全文获取类型
收费全文 | 6357篇 |
免费 | 398篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 63篇 |
化学工业 | 2116篇 |
金属工艺 | 156篇 |
机械仪表 | 111篇 |
建筑科学 | 166篇 |
矿业工程 | 16篇 |
能源动力 | 166篇 |
轻工业 | 1074篇 |
水利工程 | 24篇 |
石油天然气 | 15篇 |
无线电 | 163篇 |
一般工业技术 | 932篇 |
冶金工业 | 1130篇 |
原子能技术 | 28篇 |
自动化技术 | 599篇 |
出版年
2023年 | 52篇 |
2022年 | 306篇 |
2021年 | 544篇 |
2020年 | 175篇 |
2019年 | 150篇 |
2018年 | 231篇 |
2017年 | 227篇 |
2016年 | 250篇 |
2015年 | 191篇 |
2014年 | 253篇 |
2013年 | 411篇 |
2012年 | 308篇 |
2011年 | 380篇 |
2010年 | 251篇 |
2009年 | 240篇 |
2008年 | 210篇 |
2007年 | 219篇 |
2006年 | 148篇 |
2005年 | 121篇 |
2004年 | 118篇 |
2003年 | 93篇 |
2002年 | 75篇 |
2001年 | 50篇 |
2000年 | 43篇 |
1999年 | 31篇 |
1998年 | 202篇 |
1997年 | 220篇 |
1996年 | 153篇 |
1995年 | 109篇 |
1994年 | 51篇 |
1993年 | 76篇 |
1992年 | 26篇 |
1991年 | 16篇 |
1990年 | 23篇 |
1989年 | 23篇 |
1988年 | 18篇 |
1987年 | 15篇 |
1986年 | 15篇 |
1985年 | 22篇 |
1984年 | 33篇 |
1983年 | 25篇 |
1982年 | 43篇 |
1981年 | 49篇 |
1980年 | 57篇 |
1979年 | 29篇 |
1978年 | 37篇 |
1977年 | 112篇 |
1976年 | 240篇 |
1975年 | 14篇 |
1973年 | 16篇 |
排序方式: 共有6759条查询结果,搜索用时 31 毫秒
31.
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
32.
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
33.
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
34.
Sea trout eggs were salted in NaCl solution after 4 and 14 days of cold storage. The study indicated that the egg resistance to crushing decreased during cold storage from the initial 220 g to 180 g after 14 days. Changes in hardness of the egg membrane accelerated salt diffusion by about 30% to 80% during immersion in NaCl solution. Salting the eggs to 2.3% and 4.0% NaCl content decreased the hardness during cold storage, the decrease being larger in the roe manufactured from a lower quality raw material. In the eggs containing 5.3% and 7.0% NaCl the resistance to crushing increased during storage at 4°C to the extent similar in both egg freshness states obtained prior to salting. The salt content in sea trout eggs ranging from 23% to 7.0% only slightly activated hydrolysis and oxidation of lipid components at 4°C. Lipid oxidation was more rapid in eggs salted after 14 than in those salted after 4 days of storage in ice. Carotenoids of the salted eggs showed a decrease in undesirable cis-bonds during cold storage. Salting the sea trout eggs after 14 days of storage at 2°C shortened the storage time of the final product at 4°C by at least 1 month as compared to the salted roe kept in ice for 4 days before salting. 相似文献
35.
Tomas Herraiz Guillermo Reglero Pedro J Martin-Alvarez Marta Herraiz Maria D Cabezudo 《Journal of the science of food and agriculture》1991,55(1):103-116
Aroma components of ine resulting from fermentation of grape must from the Verdejo cultivar ere isolated by continuous liquid-liquid extraction and further fractionation on a silica gel column. One hundred and thirty-to substances, including alcohols, esters, carbonyl compounds, terpenes, acids and sulphur compounds, ere identified by using GC-MS; some had not been previously detected in ines. Data are given hich could lead to the characterisation of the Verdejo cultivar and the effect of the elaboration of young ines. The sensory contribution of some volatile compounds to the flavour of Verdejo ine is also studied. 相似文献
36.
