全文获取类型
收费全文 | 10953篇 |
免费 | 1931篇 |
国内免费 | 1523篇 |
专业分类
化学 | 8293篇 |
晶体学 | 184篇 |
力学 | 572篇 |
综合类 | 131篇 |
数学 | 1219篇 |
物理学 | 4008篇 |
出版年
2024年 | 46篇 |
2023年 | 253篇 |
2022年 | 495篇 |
2021年 | 469篇 |
2020年 | 552篇 |
2019年 | 550篇 |
2018年 | 437篇 |
2017年 | 451篇 |
2016年 | 611篇 |
2015年 | 594篇 |
2014年 | 757篇 |
2013年 | 872篇 |
2012年 | 988篇 |
2011年 | 962篇 |
2010年 | 712篇 |
2009年 | 707篇 |
2008年 | 733篇 |
2007年 | 641篇 |
2006年 | 594篇 |
2005年 | 462篇 |
2004年 | 373篇 |
2003年 | 265篇 |
2002年 | 358篇 |
2001年 | 302篇 |
2000年 | 212篇 |
1999年 | 191篇 |
1998年 | 125篇 |
1997年 | 94篇 |
1996年 | 105篇 |
1995年 | 65篇 |
1994年 | 86篇 |
1993年 | 46篇 |
1992年 | 30篇 |
1991年 | 62篇 |
1990年 | 48篇 |
1989年 | 34篇 |
1988年 | 16篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 26篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1977年 | 3篇 |
1974年 | 4篇 |
1971年 | 2篇 |
1962年 | 1篇 |
1959年 | 3篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Amorphous poly(ethylene terephthalate) was annealed at temperatures around the glass transition temperature and then heated up in differential scanning calorimeter at 20 °C min−1. It was found that the annealing favored the subsequent cold crystallization and this effect became stronger with increasing annealing temperature. The experimental results were explained by considering the structural change during the annealing. 相似文献
132.
LBL分子沉积法制备葡萄糖氧化酶电极 总被引:1,自引:0,他引:1
采用以静电力为主的逐层分子交替沉积技术制备葡萄糖氧化酶(GOD)电极.通过带有正电荷的聚二甲基二烯丙基铵盐酸盐(PDDA)和带有负电荷的GOD交替沉积在修饰有3-巯基-1-丙基磺酸钠(MPS)的金电极表面.以甲酸二茂铁为电子媒介体,用循环伏安法检测GOD电极对葡萄糖的响应.结果表明,当GOD电极组装层数小于4时,电流响应随着层数的增加而增大,超过4层时电流响应减小.其中4层GOD修饰电极的线性范围为0.55~6.63 mmol•L-1,当pH为7.0时,响应最大.同时电极的检测重现性能良好,相对标准偏差为2.4%. 相似文献
133.
Li Yan Liang Shao Ping Ren Yi Quan Zheng Man Geng Lu Guangzhou Institute of Chemistry Chinese Academy of Sciences Guangzhou China Key Laboratory of Polymer Materials for Electronics Guangdong China Graduate School of the Chinese Academy of Sciences Beijing China 《中国化学快报》2007,18(2):225-228
A series of novel liquid crystalline epoxides with lateral substituents were cured with anhydrides and the cure kinetics was investigated by non-isothermal DSC technique. The results showed that the lengths of lateral substituents have great effect on the value of Ea. The curing reaction became less active, when the liquid crystalline epoxides have long lateral substituents and were controlled by diffusion at the late stage of cure. A nematic structure was observed by POM and XRD. 相似文献
134.
Li Ting Chai Yang Zhou Li Wei Wei Wang Quan Rui Wang Feng Gang Tao 《中国化学快报》2007,18(12):1460-1462
Nation-Teflon bimembrane was used as an efficient support for the preparation and application of heterogeneous palladium catalysts.The supported palladium catalysts exhibit high activity and stability in the Suzuki cross-coupling of aryl bromides with arylboronic acids to afford the corresponding biaryls in good to excellent yields,and can be readily recovered and reused several times without significant loss of activity. 相似文献
135.
The three new lignanoids 1 – 3 and the five new phyllocladane diterpenoids 7 – 11 were isolated from the leaves of Callicarpa furfuraceae, together with two known lignanoids, lariciresinol ( 4 ) and (+)‐sesamin ( 5 ), and five known diterpenoids, 17‐norphyllocladane‐3,16‐dion ( 6 ), calliterpenone ( 12 ), calliterpenone 17‐acetate ( 13 ), (3β,16α)‐phyllocladane‐3,16,17‐triol ( 14 ), and (3β,16α)‐phyllocladane‐3,16,17‐triol 17‐acetate ( 15 ). Their structures were established by spectral‐data interpretation. 相似文献
136.
