全文获取类型
收费全文 | 688篇 |
免费 | 2篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 2篇 |
综合类 | 2篇 |
化学工业 | 34篇 |
金属工艺 | 8篇 |
机械仪表 | 8篇 |
建筑科学 | 10篇 |
能源动力 | 3篇 |
轻工业 | 13篇 |
水利工程 | 1篇 |
无线电 | 16篇 |
一般工业技术 | 31篇 |
冶金工业 | 544篇 |
原子能技术 | 1篇 |
自动化技术 | 19篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2018年 | 2篇 |
2016年 | 4篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 3篇 |
2011年 | 13篇 |
2010年 | 12篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 8篇 |
2006年 | 5篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 10篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 17篇 |
1998年 | 173篇 |
1997年 | 102篇 |
1996年 | 63篇 |
1995年 | 22篇 |
1994年 | 25篇 |
1993年 | 32篇 |
1992年 | 6篇 |
1991年 | 14篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1978年 | 3篇 |
1977年 | 11篇 |
1976年 | 29篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1970年 | 2篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有692条查询结果,搜索用时 15 毫秒
1.
Sensory activity mediates regulation of tyrosine hydroxylase (TH), the first enzyme in the dopamine biosynthetic pathway, in the rodent olfactory bulb. The current studies established for the first time primary cultures of neonatal mouse olfactory bulb expressing TH and tested whether L-type calcium channels mediate the activity-dependent regulation of the dopamine phenotype. After 1 d in vitro (DIV), a small population of TH-immunostained neurons that lacked extensive processes could be demonstrated. After an additional 2 DIV in serum-free medium, the number of TH neurons had doubled, and they exhibited long interdigitating processes. Membrane depolarization for 48 hr with 50 mM KCl produced a further 2.4-fold increase in the number of TH-immunoreactive neurons compared with control cultures. Increased TH neuron number required at least 36 hr of exposure to KCl. Forskolin, which increases intracellular cAMP levels, induced a 1.5- to 1.6-fold increase in the number of TH-immunostained neurons. Combined treatment with KCl and forskolin was not additive. Nifedipine, an L-type calcium channel blocker, completely prevented the depolarization-mediated increase in TH expression but did not block the response to forskolin. Treatment with Bay K8644, an L-type calcium channel agonist, also significantly increased the number of TH-expressing neurons. Depolarization also induced alterations in neuritic outgrowth, resulting in a stellate versus an elongate morphology that, in contrast, was not prevented by nifedipine. These results are the first demonstration that in vitro, as in vivo, depolarization increases TH expression in olfactory bulb and that L-type calcium channels mediate this activity-dependent regulation of the dopamine phenotype. 相似文献
2.
3.
4.
OBJECTIVE: To evaluate the discrepancy index between the clinical and histological diagnosis and the prevalence of epithelial dysplasia and carcinoma in 45 patients with potentially malignant epithelial oral lesions (PMEL). PATIENTS AND METHODS: We submitted 45 patients with PMEL to clinical examination and obtained a biopsy from each. The results of histological diagnosis were compared to the clinical diagnosis. RESULTS: Clinical diagnosis showed that the most common PMEL was leukoplakia followed by lichen planus and by actinic cheilitis associated with leukoplakia. The most common site was the buccal mucosa. Histological diagnosis revealed that 46.7% of the PMEL were lichen planus. The discrepancy index between clinical and histological diagnosis was 24.4%. The higher discrepancy index occurred among leukoplakias. The prevalence of epithelial dysplasia and carcinoma was 17.8%. CONCLUSIONS: We conclude that all PMEL should be submitted to a microscopic analysis because the discrepancy between clinical and histological diagnosis was present in a quarter of these lesions. Otherwise, the epithelial dysplasia and carcinoma were more frequent in the leukoplakias. 相似文献
5.
ME Goldberg BW Lex NK Mello JH Mendelson TA Bower 《Canadian Metallurgical Quarterly》1996,66(2):228-238
Research on achievement goal orientation in sport has relied primarily on traditional statistical methodology to examine group mean differences. Unfortunately, examination of the measurement model is generally ignored prior to means testing. This study reports an application of structural equation modeling (SEM) in testing measurement invariance and latent mean structure of the Task and Ego Orientation in Sport Questionnaire (TEOSQ; Duda & Nicholls, 1989) using male and female college students. A confirmatory factor analysis for testing invariance revealed invariant measurement properties and factor structures across gender, indicating that task and ego orientation are similarly conceptualized by male and female students. Subsequent testing of latent mean structures, however, showed significant gender differences with respect to ego orientation, but no difference in task orientation. The SEM procedures used in the present study demonstrate additional construct validity and internal consistency reliability for the TEOSQ and, by confirming its factor structure, provide a sound psychometric basis for its continued use in substantive studies focusing on the comparison of achievement goal orientation across gender. 相似文献
6.
7.
8.
9.
10.
This study evaluated 36 cancer patients who were enrolled in a randomized, double-blind, placebo-controlled trial conducted over a 4-week period to evaluate the efficacy of alprazolam in the treatment of anxiety associated with cancer. Hamilton Anxiety Scale scores declined significantly between baseline and the end of the first week of the study in both treatment groups. There was no significant difference in response between the patients receiving alprazolam and placebo. Similar results were obtained from other instruments. These results suggest that nondrug factors or spontaneous improvement may play a more important role than pharmacotherapy in the treatment of anxiety associated with cancer. 相似文献