全文获取类型
收费全文 | 26467篇 |
免费 | 2635篇 |
国内免费 | 1013篇 |
专业分类
电工技术 | 1517篇 |
综合类 | 1236篇 |
化学工业 | 4307篇 |
金属工艺 | 1051篇 |
机械仪表 | 1225篇 |
建筑科学 | 1706篇 |
矿业工程 | 425篇 |
能源动力 | 830篇 |
轻工业 | 2453篇 |
水利工程 | 490篇 |
石油天然气 | 668篇 |
武器工业 | 180篇 |
无线电 | 3727篇 |
一般工业技术 | 3586篇 |
冶金工业 | 2247篇 |
原子能技术 | 292篇 |
自动化技术 | 4175篇 |
出版年
2024年 | 130篇 |
2023年 | 513篇 |
2022年 | 979篇 |
2021年 | 1500篇 |
2020年 | 1064篇 |
2019年 | 930篇 |
2018年 | 1039篇 |
2017年 | 960篇 |
2016年 | 1039篇 |
2015年 | 1126篇 |
2014年 | 1453篇 |
2013年 | 1711篇 |
2012年 | 1720篇 |
2011年 | 1898篇 |
2010年 | 1504篇 |
2009年 | 1408篇 |
2008年 | 1354篇 |
2007年 | 1185篇 |
2006年 | 1014篇 |
2005年 | 816篇 |
2004年 | 662篇 |
2003年 | 549篇 |
2002年 | 570篇 |
2001年 | 505篇 |
2000年 | 339篇 |
1999年 | 396篇 |
1998年 | 782篇 |
1997年 | 490篇 |
1996年 | 401篇 |
1995年 | 258篇 |
1994年 | 217篇 |
1993年 | 222篇 |
1992年 | 131篇 |
1991年 | 127篇 |
1990年 | 103篇 |
1989年 | 116篇 |
1988年 | 73篇 |
1987年 | 64篇 |
1986年 | 71篇 |
1985年 | 73篇 |
1984年 | 65篇 |
1983年 | 57篇 |
1982年 | 59篇 |
1981年 | 43篇 |
1980年 | 49篇 |
1979年 | 39篇 |
1978年 | 33篇 |
1977年 | 57篇 |
1976年 | 73篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
71.
Two recursive algorithms are presented for calculating the coefficients of a bandpass transfer function, given the lowpass prototype transfer function. In both cases, the method is general, valid for prototypes having both poles and zeros, and provides excellent accuracy. Moreover, it is shown that the coefficients of band-rejection filters can be derived by using either algorithm.<> 相似文献
72.
73.
Cadiou J.F. Guena J. Penard E. Legaud P. Minot C. Palmier J.F. Le Person H. Harmand J.E. 《Electronics letters》1994,30(20):1690-1691
For the first time, a direct optically injection-locked oscillator based on the Esaki-Tsu effect in superlattices is reported. The microwave output power is -7 dBm at 20 GHz with an optical input power of -10 dBm at a wavelength of 1.3 μm 相似文献
74.
Duc Nguyen Hong 《Chemical engineering science》2006,61(6):1846-1853
New experimental data coupled with a numerical model and an approximate solution are proposed to predict dissociation time of hydrate plugs in oil sub-sea pipelines. The experimental hydrate plugs are dissociated by the method of symmetric depressurisation, both in a specially designed apparatus and a classical batch reactor. The agreement between the estimation of the model and the experimental data and the simplicity of the approximate equation presents an advantage in estimating the time of hydrate plug dissociation in pipelines. 相似文献
75.
A novel dynamic survivable routing in WDM optical networks with/without sparse wavelength conversion
Vinh Trong Le Xiaohong Jiang Son Hong Ngo Susumu Horiguchi Yasushi Inoguchi 《Optical Switching and Networking》2006,3(3-4):173-190
In this paper, we study the dynamic survivable routing problem, both in optical networks without wavelength conversion and in optical networks with sparse wavelength conversion, and propose a novel hybrid algorithm for it based on the combination of mobile agents technique and genetic algorithms (GA). By keeping a suitable number of mobile agents in the network to cooperatively explore the network states and continuously report cycles (that are formed by two disjoint-link routes) into the routing tables, our new hybrid algorithm can promptly determine the first population of cycles for a new request based on the routing table of its source node, without the time consuming process associated with current GA-based lightpath protection schemes. We further improve the performance of our algorithm by introducing a more advanced fitness function that is suitable for both the above networks. Extensive simulation studies on the ns-2 network simulator show that our hybrid algorithm achieves a significantly lower blocking probability than the conventional survivable routing algorithms for all the cases we studied. 相似文献
76.
