全文获取类型
收费全文 | 470032篇 |
免费 | 4634篇 |
国内免费 | 1042篇 |
专业分类
电工技术 | 8403篇 |
综合类 | 415篇 |
化学工业 | 71323篇 |
金属工艺 | 23227篇 |
机械仪表 | 16636篇 |
建筑科学 | 9772篇 |
矿业工程 | 4446篇 |
能源动力 | 9692篇 |
轻工业 | 30903篇 |
水利工程 | 6138篇 |
石油天然气 | 14913篇 |
武器工业 | 91篇 |
无线电 | 50574篇 |
一般工业技术 | 103642篇 |
冶金工业 | 73446篇 |
原子能技术 | 14673篇 |
自动化技术 | 37414篇 |
出版年
2021年 | 4201篇 |
2019年 | 4170篇 |
2018年 | 7789篇 |
2017年 | 8074篇 |
2016年 | 8527篇 |
2015年 | 4817篇 |
2014年 | 8340篇 |
2013年 | 19639篇 |
2012年 | 12515篇 |
2011年 | 16301篇 |
2010年 | 13059篇 |
2009年 | 14604篇 |
2008年 | 15449篇 |
2007年 | 15173篇 |
2006年 | 13047篇 |
2005年 | 11758篇 |
2004年 | 11412篇 |
2003年 | 11202篇 |
2002年 | 10720篇 |
2001年 | 10622篇 |
2000年 | 10339篇 |
1999年 | 9855篇 |
1998年 | 20254篇 |
1997年 | 15234篇 |
1996年 | 11925篇 |
1995年 | 9545篇 |
1994年 | 8665篇 |
1993年 | 8719篇 |
1992年 | 7275篇 |
1991年 | 7077篇 |
1990年 | 7036篇 |
1989年 | 6714篇 |
1988年 | 6444篇 |
1987年 | 6027篇 |
1986年 | 5878篇 |
1985年 | 6487篇 |
1984年 | 6219篇 |
1983年 | 5754篇 |
1982年 | 5453篇 |
1981年 | 5567篇 |
1980年 | 5403篇 |
1979年 | 5486篇 |
1978年 | 5542篇 |
1977年 | 5912篇 |
1976年 | 6959篇 |
1975年 | 5106篇 |
1974年 | 5147篇 |
1973年 | 5228篇 |
1972年 | 4467篇 |
1971年 | 4108篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
Modeling ion implantation of HgCdTe 总被引:2,自引:0,他引:2
H. G. Robinson D. H. Mao B. L. Williams S. Holander-Gleixner J. E. Yu C. R. Helms 《Journal of Electronic Materials》1996,25(8):1336-1340
Ion implantation of boron is used to create n on p photodiodes in vacancy-doped mercury cadmium telluride (MC.T). The junction
is formed by Hg interstitials from the implant damage region diffusing into the MC.T and annihilating Hg vacancies. The resultant
doping profile is n+/n-/p, where the n+ region is near the surface and roughly coincides with the implant damage, the n- region is where Hg vacancies have been annihilated revealing a residual grown-in donor, and the p region remains doped by
Hg vacancy double acceptors. We have recently developed a new process modeling tool for simulating junction formation in MC.T
by ion implantation. The interstitial source in the damage region is represented by stored interstitials whose distribution
depends on the implant dose. These interstitials are released into the bulk at a constant, user defined rate. Once released,
they diffuse away from the damage region and annihilate any Hg vacancies they encounter. In this paper, we present results
of simulations using this tool and show how it can be used to quantitatively analyze the effects of variations in processing
conditions, including implant dose, annealing temperature, and doping background. 相似文献
154.
The metabolism of the poly(A) tail is a process important for the translational regulation of maternal mRNAs in Xenopus laevis oocytes and early embryos. Two poly(A) nuclease (PAN) activities have been described in Xenopus embryo or activated egg extracts (Legagneux et al (1995) RNA 1, 1001-1008). These activities (default PAN and EgPAN) are distinguishable by their deadenylation kinetics and their substrate specificities. In this report, we show that these activities display different sensitivities to biochemical treatments. Urea and, to a lesser extent, spermidine, inhibit EgPAN at concentrations which have no effect on default PAN. Heparin activates default PAN but inhibits EgPAN. When extracts are fractionated by ultracentrifugation, the default activity is recovered in one unique fraction, whereas two fractions must be combined to reconstitute the EgPAN activity. Moreover, these two deadenylation activities are separable by size exclusion chromatography under native conditions. We conclude that these two deadenylation activities are mediated by two protein complexes. 相似文献
155.
