全文获取类型
收费全文 | 9654篇 |
免费 | 650篇 |
国内免费 | 393篇 |
专业分类
电工技术 | 315篇 |
综合类 | 510篇 |
化学工业 | 1408篇 |
金属工艺 | 362篇 |
机械仪表 | 380篇 |
建筑科学 | 706篇 |
矿业工程 | 122篇 |
能源动力 | 504篇 |
轻工业 | 718篇 |
水利工程 | 216篇 |
石油天然气 | 148篇 |
武器工业 | 40篇 |
无线电 | 1201篇 |
一般工业技术 | 1671篇 |
冶金工业 | 1147篇 |
原子能技术 | 505篇 |
自动化技术 | 744篇 |
出版年
2024年 | 19篇 |
2023年 | 155篇 |
2022年 | 167篇 |
2021年 | 283篇 |
2020年 | 233篇 |
2019年 | 242篇 |
2018年 | 225篇 |
2017年 | 301篇 |
2016年 | 306篇 |
2015年 | 290篇 |
2014年 | 422篇 |
2013年 | 770篇 |
2012年 | 481篇 |
2011年 | 745篇 |
2010年 | 542篇 |
2009年 | 551篇 |
2008年 | 506篇 |
2007年 | 583篇 |
2006年 | 546篇 |
2005年 | 407篇 |
2004年 | 407篇 |
2003年 | 313篇 |
2002年 | 328篇 |
2001年 | 236篇 |
2000年 | 184篇 |
1999年 | 168篇 |
1998年 | 230篇 |
1997年 | 151篇 |
1996年 | 135篇 |
1995年 | 94篇 |
1994年 | 83篇 |
1993年 | 68篇 |
1992年 | 56篇 |
1991年 | 59篇 |
1990年 | 62篇 |
1989年 | 50篇 |
1988年 | 35篇 |
1987年 | 24篇 |
1986年 | 20篇 |
1985年 | 37篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 16篇 |
1981年 | 7篇 |
1966年 | 7篇 |
1964年 | 22篇 |
1963年 | 11篇 |
1960年 | 9篇 |
1959年 | 7篇 |
1958年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Fatigue at high temperature is a complex phenomenon as it is influenced by a number of time-dependent processes which become
important at elevated temperatures. These processes include creep, oxidation, phase instabilities and dynamic strain ageing
(DSA), acting either independently or synergistically influence fatigue behaviour, often lowering the fatigue life. Current
design approaches employ linear summation of fatigue and creep damage with suitable factors on permissible damage to take
care of uncertainties in interaction between cyclic and time-dependent processes. It is, therefore, important to develop a
deeper understanding of the processes that occur during high temperature fatigue so that realistic life predictions could
be made.
Results on the high temperature fatigue behaviour of austenitic stainless steels, ferritic steels and nickel base alloys are
presented here. The important mechanisms of interaction of high temperature time-dependent processes with fatigue under various
conditions are discussed in detail. Emphasis is placed on cyclic stress response, fatigue life, deformation substructure and
fracture behaviour. This is followed by a review of important life prediction techniques under combined creep-fatigue loading
conditions. Life prediction techniques considered here include linear damage summation, strain range partitioning, ductility
exhaustion approach, frequency modified and frequency separation methods, techniques based on hysteresis energy and damage
rate models, and methods based on crack-cavitation interation models. 相似文献
102.
Evidence from 3 experiments reveals interference effects from structural relationships that are inconsistent with any grammatical parse of the perceived input. Processing disruption was observed when items occurring between a head and a dependent overlapped with either (or both) syntactic or semantic features of the dependent. Effects of syntactic interference occur in the earliest online measures in the region where the retrieval of a long-distance dependent occurs. Semantic interference effects occur in later online measures at the end of the sentence. Both effects endure in offline comprehension measures, suggesting that interfering items participate in incorrect interpretations that resist reanalysis. The data are discussed in terms of a cue-based retrieval account of parsing, which reconciles the fact that the parser must violate the grammar in order for these interference effects to occur. Broader implications of this research indicate a need for a precise specification of the interface between the parsing mechanism and the memory system that supports language comprehension. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
Carlson Steadman Dancila & Kardomateas 《Fatigue & Fracture of Engineering Materials & Structures》1998,21(4):403-409
Results of an experimental investigation of the fatigue growth of small corner cracks emanating from small flaws are presented. Growth-arrest behaviour was observed, and increases in crack length during growth periods were of the order of the transverse grain size. For the test material, the corner crack front intersects, on average, only three–six grains in the small crack regime monitored, so only a small number of constrained, interior grains is encountered. It is suggested that the presence of partially constrained surface grains may contribute to the 'anomalous' growth behaviour which has been observed by a number of investigators.
