全文获取类型
收费全文 | 32305篇 |
免费 | 4367篇 |
国内免费 | 3458篇 |
专业分类
电工技术 | 2634篇 |
技术理论 | 1篇 |
综合类 | 4774篇 |
化学工业 | 2267篇 |
金属工艺 | 1958篇 |
机械仪表 | 2065篇 |
建筑科学 | 1339篇 |
矿业工程 | 515篇 |
能源动力 | 471篇 |
轻工业 | 810篇 |
水利工程 | 540篇 |
石油天然气 | 541篇 |
武器工业 | 790篇 |
无线电 | 4785篇 |
一般工业技术 | 5028篇 |
冶金工业 | 641篇 |
原子能技术 | 342篇 |
自动化技术 | 10629篇 |
出版年
2024年 | 101篇 |
2023年 | 435篇 |
2022年 | 772篇 |
2021年 | 967篇 |
2020年 | 994篇 |
2019年 | 1043篇 |
2018年 | 967篇 |
2017年 | 1307篇 |
2016年 | 1337篇 |
2015年 | 1552篇 |
2014年 | 2023篇 |
2013年 | 2471篇 |
2012年 | 2370篇 |
2011年 | 2484篇 |
2010年 | 2046篇 |
2009年 | 2187篇 |
2008年 | 2009篇 |
2007年 | 2281篇 |
2006年 | 1918篇 |
2005年 | 1700篇 |
2004年 | 1397篇 |
2003年 | 1138篇 |
2002年 | 956篇 |
2001年 | 872篇 |
2000年 | 769篇 |
1999年 | 624篇 |
1998年 | 520篇 |
1997年 | 450篇 |
1996年 | 378篇 |
1995年 | 382篇 |
1994年 | 335篇 |
1993年 | 276篇 |
1992年 | 213篇 |
1991年 | 169篇 |
1990年 | 154篇 |
1989年 | 123篇 |
1988年 | 89篇 |
1987年 | 56篇 |
1986年 | 34篇 |
1985年 | 40篇 |
1984年 | 29篇 |
1983年 | 33篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Vatroslav Bubalo Vjekoslav Jerolimov Ivo Bau
i Mladen Andreis Zorica Veksli 《Polymer International》2005,54(5):848-853
The electron‐spin‐resonance (ESR) spin‐probe method, was used to study the heterogeneity of denture resins based on poly(methyl methacrylate). Results for three resins processed by microwave energy, conventional curing and cold curing (depending on the curing procedure and exposed to ageing in various environmental conditions) were compared. All three cured resins were stored over the same time (1200 h) in distilled water at ambient temperature and in artificial saliva at 348 K. The temperature‐dependent ESR spectra of a spin probe dispersed in the denture resins are analyzed in terms of line‐shapes and line‐widths. The appearance of two spectral components was taken as an indication of resin heterogeneity. The results reveal that the cold‐cured resin has a lower local density in comparison with microwave and conventionally cured resin. The amount of residual monomer also contributes to the local motion of polymer segments. The change of denture resins exposed to ageing is influenced both by the structure of the original resin and the ageing conditions. Restricted motion of a spin probe incorporated into the acrylic resins exposed to accelerated ageing suggests additional crosslinking of polymer chains. The differences are observed for all the investigated resins, but the highest change is observed with the cold‐cured resin. The ESR results are accompanied by Tg and Tm measurements. Copyright © 2005 Society of Chemical Industry 相似文献
62.
A probabilistic model for cleavage fracture with a length scale--parameter estimation and predictions of stationary crack experiments 总被引:1,自引:0,他引:1
This study presents a large experimental investigation in the transition temperature region on a modified A508 steel. Tests were carried out on single-edge-notch-bend specimens with three different crack depth over specimen width ratios to capture the strong constraint effect on fracture toughness. Three test temperatures were considered, covering a range of 85 °C. All specimens failed by cleavage fracture prior to ductile tearing. A recently proposed probabilistic model for the cumulative failure by cleavage was applied to the comprehensive sets of experimental data. This modified weakest link model incorporates a length scale, which together with a threshold stress reduce the scatter in predicted toughness distributions as well as introduces a fracture toughness threshold value. Model parameters were estimated by a robust procedure, which is crucial in applications of probabilistic models to real structures. The conformity between predicted and experimental toughness distributions, respectively, were notable at all the test temperatures. 相似文献
63.
