全文获取类型
收费全文 | 476篇 |
免费 | 18篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 5篇 |
综合类 | 12篇 |
化学工业 | 12篇 |
金属工艺 | 7篇 |
机械仪表 | 10篇 |
建筑科学 | 2篇 |
矿业工程 | 2篇 |
能源动力 | 3篇 |
轻工业 | 30篇 |
水利工程 | 6篇 |
石油天然气 | 6篇 |
无线电 | 38篇 |
一般工业技术 | 30篇 |
冶金工业 | 302篇 |
原子能技术 | 18篇 |
自动化技术 | 24篇 |
出版年
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 9篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2014年 | 9篇 |
2013年 | 5篇 |
2012年 | 9篇 |
2011年 | 9篇 |
2010年 | 9篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 9篇 |
2006年 | 6篇 |
2005年 | 10篇 |
2004年 | 7篇 |
2003年 | 4篇 |
2002年 | 14篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 7篇 |
1998年 | 70篇 |
1997年 | 56篇 |
1996年 | 40篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 21篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 8篇 |
1978年 | 6篇 |
1977年 | 16篇 |
1976年 | 53篇 |
1975年 | 7篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1966年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有507条查询结果,搜索用时 15 毫秒
421.
422.
Neuronal properties and topographic organization of the middle suprasylvian gyrus (cortical cytoarchitectonic field 7) were studied in three behaving cats with painlessly fixed heads. Two main neuronal types were found within this field. Type 1 neurons occupied the lateral part of the field and bordered representation of directionally selective neurons of the lateral suprasylvian visual area by vertical retinal meridian. Type 1 neurons had elongated and radially oriented receptive fields located in the lower part of contralateral visual field. Type 1 neurons preferred stimuli moving out or to the centre of gaze at a low or moderate speed, and many of them were depth selective. The responses were enhanced by attention, oriented to the presented stimulus. Medial part of the field 7 along the border with the area V3 was occupied by neurons with not elongated receptive fields (type 2). These neurons preferred moderate and high speeds of motion, and gratings of proper spatial frequency and orientation were effective stimuli for them. Border between representations of type 2 and type 1 neurons coincided with projection of horizontal retinal meridian. At the rostral and caudal borders of the field 7 abrupt changes of neuronal properties took place. Neurons which abutted field 7 anteriorly and posteriorly resembled hypercomplex cells and their small receptive fields were located in the central part of the visual field. Topographical considerations and receptive field properties allowed us to conclude that the medial part of the field 7 (included type 2 neurons) is functionally equivalent to the area V4 in the cortex of primates, while the lateral part (type 1 neurons) may correspond to the area V4T. 相似文献
423.
The hormonally active form of vitamin D, 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3] stimulates biological responses related to calcium homeostasis, cell differentiation, and immunomodulation in many target cells, including leukemic cells. Most of these responses are dependent upon 1 alpha,25(OH)2D3 interaction with a nuclear receptor protein. Structural analogues of 1 alpha,25(OH)2D3 might allow for separation of biological function, avoiding adverse calcemic effects. This report quantitates intestinal calcium absorption, bone calcium resorption, induction of intestinal and renal calcium-binding protein (CaBP), and occupancy of the intestinal and renal nuclear 1 alpha,25(OH)2D3 receptor in vitamin D-deficient chicks after a single dose of 1 alpha,25(OH)2D3, 1 alpha,25-dihydroxyvitamin-16-ene-23-yne-D3 (analogue V), or 22-[m-(dimethylhydroxymethyl)phenyl]-23,24,25,26,27- pentanor-1 alpha-hydroxy-vitamin D3 (analogue EV). The interaction of these compounds with chick intestinal nuclear 1 alpha,25(OH)2D3 receptor and chick plasma vitamin D-binding protein was determined in vitro; analogues V and EV bound 68% and 62% [1 alpha,25(OH)2D3 receptor] and 8% and 13% (vitamin D-binding protein), respectively, as well as 1 alpha,25(OH)2D3 (100%). 1 alpha,25(OH)2D3 doses (0.075-1.2 nmol) generated responses in intestinal calcium absorption, bone calcium resorption, intestinal CaBP, and renal CaBP. When analogue V (1.2-300 nmol) was administered, increases in bone calcium resorption and renal CaBP were noted. However, a significant response in intestinal calcium absorption and intestinal CaBP appeared only after a 300-nmol dose. Unoccupied nuclear 1 alpha,25(OH)2D3 receptor in the intestine and kidney was determined in vivo after doses of 1 alpha,25(OH)2D3, analogue V, or analogue EV. Doses (0.25-6.0 nmol) of 1 alpha,25(OH)2D3 and analogue EV reduced unoccupied receptor to 24% and 59% (intestine) and to 13% and 41% (kidney), respectively. Analogue V (6.0-600 nmol) decreased unoccupied receptor in the kidney. In the intestine analogue V (300-600 nmol) reduced unoccupied receptor only to 75%. These results confirm that some vitamin D analogues can generate selective biological responses and different levels of target organ receptor occupancy. 相似文献
424.
A sulfanilamide resistant strain Ts-5 of Pseudomonas mallei was isolated in the experiments on sulfazine therapy of malleus. The spectrum and level of the strain cross resistance to sulfanilamides and trimethoprim were studied. The frequency of the SurTrr mutants of P. mallei was determined. Efficient antibacterial drugs for the therapy of malleus caused by the sulfanilamide resistant strain are recommended. 相似文献
425.
