全文获取类型
收费全文 | 114600篇 |
免费 | 3403篇 |
国内免费 | 438篇 |
专业分类
电工技术 | 1000篇 |
综合类 | 2332篇 |
化学工业 | 18183篇 |
金属工艺 | 5260篇 |
机械仪表 | 3656篇 |
建筑科学 | 3162篇 |
矿业工程 | 615篇 |
能源动力 | 1916篇 |
轻工业 | 9505篇 |
水利工程 | 1587篇 |
石油天然气 | 506篇 |
武器工业 | 1篇 |
无线电 | 10596篇 |
一般工业技术 | 21567篇 |
冶金工业 | 8794篇 |
原子能技术 | 352篇 |
自动化技术 | 29409篇 |
出版年
2024年 | 79篇 |
2023年 | 344篇 |
2022年 | 483篇 |
2021年 | 954篇 |
2020年 | 816篇 |
2019年 | 864篇 |
2018年 | 15477篇 |
2017年 | 14402篇 |
2016年 | 11154篇 |
2015年 | 1711篇 |
2014年 | 1580篇 |
2013年 | 2888篇 |
2012年 | 5206篇 |
2011年 | 11240篇 |
2010年 | 9788篇 |
2009年 | 6937篇 |
2008年 | 8157篇 |
2007年 | 8995篇 |
2006年 | 1079篇 |
2005年 | 2020篇 |
2004年 | 1859篇 |
2003年 | 1847篇 |
2002年 | 1125篇 |
2001年 | 542篇 |
2000年 | 533篇 |
1999年 | 461篇 |
1998年 | 2104篇 |
1997年 | 1319篇 |
1996年 | 868篇 |
1995年 | 486篇 |
1994年 | 380篇 |
1993年 | 379篇 |
1992年 | 151篇 |
1991年 | 120篇 |
1990年 | 90篇 |
1989年 | 75篇 |
1988年 | 108篇 |
1987年 | 112篇 |
1986年 | 88篇 |
1985年 | 105篇 |
1984年 | 78篇 |
1982年 | 53篇 |
1981年 | 83篇 |
1980年 | 66篇 |
1977年 | 111篇 |
1976年 | 220篇 |
1968年 | 49篇 |
1966年 | 51篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
D.R. Santos‐Peñate C.M. Campos‐Rodríguez J.A. Moreno‐Pérez 《International Transactions in Operational Research》2019,26(1):340-363
The ‐centroid problem or leader–follower problem is generalized considering different customer choice rules where a customer may use facilities belonging to different firms, if the difference in travel distance (or time) is small enough. Assuming essential goods, some particular customer choice rules are analyzed. Linear programming formulations for the generalized ‐medianoid and ‐centroid problems are presented and an exact solution approach is applied. Some computational examples are included. 相似文献
32.
Lorena Rodríguez-López Myriam Rincón-Fontán Xanel Vecino Ana B. Moldes Jose M. Cruz 《Journal of surfactants and detergents》2020,23(1):79-90
Over the last few years, the global biosurfactant market has raised due to the increasing awareness among consumers, for the use of biological or bio-based products. Because of their composition, it can be speculated that these are more biocompatible and more biodegradable than their chemical homologous. However, at the moment, no studies exist in the literature about the biodegradability of biosurfactants. In this work, a biosurfactant contained in a crude extract, obtained from a corn wet-milling industry stream that ferments spontaneously in the presence of lactic acid bacteria, was subjected to a biodegradation study, without addition of external microbial biomass, under different conditions of temperature (5–45 °C), biodegradation time (15–55 days), and pH (5–7). For that, a Box–Behnken factorial design was applied, which allowed to predict the percentage of biodegradation for the biosurfactant contained in the crude extract, between the range of the independent variables selected in the study, obtaining biodegradation values between 3 and 80%. The percentage of biodegradation for the biosurfactant was calculated based on the increase in the surface tension of samples of the crude extract. Furthermore, it was also possible to predict the variation in t1/2 for the biosurfactant (time to achieve the 50% of biodegradation) under different conditions. 相似文献
33.
