全文获取类型
收费全文 | 4649篇 |
免费 | 81篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 66篇 |
综合类 | 13篇 |
化学工业 | 474篇 |
金属工艺 | 64篇 |
机械仪表 | 55篇 |
建筑科学 | 350篇 |
矿业工程 | 2篇 |
能源动力 | 99篇 |
轻工业 | 523篇 |
水利工程 | 28篇 |
石油天然气 | 3篇 |
无线电 | 227篇 |
一般工业技术 | 451篇 |
冶金工业 | 1962篇 |
原子能技术 | 54篇 |
自动化技术 | 363篇 |
出版年
2022年 | 34篇 |
2021年 | 67篇 |
2020年 | 28篇 |
2019年 | 39篇 |
2018年 | 53篇 |
2017年 | 45篇 |
2016年 | 61篇 |
2015年 | 49篇 |
2014年 | 66篇 |
2013年 | 93篇 |
2012年 | 120篇 |
2011年 | 172篇 |
2010年 | 120篇 |
2009年 | 113篇 |
2008年 | 128篇 |
2007年 | 271篇 |
2006年 | 85篇 |
2005年 | 88篇 |
2004年 | 81篇 |
2003年 | 86篇 |
2002年 | 79篇 |
2001年 | 61篇 |
2000年 | 70篇 |
1999年 | 105篇 |
1998年 | 613篇 |
1997年 | 376篇 |
1996年 | 248篇 |
1995年 | 160篇 |
1994年 | 122篇 |
1993年 | 119篇 |
1992年 | 41篇 |
1991年 | 53篇 |
1990年 | 49篇 |
1989年 | 52篇 |
1988年 | 33篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 41篇 |
1984年 | 25篇 |
1983年 | 21篇 |
1982年 | 24篇 |
1981年 | 32篇 |
1980年 | 36篇 |
1979年 | 36篇 |
1978年 | 19篇 |
1977年 | 56篇 |
1976年 | 105篇 |
1975年 | 17篇 |
1974年 | 17篇 |
1973年 | 24篇 |
排序方式: 共有4734条查询结果,搜索用时 9 毫秒
71.
Analyzing the design of networks for visual information routing is an underconstrained problem due to insufficient anatomical and physiological data. We propose here optimality criteria for the design of routing networks. For a very general architecture, we derive the number of routing layers and the fanout that minimize the required neural circuitry. The optimal fanout l is independent of network size, while the number k of layers scales logarithmically (with a prefactor below 1), with the number n of visual resolution units to be routed independently. The results are found to agree with data of the primate visual system. 相似文献
72.
73.
C Beretta-Piccoli P Weidmann R de Chatel D Hirsch FC Reubi 《Canadian Metallurgical Quarterly》1977,107(4):104-115
35 patients with benign essential hypertension were treated for 6 weeks with high doses of the mineralocorticoid-antagonist spironolactone (400 mg/day), or with the "loop-diuretic" mefruside (mean maximal dose 110 mg/day). Spironolactone caused greater reductions in blood pressure and blood volume and a more marked increase in plasma renin activity (PRA) than mefruside (p less than 0.05). It appears possible that he weaker antihypertensive effect of mefruside may relate partly to its lesser influence on circulatory volume. With both diuretics, mean decreases in blood pressure were greater in patients with low pre-therapeutic PRA than in patients with normal or high PRA. However, the diuretic-induced changes in blood pressure did not correlate with the associated variations in blood volume or PRA. Thus, the increased blood pressure sensitivity to diuretics in patients with low-renin essential hypertension did not appear to be volume or renin-dependent. Under normal conditions, the maintenance of a constant blood pressure during volume depletion may partly depend on compensatory activation of the sympathetic nervous system. Moreover, patients with low-renin essential hypertension have been found to have decreased adrenergic activity. It seems possible, therefore, that the marked blood pressure sensitivity to diuretic treatment in such patients may be the result of an impaired compensatory sympathetic response to sodium and volume depletion. Analysis of the literature suggests that the diuretic furosemide, a structural relative of mefruside, may also have less blood pressure lowering efficacy in patients with essential hypertension than the distally-acting thiazides, chlorthalidone or spironolactone. Consideration of possible differences in the blood pressure reducing potential of certain diuretics thus appears to be necessary in planning the pharmacotherapy of essential hypertension. 相似文献
74.
As is readily apparent, there is not a consensus regarding the treatment of lateral ligamentous ruptures of the ankle. Certainly, the elimination of functional instability is the goal of treatment. What actually causes this is still open to debate, but from Harrington's work, it appears that degenerative changes can result from mechanical instability. We are all aware that many athletes compete actively with "two-plane" instability of the ankle, but it remains to be seen if they will also suffer the late degenerative changes that Harrington describes. In the meantime, each physician must decide which diagnostic technique to rely upon and which treatment regimen will provide the most consistent results with the least incidence of functional instability. 相似文献
75.
