全文获取类型
收费全文 | 49307篇 |
免费 | 6351篇 |
国内免费 | 4748篇 |
专业分类
化学 | 25788篇 |
晶体学 | 358篇 |
力学 | 2229篇 |
综合类 | 241篇 |
数学 | 4283篇 |
物理学 | 13544篇 |
无线电 | 13963篇 |
出版年
2024年 | 170篇 |
2023年 | 1147篇 |
2022年 | 1364篇 |
2021年 | 1866篇 |
2020年 | 1789篇 |
2019年 | 1600篇 |
2018年 | 1381篇 |
2017年 | 1328篇 |
2016年 | 1877篇 |
2015年 | 2037篇 |
2014年 | 2476篇 |
2013年 | 3184篇 |
2012年 | 3935篇 |
2011年 | 3860篇 |
2010年 | 2785篇 |
2009年 | 2755篇 |
2008年 | 2974篇 |
2007年 | 2645篇 |
2006年 | 2562篇 |
2005年 | 2253篇 |
2004年 | 1747篇 |
2003年 | 1390篇 |
2002年 | 1245篇 |
2001年 | 1069篇 |
2000年 | 1039篇 |
1999年 | 1174篇 |
1998年 | 1033篇 |
1997年 | 934篇 |
1996年 | 990篇 |
1995年 | 856篇 |
1994年 | 779篇 |
1993年 | 678篇 |
1992年 | 620篇 |
1991年 | 486篇 |
1990年 | 415篇 |
1989年 | 298篇 |
1988年 | 266篇 |
1987年 | 235篇 |
1986年 | 168篇 |
1985年 | 182篇 |
1984年 | 152篇 |
1983年 | 131篇 |
1982年 | 98篇 |
1981年 | 66篇 |
1980年 | 58篇 |
1979年 | 38篇 |
1978年 | 30篇 |
1976年 | 31篇 |
1975年 | 36篇 |
1974年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Stephen W. Burgess Jogin R. Wu Kerry Swift Barry R. Lentz 《Journal of fluorescence》1991,1(2):105-112
Rate constants were determined for the transfer of the fluorescent lipid probe 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5-hexatrienyl)phenyl]ethyl] oxy]carbonyl]-3-sn-phosphatidylcholine (DPHpPC) between large, unilamellar extrusion vesicles composed either of dipalmitoyl phosphatidylcholine (DPPC) or of DPPC mixed with a small amount (0.5 mol%) of lyso phosphatidylcholine (Lyso PC). Transfer of the lipid probe in the presence of varying concentrations of poly(ethylene glycol) (PEG) was monitored using the SLM 48000-MHF Multi-Harmonic Fourier Transform phase and modulation spectrofluorometer to collect multifrequency phase and modulation fluorescence data sets on a subsecond time scale. The unique ability of this instrument to yield accurate fluorescence lifetime data on this time scale allowed transfer to be detected in terms of a time-dependent change in the fluorescent lifetime distribution associated with the lipid-like DPHpPC probe. This probe demonstrates two short fluoresence decay times (ca. 1.1–1.4 and 4.3–4.8 ns) in a probe-rich environment but a single long lifetime (ca. 7 ns) in a probe-poor environment. A simple two-state model for initial lipid transfer was used to analyze the multifrequency data sets collected over a 4-s time frame to obtain the time rate of change of the concentrations of donor and acceptor probe populations following rapid mixing of vesicles with PEG. The ability to measure fluorescence lifetimes on this time scale has allowed us to show that the of rate of lipid transfer increased dramatically at 35% PEG in both fusing and nonfusing vesicle systems. These results are interpreted in terms of a distinct interbilayer structure associated with intimate bilayer contact induced by high and potentially fusogenic concentrations of PEG. 相似文献
152.
