全文获取类型
收费全文 | 25610篇 |
免费 | 2857篇 |
国内免费 | 1884篇 |
专业分类
电工技术 | 2441篇 |
技术理论 | 1篇 |
综合类 | 3253篇 |
化学工业 | 1417篇 |
金属工艺 | 1291篇 |
机械仪表 | 3923篇 |
建筑科学 | 943篇 |
矿业工程 | 610篇 |
能源动力 | 370篇 |
轻工业 | 385篇 |
水利工程 | 341篇 |
石油天然气 | 484篇 |
武器工业 | 620篇 |
无线电 | 4783篇 |
一般工业技术 | 2919篇 |
冶金工业 | 872篇 |
原子能技术 | 191篇 |
自动化技术 | 5507篇 |
出版年
2024年 | 86篇 |
2023年 | 319篇 |
2022年 | 534篇 |
2021年 | 592篇 |
2020年 | 710篇 |
2019年 | 601篇 |
2018年 | 632篇 |
2017年 | 884篇 |
2016年 | 995篇 |
2015年 | 1116篇 |
2014年 | 1497篇 |
2013年 | 1453篇 |
2012年 | 1954篇 |
2011年 | 1986篇 |
2010年 | 1492篇 |
2009年 | 1560篇 |
2008年 | 1575篇 |
2007年 | 1926篇 |
2006年 | 1720篇 |
2005年 | 1382篇 |
2004年 | 1124篇 |
2003年 | 1071篇 |
2002年 | 848篇 |
2001年 | 737篇 |
2000年 | 622篇 |
1999年 | 506篇 |
1998年 | 393篇 |
1997年 | 363篇 |
1996年 | 299篇 |
1995年 | 264篇 |
1994年 | 220篇 |
1993年 | 161篇 |
1992年 | 123篇 |
1991年 | 97篇 |
1990年 | 82篇 |
1989年 | 85篇 |
1988年 | 70篇 |
1987年 | 36篇 |
1986年 | 17篇 |
1985年 | 37篇 |
1984年 | 29篇 |
1983年 | 22篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1977年 | 10篇 |
1964年 | 5篇 |
1956年 | 8篇 |
1955年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
L. M. Schroeder 《Journal of chemical ecology》1992,18(9):1583-1593
The field response ofTomicus piniperda (L.) andHylurgops palliatus (Gyll.) (Coleoptera: Scolytidae) to the attractant ethanol in combination with volatile wood constituents released from the nonhost tree speciesPopulus tremula L. (Salicaceae) andBetula pendula Roth (Betulaceae) was studied using flight barrier traps. The attraction of both species decreased when aspen or birch wood was added to the ethanol bait. The same was true forRhizophagus depressus (F.) (Coleoptera: Rhizophagidae), a predatory species associated with conifer bark beetles.Glischrochilus quadripunctatus (L-),Epuraea bickhardti St.-Claire Deville,E. unicolor (Oliv.) (Coleoptera: Nitidulidae), andRhizophagus parvutus (Payk.) (Coleoptera: Rhizophagidae) were caught in higher numbers in traps baited with both ethanol and wood of aspen or birch than in traps baited with ethanol alone. In a separate experiment, landings ofT. piniperda andH. palliatus on nonhosts (black plastic tubes) were demonstrated with sticky traps. 相似文献
92.
Gabriel Tsechpenakis Dimitris Metaxas Carol Neidle 《Computer Vision and Image Understanding》2006,104(2-3):140
We present a data-driven dynamic coupling between discrete and continuous methods for tracking objects of high dofs, which overcomes the limitations of previous techniques. In our approach, two trackers work in parallel, and the coupling between them is based on the tracking error. We use a model-based continuous method to achieve accurate results and, in cases of failure, we re-initialize the model using our discrete tracker. This method maintains the accuracy of a more tightly coupled system, while increasing its efficiency. At any given frame, our discrete tracker uses the current and several previous frames to search into a database for the best matching solution. For improved robustness, object configuration sequences, rather than single configurations, are stored in the database. We apply our framework to the problem of 3D hand tracking from image sequences and the discrimination between fingerspelling and continuous signs in American Sign Language. 相似文献
93.
94.
