全文获取类型
收费全文 | 4628篇 |
免费 | 237篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 64篇 |
综合类 | 2篇 |
化学工业 | 1274篇 |
金属工艺 | 164篇 |
机械仪表 | 90篇 |
建筑科学 | 115篇 |
矿业工程 | 12篇 |
能源动力 | 156篇 |
轻工业 | 580篇 |
水利工程 | 10篇 |
石油天然气 | 12篇 |
无线电 | 130篇 |
一般工业技术 | 725篇 |
冶金工业 | 1082篇 |
原子能技术 | 28篇 |
自动化技术 | 425篇 |
出版年
2023年 | 30篇 |
2022年 | 130篇 |
2021年 | 187篇 |
2020年 | 92篇 |
2019年 | 82篇 |
2018年 | 150篇 |
2017年 | 148篇 |
2016年 | 166篇 |
2015年 | 127篇 |
2014年 | 161篇 |
2013年 | 273篇 |
2012年 | 185篇 |
2011年 | 249篇 |
2010年 | 162篇 |
2009年 | 149篇 |
2008年 | 148篇 |
2007年 | 145篇 |
2006年 | 103篇 |
2005年 | 81篇 |
2004年 | 79篇 |
2003年 | 68篇 |
2002年 | 61篇 |
2001年 | 38篇 |
2000年 | 34篇 |
1999年 | 35篇 |
1998年 | 192篇 |
1997年 | 214篇 |
1996年 | 150篇 |
1995年 | 112篇 |
1994年 | 59篇 |
1993年 | 73篇 |
1992年 | 25篇 |
1991年 | 20篇 |
1990年 | 23篇 |
1989年 | 22篇 |
1988年 | 31篇 |
1987年 | 32篇 |
1986年 | 24篇 |
1985年 | 33篇 |
1984年 | 41篇 |
1983年 | 36篇 |
1982年 | 53篇 |
1981年 | 55篇 |
1980年 | 67篇 |
1979年 | 36篇 |
1978年 | 41篇 |
1977年 | 122篇 |
1976年 | 239篇 |
1975年 | 18篇 |
1973年 | 14篇 |
排序方式: 共有4869条查询结果,搜索用时 15 毫秒
81.
We present an overview of some recent developments in the area of mathematical modeling of maintenance decisions for multi-unit systems. The emphasis is on three main groups of multicomponent maintenance optimization models: the block replacement models, group maintenance models, and opportunistic maintenance models. Moreover, an example of a two-unit system maintenance process is provided in order to compare various maintenance policies. 相似文献
82.
In this paper we consider robust stabilization of the class of nonlinear plants of the form $$\dot x = f(x) + \sum\limits_{i = 1}^m {g_i } (x)u_i (t),$$ which are equivalent, under smooth state space coordinate transformations and nonlinear state feedback, to controllable systems. This approach is very sensitive for unknown parameters' values. Parameter adaptation may be used as a technique to robustify minimum-phase systems [3]. We give an example of a locally stable adaptive tracking system in which the last assumption is weakened. The minimum-phase plant considered in the paper is a current-controlled squirrel cage induction motor. 相似文献
83.
The noncatalytic beta-subunit is responsible for the latency of casein kinase 2 (CK2) activity toward calmodulin. Twenty-one mutants of the beta-subunit bearing either deletions or Ala substitutions for charged residues in the 5-6, 55-70, and 171-178 sequences have been assayed for their ability to substitute for wild-type beta-subunit as a suppressor of activity toward calmodulin. The only mutations that reduced the ability of the beta-subunit to suppress calmodulin phosphorylation activity, though being compatible with normal reconstitution of CK2 holoenzyme, were those affecting Asp55, Glu57 and the whole triplet Glu59-Asp-Glu61. The activity of CK2 holoenzyme, either native or reconstituted, toward calmodulin can be elicited by a variety of polybasic effectors, including polylysine, polyarginine, salmine, and histones H4, H3, and, to a lesser extent, H2a and H2b. Histone H1 and polyamines are conversely ineffective. The latent "calmodulin kinase" activity of CK2 can also be specifically unmasked by a peptide (alpha[66-86]) reproducing a basic insert of the catalytic subunit. This effect is reversed by equimolar addition of a peptide (beta[55-71]) including the 55-64 acidic stretch of the beta-subunit. Comparable polylysine stimulation was observed with the holoenzymes reconstituted with either beta wt or the beta mutants capable of assembling with the alpha-subunit, with the notable exception of those bearing Ala substitutions for acidic residues at positions 55, 57, and 59-61. These were nearly insensitive to 42 nM polylysine, which conversely promotes a more than 10-fold increase of calmodulin phosphorylation with wild-type beta.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
84.
