全文获取类型
收费全文 | 3876篇 |
免费 | 83篇 |
国内免费 | 32篇 |
专业分类
化学 | 3081篇 |
晶体学 | 51篇 |
力学 | 61篇 |
数学 | 191篇 |
物理学 | 607篇 |
出版年
2022年 | 22篇 |
2021年 | 32篇 |
2020年 | 32篇 |
2019年 | 36篇 |
2018年 | 23篇 |
2017年 | 32篇 |
2016年 | 44篇 |
2015年 | 67篇 |
2014年 | 80篇 |
2013年 | 288篇 |
2012年 | 171篇 |
2011年 | 233篇 |
2010年 | 128篇 |
2009年 | 106篇 |
2008年 | 200篇 |
2007年 | 200篇 |
2006年 | 223篇 |
2005年 | 211篇 |
2004年 | 186篇 |
2003年 | 200篇 |
2002年 | 199篇 |
2001年 | 47篇 |
2000年 | 52篇 |
1999年 | 60篇 |
1998年 | 49篇 |
1997年 | 44篇 |
1996年 | 53篇 |
1995年 | 52篇 |
1994年 | 45篇 |
1993年 | 32篇 |
1992年 | 33篇 |
1991年 | 26篇 |
1990年 | 33篇 |
1989年 | 42篇 |
1988年 | 39篇 |
1987年 | 29篇 |
1986年 | 30篇 |
1985年 | 51篇 |
1984年 | 55篇 |
1983年 | 31篇 |
1982年 | 57篇 |
1981年 | 42篇 |
1980年 | 58篇 |
1979年 | 69篇 |
1978年 | 43篇 |
1977年 | 32篇 |
1976年 | 27篇 |
1975年 | 24篇 |
1974年 | 27篇 |
1973年 | 20篇 |
排序方式: 共有3991条查询结果,搜索用时 156 毫秒
31.
Ray K Nakahara H Sakamoto A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(1-2):103-107
The fluorescence lifetimes decays and picosecond time-resolved fluorescence spectra were measured to investigate the dynamics of the excited state of sulforhodamine B (SRB) molecules adsorbed in the mono- and multilayered Langmuir-Blodgett (LB) films of octadecylamine. Steady-state and time-resolved fluorescence spectroscopy reveals that the fluorescence lifetimes and contents of the monomer and dimers in the molecular organizates depend upon the concentration of the dye in the solution and the adsorption process. SRB dye molecules adsorbed in LB films have been imaged with scanning near-field optical microscopy (SNOM). This information is exploited to map the distribution with molecular spatial resolution. SNOM provide the visual evidence of the monomers and dimers of SRB in cationic LB films. 相似文献
32.
33.
A highly selective and sensitive method of fluorometry is described for determination of the fluoride ion at the parts per billion level via the ion-pair complex formation of the fluoride ion with an expanded prophyrin [2,23-diethyl-8,17-bis(2-ethoxycarbonylethyl)-3,7,12,13,18,22-hexamethylsapphyrin (H3sap)]. The ion-pair complex gives out an enhanced fluorescence intensity at 680 nm on excitation at 450 nm. Since the present method is based on a direct reaction of the fluoride ion with the sappyrin, a 200-fold amount of the aluminum (III) ion [10−4M (M = mol dm−3)] and a 2000-fold amount of the iron(III) ion (10−3M) over the fluoride ion did not interfere with determination of the fluoride ion at concentrations as low as 5 × 10−7M in the presence of 1,2-diaminocyclohexane-N,N,N′,N′-teraacetic acid. The proposed method was applied to determination of the fluoride ion in various water samples (tap water, river water, rain water, underground water, and hot spring water) and satisfactory results were obtained. 相似文献
34.
Masatoshi Oue Akira Ishigaki Keiichi Kimura Yousuke Matsui Toshiyuki Shono 《Journal of polymer science. Part A, Polymer chemistry》1985,23(7):2033-2042
Poly- and bis(thiacrown ether) derivatives in which some oxygen atoms of benzocrown ether moiety are replaced by sulfur atoms have been synthesized. Their cation-binding abilities were investigated by using the solvent extraction method. The poly- and bis(benzothiacrown ether)s showed great affinity for silver ion, being more excellent in the affinity than the corresponding monocyclic analogs. They, however, possess very poor cation-binding ability for alkali and alkaline-earth metal ions. The poly- and bis(thiacrown ether)s also bind mercuric ions effectively, whereas the corresponding monomeric analogs do not at all. 相似文献
35.
