全文获取类型
收费全文 | 18496篇 |
免费 | 1732篇 |
国内免费 | 900篇 |
专业分类
电工技术 | 977篇 |
综合类 | 1213篇 |
化学工业 | 2973篇 |
金属工艺 | 974篇 |
机械仪表 | 956篇 |
建筑科学 | 1204篇 |
矿业工程 | 390篇 |
能源动力 | 616篇 |
轻工业 | 1217篇 |
水利工程 | 297篇 |
石油天然气 | 644篇 |
武器工业 | 197篇 |
无线电 | 2680篇 |
一般工业技术 | 2296篇 |
冶金工业 | 996篇 |
原子能技术 | 140篇 |
自动化技术 | 3358篇 |
出版年
2024年 | 60篇 |
2023年 | 261篇 |
2022年 | 507篇 |
2021年 | 750篇 |
2020年 | 559篇 |
2019年 | 532篇 |
2018年 | 594篇 |
2017年 | 592篇 |
2016年 | 674篇 |
2015年 | 710篇 |
2014年 | 850篇 |
2013年 | 1108篇 |
2012年 | 1086篇 |
2011年 | 1173篇 |
2010年 | 1123篇 |
2009年 | 1038篇 |
2008年 | 1074篇 |
2007年 | 1007篇 |
2006年 | 901篇 |
2005年 | 740篇 |
2004年 | 716篇 |
2003年 | 852篇 |
2002年 | 1096篇 |
2001年 | 877篇 |
2000年 | 431篇 |
1999年 | 299篇 |
1998年 | 306篇 |
1997年 | 209篇 |
1996年 | 166篇 |
1995年 | 137篇 |
1994年 | 96篇 |
1993年 | 112篇 |
1992年 | 61篇 |
1991年 | 61篇 |
1990年 | 43篇 |
1989年 | 39篇 |
1988年 | 28篇 |
1987年 | 26篇 |
1986年 | 29篇 |
1985年 | 24篇 |
1984年 | 28篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 17篇 |
1979年 | 15篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1975年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
E. Ech-chamikh M. Azizan E.L. Ameziane A. Bennouna M. Brunel T.T.A. Nguyen 《Solar Energy Materials & Solar Cells》1993,31(2)
Hydro-oxygenated carbon (C : H,O) and silicon (Si : H,O) layers are deposited by RF sputtering of graphite and silicon targets in a mixture of argon, hydrogen and oxygen gases. C : H,O/Si : H,O/C : H,O/Si : H,O... multilayers are obtained by sequential deposition of C : H,O and Si : H,O layers. Infrared (IR) spectroscopy, Grazing Incidence X-ray Diffraction (GIXD) and X-ray Photoelectron Spectroscopy (XPS) techniques have been used to analyse the formed multilayers. The IR spectra made on as deposited structures show the presence of Si---C, Si---O, C---O, Si---H, C---H and C=C bonds. This result indicates an interfacial reactivity between Si : H,O and C : H,O layers. The latter result is confirmed by the XPS measurements. After an annealing at 850°c for two hours under argon atmosphere (10-3 mbar), the concentration of the Si---C bonds is increased by a factor two while the Si---H and C---H bonds disappear complet The GIXD measurements show that the multilayers are amorphous when annealed below 750°C, and they are crystallized with the formation of the α-SiC phase if the heat treatment is made at 850°C. The mean size of the microcrystallites is 50 Å about. 相似文献
22.
医用聚氯乙烯材料的表面光接枝改性 总被引:6,自引:0,他引:6
研究了在不排氧氛围下 ,紫外光照射 ,以二苯甲酮 (BP)为光引发剂 ,甲基丙烯酸缩水甘油酯(GMA)在医用聚氯乙烯 (PVC)薄膜表面的气相接枝聚合。探讨了反应条件对接枝结果的影响 ,并用正交法指出了影响因素的显著性。用傅立叶红外 (FT- IR)、水接触角作为接枝改性结果的表征。FT- IR谱图表明 GMA已接枝到 PVC膜表面。水接触角由接枝前的 78°下降到 5 4° 相似文献
23.
24.
Zhang Li Chun Jin Hai Yan Ye Hong Fei Gao Yu Zhi Ning Bao Jun Mo Bang Xian 《Electron Devices, IEEE Transactions on》2002,49(6):1075-1076
A polysilicon emitter RCA transistor (an ultra-thin interfacial oxide layer exists between polysilicon and silicon emitter) is presented which can operate at 77 K for the first time. An ultra-thin (1.5 nm) interfacial oxide layer is grown deliberately between polysilicon and silicon emitter using RCA oxidation and excellent device stability is obtained after rapid thermal annealing (RTA) treatment in nitrogen atmosphere. The RCA transistor exhibits good electrical performance at very low temperature for an emitter area of 3 × 8 μm2. The maximum toggle frequency of a 1:2 static divider is 1.2 GHz and 732 MHz at 300 K and 77 K, respectively 相似文献
25.
