全文获取类型
收费全文 | 3557篇 |
免费 | 25篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 24篇 |
综合类 | 12篇 |
化学工业 | 109篇 |
金属工艺 | 30篇 |
机械仪表 | 17篇 |
建筑科学 | 21篇 |
矿业工程 | 1篇 |
能源动力 | 40篇 |
轻工业 | 118篇 |
水利工程 | 4篇 |
石油天然气 | 10篇 |
无线电 | 30篇 |
一般工业技术 | 82篇 |
冶金工业 | 3033篇 |
原子能技术 | 5篇 |
自动化技术 | 59篇 |
出版年
2023年 | 3篇 |
2022年 | 14篇 |
2021年 | 16篇 |
2020年 | 8篇 |
2019年 | 8篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 10篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 64篇 |
2012年 | 54篇 |
2011年 | 35篇 |
2010年 | 43篇 |
2009年 | 39篇 |
2008年 | 24篇 |
2007年 | 26篇 |
2006年 | 11篇 |
2005年 | 15篇 |
2004年 | 8篇 |
2003年 | 20篇 |
2002年 | 7篇 |
2001年 | 7篇 |
2000年 | 15篇 |
1999年 | 104篇 |
1998年 | 946篇 |
1997年 | 584篇 |
1996年 | 359篇 |
1995年 | 176篇 |
1994年 | 147篇 |
1993年 | 213篇 |
1992年 | 27篇 |
1991年 | 15篇 |
1990年 | 27篇 |
1989年 | 19篇 |
1988年 | 23篇 |
1987年 | 20篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 22篇 |
1980年 | 27篇 |
1979年 | 2篇 |
1978年 | 11篇 |
1977年 | 96篇 |
1976年 | 212篇 |
1975年 | 7篇 |
1973年 | 2篇 |
1955年 | 4篇 |
排序方式: 共有3595条查询结果,搜索用时 11 毫秒
91.
Mónica B. Betancor Ma. José Caballero Genciana Terova Samuela Corà Reda Saleh Tibiábin Benítez-Santana J. Gordon Bell Carmen María Hernández-Cruz Marisol Izquierdo 《Lipids》2012,47(12):1193-1207
Docosahexaenoic acid (DHA) is an essential fatty acid necessary for many biochemical, cellular and physiological functions in fish. However, high dietary levels of DHA increase free radical injury in sea bass (Dicentrarchus labrax) larvae muscle, even when vitamin E (α-tocopherol, α-TOH) is increased. Therefore, the inclusion of other nutrients with complementary antioxidant functions, such as vitamin C (ascorbic acid, vitC), could further contribute to prevent these lesions. The objective of the present study was to determine the effect of vitC inclusion (3,600?mg/kg) in high DHA (5?% DW) and α-TOH (3,000?mg/kg) microdiets (diets 5/3,000 and 5/3,000?+?vitC) in comparison to a control diet (1?% DHA DW and 1,500?mg/kg of α-TOH; diet 1/1,500) on sea bass larvae growth, survival, whole body biochemical composition and thiobarbituric acid reactive substances (TBARS) content, muscle morphology, skeletal deformities and antioxidant enzymes, insulin-like growth factors (IGFs) and myosin expression (MyHC). Larvae fed diet 1/1,500 showed the best performance in terms of total length, incidence of muscular lesions and ossification degree. IGFs gene expression was elevated in 5/3,000 diet larvae, suggesting an increased muscle mitogenesis that was confirmed by the increase in the mRNA copies of MyHC. vitC effectively controlled oxidative damages in muscle, increased α-TOH larval contents and reduced TBARS content and the occurrence of skull deformities. The results of the present study showed the antioxidant synergism between vitamins E and C when high contents of DHA are included in sea bass larvae diets. 相似文献
92.
Dimensional variation in assembly processes is one of the most important issues that affect quality. Although robust design and statistical process quality control help to reduce this problem, they cannot be used for instant variation reduction during assembly operations, especially during process ramp-up. This paper introduces a complete methodology for dimensional-related error compensation in compliant sheet metal assembly processes. The proposed methodology is divided into two steps: (1) an off-line error control-learning module using virtual assembly models to determine necessary adjustments; and (2) an in-line control implementation using a feed-forward control strategy based on the learned adjustments. The off-line learning step focuses on determining control actions or corrections to compensate for the negative effects incoming part errors have on Key Product Characteristics. Specifically, it utilizes a newly developed iterative sampling method based on Kriging fitting to efficiently determine optimal control actions. The in-line feed-forward control identifies appropriate part-by-part adjustments using these learned control actions and incoming assembly component measurements. In this paper, two case studies are presented. First, a mathematical case study presents an empirical proof for the feasibility of the Iterative Sampling and Fitting Algorithm. Second, a simulation-based case study illustrates the effectiveness of the proposed methodology to improve dimensional quality in assembly operations for compliant sheet metal parts. 相似文献
93.
