全文获取类型
收费全文 | 2602篇 |
免费 | 105篇 |
国内免费 | 9篇 |
专业分类
化学 | 1614篇 |
晶体学 | 9篇 |
力学 | 36篇 |
数学 | 250篇 |
物理学 | 581篇 |
无线电 | 226篇 |
出版年
2023年 | 17篇 |
2021年 | 30篇 |
2020年 | 31篇 |
2019年 | 42篇 |
2018年 | 19篇 |
2017年 | 37篇 |
2016年 | 72篇 |
2015年 | 70篇 |
2014年 | 63篇 |
2013年 | 119篇 |
2012年 | 128篇 |
2011年 | 139篇 |
2010年 | 83篇 |
2009年 | 72篇 |
2008年 | 117篇 |
2007年 | 152篇 |
2006年 | 102篇 |
2005年 | 92篇 |
2004年 | 83篇 |
2003年 | 74篇 |
2002年 | 101篇 |
2001年 | 53篇 |
2000年 | 50篇 |
1999年 | 24篇 |
1998年 | 30篇 |
1997年 | 38篇 |
1996年 | 42篇 |
1995年 | 32篇 |
1994年 | 35篇 |
1993年 | 35篇 |
1992年 | 33篇 |
1991年 | 32篇 |
1990年 | 30篇 |
1989年 | 36篇 |
1988年 | 22篇 |
1987年 | 22篇 |
1986年 | 16篇 |
1985年 | 27篇 |
1984年 | 34篇 |
1983年 | 24篇 |
1982年 | 22篇 |
1981年 | 20篇 |
1980年 | 31篇 |
1979年 | 21篇 |
1978年 | 49篇 |
1977年 | 27篇 |
1976年 | 33篇 |
1975年 | 32篇 |
1974年 | 21篇 |
1973年 | 30篇 |
排序方式: 共有2716条查询结果,搜索用时 15 毫秒
121.
Thanks to the successive use of two esterases with different regioselectivities and conventional organic chemistry we have synthesized (1R,2S) and (1S,2S) dehydrocoronamic acids. 相似文献
122.
I. A. Rodin A. N. Stavrianidi A. V. Braun O. A. Shpigun 《Moscow University Chemistry Bulletin》2013,68(3):127-142
Ginsenosides are the main bioactive compounds of the Panax plant genus. Ginseng and its analogues are widely used to produce traditional medicines in China, Korea, Japan, United States, and the Russian Far East. For more than 40 years, many researchers developed methods of identifying and determining and ginsenosides in plant tissues, extracts, and commercial products. Various extraction methods were used to isolate these compounds from plant materials. The separation of ginsenosides was conducted with methods such as gas chromatography, thin-layer chromatography, and high-performance liquid chromatography (HPLC). The HPLC method was used predominantly. Spectrophotometric and fluorescent monitoring and, later, light scattering and mass-spectrometry coupled with HPLC were used to determine ginsenosides. The most recent variants of these methods are presented in this review, together with a critical evaluation of the published results. 相似文献
123.
124.
2D difference gel electrophoresis reference map of a Fusarium graminearum nivalenol producing strain
Matias Pasquali Tommaso Serchi Jenny Renaut Lucien Hoffmann Torsten Bohn 《Electrophoresis》2013,34(4):505-509
Fusarium graminearum is widely studied as a model for toxin production among plant pathogenic fungi. A 2D DIGE reference map for the nivalenol‐producing strain 453 was established. Based on a whole protein extract, all reproducible spots were systematically picked and analyzed by MALDI‐TOF/TOF, leading to the identification of 1102 protein species. The obtained map contributes to the annotation of the genome by identifying previously nondescribed hypothetical proteins and will serve as a reference for future studies aiming at deciphering F. graminearum biology and chemotype diversity. 相似文献
125.
Torsten Kerber Rachel Nathaniel Kerber Xavier Rozanska Philippe Sautet Paul Fleurat‐Lessard 《Journal of computational chemistry》2013,34(13):1155-1163
We present a new software to easily perform QM:MM and QM:QM' calculations called QMX. It follows the subtraction scheme and it is implemented in the Atomic Simulation Environment (ASE). Special attention is paid to couple molecular calculations with periodic boundaries approaches. QMX inherits the flexibility and versatility of the ASE package: any combination of methods namely force field, semiempirical, first principle, and ab initio, can be used as hybrid potential energy surface (PES). Its ease of use is demonstrated by considering the adsorption of Al2Cl3Me3 on silica surface and by combining different levels of theory (from standard DFT to MP2 calculations) for the so‐called High Level cluster with standard PW91 density functional theory calculations for the Low Level environment. It is shown that the High Level cluster must contain the silanol group close to the aluminum atoms. The bridging adsorption is favored by 58 kJ mol?1 at the MP2:PW91 level with respect to the terminal position. Using large clusters at the MP2:PW91 level, it is shown that PW91 calculations are sufficient for structure optimization but that embedded methods are required for accurate energy profiles. © 2013 Wiley Periodicals, Inc. 相似文献
126.
Abstract Five homologous series of diurethanes containing mesogenic moieties were synthesized by addition reactions of ω-alkenols to aromatic diisocyanates. The thermal behaviour of the compounds was studied by differential scanning calorimetry and on the hot stage of a polarizing microscope. Thermotropic liquid crystal behaviour was found for the diurethanes having a central core of more than two aromatic rings. Smectic C mesophases were observed for the derivatives of 4,4″-p-terphenylene and nematic mesophases for the diurethanes containing a di(4-phenylene)terephthalate unit. The compounds of both series possess high transition temperatures and narrow mesomorphic ranges. 相似文献
127.
Let U(g) be the enveloping algebra of a finite dimensional reductive Lie algebra g over an algebraically closed field of prime characteristic. Let U?,P(s:) be the simply connected quantum enveloping algebra at the root of unity ? , of a complex semi-simple finite dimensional Lie algebra s:. We show, by similar proofs, that the centers of both are factorial. While the first result was established by R. Tange [32] (by different methods), the second one confirms a conjecture in [4]. We also provide a general criterion for the factoriality of the centers of enveloping algebras in prime characteristic. 相似文献
128.
Sabrina I. Kallne Thomas Braun 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(35):9465-9469
An unprecedented reaction pathway for the borylation of SCF3‐containing arenes using [Rh(Bpin)(PEt3)3] (pin=pinacolato) is reported. Catalytic processes were developed and the functionalizations proceed under mild reaction conditions. The C H activations occur with a unique regioselectivity for the position ortho to the SCF3 group, which apparently serves as directing group. Borylated SCF3 compounds can serve as versatile building blocks. 相似文献
129.
130.
The evaluation of a fully automated quantitative proton nuclear magnetic resonance spectroscopy (qNMR) processing program, including the determination of its processing uncertainty, and the calculations of the combined uncertainty of the qNMR result, is presented with details on the use of a trimmed purity average. Quantitative NMR spectra (1359) were collected over a 4-month period on various concentrations of pseudoephedrine HCl dissolved in D2O (0.0610 to 93.60 mg/mL) containing maleic acid (the internal standard) to yield signal-to-noise ratios ranging from 3 to 72,000 for analyte integral regions. The resulting 5436 purities exhibited a normal distribution about the best estimate of the true value. The median absolute deviation (MAD) statistical method was used to obtain a model of uncertainty relative to the signal-to-noise of the analyte’s integral peaks. The model was then tested using different concentrations of known purity chloroquine diphosphate. qNMR results of numerous illicit heroin HCl samples were compared to those obtained by capillary electrophoresis. Graphical Abstract
? 相似文献