全文获取类型
收费全文 | 17826篇 |
免费 | 3236篇 |
国内免费 | 2398篇 |
专业分类
化学 | 12801篇 |
晶体学 | 203篇 |
力学 | 1288篇 |
综合类 | 159篇 |
数学 | 1826篇 |
物理学 | 7183篇 |
出版年
2024年 | 62篇 |
2023年 | 381篇 |
2022年 | 640篇 |
2021年 | 638篇 |
2020年 | 751篇 |
2019年 | 655篇 |
2018年 | 587篇 |
2017年 | 521篇 |
2016年 | 818篇 |
2015年 | 821篇 |
2014年 | 1015篇 |
2013年 | 1214篇 |
2012年 | 1612篇 |
2011年 | 1650篇 |
2010年 | 1097篇 |
2009年 | 1026篇 |
2008年 | 1189篇 |
2007年 | 1031篇 |
2006年 | 1057篇 |
2005年 | 869篇 |
2004年 | 688篇 |
2003年 | 573篇 |
2002年 | 566篇 |
2001年 | 470篇 |
2000年 | 391篇 |
1999年 | 451篇 |
1998年 | 316篇 |
1997年 | 294篇 |
1996年 | 339篇 |
1995年 | 287篇 |
1994年 | 272篇 |
1993年 | 204篇 |
1992年 | 192篇 |
1991年 | 155篇 |
1990年 | 133篇 |
1989年 | 112篇 |
1988年 | 107篇 |
1987年 | 67篇 |
1986年 | 60篇 |
1985年 | 43篇 |
1984年 | 32篇 |
1983年 | 26篇 |
1982年 | 13篇 |
1981年 | 18篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1966年 | 1篇 |
1957年 | 5篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
Xiaoling Bao Jianhong Liu Qingshu Zheng Wei Pei Yimei Yang Yanyun Dai Tao Tu 《中国化学快报》1990,30(12):2266-2270
A novel protocol allowing convenient and highly selective visual recognition of melamine in raw milk via selective metallo-hydrogel formation at a concentration as low as 10 ppm without any tedious pretreatment has been developed. 相似文献
232.
4,5-二溴苯基荧光酮-溴化十六烷基三甲铵荧光熄灭法测定微量铁 总被引:2,自引:0,他引:2
本文利用DBPF为荧光试剂,在大量CTMAB存在下,用荧光熄灭法测定微量铁,λ_(ex)为362nm,λ_(em)560nm。线性范围为0.002~0.12μg/mL。三元络合物中,Fe:DBPF=1:3。 相似文献
233.
In the present paper, the behavior of a single polymer chain under various solvent conditions was modeled by self-avoiding walks (SAW) with nearest neighbors attraction Δε on a simple cubic lattice. Determination of the θ-condition wasbased on the numerical results of the mean square radius of gyration and end-to-end distance. It was found that at the θtemperatue Δε/kT equals -0.27. The exponents a in the Mark-Houwink equation with different interaction parameters areconsistent with the results of experiments: under θ-condition, a = 0.5, and for a good solvent α= 0.74-0.84, respectively. 相似文献
234.
235.
237.
[reaction: see text] A series of chiral pyrrolidinylmethanol-based dendritic ligands were synthesized for application in enantioselective aryl transfer reactions to aldehydes with the (ArBO)3/ZnEt2 system in up to 98% ee. 相似文献
238.
Stasch A Ferbinteanu M Prust J Zheng W Cimpoesu F Roesky HW Magull J Schmidt HG Noltemeyer M 《Journal of the American Chemical Society》2002,124(19):5441-5448
The reaction of the acetylene RC triple bond CH (R = Ph, CH(2)SiMe(3)) with an excess of AlH(3).NMe(3) in boiling toluene leads to the carbaalane [(AlH)(6)(AlNMe(3))(2)(CCH(2)R)(6)] (R = Ph 1, CH(2)SiMe(3) 2) in good yield. Treatment of 2 with BCl(3) under varying conditions gives the chlorinated products [(AlCl)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] 3 and [(AlCl)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(2)Cl)(6)] 4, respectively. The latter clearly demonstrates that the cluster can be stepwise functionalized within the inner and outer sphere. The X-ray single-crystal structures of 1, 2, and 4 have been determined. All compounds have in common that the central core consists of a cluster having eight aluminum and six carbon atoms. The bonding properties in this cluster are described as a new manifestation of three-dimensional surface aromaticity. Each Al(4)C fragment of the cube is formed by four bonds with three electron pairs, thus leading to a strong delocalization of the electrons. A phenomenological modeling using a three-dimensional Hückel scheme with fitted parameters to reproduce the energies from ab initio calculations revealed that the orbital scheme localized at one Al(4)C fragment possesses an orbital sextet with a large HOMO-LUMO gap. This is in line with the criteria of aromaticity. The idea of aromaticity was sustained also by qualitative valence bond reasons enumerating the different resonance structures by means of graph theoretical methods. 相似文献
239.
Yi Ming Liu Sui Ping Deng Hui Zheng Jian Ming Ouyang 《中国化学快报》2007,18(3):345-348
The ring patterns of calcium oxalate crystals were induced by domains in Langmuir-Blodgett (LB) films of dipalmitoylpho- sphatidylcboline (DPPC). The result was explained by the defects at the ring boundaries of liquid condensed (LC) and liquid expanded (LE) phases of LB film. These boundaries could provide less free energy and much more nucleating sites for COM crystals. 相似文献
240.
Isolation and purification of honokiol and magnolol from cortex Magnoliae officinalis by high-speed counter-current chromatography 总被引:5,自引:0,他引:5
High-speed counter-current chromatography was used to isolate and purify honokiol and magnolol from cortex Magnoliae Officinalis (Magnolia officinalis Rehd. et Wils.), a plant used in the traditional Chinese medicine. A crude sample, 150 mg, was successfully separated with a two-phase solvent system composed of n-hexane-ethyl acetate-methanol-water (1:0.4:1:0.4, v/v), and the fractions were analyzed by high-performance liquid chromatography. The separation produced 80 and 45 mg of honokiol and magnolol with purities of 99.2 and 98.2%, respectively, in 2.5 h. 相似文献