全文获取类型
收费全文 | 3195篇 |
免费 | 18篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 29篇 |
综合类 | 4篇 |
化学工业 | 661篇 |
金属工艺 | 47篇 |
机械仪表 | 55篇 |
建筑科学 | 155篇 |
矿业工程 | 43篇 |
能源动力 | 89篇 |
轻工业 | 263篇 |
水利工程 | 18篇 |
石油天然气 | 9篇 |
无线电 | 222篇 |
一般工业技术 | 363篇 |
冶金工业 | 883篇 |
原子能技术 | 23篇 |
自动化技术 | 351篇 |
出版年
2022年 | 38篇 |
2021年 | 50篇 |
2020年 | 38篇 |
2019年 | 26篇 |
2018年 | 26篇 |
2017年 | 36篇 |
2016年 | 46篇 |
2015年 | 38篇 |
2014年 | 46篇 |
2013年 | 241篇 |
2012年 | 81篇 |
2011年 | 95篇 |
2010年 | 81篇 |
2009年 | 91篇 |
2008年 | 80篇 |
2007年 | 115篇 |
2006年 | 90篇 |
2005年 | 79篇 |
2004年 | 79篇 |
2003年 | 72篇 |
2002年 | 76篇 |
2001年 | 51篇 |
2000年 | 42篇 |
1999年 | 59篇 |
1998年 | 54篇 |
1997年 | 55篇 |
1996年 | 63篇 |
1995年 | 55篇 |
1994年 | 69篇 |
1993年 | 53篇 |
1992年 | 46篇 |
1990年 | 58篇 |
1989年 | 44篇 |
1988年 | 40篇 |
1987年 | 39篇 |
1986年 | 50篇 |
1985年 | 41篇 |
1984年 | 49篇 |
1983年 | 38篇 |
1982年 | 48篇 |
1981年 | 39篇 |
1980年 | 36篇 |
1979年 | 54篇 |
1978年 | 43篇 |
1977年 | 40篇 |
1976年 | 26篇 |
1975年 | 34篇 |
1974年 | 43篇 |
1971年 | 26篇 |
1970年 | 25篇 |
排序方式: 共有3215条查询结果,搜索用时 15 毫秒
141.
This article examines the possibility that romantic love (with intensity, engagement, and sexual interest) can exist in long-term relationships. A review of taxonomies, theory, and research suggests that romantic love, without the obsession component typical of early stage romantic love, can and does exist in long-term marriages, and is associated with marital satisfaction, well-being, and high self-esteem. Supporting the separate roles of romantic love and obsession in long-term relationships, an analysis of a moderately large data set of community couples identified independent latent factors for romantic love and obsession and a subsample of individuals reporting very high levels of romantic love (but not obsession) even after controlling for social desirability. Finally, a meta-analysis of 25 relevant studies found that in long- and short-term relationships, romantic love (without obsession) was strongly associated with relationship satisfaction; but obsession was negatively correlated with it in long-term and positively in short-term relationships. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
142.
Hongjie Li Arthur E. Morris David G. C. Robertson 《Metallurgical and Materials Transactions B》1998,29(6):1181-1191
The thermodynamics of MnO-containing slags was reviewed, and the properties of such slags were correlated by application of
the cell model. This model, together with a previously developed unified interaction parameter model for the metal phase,
was used to simulate the gas-slag-metal conditions in the hearth of a ferromanganese submerged arc furnace. The calculated
slag and metal compositions and distribution of Mn, Si, and K between slag, metal, and fume were compared with plant data
and satisfactory agreement was obtained. A steady recirculation of potassium inside the furnace was also predicted. For a
potassium percentage in the raw materials of 0.63 pct, the amount of the recirculating potassium was about 160 kg per metric
ton of ferromanganese. Due to the recirculation, the average potassium content in the solid mix coming down to the hearth
could be as high as 7 pct. 相似文献
143.
