全文获取类型
收费全文 | 17387篇 |
免费 | 918篇 |
国内免费 | 29篇 |
专业分类
电工技术 | 194篇 |
综合类 | 45篇 |
化学工业 | 3615篇 |
金属工艺 | 336篇 |
机械仪表 | 356篇 |
建筑科学 | 752篇 |
矿业工程 | 52篇 |
能源动力 | 531篇 |
轻工业 | 1377篇 |
水利工程 | 133篇 |
石油天然气 | 51篇 |
无线电 | 1369篇 |
一般工业技术 | 3245篇 |
冶金工业 | 2856篇 |
原子能技术 | 137篇 |
自动化技术 | 3285篇 |
出版年
2023年 | 181篇 |
2022年 | 380篇 |
2021年 | 602篇 |
2020年 | 391篇 |
2019年 | 399篇 |
2018年 | 520篇 |
2017年 | 486篇 |
2016年 | 562篇 |
2015年 | 501篇 |
2014年 | 625篇 |
2013年 | 1126篇 |
2012年 | 1027篇 |
2011年 | 1224篇 |
2010年 | 868篇 |
2009年 | 804篇 |
2008年 | 853篇 |
2007年 | 831篇 |
2006年 | 628篇 |
2005年 | 561篇 |
2004年 | 399篇 |
2003年 | 404篇 |
2002年 | 377篇 |
2001年 | 254篇 |
2000年 | 213篇 |
1999年 | 247篇 |
1998年 | 367篇 |
1997年 | 291篇 |
1996年 | 261篇 |
1995年 | 226篇 |
1994年 | 198篇 |
1993年 | 188篇 |
1992年 | 147篇 |
1991年 | 98篇 |
1990年 | 157篇 |
1989年 | 153篇 |
1988年 | 105篇 |
1987年 | 114篇 |
1986年 | 118篇 |
1985年 | 119篇 |
1984年 | 102篇 |
1983年 | 93篇 |
1982年 | 107篇 |
1981年 | 107篇 |
1980年 | 83篇 |
1979年 | 86篇 |
1978年 | 83篇 |
1977年 | 88篇 |
1976年 | 87篇 |
1975年 | 53篇 |
1974年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
Although the basal ganglia have been shown to be critical for the expression of emotion in prosody and facial expressions, it is unclear whether they are also critical for recognition of emotions. Selective pathology of parts of the basal ganglia is a hallmark of individuals with Parkinson's disease, and such patients have been examined in several studies of emotion. We examined 18 patients with Parkinson's disease (11 men, 7 women) and 13 age-, education-, gender ratio-, and IQ-matched normal controls on their ability to recognize emotions signaled by facial expressions. Parkinson's patients performed entirely normally on a quantitative task of recognizing emotional facial expressions. The findings do not support the notion that the sectors of basal ganglia that are dysfunctional in Parkinson's disease are essential for recognizing emotion in facial expressions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
123.
Jos A. Grimbergen Koen Visscher Daniel S. Gomes De Mesquita G. J. Brakenhoff 《Yeast (Chichester, England)》1993,9(7):723-732
Individual yeast cells can be successfully isolated and recultured on plates with a new isolation method making use of optical trapping with infrared laser light. The cells can be selected on morphological criteria by high resolution microscopy. The isolation device is constructed from two coverslips separated by spacers, in which selected cells are transferred to a plastic capillary, using the optical trap. To test the procedure, selection experiments were done with a mixture of two Saccharomyces cerevisiae strains, distinguishable both in fluorescence microscopy and on agar plates. These experiments showed that only selected cells were isolated, and close to 100% of the isolated stationary-phase cells formed colonies on agar plates, indicating a high recovery. A lower recovery was obtained with exponential-phase cells, possibly because of a higher sensitivity to laser irradiation. Applications for this method may include the isolation of mutants with altered morphology and the isolation of subpopulations of yeast cultures, for their separate investigation or for the initiation of pure cultures. 相似文献
124.
We present anO(n log logn) time algorithm for finding a maximum matching in a permutation graph withn vertices, assuming that the input graph is represented by a permutation. 相似文献
125.
Machine Learning - In some applications, acquiring covariates comes at a cost which is not negligible. For example in the medical domain, in order to classify whether a patient has diabetes or not,... 相似文献
126.
Gary Gibson Xia Sheng Dick Henze Si‐Ty Lam Patricia Beck Yoocharn Jeon Zhang‐Lin Zhou Brad Benson Qin Liu Gregg Combs Tim Koch Kent Biggs 《Journal of the Society for Information Display》2012,20(10):552-558
Reflective displays are advantageous in applications requiring low power or daylight readability. However, there are no low‐cost reflective technologies capable of displaying bright colors. By employing photoluminescence to more efficiently use ambient light, we created a prototype display that provides bright, full color in a simple, low‐cost architecture. This prototype includes a novel electrokinetic shutter, a layer that incorporates patterned luminescent red, green, and blue sub‐pixel elements, and a novel optical out‐coupling scheme. The luminescent elements convert otherwise‐wasted portions of the incident spectrum to light in the desired color band, resulting in improved color saturation and lightness. This prototype provides a color gamut that is superior to competing reflective display technologies that utilize color filters in single‐layer side‐by‐side sub‐pixel architectures. The current prototype is capable of switching in <0.5 s; future displays based on an alternative electro‐optic shutter technology should achieve video rate operation. A transflective version of this technology has also been prototyped. The transflective version utilizes its backlight with a power efficiency that is at least three times that of a conventional liquid crystal display. These photoluminescence‐based technologies enable a host of applications ranging from low‐power mobile products and retail pricing signage to daylight readable signage for outdoor advertising segments. 相似文献
127.