The INDO calculations were performed on the three azines: pyridazine, pyrimidine, and pyrazine. The cannonical molecular orbitais obtained by these calculations were then transformed into the localized molecular orbitals. With the use of the localized molecular orbitals, the variation in the lone-pair orbital energies of these molecules were pursued in the light of the through-space and/or the through-bond interactions between the specified localized molecular orbitals in a molecule selectively. The interactions were expressed by the summation of several terms: through-space, through-bond, through-virtuals and coupling terms. 相似文献
36.
M Sugiyama T Sakamoto K Tabata K Endo K Ito M Kobayashi H Fukumi 《Chemical & pharmaceutical bulletin》1989,37(8):2122-2131
Thiazolo[3,2-a]thieno[3,2-d]-, [3,4-d]- and [2,3-d]pyrimidin-5-one derivatives (6, 11 and 16), and polymethylene condensed thieno[3,2-d]-, [3,4-d]- and [2,3-d]pyrimidin-5-one derivatives (19-21), in which the oxygen atom of the oxazolidine moiety in 3 was replaced by a sulfur atom or methylene groups, were synthesized and evaluated for gastric antisecretory activity in pylorus-ligated rats. The structure-activity relationships of these compounds are discussed. 相似文献
37.
Akira Okubo Hiroyuki Kawai Toshiro Matsunaga Tatsuji Chuman Sunao Yamazaki Shozo Toda 《Tetrahedron letters》1980,21(42):4095-4096
T1 gives a clue to assign cis- and trans-methyl carbons in 2-methyl-1-propenyl moiety. 相似文献
38.
Yoshihiro Itoh Masamitsu Inoue Tomoko Takahashi Akira Hachimori Satoshi Suzuki 《Journal of polymer science. Part A, Polymer chemistry》1995,33(7):1069-1074
Alternating and random copolymers of 9-phenanthrylmethyl methacrylate or 2-(9-carbazolyl)ethyl methacrylate with styrene were synthesized and their fluorescence properties were examined. There was no noticeable difference in the spectral features of the alternating and random copolymers in tetrahydrofuran (THF), demonstrating that this type of polymers have no quenching sites in the polymer chains. The fluorescence quenching studies indicated that the alternating copolymers permitted singlet-state energy migration as efficiently as the corresponding random copolymers but less efficiently than the random copolymers with higher chromophore contents. These results strongly suggest that to be chromophores close to each other is most important for facilitation of an intramolecular energy migration. © 1995 John Wiley & Sons, Inc. 相似文献
39.
Akira Watanabe 《Tetrahedron letters》2004,45(33):6229-6233
Oxovanadium(V)(salen) complex 4 was found to catalyze Meerwein-Ponndorf-Verley cyanation of aliphatic aldehydes with good to high enantioselectivity. This cyanation showed a positive nonlinear effect. 相似文献
40.
Microgel-like poly(allyl methacrylate) (PAMA nanosphere) was prepared by the emulsion polymerization of AMA as the reactive crosslinked polymer nanosphere with abundant pendant allyl groups. The terpolymerization of PAMA nanosphere with allyl benzoate (ABz) and vinyl benzoate (VBz) was conducted in bulk using benzoyl peroxide as initiator at 80 °C. The gelation depended on the feed ABz/VBz molar ratio since the molecular weights of resulting poly(ABz-co-VBz)s that act as the bridges increased with an increase in the mole fraction of VBz in the feed monomer. Beyond the gel point, the sol was rapidly incorporated into the gel and the increasing tendency of the gel fraction became steeper from 70 to 95 mol% of VBz as a reflection of increased chain length of bridge between PAMA nanospheres. Moreover, the swelling ratio became lower with increasing the mole percentage of VBz in the feed monomer. These results would support the preferential incorporation of PAMA nanosphere into the gel and the longer bridge can capture more nanospheres to give a much shrunken gel. 相似文献