全文获取类型
收费全文 | 500724篇 |
免费 | 14989篇 |
国内免费 | 6907篇 |
专业分类
电工技术 | 14761篇 |
技术理论 | 9篇 |
综合类 | 8946篇 |
化学工业 | 77653篇 |
金属工艺 | 26567篇 |
机械仪表 | 22145篇 |
建筑科学 | 17631篇 |
矿业工程 | 6221篇 |
能源动力 | 10886篇 |
轻工业 | 36223篇 |
水利工程 | 7013篇 |
石油天然气 | 16408篇 |
武器工业 | 1065篇 |
无线电 | 53552篇 |
一般工业技术 | 96044篇 |
冶金工业 | 64921篇 |
原子能技术 | 11904篇 |
自动化技术 | 50671篇 |
出版年
2022年 | 5773篇 |
2021年 | 8146篇 |
2020年 | 6149篇 |
2019年 | 5796篇 |
2018年 | 15317篇 |
2017年 | 16154篇 |
2016年 | 12634篇 |
2015年 | 8359篇 |
2014年 | 11261篇 |
2013年 | 20493篇 |
2012年 | 18114篇 |
2011年 | 25720篇 |
2010年 | 22344篇 |
2009年 | 22119篇 |
2008年 | 22308篇 |
2007年 | 23337篇 |
2006年 | 14814篇 |
2005年 | 16098篇 |
2004年 | 12951篇 |
2003年 | 12466篇 |
2002年 | 11710篇 |
2001年 | 10665篇 |
2000年 | 9803篇 |
1999年 | 9386篇 |
1998年 | 17204篇 |
1997年 | 13089篇 |
1996年 | 10394篇 |
1995年 | 8151篇 |
1994年 | 7271篇 |
1993年 | 6910篇 |
1992年 | 5550篇 |
1991年 | 5369篇 |
1990年 | 5175篇 |
1989年 | 5077篇 |
1988年 | 4935篇 |
1987年 | 4230篇 |
1986年 | 4145篇 |
1985年 | 4666篇 |
1984年 | 4460篇 |
1983年 | 4070篇 |
1982年 | 3896篇 |
1981年 | 4045篇 |
1980年 | 3866篇 |
1979年 | 3890篇 |
1978年 | 3973篇 |
1977年 | 4407篇 |
1976年 | 5550篇 |
1975年 | 3652篇 |
1974年 | 3497篇 |
1973年 | 3507篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
A.L. Pan H.G. ZhengZ.P. Yang F.X. Liu Z.J. Ding Y.T. Qian 《Materials Research Bulletin》2003,38(5):789-796
Small Ag particles or clusters dispersed mesoporous SiO2 composite films were prepared by a new method: First the matrix SiO2 films were prepared by sol-gel process combined with the dip-coating technique, then they were soaked in AgNO3 solutions followed by irradiation of γ-ray at room temperature and in ambient pressure. The structures of these films were examined by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and optical absorption spectroscopy. It has been shown that the Ag particles grown within the porous SiO2 films are very small, and they are isolated and dispersed from each other with very narrow size distributions. With increasing the soaking concentration and an additional annealing, an opposite peakshift effect of the surface plasmon resonance (SPR) was observed in the optical absorption measurements. 相似文献
83.
低温脂肪酶产生菌的筛选、鉴定及其部分酶学性质 总被引:15,自引:1,他引:14
从南极乔治王岛冻土来源的76株低温细菌中筛选到13株低温脂肪酶产生菌,对其中的BTsl0022菌株进行鉴定。通过生理生化特征、16s rDNA基因序列的同源性和系统发育分析发现,菌株RTsl0022属于假单胞菌属(Pseudomonas),但与已定名的假单胞菌有一定的差异,与未定名的Pseudomonas sp.PsB的亲缘关系最接近,故将其暂定名为Pseudomonas sp.BTsl0022。对该菌脂肪酶的酶学性质初步研究表明,酶的最适作用温度为24℃,对热敏感,60℃处理30min仅残留25%酶活性,酶的适宜作用pH范围在7.0~9.0,最适pH为8.0。 相似文献
84.
Lind M.G.J. Weidong Xiao Dunford W.G. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(2):409-418
This paper presents a comprehensive nonlinear model of the controlled constant voltage transformer also known as the ferroresonant transformer. Saturation is a normal mode of operation for this device. This paper derives an equivalent electrical circuit that relates to the physical structure of a typical design. The level of detail includes winding resistances, continuously nonlinear magnetizing inductances, tapped windings, and leakage inductances. The paper describes methods to extract the winding resistances, leakage inductances, and hysteresis loops of the transformer and how to fit the latter into single-valued nonlinear functions. The paper compares computer simulation results of the model with those obtained analytically and experimentally. The results show that the derived circuit will be very useful for designers of the ferroresonant transformer, which is used in uninterruptible power supplies. 相似文献
85.
