全文获取类型
收费全文 | 12307篇 |
免费 | 812篇 |
国内免费 | 460篇 |
专业分类
电工技术 | 501篇 |
综合类 | 1537篇 |
化学工业 | 1484篇 |
金属工艺 | 486篇 |
机械仪表 | 635篇 |
建筑科学 | 1219篇 |
矿业工程 | 365篇 |
能源动力 | 390篇 |
轻工业 | 1174篇 |
水利工程 | 324篇 |
石油天然气 | 253篇 |
武器工业 | 75篇 |
无线电 | 1162篇 |
一般工业技术 | 1300篇 |
冶金工业 | 346篇 |
原子能技术 | 209篇 |
自动化技术 | 2119篇 |
出版年
2024年 | 33篇 |
2023年 | 103篇 |
2022年 | 305篇 |
2021年 | 292篇 |
2020年 | 236篇 |
2019年 | 180篇 |
2018年 | 159篇 |
2017年 | 262篇 |
2016年 | 294篇 |
2015年 | 371篇 |
2014年 | 529篇 |
2013年 | 719篇 |
2012年 | 759篇 |
2011年 | 978篇 |
2010年 | 692篇 |
2009年 | 928篇 |
2008年 | 822篇 |
2007年 | 1008篇 |
2006年 | 743篇 |
2005年 | 661篇 |
2004年 | 551篇 |
2003年 | 534篇 |
2002年 | 387篇 |
2001年 | 344篇 |
2000年 | 276篇 |
1999年 | 248篇 |
1998年 | 162篇 |
1997年 | 172篇 |
1996年 | 126篇 |
1995年 | 118篇 |
1994年 | 101篇 |
1993年 | 89篇 |
1992年 | 88篇 |
1991年 | 60篇 |
1990年 | 44篇 |
1989年 | 53篇 |
1988年 | 31篇 |
1987年 | 28篇 |
1986年 | 20篇 |
1985年 | 11篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1964年 | 2篇 |
1963年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
The physical preconditions are considered for the temperature of a body to influence the force of gravity experienced by it. The results are given of experiments on weighing metal rods heated by ultrasound which confirm a dependence of the weight of the rods on their temperature. 相似文献
43.
楼兴泽 《上海第二工业大学学报》1992,9(1):1-8
本文证明了一族闭曲线C(t),t∈I,称变闭曲线,在光滑性条件下,具有正交参数u,即当C(t)表为(?)=(?)(u,t)时,有(?)·(?)≡0.接着,文中提出了一种“降维法”,即用一族平行平面将空间曲面截成平面变曲线,并讨论其若干整体性质. 相似文献
44.
We present some sufficient and necessary conditions for convergent splitting of a non-Hermitian indefinite matrix. Some sufficient
conditions to determinate a matrix with a (strongly) dominant symmetric part for a class of boundary value problem are also
obtained. These results are applicable to identify the convergence of iterative methods for solving large sparse systems of
linear equations. 相似文献
45.
The primary purpose of this work is to review the literature about what is and is not known about using ethylene vinyl acetate (EVA0 copolymer as the encapsulant (or pottant) material in photovoltaic (PV) modules. Secondary purposes include elucidating the complexity of the encapsulation problem, providing an overview about encapsulation of PV cells and modules, providing a historical overview of the relevant research and development on EVA, summarizing performance losses reported for PV systems deployed since ca. 1981, and summarizing the general problems of polymer stability in a solar environment. We also provide a critical review of aspects of reported work for cases that we believe are important.Failure modes resolved in the early work to establish reliability of deployed modules and the purposes and properties of pottants, are summarized. Typical performance losses in large field-deployed, large-scale systems ranging from 1% to 10% per year are given quantitatively, and qualitative reports of EVA discoloration are summarized with respect to ultraviolet (UV), world-wide location and site dependence.The general stability of polymers and their desirable bulk properties for solar utilization are given. The stabilization formulation for EVA, its effectiveness, and changes in it during degradation are discussed. The degradation mechanisms for the base resin, e.g., unstabilized Elvax 150TM, and stabilized EVA are indicated for literature dating to the early 1950s, and the role played by unsaturated chromophores is indicated. The limited number of studies relating discoloration and PV cell efficiency are summarized.Observed degradation of EVA or the unstabilized base resin in the laboratory and examples used to measure the degradation are summarized in sections entitled: (1) thermally-induced degradation; (2) photodegradation and photothermal degradation of EVA in different temperature regimes; (3) photobleaching and photodegradation of the UV absorber and cross-linking agent; (4) acetic acid and metal and metal-oxide catalyzed oxidative degradation; and (5) discolaration and PV cell efficiency losses.Processing effects/influences on EVA stability are discussed in sections entitled: (1) EVA raw materials and extruded, uncured films; (2) thermal encapsulation processes; (3) effects of lamination, curing, and curing peroxide on gel content and chromophores formed; and (4) incomplete shielding of curing-generated chromophores. A summary is given for the limited number of accelerated lifetime testing efforts and examples of erroneous service lifetime predictions for EVA are discussed. The known factors that effect the discoloration rate of several EVA formulations are discussed in which the reduction in rate by using UV-absorbing superstrates is a prime example. A summary is given of what is and is not known about EVA degradation mechanisms, degradation from exposures in field-deployed modeules and/or laboratory testing, and factors that contribute to EVA stability or degradation. Finally, conclusions about using Elvax 150 in EVA formulations are summarized, and future prospects for developing the next-generation pottant for encapsulating PV modules are discussed. 相似文献
46.
