全文获取类型
收费全文 | 23283篇 |
免费 | 338篇 |
国内免费 | 122篇 |
专业分类
电工技术 | 498篇 |
综合类 | 64篇 |
化学工业 | 3187篇 |
金属工艺 | 940篇 |
机械仪表 | 657篇 |
建筑科学 | 545篇 |
矿业工程 | 67篇 |
能源动力 | 600篇 |
轻工业 | 1833篇 |
水利工程 | 212篇 |
石油天然气 | 179篇 |
武器工业 | 1篇 |
无线电 | 2645篇 |
一般工业技术 | 4080篇 |
冶金工业 | 6130篇 |
原子能技术 | 420篇 |
自动化技术 | 1685篇 |
出版年
2021年 | 151篇 |
2020年 | 114篇 |
2019年 | 158篇 |
2018年 | 231篇 |
2017年 | 229篇 |
2016年 | 257篇 |
2015年 | 180篇 |
2014年 | 301篇 |
2013年 | 821篇 |
2012年 | 508篇 |
2011年 | 776篇 |
2010年 | 560篇 |
2009年 | 625篇 |
2008年 | 717篇 |
2007年 | 749篇 |
2006年 | 631篇 |
2005年 | 724篇 |
2004年 | 591篇 |
2003年 | 640篇 |
2002年 | 683篇 |
2001年 | 677篇 |
2000年 | 603篇 |
1999年 | 618篇 |
1998年 | 2159篇 |
1997年 | 1404篇 |
1996年 | 1046篇 |
1995年 | 726篇 |
1994年 | 621篇 |
1993年 | 642篇 |
1992年 | 359篇 |
1991年 | 348篇 |
1990年 | 342篇 |
1989年 | 344篇 |
1988年 | 292篇 |
1987年 | 267篇 |
1986年 | 246篇 |
1985年 | 275篇 |
1984年 | 217篇 |
1983年 | 201篇 |
1982年 | 185篇 |
1981年 | 219篇 |
1980年 | 202篇 |
1979年 | 164篇 |
1978年 | 153篇 |
1977年 | 278篇 |
1976年 | 386篇 |
1975年 | 127篇 |
1974年 | 109篇 |
1973年 | 117篇 |
1972年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
Negative refraction is a wave phenomenon beyond geometrical optics - it depends on the way waves behave when their phase velocity reaches a zero. Various forms of linear wave processes in media can be concisely described in one wave equation that is inspired by the interpretation of a medium as an effective space-time geometry. Depending on the conformal factor of the effective metric, the waves may show positive or negative refraction. For electromagnetic waves in two-dimensional dielectrics the conformal factor corresponds to the impedance. 相似文献
192.
193.
194.
195.
PA Cabrera S Parietti G Haran U Benavidez S Lloyd G Perera S Valledor MA Gemmell T Botto 《Canadian Metallurgical Quarterly》1996,26(1):79-83
Forced thinking is an incompletely understood and rarely described epileptic aura. We studied three patients with forced thinking from left frontal lesions, two neoplastic and one vascular. All three experienced repetitive, intrusive thoughts at the onset of seizures. Their forced thinking was associated with the desire to vocalize, orobuccal movements, and speech arrest. The episodes occurred with other ictal manifestations and responded to antiseizure therapy. These patients suggest that epileptic forced thinking is a heterogeneous phenomenon; forced thinking from left frontal lesions is a manifestation of expressive language and is distinct from experiential thoughts arising from temporal limbic foci. 相似文献
196.
M Tondel G Carlsson L Hardell M Eriksson S Jakobsson U Flodin A Sk?ldestig O Axelson 《Canadian Metallurgical Quarterly》1996,71(6):947-950
An experiment was conducted to elucidate the origin of tetraploids (2n = 4x = 44) of Paragonimus westermani that occur together with diploid (2n = 2x = 22) and triploid (2n = 3x = 33) types in Liaoning Province, the People's Republic of China. Metacercariae of the diploid type, obtained from Hyogo Prefecture, Japan, and those of the triploid type from Tsushima, Nagasaki Prefecture, Japan, were mixed and inoculated into dogs and cats. The following results were obtained. The flukes were found in pairs within cysts in random combinations of 2x + 2x, 2x + 3x, and 3x + 3x (7:15:7). Oocytes in the oviduct were at stages from diplotene to metaphase. In a triploid fluke encysted with a diploid fluke, the primary oocytes were intruded by sperms from the diploid fluke. In the primary oocytes of diploid as well as triploid flukes, from diplotene to diakinesis, the homologues of the nucleolar chromosomes were heteromorphic as far as the size of the short arm was concerned. This implies that the triploid is an autotriploid generated in an ancestral diploid population that was polymorphic for the nucleolar chromosome. 相似文献
197.