We present an approximate analysis of the nonlinear operation of the hollow-waveguide laser, including gain saturation and longitudinal- as well as transverse-field distribution of the laser mode. The model presented is general and can be applied to the study of an arbitrary configuration of the waveguide laser. The laser characteristics obtained reveal that the optimal position of the output mirror (which provides maximal power efficiency of the laser system with the other parameters constant) depends on the output-power level and the mirror-reflectivity coefficient. Moreover, it has been shown that when an addition device is introduced into the cavity, the power efficiency also depends on which end of the laser the light power is extracted from. 相似文献
85.
Anna Medyńska Danuta Zwolińska Ryszard Grenda Monika Miklaszewska Maria Szczepańska Agnieszka Urzykowska Katarzyna Zachwieja Katarzyna Kiliś‐Pstrusińska 《Hemodialysis international. International Symposium on Home Hemodialysis》2017,21(4):557-565
Introduction: The aim of this study was to analyze the selected psychosocial aspects of chronic kidney disease in children treated with hemodialysis (HD). Methods: The study included 25 children treated with HD aged 2 to 18 years and their parents. Data concerning the illness and socio‐demographic parameters was collected. We used the Paediatric Quality of Life Inventory (PedsQL) for patients and for their parents the PedsQL‐proxy version, General Health Questionnaire (GHQ‐12), Berlin Social Support Scales (BSSS), and the Caregivers Burden Scale (CBS) to evaluate health‐related quality of life (QoL) of HD children and their primary caregivers. Findings: In the PedsQL test, the QoL of HD children was lower than in healthy children. Children treated with HD assessed their QoL on the PedsQL questionnaire higher than the primary caregivers, on all subscales as well as an overall health‐related QoL. Scoring below 2 on the GHQ‐12 test was reported in 56% of mothers, which may indicate that psychological symptoms have intensified. There was no correlation between BSSS, CBS, and GHQ‐12. Discussion: The assessment of QoL in pediatric patients would allow for the earliest possible identification of their nonsomatic problems and irregularities. This could, consequently, contribute to improving QoL in both children with chronic kidney disease and their families. 相似文献
86.
87.
Bioimaging: Shaping Luminescent Properties of Yb3+ and Ho3+ Co‐Doped Upconverting Core–Shell β‐NaYF4 Nanoparticles by Dopant Distribution and Spacing (Small 47/2017)
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
88.
Małgorzata Misiak Michał Skowicki Tomasz Lipiński Agnieszka Kowalczyk Katarzyna Prorok Sebastian Arabasz Artur Bednarkiewicz 《Nano Research》2017,10(10):3333-3345
Versatile optimization of the synthesis method and composition of Yb3+ and Tm3+ co-doped CaF2 nanoparticles as well as a novel biofunctionalization method were developed and evaluated.Through multistep synthesis,the luminescence intensity of the Tm3+ activator was enhanced by more than 10-fold compared to standard one-step synthesis.The proposed methods were used to homogenously distribute the doping ions within the nanoparticle's volume and thus reduce luminescence quenching.Optimization of dopant ions concentration led to the selection of the most efficient visible and near-infrared up-converting nanoparticles,which were CaF2 doped with 10% Yb3+ 0.05% Tm3+ and 20% Yb3+ 0.5% Tm3+,respectively.To illustrate the suitability of the synthesized nanoparticles as bio-labels,a dedicated biofunctionalization method was used,and the nanoparticles were applied for labeling and imaging of Candida albicans cells.This method shows great promise because of extremely low background and high specificity because of the presence of the attached molecules. 相似文献
89.
Sādhanā - This paper presents the results of experimental research of the phenomena occurring in water ram during a single cycle of its operation. Apart from a brief introduction and... 相似文献
90.
The fatigue property of an asphalt mix is an important issue in pavement design. This property is often determined with the aid of a four-point bending (4PB) test in controlled deflection mode. The fatigue property is related to the decrease in the calculated complex stiffness modulus, however, due to the non- homogenous stress and strain field in the beam, the measured response does not represent the stiffness modulus of the material but a weighted stiffness value. For a correct interpretation, a fatigue damage material model like the Asphalt Concrete Pavement-Fatigue model is needed. After integration, the calculated and measured responses are compared. By varying the model parameters, an excellent comparison between the two responses is obtained up to a certain number of cycles. This number of cycles is denoted as the fatigue life N PH . The accumulated dissipated energy at the surface of the beam in the midsection can be expressed as a constant times the fatigue life N PH to the power z and also as a constant times the product of the fatigue life N PH and the initial dissipated energy in the first cycle. Using these two findings, a Wöhler curve was established similar to the one directly based on the strain amplitudes and fatigue life data. 相似文献