全文获取类型
收费全文 | 13410篇 |
免费 | 945篇 |
国内免费 | 1617篇 |
专业分类
化学 | 4349篇 |
晶体学 | 58篇 |
力学 | 1255篇 |
综合类 | 223篇 |
数学 | 7405篇 |
物理学 | 2682篇 |
出版年
2024年 | 20篇 |
2023年 | 148篇 |
2022年 | 269篇 |
2021年 | 372篇 |
2020年 | 363篇 |
2019年 | 393篇 |
2018年 | 376篇 |
2017年 | 458篇 |
2016年 | 450篇 |
2015年 | 367篇 |
2014年 | 528篇 |
2013年 | 1272篇 |
2012年 | 493篇 |
2011年 | 649篇 |
2010年 | 568篇 |
2009年 | 749篇 |
2008年 | 807篇 |
2007年 | 955篇 |
2006年 | 769篇 |
2005年 | 706篇 |
2004年 | 636篇 |
2003年 | 630篇 |
2002年 | 554篇 |
2001年 | 459篇 |
2000年 | 428篇 |
1999年 | 410篇 |
1998年 | 382篇 |
1997年 | 335篇 |
1996年 | 248篇 |
1995年 | 170篇 |
1994年 | 182篇 |
1993年 | 108篇 |
1992年 | 102篇 |
1991年 | 81篇 |
1990年 | 67篇 |
1989年 | 56篇 |
1988年 | 62篇 |
1987年 | 60篇 |
1986年 | 37篇 |
1985年 | 56篇 |
1984年 | 34篇 |
1983年 | 16篇 |
1982年 | 30篇 |
1981年 | 21篇 |
1980年 | 15篇 |
1979年 | 17篇 |
1978年 | 19篇 |
1977年 | 16篇 |
1976年 | 6篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Basinska T 《Macromolecular bioscience》2005,5(12):1145-1168
Functional hydrophilic microspheres (latex particles) have found various applications in life sciences and in medicine - particularly in latex diagnostic tests. This paper presents a comprehensive review of studies on latex particles with a hydrophilic interfacial layer composed of various hydrophilic polymers with reactive groups at the ends of macromolecules or at each monomeric unit along the chain. Typical examples of these hydrophilic polymers are poly(2-hydroxyethyl methyl methacrylate), poly(acrylic acid), poly(N,N-dimethylacrylamide), polysaccharides, poly(ethylene oxide) and polyglycidol. Hydrophilic microspheres with different morphologies (uniform or core-shell, see Figure) have been synthesized by emulsion and dispersion polymerizations. The chemical structure of polymers which constitute the interfacial layer of microspheres has been investigated using a variety of instrumental techniques (such as XPS, SSIMS and NMR) and analytical methods based on specific chemical reactions suitable for the determination of particular functional groups. Microspheres are exposed to contact with proteins in the majority of medical applications. This paper presents examples of studies on the attachment of these biomacromolecules to microspheres. The relation between the structure of the interfacial layer of microspheres and the ability of these particles for the covalent binding of proteins is discussed. Several examples of diagnostic tests, in which hydrophilic microspheres with adsorbed or covalently immobilized proteins were used as reagents, are presented. The paper also contains a short review of the application of magnetic hydrophilic particles for protein separation. Examples of hydrophilic latex particles used for hemoperfusion or heavy metal ion separation are presented. Hydrophilic microspheres with uniform or core-shell morphologies. 相似文献
22.
Toshinobu Korenaga 《Journal of fluorine chemistry》2007,128(5):557-561
A pentafluorophenyl group can act as a stereo-controlling group in oxazaborolidine-catalyzed asymmetric borane reduction through intramolecular π-π stacking interaction with a phenyl group. The intramolecular π-π interaction in oxazaborolidine bearing pentafluorophenyl group is confirmed by calculations and 1H NMR study. The interaction affects the enantioselectivity of the asymmetric reduction of acetophenone while the extent is small. 相似文献
23.
A straightforward and stereospecific synthesis of (+)-polyoxamic acid is disclosed. The key step of the synthesis involves the regio- and stereospecific bromohydration of an olefin via intramolecular participation by the sulfinyl group. 相似文献
24.
Harald Høiland 《Journal of solution chemistry》1977,6(5):291-297
The isentropic coefficients of compressibility of the homologous series of alcohols and diols R
n
CH2OH (n=2–6), CH3CHOHR
n
(n=1–5), 1,2-propanediol, 1,3- 1,4- and 2,3-butanediol, 1,5-pentanediol, and 1,7-heptanediol dissolved in propylene carbonate have been measured at 25°C. Isentropic partial molal compressibilities and group partial molal compressibilities at infinite dilution have been evaluated. The isentropic partial molal compressibilities of these alcohols and diols have been compared with the corresponding values in water. This comparison shows that the values in propylene carbonate are higher than in water by a factor of 10 due to an increased compressibility of the solvation sheath around nonpolar groups in PC. 相似文献
25.
