全文获取类型
收费全文 | 169094篇 |
免费 | 1336篇 |
国内免费 | 191篇 |
专业分类
电工技术 | 2596篇 |
综合类 | 120篇 |
化学工业 | 26654篇 |
金属工艺 | 9496篇 |
机械仪表 | 5734篇 |
建筑科学 | 3013篇 |
矿业工程 | 1887篇 |
能源动力 | 2724篇 |
轻工业 | 8857篇 |
水利工程 | 2730篇 |
石油天然气 | 8692篇 |
武器工业 | 12篇 |
无线电 | 14583篇 |
一般工业技术 | 38362篇 |
冶金工业 | 28051篇 |
原子能技术 | 6947篇 |
自动化技术 | 10163篇 |
出版年
2018年 | 2985篇 |
2017年 | 3102篇 |
2016年 | 3358篇 |
2015年 | 1678篇 |
2014年 | 2970篇 |
2013年 | 6367篇 |
2012年 | 4337篇 |
2011年 | 5429篇 |
2010年 | 4443篇 |
2009年 | 4926篇 |
2008年 | 4971篇 |
2007年 | 4896篇 |
2006年 | 4168篇 |
2005年 | 3848篇 |
2004年 | 3657篇 |
2003年 | 3546篇 |
2002年 | 3469篇 |
2001年 | 3478篇 |
2000年 | 3379篇 |
1999年 | 3230篇 |
1998年 | 7117篇 |
1997年 | 5210篇 |
1996年 | 3868篇 |
1995年 | 2955篇 |
1994年 | 2624篇 |
1993年 | 2747篇 |
1992年 | 2266篇 |
1991年 | 2318篇 |
1990年 | 2421篇 |
1989年 | 2324篇 |
1988年 | 2318篇 |
1987年 | 2199篇 |
1986年 | 2250篇 |
1985年 | 2303篇 |
1984年 | 2209篇 |
1983年 | 2141篇 |
1982年 | 1983篇 |
1981年 | 2199篇 |
1980年 | 2057篇 |
1979年 | 2272篇 |
1978年 | 2433篇 |
1977年 | 2436篇 |
1976年 | 3105篇 |
1975年 | 2245篇 |
1974年 | 2309篇 |
1973年 | 2343篇 |
1972年 | 2157篇 |
1971年 | 1911篇 |
1970年 | 1701篇 |
1969年 | 1634篇 |
排序方式: 共有10000条查询结果,搜索用时 650 毫秒
961.
Kizilyalli I.C. Rambaud M.M. Duncan A. Lytle S.A. Thoma M.J. 《Electron Device Letters, IEEE》1995,16(10):457-459
The trade-off between threshold voltage (Vth) and the minimum gate length (Lmin) is discussed for optimizing the performance of buried channel PMOS transistors for low voltage/low power high-speed digital CMOS circuits. In a low supply voltage CMOS technology it is desirable to scale Vth and Lmin for improved circuit performance. However, these two parameters cannot be scaled independently due to the channel punch-through effect. Statistical process/device modeling, split lot experiments, circuit simulations, and measurements are performed to optimize the PMOS transistor current drive and CMOS circuit speed. We show that trading PMOS transistor Vth for a smaller Lmin results in faster circuits for low supply voltage (3.3 to 1.8 V) n+-polysilicon gate CMOS technology, Circuit simulation and measurements are performed in this study. Approximate empirical expressions are given for the optimum buried channel PMOS transistor V th for minimizing CMOS circuit speed for cases involving: (1) constant capacitive load and (2) load capacitance proportional to MOS gate capacitance. The results of the numerical exercise are applied to the centering of device parameters of a 0.5 μm 3.3 V CMOS technology that (a) matches the speed of our 0.5 μm 5 V CMOS technology, and (b) achieves good performance down to 1.8 V power supply. For this process the optimum PMOS transistor Vth (absolute value) is approximately 0.85-0.90 V 相似文献
962.
963.
964.
965.
