全文获取类型
收费全文 | 6983篇 |
免费 | 864篇 |
国内免费 | 704篇 |
专业分类
化学 | 4436篇 |
晶体学 | 115篇 |
力学 | 299篇 |
综合类 | 65篇 |
数学 | 1206篇 |
物理学 | 2430篇 |
出版年
2023年 | 109篇 |
2022年 | 131篇 |
2021年 | 189篇 |
2020年 | 249篇 |
2019年 | 206篇 |
2018年 | 225篇 |
2017年 | 217篇 |
2016年 | 329篇 |
2015年 | 261篇 |
2014年 | 288篇 |
2013年 | 471篇 |
2012年 | 495篇 |
2011年 | 467篇 |
2010年 | 397篇 |
2009年 | 395篇 |
2008年 | 408篇 |
2007年 | 387篇 |
2006年 | 332篇 |
2005年 | 268篇 |
2004年 | 183篇 |
2003年 | 185篇 |
2002年 | 235篇 |
2001年 | 191篇 |
2000年 | 137篇 |
1999年 | 126篇 |
1998年 | 91篇 |
1997年 | 68篇 |
1996年 | 92篇 |
1995年 | 75篇 |
1994年 | 69篇 |
1993年 | 59篇 |
1992年 | 45篇 |
1991年 | 59篇 |
1990年 | 58篇 |
1989年 | 33篇 |
1988年 | 42篇 |
1987年 | 35篇 |
1986年 | 40篇 |
1985年 | 34篇 |
1984年 | 34篇 |
1983年 | 35篇 |
1982年 | 34篇 |
1981年 | 34篇 |
1980年 | 40篇 |
1979年 | 33篇 |
1978年 | 29篇 |
1977年 | 37篇 |
1976年 | 31篇 |
1974年 | 25篇 |
1973年 | 27篇 |
排序方式: 共有8551条查询结果,搜索用时 15 毫秒
121.
122.
A microemulsion electrokinetic chromatography method has been firstly used for the separation of the therapeutically important xanthones from Securidaca inappendiculata. The separation of the nine xanthones was systematically optimized with respect to pH, composition of microemulsion,addition of cyclodextrins, applied voltage and column temperature. Baseline separation was successfully achieved for the nine xanthones, which was also compared with that by micellar electrokinetic chromtography. 相似文献
123.
2-Azidopyrido[1,2-a]pyrimidin-4-one can exit only in the azido form and undergoes cyclo-addition reaction with 1,3-dicarbonyl compounds to form 1,2,3-triazole derivatives. Under the influence of bases or hydrochloric acid the carbonyl group is attacked with subsequent opening of the pyrimidine ring. This causes an immediate cyclization of the azide group to give a tetrazolo derivative. In a similar way a triazole ring can be formed from the appropriate hydrazino derivatives of pyrido[1,2-a]pyrimidin-4-one. 相似文献
124.
The static polarizabilities and the second-order hyperpolarizabilities of a series of tri-nuclear metal cluster models MS4(M′PPh3)2(M′PPh3)(M=Mo,W;M′=Cu,Ag,Au)have been calculated within the first-principle theoretical framework. The model clusters have two fragments of rhombic units and it is the charge ransfer from one of these moieties to the other that is responsible for nonlinear optical property. This kind of electronic delocaization, differentiated from that of planar π-system, is very interesting and is worthy for further investigation. 相似文献
125.
Summary A
tail-made polymer matrix is proposed to remove strontium ions from aqueous
solutions. The removal behavior of strontium ions on a crosslinked copolymer
containing methacrylic acid as functional groups was investigated as a function
of sorptive concentration, time, temperature and pH. It was observed that an
increase of these parameters enhanced the removal of Sr(II) ions from aqueous
solution. It is found that a maximum adsorption of Sr(II) ions can be obtained
on the crosslinked copolymer after 30 minutes and at pH 8. The increase of
Sr(II) ion concentration in the solution resulted in an increase in the amount
of Sr(II) ions adsorbed on the crosslinked copolymer containing methacrylic
acid as functional groups. However, after a maximum of Sr(II) concentration in
the solution, the percentage of adsorbed Sr(II) ions decreased. The adsorption
data are well represented by the Freundlich, Langmuir and Dubinin-Radushkevich
(D-R) isotherms. The adsorption capacity of the copolymer and the free energy
change were calculated by using the D-R isotherm. For the adsorption of Sr(II)
ions on the crosslinked copolymer the thermodynamic parameters (DH°,DS° andDG°) were
calculated.</p>
</p> 相似文献
126.
An oligosaccharide homologue named SnS-2 was isolated from the root of Scrophularia ningpoensis Hemsl.SnS-2 was purified by means of gel-permeation chromatography and ion-exchange chromatography. Its physicochemical properties, including carbohydrate content and molecular weight were determined. The structure of SnS-2 was elucidated by chemical methods along with ^1H and ^13C NMR spectroscopy, including two-dimensional DQCOSY and H-detected ^1H, ^13C HMQC experiments. These results show that SnS-2 possesses a backbone consisting of terminal α-Galp-(1→, α-Galp-(1→6), α-Glcp-(1→6) and nonreducing end β-Fruf-(2→. The bioactive assay showed that it could inhibit the growth of Lewis pulmonary carcinoma implanted in mice. 相似文献
127.
Marjan Kočevar Bojan Verček Branko Stanovnik Miha Tišler 《Monatshefte für Chemie / Chemical Monthly》1982,113(6-7):731-744
Pyrazine- and pyridinecarboxamidoximes with an amino, potentially tautomeric hydroxy or mercapto group inortho position could be transformed in the appropriate condensed azines. In this manner, representatives of pyrazolo(3,4-b)pyrazine, isoxazolo(4,5-b)pyrazine and isothiazolo(5,4-b)pyridine ring system were synthesized and some transformations investigated.Presented in part at the 8th International Congress of Heterocyclic Chemistry, Graz, 1981. 相似文献
128.
Feng K De Boni L Misoguti L Mendonca CR Meador M Hsu FL Bu XR 《Chemical communications (Cambridge, England)》2004,(10):1178-1180
Two new classes of two-photon absorbing Y-shaped molecules have been developed to possess an imidazole-thiazole core and a stilbene-type conjugation pathway with either nitro or sulfonyl as terminal electron-accepting group. 相似文献
129.
Krumova SB Todinova SJ Busheva MC Taneva SG 《Journal of photochemistry and photobiology. B, Biology》2005,78(2):165-170
The main light-harvesting chl a/b pigment-protein complex of photosystem II (LHCII) in isolated state forms macroaggregates with different ultrastructure and lipid content [I. Simidjiev, V. Barzda, L. Mustardy, G. Garab, Anal. Biochem. 250 (1997) 169-175]. The thermodynamic stability of highly delipidated tightly bound LHCII macroaggregates is studied by differential scanning calorimetry and fluorescence spectroscopy. The calorimetric profile of LHCII is asymmetric, the denaturation transition is taking place at around 72 degrees C. A shoulder, which overlaps with the main denaturation transition, appears around 58 degrees C. The denaturation temperature strongly depends on the scanning rate indicating the kinetic nature of the thermal destabilization of LHCII macroaggregates. The fluorescence data prove that the thermal denaturation of LHCII is an irreversible and kinetically controlled process. 相似文献
130.