全文获取类型
收费全文 | 119415篇 |
免费 | 5978篇 |
国内免费 | 12279篇 |
专业分类
化学 | 76843篇 |
晶体学 | 1437篇 |
力学 | 3092篇 |
综合类 | 897篇 |
数学 | 27625篇 |
物理学 | 27778篇 |
出版年
2023年 | 789篇 |
2022年 | 2079篇 |
2021年 | 1957篇 |
2020年 | 2419篇 |
2019年 | 2925篇 |
2018年 | 2555篇 |
2017年 | 3187篇 |
2016年 | 3110篇 |
2015年 | 2668篇 |
2014年 | 3920篇 |
2013年 | 8249篇 |
2012年 | 7025篇 |
2011年 | 6413篇 |
2010年 | 5245篇 |
2009年 | 7067篇 |
2008年 | 7497篇 |
2007年 | 7793篇 |
2006年 | 7060篇 |
2005年 | 5720篇 |
2004年 | 5747篇 |
2003年 | 5029篇 |
2002年 | 6446篇 |
2001年 | 4289篇 |
2000年 | 3974篇 |
1999年 | 3874篇 |
1998年 | 3369篇 |
1997年 | 2486篇 |
1996年 | 1974篇 |
1995年 | 1792篇 |
1994年 | 1579篇 |
1993年 | 1307篇 |
1992年 | 1185篇 |
1991年 | 749篇 |
1990年 | 620篇 |
1989年 | 576篇 |
1988年 | 449篇 |
1987年 | 352篇 |
1986年 | 331篇 |
1985年 | 403篇 |
1984年 | 411篇 |
1983年 | 252篇 |
1982年 | 342篇 |
1981年 | 425篇 |
1980年 | 396篇 |
1979年 | 281篇 |
1978年 | 302篇 |
1977年 | 237篇 |
1976年 | 196篇 |
1975年 | 133篇 |
1974年 | 133篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
New thiazole derivatives were synthesized and fully characterized, then coordinated with PtCl4 salt. Also, the newly synthesized Pt(IV) complexes were investigated analytically (elemental and thermogravimetric analyses), spectrally (infrared, UV–visible, mass, 1H NMR, 13C NMR, X‐ray diffraction) as well as theoretically (kinetics, modeling and docking). The data extracted led to the establishment of the best chemical and structural forms. Octahedral geometry was the only formula proposed for all complexes, which is favorable for d6 systems. The molecular ion peaks from mass spectral analysis coincide with all analytical data, confirming the molecular formula proposed. X‐ray diffraction (XRD) and scanning electron microscopy (SEM) allowed discrimination of features between crystalline particles and other amorphous morphology. By applying Gaussian09 as well as HyperChem 8.2 programs, the best structural forms were obtained, as well as computed significant parameters. Computed parameters such as softness, hardness, surface area and reactivity led us towards application in two opposing pathways: tumor inhibition and oxidation activation. The catalytic oxidation for CO was conducted over PtO2, which was yielded from calcination of the most reactive complex. The success of catalytic role for synthesized PtO2 was due to its particulate size and surface morphology, which were estimated from XRD patterns and SEM images, respectively. The antitumor activity was tested versus HCT‐116 and HepG‐2 cell lines. Mild toxicity was recorded for two of the derivatives and their corresponding complexes. This degree of toxicity is more favorable in most cases, due to exclusion of serious side effects, which is coherently attached with known antitumor drugs. 相似文献
23.
Pan Huang Dawen Xu Robert M. Reich Felix Kaiser Boping Liu Fritz E. Kühn 《Tetrahedron letters》2019,60(24):1574-1577
A first example of an Et2Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis. 相似文献
24.
文[1]提出了两个DEA的逆问题,并用搜索法来解.而本文根据所证的定理,对每个问题一般只要解二、三个线性规划问题就能得到答案. 相似文献
25.
