全文获取类型
收费全文 | 4541篇 |
免费 | 167篇 |
国内免费 | 3篇 |
专业分类
化学 | 2982篇 |
晶体学 | 23篇 |
力学 | 81篇 |
数学 | 907篇 |
物理学 | 718篇 |
出版年
2023年 | 37篇 |
2022年 | 37篇 |
2021年 | 59篇 |
2020年 | 73篇 |
2019年 | 77篇 |
2018年 | 98篇 |
2017年 | 87篇 |
2016年 | 137篇 |
2015年 | 138篇 |
2014年 | 159篇 |
2013年 | 322篇 |
2012年 | 338篇 |
2011年 | 351篇 |
2010年 | 198篇 |
2009年 | 166篇 |
2008年 | 281篇 |
2007年 | 264篇 |
2006年 | 226篇 |
2005年 | 237篇 |
2004年 | 204篇 |
2003年 | 155篇 |
2002年 | 150篇 |
2001年 | 53篇 |
2000年 | 42篇 |
1999年 | 43篇 |
1998年 | 30篇 |
1997年 | 32篇 |
1996年 | 42篇 |
1995年 | 26篇 |
1994年 | 17篇 |
1992年 | 19篇 |
1991年 | 23篇 |
1990年 | 23篇 |
1989年 | 12篇 |
1988年 | 17篇 |
1987年 | 19篇 |
1985年 | 30篇 |
1984年 | 29篇 |
1983年 | 19篇 |
1982年 | 34篇 |
1981年 | 27篇 |
1980年 | 42篇 |
1979年 | 30篇 |
1978年 | 30篇 |
1977年 | 30篇 |
1976年 | 29篇 |
1975年 | 28篇 |
1974年 | 16篇 |
1973年 | 17篇 |
1964年 | 13篇 |
排序方式: 共有4711条查询结果,搜索用时 10 毫秒
991.
Mamdouh W Uji-I H Dulcey AE Percec V De Feyter S De Schryver FC 《Langmuir : the ACS journal of surfaces and colloids》2004,20(18):7678-7685
We have investigated the two-dimensional ordering of chiral and achiral monodendrons at the liquid-solid interface. The chiral molecules self-assemble into extended arrays of dimers. As expected, the R enantiomer forms the mirror image type pattern of the chiral two-dimensional structure formed by the S enantiomer. A racemic mixture applied from solution onto the substrate undergoes spontaneous segregation: the enantiomers separate on the surface and appear in different domains. In contrast to the chiral molecules, the achiral analogue self-assembles into cyclic tetramers. Moreover, the pattern formed by the achiral molecule strongly depends on the solvent used. In the case of 1-phenyloctane, solvent molecules are coadsorbed in a 2:1 (dendron:solvent) ratio whereas in 1-octanol, no solvent molecules are coadsorbed. By the appropriate solvent choice, the distance between the potential "supramolecular containers" can be influenced. 相似文献
992.
J. Ignacio Andrés Rosario Herranz M. Teresa García López 《Journal of heterocyclic chemistry》1984,21(4):1221-1224
The synthesis of 6-methyl-7-(β-D-ribofuranosyl)imidazo[4,5-d]-v-triazin-4-one (8-methyl-2-azainosine ( 2) ) and 6-methyl-7-(β-D-glucopyranosyl)imidazo[4,5-d]-v-triazin-4-one ( 5 ) by diazotization of 5-amino-1-(β-D-ribofuranosyl)-2-methylimidazole-4-carboxamide ( 1 ) and diazotization of 5-amino-1-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-2-methylimidazole-4-carboxamide ( 3 ), followed by deacetylation of the resulting compound 4 , is described. The preparation of 6-methyl-5-(β-D-ribofuranosyl)imidazo[4,5-d]-v-triazin-4-one ( 10 ) and 6-methyl-5-(β-D-glucopyranosyl)imidazo[4,5-d]-v-triazin-4-one ( 11 ) by glycosylation of 6-methylimidazo[4,5-d]-v-triazin-4-one (8-methyl-2-azahypoxanthine, ( 7) ) is also described. Structural assignments were made on basis of analytical and 1H-nmr and uv spectral data. 相似文献
993.
Boezio AA Pytkowicz J Côté A Charette AB 《Journal of the American Chemical Society》2003,125(47):14260-14261
We have shown that Me-DuPHOS monoxide (BozPHOS) is a very effective ligand in the copper-catalyzed addition of dialkylzinc to N-phosphinoylimines providing access to alpha-chiral amines. The new ligand is particularly effective for the addition of the lesser reactive dimethylzinc. The major advantages of this process are high yields, broad substrate scope, and high enantioselectivities with low catalyst loading (3 mol %). 相似文献
994.