A progressive fibrous myopathy may result from chronic intramuscular drug abuse. This complication may mimic other rheumatic disorders and early recognition may prevent disability. The patient described here presented with fixed flexion and extension contracture of hips and knees, respectively, after abusing meperidine and other agents for 3 years. Soft tissues of thighs and buttocks were "wood hard," EMG showed absence of action potentials in affected muscles, and biopsy revealed extensive replacement of muscle with dense, acellular fibrous tissue. Possible mechanisms are discussed. 相似文献
76.
The behavior of 24 children, aged 3-6 years, was recorded on video-tape. Simultaneously the ECG was recorded telemetrically. These observations were made during two pre-school educational programs lasting 90 minutes each: "Didactic games" and "Elementary music and movement program". For each child a scale was developed to show the correlation of mean heart-rate and well defined motor-activity. It was evident that the mean heart-rate was higher during the music program than during the didactic program, corresponding to the higher motor-activity. But it was found that in the didactic program the variation of the heart-rate within short intervals was higher due to the more frequent occurrence of respiratory arrhythmias. It was also seen that during the music program the children showed no signs of exertion as they did towards the end of the didactic program. Respiratory arrhythmias were not seen in children who according to the Schellong-test were classified as stable in their cardiovascular system. The arrhythmias occurred mainly when the children showed signs of fatigue. 相似文献
77.
von Hippel William; von Hippel Courtney; Conway Leanne; Preacher Kristopher J.; Schooler Jonathan W.; Radvansky Gabriel A. 《Canadian Metallurgical Quarterly》2005,89(1):22
Four experiments tested the hypothesis that people who are concerned with impression management cope with stereotype threat through denial. Consistent with this hypothesis, temporary employees threatened by a stereotype of incompetence (Study 1) and hostel-dwelling older adults (Study 2) were more likely to deny incompetence if they were high in impression management. African Americans (Study 3) showed a similar pattern of denying cognitive incompetence, which emerged primarily when they were interviewed by a White experimenter and had attended a predominantly Black high school. In Study 4, White students who expected to take an IQ test and were threatened by a stereotype of being less intelligent than Asians were more likely to deny that intelligence is important if they were high in impression management. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
78.
Owing to the upcoming applications in the field of service robotics mobile robots are currently receiving increasing attention in industry and the scientific community. Applications in the area of service robotics demand a high degree of system autonomy, which robots without learning capabilities will not be able to meet. Learning is required in the context of action models and appropriate perception procedures. In both areas flexible adaptivity is difficult to achieve especially when high bandwidth sensors (e.g. video cameras) - which are needed in the envisioned unstructured worlds - are used. This paper proposes a new methodology for image-based navigation using a self-organized visual representation of the environment. Self-organization leads to internal representations, which can be used by the robot, but are not transparent to the user. It is shown how this conceptual gap can be bridged. 相似文献
79.
The performance of older adults and depressed people on linear order reasoning is hypothesized to be best explained by different theoretical models. Whereas depressed younger adults are found to be impaired in generative inference making, older adults are well capable of making such inferences but exhibit problems with working memory (Experiments 1 and 2). Restriction of the available study time impairs reasoning by nondepressed control participants and. as such, proves to be a good model of older adults' but not depressed participants' limitations (Experiment 3). These results are replicated comparing depressed and older participants with a control group in the same study, providing increased power and linking the results to additional control measures of processing speed and working memory (Experiment 4). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
80.
FC Sparks AG Wile KP Ramming HK Silver RW Wolk DL Morton 《Canadian Metallurgical Quarterly》1976,111(10):1057-1062
Antibody against a breast carcinoma antigen was present in patients with breast carcinoma and other cancer more often (P less than .05) than in normal women. The incidence of antibody in women with breast carcinoma correlated with the presence or absence of gross tumor, and the titer of antibody paralleled the clinical course. These results suggest importance of a host-immune response to breast carcinoma. Fifty-seven patients with stage II carcinoma of the breast were entered into a prospective randomized adjuvant chemoimmunotherapy program of cyclophosphamide, methotrexate, and fluorouracil, and BCG vaccine +/- an irradiated allogeneic tumor cell vaccine. After 24 months of study, metastases occurred in two patients (3.5%) and a new primary carcinoma developed in the contralateral breast in two others, for an overall treatment failure rate of 7%. Adjuvant chemoimmunotherapy can delay early recurrence. Long-term follow-up is needed to assess the significance of these results. 相似文献