D Sternberg A Peled E Shezen O Abramsky W Jiang F Bertolero D Zipori 《Canadian Metallurgical Quarterly》1996,2(1):29-38
The immunological agglutination reactions of physically absorbed F(ab')2 molecules onto anionic and cationic latex particles have been investigated by means of optical absorbance measurements. These measurements have been conducted under different conditions to determine the most influential factors. Surface F(ab')2 and BSA densities, particle concentration in the reaction medium and polyethylene glycol concentration are some of these factors. Sensitized cationic and anionic latexes differ considerably with respect to their colloidal stability and reactivity. As a general rule, the sensitized cationic latex has a relatively higher colloidal stability and hence, it provides reagents with a better optical response. Less than 0.025 microgram/ml of C-reactive protein has been detected using this particle enhanced optical immunoassay. 相似文献
156.
Known examples of the positive influence of electrohydroimpulse treatment on the quality of weld joints of various steels, particularly including an increase in their long-term and cyclic strength and also corrosion resistance, are analyzed. It is shown that in this case there is a reduction in residual macro- and micro-stresses and also a change in the parameters of the dislocation structure of the joint metal in the direction of stabilization of it.Translated from Problemy Prochnosti, No. 4, pp. 119–123, April, 1996. 相似文献
157.
Biryukov S.V. Polevoi V.G. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(6):1160-1170
For pt.I see ibid., vol.43, no.6, pp.1150-9 (1996). An exact solution of the electrostatic problem for calculating the surface charge and electric field distributions in an arbitrary periodic interdigital transducer (IDT) is given using the results of our companion paper. An arbitrary external electric field may be specified along the electrode structure with the unit cell containing one electrode, or several electrodes, of different widths. The potentials of the electrodes that may be specified are also arbitrary. It is shown that in the case without an external field, the solution includes all the known results as special cases. The case of shorted electrodes in the external electric field is investigated in detail. The surface charge and electric field distributions are calculated for a spatially harmonic external field with an arbitrary wavenumber. The results of the calculations are represented graphically for various ratios between the period of the electrode structure and the wavelength of the external field for the case of a unit cell containing one or two electrodes of different widths 相似文献
158.
Storage performance-metrics and benchmarks 总被引:2,自引:0,他引:2
Chen P.M. Patterson D.A. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1993,81(8):1151-1165
The metrics and benchmarks used in storage performance evaluation are discussed. The technology trends taking place in storage systems, such as disk and tape evolution, disk arrays, and solid-state disks, are highlighted. The current popular I/O benchmarks are then described, reviewed, and run on three systems: a DECstation 5000/200 running the Sprite Operating System, a SPARCstation 1+ running SunOS, and an HP Series 700 (Model 730) running HP-UX. Two approaches to storage benchmarks-LADDIS and a self-scaling benchmark with predicted performance-are also described 相似文献
159.
Wavelength conversion of optical signals over 20 nm is demonstrated using highly nondegenerate four-wave mixing in a semiconductor traveling-wave optical amplifier. This technique has the potential for extremely-high-speed operation and allows continuous tuning of both input and output wavelengths over the amplifier gain bandwidth. It is demonstrated that, even for such a large wavelength conversion range, it is possible to obtain conversion efficiencies in excess of -10 dB and high extinction ratios. The feasibility of the technique is demonstrated by system measurements at 622 Mb/s, showing a 1.1-dB power penalty at 10-9 bit error rate (BER) 相似文献
160.
The thermal expansion of tellurides of germanium, bismuth, and intermetallic compounds is investigated over the temperature range 293-973 K.Belarusian Agricultural Technical University, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 5, pp. 612–616, May 1994. 相似文献