全文获取类型
收费全文 | 23044篇 |
免费 | 1052篇 |
国内免费 | 86篇 |
专业分类
电工技术 | 132篇 |
综合类 | 64篇 |
化学工业 | 3548篇 |
金属工艺 | 338篇 |
机械仪表 | 376篇 |
建筑科学 | 560篇 |
矿业工程 | 53篇 |
能源动力 | 288篇 |
轻工业 | 3517篇 |
水利工程 | 232篇 |
石油天然气 | 117篇 |
武器工业 | 8篇 |
无线电 | 851篇 |
一般工业技术 | 2964篇 |
冶金工业 | 8623篇 |
原子能技术 | 72篇 |
自动化技术 | 2439篇 |
出版年
2024年 | 49篇 |
2023年 | 153篇 |
2022年 | 174篇 |
2021年 | 424篇 |
2020年 | 408篇 |
2019年 | 440篇 |
2018年 | 807篇 |
2017年 | 761篇 |
2016年 | 762篇 |
2015年 | 616篇 |
2014年 | 760篇 |
2013年 | 1461篇 |
2012年 | 1173篇 |
2011年 | 995篇 |
2010年 | 849篇 |
2009年 | 777篇 |
2008年 | 794篇 |
2007年 | 754篇 |
2006年 | 497篇 |
2005年 | 393篇 |
2004年 | 399篇 |
2003年 | 351篇 |
2002年 | 314篇 |
2001年 | 223篇 |
2000年 | 201篇 |
1999年 | 405篇 |
1998年 | 2836篇 |
1997年 | 1677篇 |
1996年 | 1054篇 |
1995年 | 564篇 |
1994年 | 469篇 |
1993年 | 543篇 |
1992年 | 128篇 |
1991年 | 133篇 |
1990年 | 137篇 |
1989年 | 129篇 |
1988年 | 131篇 |
1987年 | 123篇 |
1986年 | 112篇 |
1985年 | 139篇 |
1984年 | 47篇 |
1983年 | 44篇 |
1982年 | 71篇 |
1981年 | 89篇 |
1980年 | 80篇 |
1979年 | 28篇 |
1978年 | 32篇 |
1977年 | 181篇 |
1976年 | 387篇 |
1975年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
51.
Edna R Meza‐Escalante Anne‐Claire Texier Flor Cuervo‐López Jorge Gómez Francisco J Cervantes 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):372-377
BACKGROUND: Many industrial discharges, such as those generated from petrochemical refineries, contain large amounts of sulfurous, nitrogenous and organic contaminants. Denitrification has emerged as a suitable technology for the simultaneous removal of these pollutants in a single reactor unit; however, more evidence is demanded to clarify the limitations of denitrification on the simultaneous removal of sulfide and phenolic contaminants and to optimize the biological process. The aim of this study was to evaluate the capacity of a denitrifying sludge to simultaneously convert sulfide and p‐cresol via denitrification. RESULTS: Sulfide was the preferred electron donor over p‐cresol, imposing a 5 h lag phase (required for complete sulfide removal) on organotrophic denitrification. Addition of sulfide (20 mg S2? L?1) to p‐cresol‐amended denitrifying cultures also decreased the reduction rate of nitrate and nitrite, as well as the production rate of nitrogen gas. Nitrite reduction rate was the most affected step by sulfide, decreasing from 35 to 21 mg N (g VSS d)?1. A synergistic inhibitory effect of nitrate and sulfide was also observed on nitrite reduction. Despite the effects of sulfide on the respiratory rates monitored, complete removal of nitrate, sulfide and p‐cresol could be achieved after 48 h of incubation. CONCLUSION: Our results suggest that simultaneous removal of sulfide and p‐cresol could be achieved in denitrifying reactors, but a large hydraulic residence time may be required to sustain an efficient process due to inhibitory effects of sulfide. Copyright © 2008 Society of Chemical Industry 相似文献
52.
53.
In this work, we investigate the linear viscoelastic response of high molecular weight ethylene/1‐hexene copolymers, characterized by a narrow molecular weight distribution and comonomer content in the range from 0 to 10 mol %. A variation in the entanglement plateau modulus has been found in agreement with the recently developed packing length model. The packing model applied to viscoelastic data suggests decreased values of the characteristic ratio, accordingly with recent computer simulation results. The flow activation energy increases as the side chain content increases. This feature is thought to be related to the mobility of the molecules. The presence of side branches due to the comonomer hinders the mobility of the molecules, and increases the thermal barrier for the segmental motion. Then in the comonomer content range studied, the increase of the flow activation energy goes parallel with a decrease in the characteristic ratio. This result suggests that more parameters than only the stiffness of the chain modulate the thermal dependence of viscoelastic properties. A more refined study is necessary combining experiments with computer simulations in order to elucidate these aspects. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
54.
Teresa Mikołajczyk Grażyna Janowska Mariusz Wójcik Maciej Boguń Andrzej Kurzak 《应用聚合物科学杂志》2008,109(4):2513-2521
The rheological properties of spinning solutions of polyacrylonitrile in dimethyl formamide (DMF) containing various amounts of a ferromagnetic nanoaddition were investigated. The porous structure, the strength and thermal properties of fibers obtained from these solutions were assessed, as well as the uniformity of the nanoaddition distribution on the fiber surface was estimated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
55.
