全文获取类型
收费全文 | 2772篇 |
免费 | 115篇 |
国内免费 | 21篇 |
专业分类
化学 | 2300篇 |
晶体学 | 20篇 |
力学 | 18篇 |
数学 | 168篇 |
物理学 | 402篇 |
出版年
2023年 | 24篇 |
2022年 | 10篇 |
2021年 | 30篇 |
2020年 | 43篇 |
2019年 | 56篇 |
2018年 | 32篇 |
2017年 | 30篇 |
2016年 | 61篇 |
2015年 | 77篇 |
2014年 | 69篇 |
2013年 | 141篇 |
2012年 | 181篇 |
2011年 | 217篇 |
2010年 | 125篇 |
2009年 | 114篇 |
2008年 | 200篇 |
2007年 | 197篇 |
2006年 | 156篇 |
2005年 | 165篇 |
2004年 | 168篇 |
2003年 | 126篇 |
2002年 | 136篇 |
2001年 | 38篇 |
2000年 | 43篇 |
1999年 | 31篇 |
1998年 | 36篇 |
1997年 | 24篇 |
1996年 | 29篇 |
1995年 | 31篇 |
1994年 | 29篇 |
1993年 | 27篇 |
1992年 | 22篇 |
1991年 | 21篇 |
1990年 | 16篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1987年 | 11篇 |
1986年 | 24篇 |
1985年 | 28篇 |
1984年 | 26篇 |
1983年 | 8篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1975年 | 6篇 |
1973年 | 3篇 |
1972年 | 5篇 |
1970年 | 3篇 |
排序方式: 共有2908条查询结果,搜索用时 31 毫秒
991.
Matsuda Y Kobayashi M Annaka M Ishihara K Takahara A 《Langmuir : the ACS journal of surfaces and colloids》2008,24(16):8772-8778
The dimensions and intermolecular interactions of a surface-grafted and unbound free polyampholyte, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), were estimated in aqueous solutions with various ionic strengths. Free linear PMPC was synthesized by atom-transfer radical polymerization (ATRP), and static light scattering (SLS) and dynamic light scattering (DLS) were carried out for the PMPC solutions with various concentrations of NaCl, c s. The hydrodynamic radius R H and the second virial coefficient A 2 of PMPC were independent of c s (0-0.5 M), though both R H and A 2 of polyampholytes usually strongly depend on the ionic strength. PMPC-immobilized silica nanoparticles (PMPC-SiNP) were also synthesized by surface-initiated ATRP, and DLS was carried out as for the solutions of linear PMPC to investigate the dependence of the dimensions of PMPC immobilized on a solid surface on the ionic strength. The molecular weight and surface density of PMPC immobilized on SiNP were estimated from the results obtained by GPC, NMR, and thermogravimetric analysis. The independence of R H of PMPC-SiNP was also observed, but its magnitude was larger than that of linear PMPC, although the molecular weight of PMPC immobilized on SiNP was smaller than that of linear PMPC. The larger dimension of PMPC immobilized on SiNP was explained by the excluded volume effect between the immobilized polymer chains. 相似文献
992.
Takashi Kubo Hidezumi Nagata Masato Takeuchi Masaya Matsuoka Masakazu Anpo Atsushi Nakahira 《Research on Chemical Intermediates》2008,34(4):339-346
Pt nanocrystal-supported titanate nanotubes as a photocatalyst were prepared by hydrothermal treatment and subsequent heat-treatment
in H2 atmosphere (H2 reduction) of a mixture of these titanate nanotubes and H2PtCl6. TEM results showed that Pt nanoparticles (a few nm in diameter and 5 to 10 nm in length) with good crystallinity were entrapped
inside titanate naotubes and were closely precipitated on the surface of titanate nanotubes. These Pt nanocrystal-supported
titanate nanotubes possessed the high ability for HCHO decomposition. 相似文献
993.
Kojima C Hirano Y Yuba E Harada A Kono K 《Colloids and surfaces. B, Biointerfaces》2008,66(2):246-252
Gold nanoparticles (Au NPs), which are extremely useful materials for imaging and photothermal therapy, typically require a drug delivery system to transport them to the affected tissue and into the cells. Since liposomes are approved as drug carriers, complexes of liposomes with Au NPs were considered ideal solutions to deliver Au NPs to the target site in vivo. In this study, we prepared complexes of various liposomes with Au NPs via physical absorption and characterized them. The time dependency of the surface plasmon resonance of this complex, which is a unique property of Au NPs, shows that the liposomes promote the formation of stable dispersions of Au NPs under isotonic conditions, even though intact Au NPs aggregate immediately. From a release assay of calcein from liposomes and transmission electron microscopy analysis, the Au NPs were complexed with liposomes without membrane disruption. These complexes could be formed by using cationic liposomes and polyethylene glycol-modified liposomes, as well as by using phosphatidylcholine liposomes, which are useful for drug and gene delivery. We proposed this kind of complex as a nanomedicine with diagnostic and therapeutic ability. 相似文献
994.
Recent progress in the synthesis of nanostructured silica-based materials through the self-assembly process using well-designed
alkoxysilane precursors is presented. Alkoxysilanes with covalently attached hydrophobic organic tails become amphiphilic
when hydrolyzed to form silanol groups, leading to the formation of various mesostructures upon evaporation of solvents. The
precursors having large oligosiloxane heads are particularly important because of their ability to form cylindrical assemblies,
providing a direct pathway to ordered porous silica by removal of the organic groups. Our recent research includes (i) templated-synthesis
of hierarchically ordered structures and (ii) design of molecules having chemically cleavable bonds to generate pores without
calcination. 相似文献
995.
