全文获取类型
收费全文 | 57499篇 |
免费 | 4496篇 |
国内免费 | 4052篇 |
专业分类
化学 | 25874篇 |
晶体学 | 426篇 |
力学 | 4567篇 |
综合类 | 703篇 |
数学 | 12331篇 |
物理学 | 22146篇 |
出版年
2024年 | 97篇 |
2023年 | 589篇 |
2022年 | 1557篇 |
2021年 | 1501篇 |
2020年 | 1611篇 |
2019年 | 1483篇 |
2018年 | 1305篇 |
2017年 | 1530篇 |
2016年 | 1746篇 |
2015年 | 1400篇 |
2014年 | 2124篇 |
2013年 | 3636篇 |
2012年 | 2429篇 |
2011年 | 2565篇 |
2010年 | 2104篇 |
2009年 | 3238篇 |
2008年 | 3477篇 |
2007年 | 3851篇 |
2006年 | 3323篇 |
2005年 | 2625篇 |
2004年 | 2224篇 |
2003年 | 2474篇 |
2002年 | 2810篇 |
2001年 | 2126篇 |
2000年 | 2021篇 |
1999年 | 1702篇 |
1998年 | 1673篇 |
1997年 | 978篇 |
1996年 | 932篇 |
1995年 | 820篇 |
1994年 | 854篇 |
1993年 | 642篇 |
1992年 | 702篇 |
1991年 | 463篇 |
1990年 | 435篇 |
1989年 | 338篇 |
1988年 | 291篇 |
1987年 | 290篇 |
1986年 | 259篇 |
1985年 | 250篇 |
1984年 | 243篇 |
1983年 | 144篇 |
1982年 | 194篇 |
1981年 | 185篇 |
1980年 | 124篇 |
1979年 | 162篇 |
1978年 | 131篇 |
1977年 | 124篇 |
1976年 | 79篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
F. Dondi Y. D. Kahie G. Lodi P. Reschiglian C. Pietrogrande C. Bighi G. P. Cartoni 《Chromatographia》1987,23(11):844-849
Summary Using a camomile flavonoid extract as the sample and four different reversed-phase partition systems, the ability of the Simplex procedure to produce optimum gradient separation of unknown multicomponent mixtures was checked against the linear solvent strength (LSS) gradient elution theory. On the same partition systems the mean solvent strenghts were measured by experimentally determined logk vs. mobile phase composition plots. These mean solvent strengths are compared to those inferred from the optimum gradients and the usefulness of LSS theory in multicomponent mixture gradient elution optimization is discussed.Dadicated to Prof. Dr. A Liberti on the occasion of his 70th birthday. 相似文献
942.
The linearity of the relationship between σT,t2 and (1 + k)2 is studied with the view of using it for the evaluation of GC equipment. Based on appropriate analytical expressions it is concluded that in general this relationship is not linear and that practical procedures for column evaluation should be developed that take this non-linearity into account. 相似文献
943.
Fernando J. S. Oliveira Francisca P. De França 《Applied biochemistry and biotechnology》2005,122(1-3):593-603
A 23 full factorial experimental design was adopted to estimate the effects of three variables on the biodegradation of oil during
soil bioremediation: bioaugmentation seeding a mixed culture, addition of fertilizer or mineral media, and correction of initial
pH of the soil to 7.0. The tests were carried out in polyvinyl chloride reactors with 5.0 kg of crude oil-contaminated soil
at 14 g/kg. After screening the variables, soil bioremediation tests were conduced with varied C:N ratios, yielding an increase
in biodegradation of the oil heavy fraction from 24 to 65%, consumption of total n-paraffins, and a remarkable decrease in the concentration of residual polycyclic aromatic hydrocarbons of the soil. 相似文献
944.
945.
Summary A comparison of the official EPA method 515.1 for determination of chlorinated acidic pesticides and a modification of it is illustrated. Extraction of the analytes from water and their determination and quantitation is by gas chromatography-electron capture detection (GC-ECD), liquid chromatography-UV detection and liquid chromatography-particle beam mass spectrometry. Although HPLC-PBMS was found to be less sensitive than the GC-ECD method, it was, nevertheless, more sensitive than HPLC-UV. The modified method is simpler, quicker and allows more accurate determination of pesticides in aqueous samples.Deceased July 31, 1996 相似文献
946.
Bis-citrato 1a-d , bis-citramalato 2 and bis-malato 3 germanate(IV) complexes were synthesized from germanium dioxide and citric acid, citramalic acid and malic acid respectively and were identified with IR, NMR and elementary analysis. Crystal 1a is triclinic, space group P1 with a = 7.919(2), b = 7.968(3), c = 9.605(3) Å, α = 94.25(3), β = 108.03(2), γ= 113.05(3)°, Z = 1, and the final residue, R(F), is 0.033 for 2583 reflections. Crystal 2 is monoclinic, space group C2 with a = 10.226(4), b = 12.802(4), c = 6.141(1) Å, β = 100.75(2)°, Z = 2, and the final residue, R(F), is 0.034 for 934 reflections. Both 1a and 2 have slightly distorted octahedral structures with citrate or citramalate ions as a tridentate ligand that forms five-, six- and seven-membered rings with the central metal. There is a two-fold axis through the central atom of compound 2 instead of the inversion center of 1a . Same structures for these six complexes are indicated because the spectral patterns of the other four compounds, 1b-d and 3 , are similar to those of compounds 1a and 2 . 相似文献
947.
鞠 《高等学校化学学报》1992,(11)
研究了温度对碳纤维微电极上伏安曲线的影响及温度与电极电位的关系,测定了电极反应的热力学参数.由电流与温度的关系测定了去极剂的扩散活化能E_(al)和D_o,利用微电极具有高速传质的特性,测定了常规电极上为可逆反应的电极反应标准速率常数(?),并通过(?)与温度的关系测定了电极反应的活化能. 相似文献
948.
A relationship between the X-H (X = N, O, C, and so on) equilibrium bond length in a Morse oscillator and the X-H stretching overtone frequency shifts is obtained theoretically. We use the equation to discuss the empirical linear relationships that have been proposed for heterocyclics, alkanes and fluorinated benzenes. On the other hand, a unified relationship between the X-H bond angles and the experimental quantities (ω(?) and the coupling strength λ) is also presented for XH2, XH, and XH4 molecules or molecular fragments. Calculations of X-H bond angles for a number of molecules show that the results from our equations are in excellent agreement with the experimental values. Also we can extract the information of relative magnitude of bond coupling force field. 相似文献
949.
Main characteristics are described of the PRIRODA quantum-chemical program suite designed for the study of complex molecular systems by the density functional theory, at the MP2, MP3, and MP4 levels of multiparticle perturbation theory, and by the coupled-cluster single and double excitations method (CCSD) with the application of parallel computing. A number of examples of calculations are presented.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 804–810, March, 2005. 相似文献
950.
Methylenechalcogenopyran and benzopyran Fischer carbene complexes are easily obtained from commercially available chalcogenopyrones or benzopyrones and carbanion of methoxy(methyl)carbene tungsten complex. The key of the heterocyclic carbene formation is the activation of the carbonyl group by alkylation with alkyl trifluoromethanesulfonate reagent. 相似文献