全文获取类型
收费全文 | 685篇 |
免费 | 7篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 9篇 |
综合类 | 2篇 |
化学工业 | 42篇 |
金属工艺 | 5篇 |
机械仪表 | 6篇 |
建筑科学 | 16篇 |
能源动力 | 12篇 |
轻工业 | 70篇 |
水利工程 | 4篇 |
无线电 | 11篇 |
一般工业技术 | 27篇 |
冶金工业 | 457篇 |
原子能技术 | 1篇 |
自动化技术 | 32篇 |
出版年
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 3篇 |
2018年 | 8篇 |
2016年 | 6篇 |
2015年 | 3篇 |
2014年 | 5篇 |
2013年 | 19篇 |
2012年 | 13篇 |
2011年 | 8篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 16篇 |
2007年 | 18篇 |
2006年 | 7篇 |
2005年 | 11篇 |
2004年 | 13篇 |
2003年 | 8篇 |
2002年 | 11篇 |
2001年 | 3篇 |
2000年 | 8篇 |
1999年 | 14篇 |
1998年 | 141篇 |
1997年 | 78篇 |
1996年 | 66篇 |
1995年 | 32篇 |
1994年 | 23篇 |
1993年 | 22篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 9篇 |
1976年 | 28篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1968年 | 2篇 |
1966年 | 3篇 |
排序方式: 共有694条查询结果,搜索用时 234 毫秒
1.
When Teachers' and Parents' Values Differ: Teachers' Ratings of Academic Competence in Children From Low-Income Families. 总被引:1,自引:0,他引:1
The authors examined predictors of teachers' ratings of academic competence of 105 kindergarten children from low-income families. Teachers rated target children's expected competence in literacy and math and completed questions about their perceptions of congruence-dissonance between themselves and the child's parents regarding education-related values. Independent examiners assessed children's literacy and math skills. Teachers' instructional styles were observed and rated along dimensions of curriculum-centered and student-centered practices. Controlling for children's skills and socioeconomic status, teachers rated children as less competent when they perceived value differences with parents. These patterns were stronger for teachers who exhibited curriculum-centered, rather than student-centered, practices. The findings suggest a mechanism by which some children from low-income families enter a path of diminished expectations. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
2.
3.
INTRODUCTIONS: Cochlear implants are used for the rehabilitation of bilaterally deaf patients. Due to the improvements in speech processing they might be also useful for patients with residual hearing and some speech understanding. METHODS: Pre- and postoperative speech understanding scores in 26 patients receiving implants were evaluated in a retrospective study. RESULTS: The preoperative pure-tone threshold in the implanted ear was between 80 and 115 dB in the frequency range of 500 to 2000 Hz. On the contralateral side the mean threshold was 10 dB better. The mean score for the number test was 11.3%, for the monosyllables below 5%. Postoperatively speech understanding improved significantly up to 97% for numbers and 48% for monosyllables (tested with the Freiburger Speech Test). Cochlear implantation also benefits patients with residual hearing and some speech understanding with hearing aids under optimum conditions. The speech understanding scores must be below certain limits. General selection criteria cannot yet be specified. The individual decision must be based upon several criteria, especially the speech understanding scores in quiet and noise under optimum conditions. A prospective study is needed to develop generally applicable criteria. 相似文献
4.
Cytoplasmic aggregation is an early resistance-associated event that is observed in potato tissues either after penetration of an incompatible race of Phytophthora infestans, the potato late blight fungus, or after treatment with hyphal wall components (HWC) prepared from P. infestans. In potato cells in suspension culture, the number of cells with cytoplasmic aggregation increased upon treatment with HWC, but such an increase was suppressed by treatment with cytochalasin D prior to treatment with HWC. This result suggested that cytoplasmic aggregation in cultured potato cells might be connected with the association of actin filaments. To identify the molecular basis of cytoplasmic aggregation, we purified actin and actin-related proteins by affinity chromatography on a column of immobilized DNase I from cultured potato cells and isolated proteins of 43 kDa, 32 kDa and 22 kDa. Analysis of the amino-terminal amino acid sequences indicated that the 43 kDa, 32 kDa and 22 kDa proteins were potato actin, basic chitinase and osmotin-like protein, respectively. This conclusion was supported by the results of Western blotting analysis of the 43 kDa and 32 kDa proteins with antibodies against actin and basic chitinase. Binding analysis with actin coupled to actin-specific antibodies and biotinylated actin suggested that the 32 kDa and 22 kDa proteins had actin-binding activity. In addition, examination of biomolecular interactions using an optical biosensor confirmed the binding of chitinase to actin. These results imply the possibility that basic chitinase and osmotin-like protein might be involved in cytoplasmic aggregation, hereby participating. In the potato cell's defense against attack by pathogen. 相似文献
5.