Doi Y Ikeda A Akiyama M Nagano M Shigematsu T Ogawa T Takeya T Nagasaki T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(29):8892-8897
Water-soluble fullerenes have attracted attention as promising compounds that have been used to forge new paths in the field of photo-biochemistry. To prepare water-soluble fullerenes, we employed lipid-membrane-incorporated fullerenes (LMICx; x=60 or 70) by using the fullerene exchange method from a gamma-cyclodextrin (gamma-CD) cavity to vesicles. LMIC60 have low toxicity in the dark and engender cell death by photoirradiation (lambda>350 nm). Furthermore, the photodynamic activity of LMIC70 is 4.7-fold that of LMIC60 for the same photon flux (lambda>400 nm). One of the reasons for the higher phototoxicity of LMIC70 is the higher generation of singlet oxygen (1O2) in LMIC70 than in LMIC60. The difference between LMIC60 and LMIC70 is considered to be simply derived from the amount of light absorption in the 400-700 nm region that is suitable for photodynamic therapy (PDT). To the best of our knowledge, this is the first case in which biological activity of C70 and its derivatives toward HeLa cells has been assayed. 相似文献
996.
Taisuke Nakanaga Hidekazu Nagai Atsushi Suzuki Yukio Fujiwara Hidehiko Nonaka 《Journal of photochemistry and photobiology. A, Chemistry》2008,197(2-3):266-272
Multiphoton ionization and the subsequent dissociation process of metal cluster complexes Os3(CO)12 and Ir4(CO)12, prepared in a supersonic jet, were studied by means of multiphoton ionization with time-of-flight (TOF) mass detection. The ionization energies of Os3(CO)12 and Ir4(CO)12 were determined to be 7.95 and 8.3 eV, respectively, from the laser wavelength at the ionization threshold. The coordination energies of Os3(CO)12+ and Ir4(CO)12+ ions were also determined to be 1.6 and 1.2 eV, respectively, from the excitation energy needed to cause the appearance of fragment ions. The observed values agreed reasonably well with the ones calculated by using the density functional theory method. 相似文献
997.
Meier DM Urakawa A Turrà N Rüegger H Baiker A 《The journal of physical chemistry. A》2008,112(27):6150-6158
Molecular interactions between cinchonidine (CD) and 2-methyl-2-hexenoic acid (MHA) have been studied by means of NMR, ATR-IR MES, DFT, and ab initio molecular dynamics. These interactions are of particular interest due to their pivotal role in the chiral induction occurring in the heterogeneous catalytic asymmetric hydrogenation of alpha,beta-unsaturated acids. The population density of the Open(3) conformer of CD, the most populated one at room temperature in apolar solvents, considerably increased to a maximum by addition of MHA to CD in toluene. The CD-MHA complex showed prominent symmetric and asymmetric carboxylate stretching vibrations in the regions of 1350-1410 and 1520-1580 cm(-1), respectively. DFT calculations revealed that these vibrational frequencies are expected to significantly shift depending on the chemical surrounding of MHA, that is, the hydrogen bond network. Earlier postulated 1:1 binding between CD and MHA was considered unlikely; instead, a dynamic equilibrium involving the MHA monomer and dimer, the 1:3 and possibly 1:2 CD-MHA complexes, were rationalized. Stable CD-MHA structures suggested by DFT calculations are the "1:3, halfN, cyclic" and the "1:3, halfN, cyclic tilted" complexes, where three MHA molecules are connected in wire by hydrogen bonding, two having direct interaction with CD. The confinement of CD's torsional motions in the complexes, leading to a slightly distorted Open(3) conformer via specific hydrogen-bonding interactions, was clearly reproduced by ab initio molecular dynamics, and the stable and flexible nature of the interaction was verified. Theoretical IR spectra of the complexes reproduced the characteristic vibrational frequencies of the complexes observed experimentally, supporting the stability of the 1:3 and implying the possibility of even higher molecular weight CD-MHA complexes. 相似文献
998.
Kobayashi S Itomi K Morino K Iida H Yashima E 《Chemical communications (Cambridge, England)》2008,(26):3019-3021
A facile method for synthesizing diverse optically active polymers with different backbone structures was developed by the polymerization of an optically active aromatic azide bearing an acetylene unit with a rhodium catalyst followed by the click reaction of the pendant azides or by the click polymerization of the monomer. 相似文献
999.
Nobusawa K Ikeda A Tanaka Y Hashizume M Kikuchi J Shirakawa M Kitahara T Fujita N Shinkai S 《Chemical communications (Cambridge, England)》2008,(15):1801-1803
We solubilised SWNTs of short length using a mechanochemical high-speed vibration milling (HSVM) through formation of complexes between the SWNTs and chelate complexes; the mixture formed a network structure on mica. 相似文献
1000.
Makarova EA Shimizu S Matsuda A Luk'yanets EA Kobayashi N 《Chemical communications (Cambridge, England)》2008,(18):2109-2111
meso-Aryl tribenzosubporphyrin was synthesized by a self-condensation of 3-benzalphthalimidine and by a condensation of phthalimide with phenylacetic acid using boric acid as a template; the compounds derived were characterized based on a wide range of spectroscopic and electrochemical methods. 相似文献