Ying-nan Xuan Yan Gao Yong Huang Xi-gao Jian Laboratory of Cellulose Lignocellulosics Chemistry Guangzhou Institute of Chemistry Chinese Academy of Sciences Guangzhou China Institute of Chemistry Chinese Academy of Sciences Beijing China Department of Polymer Science College of Chemical Engineering Dalian University of Technology Dalian China 《高分子科学》2002,(3):225-229
A kind of novel heat-resistant, high performance engineering thermoplastic phthalazinone poly(aryl ether sulfoneketone) (PPESK) containing a carboxyl group in its side chain was prepared by the nucleophilic displacement reaction of 4-(4-hydroxylphenyl)-1(2H)-phthalazinone with di(4-chlorophenyl) sulfone, 4,4'-difluoro-benzophenone and phenolphthalin insulfolane in the presence of K_2CO_3 to produce high molecular weight polymers which can be dissolved in some polarsolvents such as chloroform and nitrobenzene at room temperature and can be easily can into flexible, yellowish andtransparent films. PPESK is an amorphous polymer having a decomposition temperature above 400℃, which indicates that ithas high thermal stability. At the same time, the thermal properties of PPESKs with dicyandiamide (DICY) as curing agentindicated that the heat-resistance properties of the PPESKs are improved after curing. The apparent activation energy (ΔE) ofthe cross-linking reaction and the reaction order (n) of PPESK/DICY were found to be 52.2 kJ/mol and ca. 1.0, respectively.Therefore, the cross-linking reaction is approximately a first order reaction. 相似文献
26.
A method is presented for the efficient computation of the representation matrices of the unitary group, U(n) in the Gelfand—Tsetlin basis (corresponding to the usual spin-symmetry adapted basis for an N electron CI). The present scheme is conceptually and computationally attractive in that it is formulated directly in terms of Weyl tableaux and also that it permits simultaneous basis vector generation and matrix element evaluation. In addition the basis vectors are ordered so that subsequent restriction to the three dimensional rotation group is facilitated. An illustrative example is also presented.Taken in part from a thesis submitted to the University of London in partial fulfilment of the requirements for the degree of PhD. 相似文献
27.
Radiation-induced polymerization of monomers, for example N-methacryl-oxysuccinimide (MASu) and diethylene glycol dimethacrylate (2G), in ethyl propionate, was performed from +25°C to –78°C. The copoly (MASu/2G) microspheres were obtained in MASu monomer compositions of 30 wt % or below. The average particle diameter of copoly(MASu/2G, 20/80 wt %) microspheres obtained at irradiation temperatures of 25°, 0°, and –43 °C were 0.81±0.29, 0.63±0.26, and 0.90±0.43 m, respectively. No microspheres were formed when irradiated at –78 °C. The reactivity of the succinimide groups on the surface of copoly(MASu/2G, 20/80 wt%) microspheres was checked by reacting with ethylene diamine. The maximal amount of reacting succinimide groups was 9.4±0.5 nol/g, which corresponds to about 1 % of the total number of succinimide groups in the microsphere. 相似文献
28.
The reaction of a rhodanine derivative (=(Z)-5-benzylidene-3-phenyl-2-thioxo-1,3-thiazolidin-4-one; 1) with (S)-2-methyloxirane (2) in the presence of SiO2 in dry CH2Cl2 for 10 days led to two diastereoisomeric spirocyclic 1,3-oxathiolanes 3 and 4 with the Me group at C(2) (Scheme 2). The analogous reaction of 1 with (R)-2-phenyloxirane (5) afforded also two diastereoisomeric spirocyclic 1,3-oxathiolanes 6 and 7 bearing the Ph group at C(3) (Scheme 3). The structures of 3, 4, 6, and 7 were confirmed by X-ray crystallography (Figs. 1 and 2). These results show that oxiranes react selectively with the thiocarbonyl group (CS) in 1. Furthermore, the nucleophilic attack of the thiocarbonyl S-atom at the SiO2-activated oxirane ring proceeds with high regio- and stereoselectivity via an SN2-type mechanism. 相似文献
29.
Leo P. Kadanoff Anthony Houghton Mehmet C. Yalabik 《Journal of statistical physics》1976,14(2):171-203
Approximate recursion relations which give upper and lower bounds on the free energy are described. Optimal calculations of the free energy can then be obtained by treating parameters within the renormalization equations variationally. As an example, a particularly simple lower bound approximation which preserves the symmetry of the Hamiltonian (the one-hypercube approximation) is described. The approximation is applied to both the Ising model and the Wilson-Fisher model. At the fixed point a parameter is set variationally and critical indices are calculated. For the Ising model the agreement with the exact results atd = 2 is surprisingly good, 0.1%, and is good atd=3 and evend=4. For the Wilson-Fisher model the recursion relation is reduced to a one-dimensional integral equation which can be solved numerically givingv=0.652 atd=3, or by expansion in agreement with the results of Wilson and Fisher to leading order in . The method is also used to calculate thermodynamic functions for thed = 2 Ising model; excellent agreement with the Onsager solution is found.Supported in part by the National Science Foundation under Grants Nos. MPS73-04886A01 and GH-41512 and by the Brown University Materials Research Laboratory supported by the National Science Foundation. M.C.Y. was supported by a grant from the Scientific and Technical Research Council of Turkey. 相似文献
30.
The authors introduce a notion of a weak graph map homotopy (they call it
M-homotopy), discuss its properties and applications. They prove that the weak graph
map homotopy equivalence between graphs coincides with the graph homotopy equivalence
defined by Yau et al in 2001. The difference between them is that the weak graph map
homotopy transformation is defined in terms of maps, while the graph homotopy transformation is defined by means of combinatorial operations. They discuss its advantages over
the graph homotopy transformation. As its applications, they investigate the mapping
class group of a graph and the 1-order MP-homotopy group of a pointed simple graph.
Moreover, they show that the 1-order MP-homotopy group of a pointed simple graph is
invariant up to the weak graph map homotopy equivalence. 相似文献