The effects of antioxidants or hot packaging and their combination on lipid oxidation were quite variable depending on the additives in turkey meat. The TBARS values of cooked patties were greatly affected by the degree of oxidation in the raw meat, and the effectiveness of antioxidants varied with added prooxidants. Ascorbate and free radical terminators had stronger antioxidant effects than iron chelators, and chelating iron alone could not eliminate lipid oxidation in either raw or cooked meat with added NaCl. The combination of hot packaging and antioxidants provided cooked patties with better protection from lipid oxidation than either treatment alone. 相似文献
198.
U. Dahmen 《Metallurgical and Materials Transactions A》1994,25(9):1857-1863
The connection between the optimum shape and orientation relationship of precipitates in a solid is examined. Three simple
criteria for precipitate morphology are compared and illustrated schematically: the principle that precipitate dimensions
tend to be inverse to the magnitude of the transformation strain; the postulate that precipitates are bounded by unrotated
planes (eigenplanes); and the proposal that interfaces are parallel to the planes of three independent dislocation loop arrays
necessary to accommodate the transformation strain completely. These principles are illustrated for different orientation
relationships, and it is shown that special features are displayed by invariant-line precipitates. The implications of these
criteria for experimental studies of precipitate morphologies are discussed and their predictions compared with results from
a recent study of lath-shaped precipitates in Cu-Cr alloys.
This article is based on a presentation made at the Pacific Rim Conference on the “Roles of Shear and Diffusion in the Formation
of Plate-Shaped Transformation Products,” held December 18-22, 1992, in Kona, Hawaii, under the auspices of ASM INTERNATIONAL’S
Phase Transformations Committee. 相似文献
199.
1. Albino Wistar rats were raised in a normobaric hypoxic environment (10% O2 in N2). Two generations of hypoxic rats were observed for changes in their haemoglobin-oxygen (Hb-O2) dissociation curves (ODC), 2,3-diphosphoglycerate (2,3-DPG), haemoglobin (Hb), and Hill co-efficients at P50 (n50). The first generation were called (H1) and the second generation (H2). The control group (N) had a normoxic environment. 2. Thirty-five rats (13 N rats, 12 H1 rats and 10 H2 rats) were used. The 2,3-DPG was significantly higher in both hypoxic groups when compared with N rats (2.02 +/- 0.51 mmol/L) but 2,3-DPG of H2 rats was significantly lower than that of H1 rats (H1 = 3.48 +/- 0.58 mmol/L and H2 = 2.76 +/- 0.54 mmol/L). The haemoglobin values were N = 2.00 +/- 0.26, H1 = 2.65 +/- 0.32 and H2 = 2.36 +/- 0.30 mmol/L, respectively. 3. We observed considerable differences in Hb-O2 affinity between the three groups of rats. In standard conditions (pH = 7.400; pCO2 = 40 mmHg at 37 degrees C) the H1 rats showed a significantly decreased Hb-O2 affinity (P50,st = 37.0 +/- 1.3 mmHg) when compared with both H2 and N rats; the H2 rats showed a significantly increased Hb-O2 affinity (P50,st = 31.1 +/- 1.5 mmHg) when compared with controls N (P50,st = 34.7 +/- 2.1 mmHg). There were no significant differences in n50 values: N = 2.88 +/- 0.44; H1 = 2.88 +/- 0.77; and H2 = 2.94 +/- 0.67.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
200.
Research in object-oriented manufacturing simulations:an assessment of the state of the art 总被引:1,自引:0,他引:1
S. Narayanan D.A. Bodner T. Govindaraj L.F. Mcginnis C.M. Mitchell U. Sreekanth 《IIE Transactions》1998,30(9):795-810
Object-oriented programming (OOP) has been revolutionizing software development and maintenance. When applied to simulation of manufacturing systems, OOP also provides an opportunity for developing new ways of thinking and modeling. In this paper, we identify existing large-scale, persistent OOP-based research efforts focusing on manufacturing system simulation, and present an integrating framework for discussing the associated modeling abstractions, implementation strategies, common themes, and distinctive features. The goal is to identify the fundamental research and application issues, assess the current state of the art, and identify key research needs. 相似文献