全文获取类型
收费全文 | 19461篇 |
免费 | 851篇 |
国内免费 | 140篇 |
专业分类
电工技术 | 328篇 |
综合类 | 32篇 |
化学工业 | 4322篇 |
金属工艺 | 597篇 |
机械仪表 | 635篇 |
建筑科学 | 373篇 |
矿业工程 | 47篇 |
能源动力 | 1400篇 |
轻工业 | 1178篇 |
水利工程 | 157篇 |
石油天然气 | 84篇 |
武器工业 | 1篇 |
无线电 | 2402篇 |
一般工业技术 | 4413篇 |
冶金工业 | 1450篇 |
原子能技术 | 178篇 |
自动化技术 | 2855篇 |
出版年
2024年 | 105篇 |
2023年 | 422篇 |
2022年 | 1001篇 |
2021年 | 1182篇 |
2020年 | 926篇 |
2019年 | 958篇 |
2018年 | 1236篇 |
2017年 | 979篇 |
2016年 | 937篇 |
2015年 | 615篇 |
2014年 | 861篇 |
2013年 | 1546篇 |
2012年 | 927篇 |
2011年 | 1091篇 |
2010年 | 882篇 |
2009年 | 830篇 |
2008年 | 732篇 |
2007年 | 598篇 |
2006年 | 484篇 |
2005年 | 370篇 |
2004年 | 283篇 |
2003年 | 247篇 |
2002年 | 191篇 |
2001年 | 181篇 |
2000年 | 173篇 |
1999年 | 171篇 |
1998年 | 292篇 |
1997年 | 238篇 |
1996年 | 221篇 |
1995年 | 169篇 |
1994年 | 160篇 |
1993年 | 152篇 |
1992年 | 103篇 |
1991年 | 131篇 |
1990年 | 100篇 |
1989年 | 99篇 |
1988年 | 84篇 |
1987年 | 88篇 |
1986年 | 75篇 |
1985年 | 86篇 |
1984年 | 74篇 |
1983年 | 71篇 |
1982年 | 61篇 |
1981年 | 70篇 |
1980年 | 48篇 |
1979年 | 31篇 |
1978年 | 27篇 |
1977年 | 26篇 |
1976年 | 35篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
An analytical model of Al0.15Ga0.85N/GaN modulation doped field effect transistor (MODFET), which uses an accurate velocity field relationship and incorporates the dominant effect of piezoelectric polarization induced charge at the AlGaN/GaN interface is presented. The effect of traps has also been taken into account. The calculated DC characteristics are in excellent agreement with the measured data. The model is extended to predict the microwave performance of the device. High current levels (>500 mA/mm), large transconductance (160.83 mS/mm) and a high cutoff frequency (9.6 GHz) have been achieved analytically and are in close agreement with the experimental data. 相似文献
992.
This paper proposes a new bimodal biometric system using feature-level fusion of hand shape and palm texture. The proposed combination is of significance since both the palmprint and hand-shape images are proposed to be extracted from the single hand image acquired from a digital camera. Several new hand-shape features that can be used to represent the hand shape and improve the performance are investigated. The new approach for palmprint recognition using discrete cosine transform coefficients, which can be directly obtained from the camera hardware, is demonstrated. None of the prior work on hand-shape or palmprint recognition has given any attention on the critical issue of feature selection. Our experimental results demonstrate that while majority of palmprint or hand-shape features are useful in predicting the subjects identity, only a small subset of these features are necessary in practice for building an accurate model for identification. The comparison and combination of proposed features is evaluated on the diverse classification schemes; naive Bayes (normal, estimated, multinomial), decision trees (C4.5, LMT), k-NN, SVM, and FFN. Although more work remains to be done, our results to date indicate that the combination of selected hand-shape and palmprint features constitutes a promising addition to the biometrics-based personal recognition systems. 相似文献
993.
Jignasu P. Mehta Prashant N. Bhatt Sudhindra N. Misra 《中国稀土学报(英文版)》2006,24(6):648-652
Pr( Ⅲ ) and Nd( Ⅲ ) can be utilized as absorption spectroscopic probes to investigate the interaction of biomolecules like Lysozyme (HEW) with Ca( Ⅱ ) in-vitro ; the most abundant metal ion in the human body system. The spectroscopic techniques involving comparative absorption, absorption difference, and quantitative intensity analysis using 4f-4f transitions are utilized for changes in the inner sphere coordination pattern of Pr( Ⅲ ) and Nd(Ⅲ ) in solution as well as in solid state. The present study deals with an important biomolecule in human metabolism, that is, Lysozyme (HEW). The absorption er-Condon the probab spectral parameters such as the oscillator strength (P), the Judd-Ofelt (Tλ) intensity parameters, and the Slatinter electronic parameters are calculated using chi square methods. The obtained results are used to determine le geometry of the complex in the solution, the nature of the bond between Pr(Ⅲ)/Nd(Ⅲ) with lysozyme, and the inner sphere coordination environment of f-f transitions. The results obtained from various experimental conditions are utilized to investigate the coordination changes in the Pr(Ⅲ)/Nd(Ⅲ) complexes caused by different coordinating sites of lysozyme, normalized bite, denticity, the solvent nature, the coordination number, the nature of bond and other parameters to mimic the interaction of the Ca( Ⅱ ) ion with such biomolecule. 相似文献
994.
