全文获取类型
收费全文 | 437808篇 |
免费 | 6914篇 |
国内免费 | 1492篇 |
专业分类
电工技术 | 8155篇 |
综合类 | 581篇 |
化学工业 | 66551篇 |
金属工艺 | 14981篇 |
机械仪表 | 12431篇 |
建筑科学 | 12506篇 |
矿业工程 | 995篇 |
能源动力 | 11607篇 |
轻工业 | 47161篇 |
水利工程 | 3482篇 |
石油天然气 | 1966篇 |
武器工业 | 28篇 |
无线电 | 56689篇 |
一般工业技术 | 80945篇 |
冶金工业 | 80727篇 |
原子能技术 | 5715篇 |
自动化技术 | 41694篇 |
出版年
2021年 | 3250篇 |
2020年 | 2296篇 |
2019年 | 2848篇 |
2018年 | 4619篇 |
2017年 | 4582篇 |
2016年 | 4955篇 |
2015年 | 4092篇 |
2014年 | 6483篇 |
2013年 | 20776篇 |
2012年 | 11291篇 |
2011年 | 15788篇 |
2010年 | 12228篇 |
2009年 | 13804篇 |
2008年 | 14937篇 |
2007年 | 15260篇 |
2006年 | 13479篇 |
2005年 | 12531篇 |
2004年 | 12008篇 |
2003年 | 11653篇 |
2002年 | 11273篇 |
2001年 | 11421篇 |
2000年 | 10558篇 |
1999年 | 11142篇 |
1998年 | 25795篇 |
1997年 | 18666篇 |
1996年 | 14641篇 |
1995年 | 11454篇 |
1994年 | 10167篇 |
1993年 | 9721篇 |
1992年 | 7288篇 |
1991年 | 6964篇 |
1990年 | 6559篇 |
1989年 | 6258篇 |
1988年 | 6004篇 |
1987年 | 5051篇 |
1986年 | 4956篇 |
1985年 | 6179篇 |
1984年 | 5744篇 |
1983年 | 4981篇 |
1982年 | 4620篇 |
1981年 | 4599篇 |
1980年 | 4378篇 |
1979年 | 4205篇 |
1978年 | 3871篇 |
1977年 | 4748篇 |
1976年 | 6500篇 |
1975年 | 3203篇 |
1974年 | 3092篇 |
1973年 | 2997篇 |
1972年 | 2365篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
E Messou SV Sangaré R Josseran C Le Corre J Guélain 《Canadian Metallurgical Quarterly》1997,90(1):44-47
BACKGROUND: Gastric sucrose permeability is a noninvasive marker that reliably increases in association with gastrointestinal injury due to use of nonsteroidal antiinflammatory drugs. Despite the effect of Helicobacter pylori infection on the gastric mucosa, in a previous study we were unable to demonstrate that H. pylori infection was associated with abnormal gastric sucrose permeability. Our goal in this study was to explore further whether H. pylori infection changed gastric permeability; therefore, we evaluated the effect of treatment of H. pylori infection on gastric permeability to sucrose and the relation of sucrose permeability to density of polymorphonuclear leukocytes. MATERIALS AND METHODS: Five hundred milliliters of a solution containing 100 gm of sucrose was ingested by the subject at bedtime. Overnight urine was collected and assayed for sucrose by high-performance liquid chromatography. Sucrose permeability was assessed both before and approximately 4 weeks after anti-H. pylori therapy. RESULTS: Seventeen asymptomatic H. pylori-infected volunteers participated; 8 were cured. Sucrose permeability was in the range commonly found in normal controls both before and after anti-H. pylori therapy (mean excretion, 76.3 mg; range, 13-171 mg). Gastric sucrose permeability correlated with the density of polymorphonulcear cell infiltration of the mucosa. Cure of the H. pylori infection was associated with a small but significant decrease in sucrose permeability (98.8 +/- 18 mg to 51.7 +/- 9.8 mg (p = .01). Sucrose permeability was greater in those with a high density of mucosal polymorphonuclear cells compared to those with lower scores (119.5 +/- 4 vs 71.4 +/- 13 for those with scores > or = 5 compared to scores < or = 4; p = .023). Failed therapy resulted in an increase in the mucosal density of polymorphonuclear infiltration and sucrose permeability (56.4 +/- 13 mg-99.7 +/- 19 mg pretreatment vs posttreatment, respectively; p = .031). CONCLUSION: H. pylori gastritis causes a small but measurable increase in gastric permeability to sucrose that may reflect epithelial transmigration of neutrophils. 相似文献
52.
Douay M. Xie W.X. Taunay T. Bernage P. Niay P. Cordier P. Poumellec B. Dong L. Bayon J.F. Poignant H. Delevaque E. 《Lightwave Technology, Journal of》1997,15(8):1329-1342
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models 相似文献
53.
Watanabe H. Komori J. Higashitani K. Sekine M. Koyama H. 《Semiconductor Manufacturing, IEEE Transactions on》1997,10(2):228-232
A novel monitoring method for plasma-charging damage is proposed. This method performs a quick and accurate evaluation using antenna PMOSFET. It was found that not only hot-carrier (HC) lifetime but transistor parameters such as initial gate current and substrate current were changed according to the degree of plasma-charging damage. However, the present work suggests that monitoring the shift of drain current after a few seconds of HC stress is a more accurate method to indicate plasma-charging damage. The monitoring method using the present test structure is demonstrated to be useful for realizing highly reliable devices 相似文献
54.
J Havick 《The Journal of communication》1997,47(2):97-111
This study employed two perspectives to investigate media attention given women congressional candidates. The first perspective is that media attention may be explained by typical and normal media processes, such as focusing on incumbents. The second perspective considers a partisan explanation in which media attention is weighted more to Democratic candidates than Republican candidates. This study employs two established sources, Vanderbilt's Television News Index and Abstract and Information Access's National Newspaper Index , to examine the national media attention of Democratic and Republican women congressional candidates in 1990 and 1992. The investigation determined that media attention is related to whether the candidates are running for the Senate or House, incumbency, and state population. The results also reveal that party is a statistically significant factor associated with media attention. The investigation also determined that ethnic candidates tend to receive slightly less attention from the print media than nonethnic candidates. 相似文献
55.
Cresswell M.W. Allen R.A. Guthrie W.F. Sniegowski J.J. Ghoshtagore R.N. Linholm L.W. 《Semiconductor Manufacturing, IEEE Transactions on》1998,11(2):182-193
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features 相似文献
56.
A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications 相似文献
57.
58.
The capacitive idling converters derived from the Cuk, SEPIC, Zeta, and flyback topologies allow soft commutation of power switches without the need for additional circuitry, making it possible to increase the switching frequency while maintaining high efficiency 相似文献
59.
60.