全文获取类型
收费全文 | 15649篇 |
免费 | 2690篇 |
国内免费 | 2219篇 |
专业分类
化学 | 11399篇 |
晶体学 | 175篇 |
力学 | 904篇 |
综合类 | 154篇 |
数学 | 1920篇 |
物理学 | 6006篇 |
出版年
2024年 | 41篇 |
2023年 | 318篇 |
2022年 | 571篇 |
2021年 | 642篇 |
2020年 | 653篇 |
2019年 | 723篇 |
2018年 | 565篇 |
2017年 | 534篇 |
2016年 | 777篇 |
2015年 | 819篇 |
2014年 | 974篇 |
2013年 | 1188篇 |
2012年 | 1418篇 |
2011年 | 1417篇 |
2010年 | 1004篇 |
2009年 | 1022篇 |
2008年 | 1046篇 |
2007年 | 884篇 |
2006年 | 818篇 |
2005年 | 668篇 |
2004年 | 564篇 |
2003年 | 450篇 |
2002年 | 516篇 |
2001年 | 391篇 |
2000年 | 322篇 |
1999年 | 335篇 |
1998年 | 264篇 |
1997年 | 231篇 |
1996年 | 214篇 |
1995年 | 179篇 |
1994年 | 152篇 |
1993年 | 157篇 |
1992年 | 103篇 |
1991年 | 103篇 |
1990年 | 86篇 |
1989年 | 81篇 |
1988年 | 72篇 |
1987年 | 41篇 |
1986年 | 39篇 |
1985年 | 47篇 |
1984年 | 28篇 |
1983年 | 19篇 |
1982年 | 24篇 |
1981年 | 11篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1972年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
Yanjun Wang Shaoyun Chen Heng Chen Xingzhou Yuan Yongchun Zhang 《Journal of Energy Chemistry》2013,22(6):902-906
Removal of carbonyl sulfide (COS) from CO2 stream is significant for the production and utilization of food grade CO2. This study investigates the adsorption performance of Ag/NaZSM-5 as adsorbent prepared by incipient wetness impregnation for the removal of COS from a CO2 stream in a fixed-bed adsorption apparatus. Effects of various conditions on the preparation of adsorbent, adsorption and desorption were intensively examined. The results revealed that COS can be removed to below 1×10?9 from a CO2 stream (1000 ppm COS/CO2) using Ag/NaZSM-5 (10 wt% AgNO3) with an adsorption capacity of 12.86 mg-g?1. The adsorbent can be fully regenerated using hot air at 450 °C. The adsorption ability remained stable even after eight cycles of regeneration. 相似文献
952.
953.
Bao-Min Wang Zhang Yuan Zhi-Qiang Guo Hai-Nan Ma Chuan Fook Lai 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2013,87(13):2253-2259
As a new nano-scale functional material, it is necessary to achieve a uniform distribution in the composites for gaining the CNFs’ excellent reinforcing effect. In this paper, CNFs were purified by the method of high temperature annealing treatment. Six surfactants, methylcellulose (MC), hydroxypropyl methylcellulose (HPMC), sodium dodecyl sulfate (SDS), dodecylamine (DDA), N, N-dimethyl formamide (DMF) and cetyltrimethyl ammonium bromide (CTAB) were used individually and combinatorially in a certain concentration to disperse the CNFs in aqueous solution. To achieve a good dispersion of the CNFs, a method utilizing ultrasonic processing was employed. The CNFs treated by the method of high temperature annealing treatment were characterized by differential thermal analysis (DTA) and thermogravimetry analysis (TGA), and the ultrasonication-driven dispersion of CNFs in aqueous solutions were monitored by UVvis spectroscopy and transmission electron microscopy (TEM). The experiments reveal that the method of high temperature annealing treatment purified the CNFs and the maximum achievable dispersion of CNFs corresponds to the maximum UV absorbance of the solution. All results show that the surfactants mixture of MC and SDS in a certain concentration of 0.4 and 2.0 g/L has the maximum dispersion effect on CNFs in aqueous solution, the optimum concentration ratio of MC, SDS, and CNFs was 2: 10: 1. 相似文献
954.
955.
956.