This paper describes the design and synthesis of a family of pore-forming amphiphiles. Two of these amphiphiles, which are derived from cholic acid, lysine, and p-phenylenediamine, can produce pores in lipid bilayers as individual molecules. In sharp contrast, analogous amphiphiles that do not contain a rigid 1,4-phenylenediamide moiety favor the formation of dimer-based pores. Kinetic evidence in support of monomer- and dimer-based pores has been obtained from Na+ transport measurements across bilayers made from 1-palmitoyl-2-oleoyl-2-sn-glycero-3-phosphocholine (POPC). Structure-activity studies that have been carried out with pore-forming, dimer-based amphiphiles have also revealed a significant activity dependence on their overall compactness. The practical potential of pore-forming amphiphiles with controllable supramolecular properties is briefly discussed. 相似文献
137.
A GPI-anchored dipeptide of sperm CD52 antigen was prepared through a convergent synthesis. First, the dipeptide with its C-terminus free and the GPI with its nonreducing end phosphoethanolamine bearing a free amino group were synthesized separately. Then, the two building blocks were coupled with use of EDC/HOBt as the condensation reagent. Finally, the GPI-anchored peptide was deprotected to give the target molecule 1. 相似文献
138.
ShaoNongCHEN ShaoYuanCHEN HanDongSUN WenZhongLIN YaoZuCHEN 《中国化学快报》2004,15(5):539-542
Two novel ent-kauranoids with new sub-skeleton types, gesneroidins G and H were isolated as white powder from the ether extract of the leaves of Isodon gesneroides through normal phase column chromatography. Their structures were elucidated as 3β,6α,7β-triacetoxyl-15-hydroxyl-14-oxo-ent- 15,16-seco-kaur-11,17-olide and Iα-hydroxyl-3β,6α,7β,11 β-tetraacetoxyl-ent-nor-15,17-kaur-8,16-olide on the basis of the spectral evidences including ID and 2D NMR spectra. 相似文献
139.
Valerio Magnasco Massimo Ottonelli Giuseppe Figari Marina Rui Camilla Costa 《Journal of Molecular Structure》1998,430(1-3):231-239
The real spherical tensor theory of long-range intermolecular coefficients developed in previous papers is applied to derive explicit formulae for the first three dispersion coefficients for like centrosymmetric linear molecules. The expansion of angle-dependent coefficients in associated Legendre polynomials allows one to identify the isotropic and anisotropic components of the dispersion interaction in terms of London dispersion constants, the treatment of higher coefficients being simplified by the coupling of the elementary (l, l′)-polarizations to resultant angular momenta LA and LB onto each molecule. The contributions from all coupling schemes are given explicitly for C6, C8, C10, and numerical results are presented for H2-H2 using two-term reduced spectra values from the Kaiserlautern group. 相似文献
140.
Solvent effects on the electrochemistry and spectroscopic properties of alkyl- and aryl-substituted corroles in nonaqueous media are reported. The oxidation and reduction of six compounds containing zero to seven phenyl or substituted phenyl groups on the macrocycle were studied in four different nonaqueous solvents (CH(2)Cl(2), PhCN, THF, and pyridine) containing 0.1 M tetra-n-butylammonium perchlorate. Dimers were formed upon oxidation of all corroles in CH(2)Cl(2), but this was not the case in the other three solvents, where either monomers or dimers were formed upon oxidation depending upon the solvent Gutmann donor number and the number or location of aryl substituents on the macrocycle. The half-wave potentials were analyzed as a function of the number of aryl substituents on the macrocycle as well as the concentration of added pyridine to PhCN solutions of the compound, and these data were combined with data from the spectroelectrochemistry experiments to determine the stoichiometry of the species actually in solution after the first oxidation or first reduction of each compound. The results of these experiments indicate that reduction of the bispyridine adduct (Cor)Co(III)(py)(2) proceeds via the monopyridine complex (Cor)Co(III)(py) to give in each case the unligated cobalt(II) corrole [(Cor)Co(II)](-). In contrast, pyridine remains coordinated after electrooxidation, and the final product was characterized as [(Cor)Co(III)(py)(2)](+). 相似文献