全文获取类型
收费全文 | 6199篇 |
免费 | 189篇 |
国内免费 | 650篇 |
专业分类
林业 | 530篇 |
农学 | 776篇 |
基础科学 | 287篇 |
941篇 | |
综合类 | 3216篇 |
农作物 | 378篇 |
水产渔业 | 132篇 |
畜牧兽医 | 438篇 |
园艺 | 208篇 |
植物保护 | 132篇 |
出版年
2024年 | 32篇 |
2023年 | 80篇 |
2022年 | 153篇 |
2021年 | 193篇 |
2020年 | 173篇 |
2019年 | 206篇 |
2018年 | 133篇 |
2017年 | 279篇 |
2016年 | 338篇 |
2015年 | 268篇 |
2014年 | 357篇 |
2013年 | 395篇 |
2012年 | 694篇 |
2011年 | 648篇 |
2010年 | 546篇 |
2009年 | 489篇 |
2008年 | 427篇 |
2007年 | 412篇 |
2006年 | 330篇 |
2005年 | 224篇 |
2004年 | 139篇 |
2003年 | 112篇 |
2002年 | 82篇 |
2001年 | 62篇 |
2000年 | 59篇 |
1999年 | 38篇 |
1998年 | 33篇 |
1997年 | 25篇 |
1996年 | 23篇 |
1995年 | 18篇 |
1994年 | 16篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有7038条查询结果,搜索用时 0 毫秒
991.
超临界CO_2流体萃取葡萄籽油的优化工艺 总被引:2,自引:0,他引:2
采用超临界CO2流体萃取法,以葡萄籽为原料,通过单因素试验和正交试验设计,探讨了葡萄籽粉粒度、萃取压力、时间和温度等因素对葡萄籽油萃取率的影响.结果表明,萃取最佳工艺参数为葡萄籽粉粒度60目,萃取压力30 MPa,萃取时间2.5 h,萃取温度40℃,CO2流量40 kg/h,油脂萃取率达18.4%以上. 相似文献
992.
993.
以兖州市城区为例,以高分辨率CCD航空影像为数据源,进行城区土地利用类型信息提取方法的研究。 相似文献
994.
T Jauffrais J Kilcoyne V Séchet C Herrenknecht P Truquet F Hervé JB Bérard C Nulty S Taylor U Tillmann CO Miles P Hess 《Marine drugs》2012,10(6):1360-1382
Azaspiracid (AZA) poisoning has been reported following consumption of contaminated shellfish, and is of human health concern. Hence, it is important to have sustainable amounts of the causative toxins available for toxicological studies and for instrument calibration in monitoring programs, without having to rely on natural toxin events. Continuous pilot scale culturing was carried out to evaluate the feasibility of AZA production using Azadinium spinosum cultures. Algae were harvested using tangential flow filtration or continuous centrifugation. AZAs were extracted using solid phase extraction (SPE) procedures, and subsequently purified. When coupling two stirred photobioreactors in series, cell concentrations reached 190,000 and 210,000 cell · mL(-1) at steady state in bioreactors 1 and 2, respectively. The AZA cell quota decreased as the dilution rate increased from 0.15 to 0.3 day(-1), with optimum toxin production at 0.25 day(-1). After optimization, SPE procedures allowed for the recovery of 79 ± 9% of AZAs. The preparative isolation procedure previously developed for shellfish was optimized for algal extracts, such that only four steps were necessary to obtain purified AZA1 and -2. A purification efficiency of more than 70% was achieved, and isolation from 1200 L of culture yielded 9.3 mg of AZA1 and 2.2 mg of AZA2 of >95% purity. This work demonstrated the feasibility of sustainably producing AZA1 and -2 from A. spinosum cultures. 相似文献
995.
996.
997.
998.
999.
Amal Abdelhamid Sirine Lajili Mohamed Amine Elkaibi Yosra Ben Salem Ameni Abdelhamid Christian D. Muller 《Journal Of Aquatic Food Product Technology》2013,22(9):892-909
Brown seaweeds produce useful bioactive substances with high cosmetic and pharmacological values due to the presence of antioxidant derivatives, mainly phlorotannins (PHT), which are of particular interest. A central composite rotatable design (CCRD) with three variables (extraction time, dry material-to-solvent ratio and ethanol concentration) and two responses was performed to optimize the microwave-assisted extraction (MAE) of phlorotannins from Cystoseira sedoides using response surface methodology (RSM). Results showed that the independent variables significantly affected both phlorotannin content and the scavenging capacity. The optimum operating conditions were extraction time, 101.74 sec; dry material-to-solvent ratio, 1:10 g/mL; and ethanol extraction, 50%. Under these conditions, the predicted values of PHT content and radical scavenging activity-IC50 were close to the observed values and were 383.887 µg PGE/g Dm and 18.353 µg/mL, respectively. Characterization of the phlorotannin-rich fraction was conducted by high-performance liquid chromatography and Fourier transform infrared spectroscopy. The evaluation of the anticancer activity against MCF-7 breast cancer cell line showed a potent activity to trigger apoptotic death in more than a half of the MCF-7 cells, with an estimated IC50 value of 78 μg/mL. In addition, this fraction induced a notable growth regression effect on 3D spheroids model in a concentration-dependent manner, with a growth rate of about 1.17, at 200 µg/mL.Abbreviations: CCRD: Central composite rotatable design; Dm: Dry material; DMBA: 2,4-dimethoxy benzaldehyde; DMSO: Dimethyl sulfoxide; DPPH: 1,1-diphenyl-2-picrylhydrazyl; EDTA: Ethylene diamine tetraacetic acid; FBS: Fetal bovine serum; FT-IR: Fourier transform infrared; HPLC: High-performance liquid chromatography; IC50: Half-maximal inhibitory concentration; MAE: Microwave-assisted extraction; Min: minutes; PBS: Phosphate buffered saline; PGE: Phloroglucinol equivalent; PHT: Phlorotannins; PHT-SED: phlorotannins derived from Cystoseira sedoides; PI: Propidium iodide; RSA: Radical scavenging activity; RSM: Response surface methodology; Sec: seconds 相似文献
1000.
3种椰子基因组DNA提取方法的比较 总被引:1,自引:1,他引:0
旨在得到一套快速提取椰子DNA的方法。采用CTAB小样法、SDS-CTAB法以及PVP法提取椰子组织的DNA,并通过后续的PCR扩增和酶切等实验比较了3种方法所提取的DNA质量的优劣。将CTAB小样法提取的DNA与SDS-CTAB法和PVP法提取的DNA进行了比较,CTAB小样法提取的DNA的OD260/OD280(1.839)较另外2种方法SDS-CTAB法(1.709)和PVP法(1.613)的值更高,CTAB小样法提取的DNA适合于PCR扩增,扩增的条带清晰,且特异性好。此外,CTAB小样法提取的DNA,酶切也较为均匀。CTAB小样法能高效地提取椰子的DNA,并且能一次提取大量的高质量DNA样品,因而能满足高通量的实验要求,同提取DNA能较好地满足下游的分子生物学研究。 相似文献