全文获取类型
收费全文 | 1802篇 |
免费 | 32篇 |
国内免费 | 6篇 |
专业分类
化学 | 945篇 |
晶体学 | 46篇 |
力学 | 68篇 |
数学 | 312篇 |
物理学 | 469篇 |
出版年
2022年 | 21篇 |
2021年 | 26篇 |
2020年 | 20篇 |
2019年 | 18篇 |
2016年 | 24篇 |
2015年 | 20篇 |
2014年 | 27篇 |
2013年 | 72篇 |
2012年 | 72篇 |
2011年 | 69篇 |
2010年 | 45篇 |
2009年 | 46篇 |
2008年 | 75篇 |
2007年 | 82篇 |
2006年 | 74篇 |
2005年 | 69篇 |
2004年 | 39篇 |
2003年 | 45篇 |
2002年 | 44篇 |
2001年 | 34篇 |
2000年 | 45篇 |
1999年 | 15篇 |
1998年 | 21篇 |
1997年 | 19篇 |
1996年 | 36篇 |
1995年 | 39篇 |
1994年 | 34篇 |
1993年 | 31篇 |
1992年 | 29篇 |
1991年 | 15篇 |
1990年 | 32篇 |
1989年 | 22篇 |
1988年 | 15篇 |
1987年 | 20篇 |
1986年 | 26篇 |
1985年 | 27篇 |
1984年 | 30篇 |
1983年 | 25篇 |
1982年 | 28篇 |
1981年 | 26篇 |
1980年 | 23篇 |
1979年 | 18篇 |
1978年 | 28篇 |
1977年 | 35篇 |
1976年 | 22篇 |
1975年 | 23篇 |
1974年 | 20篇 |
1973年 | 18篇 |
1972年 | 16篇 |
1970年 | 15篇 |
排序方式: 共有1840条查询结果,搜索用时 15 毫秒
71.
W. Koen C. Bollig H. Strauss M. Schellhorn C. Jacobs M. J. D. Esser 《Applied physics. B, Lasers and optics》2010,99(1-2):101-106
We developed a compact Ho:YLF oscillator–amplifier system in a novel setup to utilise the unpolarised pump power from a fibre laser efficiently, and produced 21.3 mJ at 1 kHz, with an M 2 better than 1.1. The amplified energies agreed well with the predicted values from a two dimensional rotational symmetric amplifier model that we developed. The model considers upconversion losses and ground-state depletion, as well as the spatial distribution of the pump beam. 相似文献
72.
This study reveals that Fourier transform infrared is an effective analytical tool in probing the extent of hydrolysis of
cerium and gadolinium acetylacetonates dissolved in methanol. It is found that these acetylacetonates have relatively fast
hydrolysis rates at the early stage of hydrolysis (<6 h). However, their hydrolysis rates become very slow beyond 6-h of hydrolysis
and decrease to near zero after 55-h of hydrolysis. As a result, hydrolysis cannot be completed even after 170 h at room temperature.
These phenomena suggest that the first and second acetylacetone ligands chelated to Ce3+ and Gd3+ ions can actually be hydrolyzed with relative ease at room temperature, similar to alkoxide ligands. It is the last acetylacetone
ligand that is very difficult to be hydrolyzed. 相似文献
73.
Ewa Gniazdowska Przemysław Koźmiński Leon Fuks 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(2):1171-1177
Two types of technetium-99m complexes: (i) with the Hynic ligand linked to Substance P(1–11) and (ii) of the type ‘4 + 1’ consisting of tetradentate tripodal chelator tris(2-mercaptoethyl)-amine and monodentate isocyanide ligand previously coupled with Substance P(1–11), have been prepared on the n.c.a. scale. The obtained conjugates exhibit different lipophilicity and high stability in neutral aqueous solutions, even in the presence of excess concentration of histidine/cysteine competitive standard ligands. The conjugate (99mTc(NS3)(CN))2–SP containing two technetium-99m species in the molecule may be expected to be an extremely good diagnostic radiopharmaceutical. 相似文献
74.
N. De Geyter A. Sarani T. Jacobs A. Yu. Nikiforov T. Desmet P. Dubruel 《Plasma Chemistry and Plasma Processing》2013,33(1):165-175
In this work, poly-ε-caprolactone samples are modified by an atmospheric pressure plasma jet in pure argon and argon/water vapour mixtures. In a first part of the paper, the chemical species present in the plasma jet are identified by optical emission spectroscopy and it was found that plasmas generated in argon/0.05 % water vapour mixtures show the highest emission intensity of OH (A–X) at 308 nm. In a subsequent section, plasma jet surface treatments in argon and argon/water vapour mixtures have been investigated using contact angle measurements and X-ray photoelectron spectroscopy. The polymer samples modified with the plasma jet show a significant decrease in water contact angle due to the incorporation of oxygen-containing groups, such as C–O, C=O and O–C=O. The most efficient oxygen inclusion was however found when 0.05 % of water vapour is added to the argon feeding gas, which correlates with the highest intensity of OH (X) radicals. By optimizing the OH (X) radical yield in the plasma jet, the highest polymer modification efficiency can thus be obtained. 相似文献
75.
