全文获取类型
收费全文 | 30697篇 |
免费 | 1226篇 |
国内免费 | 112篇 |
专业分类
电工技术 | 378篇 |
综合类 | 229篇 |
化学工业 | 5077篇 |
金属工艺 | 631篇 |
机械仪表 | 592篇 |
建筑科学 | 968篇 |
矿业工程 | 94篇 |
能源动力 | 932篇 |
轻工业 | 3875篇 |
水利工程 | 242篇 |
石油天然气 | 150篇 |
武器工业 | 6篇 |
无线电 | 2243篇 |
一般工业技术 | 4101篇 |
冶金工业 | 8549篇 |
原子能技术 | 240篇 |
自动化技术 | 3728篇 |
出版年
2024年 | 50篇 |
2023年 | 150篇 |
2022年 | 495篇 |
2021年 | 788篇 |
2020年 | 536篇 |
2019年 | 600篇 |
2018年 | 684篇 |
2017年 | 769篇 |
2016年 | 719篇 |
2015年 | 551篇 |
2014年 | 848篇 |
2013年 | 1415篇 |
2012年 | 1252篇 |
2011年 | 1580篇 |
2010年 | 1150篇 |
2009年 | 1203篇 |
2008年 | 1097篇 |
2007年 | 961篇 |
2006年 | 771篇 |
2005年 | 836篇 |
2004年 | 904篇 |
2003年 | 816篇 |
2002年 | 789篇 |
2001年 | 694篇 |
2000年 | 538篇 |
1999年 | 581篇 |
1998年 | 2806篇 |
1997年 | 1732篇 |
1996年 | 1195篇 |
1995年 | 750篇 |
1994年 | 581篇 |
1993年 | 674篇 |
1992年 | 230篇 |
1991年 | 299篇 |
1990年 | 245篇 |
1989年 | 212篇 |
1988年 | 223篇 |
1987年 | 186篇 |
1986年 | 187篇 |
1985年 | 194篇 |
1984年 | 129篇 |
1983年 | 98篇 |
1982年 | 127篇 |
1981年 | 131篇 |
1980年 | 133篇 |
1979年 | 92篇 |
1978年 | 77篇 |
1977年 | 189篇 |
1976年 | 376篇 |
1975年 | 85篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
分析化学实验成绩评定软件的开发 总被引:1,自引:0,他引:1
介绍了分析化学实验成绩评定软件的主要内容、设计思想及功能 ,该软件采用VisualFoxPro5 0中文版编程 ,可用于分析化学实验成绩的评定。内容包括 :实验数据输入、实验数据修改、实验数据处理、实验结果查询、实验数据打印、修改学生名单等。本软件具有操作简单、使用方便等特点 相似文献
922.
923.
We consider the issue of exploiting the structural form of Esterel programs to partition the algorithmic RSS (reachable state space) fix-point construction used in model-checking techniques. The basic idea sounds utterly simple, as seen on the case of sequential composition: in P; Q, first compute entirely the states reached in P, and then only carry on to Q, each time using only the relevant transition relation part. Here a brute-force symbolic breadth-first search would have mixed the exploration of P and Q instead, in case P had different behaviors of various lengths, and that would result in irregular BBD representation of temporary state spaces, a major cause of complexity in symbolic model-checking.Difficulties appear in our decomposition approach when scheduling the different transition parts in presence of parallelism and local signal exchanges. Program blocks (or “Macro-states”) put in parallel can be synchronized in various ways, due to dynamic behaviors, and considering all possibilities may lead to an excessive division complexity. The goal is here to find a satisfactory trade-off between compositional and global approaches. Concretely we use some of the features of the TiGeR BDD library, and heuristic orderings between internal signals, to have the transition relation progress through the program behaviors to get the same effect as a global RSS computation, but with much more localized transition applications. We provide concrete benchmarks showing the usefulness of the approach. 相似文献
924.
分级移动IPv6中一种新的自适应MAP选择算法* 总被引:3,自引:0,他引:3
分级移动IPv6中存在单点故障和负荷集中问题。提出一种基于分布式MAP结构的自适应MAP选择算法,综合考虑移动节点的当前速度、会话到达率、MAP负荷及距离等因素,以MN注册后将产生的移动性管理信令开销最小为依据进行选择。仿真结果表明,自适应MAP选择算法能够根据移动节点和网络的当前特性优化地选择不同的MAP进行注册,使移动性管理信令开销最小,具有较好的负荷分担效果,并一定程度上增强了分级结构的鲁棒性。与最远/近MAP选择方案相比,自适应MAP选择算法能够提高网络的吞吐量及减少平均切换时延。 相似文献
925.
Organ blood flow is controlled, in part, by changes in diameter of resistance vessels. In thick tissue, vessels can be imaged with a microscope using contrast-enhancing methods (e.g., fluorescence) and image analysis techniques can be used for quantitative diameter estimations. However, a change in the position of a vessel with respect to the plane of focus can be misinterpreted as a diameter change. In order to address this problem, a 3D image in a light microscope is obtained by serial optical sectioning, and a 3D deconvolution procedure (Avinash et al., 1991, "Fourteenth Association for Research in Otolaryngology Midwinter Meeting, St. Petersberg, FL," Abstract 156) is used to deblur 3D image data. Deblurred sections are computationally projected onto a 2D plane to give an extended-focus image, from which diameter estimates of microvessels are made using a quantitative, 2D diameter-tracking algorithm (Miles, 1987, "Semiautomatic Quantitative Image Analysis of Dynamic in Vivo Cochlear Microvessel Diameters." Ph.D. dissertation, Univ. Michigan; Miles and Nuttall, 1992, IEEE Trans. Biomed. Eng.). Justification for 3D preprocessing before diameter analysis is provided by absolute and relative error analyses using computer-generated synthetic vessels. The 3D diameter analysis technique is validated using a capillary tube of known diameter, filled with fluorescent solution. Demonstration of its applicability is shown in diameter measurements from the vessels of guinea pig cochlea. Our approach, using extended-focus images, minimizes overestimation of microvascular diameters and underestimation of relative diameter changes. Therefore, unambiguous diameter measurements are possible with extended-focus images. 相似文献
926.