26.
Jonathan P. Belnoue Giang D. Nguyen Alexander M. Korsunsky 《International Journal of Fracture》2007,144(1):53-60
This paper presents a new 1-D non-local damage-plasticity deformation model for ductile materials. It uses the thermodynamic
framework described in Houlsby and Puzrin (2000) and holds, nevertheless, some similarities with Lemaitre’s (1971) approach.
A 1D finite element (FE) model of a bar fixed at one end and loaded in tension at the other end is introduced. This simple
model demonstrates how the approach can be implemented within the finite element framework, and that it is capable of capturing
both the pre-peak hardening and post-peak softening (generally responsible for models instability) due to damage-induced stiffness
and strength reduction characteristic of ductile materials. It is also shown that the approach has further advantages of achieving
some degree of mesh independence, and of being able to capture deformation size effects. Finally, it is illustrated how the
model permits the calculation of essential work of rupture (EWR), i.e. the specific energy per unit cross-sectional area that
is needed to cause tensile failure of a specimen. 相似文献
27.
本文提出了强扩散准则,强雪崩效应以及扩散效应的逼近优势等相关概念,给出了差分均匀性与强k阶扩散准则之间的相互关系,利用给出的设计准则改进了Rijndael密码的S盒。 相似文献
28.
Nguyen An Tien I. Ya. Mittova O. V. Almjasheva S. A. Kirillova V. V. Gusarov 《Glass Physics and Chemistry》2008,34(6):756-761
Nanocrystalline LaFeO3 is prepared by the dehydration of coprecipitated lanthanum and iron(III) hydroxides. It is shown that the behavior of the samples during heating and the size distribution of LaFeO3 nanocrystals can be considerably different depending on the scheme used for coprecipitation of lanthanum and iron hydroxides; independently of the method employed for coprecipitation of the initial compounds, sintering of the samples at 950°C leads to the formation of lanthanum orthoferrite crystals up to 100 nm in size. 相似文献
29.
Fractional lambda switching (FlambdaS) is a novel approach for traffic management over all-optical networks with sub-wavelength provisioning capability. The unique characteristic of FlambdaS is the utilization of UTC (coordinated universal time) for switching with minimum or no buffers. Several central research issues are still open in FlambdaS and need to be formally defined and analyzed. In this paper, we introduce three novel switch designs that are based on the use of tunable lasers (which can be replaced in the future with wavelength converters). First, the paper presents analytical results of scheduling feasibility, which measures the total number of possible different schedules for each switch design. Then it is shown that the architecture with the highest scheduling feasibility is strictly non blocking in the space domain. Next, the paper provides a closed form analysis of the blocking probability in the time domain, which is applicable for any strictly non-space blocking switch, using combinatorics. In addition, the paper provides measures of the switching hardware complexity, which, for the strictly non-blocking architecture, has the same switching complexity as Clos interconnection network, i.e., O(N'radic(N')) where N' is the number of optical channels. 相似文献
30.
T.S. Nguyen A.P.S. Selvadurai G. Armand 《International Journal of Rock Mechanics and Mining Sciences》2005,42(5-6):639
Buffer materials being considered as engineered barriers in nuclear fuel waste (NFW) disposal systems possess a pronounced nonlinear behaviour in the unsaturated state. In order to simulate such non-linear responses,the authors adopted an incrementally nonlinear poro-elastic approach where the coefficients of the governing equations are assumed to be functions of suction and the void ratio. These functions are in turn developed from a state-surface equation obtained from suction-controlled oedometric tests. In this paper we show the derivation of the governing equations of the poro-elastic model. A finite element computer code, FRACON, was developed by the authors to numerically solve the above equations. We first use the code to simulate laboratory tests to characterize the swelling properties of a typical bentonite. That same bentonite was used in the FEBEX in-situ heater experiment, conducted at the Grimsel site, Switzerland. The FRACON code was also used to perform blind predictions of the FEBEX heater experiment. It is shown that the model correctly predicts drying of the bentonite near the heaters and re-saturation near the rock interface. The evolution of temperature and the heater thermal output were also reasonably well predicted by the model. The trends in the total stresses developed in the bentonite were correctly predicted; the absolute values however were underestimated probably due to the omission of pore pressure build-up in the rock mass. 相似文献