1Introduction Reconstructivesurgeryisoneofthehottestre searchedsubjectsthatdealingwithbonedefects.Thetra ditionalmethodisimplantationoffreshautograftbonebe causeofitsnon immunoreactiveproperty.Butautologousbonewasnotabundantinsomecases.Sowefoundbeta trica… 相似文献
64.
The discrimination problem for two normal populations with the same covariance matrix when additional information on the population is available is considered. A study of the robustness properties against training sample contamination of classification rules that incorporate this additional information is performed. These rules have received recently attention where their total misclassification probability (TMP) is proved to be lower than Fisher's linear discriminant rule. The results of a simulation study on the TMP which compares the behaviour of the new rules against Fisher's rule and some of its robustified versions under different types of contamination are presented. These results show that the rules that incorporate the additional information not only have lower TMP, but they also prevent against some types of contamination. In order to achieve prevention from all types of contamination a robustifed version of these rules is recommended. 相似文献
65.
Evans Jonathan St. B. T.; Handley Simon J.; Over David E. 《Canadian Metallurgical Quarterly》2003,29(2):321
The authors report 3 experiments in which participants were invited to judge the probability of statements of the form if p then q given frequency information about the cases pq, p?q, ?pq, and ?p?q (where ? = not). Three hypotheses were compared: (a) that people equate the probability with that of the material conditional, 1 - P(p?q); (b) that people assign the conditional probability, P(q/p); and (c) that people assign the conjunctive probability P(pq). The experimental evidence allowed rejection of the 1st hypothesis but provided some support for the 2nd and 3rd hypotheses. Individual difference analyses showed that half of the participants used conditional probability and that most of the remaining participants used conjunctive probability as the basis of their judgments. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
66.
The formation of aluminum matrix composites fabricated by exothermic dispersion reaction in A1-TiO2-B2O3 system was investigated. The thermal analysis results show that the reactions are spontaneous and exothermic. The Gibbs free energy of α-Al2O3 is the lowest among all the combustion products, followed by TiB2 and Al3Ti. It is noted that when the B2O3/TiO2 mole ratio is below 1, the reaction products are composed of particle-like α-Al2O3, TiB2 and rod-like Al3Ti. The α-Al2O3 crystallites, resulting from the reaction between A1 and TiO2 or B2O3, are segregated at the grain boundaries due to a lower wettability with the matrix. SEM micrographs show that rod-like Al3Ti phase distributes uniformly in the matrix. When the BEO3/TiO2 mole ratio is around 1, the Al3Ti phase almost disappears in the composites, and the distribution of α-Al2O3 particulates is improved evidently. 相似文献
67.
Jiang Minhong Gu Zhengfei Cheng Gang 《中国稀土学报(英文版)》2005,23(6):723-723
Polymer matrix RE-Fe giant magnetostrictire composite (GMPC) was prepared using bonding and magnetic field forming technique, and magnetostriction of samples was measured for different compressive stress. The experimental results show thai there is certain compressive effect in GMPC. And the influence of compressive stress on magnetostriction of sample was investigated. It offers essential reference for application and device design of GMPC. 相似文献
68.
69.
大坝洪水漫顶风险评估 总被引:2,自引:1,他引:1
洪水漫顶是导致大坝溃坝的主要原因之一,大坝洪水漫顶风险评估是大坝风险评估的重要组成部分。为此,简要介绍了大坝洪水漫顶的风险模型,并通过实例详细地讨论了模型中各有关参数的不确定性处理方法,探讨了入库洪水的不确定性对洪水漫顶风险率的影响以及按规范设计的大坝的防洪能力问题。 相似文献
70.
In this paper, we present a general method to calculate the inverse and direct dynamic models of parallel robots. The models
are expressed in a closed form by a single equation in which all the elements needed are expressed. The solution is given
in terms of the dynamic models of the legs, the dynamics of the platform and some Jacobian matrices. The proposed method is
applied in this paper on two parallel robots with different structures.
Categories (2), (3). 相似文献