全文获取类型
收费全文 | 1404篇 |
免费 | 11篇 |
学科分类
工业技术 | 1415篇 |
出版年
2019年 | 14篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 14篇 |
2015年 | 13篇 |
2014年 | 19篇 |
2013年 | 32篇 |
2012年 | 37篇 |
2011年 | 59篇 |
2010年 | 38篇 |
2009年 | 45篇 |
2008年 | 47篇 |
2007年 | 38篇 |
2006年 | 36篇 |
2005年 | 36篇 |
2004年 | 37篇 |
2003年 | 27篇 |
2002年 | 25篇 |
2001年 | 36篇 |
2000年 | 16篇 |
1999年 | 38篇 |
1998年 | 125篇 |
1997年 | 87篇 |
1996年 | 46篇 |
1995年 | 45篇 |
1994年 | 29篇 |
1993年 | 37篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 21篇 |
1989年 | 14篇 |
1988年 | 22篇 |
1987年 | 22篇 |
1986年 | 21篇 |
1985年 | 24篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 17篇 |
1981年 | 17篇 |
1980年 | 19篇 |
1979年 | 13篇 |
1978年 | 14篇 |
1977年 | 14篇 |
1976年 | 30篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1973年 | 11篇 |
1972年 | 8篇 |
1971年 | 10篇 |
1970年 | 9篇 |
排序方式: 共有1415条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
5.
Aqueous extracts of the coralline red algaeBossiella orbigniana have been shown to catalyze the enzymatic oxidation of arachidonic acid to a previously unreported ω6 eicosapentaenoic acid
product. This unique fatty acid contains a conjugated tetraene with absorption maxima at 293, 306, and 321 nm, and was identified
by spectral methods as 5(Z),8(Z),10(E),12(E),14(Z)-eicosapentaenoic acid. The compound was given the trivial name bosseopentaenoic
acid. Under experimental conditions, production of bosseopentaenoic acid was linear up to 2 hr and dioxygen was consumed.
Bosseopentaenoic acid, along with several other conjugated tetraenes, was also present in the algae endogenously as revealed
by a comparison of the ultraviolet (UV) spectra and the high-performance liquid chromatographic (HPLC) pattern of the purified
product and the organic extract ofBossiella. 相似文献
6.
ABSTRACT: The effect of post-cooking holding-time on sensory assessment of low (89 g/kg) and high (218 g/kg) fat beefburgers was assessed. Burgers were served to panelists approximately 3 or 18 min after cooking. Fat content influenced fattiness, moistness/juiciness and overall appearance (P < 0.05), overall acceptability and overall texture (P< 0.01) and tenderness and crumbliness (p<0.001). Burgers with the higher fat content had higher scores. Holding-time influenced sensory overall appearance only with lower scores at extended holding times (P < 0.01). Treatment differences were small, mostly less than one sensory scale unit. Higher lightness and yellowness values were found for burgers with higher fat contents. 相似文献
7.
Neal E. Craft Katherine S. Epler Therese A. Butler Willie E. May Regina G. Ziegler 《Journal of research of the National Institute of Standards and Technology》1993,98(3):355-359
Aliquots of serum collected in a large case-control study of cervical cancer were stored at −70°C for up to 4 years during implementation of the study. When 500 μL serum aliquots were thawed in preparation for carotenoid and vitamin A assays, volumes were noticeably variable and fell below 500 μL in the majority of the samples. We were concerned about evaporation/sublimation during storage of the samples because loss of water would concentrate the analytes of interest. We evaluated the use of density and sodium ion concentration measurements to confirm its occurrence. We found that serum density was an unreliable indicator of extent of volume loss since the anticipated increases in density due to evaporation were of the same magnitude as inter-individual variation in serum density. In contrast, Na+ concentration is tightly regulated and would rise if water had been lost from the samples. In a representative sample of serum aliquots from the case-control study, 24 of 25 vials contained less than 500 μL of serum. The mean sodium ion concentration (138.1 ± 3.6 mmol/L) was within the normal range for human serum of 136–145 mmol/L, and no correlation was observed between serum volume and Na+ concentration. These results strongly suggest that the observed low volumes were not due to evaporative losses. Instead, the variably low volumes of serum aliquots were probably due to pipetting errors in the initial aliquotting resulting from the use of air-displacement pipettes. 相似文献
8.
Several parameters and their limitations to prepare monodisperse polystyrene particles were discussed. Polystyrene latexes B, C and D of diameter 129.8, 142.8 and 264.5 nm, respectively, were synthesized by emulsion polymerization method. The latex D is almost monodisperse with very low polydispersity of 0.005 while B and C are having polydispersity of 0.1837 and 0.1601. The particle size and particle size distribution of the latexes were determined by a TEM and Brookhaven particle size analyzer. It was observed that the particle size of the latexes decreased with increasing initiator (ammonium persulfate) or surfactant (SDS) concentrations. The surface area of the latexes were calculated by using BET equation on the basis of the amount of nitrogen gas adsorbed at the surface of the particles to form a monolayer. It was observed that the surface area of latex D is less than B and C because of the bigger size of the particles. The average molecular weights, zeta potentials and densities of the latexes were also presented. 相似文献
9.
10.
D.L. Butler P.S. Cho M.W. Chbat J. Goldhar F.-S. Choa G.L. Burdge 《Photonics Technology Letters, IEEE》1996,8(6):779-781
We demonstrate stable operation of a NOLM using orthogonally polarized control and signal beams in nonpolarization-preserving, single-mode fiber. The NOLM can transcribe data from an optically incoherent input at one wavelength to a coherent output over a range of wavelengths. Operation of the NOLM without tuning for the input bit rate is possible over a range of bit rates from less than 1 Gb/s to more than 50 Gb/s. 相似文献