全文获取类型
收费全文 | 38272篇 |
免费 | 4567篇 |
国内免费 | 3632篇 |
专业分类
电工技术 | 3233篇 |
技术理论 | 2篇 |
综合类 | 6732篇 |
化学工业 | 1710篇 |
金属工艺 | 819篇 |
机械仪表 | 2676篇 |
建筑科学 | 2640篇 |
矿业工程 | 782篇 |
能源动力 | 763篇 |
轻工业 | 2317篇 |
水利工程 | 1039篇 |
石油天然气 | 860篇 |
武器工业 | 493篇 |
无线电 | 5196篇 |
一般工业技术 | 3705篇 |
冶金工业 | 782篇 |
原子能技术 | 489篇 |
自动化技术 | 12233篇 |
出版年
2024年 | 133篇 |
2023年 | 482篇 |
2022年 | 873篇 |
2021年 | 979篇 |
2020年 | 1010篇 |
2019年 | 932篇 |
2018年 | 941篇 |
2017年 | 1147篇 |
2016年 | 1262篇 |
2015年 | 1358篇 |
2014年 | 2032篇 |
2013年 | 2298篇 |
2012年 | 2701篇 |
2011年 | 2920篇 |
2010年 | 2301篇 |
2009年 | 2487篇 |
2008年 | 2571篇 |
2007年 | 2970篇 |
2006年 | 2647篇 |
2005年 | 2348篇 |
2004年 | 1947篇 |
2003年 | 1626篇 |
2002年 | 1341篇 |
2001年 | 1142篇 |
2000年 | 991篇 |
1999年 | 828篇 |
1998年 | 668篇 |
1997年 | 577篇 |
1996年 | 537篇 |
1995年 | 473篇 |
1994年 | 404篇 |
1993年 | 287篇 |
1992年 | 256篇 |
1991年 | 214篇 |
1990年 | 194篇 |
1989年 | 174篇 |
1988年 | 117篇 |
1987年 | 68篇 |
1986年 | 33篇 |
1985年 | 38篇 |
1984年 | 27篇 |
1983年 | 34篇 |
1982年 | 24篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1965年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 672 毫秒
111.
112.
Abstract— Recent commercial liquid‐crystal‐display (LCD) televisions are larger and brighter than traditional televisions, thus impacting the viewing conditions in which they are viewed. These changes in viewing conditions may require different electro‐optical transfer functions (EOTFs) for LCD TVs than those for conventional TVs. Here, the way various EOTFs affect the preferred image quality of test images with changes in brightness and surround illumination conditions are examined. The first method used a gain, offset, and gamma (GOG) function with a range of gamma values, and the second method altered the intrinsic EOTFs. Image preference for the simulated EOTFs was determined using a paired‐comparison experiment for ten images. The first experiment took place in a darkened room at two display luminance levels. The results indicated that a gamma of 1.6 was most preferred overall although more so at a lower screen luminance level. In a second experiment, the procedure was repeated with a dim surround of 10% of the display's white point. With this surround, preference for a gamma value of around 1.6 at both screen luminance levels was more enhanced. These results indicated that image preference for different EOTFs is dependent on display luminance and that this dependence is maintained with a dim surround. 相似文献
113.
Fumio Negoro 《Knowledge》2003,16(7-8):383-397
The purpose of our study is to build up relationships between requirement and source programs with our originally thought-out rules. When other rules to be derived from these original rules are applied to software development, even a single instruction in a programming language could be determined, and the program would satisfy the requirement. More specifically speaking, these rules will turn into a formula or a prototype of software programs. Hence, when the variables in the requirement are placed in the formula, we can get a required program in an automatic way. 相似文献
114.
An optimal control problem with nonsmooth performance criterion described by a system of ordinary differential equations is considered. Necessary first-order optimality conditions are obtained. 相似文献
115.
