全文获取类型
收费全文 | 10617篇 |
免费 | 586篇 |
国内免费 | 46篇 |
学科分类
工业技术 | 11249篇 |
出版年
2024年 | 32篇 |
2023年 | 98篇 |
2022年 | 250篇 |
2021年 | 423篇 |
2020年 | 295篇 |
2019年 | 341篇 |
2018年 | 384篇 |
2017年 | 394篇 |
2016年 | 369篇 |
2015年 | 261篇 |
2014年 | 372篇 |
2013年 | 668篇 |
2012年 | 518篇 |
2011年 | 591篇 |
2010年 | 416篇 |
2009年 | 451篇 |
2008年 | 381篇 |
2007年 | 327篇 |
2006年 | 283篇 |
2005年 | 201篇 |
2004年 | 202篇 |
2003年 | 245篇 |
2002年 | 262篇 |
2001年 | 202篇 |
2000年 | 135篇 |
1999年 | 174篇 |
1998年 | 856篇 |
1997年 | 561篇 |
1996年 | 363篇 |
1995年 | 197篇 |
1994年 | 155篇 |
1993年 | 170篇 |
1992年 | 52篇 |
1991年 | 53篇 |
1990年 | 51篇 |
1989年 | 46篇 |
1988年 | 64篇 |
1987年 | 34篇 |
1986年 | 37篇 |
1985年 | 31篇 |
1984年 | 10篇 |
1982年 | 15篇 |
1981年 | 16篇 |
1980年 | 23篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 52篇 |
1976年 | 125篇 |
1975年 | 11篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
讨论了在VMI管理思想下对具有随机需求特性的多客户库存分配问题 ,重点论述了有效近似算法的设计过程 ,最后基于一组模拟数据给出了一个算例。 相似文献
2.
Piedade M. Sousa L. A. de Almeida T. M. Germano J. da Costa B. A. Lemos J. M. Freitas P. P. Ferreira H. A. Cardoso F. A. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(11):2384-2395
This paper presents a hand-held microsystem based on new fully integrated magnetoresistive biochips for biomolecular recognition (DNA hybridization, antibody antigen interaction, etc.). Magnetoresistive chip surfaces are chemically treated, enabling the immobilization of probe biomolecules such as DNA or antibodies. Fluid handling is also integrated in the biochip. The proposed microsystem not only integrates the biochip, which is an array of 16times16 magnetoresistive sensors, but it also provides all the electronic circuitry for addressing and reading out each transducer. The proposed architecture and circuits were specifically designed for achieving a compact, programmable and portable microsystem. The microsystem also integrates a hand-held analyzer connected through a wireless channel. A prototype of the system was already developed and detection of magnetic nanoparticles was obtained. This indicates that the system may be used for magnetic label based bioassays 相似文献
3.
4.
Marcia Cristina Kaezer Fran a Rosane Aguiar da Silva San Gil Jean-Guillaume Eon 《Catalysis Today》2003,78(1-4):105-115
γ-Al2O3 supported vanadium oxides were modified by tungsten and molybdenum oxides in order to improve dispersion and selectivity towards olefins in propane oxidative dehydrogenation (ODH). Both vanadium–tungsten and vanadium–molybdenum catalysts were obtained by adsorption of mixed isopolyanions (VW5O195−, V2W4O194−, VMo5O195− and V2Mo4O194−) from aqueous solutions. The isopolyanion solutions were characterized by UV-Vis and 51V NMR spectroscopy. Vanadium, vanadium–tungsten and vanadium–molybdenum precursors and catalysts were also characterized by UV-Vis (diffuse reflectance) and solid state 51V NMR spectroscopy. An improved selectivity to propene in the presence of tungsten and molybdenum in VOx/γ-Al2O3 was observed and attributed to dilution of vanadium by tungsten or molybdenum oxides on the γ-Al2O3 surface. 相似文献
5.
6.
7.
BACKGROUND: The enterococci have become important nosocomial pathogens. They can cause multiple site infections and enterococcal bacteremia becomes more frequently associated with a high mortality rate. Previous studies of enterococcal bacteremia showed a variety of results. To establish the significance and importance of enterococci as nosocomial pathogens in this hospital, to characterize their clinical pictures and to search for the risk factors for mortality, this retrospective study was performed. METHODS: There were 208 cases of enterococcal bacteremia which occurred from 1988 to 1992. Twenty-seven cases had no medical charts, dismissing possibility of evaluation. Finally, 181 cases of enterococcal bacteremia were analysed. RESULTS: One hundred and eighteen episodes were nosocomial infections. Polymicrobial bacteremia occurred in 68.5% of the patients and the most common co-isolate was Pseudomonas aeruginosa. Those patients (78.5%) with underlying diseases and malignancies were the most common underlying problems. The portal of entry could be found in 69.6 percent of patients, with the gastrointestinal tract the most common sources. Antimicrobial susceptibility testing showed high gentamicin resistance rate (89.5%), and ampicillin still had about 80 percent sensitivity rate. The group who received specific antibiotic therapy for enterococcus showed lower mortality (36.4% versus 47.6%). Only one case had infective endocarditis. Forty-nine patients suffered from septic shock, the cause of 30 deaths. Totally 75 patients died during hospitalization. Besides sepsis, another major cause of death was their underlying diseases itself. CONCLUSIONS: Enterococci have no doubt become important nosocomial pathogens and enterococcal bacteremia were associated with high mortality, especially in elderly patients with underlying diseases such as malignancy or diabetes. When clinically dealing with sepsis from the gastrointestinal or biliary tract, especially when previous cephalosporins therapy showed no response, the possibility of enterococcal bacteremia should always be considered. 相似文献
8.
9.
10.
Larissa Canilha Walter Carvalho Marco Giulietti Maria Das Graças Almeida Felipe João Batista Almeida E Silva 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):715-721
BACKGROUND: Xylitol bioproduction from lignocellulosic residues comprises hydrolysis of the hemicellulose, detoxification of the hydrolysate, bioconversion of the xylose, and recovery of xylitol from the fermented hydrolysate. There are relatively few reports on xylitol recovery from fermented media. In the present study, ion‐exchange resins were used to clarify a fermented wheat straw hemicellulosic hydrolysate, which was then vacuum‐concentrated and submitted to cooling in the presence of ethanol for xylitol crystallization. RESULTS: Sequential adsorption into two anion‐exchange resins (A‐860S and A‐500PS) promoted considerable reductions in the content of soluble by‐products (up to 97.5%) and in medium coloration (99.5%). Vacuum concentration led to a dark‐colored viscous solution that inhibited xylitol crystallization. This inhibition could be overcome by mixing the concentrated medium with a commercial xylitol solution. Such a strategy led to xylitol crystals with up to 95.9% purity. The crystallization yield (43.5%) was close to that observed when using commercial xylitol solution (51.4%). CONCLUSION: The experimental data demonstrate the feasibility of using ion‐exchange resins followed by cooling in the presence of ethanol as a strategy to promote the fast recovery and purification of xylitol from hemicellulose‐derived fermentation media. Copyright © 2008 Society of Chemical Industry 相似文献