全文获取类型
收费全文 | 5980篇 |
免费 | 280篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 89篇 |
综合类 | 4篇 |
化学工业 | 1761篇 |
金属工艺 | 204篇 |
机械仪表 | 136篇 |
建筑科学 | 165篇 |
矿业工程 | 22篇 |
能源动力 | 218篇 |
轻工业 | 628篇 |
水利工程 | 13篇 |
石油天然气 | 11篇 |
武器工业 | 3篇 |
无线电 | 243篇 |
一般工业技术 | 888篇 |
冶金工业 | 1117篇 |
原子能技术 | 27篇 |
自动化技术 | 741篇 |
出版年
2023年 | 26篇 |
2022年 | 135篇 |
2021年 | 262篇 |
2020年 | 111篇 |
2019年 | 100篇 |
2018年 | 188篇 |
2017年 | 181篇 |
2016年 | 223篇 |
2015年 | 160篇 |
2014年 | 209篇 |
2013年 | 376篇 |
2012年 | 258篇 |
2011年 | 319篇 |
2010年 | 252篇 |
2009年 | 205篇 |
2008年 | 213篇 |
2007年 | 203篇 |
2006年 | 138篇 |
2005年 | 131篇 |
2004年 | 120篇 |
2003年 | 109篇 |
2002年 | 96篇 |
2001年 | 71篇 |
2000年 | 51篇 |
1999年 | 58篇 |
1998年 | 206篇 |
1997年 | 233篇 |
1996年 | 173篇 |
1995年 | 124篇 |
1994年 | 80篇 |
1993年 | 90篇 |
1992年 | 31篇 |
1991年 | 32篇 |
1990年 | 41篇 |
1989年 | 28篇 |
1988年 | 42篇 |
1987年 | 46篇 |
1986年 | 30篇 |
1985年 | 45篇 |
1984年 | 58篇 |
1983年 | 50篇 |
1982年 | 65篇 |
1981年 | 74篇 |
1980年 | 73篇 |
1979年 | 43篇 |
1978年 | 46篇 |
1977年 | 130篇 |
1976年 | 240篇 |
1975年 | 23篇 |
1973年 | 15篇 |
排序方式: 共有6270条查询结果,搜索用时 15 毫秒
31.
The development of biaxial segmental orientation and stress in a flexible-chain polymer fluid subjected to steady biaxial extensional flow is analyzed. Closed-formula model based on the Padè approximation of the inverse Langevin function in the non-Gaussian distribution of the chain end-to-end vectors is considered. The approach is free from the limitations related to finite chain extensibility and slow convergence of the series expansion formulations at higher chain deformations.Segmental orientation is characterized by the average orientation tensor, related axial orientation factors and global orientation anisotropy. Orientational behavior and corresponding stresses in the biaxial elongational potential flow are discussed in a wide range of elongation rates. Orientation characteristics calculated for the biaxial flow deformation are much higher than those predicted for the affine biaxial stretch deformation in polymer solids. 相似文献
32.
The effect of methanol, acetone, formalin and glucose on the nitrification process in the packed bed reactors has been investigated. For the utilized compounds the inhibition constant Ki was determined according to Dixon's method. The determined values were as follows: methanol Ki = 116.0 mg l?1; acetone Ki = 804.2 mg l?1; formalin Ki = 61.5 mg l?1. The value of Ki for glucose has not been determined because glucose in applied concentration up to 11,325 mg l?1 had no effect on the nitrification course. 相似文献
33.
Maciej W. Rogoziski 《Systems & Control Letters》1989,12(5):449-453
An optimal predictor is developed for a singular random process generated by a known system driven by a white noise sequence. The properties of the predictor are compared with those of the optimal predictor for a nonsingular random process. 相似文献
34.
