全文获取类型
收费全文 | 279798篇 |
免费 | 3089篇 |
国内免费 | 1307篇 |
专业分类
电工技术 | 4828篇 |
综合类 | 521篇 |
化学工业 | 40716篇 |
金属工艺 | 11184篇 |
机械仪表 | 8432篇 |
建筑科学 | 6451篇 |
矿业工程 | 1576篇 |
能源动力 | 6991篇 |
轻工业 | 22604篇 |
水利工程 | 3040篇 |
石油天然气 | 5784篇 |
武器工业 | 43篇 |
无线电 | 33593篇 |
一般工业技术 | 56720篇 |
冶金工业 | 51205篇 |
原子能技术 | 7507篇 |
自动化技术 | 22999篇 |
出版年
2021年 | 2192篇 |
2019年 | 2088篇 |
2018年 | 3600篇 |
2017年 | 3689篇 |
2016年 | 3937篇 |
2015年 | 2515篇 |
2014年 | 4379篇 |
2013年 | 12015篇 |
2012年 | 7121篇 |
2011年 | 9779篇 |
2010年 | 7570篇 |
2009年 | 8793篇 |
2008年 | 9144篇 |
2007年 | 9199篇 |
2006年 | 7861篇 |
2005年 | 7287篇 |
2004年 | 7232篇 |
2003年 | 7014篇 |
2002年 | 6743篇 |
2001年 | 6884篇 |
2000年 | 6512篇 |
1999年 | 6797篇 |
1998年 | 16402篇 |
1997年 | 11655篇 |
1996年 | 8976篇 |
1995年 | 6883篇 |
1994年 | 6049篇 |
1993年 | 6081篇 |
1992年 | 4414篇 |
1991年 | 4193篇 |
1990年 | 4090篇 |
1989年 | 4078篇 |
1988年 | 3784篇 |
1987年 | 3402篇 |
1986年 | 3408篇 |
1985年 | 3754篇 |
1984年 | 3475篇 |
1983年 | 3226篇 |
1982年 | 3038篇 |
1981年 | 3049篇 |
1980年 | 3037篇 |
1979年 | 2843篇 |
1978年 | 2876篇 |
1977年 | 3155篇 |
1976年 | 4135篇 |
1975年 | 2432篇 |
1974年 | 2390篇 |
1973年 | 2411篇 |
1972年 | 2026篇 |
1971年 | 1786篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
M. Landí n M. P. Gonz lez C. Souto A. Concheiro J. L. G mez-Amoza R. Martí nez-Pacheco 《Drug development and industrial pharmacy》1993,19(10):1211-1220
In tests of direct-compression hydrochlorothiazide tablets prepared with either of two varieties of microcrystalline cellulose (Avicel PH 101 and Avicel PH 102), PH 102 tablets had better mechanical properties (owing to lower compressibility of mixtures and greater Interparticle bonding), while PH 101 tablets released the active principle faster. These differences are related to observed differences In tablet micropore structure. 相似文献
992.
993.
994.
995.
One hundred and ninety-five teeth in 35 patients with periodontitis who had received both endodontic and periodontal treatment were evaluated 9 years after endodontic treatment and 8 years after periodontal treatment. Some 91.4% of cases were well maintained and 8.6% showed a deterioration in their periodontal condition. Twelve of the 195 teeth with endodontic treatment were lost, eight for periodontal reasons, three as a result of fracture and one because of caries, and the periodontal condition of 10 teeth had worsened. An apical lesion formed on one tooth. The results indicate that the risk of endodontic failure in this group of 195 teeth is very low, and that there is little risk of tooth loss for periodontal reasons, provided that the patients receive supportive periodontal treatment. 相似文献
996.
This article presents recent techniques in the field of dual-polarization printed antennas for designing shielded radiating structures with high-quality performances in terms of cross-polarization level and input-port isolation. The use of gridded patches provides a natural solution to filtering surface currents and is of key importance in limiting inter-element coupling in arrays. Experimental results obtained on various designs are presented 相似文献
997.
G Bottino G Antognozzi R Degrandi C Augeri G Bogliolo P Zoccali 《Canadian Metallurgical Quarterly》1995,17(2-3):63-66
Blood concentration of endogenous beta-endorphines can change during the clinical evolution of chronic bronchopneumopathies. The authors assessed the beta-endorphine concentrations in the pulmonary arterial and systemic arterial blood in 8 asthmatic patients during a symptom-free period and after methacholine-induced bronchospasm. The beta-endorphine analysis was performed in duplicate dor each sample, by means of a RIA assay. There is not difference in the systemic arterial blood concentration of beta-endorphines between asthmatic patients and normal subjects. Furthermore, there is no change in the beta-endorphine blood concentration during the passage through the pulmonary tissue after methacoline-induced bronchospasm. 相似文献
998.
Neuronal somata in the rat kidney are very often part of ganglionated plexus and contain nitric oxide synthase (NOS). Examining serial 100 microns slices of whole kidneys, we identified three subpopulations of neuronal somata by: (a) staining for NADPH-diaphorase (NADPH-d) histochemistry followed by the demonstration of dopamine beta-hydroxylase (DBH) by immunoperoxidase, and (b) staining for DBH by immunofluorescence followed by the demonstration of NADPH-d histochemical activity. The largest subpopulation of neuronal somata displayed both DBH immunoreactivity and NADPH-d histochemical activity. The second largest group of somata showed NADPH-d activity only. A small group of neuronal somata showed only DBH immunoreactivity. The presence of catecholaminergic characteristics in NOS-containing neuronal somata is unusual and raises the question as to their origin. Their heterogeneity suggests different functions for the different subpopulations. 相似文献
999.
Previously established dose-response curves indicated that modafinil 20-40 mg/kg i.p. elicited in mice an obvious stimulation of locomotor activity roughly similar to that induced by (+)amphetamine 2-4 mg/kg. The effects of various agents modifying dopamine transmission were compared on the locomotor response to both drugs. The preferential D2 dopamine receptor antagonist haloperidol 37.5-150 micrograms/kg i.p. suppressed the stimulant effect of (+)amphetamine in a dose dependent manner, but not that of modafinil. The D1 dopamine receptor antagonist SCH 23390 (7.5-30 micrograms/kg s.c.) reversed the (+)amphetamine but not the modafinil induced hyperactivity. The tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (200 mg/kg) suppressed the hyperactivity induced by 4 mg/kg dexamphetamine but not that induced by 20 mg/kg modafinil. Associating L-DOPA 150 mg/kg and benserazide 37.5 mg/kg with (+)amphetamine 2 mg/kg resulted in stereotyped climbing behavior, that was not observed with modafinil 10-80 mg/kg. The profound akinesia induced by reserpine (4 mg/kg s.c.; 5 h before testing) was reversed by (+)amphetamine 2 mg/kg but not by modafinil 40 mg/kg. Finally, on synaptosomes prepared from mouse striata preloaded with [3H]dopamine, modafinil 10(-5) M did not increase the spontaneous [3H]dopamine release whereas (+)amphetamine, at the same concentration, doubled it. From all these differences between the two drugs, it is concluded that the mechanism underlying the modafinil induced stimulant locomotor effect differs completely from that of (+)amphetamine. 相似文献
1000.