全文获取类型
收费全文 | 516774篇 |
免费 | 6301篇 |
国内免费 | 1410篇 |
专业分类
电工技术 | 10116篇 |
综合类 | 871篇 |
化学工业 | 76378篇 |
金属工艺 | 18661篇 |
机械仪表 | 15558篇 |
建筑科学 | 12876篇 |
矿业工程 | 1842篇 |
能源动力 | 13702篇 |
轻工业 | 47335篇 |
水利工程 | 4690篇 |
石油天然气 | 7034篇 |
武器工业 | 75篇 |
无线电 | 66091篇 |
一般工业技术 | 97867篇 |
冶金工业 | 95782篇 |
原子能技术 | 9639篇 |
自动化技术 | 45968篇 |
出版年
2021年 | 3947篇 |
2019年 | 3800篇 |
2018年 | 6429篇 |
2017年 | 6351篇 |
2016年 | 6681篇 |
2015年 | 4488篇 |
2014年 | 7708篇 |
2013年 | 23420篇 |
2012年 | 12581篇 |
2011年 | 17348篇 |
2010年 | 13582篇 |
2009年 | 15537篇 |
2008年 | 16553篇 |
2007年 | 16346篇 |
2006年 | 14770篇 |
2005年 | 13500篇 |
2004年 | 13124篇 |
2003年 | 12836篇 |
2002年 | 12370篇 |
2001年 | 12470篇 |
2000年 | 11964篇 |
1999年 | 12433篇 |
1998年 | 29074篇 |
1997年 | 21044篇 |
1996年 | 16627篇 |
1995年 | 12958篇 |
1994年 | 11627篇 |
1993年 | 11286篇 |
1992年 | 8739篇 |
1991年 | 8277篇 |
1990年 | 8082篇 |
1989年 | 7649篇 |
1988年 | 7434篇 |
1987年 | 6373篇 |
1986年 | 6364篇 |
1985年 | 7533篇 |
1984年 | 6914篇 |
1983年 | 6392篇 |
1982年 | 5836篇 |
1981年 | 6097篇 |
1980年 | 5634篇 |
1979年 | 5483篇 |
1978年 | 5212篇 |
1977年 | 6158篇 |
1976年 | 7812篇 |
1975年 | 4666篇 |
1974年 | 4489篇 |
1973年 | 4545篇 |
1972年 | 3685篇 |
1971年 | 3365篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
A case of traumatic extracranial vertebral arterial dissection leading to vertebrobasilar thrombosis and respiratory compromise requiring mechanical ventilation was managed with intraarterial thrombolysis and stenting of the vertebral intimal dissection. In contrast to similar, previously reported cases, this critically ill patient made a full recovery, returning to his job as a secondary school teacher. 相似文献
162.
Manku T. McGregor J.M. Nathan A. Roulston D.J. Noel J.-P. Houghton D.C. 《Electron Devices, IEEE Transactions on》1993,40(11):1990-1996
Results of the drift hole mobility in strained and unstrained SiGe alloys are reported for Ge fractions varying from 0 to 30% and doping levels of 1015-1019 cm-3. The mobilities are calculated taking into account acoustic, optical, alloy, and ionized-impurity scattering. The mobilities are then compared with experimental results for a boron doping concentration of 2×1019 cm-3. Good agreement between experimental and theoretical values is obtained. The results show an increase in the mobility relative to that of silicon 相似文献
163.
Kringlebotn J.T. Morkel P.R. Reekie L. Archambault J.-L. Payne D.N. 《Photonics Technology Letters, IEEE》1993,5(10):1162-1164
We report a 7.6-mW single-frequency fiber laser operating at 1545 nm, using for the first time an Er3+:Yb3+ doped fiber and a fiber grating output coupler. The laser did not exhibit self-pulsation, which is a typical problem in short three-level fiber lasers, and had a relative intensity noise (RIN) level below -145.5 dB/Hz at frequencies above 10 MHz. The linewidth of the laser was limited by the relaxation oscillation sidebands in the optical spectrum and was typically less than 1 MHz 相似文献
164.
165.
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
166.
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
167.
S. R. Meschyan 《Soil Mechanics and Foundation Engineering》1996,33(1):16-20
A comparison is made between different alternate schemes for determination of the strength of soils possessing rheological
properties on the basis of our own experimental data. An original method is proposed for determination of the ultimate long-term
strength from tests on the conditionally instantaneous failure of soil after preliminary deformation in a creep regime, as
well as from tests in a controlled-deformation regime.
Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 14–18, January–February, 1996. 相似文献
168.
We propose and evaluate a medium-access control (MAC) protocol for synchronous cellular packet direct-sequence code-division multiple-access (DS/CDMA). The protocol is designed for handling a variety of multimedia traffic types in an integrated wireless-access network (IWAN). For instance, the protocol is suited for carrying multiple traffic types of different priorities. An analytical model for the equilibrium state has been developed for the proposed protocol. A comparative evaluation of the protocol is done for three different radio frequency bandwidths currently under consideration for personal communication services (PCS), i.e., 1.25 MHz, 5 MHz, and 10 MHz. Our results demonstrate that the proposed protocol is both robust and flexible for the intended IWAN applications. It offers a significant multiplexing gain as the bandwidth increases 相似文献
169.
The nature of pairing mechanism as well as transition temperature of yttrium cuprates is discussed using the strong coupling
theory. An interaction potential has been developed for the layered structure with two conducting CuO2(a–b) layers in a unit cell. The interaction potential properly takes care of electron-electron, electron-phonon and electron-plasmon
interactions. Furthermore, the electron-phonon coupling parameter (λ), the modified Coulomb repulsive parameter (μ*) and the 2D acoustic phonon (plasmon) energy as a function of oxygen deficiency is worked out. Finally, the superconducting
transition temperature (T
c) is then evaluated by using these coupling parameters and obtainedT
c = 95(92)K for Y(Yb)Ba2Cu3O7−δ
superconductors withδ = 0·0. The model parameters estimated from the layered structure approach are consistent with the strong coupling theory.
The result deduced on the variation ofT
c withδ are in fair agreement with the earlier reported data on yttrium cuprates. The analysis of the above results are discussed. 相似文献
170.
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