A theoretical model is presented by which a true expression of pregnancy rate resulting from stimulated cycles can be calculated. This includes the transfer of both fresh and cryopreserved embryos. It is concluded that the total reproductive potential of a single cycle of stimulation can only be evaluated by including pregnancies arising from all fresh and frozen embryo transfers resulting from that cycle. 相似文献
6.
Scanning electron microscopy was used to study the effect of cyclophosphamide (Cy) on molar development in 18 Sprague-Dawley rats from 15 to 48 days of age after birth. Doses of 30 mg/kg body weight of Cy dissolved in 1 ml 0.9% NaCl were given to the rats at 10 and 13 days of age. Eighteen control rats had injections of 1 ml 0.9% NaCl at the same ages. The most obvious changes in the experimental teeth were found in the developing roots of the first and second molars and in both the crown and roots of the third molar. The roots of the first and second molars were short and showed apical closure in the experimental rats. In addition to the disturbances in crown and root formation, the third molars were also significantly reduced in total size as compared with the third molars in the control rats. 相似文献
7.
J Kongerud KI Myhre OA Hauge H Kjuus E Melbostad TB Aasen 《Canadian Metallurgical Quarterly》1996,116(6):759-763
The Norwegian Societies of Thoracic Medicine and Occupational Medicine established a working group to standardise diagnostic procedures and evaluation of work-related respiratory disorders. In cases of suspected work-related diseases the physician may be asked by the National Insurance Administration or an insurance company to make a statement which will be one of the documents used to decide the patient's right to compensation benefit. We discuss the role of the physician as an independent expert. This is different from his role as clinician. The statement should include a balanced presentation of information from different sources, including health and occupational history, and the employer's information about the work environment (quantitative and qualitative exposure data). The statement must also include the results of a clinical examination and an assessment of functional status based on objective tests. The paper contains recommendations for evaluation of permanent impairment in light of the present Norwegian laws and regulations. 相似文献
8.
9.
The use of damage concepts in component life assessment 总被引:1,自引:0,他引:1
R. K. Penny 《International Journal of Pressure Vessels and Piping》1996,66(1-3):263-280
The damage concepts introduced by Kachanov several decades ago have rarely been used in practical application, in spite of their simplicity. Because there are no alternatives of note to Kachanov's ideas, this paper re-examines the basic premises involved in damage concepts, with a view to deriving results which will be credible to those responsible for component life management. This has led to possible schemes for economical data acquisition as well as to simplified life assessment procedures which are described in the paper.
For metallurgically stable materials, long term creep strain and rupture data can be described simply in terms of two material constants and the results from short term tests for initial creep rates and strength. These data are all bounded by a single term β which depends on the stress level in relation to the short term strength. Examples are given for stiffness and strength reductions caused by damage. A simple relationship between current strain rate and remaining life should be of use in routine plant measurements. 相似文献
10.
KI Schwendner AE Mikesky WS Holt M Peacock DB Burr 《Canadian Metallurgical Quarterly》1997,52(3):M155-M160
BACKGROUND: Significant morbidity and mortality are associated with falls in older adults. We tested the hypothesis that older women with a history of falls demonstrate decreased muscle endurance and longer recovery times following fatiguing exercise. METHODS: We evaluated dynamic endurance and recoverability of the quadriceps femoris of 29 young women (YW) (M age = 21.7), 26 older women with a history of falls (FA) (M age = 73.3), and 27 older women with no history of falls (NF) (M age = 71.2) using an isokinetic dynamometer. Subjects performed repeated maximal concentric knee extensions until the force output of two consecutive repetitions fell below 50% of their maximal voluntary contraction (MVC). Recovery was defined as the time required for the return of force output > or = 80% MVC for 2 consecutive repetitions, within a set consisting of 3 maximal contractions. One minute rest was allowed between sets. We collected electromyographic (EMG) data from the quadriceps during all testing to evaluate spectral shifts. RESULTS: ANOVA with a post-hoc Bonferroni-Dunn test revealed time to fatigue was significantly faster in FA than YW (p < .02) and in FA than NF (p < .05), but not different between YW and NF. Time to recovery was significantly slower in FA than YW (p = .01), but not different between YW and NF, or between FA and NF, EMG median frequency power shift (from the beginning to the end of the test) was significantly less in FA (p < .001) than either YW (p < .002) or NF (p < .05). CONCLUSIONS: Older women with a history of falls demonstrate decreased muscular endurance compared to YW and NF, and increased time to recover from fatiguing exercise when compared to young women. 相似文献