In this paper, we propose an approach that combines the unsupervised and supervised learning techniques for unconstrained
handwritten numeral recognition. This approach uses the Kohonen self-organizing neural network for data classification in
the first stage and the learning vector quantization (LVQ) model in the second stage to improve classification accuracy. The
combined architecture performs better than the Kohonen self-organizing map alone. In the proposed approach, the collection
of centroids at different phases of training plays a vital role in the performance of the recognition system. Four experiments
have been conducted and experimental results show that the collection of centroids in the middle of the training gives high
performance in terms of speed and accuracy. The systems developed also resolve the confusion between handwritten numerals. 相似文献
95.
CDMA时变色散信道的两级盲辨识算法 总被引:1,自引:0,他引:1
本文通过对时变信道的扩展函数在时频域进行正则采样,得到了CDMA时变系统的离散正则模型。针对该模型提出了一种具有较低运算量的两级盲辨识算法。为避免两级算法产生的误差传播效应,文章将理想SIMO模型等效为加性噪声模型来处理。与基展开模型方法相比,该算法具有不需利用观测数据的高阶统计量估计展开基频率的优点。文章通过仿真验证了该算法是可行的。 相似文献
96.
Temperature dependences of shrinkage forces appearing in oriented polymer samples when heated at constant length were recorded for polycarbonate, polyethylene terephthalate, polyethylene and polypropylene. The influence of various processing conditions on thermally stimulated shrinkage forces is demonstrated. A four-state model is proposed which qualitatively describes the temperature dependences of shrinkage forces in amorphous polymers. 相似文献
97.
The smooth fractionator 总被引:8,自引:0,他引:8
H. J. G. Gundersen 《Journal of microscopy》2002,207(3):191-210
A modification of the general fractionator sampling technique called the smooth fractionator is presented. It may be used in almost every situation in which sampling is performed from distinct items that are uniquely defined, often they are physically separated items or clusters like pieces, blocks, slabs, sections, etc. To each item is associated a ‘guesstimate’ or an associated variable with a more‐or‐less close – and possibly biased ? relationship to the content of the item. The smooth fractionator is systematic sampling among the items arranged according to the guesstimates in a unique, symmetric sequence with one peak and minimal jumps. The smooth fractionator is both very simple to implement and so efficient that it should probably always be used unless the natural sequence of the sampling items is equally smooth. So far, there is no theory for the prediction of the efficiency of smooth fractionator designs in general, and their properties are therefore illustrated with a range of real and simulated examples. At the cost of a slightly more elaborate sampling scheme, it is, however, always possible to obtain an unbiased estimate of the real precision and of some of the variance components. The only real practical problem for always obtaining a high precision with the smooth fractionator is specimen inhomogeneity, but that is detectable at almost no extra cost. With careful designs and for sample sizes of about 10, the sampling variation for the primary, smooth fractionator sampling step may in practice often be small enough to be ignored. 相似文献
98.
Control over crystallographic orientation in ceramic thin films is important for highly anisotropic structures. Layered perovskites, like Bi4 Ti3 O12 , have interesting properties associated with their ferroelectric nature, which may be fully exploited only when films are highly textured. Textured films of this titanate were fabricated via a sol–gel technique without using epitaxial growth. Orientation in the film is confirmed by XRD and SEM, and supported by refractive index and dielectric measurements. In an attempt to explain the orienting effect, light scattering experiments were conducted to yield information about the molecular size, shape, and conformation of macromolecules as the sol–gel solution ages and condensation reactions proceed. These experiments clearly show an increase in the size of molecular clusters with time. We believe that it is the organization of these large clusters during spin coating, and the relationship of the backbone chemistry to the crystal structure of Bi4 Ti3 O12 , that are responsible for the observed orientation. 相似文献
99.
Two series of polypropylenes with different molecular weight distribution and tacticity characteristics were injection molded into flexural test specimens by varying cylinder temperature and the effects of the molecular weight distribution and tacticity on the structure and properties of the moldings were studied. Measured propertied were flexural modulus, flexural strength, heat distortion temperature, Izod impact strength, and mold shrinkage and structures studied were crystallinity, the thickness of skin layer, a*‐axis‐oriented component fraction and crystalline orientation functions. The relations between the structures and properties were also studied. It was found that the molecular weight distribution and tacticity characteristics affect the properties mainly through the molecular orientation and crystallinity, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2142–2156, 2002 相似文献
100.
费景高 《计算机工程与科学》1992,14(4):55-68
本文提出求解微分代数方程的一类并行算法,进行误差估计。对于一个模型问题进行稳定性分析,画出稳定区域。计算实例表明算法是有效的。 相似文献