The measurements of diphenylhexatriene (DPH) and trimethylammonium diphenylhexatriene (TMA-DPH) fluorescence anisotropy in egg yolk lecithin (EYL) and of DPH anisotropy in dipalmitoylphosphatidylcholine (DPPC) liposomes containing different concentrations of oxidized and reduced ubiquinone (UQ) and plastoquinone (PQ) homologues have been performed. All the oxidized UQ homologues strongly induced ordering of EYL membrane structure, whereas in DPPC liposomes, above the phase transition temperature, the most pronounced effect showed UQ-4. PQ-2 and PQ-9 were less effective than the corresponding ubiquinones in this respect. The reduced forms of UQ and PQ homologues increased the order of membrane lipids to a smaller extent than the corresponding quinones both in the interior of the membrane and closer to its surface. Nevertheless, the investigated prenylquinols showed stronger increase in the membrane order than alpha-tocopherol or alpha-tocopherol acetate, which could be connected with binding of prenylquinol head groups to phospholipid molecules by hydrogen bonds. The strong ordering influence of ubiquinones on the membrane structure was attributed to methoxyl groups of the UQ quinone rings. 相似文献
966.
Dielectric properties and conduction of the epoxy and its composites were measured over the temperature range — 20 to 70°C and the frequency range 10–4-10–1 Hz. Dielectric properties were obtained by performing Fouriertransforms on the charging and discharging curves. The resulting isothermal frequency spectra of dielectric constants and dielectric loss factors were analysed using the Cole-Cole law to obtain the activation energy for each material. The activation energies were also obtained for isothermal d.c. current. Current density-electric field-temperature characteristics are obtained for field levels up to 60 kV cm–1, with step excitation of the applied field and currents recorded after a delay time of 10 min. Current density and electric field were computed and plotted for constant temperature. The linear (ohmic) curves were obtained for fields up to about 60 kV cm–1 for temperatures up to about 20 °C. The non-linearity at the higher fields and temperatures did not imply the occurrence of non-ionic conduction. It has been demonstrated that both electric conduction and relaxation behaviour were ionic and could be fit by the Nakajima model for the unfilled epoxy and the Taylor model for the composites. 相似文献
967.
This article examines the design of the exact readout system of a digital angle transducer in which the possible quasi-sinusoidality
of the angle sensor and the simplification of the conversion unit are automatically compensated for by additional devices
so as to not significantly affect the accuracy with which angular position is converted into code.
Translated from Izmeritel'naya Tekhnika, No. 5, pp. 26–27, May, 1996. 相似文献
968.
C Guimar?es Madeira SA Jorge S Kakehashi I de Oliveira 《Canadian Metallurgical Quarterly》1996,30(2):217-228
The disposition behavior of trientine, a selective copper-chelating drug for Wilson's disease, and its metabolites in normal patients with Wilson's disease and rats were studied. A high concentration of metabolites appeared in blood samples of patients and rats in the early stage after administration of trientine. Furthermore, large amount of trientine metabolites were excreted into the urine of patients. These results suggest that trientine is remarkably subjected to a first-pass effect. The drug concentration area under the curve (AUC) of the unchanged form and the metabolites of trientine in patients was not dependent on the administered dosage. It seems that the absorption process is an important factor for the disposition behavior of trientine, we have also investigated the uptake characteristics of trientine by rat intestinal brush-border membrane vesicles. The uptake characteristics of trientine were similar to the physiological polyamines, spermine and spermidine. The uptake rate of trientine was dose-dependently inhibited by spermine and spermidine. Moreover, spermine competitively inhibited the uptake of trientine with a Ki value of 18.6 muM. This value is very close to the Km value for spermine (30.4 muM). These data suggested that the uptake mechanism of trientine in rat small intestinal brush-border membrane vesicles was almost identical to that of spermine and spermidine, and that the physiological polyamines seem to have the ability to inhibit the absorption of trientine from the gastrointestinal tract. 相似文献
969.
Accelerated tests for oxidative rancidity of blanched peanuts, blanched dry-roasted peanuts, blanched oil-roasted peanuts and shelled Persian walnuts were performed at high and low oxygen content at controlled intermediate and low relative humidities. The results confirmed and quantified the importance of oxygen content, relative humidity and roasting process in the oxidative rancidity of peanuts and walnuts. There is a potential to extend shelf-life of roasted peanuts and walnuts by edible coatings with low oxygen permeability or nitrogen-flushing with oxygen barrier packaging. Static headspace chromatography was useful to monitor oxidative rancidity in walnuts and roasted peanuts. 相似文献
970.