全文获取类型
收费全文 | 6945篇 |
免费 | 782篇 |
国内免费 | 421篇 |
专业分类
电工技术 | 122篇 |
综合类 | 502篇 |
化学工业 | 478篇 |
金属工艺 | 68篇 |
机械仪表 | 497篇 |
建筑科学 | 192篇 |
矿业工程 | 70篇 |
能源动力 | 48篇 |
轻工业 | 69篇 |
水利工程 | 38篇 |
石油天然气 | 82篇 |
武器工业 | 261篇 |
无线电 | 4187篇 |
一般工业技术 | 874篇 |
冶金工业 | 242篇 |
原子能技术 | 57篇 |
自动化技术 | 361篇 |
出版年
2023年 | 38篇 |
2022年 | 66篇 |
2021年 | 110篇 |
2020年 | 127篇 |
2019年 | 94篇 |
2018年 | 112篇 |
2017年 | 214篇 |
2016年 | 185篇 |
2015年 | 239篇 |
2014年 | 463篇 |
2013年 | 438篇 |
2012年 | 625篇 |
2011年 | 544篇 |
2010年 | 455篇 |
2009年 | 456篇 |
2008年 | 582篇 |
2007年 | 555篇 |
2006年 | 595篇 |
2005年 | 468篇 |
2004年 | 385篇 |
2003年 | 247篇 |
2002年 | 151篇 |
2001年 | 157篇 |
2000年 | 99篇 |
1999年 | 126篇 |
1998年 | 82篇 |
1997年 | 62篇 |
1996年 | 69篇 |
1995年 | 45篇 |
1994年 | 54篇 |
1993年 | 45篇 |
1992年 | 39篇 |
1991年 | 41篇 |
1990年 | 39篇 |
1989年 | 32篇 |
1988年 | 20篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1971年 | 5篇 |
1959年 | 3篇 |
1958年 | 2篇 |
1957年 | 4篇 |
1955年 | 2篇 |
1954年 | 5篇 |
排序方式: 共有8148条查询结果,搜索用时 53 毫秒
91.
Pupil stability is one of the factors which limit the performance and operational stability of adaptive optics (AO) systems. This paper analyses two pupil-tracking methods to measure the lateral pupil shift: the first one utilizes the fluxes in all outer edge sub-apertures of a Shack–Hartmann sensor and the second one utilizes the real-time interaction matrix used in an AO system. Experiments with 9?×?9 Shack–Hartmann sensor are conducted to verify both pupil-tracking algorithms. The results show that both algorithms are effective, after two correction steps, the residual pupil shift is reduced to less than 5% of a Shack–Hartmann sub-aperture. 相似文献
92.
93.
A modal wavefront sensor for ocular aberrations exhibits two main advantages compared to a conventional Shack–Hartmann sensor. As the wavefront is detected in the Fourier plane, the method is robust against local loss of information (e.g. local opacity of ocular lens as in the case of cataract), and is not dependent on the spatial distribution of wavefront sampling. We have proposed a novel method of wavefront sensing for ocular aberrations that directly detects the strengths of Zernike aberrations. A multiplexed Fourier computer-generated hologram has been designed as the binary phase element (BPE) for the detection of second-order and higher-order ocular aberrations (HOAs). The BPE design has been validated by comparing the simulated far-field pattern with the experimental results obtained by displaying it on a spatial light modulator. Simulation results have demonstrated the simultaneous wavefront detection with an accuracy better that ~λ/30 for a measurement range of ±2.1λ with reduced cross-talk. Sensor performance is validated by performing a numerical experiment using the City data set for test waves containing second-order and HOAs and measurement errors of 0.065?µm peak-to-valley (PV) and 0.08?µm (PV) have been obtained, respectively. 相似文献
94.
We show that Maxwell's fish-eye lens can make a semi-circular perfect electric conductor look like a circular one. Such an effect can also be achieved (not perfectly) by using negative index metamaterials, but only within a single frequency. Maxwell's fish-eye lens, however, can work for a set of eigenfrequencies. Numerical simulations are performed to verify the effect. 相似文献
95.
The original carpet cloak was designed by a numerical method, the quasi-conformal mapping. There- fore its refractive index profile was obtained numerically. In this letter, we propose a new carpet cloak based on the optical conformal mapping, with an analytical form of a refractive index profile, thereby facilitating future experimental designs. 相似文献
96.
Assaf Gal Vlad Brumfeld Steve Weiner Lia Addadi Dan Oron 《Advanced materials (Deerfield Beach, Fla.)》2012,24(10):OP77-OP83
Cystoliths are amorphous calcium carbonate bodies that form in the leaves of some plant families. Cystoliths are regularly distributed in the epidermis and protrude into the photosynthetic tissue, the mesophyll. The photosynthetic pigments generate a steep light gradient in the leaf. Under most illumination regimes the outer mesophyll is light saturated, thus the photosynthetic apparatus is kinetically unable to use the excess light for photochemistry. Here we use micro‐scale modulated fluorometry to demonstrate that light scattered by the cystoliths is distributed from the photosynthetically inefficient upper tissue to the efficient, but light deprived, lower tissue. The results prove that the presence of light scatterers reduces the steep light gradient, thus enabling the leaf to use the incoming light flux more efficiently. MicroCT and electron microscopy confirm that the spatial distribution of the minerals is compatible with their optical function. During the study we encountered large calcium oxalate druses in the same anatomical location as the cystoliths. These druses proved to have similar light scattering functions as the cystoliths. This study shows that certain minerals in the leaves of different plants distribute the light flux more evenly inside the leaf. 相似文献
97.
98.
The dressed parametric four-wave mixing (FWM) process has been investigated in hot atomic rubidium vapor. We use a strong pumping field to generate entangled photon pairs of spontaneous parametric FWM (SP-FWM) which can be enhanced by an external dressing effect. Seeding probe beam into the Stokes or anti-Stokes (SP-FWM) channel will form the parametric amplified FWM (PA-FWM) process, then the non-linear gain and electromagnetically induced absorption (EIA) are observed, caused by the internal dressing effect. However, with scanning of pumping field the absorbing background will vanish, which will result in drastic increase in PA-FWM signal gain. 相似文献
99.
Huriye Akdas-Kilig Jean-Pierre MalvalFabrice Morlet-Savary Anu SinghLoic Toupet Isabelle Ledoux-RakJoseph Zyss Hubert Le Bozec 《Dyes and Pigments》2012,92(1):681-688
Two new 4,4′-bis(donor)-6,6′-diphenyl- 2,2′-bipyridine ligands and their corresponding D2d (CuI, AgI, ZnII) octupolar metal complexes were synthesized, and their linear and nonlinear optical properties were investigated. A single crystal X-ray structure was also determined for the bis[4,4′-bis(diethylaminostyryl)-6,6′-diphenyl-bipyridine]copper(I) complex, which revealed a distorded pseudo-tetrahedral geometry. Molecular second-order nonlinear optical properties were determined for the complexes using the Harmonic Light Scatterring technique at 1.91 μm. These metallo-chromophores display large first hyperpolarizabilities β1.91 in the range of 211-340 × 10−30 esu, which increase with the Lewis acidity of the metal ion. The two-photon absorption properties of the bipyridyl ligands and related complexes were determined using either the two-photon emission method for fluorescent compounds or the open aperture Z-scan technique for non emissive ones. The complexes display red-shifted two-photon absorption bands compared to their metal-ion free chromophores, as well as a large increase of the maximum two-photon absorption cross-sections. 相似文献
100.