全文获取类型
收费全文 | 241440篇 |
免费 | 2947篇 |
国内免费 | 426篇 |
专业分类
电工技术 | 4294篇 |
综合类 | 257篇 |
化学工业 | 39447篇 |
金属工艺 | 9389篇 |
机械仪表 | 7401篇 |
建筑科学 | 5460篇 |
矿业工程 | 1393篇 |
能源动力 | 5160篇 |
轻工业 | 24823篇 |
水利工程 | 2480篇 |
石油天然气 | 5092篇 |
武器工业 | 32篇 |
无线电 | 25070篇 |
一般工业技术 | 44847篇 |
冶金工业 | 45570篇 |
原子能技术 | 5960篇 |
自动化技术 | 18138篇 |
出版年
2021年 | 2110篇 |
2019年 | 2020篇 |
2018年 | 3501篇 |
2017年 | 3430篇 |
2016年 | 3693篇 |
2015年 | 2239篇 |
2014年 | 3902篇 |
2013年 | 10205篇 |
2012年 | 6158篇 |
2011年 | 8305篇 |
2010年 | 6552篇 |
2009年 | 7240篇 |
2008年 | 7596篇 |
2007年 | 7733篇 |
2006年 | 6903篇 |
2005年 | 6061篇 |
2004年 | 5832篇 |
2003年 | 5610篇 |
2002年 | 5682篇 |
2001年 | 5567篇 |
2000年 | 5395篇 |
1999年 | 5307篇 |
1998年 | 12614篇 |
1997年 | 8923篇 |
1996年 | 6876篇 |
1995年 | 5348篇 |
1994年 | 4751篇 |
1993年 | 4637篇 |
1992年 | 3674篇 |
1991年 | 3400篇 |
1990年 | 3607篇 |
1989年 | 3490篇 |
1988年 | 3313篇 |
1987年 | 2901篇 |
1986年 | 2939篇 |
1985年 | 3380篇 |
1984年 | 3224篇 |
1983年 | 2895篇 |
1982年 | 2742篇 |
1981年 | 2824篇 |
1980年 | 2721篇 |
1979年 | 2632篇 |
1978年 | 2688篇 |
1977年 | 2950篇 |
1976年 | 3818篇 |
1975年 | 2372篇 |
1974年 | 2245篇 |
1973年 | 2378篇 |
1972年 | 1977篇 |
1971年 | 1861篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
Z Amma E Kis M Józan-Jilling G Wagner T Gesztesi 《Canadian Metallurgical Quarterly》1997,138(29):1859-1861
Two chronic haemodialyzed patients with digitalis intoxication are reported. One of them took digoxin 0.25 mg three times daily for an unknown period and the other took digitoxin 0.1 mg twice daily for two weeks. The symptoms of intoxication were mainly concealed by uremic syndrome. The diagnosis was established by noticed sinus bradycardia, first- and second-degree atrioventricular block in ECG and the determination of sera levels of glycosides (serum digoxin concentration was 7.36 ng/ml, serum digitoxin concentration was 46.5 ng/ml) in both cases. Considering the probable long elimination period of digitalis and the potentially life-threatening situation the patients were given digoxin-specific antibody (Fab) fragments with potassium replacement therapy. The symptoms disappeared within a few hours after therapy, side effects and rebound toxicity did not develop. In connection with these cases the aim of this report is to publish a method which can reverse the life-threatening digitalis intoxication in patients suffering from renal failure as well. As to the above method, the authors have not found any similar case reports in the Hungarian medical literature. 相似文献
942.
A new method is presented for computing the electric lead field of a realistic head shape model which has piecewise homogenous conductivity. The basic formulae are derived using the well-known reciprocity theorem. Previously described methods are also based upon this theorem, but these first calculate the electric potential inside the head by a scalar boundary element method (BEM), and then approximate the ohmic current density by some sort of gradient. In contrast, this paper proposes the direct evaluation of the ohmic current density by discretizing the vector Green's second identity which leads to a rector version of BEM. This approach also allows the derivation of the same equations for the three concentric spheres model as obtained by Rush and Driscoll (1969). The results of simulations on a spherical head model indicate that the use of a vector BEM leads to an improvement of accuracy in the computation of the ohmic current density with respect to those reported previously, in term of different measures of error 相似文献
943.
An optimal design for the RLSA (radial line slot array) antenna useful for DBS reception is presented. Classical geometries and structures given in the literature are first used. It is found that in some cases these are not suitable. So, optimization techniques by using the right objective functions have been applied. Two different methods were developed and three antennas were designed. Numerical results and comparisons with other similar antennas give the advantages of our design 相似文献
944.
Gunapala S.D. Bundara S.V. Liu J.K. Winn Hong Mani Sundaram Maker P.D. Muller R.E. Shott C.A. Carralejo R. 《Electron Devices, IEEE Transactions on》1998,45(9):1890-1895
A 9-μm cutoff 640×486 snap-shot quantum well infrared photodetector (QWIP) camera has been demonstrated. The performance of this QWIP camera is reported including indoor and outdoor imaging. The noise equivalent differential temperature (NEΔT) of 36 mK has been achieved at 300 K background with f/2 optics. This is in good agreement with expected focal plane array sensitivity due to the practical limitations on charge handling capacity of the multiplexer, read noise, bias voltage, and operating temperature 相似文献
945.