In 24 cats (Uppsala, Sweden) with neurological signs of "staggering disease" and typical neuropathology, 44% had Borna disease virus (BDV)-specific antibodies. In 173 cat sera (Berlin, Germany) of animals with unknown record, 7% were BDV positive. Out of 24 cats with undefined neurological disorders, 13% were BDV positive. Similarities in staggering disease of cats and Borna disease of horses and sheep suggest related etiological agents. 相似文献
927.
SV Buldyrev AL Goldberger S Havlin Peng C-K M Simons HE Stanley 《Canadian Metallurgical Quarterly》1993,47(6):4514-4523
We propose a generalized Lévy walk to model fractal landscapes observed in noncoding DNA sequences. We find that this model provides a very close approximation to the empirical data and explains a number of statistical properties of genomic DNA sequences such as the distribution of strand-biased regions (those with an excess of one type of nucleotide) as well as local changes in the slope of the correlation exponent alpha. The generalized Lévy-walk model simultaneously accounts for the long-range correlations in noncoding DNA sequences and for the apparently paradoxical finding of long subregions of biased random walks (length lj) within these correlated sequences. In the generalized Lévy-walk model, the lj are chosen from a power-law distribution P(lj) varies as lj(-mu). The correlation exponent alpha is related to mu through alpha = 2-mu/2 if 2 < mu < 3. The model is consistent with the finding of "repetitive elements" of variable length interspersed within noncoding DNA. 相似文献
928.
A. Alessandrello C. Brofferio D. V. Camin O. Cremonesi E. Fiorini E. Garcia A. Giuliani P. de Marcillac M. Pavan G. Pessina E. Previtali L. Zanotti 《Journal of Low Temperature Physics》1993,93(3-4):201-206
A 334g TeO2 crystal is operating since January '93 at Gran Sasso National Laboratories as a thermal detector to search for neutrinoless decay of130Te. The reduction of environmental radioactivity is accomplished by means of a 10 cm thick external lead shielding and a plexiglas box against222Rn, while an inner ultra-low activity lead shield of at least 3.5 cm in every direction suppresses the residual local radioactivity near the crystal. The good energy resolution and the peak-to-Compton efficiency of the detector allow to understand the main features of the residual background. In particular, we are able to reach a sensitivity in the internal contamination of238U and232Th of the crystal of the order of 10–13 g/g, better than that of modern mass spectroscopy methods. Pulse acquisition and analysis techniques are reported and discussed.Present limit on neutrinoless decay half-life time of130Te obtained with this detector is of the order of 1022y at 68% C.L., exceeding by one order of magnitude the value quoted by the inclusive geochemical measurements, which have therefore to be attributed mainly to the 2-neutrino channel.On leave from the Dept. of Physics, University of Zaragoza 相似文献
929.
Tilmans H.A.C. van de Peer D.J. Beyne E. 《Journal of microelectromechanical systems》2000,9(2):206-217
A variety of microelectromechanical system devices requires encapsulation of their crucial fragile parts in a hermetically sealed cavity for reasons of protection. Hermeticity of the cavity and controllability of the ambient (gas pressure and gas composition) can be critical to the device performance. In order to minimize damage during handling, the cavity is preferably realized at the same time the device is fabricated, i.e., at wafer level. This paper reports the development of a hermetic packaging technique satisfying all the above. The method is referred to as the indent-reflow-sealing (IRS) technique, which relies on a multiple-chip fluxless solder-based joining technique and seal. Key process steps are the creation of an indent in the solder, the plasma pretreatment of the bonding surfaces, the pre-bonding (or sticking) of the chips and, the closing of the indent during a low-temperature (220°C-350°C) solder reflow in a clean controlled ambient using a designated oven. As opposed to other methods, the IRS method allows a greater flexibility with respect to the choice of the sealing gas and pressure, thereby offering a very hermetic seal and compatibility with low-cost high-throughput batch fabrication techniques. Flip-chip assemblies based on SnPb (67/37) solder and Au as the top surface metallization, have been reflowed in a forming gas ambient and have next been characterized on shear strength, hermeticity, and susceptibility to thermal stresses. The method has been successfully implemented in the process flow of an electromagnetic microrelay for the realization of the cavity housing the electrical contacts 相似文献
930.
In this paper, large signal non linear P parameters are rigorously defined, allowing the characterization of non linear active n-port circuits in the frequency domain with the aim of computer aided design of power microwave devices. No a priori conditions bind the parameters to the variables describing the input signal. However the following rules apply to the parameters: they may be function of any input variables of the n-port circuit; the expression of the large-signal parameters should become identical to the expression of the linear parameters characterizing the n-port circuit under linear operating conditions when the values of the input variables tend to zero. An application of the definition to afet is demonstrated. 相似文献