全文获取类型
收费全文 | 2083篇 |
免费 | 60篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 1篇 |
综合类 | 4篇 |
化学工业 | 29篇 |
金属工艺 | 10篇 |
机械仪表 | 6篇 |
建筑科学 | 7篇 |
矿业工程 | 2篇 |
能源动力 | 5篇 |
轻工业 | 14篇 |
水利工程 | 53篇 |
无线电 | 23篇 |
一般工业技术 | 30篇 |
冶金工业 | 1904篇 |
原子能技术 | 2篇 |
自动化技术 | 57篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2018年 | 15篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 27篇 |
2014年 | 18篇 |
2013年 | 22篇 |
2012年 | 5篇 |
2011年 | 7篇 |
2010年 | 8篇 |
2009年 | 8篇 |
2008年 | 4篇 |
2007年 | 6篇 |
2006年 | 10篇 |
2005年 | 17篇 |
2004年 | 7篇 |
2003年 | 9篇 |
2002年 | 17篇 |
2001年 | 11篇 |
2000年 | 3篇 |
1999年 | 58篇 |
1998年 | 614篇 |
1997年 | 375篇 |
1996年 | 220篇 |
1995年 | 109篇 |
1994年 | 89篇 |
1993年 | 101篇 |
1992年 | 15篇 |
1991年 | 23篇 |
1990年 | 16篇 |
1989年 | 27篇 |
1988年 | 30篇 |
1987年 | 21篇 |
1986年 | 16篇 |
1985年 | 15篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 15篇 |
1978年 | 2篇 |
1977年 | 45篇 |
1976年 | 99篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1955年 | 4篇 |
排序方式: 共有2147条查询结果,搜索用时 10 毫秒
31.
32.
33.
Alternating treatments designs were used to compare the effects of trial repetition (one response within five trials per word) versus response repetition (five response repetitions within one trial per word) on sight-word acquisition for 3 elementary students diagnosed with specific learning disabilities in reading. Although both interventions occasioned the same number of accurate responses per word during training, the trial-repetition condition, which involved complete antecedent-response-feedback sequences, resulted in more words mastered for all 3 students. 相似文献
34.
Induction of the mitochondrial permeability transition in vitro is well-characterized and widely implicated in the mechanism of oxidant-induced cell death. Despite an abundance of in vitro evidence, implication of mitochondrial dysfunction in the mechanism of chemical toxicity in vivo awaits demonstration of the induction of the mitochondrial permeability transition in tissues from intoxicated animals. Menadione (2-methyl-1,4-naphthoquinone), an agent known to induce the permeability transition in isolated liver mitochondrial in vitro, was administered as a single bolus to adult male rats, and hepatic mitochondria were isolated 24 h later. Mitochondria from menadione-treated rats exhibited an increased sensitivity to calcium-induced inhibition of state 3 respiration and loss of respiratory control, as well as a greater sensitivity to calcium-induced calcium release that was inhibited by cyclosporine A. Associated with this was the depolarization of membrane potential and swelling of mitochondria from menadione-treated animals, but not control animals. Both the calcium-dependent depolarization and swelling of mitochondria from menadione-treated rats were inhibited by adding either cyclosporine A or ruthenium red. The results are consistent with the induction of the mitochondrial permeability transition and provide the first evidence for the manifestation of an increased sensitivity to this response as a result of chemical exposure in vivo. 相似文献
35.
Current microarray databases use different terminologies and structures and thereby limit the sharing of data and collating of results between laboratories. Consequently, an effective integrated microarray data model is required. One important process to develop such an integrated database is schema matching. In this paper, we propose an effective schema matching approach called MDSM, to syntactically and semantically map attributes of different microarray schemas. The contribution from this work will be used later to create microarray global schemas. Since microarray data is complex, we use microarray ontology to improve the measuring accuracy of the similarity between attributes. The similarity relations can be represented as weighted bipartite graphs. We determine the best schema matching by computing the optimal matching in a bipartite graph using the Hungarian optimisation method. Experimental results show that our schema matching approach is effective and flexible to use in different kinds of database models such as; database schema, XML schema, and web site map. Finally, a case study on an existing public microarray schema is carried out using the proposed method. 相似文献
36.
OBJECTIVE: To identify the individual, dyad, and family variables that influence young women's perceptions of risk for sexually transmitted diseases (STDs), including human immunodeficiency virus (HIV). DESIGN: Cross-sectional telephone survey using forced-choice questioning. Data were analyzed using first-order correlations and logistic regression. SETTING: Participants were recruited from a mid-Atlantic study of young adults and from volunteers at a mid-Atlantic university and surrounding community. PARTICIPANTS: A convenience sample of 93 sexually active, unmarried, heterosexual women, ages 17-26 years. The majority of the study sample was white. MAIN OUTCOME MEASURE: Respondents were asked to estimate their own level of risk for STDs, including HIV, using the responses no, low, moderate, and high risk. Responses were later recoded into no risk versus some risk. RESULTS: Communication with parents about sexual risk decreased the odds that women would see themselves as being at no risk. Consistent condom use, relationship satisfaction, and perceiving the partner as no risk increased the odds that women would believe they were at no risk. CONCLUSIONS: Nurses can incorporate these and other study findings into the design of sexual risk reduction programs. Programs that enhance parent-teen communication about sexual risks and assist young women to examine their perceptions of their partners may be more effective than programs that provide information only. 相似文献
37.