Chin-Teng Lin Chang-Mao Yeh Sheng-Fu Liang Jen-Feng Chung Kumar N. 《Fuzzy Systems, IEEE Transactions on》2006,14(1):31-41
Fuzzy neural networks (FNNs) for pattern classification usually use the backpropagation or C-cluster type learning algorithms to learn the parameters of the fuzzy rules and membership functions from the training data. However, such kinds of learning algorithms usually cannot minimize the empirical risk (training error) and expected risk (testing error) simultaneously, and thus cannot reach a good classification performance in the testing phase. To tackle this drawback, a support-vector-based fuzzy neural network (SVFNN) is proposed for pattern classification in this paper. The SVFNN combines the superior classification power of support vector machine (SVM) in high dimensional data spaces and the efficient human-like reasoning of FNN in handling uncertainty information. A learning algorithm consisting of three learning phases is developed to construct the SVFNN and train its parameters. In the first phase, the fuzzy rules and membership functions are automatically determined by the clustering principle. In the second phase, the parameters of FNN are calculated by the SVM with the proposed adaptive fuzzy kernel function. In the third phase, the relevant fuzzy rules are selected by the proposed reducing fuzzy rule method. To investigate the effectiveness of the proposed SVFNN classification, it is applied to the Iris, Vehicle, Dna, Satimage, Ijcnn1 datasets from the UCI Repository, Statlog collection and IJCNN challenge 2001, respectively. Experimental results show that the proposed SVFNN for pattern classification can achieve good classification performance with drastically reduced number of fuzzy kernel functions. 相似文献
995.
P. Prem Kumar Indrani Kar Laxmidhar Behera 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2006,36(6):1442-1449
This correspondence proposes two novel control schemes with variable state-feedback gain to stabilize a Takagi-Sugeno (T-S) fuzzy system. The T-S fuzzy model is expressed as a linear plant with nonlinear disturbance terms in both schemes. In controller I, the T-S fuzzy model is expressed as a linear plant around a nominal plant arbitrarily selected from the set of linear subsystems that the T-S fuzzy model consists of. The variable gain then becomes a function of a gain parameter that is computed to neutralize the effect of disturbance term, which is, in essence, the deviation of the actual system dynamics from the nominal plant as the system traverses a specific trajectory. This controller is shown to stabilize the T-S fuzzy model. In controller II, individual linear subsystems are locally stabilized. Fuzzy blending of individual control actions is shown to make the T-S fuzzy system Lyapunov stable. Although applicability of both control schemes depends on the norm bound of unmatched state disturbance, this constraint is relaxed further in controller II. The efficacy of controllers I and II has been tested on two nonlinear systems 相似文献
996.
Although 2DLDA algorithm obtains higher recognition accuracy, a vital unresolved problem of 2DLDA is that it needs huge feature matrix for the task of face recognition. To overcome this problem, this paper presents an efficient approach for face image feature extraction, namely, (2D)2LDA method. Experimental results on ORL and Yale database show that the proposed method obtains good recognition accuracy despite having less number of coefficients. 相似文献
997.
Tuah N.J. Kumar M. Venkatesh S. Das S.K. 《Parallel and Distributed Systems, IEEE Transactions on》2002,13(5):471-484
Speculative prefetching has been proposed to improve the response time of network access. Previous studies in speculative prefetching focus on building and evaluating access models for the purpose of access prediction. This paper investigates a complementary area which has been largely ignored, that of performance modeling. We analyze the performance of a prefetcher that has uncertain knowledge about future accesses. Our performance metric is the improvement in access time, for which we derive a formula in terms of resource parameters (time available and time required for prefetching) and speculative parameters (probabilities for next access). We develop a prefetch algorithm to maximize the improvement in access time. The algorithm is based on finding the best solution to a stretch knapsack problem, using theoretically proven apparatus to reduce the search space. An integration between speculative prefetching and caching is also investigated 相似文献
998.
Many classification problems involve high dimensional inputs and a large number of classes. Multiclassifier fusion approaches
to such difficult problems typically centre around smart feature extraction, input resampling methods, or input space partitioning
to exploit modular learning. In this paper, we investigate how partitioning of the output space (i.e. the set of class labels) can be exploited in a multiclassifier fusion framework to simplify such problems and to yield
better solutions. Specifically, we introduce a hierarchical technique to recursively decompose a C-class problem into C_1 two-(meta) class problems. A generalised modular learning framework is used to partition a set of classes into two disjoint
groups called meta-classes. The coupled problems of finding a good partition and of searching for a linear feature extractor
that best discriminates the resulting two meta-classes are solved simultaneously at each stage of the recursive algorithm.
This results in a binary tree whose leaf nodes represent the original C classes. The proposed hierarchical multiclassifier framework is particularly effective for difficult classification problems
involving a moderately large number of classes. The proposed method is illustrated on a problem related to classification
of landcover using hyperspectral data: a 12-class AVIRIS subset with 180 bands. For this problem, the classification accuracies
obtained were superior to most other techniques developed for hyperspectral classification. Moreover, the class hierarchies
that were automatically discovered conformed very well with human domain experts’ opinions, which demonstrates the potential
of using such a modular learning approach for discovering domain knowledge automatically from data.
Received: 21 November 2000, Received in revised form: 02 November 2001, Accepted: 13 December 2001 相似文献
999.
1000.
The design of tractors manufactured in low-income countries like India has not changed much in the past two decades, especially from an ergonomic point of view. Moreover, in these countries tractors are used for transportation purposes in addition to farming operations. Therefore, the design criteria for these tractors need to be different from those in high-income countries. This paper describes the development of an ergonomic facility for improvement of tractor design. An ergonomic evaluation facility has been developed consisting of a work place envelope for the Indian population, a layout measuring device and an ergonomic rig. This facility can be used for comparative evaluation of the display and control layouts of different tractors in order to develop an optimum layout. The ergonomic rig has the facility to simulate the improved layout for subjective evaluation. 相似文献