A novel microsystem device in poly(dimethylsiloxane) (PDMS) for MS detection is presented. The microchip integrates sample injection, capillary electrophoretic separation, and electrospray emitter in a single substrate, and all modules are fabricated in the PDMS bulk material. The injection and separation flow is driven electrokinetically and the total amount of external equipment needed consists of a three-channel high-voltage power supply. The instant switching between sample injection and separation is performed through a series of low-cost relays, limiting the separation field strength to a maximum of 270 V/cm. We show that this set-up is sufficient to accomplish electrospray MS analysis and, to a moderate extent, microchip separation of standard peptides. A new method of instant in-channel oxidation makes it possible to overcome the problem of irreversibly bonded PDMS channels that have recovered their hydrophobic properties over time. The fast method turns the channel surfaces hydrophilic and less prone to nonspecific analyte adsorption, yielding better separation efficiencies and higher apparent peptide mobilities. 相似文献
995.
Axel Klein Prof. Dr. Natascha Hurkes André Kaiser Wolfram Wielandt 《无机化学与普通化学杂志》2007,633(10):1659-1665
The red colour of the novel organonickel complex [(dppz)Ni(Mes)Br] (dppz = dipyrido[3,2‐a:2′,3′‐c]phenazine, Mes = 2,4,6‐trimethylphenyl) originates from long‐wavelength MLCT/L′LCT charge transfer bands. However, luminescence in dilute solution comes presumably from the 3π‐π* (phenazine) excited state. The red‐shifted emission exhibited in concentrated solutions is assigned to dimers. In the solid state emission is quenched. The crystal structure reveals two different types of π‐π stacking along the crystallographic a axis. 相似文献
996.
András Krámli Nándor Simányi Domokos Szász 《Probability Theory and Related Fields》1986,72(4):603-617
Summary By developing further the method of our previous paper [2] based upon the Keldysh expansion of the resolvent, the asymptotics of the stationary distribution of a random walk with internal states between two barriers at 0 and L is obtained when L.Work supported by the Central Research Fund of the Hungarian Academy of Sciences (Grant No. 476/82) 相似文献
997.
The variationally stable method of Gao and Starace [B. Gao and A. F. Starace, Phys. Rev. Lett. 61, 404 (1988); Phys. Rev. A 39, 4550 (1989)] has been applied for the first time to the study of multiphoton processes in molecular systems. The generalization in theory is presented, as well as the calculation of properties such as the static and dynamic polarizabilities of the hydrogen molecule and the generalized two-photon ionization cross section. The Schwinger variational iterative method [R. R. Lucchese and V. McKoy, Phys. Rev. A 21, 112 (1980)] has been applied in the achievement of the photoelectron wave function, while a Hartree-Fock representation has been used for the target. This research has been motivated by the scarceness of ab initio calculations of molecular multiphoton ionization cross sections in the literature. 相似文献
998.
A finite element method in Cartesian coordinates in three dimensions is described to solve the time-dependent Schrödinger equation for H
2
+
in the presence of time-dependent electromagnetic fields. The ionization rates, nonlinear optical polarizabilities and harmonic generation spectrum of H
2
+
have been calculated for field directions parallel or perpendicular to the hydrogen molecule ion axis. Comparisons of the present numerical results with previously published calculations show that the finite element method reproduces perturbative results and can treat nonperturbativity arbitrary intense short pulses as it includes automatically both bound and continuum electronic states. 相似文献
999.
Aqueous ammonium sulfide was found to be an ideal substitute for hydrogen sulfide for the thiolysis of activated amides. High yields of the corresponding thioamides were obtained for a broad range of substrates, using two different procedures that are both operationally simple and inexpensive, as well as amenable to large-scale preparation. Preliminary results indicate that aqueous ammonium sulfide may also replace hydrogen sulfide in the synthesis of thionoesters from amides. 相似文献
1000.
A computer program is described for the estimation of carbon-13 chemical shifts. It automatically selects and applies the additivity rules appropriate for the individual carbon atoms of the structure entered. Besides connectivity, the configuration and conformation can be entered and evaluated for some types of structure. All rule parameters (base values and increments) can be extended or modified by the user. New rules based on the corresponding linear relationships can also be added. A test against 168 807 known chemical shifts shows that the implemented rules cover roughly 97% of all cases. The standard deviation of the predicted values relative to the experimental values is 5.5 ppm. 相似文献