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排序方式: 共有1433条查询结果,搜索用时 15 毫秒
161.
A fiber-optic Fabry–Perot (F–P) acoustic emission (AE) sensor system based on an improved double wavelength stabilization technique is described. Without stabilization, the sensor system drifts out of quadrature due to the presence of low-frequency dynamic strains. The stabilization is achieved by using a dense wavelength division multiplexer (DWDM) to generate two quadrature phase-shifted output signals. An optimum model of double wavelength stabilization is established. The filtering wavelengths of DWDM are calculated using an optimization design method. The performance of the developed sensor system was verified by two preliminary tests. One was a test on the stabilization of operating point of fiber-optic F–P sensor, and other was the detection of simulated AE signals generated by the impact and pencil lead breaking. The test results demonstrate that simulated AE signals are successfully detected using this stabilized sensor system, which solves the fade-out problem. 相似文献
162.
Simultaneous downlink performance improvement and uplink wavelength reuse in a full-duplex millimeter-wave (MMW) radio-over-fiber (RoF) system by using a simple and cost-effective all-fiber optical interleaver are proposed and demonstrated. The MMW RoF downlink performance improvement is based on suppressing optical carrier-to-sideband ratio (OCSR), with which the mechanism is confirmed by theoretic analysis and derived experimental results. Measured results show that, by suppressing OCSR using a fabricated all-fiber optical interleaver, the downlink optical receiver sensitivity is improved about 2.1 dB. The downlink data rate is 1.25 Gbit/s and the carrier frequency is 58.1 GHz; the link consists of 6 km optical single-mode fiber and 1 m wireless connection. On the other hand, with the interleaver suppressing downlink OCSR, simultaneously an optical carrier is recovered from the RoF downlink and is reused for RoF uplink transmission. The uplink is operated at 62.9 GHz and the data rate is the same 1.25 Gbit/s. With the recovered optical carrier, a laser-free remote access point is achieved. The principle, structure, and fabrication of an all-fiber optical interleaver are also presented in this paper. 相似文献
163.
Junhai Liu Wenjuan Han Huaijin Zhang Jiyang Wang Valentin Petrov 《Optics Communications》2008,281(21):5393-5395
By employing a tunable Ti:sapphire laser, we conducted an investigation into the effects of pump wavelength deviation on the laser performance of Yb:KLu(WO4)2 crystal. Pumping efficiencies exceeding 70% could be reached under lasing conditions with a 3-mm crystal of Yb concentration of 5.24 at.%, when the pumping wavelength was within the main absorption band centered at 981 nm extending from 974 to 990 nm. For different pumping wavelengths, the laser exhibited a single output–input relation with respect to absorbed pump power, giving an average slope efficiency amounting to 51%. 相似文献
164.
This paper presents the analytical and simulation responses of the closed orbit distortion in the SSRF storage ring to random and plane wave like magnet vibrations respectively. It is shown that the use of girder is very beneficial in the view of suppressing this response function. Effect of the independently supported gradient bending magnets to the closed orbit response is given. An analytic formula is written to give a rough estimate of the closed orbit distortion due to ground motion, taking into account the closed orbit response function and girder transfer function. As an example, the result of SSRF case is given. 相似文献
165.
166.
角度调谐滤光片特性分析及膜系设计 总被引:5,自引:2,他引:3
对窄带滤光片的倾斜入射特性作了分析.斜入射时其透射通带和峰值会向短波方向移动,透射曲线的稳定性跟滤光片的间隔层结构相关,多腔间使用相同的间隔层可以保证斜入射时有稳定的峰值透射率和带宽,利用该特点可以制备角度调谐窄带滤光片.透射光S和P偏振分量的中心波长随入射角度的增大出现分离现象,产生较大的偏振相关损耗.通过搭配不同厚度的高低折射率材料作为间隔层,改变其有效折射率,使其两个偏振分量的中心波长实现重合.设计了符合密集波分复用(Dense Wavelength Division Multiplexing,DWDM)系统要求的低偏振相关损耗四腔窄带角度调谐滤光片膜系,其可调谐范围达20 nm以上,并评估了所设计角度调谐滤光片的调谐性能. 相似文献
167.