The choice of a highly resistive substrate for silicon millimeter-wave integrated circuits (SIMMWIC) imposed by the requirement of low RF-substrate losses requires the adaptation of a CMOS process on float zone silicon (FZ). A comparison of n- and p-channel devices realized on high resistivity substrate (p-type, 5000 Ω·cm) and standard CMOS substrates (CZ, n-type, 4-6 Ω·cm) is given. Using careful process design, we obtained device characteristics on FZ-substrates that are closely similar to those on standard material, thus allowing direct transfer of existing circuit designs 相似文献
946.
Two tandemly located flagellin genes, flaA and flaB, with 79% nucleotide sequence identity were identified in Aeromonas salmonicida A449. The fla genes are conserved in typical and atypical strains of A. salmonicida, and they display significant divergence at the nucleotide level from the fla genes of the motile species Aeromonas hydrophila and Aeromonas veronii biotype sobria. flaA and flaB encode unprocessed flagellins with predicted Mrs of 32,351 and 32,056, respectively. When cloned under the control of the Ptac promoter, flaB was highly expressed when induced in Escherichia coli DH5alpha, and the FlaB protein was detectable even in the uninduced state. In flaA clones containing intact upstream sequence, FlaA was barely detectable when uninduced and poorly expressed on induction. The A. salmonicida flagellins are antigenically cross-reactive with the A. hydrophila TF7 flagellin(s) and evolutionarily closely related to the flagellins of Pseudomonas aeruginosa and Vibrio anguillarum. Electron microscopy showed that A. salmonicida A449 expresses unsheathed polar flagella at an extremely low frequency under normal laboratory growth conditions, suggesting the presence of a full complement of genes whose products are required to make flagella; e.g., immediately downstream of flaA and flaB are open reading frames encoding FlaG and FlaH homologs. 相似文献
947.
948.
O. N. Zavrazhnaya I. N. Oleinikov E. D. Naumov V. V. Petrov 《Chemical and Petroleum Engineering》1993,29(11):555-559
Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 11, pp. 28–30, November, 1993. 相似文献
949.
D.L Orphal C.E Anderson Jr. R.R Franzen J.D Walker P.N Schneidewind M.E Majerus 《International Journal of Impact Engineering》1993,14(1-4):551-560
Calculations of steel target penetration by L/D ≤ 1 tungsten and tungsten alloy projectiles have been extended to L/D = 1/32 over the velocity range 1.5 to 5 km/s. The ratio of crater to projectile diameter tends to 1 as L/D decreases over this entire velocity range. For impact velocities of 1.5 and 3 km/s, penetration depth normalized by projectile length, P/L, increases with decreasing projectile L/D up to a maximum value and then decreases for still lower L/D. Experiments at impact velocities of 2 and 3 km/s confirm these results. For 5 km/s impact velocity, the calculations show P/L increasing with decreasing projectile L/D over the entire range 1/32 ≤ L/D ≤ 1. The projectile L/D for which the maximum P/L occurs appears to depend on the impact velocity. P/L generally scales with impact velocity as P/L vf(L/D) where f(L/D) ranges from 0 for a long rod to, we believe, 2 in the limit as projectile L/D approaches zero. The calculations show for 1/8 ≤ L/D ≤ 1/2, P/L v0.9; for L/D = 1/16, P/L v1.5; and for L/D = 1/32, the new results give P/L v1.9. 相似文献
950.
Dr.-Ing. Ch. Dörnemann Prof. Dr.-Ing. E. Handschin 《Electrical Engineering (Archiv fur Elektrotechnik)》1992,76(1):33-40
Übersicht Der Betriebszustand eines Verteilungsnetzes wird durch die Strombelastung aller Betriebsmittel beschrieben. Mit Hilfe einer statischen Estimationsmethode werden aus einzelnen Messungen und der Kenntnis der Verbrauchsdaten typische Verbraucherkurven (TVK) berechnet, die das elektrische Verhalten verschiedener Verbrauchergruppen widerspiegeln. Auf dieser Basis ist eine betriebsmittelbezogene Lastmodellierung an beliebigen Betriebsmitteln in Abhängigkeit der Verbraucherzusammensetzung unter Berücksichtigung externer Einflüsse wie der Temperatur möglich. Die so gewonnenen Belastungsverläufe erlauben eine Beschreibung des Netzzustands in den Verteilungsnetzen.
Bus load modelling in distribution systems
Contents The operating state of a distribution system is determined by the bus load current. Based on individual substation measurements and the load composition typical load curves are calculated using statistical estimation theory. These typical load curves describe the electrical behaviour of the different load types (e.g. household, storage heating, commerce etc.). As soon as the typical load curves are determined it is possible to calculate the bus load current in any substation taking external influences such as temperature into consideration. The bus load current serve as load models which completely describe the operating state of the distribution system.相似文献