G. Panina 《Central European Journal of Mathematics》2003,1(2):157-168
All 3-dimensional convex polytopes are known to be rigid. Still their Minkowski differences (virtual polytopes) can be flexible
with any finite freedom degree. We derive some sufficient rigidity conditions for virtual polytopes and present some examples
of flexible ones. For example, Bricard's first and second flexible octahedra can be supplied by the structure of a virtual
polytope. 相似文献
26.
Pavan Mathur 《Journal of Chemical Sciences》2006,118(6):553-568
New tetradentatebis-benzimidazole ligands have been synthesized and utilized to prepare copper (II) complexes. Some of these copper (II) complexes
have been characterized structurally. The copper (II) in these complexes is found to possess varying geometries. A distorted
octahedral geometry is found with a highly unsymmetrical bidentate nitrate group. An unusual polymeric one-dimensional structure
is observed where copper (II) is in a distorted square pyramidal geometry with a monodentate nitrate ion, having long Cu-O
bond, while a distorted triagonal bipyramidal geometry is found with two carbonyl O atoms and a Cl atom in the equatorial
plane, and two benzimidazole imine N atoms occupy the axial position. These compounds are found to activate the cumylperoxyl
group, and this has been utilized in the facile oxidation of aromatic alcohols to aldehydes, where they act as catalysts with
large turnovers. The yields of the respective products vary from 32 to 65%. The role of molecular oxygen has been studied
and an attempt has been made to identify the “active copper species”. Activation of molecular oxygen has also been observed
and has been used for oxidative dealkylation of a hindered phenol, producing di-butyl quinones with yields of 20–25% and 10–12
fold catalytic turnover. Dihydroxybenzenes and substituted catechols are also readily oxidized to the corresponding quinones,
in oxygen-saturated solvents. Yields of 84% have been observed with 34-fold catalyst turnover, with di-t-butylcatechol. The activity of these copper (II) —bis-benzmidazolediamide compounds is reminiscent of the functioning of copper centres in galactose oxidase, tyrosinase and catechol
oxidase. 相似文献
27.
D. J. Plazek C. A. Bero S. Neumeister G. Floudas G. Fytas K. L. Ngai 《Colloid and polymer science》1994,272(11):1430-1438
By making creep and recoverable creep measurements of a nearly monodisperse low molecular weight poly(methyl phenyl siloxane) sample, we have found on decreasing temperature towardsT
g that there is continuously a change in the viscoelastic spectrum concomitant with a decrease of the steadystate recoverable compliance. This behavior is exactly the same as previously observed in low molecular weight poly(styrene), proving that this spectacular anomaly in the viscoelasticity of low molecular weight polymers is general and deserves an explanation. Photon correlation spectroscopic measurements performed on the same sample have extended the observation of the viscoelastic response to shorter times and the result corroborates the trend of variation established by the creep data.Dedicated to Prof.Dr. E. W. Fischer on his 65th Birthday. Prof.Dr. Fischer is known for his valuable contribution to fosterine, international collaboration of research in polymer science. This work is an example of his contribution because it would not be possible without him bringing us together. One of us (KLN) would like to take this opportunity to thank Prof. Dr. Fischer for his unwaiving support of the 1st (Crete) and the 2nd (Alicante) International Discussion Meeting on Relaxations in Complex Systems 相似文献
28.
29.
Peter Imkeller 《Probability Theory and Related Fields》1996,106(1):105-135
Summary. The analytic treatment of problems related to the asymptotic behaviour of random dynamical systems generated by stochastic
differential equations suffers from the presence of non-adapted random invariant measures. Semimartingale theory becomes accessible
if the underlying Wiener filtration is enlarged by the information carried by the orthogonal projectors on the Oseledets spaces
of the (linearized) system.
We study the corresponding problem of preservation of the semimartingale property and the validity of a priori inequalities
between the norms of stochastic integrals in the enlarged filtration and norms of their quadratic variations in case the random
element F enlarging the filtration is real valued and possesses an absolutely continuous law. Applying the tools of Malliavin’s calculus,
we give smoothness conditions on F under which the semimartingale property is preserved and a priori martingale inequalities are valid.
Received: 12 April 1995 / In revised form: 7 March 1996 相似文献
30.