全文获取类型
收费全文 | 250030篇 |
免费 | 1722篇 |
国内免费 | 272篇 |
专业分类
电工技术 | 4048篇 |
综合类 | 92篇 |
化学工业 | 40638篇 |
金属工艺 | 15172篇 |
机械仪表 | 10087篇 |
建筑科学 | 4201篇 |
矿业工程 | 3764篇 |
能源动力 | 3924篇 |
轻工业 | 9726篇 |
水利工程 | 4087篇 |
石油天然气 | 13015篇 |
武器工业 | 28篇 |
无线电 | 20268篇 |
一般工业技术 | 63073篇 |
冶金工业 | 32159篇 |
原子能技术 | 11147篇 |
自动化技术 | 16595篇 |
出版年
2021年 | 2832篇 |
2019年 | 2763篇 |
2018年 | 5464篇 |
2017年 | 5746篇 |
2016年 | 6080篇 |
2015年 | 3086篇 |
2014年 | 5369篇 |
2013年 | 10185篇 |
2012年 | 7400篇 |
2011年 | 9012篇 |
2010年 | 7353篇 |
2009年 | 8152篇 |
2008年 | 8222篇 |
2007年 | 7904篇 |
2006年 | 6391篇 |
2005年 | 5594篇 |
2004年 | 5512篇 |
2003年 | 5316篇 |
2002年 | 5160篇 |
2001年 | 4961篇 |
2000年 | 4949篇 |
1999年 | 4261篇 |
1998年 | 7181篇 |
1997年 | 5838篇 |
1996年 | 4426篇 |
1995年 | 3661篇 |
1994年 | 3426篇 |
1993年 | 3626篇 |
1992年 | 3214篇 |
1991年 | 3359篇 |
1990年 | 3481篇 |
1989年 | 3369篇 |
1988年 | 3267篇 |
1987年 | 3260篇 |
1986年 | 3156篇 |
1985年 | 3314篇 |
1984年 | 3253篇 |
1983年 | 3147篇 |
1982年 | 2993篇 |
1981年 | 3045篇 |
1980年 | 3071篇 |
1979年 | 3257篇 |
1978年 | 3490篇 |
1977年 | 3460篇 |
1976年 | 3911篇 |
1975年 | 3209篇 |
1974年 | 3293篇 |
1973年 | 3341篇 |
1972年 | 2987篇 |
1971年 | 2754篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
831.
Results are presented from a model (numerical) experiment performed to check the efficiency of three groups of direct data-analysis
algorithms to be used in satellite location of ground or ocean sources of radiation. The methodology behind the experiment
is also explained.
Translated from Izmeritel'naya Tekhnika, No. 12, pp. 40–44, December, 1996. 相似文献
832.
A generalized mathematical model of the interaction between hydrogen and structural defects in metals is analyzed. The temporal dependence of hydrogen permeation flow is examined for three typical cases. The approximations to the general equation for hydrogen permeation flow obtained enable one to determine the interaction from experimental data. The extreme values of permeation flow are analyzed. A method for determining the kinetic parameters of interaction for a given permeation flow is suggested. The conclusion is made that, within the framework of the generalized model, it is possible to establish the mechanism of hydrogen trapping.Dnepropetrovsk Institute of Chemical Engineering, Dnepropetrovsk. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 5, pp. 25–29, September–October, 1993. 相似文献
833.