WANG Wei YUAN XiaQing LIU XuHui GAO Qiang QI HongLan ZHANG ChengXiao 《中国科学:化学(英文版)》2013,56(7):1009-1016
A selective DNA sensing with zeptomole detection level is developed based on coulometric measurement of gold nanoparticle (AuNPs)-mediated electron transfer (ET) across a self-assembled monolayer on the gold electrode. After immobilization of a thiolated hairpin-structured DNA probe, an alkanethiol monolayer was self-assembled on the resultant electrode to block [Fe(CN)6 ]-3-/4in a solution from accessing the electrode. In the presence of DNA target, hybridization between the DNA probe and the DNA target breaks the stem duplex of DNA probe. Consequently, stem moiety at the 3′-end of the DNA probes was removed from the electrode surface and made available for hybridization with the reporter DNA-AuNPs conjugates (reporter DNA-AuNPs). The thiolated reporter DNA matches the stem moiety at the 3′-end of the DNA probe. AuNPs were then enlarged by immersing the electrode in a growth solution containing HAuCl 4 and H2O2 after the reporter DNA-AuNPs bound onto the electrode surface. The enlarged AuNPs on the electrode restored the ET between the electrode and the [Fe(CN)6]3 -/4- , as a result, amplified signals were achieved for DNA target detection using the coulometric measurement of Fe(CN)6 3- electro-reduction by prolonging the electrolysis time. The quantities of ET on the DNA sensor increased with the increase in DNA target concentration through a linear range of 3.0 fM to 1.0 pM when electrolysis time was set to 300 s, and the detection limit was 1.0 fM. Correspondingly, thousands of DNA (zeptomole) copies were detected in 10L samples. Furthermore, the DNA sensor showed excellent differentiation ability for single-base mismatch. 相似文献
957.
A novel flame retardant (PSiN), containing silicon and nitrogen, was synthesized using N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane (KH-602) and diphenylsilanediol through solution polycondesation and it was used together with potassium-4-(phenylsulfonyl)benzenesulfonate (KSS) to prepare a flame-retardant system for polycarbonate (PC). The structure and thermal property of PSiN were characterized by Fourier transform infrared spectroscopy (FTIR), 1HNMR and thermogravimetric analysis (TG) tests. Flammability and thermal behaviors of PC/KSS/PSiN systems were estimated by limited oxygen index (LOI), cone calorimeter, vertical burning test (UL-94), and TG tests. The results showed that the flame retardancy and char residues of PC/KSS system were improved with the addition of PSiN. When 1 mass% PSiN and 0.5 mass% KSS were incorporated, the LOI value of PC was found to be 46, and class V-0 of the UL-94 test. Moreover, both the heat release rate and the total heat release of PC/KSS/1 mass% PSiN decreased compared with those of PC and PC/KSS systems. The microstructures observed by scanning electron microscopy and FTIR indicated that the surface of the char for PC/KSS/PSiN system hold a more cohesive and denser char structure when compared with the pure PC and PC/KSS system. 相似文献
958.
959.
以硝酸锌[Zn(NO3)2.6H2O]和尿素[CO(NH2)2]作前驱体,通过微波诱导燃烧技术可控合成具有不同形貌的ZnO纳米晶体,并用热重分析和差热分析进行了研究。对各种生长条件:微波功率,辐射时间和尿素/Zn2+物质的量的比对ZnO纳米晶体形貌的影响作了分析。结果表明:尿素/Zn2+物质的量的比对ZnO纳米材料的形貌具有显著影响。X衍射图表明合成的ZnO纳米结构呈六角形。傅里叶变换红外光谱图中400~500 cm-1处明显的峰为Zn-O的振动峰。ZnO纳米结构的发光光谱在366 nm的带边发射,因缺陷又由许多可见光发射峰组成。用扫描电子显微镜、透射电子显微镜、选区电子衍射研究了花状ZnO纳米结构的增长机理。本方法仅需几分钟就获得的了ZnO纳米结构。 相似文献
960.
超高效液相色谱串联质谱法同时快速测定牛奶中不同类型的11种兽药残留 总被引:1,自引:0,他引:1
建立了超高效液相色谱串联质谱测定牛奶中四环素类、青霉素类、磺胺类和泰乐菌素等11种兽药残留的检测方法。样品经乙腈超声提取后离心分离,上层清液稀释10倍后过0.2μm滤膜上机测定。在优化条件下,11种兽药在其线性范围内的相关系数均在0.998以上,定量下限(LOQ,S/N=10)为0.3~15μg/kg,在低、中、高3个水平下的加标回收率为81%~117%,相对标准偏差为0.6%~10.2%。方法用于实际牛奶样品中兽药残留量的测定,结果满意。 相似文献