The paper presents a model for the collaboration among independent freight forwarding entities. In the modern highly competitive transportation branch freight forwarders reduce their fulfillment costs by exploiting different execution modes (self-fulfillment and subcontraction). For self-fulfillment they use their own vehicles to execute the requests and for subcontracting they forward the orders to external freight carriers. Further enhancement of competitiveness can be achieved if the freight forwarders cooperate in coalitions in order to balance their request portfolios. Participation in such a coalition gains additional profit for the entire coalition and for each participant, therefore reinforcing the market position of the partners. The integrated operational transport problem as well as existing collaboration approaches are introduced. The presented model for collaboration is based on theoretical foundations in the field of combinatorial auctions and operational research game theory. It is applicable for coalitions of freight forwarders, especially for the collaboration of Profit Centres within large freight forwarding companies. The proposed theoretical approach and the presented collaboration model are suitable for a coalition of freight forwarding companies with nearly similar potential on the market. 相似文献
37.
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
38.
Morphology of carbon black (CB)‐filled rubber was studied with AFM and SEM and the classification of filler agglomerates, based on their internal structure and filler–matrix interactions, has been proposed. It varies according to the activity of CB and the kind of rubber. It has been shown that fracture of rubber starts either inside filler agglomerates (de‐cohesion) or in a filler–matrix interphase (de‐adhesion) initiating wear of the material. Microscopic observations correlate well with TGA and EPR data of wear debris collected during friction of rubber. The increase of thermal stability of CB and the appearance of additional spin signals, respectively, for elongated samples or debris, are proposed to be associated with de‐cohesion or de‐adhesion of the agglomerates. New approach to the fracture of rubber called “fatal agglomerate concept” is presented. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
39.
Linear oligosiloxanes functionalized with bulky side chain tris(trimethylsilyl)hexyl (TTSH) substituents were transformed into cross-linked materials by UV 193 nm excimer pulsed laser ablation. The process occurred without any catalyst, by reactions of radicals formed in UV laser induced photolysis of side tris(trimethylsilyl)hexyl groups. Chemical changes were monitored by FTIR, LC/UV, GC/MS and solubility tests. 相似文献
40.
Norman Fenton Martin Neil William Marsh Peter Hearty Łukasz Radliński Paul Krause 《Empirical Software Engineering》2008,13(5):499-537
Standard practice in building models in software engineering normally involves three steps: collecting domain knowledge (previous
results, expert knowledge); building a skeleton of the model based on step 1 including as yet unknown parameters; estimating
the model parameters using historical data. Our experience shows that it is extremely difficult to obtain reliable data of
the required granularity, or of the required volume with which we could later generalize our conclusions. Therefore, in searching
for a method for building a model we cannot consider methods requiring large volumes of data. This paper discusses an experiment
to develop a causal model (Bayesian net) for predicting the number of residual defects that are likely to be found during
independent testing or operational usage. The approach supports (1) and (2), does not require (3), yet still makes accurate
defect predictions (an R
2 of 0.93 between predicted and actual defects). Since our method does not require detailed domain knowledge it can be applied
very early in the process life cycle. The model incorporates a set of quantitative and qualitative factors describing a project
and its development process, which are inputs to the model. The model variables, as well as the relationships between them,
were identified as part of a major collaborative project. A dataset, elicited from 31 completed software projects in the consumer
electronics industry, was gathered using a questionnaire distributed to managers of recent projects. We used this dataset
to validate the model by analyzing several popular evaluation measures (R
2, measures based on the relative error and Pred). The validation results also confirm the need for using the qualitative factors
in the model. The dataset may be of interest to other researchers evaluating models with similar aims. Based on some typical
scenarios we demonstrate how the model can be used for better decision support in operational environments. We also performed
sensitivity analysis in which we identified the most influential variables on the number of residual defects. This showed
that the project size, scale of distributed communication and the project complexity cause the most of variation in number
of defects in our model. We make both the dataset and causal model available for research use. 相似文献