全文获取类型
收费全文 | 14182篇 |
免费 | 503篇 |
国内免费 | 57篇 |
专业分类
电工技术 | 269篇 |
综合类 | 16篇 |
化学工业 | 2753篇 |
金属工艺 | 412篇 |
机械仪表 | 379篇 |
建筑科学 | 252篇 |
矿业工程 | 72篇 |
能源动力 | 798篇 |
轻工业 | 1265篇 |
水利工程 | 197篇 |
石油天然气 | 88篇 |
无线电 | 1708篇 |
一般工业技术 | 3085篇 |
冶金工业 | 1634篇 |
原子能技术 | 213篇 |
自动化技术 | 1601篇 |
出版年
2024年 | 35篇 |
2023年 | 192篇 |
2022年 | 471篇 |
2021年 | 549篇 |
2020年 | 443篇 |
2019年 | 447篇 |
2018年 | 619篇 |
2017年 | 568篇 |
2016年 | 543篇 |
2015年 | 302篇 |
2014年 | 489篇 |
2013年 | 985篇 |
2012年 | 591篇 |
2011年 | 777篇 |
2010年 | 609篇 |
2009年 | 592篇 |
2008年 | 552篇 |
2007年 | 453篇 |
2006年 | 395篇 |
2005年 | 310篇 |
2004年 | 279篇 |
2003年 | 244篇 |
2002年 | 216篇 |
2001年 | 158篇 |
2000年 | 167篇 |
1999年 | 175篇 |
1998年 | 375篇 |
1997年 | 245篇 |
1996年 | 264篇 |
1995年 | 241篇 |
1994年 | 195篇 |
1993年 | 194篇 |
1992年 | 162篇 |
1991年 | 166篇 |
1990年 | 139篇 |
1989年 | 123篇 |
1988年 | 145篇 |
1987年 | 129篇 |
1986年 | 105篇 |
1985年 | 132篇 |
1984年 | 108篇 |
1983年 | 124篇 |
1982年 | 115篇 |
1981年 | 109篇 |
1980年 | 86篇 |
1979年 | 59篇 |
1978年 | 48篇 |
1977年 | 60篇 |
1976年 | 80篇 |
1975年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
61.
In this article, linear programming and fuzzy optimization models are developed for planning and management of available land-water-crop system of Mahanadi-Kathajodi delta in eastern India. The models are used to optimize the economic return, production and labour utilization, and to search the related cropping patterns and intensities with specified land, water, fertilizer and labour availability, and water use pattern constraints. Due to extreme backwardness of the study area, it has been decided to keep all the three objectives of the linear programming models at the same priority level to obtain the compromised solution in a fuzzy environment that incorporates the imprecision in fuzzy goals and fuzzy constraints. These non-structural models facilitate the conjunctive use of available surface water and groundwater resources. A comparative evaluation along with the benefit-cost ratios of the existing and proposed farming systems is also presented. 相似文献
62.
Yuan Y. Jambunathan R. Singh J. Bhattacharya P. 《Quantum Electronics, IEEE Journal of》1997,33(3):408-415
The performance characteristics of a coupled cavity InGaAsP-InP MQW laser/active waveguide made by one-step epitaxy and well-controlled reactive ion etching (RIE) have been theoretically analyzed and experimentally determined. A theoretical model based on a finite-difference time-domain (FDTD) technique was used to simulate the propagation of an optical wave launched in the coupled system and determine the reflectivity of the facets created by RIE. The calculated effective reflectivity of the coupling region consisting of two facets and an air gap is between 0.45 and 0.55, which is in good agreement with the experimentally measured value of 0.5. The reflectivity of a single etched mirror derived from this value is estimated to be 0.3. A 120-μm-long monolithically integrated active waveguide when biased as a modulator and excited by the laser shows a maximum extinction ratio of 8 dB and a modulation bandwidth ⩾14 GHz at a dc bias of -0.5 V with a bias swing of 2 V 相似文献
63.
R Singh 《Microelectronics Reliability》1998,38(9):1471-1483
This paper describes the role of single wafer processing in the development of sub-quarter micron silicon integrated circuits (ICs). The issues related to device processing, choice of materials, performance, reliability, and manufacturing are covered. Single wafer processing based rapid photothermal processing (dominant photons with wavelength less than about 800 nm) is an ideal answer to almost all the thermal processing requirements of current and future Si ICs. For process integration, a new model for process optimization based on minimization of thermal stress is proposed. For breaking the sub-100 nm manufacturing barriers, high throughput lithography based on direct writing is a proposed solution. 相似文献
64.
DI Rodenhiser JD Andrews DN Mancini JH Jung SM Singh 《Canadian Metallurgical Quarterly》1997,373(2):185-195
Glutamatergic synaptic potentials induced by micromolar concentrations of the potassium conductance blocker 4-aminopyridine (4-AP) were recorded intracellularly from rat neostriatal neurons in the presence of 10 microM bicuculline (BIC). These synaptic potentials originate from neostriatal cortical and thalamic afferents and were completely blocked by 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) plus 100 microM D-2-amino-5-phosphonovaleric acid (2-APV). Their inter-event time intervals could be fitted to exponential distributions, suggesting that they are induced randomly. Their amplitude distributions had most counts around 1 mV and fewer counts with values up to 5 mV. Since input resistance of the recorded neurons is about 40 M omega, the amplitudes agree to quantal size measurements in mammalian central neurons. The action of a D2 agonist, quinpirole, was studied on the frequency of these events. Mean amplitude of synaptic potentials was preserved in the presence of 2-10 microM quinpirole, but the frequency of 4-AP-induced glutamatergic synaptic potentials was reduced in 35% of cases. The effect was blocked by the D2 antagonist sulpiride (10 microM). Input resistance, membrane potential, or firing threshold did not change during quinpirole effect, suggesting a presynaptic site of action for quinpirole in some but not all glutamatergic afferents that make contact on a single cell. The present experiments show that dopaminergic presynaptic modulation of glutamatergic transmission in the neostriatum does not affect all stimulated afferents, suggesting that it is selective towards some of them. This may control the quality and quantity of afferent flow upon neostriatal neurons. 相似文献
65.
The mechanism of the hypolipidemic effect of n-3 fatty acids was studied using isolated rat hepatocytes maintained in culture. EPA and DHA caused a significant reduction in the incorporation of 3[H]-leucine into apoB associated with the VLDL produced by hepatocytes in culture when compared to that in presence of palmitic acid. Presence of indomethacin, an inhibitor of cyclo-oxygenase reversed the effect of EPA on VLDL synthesis while diethyl carbamazine an inhibitor of lipoxygenase did not show any effect suggesting that the effect of EPA may be mediated through prostaglandins. This was further tested by invivo experiments where animals were fed fish oil containing diet with and without aspirin, which inhibits formation of prostaglandins. The incorporation of 3[H]-leucine into apo B and 14[C]-acetate into cholesterol of VLDL produced by hepatocytes from aspirin treated animals were significantly high. The reversal of the effect of n-3 fatty acids by agents which inhibit the formation of prostaglandin suggests that the n-3 fatty acids may exert their effect on VLDL production by liver cells through prostaglandins. 相似文献
66.
67.
68.
69.