上海同步辐射装置(SSRF)储存环铝合金超高真空室已研制成功,该机加真空室的尺寸大、尺寸精度、形位公差及粗糙度要求极高,不同于常规的大型超高真空室。在预研件加工中,成功地解决了一系列问题,如光洁度提高困难,加工成型后变形大;加工尺寸和精度受环境温度影响较大等。本文详细阐述了储存环真空室材料和热处理状态的选择依据,为了保证尺寸精度和形位公差所采取的工艺措施,分析了粗糙度的形成机理和影响因素,从刀具材料、几何角度、切削参数、冷却液选型等多方面提出了解决办法。 相似文献
77.
This paper concerns the plasticity constitutive laws in small strain. In the thermodynamic approach developed here, the key concept is that of internal variables. The differential nature of plasticity law has been pointed out for a long time. If we unite the invariance condition of these laws in a state variable transformation, this involves, ultimately, that the natural mathematic frame of plasticity theory is Differential Geometry. The system state is defined as a point of a differentiable manifold. The state variable are the local coordinates of this point in a chart. The internal stresses are the components of a covariant vector of the cotangent bundle to internal state manifold and the elastic domain is a convex part of cotangent vector space. The plastic yield criteria such as von Mises condition define a Riemannian structure over the manifold. The metric element is identified with the internal dissipation element. Constitutive laws link the covariant derivatives of the thermodynamic stress with the state variable. Hardening modulus splits up in two parts, kinematic hardening and metric hardening. This last is defined by Christoffel connection coefficients. Applied to von Mises isotropic yield condition, the metric hardening is identified with isotropic hardening. The Baltov-Sawczuk model is also analysed. The use of appropriate polar coordinates simplifies significantly the computations. Generalization to a significant category of non-differentiable yield criteria, such as Tresca condition, is considered by introducting a metric tensor family. The adaptation of Drucker's postulate to the proposed model requires the introduction of parallel transport of the internal stress covector. Generally, this transport is different over distinctive paths joining two points. This fact expresses internal state manifold curvature. The Riemann-Christoffel tensor is computed for von Mises, Baltov-Sawczuk and Tresca models. 相似文献
78.
Observation and Analysis of Gypsum Particleboard using SEM 总被引:2,自引:0,他引:2
冯谦 《武汉理工大学学报(材料科学英文版)》2007,22(1):44-47
The microstructures of gypsum board and gypsum particleboard were observed by SEM. The effects of retarder and waterproof agent on the shape and the average dimension of the gypsum crystal were discussed. The mechanism was investigated as well. Four typical instances, i e, the gypsum crystal shape, the gypsum combined with particles on the particles surface, the gypsum combined with particles on the wood cross section and the gypsum combined with particles inside the wood cell cavity were selected and observed. Furthermore, the agglomeration and cementation mechanism between gypsum and particle were studied. 相似文献
79.
Porous alumina films can be found in a wide variety of materials, including filters, thermal insulation components, dielectrics, biomedical and catalyst supports, coatings and adsorbents. Production methods for these films are as equally diverse as their applications. In this work, a hybrid process based upon chemical vapor deposition and gas-to-particle conversion is presented as an alternative technique for producing porous alumina films, with the main advantages of solvent-free, low substrate-temperature operation. In this process, nanoparticles were produced in the vapor phase by reaction of aluminum acetylacetonate in the presence of oxygen. Downstream of this reaction zone, these nanoparticles were collected via thermophoresis onto a cooled substrate, forming a porous film. Some deposited films were subjected to post-processing in the form of annealing in air. Fourier-transform infrared spectra and X-ray energy-dispersive spectroscopy analysis confirmed the production of alumina at processing temperatures above 973 K. X-Ray diffraction revealed that the films were amorphous. Film thickness, ranging from 30 to 250 μm, and the average deposition rate were determined from scanning electron microscopy results. From transmission electron microscopy, the average primary particle size was determined to be approximately 18 nm and the formation of nanoparticle aggregates was evident. Annealing of the films at temperatures ranging from 523 to 1173 K in the presence of air did not have an effect on particle size. The specific surface area of the powder composing the films ranged from 10 to 185 m2 g−1, as determined from nitrogen gas adsorption by the Brunauer–Emmett–Teller method. 相似文献
80.
Nguyen-Huy Dung Pardo Marie-Paule Dogguy.Smiri Leïla 《Materials Research Bulletin》1982,17(3):293-300
The Mn0.23Ga1.85S3 phase belongs to the solid solution , stable at low temperature in the Ga2S3MnS system. It is hexagonal superstructure of the wurtzite, with the Ga2S3α′ type (; Z = 6; space groupe P61 or P65). Its crystal structure has been refined by the least squares method to a final R = 0.06 with 323 independant reflections. This structure is closely related to Ga2S3 α described by Hahn and Frank, and differs only by the partial occupation of the vacant metal site of Ga2S3 by Mn atoms in statistical disorder. 相似文献