The crack growth histories of the test data presented exhibit considerable scatter. It is shown that a Student's t -test can be used to estimate confidence intervals in order to provide a measure of the observed scatter. The variation in confidence intervals in the transition from small to long fatigue crack growth is discussed. 相似文献
The crack growth histories of the test data presented exhibit considerable scatter. It is shown that a Student's t -test can be used to estimate confidence intervals in order to provide a measure of the observed scatter. The variation in confidence intervals in the transition from small to long fatigue crack growth is discussed. 相似文献
104.
105.
A novel frequency-selective metamaterial with negative permittivity and permeability for improving directivity and gain of a helix antenna is presented in this paper.The proposed metamaterial is composed of two Z-shape resonators printed on opposite sides of a dielectric substrate.Two forms of multilayered cells are found to be suitable for antennas and waveguides applications.In addition,a new method of designing a metamaterial-based helix antenna is presented with high directivity and gain.A comparison on radiation properties is given between the conventional and the new metamaterial-based helix antennas.Two comparisons on radiation properties are performed:(1) the effect of proposed Z-structure on monopole,dipole,and helix antennas;(2) the effect of OE3,split-ring resonator (SRR),and proposed Z-structure unit cells on the performance of helix antennas.The results show improvement of parameters such as directivity,gain,and radiation power of the new metamaterial-based helix antenna.Therefore,the combination of Z-structure with the helix antenna shows the best performance. 相似文献
106.
An improved bacterial foraging algorithm for combined static/dynamic environmental economic dispatch
Nicole Pandit Anshul Tripathi Shashikala Tapaswi Manjaree Pandit 《Applied Soft Computing》2012,12(11):3500-3513
Economic dispatch is carried out at the energy control center to find out the optimal output of thermal generating units such that power balance criterion is met, unit operating limits are satisfied and the fuel cost is minimized. With growing environmental awareness and strict government regulations throughout the world, it has become essential to optimize not only the total fuel cost but also the harmful emissions, both, under static as well as dynamic conditions. The static environment economic dispatch finds the optimal output of generating units for a fixed load demand at a given time, while the dynamic environmental economic dispatch schedules the output of online generators with changing power demands over a certain time period (normally one day) so as to minimize these two conflicting objectives, simultaneously. In this paper, the price penalty factor approach is employed for simultaneous minimization of cost and emission. The generator ramp rate constraints, non-convex and discontinuous nature of cost function and the large number of generators in practical power plants, make this problem very difficult to solve. Here, a fuzzy ranking approach is employed to identify the solution which offers the best compromise between cost and emission objectives. 相似文献
107.
Three consumer products (a television set, a personal computer and a typewriter), all considered portable by their respective manufacturers, were evaluated experimentally for portability. Products were not considered portable if the physical and subjective workloads resulting from carrying them over specified distances were excessive. Twenty-two males and six females participated in the experimental investigation and carried the three products for distances of 45·72, 91·44. 137·16 and 182·88 m. Their pulse and ratings of perceived exertion (RPE) of the arms and whole body were recorded and used as measures of physical and perceived workloads. Both physiological and subjective responses to carrying products were significantly influenced by the type of product and carrying distance, regardless of the gender of the person performing the carrying. The results of this study and the design guidelines provided in the literature for one-handed and two-handed carrying tasks led to the conclusion that, of the three products, only the television set could be considered portable. 相似文献
108.
It has been suggested by Kayser that finite-size effects associated with capillary waves might play a significant role in some surface tension measurements; for capillary rise between plates a distance D apart, an effect varying as 1/D and apparently observable in measurements, was proposed. In reconsidering this problem, one must analyze the thermodynamics of finite-size corrections to surface tension. In particular, one sees that capillary rise between plates does not measure the interfacial free energy density but, rather, a derivative of the interfacial free energy with respect to a system dimension. The quantity needed to draw definite conclusions, the finite-size residual free energy, can be calculated within the harmonic or Gaussian capillary wave model in d spatial dimensions with the aid of Poisson summation techniques and should yield the correct leading asymptotic behavior. For d=3 and experimentally relevant parameter values, the results are independent of the short-wavelength cutoff needed in the model and can be checked against the theory of conformai covariance at two-dimensional critical points. It is found that the finite-size effects in capillary-rise measurements of surface tension vary as 1/D
2 (with a universal coefficient) but are too small to be seen in current experiments.Invited paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A. 相似文献
109.
提出并研制成一种新型硅三端负阻器件。该器件由一n沟耗尽型MOS管、一横向pnp双极晶体管和一个电阻集成而得。它具有“双负阻”特性和正阻区阻值易于控制等特点。由理论计算出的器件I_c—V_(CB)特性和负阻参数与实验结果符合良好。 相似文献
110.
本文阐述了充分考虑矿石性质,探索出混合浮选的分步流程,恰当的施用多元扑收剂所产出的“协同效应”,稳定和强化选别工艺,收到提高选金技术指标的效果。 相似文献