David W. Gammon Henok H. Kinfe Dirk E. De Vos Pierre A. Jacobs Bert F. Sels 《Journal of carbohydrate chemistry》2013,32(3):141-157
Protected glycals and α‐1,2‐cyclopropanated sugars were converted in high yields and selectivities in less than 2 h at low temperatures to 2‐deoxy‐2‐iodoglycosyl acetates or novel 2‐deoxy‐2‐iodomethylglycosyl acetates using the simple, inexpensive reagent mixture of ammonium iodide, hydrogen peroxide, and acetic anhydride/acetic acid in acetonitrile. The protected glycals gave rise to 2‐deoxy‐2‐bromoglycosyl acetates when ammonium bromide was used instead of the iodide, although longer reaction times were required and selectivities were inferior. Other simple olefins such as styrene and indene were also converted to their corresponding 1,2‐trans‐iodoacetates. 相似文献
76.
Abdirahman Elmi Fatouma Mohamed Abdoul-Latif Rosella Spina Franois Dupire Stphanie Philippot Champy Marie-France Hugues Jacobs Dominique Laurain-Mattar 《Molecules (Basel, Switzerland)》2021,26(10)
For the first time, the study of the antioxidant activity, the characterization of the phytoconstituants, and the evaluation of in vitro and in vivo toxicity of A. djiboutiensis leave and latex are performed. The antioxidant activity of both latex (ADL) and the methanolic extract of leaves (ADM) is determined using 1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis 3-ethylbenzothiazoline-6-sulphonic acid (ABTS) scavenging radical methods and ferric reducing/antioxidant power (FRAP) assay. The phytochemical study of latex is done using Liquid Chromatography-Mass Spectrometry (LC-MS/MS) and a molecular networking-based approach. The evaluation of in vivo toxicity is performed on mice by oral gavage with a suspension of ADL. Our results show that weak antioxidant activity of ADL and ADM in opposition to their high polyphenol, 83.01 mg and 46.4 mg expressed in gallic acid equivalent (GAE)/g of dry weight (DW), respectively, and flavonoid contents 13.12 mg and 4.25 mg expressed in quercetin equivalent (QE)/g dry weight (DW), respectively. Using the Global Natural Products Social Molecular Networking (GNPS) website, nine (9) anthraquinones derivatives, ten (10) chromones derivatives, two (2) flavonols/ chromones isomers are annotated in the molecular network. The treated mice do not display abnormalities in their general physical appearance and biochemistry parameters, compared to the controls. Only glucose and calcium levels are slightly higher in male treated mice compared to the vehicles. 相似文献
77.
We investigate the phase diagram of the anisotropic spin-1/2 triangular lattice antiferromagnet, with interchain diagonal exchange J' much weaker than the intrachain exchange J. We find that fluctuations lead to a competition between (commensurate) collinear antiferromagnetic and (zigzag) dimer orders. Both states differ in symmetry from the spiral order known to occur for larger J', and are therefore separated by quantum phase transitions from it. The zero-field collinear antiferromagnet is succeeded in a magnetic field by magnetically ordered spin-density-wave and cone phases, before reaching the fully polarized state. Implications for the anisotropic triangular magnet Cs2CuCl4 are discussed. 相似文献
78.
Leon N. Schneider Dr. Eva-Maria Tanzer Krauel Dr. Carl Deutsch Dr. Klaus Urbahns Tobias Bischof Kristina A. M. Maibom Dr. Johannes Landmann Dr. Fabian Keppner Dr. Christoph Kerpen Dr. Michael Hailmann Ludwig Zapf Tanja Knuplez Dr. Rüdiger Bertermann Dr. Nikolai V. Ignat'ev Prof. Dr. Maik Finze 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(42):10973-10978
Fluorinated groups are essential for drug design, agrochemicals, and materials science. The bis(trifluoromethyl)amino group is an example of a stable group that has a high potential. While the number of molecules containing perfluoroalkyl, perfluoroalkoxy, and other fluorinated groups is steadily increasing, examples with the N(CF3)2 group are rare. One reason is that transfer reagents are scarce and metal-based storable reagents are unknown. Herein, a set of CuI and AgI bis(trifluoromethyl)amido complexes stabilized by N- and P-donor ligands with unprecedented stability are presented. The complexes are stable solids that can even be manipulated in air for a short time. They are bis(trifluoromethyl)amination reagents as shown by nucleophilic substitution and Sandmeyer reactions. In addition to a series of benzylbis(trifluoromethyl)amines, 2-bis(trifluoromethyl)amino acetate was obtained, which, upon hydrolysis, gives the fluorinated amino acid N,N-bis(trifluoromethyl)glycine. 相似文献
79.
80.
Gram‐Scale Enantioselective Formal Synthesis of Morphine through an ortho–para Oxidative Phenolic Coupling Strategy
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Matthieu Tissot Dr. Robert J. Phipps Dr. Catherine Lucas Dr. Rafael M. Leon Dr. Robert D. M. Pace Dr. Tifelle Ngouansavanh Prof. Matthew J. Gaunt 《Angewandte Chemie (International ed. in English)》2014,53(49):13498-13501
A gram‐scale catalytic enantioselective formal synthesis of morphine is described. The key steps of the synthesis involve an ortho–para oxidative phenolic coupling and a highly diastereoselective “desymmetrization” of the resulting cyclohexadienone that generates three of the four morphinan ring junction stereocenters in one step. The stereochemistry is controlled from a single carbinol center installed through catalytic enantioselective hydrogenation. These transformations enabled the preparation of large quantities of key intermediates and could support a practical and scalable synthesis of morphine and related derivatives. 相似文献