Airborne scatterometers: investigating ocean backscatter under low and high-wind conditions 总被引:1,自引:0,他引:1
Carswell J.R. Carson S.C. McIntosh R.E. Li F.K. Neumann G. McLaughlin D.J. Wilkerson J.C. Black P.G. Nghiem S.V. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1994,82(12):1835-1860
Attempting to understand and predict weather on a local and global basis has challenged both the scientific and engineering communities. One key parameter in understanding the weather is the ocean surface wind vector because of its role in the energy exchange at the air-sea surface. scatterometers, radars that measure the reflectivity of a target offer a tool with which to remotely monitor these winds from tower-, aircraft-, and satellite-based platforms. This paper introduces three current airborne scatterometer systems, and presents data collected by these instruments under low-, moderate-, and high-wind conditions. The paper focuses on airborne scatterometers because of their ability to resolve submesoscale variations in wind fields. Discrepancies between existing theory and the observations are noted and the concerns in measuring low-wind speeds discussed. Finally, the application of using this technology for estimating the surface-wind vector during a hurricane is demonstrated 相似文献
834.
Maxwell G.D. Kashyap R. Sherlock G. Collins J.V. Ainslie B.J. 《Electronics letters》1994,30(18):1486-1487
The authors report the first demonstration of a semiconductor external cavity waveguide laser, modulated at 2.5 Gbit/s over 100 km of standard optical fibre using a UV written grating in a planar silica waveguide as the feedback element 相似文献
835.
P Cruz R Almeida M Gon?alves G Marote J Silva C Cavaleiro V Jacinto 《Canadian Metallurgical Quarterly》1994,7(5):277-280
Ocular paresis is a usual diagnosis in neuro-ophthalmologic consultation, and its aetiology is indeed a challenge. The authors studied 3400 records concerning this consultation, between 1982 and the third quarter of 1993. During this period 221 cases with ocular paresis were selected. During this retrospective study we point out the following items: the cranial nerve affected; the neuro-ophthalmologic semiology; the aetiology and clinical evolution, according to the age groups. From 221 cases selected, 111 were paresis from the VIth pair (50.2%), 88 from the IIIrd pair (39.8%), 14 multiple paresis (6.4%) and 8 paresis from the IVth pair (3.6%). The most frequent complaint was diplopia (> 90%). As far as the aetiological diagnosis is concerned, this was easier to establish in patients > 50 years of age. In this age group the most usual aetiology was vascular and traumatic pathologies. In younger patients the most frequent pathologies were traumatic and tumoral. The prognostic was better in the vascular group, the paresis recovery being > 50% in all other pathologies, except the tumoral one. 相似文献
836.
837.
838.
U Kachintorn O Chinapak V Vongphanich C Kositchaiwat S Lekhayananda U Khow-ean C Suttinont V Saowaros N Kludchareon M Leethochawalit 《Canadian Metallurgical Quarterly》1995,78(12):641-647
BACKGROUND: Roxatidine acetate is a novel H2-receptor antagonist and several studies have shown that it is effective in healing duodenal ulcers. We evaluated the efficacy of roxatidine in a non-western society with particular different features and its healing of duodenal ulcers was compared in Thailand with that of ranitidine. METHOD: The design was controlled, randomized, double-blind, and multicenter. The study recruited a total of 215 patients who were endoscoped at the start of the trial and then randomized to receive a single capsule of roxatidine acetate, 150 mg, or an identical capsule containing ranitidine, 300 mg, both to be taken at night. Patients were evaluated at 1, 2, and 4 weeks, including endoscopy at the last session, as well as at 6 weeks with repeat endoscopy if the ulcer had not healed. RESULT: Both drugs relieved pain rapidly, usually within a week, and at repeat endoscopy at 4 weeks most ulcers (78%) were healed, 77.0 and 79.5 per cent in ranitidine and roxatidine, and in those patients in whom healing was not completed the healing rate had risen appreciably to 89.8 and 93.8 per cent respectively at 6 weeks. Small ulcers tended to heal quicker than larger ones, but smoking and alcohol intake had no negative effects on the results. CONCLUSION: The study was valid proof that roxatidine, in a single evening dose of 150 mg, was found to be both safe and effective in the rapid healing of duodenal ulcers when compared with 300 mg ranitidine. 相似文献
839.
E V?is?nen 《Canadian Metallurgical Quarterly》1995,111(22):2186-2187
840.