全文获取类型
收费全文 | 72949篇 |
免费 | 6795篇 |
国内免费 | 4098篇 |
专业分类
化学 | 24958篇 |
晶体学 | 231篇 |
力学 | 4669篇 |
综合类 | 1104篇 |
数学 | 32656篇 |
物理学 | 20224篇 |
出版年
2024年 | 132篇 |
2023年 | 654篇 |
2022年 | 2115篇 |
2021年 | 2031篇 |
2020年 | 1726篇 |
2019年 | 1858篇 |
2018年 | 1575篇 |
2017年 | 1636篇 |
2016年 | 1945篇 |
2015年 | 1817篇 |
2014年 | 2796篇 |
2013年 | 5254篇 |
2012年 | 3114篇 |
2011年 | 3738篇 |
2010年 | 3555篇 |
2009年 | 4219篇 |
2008年 | 4418篇 |
2007年 | 4484篇 |
2006年 | 3580篇 |
2005年 | 2974篇 |
2004年 | 2555篇 |
2003年 | 2619篇 |
2002年 | 4925篇 |
2001年 | 2306篇 |
2000年 | 1797篇 |
1999年 | 1614篇 |
1998年 | 1505篇 |
1997年 | 1224篇 |
1996年 | 1116篇 |
1995年 | 939篇 |
1994年 | 880篇 |
1993年 | 773篇 |
1992年 | 756篇 |
1991年 | 588篇 |
1990年 | 504篇 |
1989年 | 387篇 |
1988年 | 390篇 |
1987年 | 325篇 |
1986年 | 338篇 |
1985年 | 457篇 |
1984年 | 353篇 |
1983年 | 219篇 |
1982年 | 400篇 |
1981年 | 562篇 |
1980年 | 494篇 |
1979年 | 541篇 |
1978年 | 435篇 |
1977年 | 328篇 |
1976年 | 279篇 |
1973年 | 209篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
1.
Thalia Tsiaka Panagiotis Zoumpoulakis Vassilia J. Sinanoglou Constantinos Makris Georgios A. Heropoulos Antony C. Calokerinos 《Analytica chimica acta》2015
High-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE. 相似文献
2.
Azobenzene‐Functionalized Cage Silsesquioxanes as Inorganic–Organic Hybrid,Photoresponsive, Nanoscale,Building Blocks 下载免费PDF全文
Prof. Hongzhi Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4731-4738
Mono‐ and octa‐azobenzene‐functionalized cage silsesquioxanes were easily synthesized by the reaction of 4‐bromoazobenzene with monovinyl‐substituted octasilsesquioxane and cubic octavinylsilsesquioxane through the Heck coupling reaction. Excited‐state energies obtained from time‐dependent density functional theory (TDDFT) and the CAM‐B3LYP functional correlate very well with experimental trans–cis photoisomerization results from UV/Vis spectroscopy. These azobenzene‐functionalized cages exhibit good thermal stability and are fluorescent with maximum emission at approximately 400 nm, making them potential materials for blue‐light emission. 相似文献
3.
阐明了引入溶剂渗透因子的必要性,较详细地介绍了两种渗透因子及它们间的关系。 相似文献
4.
关于一类二次哈密尔顿系统在二次扰动下的极限环个数问题 总被引:2,自引:0,他引:2
本文研究了一类具有两个鞍点和一个中心的通用二次哈密尔顿向量场在二次扰动下的三参数开折,证明极限环的最小上界为2。 相似文献
5.
We employ a first-principles plane wave method with the
relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter
(HGH) scheme in the frame of DFT to calculate
the equilibrium lattice parameters and the thermodynamic properties of
AlB2 compound with hcp structure. The obtained lattice parameters are in
good agreement with the available experimental data and those calculated by
others. Through the quasi-harmonic Debye model, obtained successfully are
the dependences of the
normalized lattice parameters a/a0 and c/c0 on pressure P, the normalized
primitive cell volume V/V0 on pressure P, the variation of the thermal
expansion α with pressure P and temperature T, as well as the Debye
temperature \ThetaD and the heat capacity CV on pressure P and
temperature T. 相似文献
6.
7.
Shougo Higashi 《Surface science》2006,600(3):591-597
We have studied the individual adsorption of Mn and Bi, and their coadsorption on Cu(0 0 1) by low-energy electron diffraction (LEED). For Mn, we have determined the c(2 × 2) structure formed at 300 K, whose structure had been determined by several methods. We reconfirmed by a tensor LEED analysis that it is a substitutional structure and that a previously reported large corrugation (0.30 Å) between substitutional Mn and remaining surface Cu atoms coincides perfectly with the present value. In the individual adsorption of Bi, we have found a c(4 × 2) structure, which is formed by cooling below ∼250 K a surface prepared by Bi deposition of ∼0.25 ML coverage at 300 K where streaky half-order LEED spots appear. The c(4 × 2) structure has been determined by the tensor LEED analysis at 130 K and it is a substitutional structure. In the coadsorption, we found a c(6 × 4) structure, which has been determined by the tensor LEED analysis. It is very similar to the previously determined structure of the c(6 × 4) formed by coadsorption of Mg and Bi, and embedded MnBi4 clusters are arranged in the top Cu layer instead of MgBi4. Large lateral displacements of Bi atoms in the c(6 × 4)-(Mn + Bi) suggest that the Mn atoms undergo the size-enhancement caused by their large magnetic moment. 相似文献
8.
Mikhail Andramonov 《Journal of Global Optimization》2002,24(2):115-132
We consider applications of disjunctive programming to global optimization and problems with equilibrium constraints. We propose a modification of the algorithm of F. Beaumont for disjunctive programming problems and show its numerical efficiency. 相似文献
9.
Exact closed-form solutions are exhibited for the Hopf equation for stationary incompressible 3D Navier-Stokes flow, for the cases of homogeneous forced flow (including a solution with depleted nonlinearity) and inhomogeneous flow with arbitrary boundary conditions. This provides an exact method for computing two- and higher-point moments, given the mean flow. 相似文献
10.
Camillo Costantini 《Topology and its Applications》2006,153(7):1056-1078
For X a metrizable space and (Y,ρ) a metric space, with Y pathwise connected, we compute the density of (C(X,(Y,ρ)),σ)—the space of all continuous functions from X to (Y,ρ), endowed with the supremum metric σ. Also, for (X,d) a metric space and (Y,‖⋅‖) a normed space, we compute the density of (UC((X,d),(Y,ρ)),σ) (the space of all uniformly continuous functions from (X,d) to (Y,ρ), where ρ is the metric induced on Y by ‖⋅‖). We also prove that the latter result extends only partially to the case where (Y,ρ) is an arbitrary pathwise connected metric space.To carry such an investigation out, the notions of generalized compact and generalized totally bounded metric space, introduced by the author and A. Barbati in a former paper, turn out to play a crucial rôle. Moreover, we show that the first-mentioned concept provides a precise characterization of those metrizable spaces which attain their extent. 相似文献