^17O系统的R矩阵分析 总被引:2,自引:1,他引:1
采用多道多能级R矩阵理论,全面系统地分析~(17)O系统中10.5 MeV激发能以下有关~(16)O(n,n)~(16)O·~(16)O(n,a)~(13)C和~(13)C(a,a)~(13)C的全部实验数据。有关~(16)O的中子反应截面计算值被收入中国评价数据库CENDL-2和美国的评价数据库ENDF/B-6。对在R矩阵分析中如何确定本底、道半径和边界条件等问题予以讨论。 相似文献
47.
Giuseppe G. G. Manzardo Sandra Kürsteiner-Laube und Daniel Perrin 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1996,203(6):501-506
In diethyl ether extracts from celeriac (Apium graveolens L. var.rapaceum) all four stereoisomers of (3a–7a)-cis-3-butylhexahydrophthalide were found to be present. The analyses were carried out by means of GC, enantioselective GC and GC-MS. The assignment of the relative configuration of the diastereomers3 and4 was accomplished by NOE difference spectroscopy. 相似文献
48.
Phase separation during polymerization was studied in a model system consisting of a diepoxide based on diglycidyl ether of bisphenol A (DGEBA), variable amounts of ethylenediamine (EDA) and the mass of castor oil (CO) necessary to obtain a mass fraction equal to 0-15 in a final system where the stoichiometric ratio of amine to epoxy equivalents, r, was equal to 1. A two-step polymerization process was performed by curing first a system with r = 0-5, during variable times before phase separation, and then carrying the system to r = 1. Thermodynamic analysis of samples with different r values led to a linear relationship between the Flory-Huggins interaction parameter and r. The concentration (P) and average size (D?) of dispersed-phase particles followed opposite trends, i.e. P increased while D? decreased, when either r was increased or the time of curing in the first step of a two-step process was decreased. This was explained by assuming that the competition between nucleation and growth was determined by the viscosity at the cloud point, ηcp. Low values of ηcp favoured growth over nucleation and led to fewer but larger particles. 相似文献
49.
A study on the prediction of heat transfer coefficient (HTC) and pressure drop of refrigerant mixtures is reported. HTCs and pressure drops of prospective mixtures to replace R12 and R22 are predicted on the same cooling capacity basis. Results indicate that nucleate boiling is suppressed at qualities greater than 20.0% for all mixtures and evaporation becomes the main heat transfer mechanism. For the same capacity, some mixtures containing R32 and R152a show 8.0–10.0% increase in HTCs. Some mixtures with large volatility difference exhibit as much as 55.0% reduction compared with R12 and R22, caused by mass transfer resistance and property degradation due to mixing (32.0%) and reduced mass flow rates (23.0%). Other mixtures with moderate volatility difference exhibit 20.0–30.0% degradation due mainly to reduced mass flow rates. The overall impact of heat transfer degradation, however, is insignificant if major heat transfer resistance exists in the heat transfer fluid side (air system). If the resistance in the heat transfer fluid side is of the same order of magnitude as that on the refrigerant side (water system), considerable reduction in overall HTC of up to 20% is expected. A study of the effect of uncertainties in transport properties on heat transfer shows that transport properties of liquid affect heat transfer more than other properties. Uncertainty of 10.0% in transport properties causes a change of less than 6% in heat transfer prediction. 相似文献
50.
Transport properties of 1,1-difluoroethane (R152a) 总被引:2,自引:0,他引:2
R. Krauss V. C. Weiss T. A. Edison J. V. Sengers K. Stephan 《International Journal of Thermophysics》1996,17(4):731-757
Based on reliable. carefully selected data sets. equations for the thermal conductivity and the viscosity of the refrigerant R 112a are presented. They are valid at temperatures from 240 to 440 K, pressures up to 20 MPa. and densities up to 1050 kg · m–3. including the critical region. 相似文献