Lei Li Yuhuan Wu Fu‐Sheng Du Zi‐Chen Li 《Journal of polymer science. Part A, Polymer chemistry》2019,57(3):334-341
We report the modular and facile synthesis of three novel polymers able to photodegrade by UV and visible light via the Passerini multicomponent polymerizations of 1,6‐hexanedioic acid and 1,6‐diisocyanohexane with 5‐methoxy‐2‐nitrobenzaldehyde ( M2 ), 4,5‐dimethoxy‐2‐nitrobenzaldehyde ( M3 ) or 7‐(N,N‐diethylamino)‐4‐formylcoumarin ( M4 ) respectively. This synthetic strategy takes the advantage of the in situ formation of a photolabile chromophore via the Passerini reaction of an aromatic aldehyde with an acid and an isocyanide, thus it is a versatile approach to regulating the photochemical property of the photolabile chromophores by just changing the aldehyde structure. Importantly, two polymers ( P3 and P4 ) even exhibit NIR degradability due to the two‐photon absorption, and their nanoparticles formulated by the single emulsion method have been used as the NIR‐responsive nanocarriers for hydrophobic dyes. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 334–341 相似文献
168.
This article presents a wavelength selection framework for mixture identification problems. In contrast with multivariate calibration, where the mixture constituents are known and the goal is to estimate their concentration, in mixture identification the goal is to determine which of a large number of chemicals is present. Due to the combinatorial nature of this problem, traditional wavelength selection algorithms are unsuitable because the optimal set of wavelengths is mixture dependent. To address this issue, our framework interleaves wavelength selection with the sensing process, such that each subsequent wavelength is determined on-the-fly based on previous measurements. To avoid early convergence, our approach starts with an exploratory criterion that samples the spectrum broadly, then switches to an exploitative criterion that selects increasingly more relevant wavelengths as the solution approaches the true constituents of the mixture. We compare this “active” wavelength selection algorithm against a state-of-the-art passive algorithm (successive projection algorithm), both experimentally using a tunable spectrometer and in simulation using a large spectral library of chemicals. Our results show that our active method can converge to the true solution more frequently and with fewer measurements than the passive algorithm. The active method also leads to more compact solutions with fewer false positives. 相似文献
169.
Ujjwal Mandal Subhadip Ghosh Dibyendu Kumar Das Aniruddha Adhikari Shantanu Dey Kankan Bhattacharyya 《Journal of Chemical Sciences》2008,120(1):15-23
Fluorescence resonance energy transfer (FRET) from Coumarin 153 (C153) to Rhodamine 6G (R6G) in a secondary aggregate of a
bile salt (sodium deoxycholate, NaDC) is studied by femtosecond up-conversion. The emission spectrum of C153 in NaDC is analysed
in terms of two spectra-one with emission maximum at 480 nm which corresponds to a non-polar and hydrophobic site and another
with maximum at ∼530 nm which arises from a polar hydrophilic site. The time constants of FRET were obtained from the rise
time of the emission of the acceptor (R6G). In the NaDC aggregate, FRET occurs in multiple time scales — 4 ps and 3700 ps.
The 4 ps component is assigned to FRET from a donor (D) to an acceptor (A) held at a close distance (R
DA ∼ 17 ?) inside the bile salt aggregate. The 3700 ps component corresponds to a donor-acceptor distance ∼48 ?. The long (3700
ps) component may involve diffusion of the donor. With increase in the excitation wavelength (λ
ex) from 375 to 435 nm, the relative contribution of the ultrafast component of FRET (∼4 ps) increases from 3 to 40% with a
concomitant decrease in the contribution of the ultraslow component (∼3700 ps) from 97 to 60%. The λ
ex dependence is attributed to the presence of donors at different locations. At a long λ
ex (435 nm) donors in the highly polar peripheral region are excited. A short λ
ex (375 nm) ‘selects’ donor at a hydrophobic location. 相似文献
170.