全文获取类型
收费全文 | 751篇 |
免费 | 29篇 |
专业分类
化学 | 426篇 |
晶体学 | 16篇 |
力学 | 34篇 |
数学 | 50篇 |
物理学 | 254篇 |
出版年
2023年 | 12篇 |
2022年 | 25篇 |
2021年 | 22篇 |
2020年 | 31篇 |
2019年 | 20篇 |
2018年 | 21篇 |
2017年 | 28篇 |
2016年 | 30篇 |
2015年 | 14篇 |
2014年 | 33篇 |
2013年 | 83篇 |
2012年 | 59篇 |
2011年 | 45篇 |
2010年 | 46篇 |
2009年 | 39篇 |
2008年 | 32篇 |
2007年 | 32篇 |
2006年 | 28篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 5篇 |
2002年 | 8篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 12篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1967年 | 3篇 |
1962年 | 2篇 |
排序方式: 共有780条查询结果,搜索用时 15 毫秒
691.
Manoj Kumar Yadav Vijay Kumar Bijender Singh Santosh Kumar Tiwari 《Applied biochemistry and biotechnology》2017,181(1):142-156
Multi-phase anaerobic reactor for H2 and CH4 production from paperboard mill wastewater was studied. The reactor was operated at hydraulic retention times (HRTs) of 12, 18, 24, and 36 h, and organic loading rates (OLRs) of 2.2, 1.5, 1.1, and 0.75 kg chemical oxygen demand (COD)/m3 day, respectively. HRT of 12 h and OLR of 2.2 kg COD/m3 day provided maximum hydrogen yield of 42.76?±?14.5 ml/g CODremoved and volumetric substrate uptake rate (?rS) of 16.51?±?4.43 mg COD/L h. This corresponded to the highest soluble COD/total COD (SCOD/TCOD) ratio of 56.25?±?3.3 % and the maximum volatile fatty acid (VFA) yield (YVFA) of 0.21?±?0.03 g VFA/g COD, confirming that H2 was mainly produced through SCOD conversion. The highest methane yield (18.78?±?3.8 ml/g CODremoved) and ?rS of 21.74?±?1.34 mgCOD/L h were achieved at an HRT of 36 h and OLR of 0.75 kg COD/m3 day. The maximum hydrogen production rate (HPR) and methane production rate (MPR) were achieved at carbon to nitrogen (C/N) ratio of 47.9 and 14.3, respectively. This implies the important effect of C/N ratio on the distinction between the dominant microorganism bioactivities responsible for H2 and CH4 production. 相似文献
692.
A simple and convenient assay based on single-drop microextraction with infrared spectroscopy is reported for the determination of selenium. The extraction conditions were carefully optimized and selenium was preconcentrated through single-drop microextraction in 1,2-dichloroethane containing N-hydroxy-N-phenyl-N′-(o-tolyl) benzimidamide. The method is selective and almost all common ions including molybdenum(VI), chromium(VI), and tungsten(VI) did not interfere with the isolation protocol. The selenite band at 875?±?2?cm?1, which is assigned to the asymmetric vibrational stretch (υ3), was used for the quantification of selenium. Low limits of detection and quantification of 2.0 and 6.6?µg?L?1 demonstrate the sensitivity of the method. Good precision was evaluated by the standard deviation (2.0?µg?L?1) and relative standard deviation (0.5%) for 8?µg?L?1 was achieved for 10 measurements. The method was used to analyze human blood, urine, and water for selenium. 相似文献
693.
Keshri Nath Tiwari Mane Rajendra Uttam Puja Kumari Piyush Vatsa S. M. Prabhakaran 《合成通讯》2017,47(10):1013-1019
An efficient synthesis of acridinediones in two steps have been achieved using water as a reaction media without chromatographic purification. First step involves the reaction of dimedone with ammonium acetate to yield enaminone in water which on further reaction with various aldehydes yields acridinedione in aqueous media. The reaction merits the use of water as solvent, no additive catalyst and provides high yield of products with good purity. 相似文献
694.
The development of new catalyst-free green and efficient protocol to access 5′-thioxospiro[indoline-3,3′-[1,2,4]triazolidin]-2-ones/spiro[indoline-3,3′-[1,2,4]triazolidine]-2,5′-diones, potential privileged scaffolds for drug discovery, is disclosed. Key feature of this methodology is the dual use of glycerol—a recyclable, bioorganic compound, as a solvent cum promoter. Other highlights include use of inexpensive reagents, mild reaction conditions, operational simplicity, short reaction time, no need for chromatographic purification, and high yields. 相似文献
695.
Harnessing new materials for developing high-energy storage devices set off research in the field of organic supercapacitors. Various attractive properties like high energy density, lower device weight, excellent cycling stability, and impressive pseudocapacitive nature make organic supercapacitors suitable candidates for high-end storage device applications. This review highlights the overall progress and future of organic supercapacitors. Sustainable energy production and storage depend on low cost, large supercapacitor packs with high energy density. Organic supercapacitors with high pseudocapacitance, lightweight form factor, and higher device potential are alternatives to other energy storage devices. There are many recent ongoing research works that focus on organic electrolytes along with the material aspect of organic supercapacitors. This review summarizes the current research status and the chemistry behind the storage mechanism in organic supercapacitors to overcome the challenges and achieve superior performance for future opportunities. 相似文献
696.
697.
To establish the fact that the performance of a solid state battery is predominantly governed by the cathode, primary electrochemical
cells were fabricated using FeH(SO4)2-xH2O solid electrolyte having proton transport number close to unity (prepared by chemical route) taken in conjunction with five
different cathodes MnO2, PbO2, V6O13, I2 and TMAI iodine complex. Amongst these, better discharge characteristics along with thermodynamic and chemical stability
of the cell were offered by TMAI iodine complex based cathode. Beside these, it provided short-circuit current, capacity and
energy density of the order of 5 mA 4.5 mAh and 2.67 Wh/kg respectively due to the presence of highly active iodine, which
is not free in TMAI compared to the cathode made of simply I2.
Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003. 相似文献
698.
699.
We present a simple algorithm for approximating all roots of a polynomial p(x) when it has only real roots. The algorithm is based on some interesting properties of the polynomials appearing in the Extended Euclidean Scheme for p(x) and p′(x). For example, it turns out that these polynomials are orthogonal; as a consequence, we are able to limit the precision required by our algorithm in intermediate steps. A parallel implementation of this algorithm yields a P-uniform NC2 circuit, and the bit complexity of its sequential implementation is within a polylog factor of the bit complexity of the best known algorithm for the problem. 相似文献
700.