全文获取类型
收费全文 | 1521篇 |
免费 | 71篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 30篇 |
综合类 | 3篇 |
化学工业 | 378篇 |
金属工艺 | 43篇 |
机械仪表 | 58篇 |
建筑科学 | 27篇 |
矿业工程 | 2篇 |
能源动力 | 77篇 |
轻工业 | 163篇 |
水利工程 | 10篇 |
石油天然气 | 27篇 |
无线电 | 193篇 |
一般工业技术 | 247篇 |
冶金工业 | 105篇 |
原子能技术 | 8篇 |
自动化技术 | 231篇 |
出版年
2023年 | 20篇 |
2022年 | 33篇 |
2021年 | 51篇 |
2020年 | 36篇 |
2019年 | 48篇 |
2018年 | 71篇 |
2017年 | 50篇 |
2016年 | 54篇 |
2015年 | 44篇 |
2014年 | 43篇 |
2013年 | 126篇 |
2012年 | 69篇 |
2011年 | 83篇 |
2010年 | 74篇 |
2009年 | 66篇 |
2008年 | 56篇 |
2007年 | 58篇 |
2006年 | 38篇 |
2005年 | 33篇 |
2004年 | 20篇 |
2003年 | 34篇 |
2002年 | 25篇 |
2001年 | 32篇 |
2000年 | 21篇 |
1999年 | 23篇 |
1998年 | 41篇 |
1997年 | 21篇 |
1996年 | 30篇 |
1995年 | 18篇 |
1994年 | 15篇 |
1993年 | 8篇 |
1992年 | 15篇 |
1991年 | 18篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 16篇 |
1985年 | 20篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有1602条查询结果,搜索用时 15 毫秒
51.
We consider a single-input-single-output (SISO) nonlinear system that has a well-defined normal form with asymptotically stable zero dynamics. Using only knowledge of the relative degree and the sign of the high-frequency gain, we design an output feedback integral controller that asymptotically regulates the output to a bounded time-varying reference signal with a constant limit. We give regional as well as semi-global results. We also show that, for relative degree one and two systems, the proposed integral controller reduces to the classical PI and PID controllers, respectively 相似文献
52.
This short paper reports a simple method to image low density lipoproteins (LDL) using atomic force microscopy (AFM). This instrument allows imaging of biological samples in liquid and presents the advantage of needing no sample preparation such as staining or fixation that may affect their general structure. Dimensions (diameter and height) of individual LDL particles were successfully measured. AFM imaging revealed that LDL have a quasi-spherical structure on the x and y axis with an oblate spheroid structure in the z axis (i.e., height). LDLs were found to have an average diameter of 23 +/- 3 nm. The obtained mean height was 10 +/- 2 nm. 相似文献
53.
Program diagnosis systems were developed to help users solve programming problems. By providing guidence on errors and misconceptions, these systems can help the users in writing programs and understanding their dynamic behavior. Features of software visualization which aim at providing visual and concrete depictions to the abstractions and operations of programs have also shown to be making programs more understandable. The main theme of this paper is to asses the usefulness of incorporating features of software visualization into the design of program diagnosis systems intended for novices. We report an empirical evaluation to assess the effectiveness of supporting visualization features during problem solving. The system used in the evaluation integrates visualzation and immediacy features and supports a model-tracing based approach to program diagnosis. Unlike other similar systems, our prototype system supports a more flexible style of interaction by increasing the grain size of diagnosis to a complete programming statement. The evaluation reported here seems to suggest that when supported with visualization features, systems for program diagnosis tend to be more effective in helping the users during problem solving. 相似文献
54.
Gertrud K. Nürnberg Lewis A. Molot Eavan O'Connor Hamdi Jarjanazi Jennifer Winter Joelle Young 《Journal of Great Lakes research》2013
Hypoxia and cyanobacterial blooms were extensive in Lake Simcoe during the 1980s and are still a problem to a lesser degree despite extensive nutrient load reduction from the catchment basin. The continuing signs of productivity indicate a potential internal phosphorus (P) source. Internal P load, as a redox-dependent release from bottom sediments, is hard to determine in a large, relatively shallow and partially unstratified lake such as Lake Simcoe. Of the lake's three major basins, only Kempenfelt Bay stratifies long enough to develop hypoxia in the stagnant summer hypolimnion. The following indications of sediment P release are available from historic data: 1) hypolimnetic hypoxia still occurs in Kempenfelt Bay although the hypoxic factor (number of days that an area equal to the bay's surface area is overlain by water of ≤ 2 mg/L dissolved oxygen, DO) has decreased substantially and significantly from 15.8 d/yr (1980–1994) to 4.0 d/yr (1995–2011); 2) hypoxic factors for other lake sections and at different DO levels also indicate widespread hypoxia; 3) concentrations of redox dependent metals, Fe and Mn, increase with depth; and 4) euphotic zone P and chlorophyll concentrations increase and water clarity decreases during fall turnover. Cyanobacterial blooms appear to occur in response to internal load as supported by occasional cyanobacteria counts. These indicators provide evidence that internal loading is likely occurring and affecting the water quality in Lake Simcoe. We expect that further monitoring, specific for internal load, will corroborate these results. 相似文献
55.