The authors investigated subgroup differences on a multiple-choice and constructed-response test of scholastic achievement in a sample of 197 African American and 258 White test takers. Although both groups had lower mean scores on the constructed-response test, the results showed a 39% reduction in subgroup differences compared with the multiple-choice test. The results demonstrate that the lower subgroup differences were explained by more favorable test perceptions for African Americans on the constructed-response test. In addition, the two test formats displayed comparable levels of criterion-related validity. The results suggest that the constructed-response test format may be a viable alternative to the traditional multiple-choice test format in efforts to simultaneously use valid predictors of performance and minimize subgroup differences in high-stakes testing. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
144.
Scalf Paige E.; Banich Marie T.; Kramer Arthur F.; Narechania Kunjan; Simon Clarissa D. 《Canadian Metallurgical Quarterly》2007,33(2):298
Recent data have shown that parallel processing by the cerebral hemispheres can expand the capacity of visual working memory for spatial locations (J. F. Delvenne, 2005) and attentional tracking (G. A. Alvarez & P. Cavanagh, 2005). Evidence that parallel processing by the cerebral hemispheres can improve item identification has remained elusive. The authors used a novel variant of the attentional blink paradigm to show that the attentional blink is reduced if targets are divided between the hemispheres rather than directed to a single hemisphere. Parallel processing by the cerebral hemispheres can thus expand the capacity of processes involved in item identification. The authors also show that prior engagement of the attentional system may compromise the processing of items directed to the right visual field. This pseudoextinction may explain the failures of previous attempts to demonstrate that parallel processing can improve item identification (J. F. Delvenne, 2005; S. J. Luck, S. A. Hillyard, G. R. Mangun, & M. S. Gazzaniga, 1989). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
145.
AJ Kudla NC Jones RS Rosenthal K Arthur KL Clase BB Olwin 《Canadian Metallurgical Quarterly》1998,142(1):241-250
STUDY OBJECTIVES: The aims of this study were: to evaluate the performance of a novel arterial biopsy catheter in obtaining pulmonary endovascular samples in hypertensive dogs; to compare the results of pulmonary endoarterial biopsy in hypertensive vs normotensive dogs; and to assess the histologic changes in the hypertensive model. DESIGN AND INTERVENTIONS: Thirty-four dogs (27 with normal pulmonary arterial pressures and seven with pulmonary hypertension) were catheterized through an external jugular vein to obtain endovascular biopsy samples from distal pulmonary arteries 2 to 3 mm in luminal diameter. To induce pulmonary hypertension, seven dogs were given repeated infusions of 0.6- to 0.9-mm ceramic microspheres into the superior vena cava. Endoarterial samples were obtained at pulmonary systolic arterial pressures ranging from 10 to 110 mm Hg. MEASUREMENTS AND RESULTS: Sixty-two biopsy catheterization procedures were performed in the 34 dogs. After 12 initial procedures of technique refinement, endoarterial samples were obtained in each of the last 50 procedures (21 in normotensive dogs and 29 in hypertensive dogs). The average number of endovascular biopsy samples retrieved was 7.1 (range, 2 to 12) from a mean of 8.6 (range, 2 to 15) biopsy attempts per catheterization (success rate=83%). The average biopsy piece measured 1.13 mm in length, 0.33 mm in depth, and up to 1.0 mm in width. The biopsy success rates and endoarterial sample sizes were similar in normotensive and hypertensive dogs. Smooth muscle cells and endothelial cells were grown from the biopsy samples. There were no significant procedural complications, except for one self-limited hemorrhage. Histologically, samples obtained from dogs with pulmonary hypertension showed characteristic changes when compared with biopsies from normotensive dogs. CONCLUSION: This new endoarterial biopsy catheter was safe and effective when used to obtain pulmonary endoarterial samples in dogs with normal and experimentally elevated pulmonary arterial pressures. The quality and quantity of the biopsy samples allowed identification of pathologic changes. 相似文献
146.
147.
