全文获取类型
收费全文 | 4244篇 |
免费 | 142篇 |
国内免费 | 42篇 |
专业分类
化学 | 2843篇 |
晶体学 | 34篇 |
力学 | 155篇 |
数学 | 399篇 |
物理学 | 919篇 |
综合类 | 78篇 |
出版年
2024年 | 18篇 |
2023年 | 35篇 |
2022年 | 255篇 |
2021年 | 200篇 |
2020年 | 144篇 |
2019年 | 135篇 |
2018年 | 164篇 |
2017年 | 115篇 |
2016年 | 163篇 |
2015年 | 158篇 |
2014年 | 160篇 |
2013年 | 313篇 |
2012年 | 257篇 |
2011年 | 281篇 |
2010年 | 158篇 |
2009年 | 142篇 |
2008年 | 149篇 |
2007年 | 171篇 |
2006年 | 131篇 |
2005年 | 136篇 |
2004年 | 87篇 |
2003年 | 79篇 |
2002年 | 72篇 |
2001年 | 74篇 |
2000年 | 54篇 |
1999年 | 63篇 |
1998年 | 27篇 |
1997年 | 27篇 |
1996年 | 43篇 |
1995年 | 40篇 |
1994年 | 27篇 |
1993年 | 31篇 |
1992年 | 33篇 |
1991年 | 41篇 |
1990年 | 19篇 |
1989年 | 21篇 |
1988年 | 28篇 |
1987年 | 26篇 |
1986年 | 26篇 |
1985年 | 38篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 11篇 |
1980年 | 28篇 |
1979年 | 21篇 |
1978年 | 27篇 |
1977年 | 28篇 |
1976年 | 18篇 |
1968年 | 10篇 |
排序方式: 共有4428条查询结果,搜索用时 38 毫秒
971.
M. S. Zavakhina I. S. Khan M. O. Barsukova A. A. Sapianik D. G. Samsonenko D. N. Dybtsev V. P. Fedin 《Russian Chemical Bulletin》2018,67(7):1268-1272
The inclusion compound of zinc lactate terephthalate with R-butan-2-ol, [Zn2(R-BusOH) (bdc)(S-lac)]?(R-BusOH) (BusOH is butan-2-ol, H2bdc is terephthalic acid, S-H2lac is lactic acid), was prepared by soaking crystals of [Zn2(dmf)(bdc)(S-lac)]?DMF in pure R-butan-2-ol. The positions of chiral alcohol molecules in voids of the chiral framework and the host–guest contacts were determined by X-ray diffraction. These data provide an explanation for the origin of chiral discrimination of zinc lactate terephthalate toward the R-isomer of butan-2-ol. 相似文献
972.
The expeditious route for the synthesis of γ-butyrolactone fused cyclooctene starting from the γ-butyrolactone fused cyclopentane through bicyclo[4.2.1]nonan-9-one is reported. Retro-Dieckmann’s condensation of bicyclo[4.2.1]nonan-9-one in presence of sodium methoxide and methanol furnished γ-butyrolactone fused cyclooctene in good yield. Surprisingly, the stereochemistry of ring-junction of γ-butyrolactone fused cyclooctene is different from the γ-butyrolactone fused cyclopentane, and the position of new ester group, which were confirmed unambiguously by X-ray analysis. 相似文献
973.
974.
975.
976.
Rukhsana I. Kureshy Surendra Singh Noor-ul H. Khan Sayed H.R. Abdi Santosh Agrawal Vishal J. Mayani Raksh V. Jasra 《Tetrahedron letters》2006,47(30):5277-5279
Catalytic asymmetric ring opening of cyclohexene oxide and meso-stilbene oxide with anilines was catalyzed by a Ti-(S)-(−)-BINOL complex to afford β-amino alcohols in high yield (up to 95%) and good enantioselectivities (ee up to 55%) under microwave irradiation. The reaction using a microwave was found to be 10 times faster than traditional oil-bath heating with retention of enantioselectivity. 相似文献
977.
Pseudo-first order rate constants (kobs) for alkaline hydrolysis of phthalimide (PTH), obtained at constant concentration of cetyltrimethylammonium bromide (CTABr) and 35°C, vary with the concentration of organic salts ([MX]) according to the relationship: kobs = (k0 + K [MX])/(1 + K [MX]) where and K are empirical parameters. The values of K at 0.01 M CTABr are nearly 2 times larger than the corresponding K values at 0.02 M CTABr for sodium benzoate, disodium phthalate and disodium isophthalate. 相似文献
978.
Copper(II) complexes were prepared with the new N(2)S(thioether) ligand 2-methylthio-N-(2-pyridylmethyl)acetamide (2-HL(N2S)). [Cu(2-L(N2S))Cl(MeOH)], which formed in the presence of excess triethylamine, is a distorted square pyramidal complex containing the ligand with the amide nitrogen deprotonated. The structurally analogous complex, [Cu(2-HL(N2S))Cl(2)], which formed in the absence of triethylamine, contains 2-HL(N2S) in the tautomeric imidic acid form. Neutral copper(II) N(2)S(thioether)S(thiolate) species were generated by addition of alkyl or aromatic thiolates to [Cu(2-L(N2S))Cl(MeOH)] and an unusual decomposition pathway was discovered. 相似文献
979.
Fasih A. Siddiqi Santosh K. Saksena Ibadur Rahman Khan 《Journal of polymer science. Part A, Polymer chemistry》1977,15(8):1935-1956
Diffusion rate of biologically important electrolytes through parchment-supported silver chloride membrane have been determined by the use of Nernst-Planck equation at various temperatures taking into account membrane resistance Rm, membrane potential Em, etc. The diffusion rates were found to be primarily dependent upon the difference in the hydration energies of the counterion in the external solution. On the basis of Eisenman-Sherry theory the diffusion rate sequence of alkali metal cations point towards the weak field strengths of the fixed charge groups. The various thermodynamic parameters, namely, ΔH?, ΔF?, and ΔS? were evaluated. The values of ΔS? found to be negative, indicating that the diffusion is taking place with partial immobilization in the membrane phase. A formal relation between ΔHhydration, ΔFhydration, and ΔShydration of cations with the corresponding values of ΔH?, ΔF?, and ΔS? for diffusion was also found to exist for the investigated system. 相似文献
980.