The recently described gastrointestinal glutathione peroxidase (GI-GPx) is the fourth member of the family of the selenoenzymes glutathione peroxidases (GPx). In contrast to the more uniform distribution of, for example, the classical glutathione peroxidase (cGPx), it is expressed exclusively in the gastrointestinal tract and has, therefore, been suggested to function as a primary barrier against alimentary hydroperoxides. In order to get an idea of its relative importance we investigated its position in the hierarchy of selenoprotein expression. The selenium-dependent expression of GI-GPx was analyzed in comparison with that of other GPx types at the level of mRNA and protein in HepG2 and CaCo-2 cells. Furthermore, the selenocysteine insertion sequence (SECIS) efficiencies of GI-GPx, phospholipid hydroperoxide glutathione peroxidase (PHGPx) and cGPx in response to selenium were determined by a reporter-gene assay in human hepatoma cells and baby hamster kidney cells. GI-GPx mRNA levels increased during selenium deficiency, whereas cGPx mRNA levels decreased and PHGPx mRNA levels remained almost unaffected. In cells grown in selenium-poor media, all GPx-types were low in both activity and immunochemical reactivity. Upon selenium repletion immunoreactive GI-GPx protein reached a plateau after 10 h, whereas cGPx started to be expressed at 24 h and did not reach its maximum level before 3 days. SECIS efficiencies decreased in the order PHGPx > cGPx > GI-GPx. The augmentation of SECIS efficiencies by selenium was highest for cGPx and intermediate for PHGPx, whereas it was marginal for GI-GPx. The high mRNA stability under selenium restriction, the speed of biosynthesis upon selenium repletion and the marginal effect of selenium on the SECIS efficiency indicate that of the GPx isotypes, GI-GPx ranks highest in the hierarchy of selenoproteins and point to a vital role of GI-GPx in the gastrointestinal tract. 相似文献
38.
Hung-Sung Lin Chun-Ming Chen Kuo-Hsiung Chen Afung Wang CH Chao 《Microelectronics Reliability》2007,47(9-11):1604
The difficulties in identifying the precise defect location and real leakage path is increasing as the integrated circuit design and process have become more and more complicated in and below deep sub-micron technology node. Most of the defects causing chip leakage are detectable with only one of the failure analysis (FA) tools such as liquid crystal detection (LCD) or photon emission microscope (PEM). However, due to process marginalities some defects are often not detectable with only one FA tool [Hung-Sung Lin, Wen-Tung Chang, Chun-Lin Chen, Tsui-Hua Huang, Vivian Chiang, Chun-Ming Chen. A study of asymmetrical behaviour in advanced nano SRAM devices. In: 13th IPFA proceedings; July 2006. p. 63–6; Kruseman Bram, Majhi Ananta, Hora Camelia, Eichenberger Stefan, Meirlevede Johan. Systematic defects in deep sub-micron technologies. ITC international test conference, 2004. p. 290–9.]. This paper present an example of an abnormal power consumption process related defect which could only be detected with more advanced FA tools. 相似文献
39.
In a macerated skull from a 20 year-old body we found, bilaterally, a variation corresponding to the nasoturbinal concha of quadrupeds. According to the data in the literature, the remnants of this concha may be named either "agger nasi" or "agger cell". These formations may impede the approach to the frontal sinus or the lacrimal sac, respectively. A nasoturbinal concha is extremely rare in adults and should be considered when approaching the frontal sinus. 相似文献
40.
PJ Heins KA Karpinia JW Maruniak JE Moorhead CH Gibbs 《Canadian Metallurgical Quarterly》1998,69(7):812-818
Probing pain threshold (PPT) assessments were conducted in the facial and oral sulci of maxillary central incisors and first molars of 10 periodontally healthy adults. All subjects were systemically healthy, free of pain, and reported no current medication usage. A computer-linked electronic probe, modified to deliver steadily increasing forces up to 200 grams, was used to collect the data. The system contained a subject operated "off-switch" which, upon activation, signaled the computer to record the subject's PPT. Assessments of each subject's PPTs were conducted on 3 separate occasions at 7-day intervals. Results indicated that the facial sulci of the incisors were the most pain sensitive. They displayed a mean PPT of 50.9 +/- 26.6 grams. The oral sulci of the incisors exhibited a mean PPT of 76.5 +/- 45.2 grams. Facial and oral sulci of the molars evidenced mean PPT values of 102.6 +/- 52.1 grams and 113.5 +/- 51.3 grams, respectively. These data suggest that sulci associated with incisor teeth are nearly twice as pain sensitive as sulci associated with molar teeth. In addition, facial sulci are significantly more pain sensitive than oral sulci. Data did not indicate a visit effect nor a side-of-mouth effect on PPT values. 相似文献