Selecting the most appropriate heuristic for solving a specific problem is not easy, for many reasons. This article focuses on one of these reasons: traditionally, the solution search process has operated in a given manner regardless of the specific problem being solved, and the process has been the same regardless of the size, complexity and domain of the problem. To cope with this situation, search processes should mould the search into areas of the search space that are meaningful for the problem. This article builds on previous work in the development of a multi-agent paradigm using techniques derived from knowledge discovery (data-mining techniques) on databases of so-far visited solutions. The aim is to improve the search mechanisms, increase computational efficiency and use rules to enrich the formulation of optimization problems, while reducing the search space and catering to realistic problems. 相似文献
94.
95.
96.
Progress towards a methodology for high throughput 3D reconstruction of soot nanoparticles via electron tomography
下载免费PDF全文
![点击此处可从《Journal of microscopy》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The aim of this work is to make progress towards the development of 3D reconstruction as a legitimate alternative to traditional 2D characterization of soot. Time constraints are the greatest opposition to its implementation, as currently reconstruction of a single soot particle takes around 5–6 h to complete. As such, the accuracy and detail gains are currently insufficient to challenge 2D characterization of a representative sample (e.g. 200 particles). This work is a consideration of the optimization of the steps included within the computational reconstruction and manual segmentation of soot particles. Our optimal process reduced the time required by over 70% in comparison to a typical procedure, whilst producing models with no appreciable decrease in quality. 相似文献
97.
Monica Cavia‐Saiz Maria D Busto Maria Concepción Pilar‐Izquierdo Natividad Ortega Manuel Perez‐Mateos Pilar Muñiz 《Journal of the science of food and agriculture》2010,90(7):1238-1244
BACKGROUND: This study was designed to evaluate and compare antioxidant capacity and radical scavenging activity of naringin and its aglycone by different in vitro assays. The effects of flavanones on lipid peroxidation, glutathione (GSH) oxidation and DNA cleavage were also assessed. RESULTS: The results showed that naringenin exhibited higher antioxidant capacity and hydroxyl and superoxide radical scavenger efficiency than naringin. Our results evidenced that glycosylation attenuated the efficiency in inhibiting the enzyme xanthine oxidase and the aglycone could act like a more active chelator of metallic ions than the glycoside. Additionally, naringenin showed a greater effectiveness in the protection against oxidative damage to lipids in a dose‐dependent manner. Both flavanones were equally effective in reducing DNA damage. However, they show no protective effect on oxidation of GSH. CONCLUSION: The data obtained support the importance of characterizing the ratio naringin/naringenin in foods when they are evaluated for their health benefits. Copyright © 2010 Society of Chemical Industry 相似文献
98.
Dolors Izquierdo Montserrat Roura Míriam Prez-Trujillo Sandra Soto-Heras María-Teresa Paramio 《International journal of molecular sciences》2022,23(8)
In goats, embryo oocyte competence is affected by follicle size regardless the age of the females. In previous studies we have found differences in blastocyst development between oocytes coming of small (<3 mm) and large follicles (>3 mm) in prepubertal (1–2 months-old) goats. Oocyte competence and Follicular Fluid (FF) composition changes throughout follicle growth. The aim of this study was to analyze Fatty Acids (FAs) composition and metabolomic profiles of FF recovered from small and large follicles of prepubertal goats and follicles of adult goats. FAs were analyzed by chromatography and metabolites by 1H-Nuclear Magnetic Resonance (1H-NMR) Spectrometry. The results showed important differences between adult and prepubertal follicles: (a) the presence of α,β-glucose in adult and no detection in prepubertal; (b) lactate, -N-(CH3)3 groups and inositol were higher in prepubertal (c) the percentage of Linolenic Acid, Total Saturated Fatty Acids and n-3 PUFAs were higher in adults; and (d) the percentage of Linoleic Acid, total MUFAs, PUFAs, n-6 PUFAs and n-6 PUFAs: n-3 PUFAs ratio were higher in prepubertal goats. Not significant differences were found in follicle size of prepubertal goats, despite the differences in oocyte competence for in vitro embryo production. 相似文献
99.
An upper limit for hydrogen storage at 77 K on activated carbons was clearly observed in the present experimental work. Such a limit is around 6.4 wt.%, i.e., close to the theoretical limit of 6.8 wt.%. Results of hydrogen storage were obtained in three independent laboratories using volumetric and gravimetric devices. Lab-made activated carbons (ACs) were found to have higher capacities than those of the commercial material AX-21. A maximum excess hydrogen storage capacity of 6.0 wt.% at 77 K and 4 MPa was obtained. This maximum was reduced to 0.6 wt.% at 298 K and 5 MPa. ACs with surface areas (SBET) as high as 3220 m2 g−1 were prepared from chemical activation of anthracites with alkali (Na and K) hydroxides. At 77 K and 4 MPa, excess hydrogen storage capacity was directly correlated with SBET for ACs having SBET values lower than 2630 m2/g. Hydrogen uptake at 77 K also correlated with micropore volume and strongly depended on average pore diameter. 相似文献
100.
M. DE LA SEN 《International journal of control》2013,86(6):1769-1775
In this note, it is proved that stability of composite systems including parallel subsystems can be achieved for certain sets of initial conditions and additional stability assumptions for the non-hyperstable subsystems. It is required that at least one subsystem be asymptotically hyperstable. 相似文献