全文获取类型
收费全文 | 429589篇 |
免费 | 5538篇 |
国内免费 | 1385篇 |
专业分类
电工技术 | 7698篇 |
综合类 | 255篇 |
化学工业 | 67688篇 |
金属工艺 | 18183篇 |
机械仪表 | 12718篇 |
建筑科学 | 10547篇 |
矿业工程 | 2534篇 |
能源动力 | 10644篇 |
轻工业 | 39034篇 |
水利工程 | 4549篇 |
石油天然气 | 9331篇 |
武器工业 | 18篇 |
无线电 | 47371篇 |
一般工业技术 | 83706篇 |
冶金工业 | 78156篇 |
原子能技术 | 10591篇 |
自动化技术 | 33489篇 |
出版年
2021年 | 3144篇 |
2019年 | 2998篇 |
2018年 | 5373篇 |
2017年 | 5323篇 |
2016年 | 5670篇 |
2015年 | 3787篇 |
2014年 | 6424篇 |
2013年 | 18599篇 |
2012年 | 10504篇 |
2011年 | 14407篇 |
2010年 | 11719篇 |
2009年 | 13414篇 |
2008年 | 13708篇 |
2007年 | 13514篇 |
2006年 | 11823篇 |
2005年 | 11030篇 |
2004年 | 10352篇 |
2003年 | 9929篇 |
2002年 | 9933篇 |
2001年 | 9793篇 |
2000年 | 9336篇 |
1999年 | 9501篇 |
1998年 | 23072篇 |
1997年 | 16873篇 |
1996年 | 13161篇 |
1995年 | 10038篇 |
1994年 | 8849篇 |
1993年 | 8701篇 |
1992年 | 6578篇 |
1991年 | 6487篇 |
1990年 | 6241篇 |
1989年 | 6270篇 |
1988年 | 6173篇 |
1987年 | 5313篇 |
1986年 | 5292篇 |
1985年 | 6072篇 |
1984年 | 5742篇 |
1983年 | 5269篇 |
1982年 | 4955篇 |
1981年 | 5111篇 |
1980年 | 4853篇 |
1979年 | 4808篇 |
1978年 | 4877篇 |
1977年 | 5592篇 |
1976年 | 7197篇 |
1975年 | 4375篇 |
1974年 | 4190篇 |
1973年 | 4263篇 |
1972年 | 3701篇 |
1971年 | 3403篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
921.
LiFePO4 is a potential candidate for the cathode material of the lithium secondary batteries. A co-precipitation method was adopted to prepare LiFePO4 because it is simple and cheap. Nitrogen gas was needed to prevent oxidation of Fe2+ in the aqueous solution. The co-precipitated precursor shows the high reactivity with the reductive gas, and the single phase of LiFePO4 is successfully synthesized with the aid of carbon under less reductive conditions. LiFePO4 fine powder prepared by co-precipitation method shows high rate capability, impressive specific capacity and cycle property. 相似文献
922.
In this paper, two brittle fracture problems are numerically simulated: the failure of a ceramic ring under centrifugal loading and crack branching in a PMMA strip. A three‐dimensional finite element package in which cohesive elements are dynamically inserted has been developed. The cohesive elements' strength is chosen to follow a modified weakest link Weibull distribution. The probability of introducing a weak cohesive element is set to increase with the cohesive element size. This reflects the physically based effect according to which larger elements are more likely to contain defects. The calculations illustrate how the area dependence of the Weibull model can be used to effectively address mesh dependency. On the other hand, regular Weibull distributions have failed to reduce mesh dependency for the examples shown in this paper. The ceramic ring calculations revealed that two distinct phenomena appear depending on the magnitude of the Weibull modulus. For low Weibull modulus, the fragmentation of the ring is dominated by heterogeneities. Whereas many cracks were generated, few of them could propagate to the outer surface. Monte Carlo simulations revealed that for highly heterogeneous rings, the number of small fragments was large and that few large fragments were generated. For high Weibull modulus, signifying that the ring is close to being homogeneous, the fragmentation process was very different. Monte Carlo simulations highlighted that a larger number of large fragments are generated due to crack branching. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
923.
