed at Princeton Plasma Physics Laboratory. XGC1 uses the particle-in-cell method to simulate gyrokinetic neoclassical physics and turbulence (Chang et al. Phys Plasmas 16(5):056108, 2009; Ku et al. Nucl Fusion 49:115021, 2009; Admas et al. J Phys 180(1):012036, 2009). M3D-\(C^1\) solves the two-fluid resistive magnetohydrodynamic equations with the \(C^1\) finite elements (Jardin J comput phys 200(1):133–152, 2004; Jardin et al. J comput Phys 226(2):2146–2174, 2007; Ferraro and Jardin J comput Phys 228(20):7742–7770, 2009; Jardin J comput Phys 231(3):832–838, 2012; Jardin et al. Comput Sci Discov 5(1):014002, 2012; Ferraro et al. Sci Discov Adv Comput, 2012; Ferraro et al. International sherwood fusion theory conference, 2014). This paper presents the software tools and libraries that were combined to form the geometry and automatic meshing procedures for these codes. Specific consideration has been given to satisfy the mesh configuration and element shape quality constraints of XGC1 and M3D-\(C^1\). 相似文献
47.
48.
KW Albegger 《Canadian Metallurgical Quarterly》1976,214(1):27-48
Neither the concept of the Reticulo-Endothelial-System (RES) Aschoff's (1924) nor that of the Reticulo-Histiocyte-System (RHS) provides a satisfactory framework into which the present knowledge of the phagocytic mononuclear cells can be fitted. Current knowledge concerning morphology, histochemistry (peroxydase and esterase activity), immunology (specific surface antigens, receptors on the cell membranes), function (immune phagocytosis, pinocytosis), kinetics (3H-thymidine labelling) and culture makes it possible to place all highly phagocytic mononuclear cells and their precursors in one system, which is called the Mononuclear-Phagocytic-System (MPS) (Langevoort, Cohn, Hirsch, Humphrey, Spector, van Furth, 1969). Kinetic studies with labelled cells have shown, that mononuclear phagocytes originate from precursor cells in the bone marrow (stem cell leads to monoblasts leads to promonocytes), than are circulating in the peripheral blood as monocytes and are transformed to tissue macrophages entering tissues. The MPS comprises following cells in following organs: connective tissue (histiocytes resp. macrophages); liver (Kupffer-cells); lung (alveolar macrophages); lymph nodes (free and fixed macrophages); bone marrow (macrophages); serous cavities (pleural and peritoneal macrophages); bone tissue (osteoclasts?); nervous system (microglial cells) (SEE Table 1). The reticular cells, endothelial cells and fibroblasts (fibrocytes) can therefore not be included in the MPS. Besides differences in morphology, histochemistry and function, they derive from mesenchymal cells and not from the bone marrow as the MPS. The present investigation demonstrates the structure and significance of the MPS in various kinds of chronic-specific and non-specific rhinosinusitis. On semithin sections two kinds of macrophages can be distinguished light-microscopically: 1. Larger macrophages with many phagosomes (storage cells) (Fig. 1A), which can exhibit sometimes a ring-shape on sections embracing greater parts of the interstitium (Fig. 1B). Such forms are mainly found in chronic (maxillary) sinusitis and are interpretated as "scavenger" macrophages. 2. The second type consists of smaller macrophages with extremely ruffling of the cell surface, which is interpretated as an expression of highly (specific?) stimulated states. These later macrophages can be seen mainly in edematous nasal polyps, which might be caused by allergic reactions of the anaphylactic type. The fine structure of the phagocytes is to some extent dependent on the actual development and functional state: there are "immature" macrophages, which are practically indistinguishable from blood monocytes (Fig. 2A); some of them can be stimulated and can therefore show many surface foldings and projections (Fig. 2B). The "mature" macrophage shows a well developed Golgi-area and many secondary lysosomes (Fig. 3). The storage type of the macrophages, which can predominate in some cases of chronic maxillary sinusitis, is characterized by many electron-lucent vacuoles (Fig. 4)... 相似文献
49.
50.