The nonisothermal crystallization kinetics of a metallocene-made isotactic polypropylene (m-iPP) and its compounds with 0.1 wt % and 0.3 wt % of a sorbitol derivative [1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS); an α nucleator] were investigated by differential scanning calorimetry at different cooling rates from the melt. The nucleation efficiency was proved by a significant increase in the crystallization temperatures (accompanied by a slight augmentation of the degree of crystallinity and a decrease in the crystal sizes). This increase in the crystallization temperatures led to higher amounts of fractional content in the γ polymorph, even though DMDBS was supposed to be a nucleator for the α form. The Avrami and Ozawa methods effectively described only the early stage of crystallization, whereas a combined Avrami–Ozawa method was valid for the whole crystallization process. The values of the exponent for this method decreased for nucleated samples in the later stage of crystallization, especially in the case of m-iPP with 0.3 wt % DMDBS added (m-iPP03). The activation energy of the process and the surface free energy were also estimated. The production of considerable proportions of the γ polymorph in m-iPP03 corresponded to higher values of the activation energy and lower values of the surface free energy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
56.
Isabel Vega Emiliano Fernández Carmen Mijangos Norma D'Accorso Daniel López 《应用聚合物科学杂志》2008,110(2):695-700
The authors report on the viscoelastic characterization of guar hydrogels obtained through complexation reactions with borax ions. These gels are compared with hydrogels obtained from poly(vinyl alcohol) of different degree of hydrolysis through complexation reactions with congo red. The effect of the degree of hydrolysis and both, the concentration of PVA and the concentration of congo red, on the viscoelastic properties of the hydrogels is analyzed. The potential use of the PVA‐based hydrogels as hydraulic fracturing liquids is discussed in relation to the commonly used fracturing liquid based on the guar–borax system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
57.
S. Thió-Henestrosa J.J. Egozcue V. Pawlowsky-Glahn L.Ó. Kovács G.P. Kovács 《Computers & Geosciences》2008,34(12):1682-1696
A statistical analysis of compositional data based on the Aitchison geometry of the simplex requires an appropriate basis for representing the data. A simple and intuitive way of building such a basis employs a sequential binary partition of the compositional vector. The partition, together with some statistical summaries of the coordinates, or balances, can be represented in a dendrogram-type graph. In this paper we introduce an implementation of this methodology inside CoDaPack, which is freeware. An example with real data illustrates the use of the Balance-Dendrogram routine. 相似文献
58.
Sera from 82 cases of leptospirosis (confirmed by micro-agglutination tests or IFAT) and 108 patients with other diseases were investigated using the microcapsule agglutination test (MCAT) for leptospirosis. The overall sensitivity (90.2%), specificity (96.3%), positive predictive value (94.9%), negative predictive value (92.9%), and accuracy of the MCAT (93.7%) were encouraging. MCAT is simple, can be performed by unskilled personnel with minimum laboratory facilities, and produces results in 3 h. MCAT would be a reliable serodiagnostic test for rapidly screening individuals for leptospirosis, in various geographical areas of Thailand. 相似文献
59.
Perchloric acid (70%) was used to create simulated periapical lesions in tooth sockets of 15 dentate cadaver jaw specimens. Using the Trophy USA direct digital radiographic system, linear images were captured at selected time intervals after initial acid application and altered by contrast reversal, pseudocolor enhancement, and two forms of histogram equalization. The 525 total images were randomized for display on a computer monitor for evaluation by five endodontists. Images were evaluated twice by each rater, with viewings 1 to 2 wk apart. Statistical analysis determined interrater variability, intrarater reproducibility, and the relative merits of each enhancement technique. At 8, 12, 16, and 24 h after acid application, both techniques of histogram equalization yielded a statistically significant improvement over reverse contrast in perception of periapical patholais. Linear and pseudocolor-enhanced images were also significantly more diagnostic than reverse contrast at 12, 16, and 24 h. Intrarater reproducibility showed moderate agreement, but analysis showed only a fair level of interrater agreement. 相似文献
60.
F Tárkányi F Szelecsényi P Kopecky T Molnár L Andó P Mikecz GY Tóth A Rydl 《Canadian Metallurgical Quarterly》1994,45(2):239-249
Proton induced nuclear reactions on enriched 111Cd and 112Cd have been studied up to 30 MeV in the context of routine production of the medically used isotope 111In with low and medium energy cyclotrons. The excitation functions of 111Cd(p,n)111m,gIn and 112Cd(p,2n)111m,gIn as production reactions and 111Cd(p,2n)110mIn, 111Cd(p,2n)110In, 111Cd(p,3n)109ml,m2,In, 112Cd(p,3n)110mIn, 112Cd(p,3n)110gIn as competing processes have been measured using the activation method involving the stacked-foil technique. The deduced thick target yields are compared with those obtained experimentally. 相似文献