Herbert S. Bennett 《Journal of research of the National Institute of Standards and Technology》2007,112(4):209-221
In this paper, we present the theory for calculating Raman line shapes as functions of the Fermi energy and finite temperatures in zinc blende, n-type GaAs for donor densities between 1016 cm−3 and 1019 cm−3. Compared to other theories, this theory is unique in two respects: 1) the many-body effects are treated self-consistently and 2) the theory is valid at room temperature for arbitrary values of the ratio R = (Q2/α), where Q is the magnitude of the normalized wave vector and α is the normalized frequency used in the Raman measurements. These calculations solve the charge neutrality equation self-consistently for a two-band model of GaAs at 300 K that includes the effects of high carrier concentrations and dopant densities on the perturbed densities of states used to calculate the Fermi energy as a function of temperature. The results are then applied to obtain the carrier concentrations from Fermi energies in the context of line shapes in Raman spectra due to the coupling between longitudinal optical phonons and plasmons. Raman measurements have been proposed as a non-destructive method for wafer acceptance tests of carrier density in semiconductor epilayers. The interpretation of Raman spectra to determine the majority electron density in n-type semiconductors requires an interdisciplinary effort involving experiments, theory, and computer-based simulations and visualizations of the theoretical calculations. 相似文献
116.
The paper considers vulnerable multi-state series-parallel systems operating under influence of external impacts. Both the external impacts and internal failures affect system survivability, which is determined as the probability of meeting a given demand. The external impacts are characterized by several destructive factors affecting the system or its parts simultaneously.In order to increase the system's survivability a multilevel protection against the destructive factors can be applied to its subsystems. In such systems, the protected subsystems can be destroyed only if all of the levels of their protection are destroyed.The paper presents an algorithm for evaluating the survivability of series-parallel systems with arbitrary configuration of multilevel protection against multiple destructive factor impacts. The algorithm is based on a composition of Boolean and the Universal Generating Function techniques.Illustrative examples are presented. 相似文献
117.
大变量逻辑函数最佳覆盖问题研究 总被引:2,自引:0,他引:2
逻辑函数的最佳覆盖,一直是逻辑综合领域的关键环节。尤其是大变量逻辑函数最佳覆盖,对复杂的逻辑综合更为重要,但也更加困难。本文在对逻辑覆盖算法研究的基础上,提出了适合大变量逻辑函数最佳覆盖的Beister改进算法。经过大量算题的测试表明,改进的列覆盖算法在时间复杂度和选择效果方面均优于Beister算法。 相似文献
118.
Tian-Ge Shao Jian-Guo Wang 《中国电子科技》2007,5(3):255-259
In this paper, the spatial resolutions at different directions of bistatic synthetic aperture radar (BiSAR) have been derived from the ambiguity function. Compared with monostatic signal to noise ratio, BiSAR's resolutions of a fixed point target are varying with slow time since BiSAR system is space-variant. Constraints for the assumption of space-invariant bistatic topology are proposed in the paper. Moreover, under the assumption of invariance, the change of resolutions at different point in the image scene is taken into account, and we have specified two key parameters that affect resolutions directly and analyzed the way how they influence on the resolutions. 相似文献
119.
Magnesiumandmagnesiumalloyshavebeenin vestigatedashydrogenstoragematerialsforseveralde cadesbecausefarmorehydrogenbyweightcanbestoredinthemthaninmostoftheothercurrentlyknownhydrogenstoragealloys .Moreover ,thehighnaturalabundanceofMg ,itslightmassandenviron mentalcompatibilitypotentiallymakemagnesiumoneofthemostprospectivecandidatesforfuturehydrogenstoragematerials .Unfortunately ,thepracticalappli cationofMganditsalloyshasbeenlimitedonlytocertainstoragedevicebecauseoftheirpoorhydriding dehydr… 相似文献
120.
This paper presents an application of digital signal processing to data acquired by the radio imaging method (RIM) that was adopted to measure moisture distribution inside the human body. RIM was originally developed for the mining industry; we are applying the method to a biomedical measurement because of its simplicity, economy, and safety. When a two‐dimensional image was constructed from the measured data, the method provided insufficient resolution because the wavelength of the measurement medium, a weak electromagnetic wave in a VHF band, was longer than human tissues. We built and measured a phantom, a model simulating the human body, consisting of two water tanks representing large internal organs. A digital equalizer was applied to the measured values as a weight function, and images were reconstructed that corresponded to the original shape of the two water tanks. As a result, a two‐dimensional image containing two individual peaks corresponding to the original two small water tanks was constructed. The result suggests the method was applicable to biomedical measurement by the assistance of digital signal processing. This technique may be applicable to home‐based medical care and other situations in which safety, simplicity, and economy are important. 相似文献