Concrete interlocking blocks (CIBs) are utilized in a variety of commercial, municipal, and industrial applications. Superior engineering properties, low maintenance, ease of placement and removal, reuse of original blocks, aesthetic appeal, and immediate availability are the primary reasons for choosing concrete block pavement over other paving surfaces. It is a common practice to pigment building materials, such as mortar, concrete pavers, concrete roof tiles, and prefabricated concrete products; CIBs are colored using iron oxide pigments. This article presents experimental results detailing the properties of CIBs dyed with pigments. The results of these experiments are as follows: Because the particles of iron oxide pigments are finer than those of brown iron oxide, interlocking blocks mixed with the former acquired higher color strength than with the latter. Additional analysis determined a definite relationship between the flexural strength and the absorption ratio of pigment-dyed blocks; the correlation coefficient (R2) of interlocking blocks at 91 days was .90. It is suggested that if iron oxide pigments are to be used to color CIBs, the pigment-to-cement ratio should be below 4%. 相似文献
86.
Ysebaert G. Vanbleu K. Cuypers G. Moonen M. Pollet T. 《Signal Processing, IEEE Transactions on》2003,51(7):1916-1927
In discrete multitone receivers, the classical equalizer structure consists of a (real) time domain equalizer (TEQ) combined with complex one-tap frequency domain equalizers. An alternative receiver is based on a per tone equalization (PTEQ), which optimizes the signal-to-noise ratio (SNR) on each tone separately and, hence, the total bitrate. In this paper, a new initialization scheme for the PTEQ is introduced, based on a combination of least mean squares (LMS) and recursive least squares (RLS) adaptive filtering. It is shown that the proposed method has only slightly slower convergence than full square-root RLS (SR-RLS) while complexity as well as memory cost are reduced considerably. Hence, in terms of complexity and convergence speed, the proposed algorithm is in between LMS and RLS. 相似文献
87.
D. Vignolles D. Smirnov G. Rikken B. Raquet H. Rakoto C. Proust M. Nardone J. Léotin F. Lecouturier M. Goiran O. Drachenko J. M. Broto L. Brossard A. Audouard 《Journal of Low Temperature Physics》2003,133(1-2):97-120
An overview over past and present activities and future developments at the Toulouse pulsed magnetic field facility is given, both as far as technical developments of the infrastructure, as well as low temperature physics performed at the LNCMP are concerned. 相似文献
88.
Often scientific instruments on exploratory satellites are used to collect cosmic particles. These instruments, such as the Faraday cup, require a high-voltage regulated power source. On the proposed solar probe satellite there will be instruments which will collect cosmic particles close to the sun. Naturally temperature effects on the voltage regulator are a concern. Specifically power dissipation within the regulator must stay within stringent guidelines. The high-voltage regulator circuit is a resonant flyback topology with a dissipative series switch whose on resistance controls the output voltage level. The extreme temperatures in space will change the inductance of the flyback transformer which will affect the output voltage. State space analysis techniques are used to determine how the value of the transformer inductance and capacitance in the flyback converter affects the output voltage and consequently the power dissipated by the transformer and the switch. The accuracy of the analysis is verified by comparing results with those obtained from an experimental circuit. The results can then be used to help the designer chose nominal capacitance and inductance values that will work over the temperature range of interest. 相似文献
89.
A mechanism of soldering of an aluminum alloy die casting to a steel die is proposed. A soldering critical temperature is
postulated, at which iron begins to react with aluminum to form an aluminum-rich liquid phase and solid intermetallic compounds.
The liquid joins the die with the casting upon solidification. The critical temperature is determined by the elements in both
the casting alloy and the die material and is equal to the solidus temperature of the resulting alloy. The critical temperature
is used to predict the onset of die soldering, and the local liquid fraction is related to the soldering tendency. Experiments
have been carried out to validate the concept and to determine the critical temperature for die soldering in an iron-aluminum
system. Thermodynamic calculations are used to determine the critical temperature and soldering tendency for the cases of
pure aluminum and a 380 alloy in a steel mold. Factors affecting the soldering tendency are discussed, and methods for reducing
die soldering are suggested. 相似文献
90.
J.M. Roth T.G. Ulmer N.W. Spellmeyer S. Constantine M.E. Grein 《Photonics Technology Letters, IEEE》2004,16(9):2009-2011
We demonstrate a novel 40-GHz mode-locked fiber laser that utilizes a single active device to provide both gain and mode-locking. The laser produces pulses as short as 2.2 ps, is tunable over a 27-nm band centered at 1553 nm, and exhibits long-term stability without cavity-length feedback control. The pulse train at 1556 nm was used in a 40-Gb/s transmission experiment over 45 km with a low 0.4-dB power penalty. 相似文献