The conventional method of extracting the minority carrier diffusion length using the electron beam-induced current (EBIC) technique requires that the electron beam be placed at region more than two diffusion lengths away from the collector. The EBIC signals obtained under this condition usually has low signal to noise ratio. In addition, the true diffusion length of the sample is initially unknown and hence it is difficult to estimate how close the beam can be placed from the collector. To overcome all these difficulties, a new method of extracting minority carrier diffusion length from the EBIC signal is proposed. It is shown that this method can be applied to EBIC signals obtained from regions close to the collector. It is also shown that the surface recombination velocity of the sample can also be obtained using this method. This theory is verified using EBIC data generated from a device simulation software. 相似文献
153.
使用智能同步广播激励器,并采用CCTV传输的1MHz标频信号,就有可能实现自适应相位跟踪同步广播。这将大大节省中波段的频率资源。 相似文献
154.
155.
对EDGE技术进行了介绍,并对EDGE技术的现网测试进行了说明,对于EDGE技术的功能特点及现网应用的模型、性能指标进行了研究和探讨。 相似文献
156.
The authors have proposed some modifications of the reduced update Kalman filter (RUKF) as applied to filtering of images corrupted by additive noise. They have reduced the computational complexity by reducing the state dimensionality. By doing so, it is shown that the computational requirement is reduced by an order of magnitude while the loss of performance is only marginal. Next, the RUKF is modified using the score function based approach to accommodate non-Gaussian noise. The image is modeled as a nonstationary mean and stationary variance autoregressive Gaussian process. It is shown that the stationary variance assumption is reasonable if the nonstationary mean is computed by an edge and detail preserving efficient estimator of local nonstationary mean. Such an estimator, called the hybrid multistage medium D (HMSMD) filter, is also described. Detailed experimental results are provided which indicate the success of the new filtering scheme 相似文献
157.
This paper presents a new formulation useful for modeling waveguides constructed from lossy inhomogeneous anisotropic media. Our approach is based on a pair of Sturm-Liouville type wave equations that have been derived to handle inhomogeneous, diagonalized complex permittivity and permeability tensors. The method of lines is then applied to these wave equations, and related field equations, creating an indirect eigenvalue problem that correctly models this class of structure. Some refinements to the method of lines are also proposed, particularly, regarding the construction of the modal matrices found in the eigenvalue problem. Using our approach, modal dispersion curves have been computed for millimeter-wave and optical structures. Comparisons made with results available from the literature validate our approach 相似文献
158.
Shu-Yuan Chin Chung-Yu Wu 《Solid-State Circuits, IEEE Journal of》1996,31(8):1201-1207
This paper describes the design of a CMOS capacitor-ratio-independent and gain-insensitive algorithmic analog-to-digital (A/D) converter. Using the fully differential switched-capacitor technique, the A/D converter is insensitive to capacitor-ratio accuracy as well as finite gain and offset voltage of operational amplifiers. The switch-induced error voltage becomes the only major error source, which is further suppressed by the fully differential structure. The proposed A/D converter is designed and fabricated by 0.8 μm double-poly double-metal CMOS technology. The op-amp gain is only 60 dB and no special layout care is done for capacitor matching. Experimental results have shown that 14-b resolution at the sampling frequency of 10 kHz can be achieved in the fabricated A/D converter. Thus it can be used in the applications which require low-cost high-resolution A/D conversion 相似文献
159.
The article referenced above was first published online on 7 August 2007 with incorrect pagination; the pagination has now been corrected online and in print. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
160.
NaiQi Wu MengChu Zhou 《Mechatronics, IEEE/ASME Transactions on》2007,12(1):63-72
It is a great challenge to effectively manage automated manufacturing systems in which automated guided vehicles (AGVs) are adopted to handle materials, because of such features as prior unknown AGV requests and changing AGV initial positions. This paper aims to find the shortest time routes, while both deadlock and blocking in AGV systems are avoided. It first finds the shortest routes based on a guide path layout, and then performs rerouting, whenever necessary, to avoid deadlock and blocking according to a deadlock avoidance policy, previously developed by the authors. The proposed approach can offer better solutions than existing methods. For some cases, it can find a solution, while the existing ones cannot 相似文献