全文获取类型
收费全文 | 33453篇 |
免费 | 4040篇 |
国内免费 | 2464篇 |
专业分类
电工技术 | 4195篇 |
综合类 | 4154篇 |
化学工业 | 834篇 |
金属工艺 | 882篇 |
机械仪表 | 2541篇 |
建筑科学 | 1919篇 |
矿业工程 | 983篇 |
能源动力 | 397篇 |
轻工业 | 887篇 |
水利工程 | 735篇 |
石油天然气 | 594篇 |
武器工业 | 383篇 |
无线电 | 8304篇 |
一般工业技术 | 2448篇 |
冶金工业 | 454篇 |
原子能技术 | 303篇 |
自动化技术 | 9944篇 |
出版年
2024年 | 153篇 |
2023年 | 490篇 |
2022年 | 858篇 |
2021年 | 1015篇 |
2020年 | 974篇 |
2019年 | 722篇 |
2018年 | 667篇 |
2017年 | 877篇 |
2016年 | 1032篇 |
2015年 | 1319篇 |
2014年 | 2079篇 |
2013年 | 1983篇 |
2012年 | 2559篇 |
2011年 | 2885篇 |
2010年 | 2282篇 |
2009年 | 2350篇 |
2008年 | 2406篇 |
2007年 | 2760篇 |
2006年 | 2484篇 |
2005年 | 2162篇 |
2004年 | 1633篇 |
2003年 | 1355篇 |
2002年 | 1015篇 |
2001年 | 813篇 |
2000年 | 642篇 |
1999年 | 455篇 |
1998年 | 318篇 |
1997年 | 275篇 |
1996年 | 244篇 |
1995年 | 254篇 |
1994年 | 186篇 |
1993年 | 137篇 |
1992年 | 99篇 |
1991年 | 91篇 |
1990年 | 82篇 |
1989年 | 63篇 |
1988年 | 52篇 |
1987年 | 27篇 |
1986年 | 22篇 |
1985年 | 26篇 |
1984年 | 26篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1959年 | 5篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
Expanded gamut printing is an approach in color reproduction that expands the color gamut of conventional CMYK printing processes via the use of additional colorants, such as Orange, Green, and Violet inks. This study evaluates the ability of commercial color management software to create an accurate solution for an expanded gamut printing system. In this study, two printing processes were used, an Epson SureColor P9000 inkjet printer/proofer and an HP Indigo 7900 digital production press, both with 7-color expanded gamut ink sets. Software solutions from Alwan, CGS ORIS, ColorLogic, GMG Color, Heidelberg, and Kodak were evaluated. The systems were tested to see how well they could reproduce the colors in the entire PANTONE+ Solid Coated spot color library. It is shown that the solutions are able to reproduce 89% to 94% of the spot colors on the Epson P9000 inkjet printer and 77% to 87% of the library on the Indigo 7900, both to less than two CIEDE2000 (a typical tolerance in label and packaging work). The number of color patches in expanded gamut characterization test charts was noted, as this is still an area of proprietary, nonstandardized working practice. There are many different colorant combinations that can make the same color in expanded gamut printing. The ink build created by the different software solutions was studied, as it relates to press stability through appropriate choice of colorants. Pantone and Adobe provide everyday commercial tools for expanded color workflows. The study identified some issues with products from these companies that could confuse a less-skilled user in a busy production environment. The conclusion of the study is that expanded gamut solutions for spot color printing produce totally acceptable results for digital printing processes; expanded gamut printing is ready, here and now. The findings show that expanded gamut printing can replace cumbersome conventional spot color workflows creating considerable savings and advantages, especially for label and packaging printers. 相似文献
22.
Maria Grazia Basanisi Gianfranco La Bella Gaia Nobili Rosa Coppola Annita Maria Damato Maria Assunta Cafiero Giovanna La Salandra 《International Journal of Food Science & Technology》2020,55(3):1145-1150
The authenticity and traceability of meat products are issues of primary importance to ensure food safety. Unfortunately, food adulteration (e.g. the addition of inexpensive cuts to minced meat products) and mislabelling (e.g. the inclusion of meat from species other than those declared) happens frequently worldwide. The aim of this study was to apply a droplet digital PCR assay for the detection and quantification (copies μL−1) of the beef, pork, horse, sheep, chicken and turkey in meat products. The analysis conducted on commercial meat showed the presence of traces of DNA from other animal species than those declared. We show that the method is highly sensitive, specific and accurate (accuracy = 100%). This method could be adopted by competent food safety authorities to verify compliance with the labelling of meat products and to ensure quality and safety throughout the meat supply chain, from primary production to consumption. 相似文献
23.
Biological information is stored in DNA, RNA and protein sequences, which can be understood as genotypes that are translated into phenotypes. The properties of genotype–phenotype (GP) maps have been studied in great detail for RNA secondary structure. These include a highly biased distribution of genotypes per phenotype, negative correlation of genotypic robustness and evolvability, positive correlation of phenotypic robustness and evolvability, shape-space covering, and a roughly logarithmic scaling of phenotypic robustness with phenotypic frequency. More recently similar properties have been discovered in other GP maps, suggesting that they may be fundamental to biological GP maps, in general, rather than specific to the RNA secondary structure map. Here we propose that the above properties arise from the fundamental organization of biological information into ‘constrained'' and ‘unconstrained'' sequences, in the broadest possible sense. As ‘constrained'' we describe sequences that affect the phenotype more immediately, and are therefore more sensitive to mutations, such as, e.g. protein-coding DNA or the stems in RNA secondary structure. ‘Unconstrained'' sequences, on the other hand, can mutate more freely without affecting the phenotype, such as, e.g. intronic or intergenic DNA or the loops in RNA secondary structure. To test our hypothesis we consider a highly simplified GP map that has genotypes with ‘coding'' and ‘non-coding'' parts. We term this the Fibonacci GP map, as it is equivalent to the Fibonacci code in information theory. Despite its simplicity the Fibonacci GP map exhibits all the above properties of much more complex and biologically realistic GP maps. These properties are therefore likely to be fundamental to many biological GP maps. 相似文献
24.
文章介绍了3种宽带数字储频的基本结构,分析了宽带数字储频的一个重要指标——量化噪声,根据输出信号频谱的杂散电平比较了三种结构的优劣。 相似文献
25.
26.
An optoelectronic method is considered for noncontacting reconstruction of the surface profile of three-dimensional objects of large dimensions. The optimal conditions for performing measurements are identified. It is shown that the proposed method, in contrast to the already known methods, does not require fine tuning of the equipment. A numerical method is given for compensating distortions caused by aberrations. A method is described for reconstructing the surface profile cell by cell which increases the accuracy of measurements. 相似文献
27.
28.
论文提出利用用户提供的个性化信息来随机产生关联大素数,保证了素数选取的随机化、个性化,提高了RSA算法的安全性。 相似文献
29.
为了提高现代网络信息传输的安全性,利用无理数小数点后数字的无穷性、无规律性、分布均匀性,提出一种全新的加密算法,并用它所产生的密钥流进行数字签名,实现身份验证不可抵赖、信息传输无篡改,确保信息传输的完整性、真实性,达到提高加密效率、相互认证的效果。 相似文献
30.