V. V. Mamutin O. V. Bondarenko A. P. Vasil’ev A. G. Gladyshev A. Yu. Egorov N. V. Kryzhanovskaya V. S. Mikhrin V. M. Ustinov 《Technical Physics Letters》2007,33(5):384-387
The optical properties of heterostructures comprising InAs/InGaAsN quantum wells in strain-compensated GaAsN/InGaAsN superlattices have been studied. It is demonstrated that, using such superlattices of various design and thickness and with additional InAs monolayer spacers, it is possible to control the wavelength of room-temperature emission from InGaAsN quantum wells within 1.3–1.6 μm without deteriorating the output radiation characteristics, which opens additional prospects for the development of lasers on GaAs substrates for telecommunication applications. 相似文献
924.
A novel finger‐sensing nanocomposite with remarkable and reversible piezoresistivity is successfully fabricated by dispersing homogeneously conductive graphite nanosheets (GNs) in a silicone rubber (SR) matrix. Because of the high aspect ratio of the graphite nanosheets, the nanocomposite displays a very low percolation threshold. The SR/GN nanocomposite with a volume fraction of conductive nanosheets closest to that for the percolation threshold presents a sharp positive‐pressure coefficient effect of the resistivity under very low pressure, namely, in the finger‐pressure range (0.3–0.7 MPa), whereby the abrupt transition could be attributed to compressive‐stress‐induced deformation of the conducting network. The super‐sensitive piezoresistive behavior of the nanocomposite is accounted for by an extension of the tunneling conduction theory which provides a good approximation to the piezoresistive effect. 相似文献
925.
G. N. Churilov R. B. Weisman N. V. Bulina N. G. Vnukova A. P. Puzir L. A. Solovyov S. M. Bachilo D. A. Tsyboulski G. A. Glushenko 《Fullerenes, Nanotubes and Carbon Nanostructures》2003,11(4):371-382
The addition of metallic Ir and Pt to a fullerene-forming, atmospheric-pressure plasma reactor was found to influence the generation of carbonaceous products. It was observed that the added metals were efficiently dispersed into the plasma and that their presence increased the yield of fullerenes. The addition of Ir led to a noticeable shift in the fullerene distribution towards C60, whereas the addition of Pt increased the proportion of C60 oxides and decreased the proportion of higher fullerenes. Addition of Ir also caused a reduction of the soot particle size and the formation of a considerable quantity of carbon nanotubes. 相似文献
926.
927.
G. S. Ghali 《Water Resources Management》1989,3(1):35-47
The mathematical model which was developed in part I of this work for multi-dimensional analysis of soil moisture in irrigated fields is converted into computer algorithms. The algorithms are capable of emulating many field conditions of practical applications during both design and operation phases. The model is subjected to various tests, the results of which are reported here. The tests in various modes of simulations verified the numerical performance of the model and the accuracy of its predictions. The model provides a powerful tool for detailed studies of soil moisture dynamics in one or multi-dimensional problems irrigated fields 相似文献
928.
The phase relations of the ternary system Cu-In-Se were studied at 750° C by quenching experiments. Special attention was given to the region CuInSe2In2Se3-In4Se3. Only four ternary phases with extended homogeneity ranges were found to exist. They were characterized by X-ray powder diffraction, electron microprobe analysis (EK8PA)' end optical microscopy. Differential thermal analysis (DTA) investigations allowed us to construct theT-x diagram of the Cu2Se-In2Se3. out between 47 and 100 mol% In2Se3. Besides, it was also possible to give a tentative diagram of the solid-liquid equilibria at 750° C and to get some information on the sub-solid existence fields beside the Cu2Se-In2Se3 cut. 相似文献
929.
930.