全文获取类型
收费全文 | 4713篇 |
免费 | 108篇 |
国内免费 | 32篇 |
专业分类
化学 | 3121篇 |
晶体学 | 22篇 |
力学 | 103篇 |
数学 | 624篇 |
物理学 | 983篇 |
出版年
2023年 | 32篇 |
2022年 | 59篇 |
2021年 | 80篇 |
2020年 | 57篇 |
2019年 | 73篇 |
2018年 | 63篇 |
2017年 | 55篇 |
2016年 | 107篇 |
2015年 | 104篇 |
2014年 | 107篇 |
2013年 | 193篇 |
2012年 | 230篇 |
2011年 | 316篇 |
2010年 | 163篇 |
2009年 | 145篇 |
2008年 | 253篇 |
2007年 | 270篇 |
2006年 | 226篇 |
2005年 | 220篇 |
2004年 | 185篇 |
2003年 | 167篇 |
2002年 | 141篇 |
2001年 | 78篇 |
2000年 | 73篇 |
1999年 | 65篇 |
1998年 | 47篇 |
1997年 | 42篇 |
1996年 | 62篇 |
1995年 | 59篇 |
1994年 | 49篇 |
1993年 | 77篇 |
1992年 | 55篇 |
1991年 | 55篇 |
1990年 | 46篇 |
1989年 | 51篇 |
1988年 | 41篇 |
1987年 | 55篇 |
1986年 | 36篇 |
1985年 | 58篇 |
1984年 | 51篇 |
1983年 | 34篇 |
1982年 | 51篇 |
1981年 | 44篇 |
1980年 | 33篇 |
1979年 | 48篇 |
1978年 | 50篇 |
1976年 | 38篇 |
1975年 | 44篇 |
1974年 | 48篇 |
1973年 | 33篇 |
排序方式: 共有4853条查询结果,搜索用时 15 毫秒
21.
The solutions of linear polymers traditionally used for DNA separation have been employed for the capillary electrophoresis (CE) of diastereomers of chemically modified DNA. The selectivity of diastereomeric separation of the phosphorothioate (PS) and 2'-O-methylated (2-OMe) PS oligonucleotides depends on the nature of the polymer additive in the CE background electrolyte. The selectivity of separation for different polymers increases in the line: linear polyacrylamide < polyethylene glycol < polyvinyl pyrrolidone. The separation of oligomer diastereomers was shown to be primarily based on the hydrophobic interaction with the polymer network that acts as a pseudostationary phase. While lowering the temperature resulted in improved separation, the addition of organic modifiers such as formamide, methanol or acetonitrile counteracts the solute adsorption on the polymer network, and decreases the selectivity of DNA diastereoseparation. The effect of molecular mass and concentration of the polymer on the separation selectivity was investigated. 相似文献
22.
23.
Let A(X) be the space defined by Waldhausen whose homotopy groups define the algebraic K-groups of the space X and let
. Here (X) denotes the free loop space of X and Q denotes the functor . For X = Y, the suspension of a connected space Y, we shall prove that the homotopy fibers Ã(X), B(X) of the maps A(X) A (point), B(X) B (point) are equivalent as infinite loop spaces. 相似文献
24.
25.
26.
We report a general method for the synthesis of free-standing, self-assembled MOF monolayers (SAMMs) at an air–water interface using polymer-brush coated MOF nanoparticles. UiO-66, UiO-66-NH2, and MIL-88B-NH2 were functionalized with a catechol-bound chain-transfer agent (CTA) to graft poly(methyl methacrylate) (PMMA) from the surface of the MOF using reversible addition-fragmentation chain transfer polymerization (RAFT). The polymer-coated MOFs were self-assembled at the air–water interface into monolayer films ∼250 nm thick and capable of self-supporting at a total area of 40 mm2. Mixed-particle films were prepared through the assembly of MOF mixtures, while multilayer films were achieved through sequential transfer of the monolayers to a glass slide substrate. This method offers a modular and generalizable route to fabricate thin-films with inherent porosity and sub-micron thickness composed of a variety of MOF particles and functionalities.We report a general method for the synthesis of free-standing, self-assembled MOF monolayers (SAMMs) at an air–water interface using polymer-brush coated MOF nanoparticles. 相似文献
27.
Monolayers of single-stranded DNA (ssDNA) immobilized on surfaces form the basis of a number of important biotechnology applications, including DNA microarrays and biosensors. The organization of ssDNA as layer on a solid substrate allows one to investigate various properties of the DNA in a controlled manner and to use DNA for analytical applications as well as for exploring futuristic schemes for molecular electronics. It is commonly assumed that the adsorbed DNA layer contains some structural water and the cations. Here we show, based on XPS studies, that when monolayers of ssDNA are formed from sodium phosphate buffer and washed thoroughly, no Na+ signal is detected. A finite concentration of ions is observed when the DNA is made from a solution of Mg2+ ions, but it is still only a fifth of what it would be if all the phosphate ions were fully neutralized by the metal cations. 相似文献
28.
Analytical procedures for quantification of peptides in pharmaceutical research by liquid chromatography–mass spectrometry 总被引:6,自引:0,他引:6
John H Walden M Schäfer S Genz S Forssmann WG 《Analytical and bioanalytical chemistry》2004,378(4):883-897
Peptide quantification by liquid chromatography–mass spectrometry (LC–MS) combines the high resolving power of reversed-phase (RP) chromatography with the excellent selectivity and sensitivity of mass spectrometric detection. On the basis of comprehensive practical experience in the analysis of small molecules, pharmaceutical research is developing technologies for analysis of a growing number of peptidic drug candidates. This article is a detailed review of procedures based on LC–MS techniques for quantitative determination of peptides. With the focus on pharmaceutical applications several technologies for sample preparation, various aspects of peptide chromatography, important characteristics of ESI–MS, selectivity of MS-detection modes, the large variability of internal standards, and modern instrumentation are discussed. The demand for reliable, robust, sensitive, and accurate methods is discussed using numerous examples from the literature, complemented by experiments and results from our laboratory. 相似文献
29.
In an approach to SRS-A and analogues thereof, the key (5, 6)-epoxy alcohol and its 6-epimer were prepared starting from -araboascorbic acid and -diethyl tartrate, respectively. 相似文献
30.
Polyethylene based composites are attractive materials for advanced circuit board applications because of their unique combination of properties: low dielectric constant and loss factor, light weight, high flexural modulus and low thermal expansion coefficient controlled in all spatial directions. This investigation describes a process to consolidate chopped fibers of ultra‐high molecular weight polyethylene concurrently with its bonding to a copper foil. Bonding is affected by a thin sheet of low‐density polyethylene, incorporating a crosslinking agent with a concentration gradient across the sheets thickness. In this single step process, the composite material is formed and bonded to the metal foil, achieving good adhesion without the use of extraneous glue. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献