Mobile software applications have to cope with a particular environment that involves small size, limited resources, high autonomy requirements, competitive business models and many other challenges. To provide development guidelines that respond to these needs, several practices have been introduced; however, it is not clear how these guidelines may contribute to solve the issues present in the mobile domain. Furthermore, the rapid evolution of the mobile ecosystem challenges many of the premises upon which the proposed practices were designed. In this paper, we present a survey of the literature on software assurance practices for mobile applications, with the objective of describing them and assessing their contribution and success. We identified, organized and reviewed a body of research that spans in three levels: software development processes, software product assurance practices, and software implementation practices. By carrying out this literature survey, we reviewed the different approaches that researchers on Software Engineering have provided to address the needs that raise in the mobile software development arena. Moreover, we review the evolution of these practices, identifying how the constant changes and modernization of the mobile execution environment has impacted the methods proposed in the literature. Finally, we introduced discussion on the application of these practices in a real productive setting, opening an area for further research that may determine if practitioners have followed the proposed assurance paradigms. 相似文献
34.
D. Solís-Cortés E. Navarrete-Astorga J.L. Costa-Krämer J. Salguero-Fernandez R. Schrebler D. Leinen E.A. Dalchiele J.R. Ramos-Barrado F. Martín 《Ceramics International》2019,45(5):5577-5587
C-axis textured thin films of gallium-doped indium zinc oxide (GIZO) with a 2% ratio of Ga/Zn, were obtained via RF-magnetron sputtering with high transparency and electrical conductivity. A Box-Behnken response surface design was used to evaluate the effects of the deposition parameters (In2O3 target power, deposition time, and substrate temperature) on the chemical composition, optical, electrical, and structural properties of the GIZO films. The optical constants and the electrical properties were obtained using optical models. The GIZO stoichiometry, and therefore the In/Zn atomic ratio, affected the crystallinity, crystalline parameters, band gap, and charge carrier mobility of the GIZO films. The charge carrier density was related to the change in the crystalline parameters of the hexagonal structure and the In/Zn atomic ratio. The best electrical conductivity values (1.75?×?103 Ω?1 cm?1) were obtained for GIZO films with In/Zn ratio ≥?1. Several figures of merit (FOM) defined for the visible and solar regions were comparatively used to select the optimal In/Zn atomic ratio that provided the best balance between the conductivity and the transparency. The optimal In/Zn ratio was in a range of 0.85–0.90 for the GIZO films. 相似文献
35.
Dr. Blijke S. Kroezen Gabriele Conti Benedetta Girardi Dr. Jonathan Cramer Dr. Xiaohua Jiang Dr. Said Rabbani Jennifer Müller Maja Kokot Enrico Luisoni Prof. Daniel Ricklin Dr. Oliver Schwardt Prof. Beat Ernst 《ChemMedChem》2020,15(18):1706-1719
Siglecs are members of the immunoglobulin gene family containing sialic acid binding N-terminal domains. Among them, Siglec-8 is expressed on various cell types of the immune system such as eosinophils, mast cells and weakly on basophils. Cross-linking of Siglec-8 with monoclonal antibodies triggers apoptosis in eosinophils and inhibits degranulation of mast cells, making Siglec-8 a promising target for the treatment of eosinophil- and mast cell-associated diseases such as asthma. The tetrasaccharide 6’-sulfo-sialyl Lewisx has been identified as a specific Siglec-8 ligand in glycan array screening. Here, we describe an extended study enlightening the pharmacophores of 6’-sulfo-sialyl Lewisx and the successful development of a high-affinity mimetic. Retaining the neuraminic acid core, the introduction of a carbocyclic mimetic of the Gal moiety and a sulfonamide substituent in the 9-position gave a 20-fold improved binding affinity. Finally, the residence time, which usually is the Achilles tendon of carbohydrate/lectin interactions, could be improved. 相似文献
36.
This paper presents an integrated passive damping approach in hybrid metal-CFRP parts for structural applications. In this concept a viscoelastic material is embedded in the joint zone of the hybrid component. To examine the connection strength single-lap-joint specimens were produced and tested and the influence of the used material combinations, different surface structures, and different process parameters i.e. the moment of cross-linking were evaluated. Afterwards, the metal-CFRP hybrids were tested in quasi-static tests to assess their connection strength and failure behaviour. Dynamic cyclic tensile tests with step-wise increased loading conditions were performed to determine the specimens damping behaviour and to estimate their fatigue performance. Finally, these results are compared to a state of the art metal-CFRP hybrid with rivets connecting both materials. 相似文献
37.
38.
In this paper, we consider the classical finite mixture model, which is an effective tool for modeling lifetime distributions for random samples from heterogeneous populations. We discuss new results on stochastic comparison for two finite mixtures when each of them is drawn from one of the following semiparametric families, i.e., proportional hazards, accelerated lifetime and proportional reversed hazards. 相似文献
39.
40.