Shilton A Lai DT Santhiranayagam BK Palaniswami M 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2012,42(3):950-955
This note presents an analysis of the octonionic form of the division algebraic support vector regressor (SVR) first introduced by Shilton A detailed derivation of the dual form is given, and three conditions under which it is analogous to the quaternionic case are exhibited. It is shown that, in the general case of an octonionic-valued feature map, the usual "kernel trick" breaks down. The cause of this (and its interpretation) is discussed in some detail, along with potential ways of extending kernel methods to take advantage of the distinct features present in the general case. Finally, the octonionic SVR is applied to an example gait analysis problem, and its performance is compared to that of the least squares SVR, the Clifford SVR, and the multidimensional SVR. 相似文献
128.
Daniel Camps-Mur Manil Dev Gomony Xavier Pérez-Costa Sebastià Sallent-Ribes 《Computer Networks》2012,56(12):2896-2911
The Wi-Fi technology, driven by its tremendous success, is expanding into a wide variety of devices and applications. However, many of these new devices, like handheld devices, pose new challenges in terms of QoS and energy efficiency. In order to address these challenges, in this paper we study how the novel MAC aggregation mechanisms developed in the 802.11n standard can be used to enhance the current 802.11 QoS and power saving protocols. Our contribution is twofold. First, we present a simulation study that illustrates the interactions between 802.11n and the current 802.11 QoS and power saving protocols. This study reveals that the 802.11n MAC aggregation mechanisms perform better when combined with the power save mode included in the original 802.11 standard than with the 802.11e U-APSD protocol. Second, we design CA-DFA, an algorithm that, using only information available at layer two, adapts the amount of 802.11n aggregation used by a Wi-Fi station according to the level of congestion in the network. A detailed performance evaluation demonstrates the benefits of CA-DFA in terms of QoS, energy efficiency and network capacity with respect to state of the art alternatives. 相似文献
129.
James?Eves Vassili?V.?ToropovEmail author Harvey?M.?Thompson Nik?Kapur Jian?Fan Daniel?Copley Adrian?Mincher 《Structural and Multidisciplinary Optimization》2012,45(5):739-745
Supersonic jet pumps are simple devices with no moving parts, where a high velocity (primary) flow is used to pump a second
fluid. In this paper, Computational Fluid Dynamics (CFD) is combined with an optimization framework in order to develop a
tool for the rapid generation of jet pump designs. A key feature of the problem formulation is the transformation of the jet
pump design parameters in terms of geometric ratios. This approach dramatically reduces the number of unrealistic designs
covered by the Design of Experiments. Optimal Latin Hypercubes for surrogate model building and model validation points are
constructed using a permutation genetic algorithm and design points are evaluated using CFD. Surrogate models of primary and
entrained flow rates are built using a Moving Least Squares approach. A series of optimizations for various pump sizes are
performed using a genetic algorithm and Sequential Quadratic Programming, with responses calculated from the surrogates. This
approach results in a set of optimized designs, from which pumps for a wide range of flow rates can be interpolated. 相似文献
130.
Mechanical alloying was used to synthesize NixZr1–x alloys from mixtures of intermetallic compound powders, and also from mixtures of intermetallic compound powders and pure elemental powders. The mechanically alloyed powders were amorphous in the range 0.24 x 0.85. This range is larger than amorphous alloys produced by the melt-spinning technique and mechanical alloying of elemental crystalline powders. Two-phase mixtures of the amorphous phase and the corresponding crystalline terminal solid solution were formed in the range 0.10 x 0.22, and x=0.90. It is found that the morphological development during mechanical alloying of these powders is different from mechanical alloying using only pure ductile crystalline elemental powders. The thermal stability has been investigated. The enthalpy and activation energy of crystallization for Ni-Zr amorphous powders prepared by mechanical alloying are lower than those for melt-spun samples of the same composition. The crystallization temperature of the mechanically alloyed Ni-Zr amorphous powders is higher than that of meltspun samples in the composition range Ni20Zr80 to Ni33Zr67 and Ni40Zr60 to Ni60Zr40. The presence of tiny crystallites as nucleation centres and high oxygen levels in the mechanically alloyed amorphous alloys might be responsible for the differences in crystallization behaviour. A new crystalline metastable phase was observed during crystallization studies of Ni24Zr76 amorphous powder. 相似文献