Investigated the effects of self-regulation as a moderator of the relations between coping efforts and psychological symptoms of children of divorce. The interactions of two dimensions of self-regulation (task orientation and approach-flexibility) and two dimensions of coping (active and avoidant) predicting children's postdivorce symptoms were tested using a sample of 199 divorced mothers and their children, ages 8 to 12. The approach-flexibility dimension moderated the relations of both active and avoidant coping with children's self-report of anxiety. At higher levels of approach-flexibility, active coping was negatively related to anxiety, while at lower levels of approach-flexibility, active coping was unrelated to anxiety. Avoidant coping was unrelated to anxiety at higher levels of approach-flexibility, whereas at lower levels of approach-flexibility, avoidant coping was positively related to anxiety. The task orientation dimension did not interact with coping, but had direct, independent effects on children's self-report of conduct problems, depression, and parent-report of internalizing and externalizing behavior problems. The implications for understanding children's coping with divorce and future directions for research are discussed. 相似文献
426.
Identification of a common low density lipoprotein receptor mutation (C163Y) in the west of Scotland
WK Lee L Haddad MJ Macleod AM Dorrance DJ Wilson D Gaffney MH Dominiczak CJ Packard IN Day SE Humphries AF Dominiczak 《Canadian Metallurgical Quarterly》1998,35(7):573-578
BACKGROUND: The pathological processes by which Helicobacter pylori infection leads to the development of gastroduodenal disease are still incompletely understood. Oxygen-derived free radicals are important mediators of inflammation and potential carcinogens. Furthermore, dietary studies have suggested that antioxidant vitamins may protect against gastric cancer. OBJECTIVE: To determine plasma free radical activity and antioxidant vitamin levels in dyspeptic patients and to correlate the results with H. pylori infection and tobacco smoking. SUBJECTS: Forty-three patients undergoing routine endoscopy for investigation of dyspepsia. METHODS: Plasma free radical activity was determined by measurement of thiobarbituric acid-reactive substances (TBARS). Plasma samples were also assayed for the antioxidant vitamins A, C and E. Gastroduodenal biopsies were obtained from all patients for histological examination. RESULTS: Plasma TBARS levels were significantly higher in H. pylori positive versus negative subjects (P < 0.03), smokers versus non-smokers (P < 0.04) and males versus females (P < 0.01). Multiple regression analysis revealed that after correcting for male sex and smoking there was no significant association between plasma free radical activity and H. pylori infection. Smokers had significantly lower levels of plasma vitamin C than non-smokers (P< 0.05); no differences were seen in vitamin A and E levels. Gender and H. pylori infection did not significantly affect plasma antioxidant vitamin levels. Gastroduodenal disease was present in all of the smokers compared with 67% of the non-smokers (P < 0.05); 69% of the smokers were H. pylori positive versus 53% of the non-smokers. CONCLUSIONS: Tobacco smoking and male sex, both recognized risk factors for gastroduodenal disease, appear to be the major determinants of increased plasma free radical activity in dyspeptic subjects, rather than H. pylori infection. The reason for the higher prevalence of H. pylori infection and gastroduodenal disease in dyspeptic smokers is unclear but may relate to weakened antioxidant defences. 相似文献
427.
The results of computed tomography (CT) was compared with ultrasonographic and angiographic findings in 168 patients. All data of radiation diagnosis of abdominal aortic aneurysms (AAA) were compared with those of operations and morphological studies of the resected fragments of the aortic parts changed due to aneurysms. These comparisons provided a detailed characterization of the potentialities of CT performed on a third-generation unit in the presurgical diagnosis of this abnormality. At the same time, detailed XCT findings (semeiotics of AAA and their complications, such infiltration, dissection, and rupture) are given. The study shows benefits of the refined AAA by applying routine CT. The paper gives a diagnostic algorithm of using radiation studies (ultrasonography, CT, angiography) in the diagnosis of AAA. Third-generation CT units widely used in clinical practice are shown to provide necessary and complete information on the magnitude of AAA. This makes it possible to extend the capacities of timely detection of this abnormality and to make a successful surgical intervention. 相似文献
428.
本文对含Mn60-90wt-%的MnCu合金在123—423K温度范围内进行了低频和声频内耗测量,研究马氏体相变和马氏体中各种界面对内耗的贡献.结果指出,马氏体相变内耗可分解为两部分,即相变中的稳定内耗峰(阶梯变温测量时,T=0)和低温背景内耗.相变内耗主要是由马氏体和母相界面的运动产生的;低温背景内耗是由马氏体片间界面的运动产生的,且表现出强烈的振幅效应,其强弱决定于马氏体片间界面的数量.马氏体片间界面的运动产生的非线弹应变导致了附加的模量亏损和非线性共振行为.高Mn合金(Mn>80wt-%)中的弛豫型内耗峰研究指出,该峰的弛豫时间分布参数服从β= 相似文献
429.
V. N. Karnaukhov M. G. Mozerov 《Journal of Communications Technology and Electronics》2016,61(12):1426-1431
In this study, an original method for restoration of multispectral images by means of gradient reconstruction is proposed. The method uses a simple relationship between the gradient at the neighboring points in the distorted image and the gradient at distant points in the initial image. The result of restoration by the proposed algorithm excels the result obtained by the standard method based on the Wiener filtering. A new method for estimation of the parameters of the distorting motion-blur operator is also proposed. In this case, the blurred image is considered as a superposition of M shifted original images, and the autocorrelation convolution of the distorted image can be represented as a linear combination of M 2 mutual convolutions of several identical shifted images. Thus, the autocorrelation function of the distorted image is a straight line passing through the center, and the direction of this line and its length coincides with the parameters of the distorting operator. As compared to the best present-day algorithms, the proposed method exhibits higher accuracy of parameter estimation. In addition, computation of parameters with the use of this method takes much less time than with the use of popular estimation algorithms based on the Radon transform. 相似文献
430.