Studies on the influence of anthracene coal extracts on the carbonization process of medium- and high-rank coals were undertaken. Extracts from flame coal (Int. Class. 900) and gas-coking coal (Int. Class. 632) were used as additives. The blends prepared from the examined coals and the extracts exhibited better coking properties than the parent coals. The addition of extract to the coals gave an increase in the microstrength of the resultant cokes. The effects of co-carbonization of coking coals with extracts were increases in the size of the optical texture as well as in the degree of structural ordering of cokes. In the co-carbonization of semicoking coal with addition of coal extracts, a reduction in the size of the anisotropic units and a decrease in the crystallite height of cokes were observed. No modification of the basic anisotropy of coke from anthracite by coal extract was observed. With increasing extract content in anthracite/extract blends there was an increase in the degree of structural ordering of co-carbonization products. Extract addition was unable to modify the behaviour of fusinite. Based on the results of investigation of the influence of coal extracts on the carbonization of different-rank coals, a division of coals according to the modification of the optical texture of coke is given. 相似文献
35.
The article presents a review of most important research results as well as opinions about the role and importance of body image disturbances in the development and the course of eating disorders. It also contains a review of definitions of body image, and techniques used in the evaluation of this type of disorders. 相似文献
36.
A Gregor E Kostrzewska S Tarczyńska-Nosal H Stachurska 《Canadian Metallurgical Quarterly》1994,49(12-13):284-286
Fluorescence spectra of plasma porphyrin were measured in 6 patients with the acute intermittent porphyria (AIP), 30 patients with variegate porphyria (PV), 2 patients with hereditary coproporphyria, 2 patients with porphyria cutanea tarda, and in 6 patients with erythropoietic protoporphyria (EPP). It was found that the excitation and emission wavelengths at which maximum fluorescence is seen may help to diagnose and differentiate PV and EPP. In patients with AIP spectrum characteristic for porphyria of such a type was noted in all patients during the attack of disease and in only 33% of patients in remission. Fluorescence spectrum was normal in asymptomatic family members. In variegate porphyria spectrum with a characteristic maximum of fluorescence was noted in all patients during an attack and remission, and 62% of the asymptomatic family members. 相似文献
37.
38.
Radio-protective effectiveness of short-term (19 and 4 h before, 4 and 24 h after irradiation), long-term (3 times/week during 30 days after irradiation) and delayed (1 or 2 days after irradiation) enrichment with crystallized beta-carotene, in single doses of 0.1, 1.0 or 5.0 mg was evaluated in experimental acute external gamma-irradiation (0.029 Gy/sec) within the range of absorbed doses 9--6 Gy. The results obtained have permitted the authors to recommend the ration enriched with carotinoid for prevention and therapy of acute radiation injuries. 相似文献
39.
Andrzej Malag Jacek Ratajczak Jerzy Gazecki 《Materials Science and Engineering: B》1993,20(3):332-338
Selective wet chemical etching of the AlxGa1−xAs/GaAs system has been applied to heterostructure characterization. Samples of LPE grown AlGaAs/GaAs laser double-heterostructures and separate confinement heterostructures as well as antiresonant reflecting optical waveguides heterostructures were treated with “I2 solution” (I2:KI:H2O) and hydrochloric acid. These compounds selectively etch the ternary AlxGa1−xAs layers, but with different “threshold composition” xth values (the x value is that above which the etching rate of a given compound increases sharply). Selectively etched samples have been examined by SEM. The experimental dependence of etching rate on the x value for I2 solution has been derived. From this dependence, the x composition of any ternary layer can be estimated simply. Observations were made of the “microscopic” properties of the heterostructure, such as the smoothness of the interfaces and the uniformity of layers. All imperfections resulting from the growth process, such as interface perturbations or compositional nonuniformity of layers, are clearly seen. An additional advantage of this etching technique is its simplicity. It allows quick examination of grown heterostructure for the selection of wafers for further processing. 相似文献
40.
The scope of the paper is the assessment of the technical risk involved in long-term operation of power units. Detailed analyses have been conducted for steam turbine components. The sources and consequences of risk have been identified and the probability of turbine components failure calculated. The quantitative assessment of the risk has been made and possibilities of its reduction discussed. 相似文献