全文获取类型
收费全文 | 83342篇 |
免费 | 3707篇 |
国内免费 | 256篇 |
专业分类
电工技术 | 940篇 |
综合类 | 734篇 |
化学工业 | 13072篇 |
金属工艺 | 1417篇 |
机械仪表 | 1828篇 |
建筑科学 | 2181篇 |
矿业工程 | 503篇 |
能源动力 | 1383篇 |
轻工业 | 8853篇 |
水利工程 | 981篇 |
石油天然气 | 245篇 |
武器工业 | 9篇 |
无线电 | 3841篇 |
一般工业技术 | 10385篇 |
冶金工业 | 28951篇 |
原子能技术 | 377篇 |
自动化技术 | 11605篇 |
出版年
2023年 | 593篇 |
2022年 | 638篇 |
2021年 | 1277篇 |
2020年 | 990篇 |
2019年 | 1157篇 |
2018年 | 2159篇 |
2017年 | 2328篇 |
2016年 | 2751篇 |
2015年 | 2061篇 |
2014年 | 2057篇 |
2013年 | 3680篇 |
2012年 | 4483篇 |
2011年 | 4860篇 |
2010年 | 2564篇 |
2009年 | 2571篇 |
2008年 | 2320篇 |
2007年 | 2201篇 |
2006年 | 1704篇 |
2005年 | 4194篇 |
2004年 | 3338篇 |
2003年 | 2822篇 |
2002年 | 1652篇 |
2001年 | 1349篇 |
2000年 | 786篇 |
1999年 | 1132篇 |
1998年 | 8334篇 |
1997年 | 5287篇 |
1996年 | 3483篇 |
1995年 | 2102篇 |
1994年 | 1553篇 |
1993年 | 1657篇 |
1992年 | 490篇 |
1991年 | 534篇 |
1990年 | 483篇 |
1989年 | 460篇 |
1988年 | 478篇 |
1987年 | 377篇 |
1986年 | 340篇 |
1985年 | 339篇 |
1984年 | 209篇 |
1983年 | 192篇 |
1982年 | 280篇 |
1981年 | 333篇 |
1980年 | 356篇 |
1979年 | 155篇 |
1978年 | 176篇 |
1977年 | 894篇 |
1976年 | 1911篇 |
1975年 | 160篇 |
1973年 | 130篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
51.
52.
53.
Machine Learning - We propose a data-driven approach to quantify the uncertainty of models constructed by kernel methods. Our approach minimizes the needed distributional assumptions, hence,... 相似文献
54.
55.
Maria A. Ospina Monica Pizarro Thierry Tran Julien Ricci John Belalcazar Jorge L. Luna Luis F. Londoño Sandra Salazar Hernan Ceballos Dominique Dufour Luis A. Becerra Lopez-Lavalle 《International Journal of Food Science & Technology》2021,56(3):1343-1353
The objective of this study was to characterise the nutritional potential of leaves and identify a diversity centre with low cyanide and high nutrient content among 178 Latin American cassava genotypes. This field-based collection represents the seven diversity centres, held at The International Center for Tropical Agriculture (CIAT Palmira, Colombia) by the Cassava Program. The cyanide, all-trans-β-carotene and lutein concentrations in cassava leaves ranged from 346 to 7484 ppm dry basis (db), from 174–547 μg g−1 db and 15–181 μg g−1 db, respectively. Cassava leaves also showed significant levels of essential amino acids leucine, lysine, phenylalanine, valine and threonine, and average total protein content of 26.24 g 100 g−1 db. Among seven diversity centres, South American rainforest group showed low cyanide and high carotene content in leaves. In addition, VEN77 and PAN51 genotypes stood out for having low cyanide in leaves and roots and high carotene in leaves. This genetic diversity can be used to select high potential progenitors for breeding purposes. 相似文献
56.
57.
P. Carrasqueira H. Rocha J. M. Dias T. Ventura B. C. Ferreira M. C. Lopes 《International Transactions in Operational Research》2023,30(1):206-223
Radiation therapy is a technology-driven cancer treatment modality that has experienced significant advances over the last decades, due to multidisciplinary contributions that include engineering and computing. Recent technological developments allow the use of noncoplanar volumetric modulated arc therapy (VMAT), one of the most recent photon treatment techniques, in clinical practice. In this work, an automated noncoplanar arc trajectory optimization framework designed in two modular phases is presented. First, a noncoplanar beam angle optimization algorithm is used to obtain a set of noncoplanar irradiation directions. Then, anchored in these directions, an optimization strategy is proposed to compute an optimal arc trajectory. The computational experiments considered a pool of twelve difficult head-and-neck tumor cases. It was possible to observe that, for some of these cases, the optimized noncoplanar arc trajectories led to significant treatment planning quality improvements, when compared with coplanar VMAT treatment plans. Although these experiments were done in a research environment treatment planning software (matRad), the conclusions can be of interest for a clinical setting: automated procedures can simplify the current treatment workflow, produce high-quality treatment plans, making better use of human resources and allowing for unbiased comparisons between different treatment techniques. 相似文献
58.
Miroslav Kárný Marko Ruman 《International Journal of Adaptive Control and Signal Processing》2021,35(5):660-675
Any knowledge extraction relies (possibly implicitly) on a hypothesis about the modelled-data dependence. The extracted knowledge ultimately serves to a decision-making (DM). DM always faces uncertainty and this makes probabilistic modelling adequate. The inspected black-box modeling deals with “universal” approximators of the relevant probabilistic model. Finite mixtures with components in the exponential family are often exploited. Their attractiveness stems from their flexibility, the cluster interpretability of components and the existence of algorithms for processing high-dimensional data streams. They are even used in dynamic cases with mutually dependent data records while regression and auto-regression mixture components serve to the dependence modeling. These dynamic models, however, mostly assume data-independent component weights, that is, memoryless transitions between dynamic mixture components. Such mixtures are not universal approximators of dynamic probabilistic models. Formally, this follows from the fact that the set of finite probabilistic mixtures is not closed with respect to the conditioning, which is the key estimation and predictive operation. The paper overcomes this drawback by using ratios of finite mixtures as universally approximating dynamic parametric models. The paper motivates them, elaborates their approximate Bayesian recursive estimation and reveals their application potential. 相似文献
59.
Lydia Saidi Dr. Djenisa H. A. Rocha Dr. Oualid Talhi Dr. Yamina Bentarzi Prof. Dr. Bellara Nedjar-Kolli Dr. Khaldoun Bachari Dr. Filipe A. Almeida Paz Dr. Luisa A. Helguero Prof. Dr. Artur M. S. Silva 《ChemMedChem》2019,14(10):1041-1048
Breast and prostate cancers are frequently treated with chemotherapy. Several novel chemicals are being reported for this purpose, particularly synthetic and natural benzophenones. This work reports the synthesis of substituted 2-hydroxybenzophenones through 1,4-conjugate addition/intramolecular cycloaddition/dehydration of nitromethane on key intermediate chromones. Structures were extensively studied by means of 2D NMR spectroscopy and single-crystal XRD. Their cytotoxicity was evaluated in vitro in two breast cancer cell lines (MDA-MB-231 and T47-D) and one prostate cancer cell line (PC3). The most potent compound exhibited good cytotoxic effects against the three cancer cell lines (IC50 values ranging from 12.09 to 26.49 μm ) and induced cell-cycle retardation only on prostate cancer cells, which suggested that it might exert cell-type-specific effects. 相似文献
60.
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