Krzysztof Fleszar Christoforos Charalambous Khalil S. Hindi 《Journal of Intelligent Manufacturing》2012,23(5):1949-1958
The NP-hard problem of scheduling jobs on unrelated parallel machines, in the presence of machine-dependent and sequence-dependent setup times, with the objective of minimizing the makespan, is considered. A variable neighborhood descent search algorithm, hybridized with mathematical programming elements, is presented and its performance is evaluated on a large set of benchmark problem instances. The extensive computational experiments show that the proposed algorithm outperforms previously proposed methods in terms of solution quality as well as computation time. 相似文献
56.
S. M. Khalil 《Journal of Low Temperature Physics》2006,143(1-2):31-44
A study was made of the effect of Cd additions on the superconducting and mechanical properties of Bi1.82Pb0.36Sr2Ca2 CdxCu3Oy (x = 0.0, 0.15, 0.25, 0.35 and 0.55). Characterization of the Cd-samples using XRD, DTA, and SEM techniques, has confirmed that remarkably formation of low-T
c
phase (2212) by the addition of Cd up to 0.35. High-resolution electrical resistivity ρ (T) data on the composition of Cd = 0.35 have been taken for investigating critically the superconducting fluctuations. Using the Aslamazov and Larkin (AL) and Lawrence and Doniach (LD) models of excess conductivity. Excess conductivity analysis shows that this composition (Cd = 0.35) is 2D in the temperature range 137.8–163.7 K and a 3D one below 137.8 K. Thus, a crossover from 2D to 3D is observed at 137.8 K. Sample microhardness and density are greatly improved by Cd-additions (0.35). This trend is probably due to the intercalation of cadmium between superconducting grains in compositions may provide a plastic-flow region that allows relaxation of undesirable stresses resulting from the grain anisotropy of superconductors. 相似文献
57.
The effects of the binder composition, the powder loading, the thermal properties of feedstocks, and the injection molding parameters on the compact shape retention for metal injection molding 17-4PH stainless steel were investigated. The high-density polyethylene is more effective than ethylene vinyl acetate as a second component of the wax-based binder to retain compact shape due to its higher pyrolytic temperature and less heat of fusion. The compact distortion decreases with increasing the powder loading, molding pressure and molding temperature. There exists an optimal process combination including the powder loading of 68 %, molding pressure of 120 MPa and molding temperature of 150℃. Under this process condition, the percentage of distorted compacts is the lowest. 相似文献
58.
A new interconnection network is proposed for the construction of a massively parallel computer system. The systematic construction of this interconnection network, denoted RCC-FULL, is performed by methodically connecting together a number of basic atoms where a basic atom is a set of fully interconnected nodes. Key communication characteristics are derived and evaluated for RCC-FULL and efficient routing algorithms, which need only local information to route messages between any two nodes, are also derived. AnO(log (N)) sorting algorithm is shown for RCC-FULL and RCC-FULL is shown to emulate deterministically the CRCW PRAM model, with onlyO(log (N)) degradation in time performance. Finally, the hardware cost for the RCC-FULL is estimated as a function of its pin requirements and compared to that of the binary hypercube and most instances of RCC-FULL have substantially lower cost. Hence, RCC-FULL appears to be a particularly effective network for PRAM emulation, and might be considered as a universal network for future supercomputing systems. 相似文献
59.
Performance recovery under output feedback sampled-data stabilization of a class of nonlinear systems 总被引:1,自引:0,他引:1
This paper studies sampled-data output feedback control of a class of nonlinear systems. It is shown that the performance of a stabilizing continuous-time state feedback controller can be recovered by a sampled-data output feedback controller when the sampling period is sufficiently small. The output feedback controller uses a deadbeat discrete-time observer to estimate the unmeasured states. Two schemes are proposed to overcome large initial transients when the controller is switched on. 相似文献
60.
The low temperature photoluminescence under bias (PLb) and the photoconductivity (PC) of a p-i-n GaInNAs/GaAs multiple quantum well sample have been investigated. Under optical excitation with photons of energy greater than the GaAs bandgap, PC and PLb results show a number of step-like increases when the sample is reverse biased. The nature of these steps, which depends upon the temperature, exciting wavelength and intensity and the number of quantum wells (QWs) in the device, is explained in terms of thermionic emission and negative charge accumulation due to the low confinement of holes in GaInNAs QWs. At high temperature, thermal escape from the wells becomes much more dominant and the steps smear out. 相似文献