全文获取类型
收费全文 | 510408篇 |
免费 | 6213篇 |
国内免费 | 1792篇 |
专业分类
电工技术 | 10100篇 |
综合类 | 791篇 |
化学工业 | 75638篇 |
金属工艺 | 19613篇 |
机械仪表 | 14625篇 |
建筑科学 | 13221篇 |
矿业工程 | 1271篇 |
能源动力 | 13673篇 |
轻工业 | 49743篇 |
水利工程 | 4055篇 |
石油天然气 | 4805篇 |
武器工业 | 11篇 |
无线电 | 64726篇 |
一般工业技术 | 94716篇 |
冶金工业 | 100030篇 |
原子能技术 | 8404篇 |
自动化技术 | 42991篇 |
出版年
2021年 | 3558篇 |
2019年 | 3327篇 |
2018年 | 5500篇 |
2017年 | 5297篇 |
2016年 | 5556篇 |
2015年 | 4143篇 |
2014年 | 7002篇 |
2013年 | 23247篇 |
2012年 | 11805篇 |
2011年 | 16530篇 |
2010年 | 13168篇 |
2009年 | 14912篇 |
2008年 | 15860篇 |
2007年 | 15857篇 |
2006年 | 14276篇 |
2005年 | 13241篇 |
2004年 | 12861篇 |
2003年 | 12634篇 |
2002年 | 12514篇 |
2001年 | 12730篇 |
2000年 | 11947篇 |
1999年 | 12821篇 |
1998年 | 31767篇 |
1997年 | 22658篇 |
1996年 | 17618篇 |
1995年 | 13370篇 |
1994年 | 12081篇 |
1993年 | 11677篇 |
1992年 | 8585篇 |
1991年 | 8317篇 |
1990年 | 7855篇 |
1989年 | 7585篇 |
1988年 | 7447篇 |
1987年 | 6212篇 |
1986年 | 6303篇 |
1985年 | 7495篇 |
1984年 | 6762篇 |
1983年 | 6240篇 |
1982年 | 5677篇 |
1981年 | 5836篇 |
1980年 | 5418篇 |
1979年 | 5226篇 |
1978年 | 4996篇 |
1977年 | 6165篇 |
1976年 | 8415篇 |
1975年 | 4298篇 |
1974年 | 4150篇 |
1973年 | 4127篇 |
1972年 | 3406篇 |
1971年 | 3021篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
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
152.
LW Seymour H Soyez A De Marre MA Shoaibi EH Schacht 《Canadian Metallurgical Quarterly》1996,11(5):351-365
Prodrugs of mitomycin C (MMC) based on soluble poly-[N-(2-hydroxyethyl)-L-glutamine] (pHEG) polymers have been evaluated as tumour-targeted drugs. These materials are designed to exploit the enhanced permeability of tumour vasculature, combining a passive tumour tropism with decreased systemic liberation of free MMC. A tri- or tetrapeptide linkage (e.g. Gly-Phe-Ala-Leu) between pHEG and the aziridine nitrogen of MMC can combine good hydrolytic stability with rapid cleavage by lysosomal enzymes, releasing free MMC. The conjugates showed decreased systemic toxicity and could be administered to mice at a total MMC dose of 15 mg/kg i.v., compared with just 6 mg/kg for free MMC. Conjugates also showed better activity against animal models of established tumours, achieving up to 77% increased life span (ILS) against solid P388 leukaemia, compared with only 23% for free MMC, and up to 121% ILS against solid C26 colorectal carcinoma, compared with no activity for the free drug. Improving the therapeutic index of anticancer drugs by combining tumour tropism with decreased systemic toxicity is a versatile approach that should produce a new generation of improved anticancer agents. 相似文献
153.
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
154.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9 相似文献
155.
In summary, recent literature indicates that the complications of chronic otitis media have been decreasing. However, even with the advent of modern and more powerful antimicrobials and aggressive surgical eradication of disease, the morbidity and mortality are still high. Some complications may initially be quite obvious and some complications may be quite subtle. Therefore, the most important tools in making early diagnosis are careful history and physical examination, and a high index of suspicion for impending complications. 相似文献
156.
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
157.
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
158.
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
159.
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
160.
Ion beam assisted deposition (IBAD) of thin films is still a new technology with respect to the number of applications. A broader industrial application depends on the availability and versatility of facilities which are able to process various kinds of workpieces under appropriate conditions. Recently, IBAD facilities of the second generation were described in literature and are partially commercially available. In the present report such IBAD machines with their special features such as number and kind of ion sources and evaporators are described. Particularly, the set-up of the ALLIGATOR, a versatile IBAD device for coating complex workpieces under ion bombardment with a broad range of ion energies, is described. As an application example, recent results on the treatment of medical implants are discussed. In -vivo tests of coated cardiovascular stents showed that the deposited noble metal films were effective in influencing the corrosivity and thromboresistance of the implant 相似文献