H Christou A Yoshida V Arthur T Morita S Kourembanas 《Canadian Metallurgical Quarterly》1998,18(6):768-776
Vascular endothelial growth factor (VEGF) is a potent mitogenic and permeability factor targeting predominantly endothelial cells. At least two tyrosine kinase receptors, Flk-1 and Flt-1, mediate its action and are mostly expressed by endothelial cells. VEGF and VEGF receptor expression are upregulated by hypoxia in vivo and the role of VEGF in hypoxia-induced angiogenesis has been extensively studied in a variety of disease entities. Although VEGF and its receptors are abundantly expressed in the lung, their role in hypoxic pulmonary hypertension and the accompanying vascular remodeling are incompletely understood. We report in this in vivo study that hypoxia increases mRNA levels for both VEGF and Flk-1 in the rat lung. The kinetics of the hypoxic response differ between receptor and ligand: Flk-1 mRNA showed a biphasic response to hypoxia with a significant, but transient, rise in mRNA levels observed after 9-15 h of hypoxic exposure and the highest levels noted after 3 wk. In contrast, VEGF mRNA levels did not show a significant increase with acute hypoxia, but increased progressively after 1-3 wk of hypoxia. By in situ hybridization, VEGF mRNA was localized predominantly in alveolar epithelial cells with increased signal in the lungs of hypoxic animals compared with controls. Immunohistochemical staining with anti-VEGF antibodies localized VEGF peptide throughout the lung parenchyma and was increased in hypoxic compared with normoxic animals. Furthermore, hypoxic animals had significantly higher circulating VEGF concentrations compared with normoxic controls. Lung vascular permeability as measured by extravasation of Evans Blue dye was not significantly different between normoxic and hypoxic animals, although a tendency for increased permeability was seen in the hypoxic animals. These findings suggest a possible role for VEGF in the pulmonary response to hypoxia. 相似文献
148.
Four experiments were conducted to examine whether attentional set affects the ability of visual transients (onsets and offsets) to capture attention. In the experiments, visual search for an identity-defined target was conducted. In the first 3 experiments, the target display either onset entirely or was revealed by offsetting camouflaging line segments to reveal letters. Prior to the target display, there was a noninformative cue, either an onset or an offset, at one of the potential target locations. Cues that shared the same transient feature as the target display captured attention. The lack of predictable target transients led to attentional capture by all forms of transients. The final experiments with luminance changes without offsets or onsets showed attentional capture when the luminance changes were large. The results suggest that attentional set can be broadly or narrowly tuned to detect changes in luminance. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
149.
Objective: To investigate the concurrent validity of the Cognitive Test for the Blind (CTB) as an intellectual assessment for the visually impaired or blind (VI/B) population. The ecological validity of the CTB was also examined. Design: Correlational analyses. Participants: Two hundred ninety-two persons with visual impairment or blindness. Main Outcome Measure: The CTB Verbal section, the Wechsler Adult Intelligence Scale-Revised (WAIS-R) Verbal section, and the Survey of Functional Adaptive Behavior. Results: A correlation of .72 was obtained between the CTB and the WAIS-R. The correlations of the CTB Total and WAIS-R Verbal sections with overall adaptive functioning were .50 and .47, respectively. Conclusions: The CTB offers valid assessment of intellectual functioning for persons with visual impairment or blindness, as well as other useful information that may aid in the treatment planning process. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
150.
Patients with frontal lobe lesions and control participants were assessed on 2 tests of semantic knowledge. In the triadic comparison task, participants were shown all possible triplets of 12 animal names and judged which 2 of each triplet were most alike. In the ordered similarity task, participants rank ordered animals in terms of their similarity to a target animal. For both tasks, semantic structure-- derived from multidimensional scaling techniques-- revealed similar representations in patients with frontal lobe lesions and control participants. Additional pathfinder analyses also produced networks that did not differ between groups. These patients exhibited intact semantic knowledge despite deficits on tests of free recall and verbal fluency that involved the same semantic category and exemplars. Thus, intact representation of semantic knowledge in frontal patients stands in contrast to their marked deficits in strategic retrieval of semantic knowledge. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献