全文获取类型
收费全文 | 1669篇 |
免费 | 44篇 |
国内免费 | 5篇 |
专业分类
化学 | 1175篇 |
晶体学 | 10篇 |
力学 | 45篇 |
综合类 | 1篇 |
数学 | 229篇 |
物理学 | 258篇 |
出版年
2023年 | 13篇 |
2022年 | 30篇 |
2021年 | 49篇 |
2020年 | 42篇 |
2019年 | 34篇 |
2018年 | 30篇 |
2017年 | 34篇 |
2016年 | 49篇 |
2015年 | 40篇 |
2014年 | 53篇 |
2013年 | 88篇 |
2012年 | 95篇 |
2011年 | 103篇 |
2010年 | 71篇 |
2009年 | 66篇 |
2008年 | 93篇 |
2007年 | 99篇 |
2006年 | 74篇 |
2005年 | 79篇 |
2004年 | 70篇 |
2003年 | 46篇 |
2002年 | 55篇 |
2001年 | 14篇 |
2000年 | 19篇 |
1999年 | 10篇 |
1998年 | 10篇 |
1997年 | 13篇 |
1996年 | 14篇 |
1995年 | 20篇 |
1994年 | 17篇 |
1993年 | 16篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 14篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 14篇 |
1977年 | 6篇 |
1976年 | 12篇 |
1975年 | 6篇 |
1974年 | 12篇 |
1973年 | 7篇 |
1970年 | 8篇 |
1933年 | 5篇 |
排序方式: 共有1718条查询结果,搜索用时 15 毫秒
41.
By adopting the convention that shared double bonds in polycyclic conjugated hydrocarbons contribute with one -electron and unshared ones with two -electrons, a partition of -electrons in each ring (-electron content, EC) can be obtained by averaging over all Kekulé structures, which are assumed to have equal weights. This affords a simple measure of local aromaticity that is comparable with other such local aromaticity indices in polycyclic benzenoids. 相似文献
42.
A set of original, analytical equations useful for theoretical calculation of the electron paramagnetic resonance (EPR) signal intensity are presented for the multitude of sample shapes, which range from point-like, line-like, planar, rectangular, cubical, circular, cylindrical, spherical to an irregularly shaped sample. The samples can be situated at any available position within the prescribed part of the microwave cavity (a central cylinder of diameter 11 mm and length 23.5 mm, in either a Bruker single TE102 or double TE104 rectangular cavity, with the modulation coils situated in the left and right side cavity walls, which is connected to a X-band, field-modulated CW Bruker EPR spectrometer). The theoretical computations of EPR signal intensity can be used in the computer simulations in which: (i) the EPR signal intensity profiles are constructed; (ii) the optimal sample positions in the cavity to give a maximum value of signal intensity are found; (iii) the errors associated with sample positioning within the cavity when compared to a second sample of a different size, shape or position are studied. 相似文献
43.
Milan Ihnat 《Analytica chimica acta》1976,82(2):293-309
A Varian Techtron model 63 carbon rod atomizer is used for the atomic absorption spectrometric determination of nanogram quantities of selenium. The pronounced interferences from the matrices in biological digests can be obviated by isolating selenium from sample matrices by precipitation with ascorbic acid. The precision of the determination is improved by incorporating 5000 μg Ni ml?1 in the analytical solutions. Selenium at μg g?1 and sub-μg g?1 levels in a variety of biological samples can be determined. The detection limit is 25 ng Se g?1. 相似文献
44.
Erich Widmer Milan Soukup Reinhard Zell Emil Broger Hans Peter Wagner Marquard Imfeld 《Helvetica chimica acta》1990,73(4):861-867
Starting from the readily available, optically active (4R)-4-hydroxy-2,2,6-trimethylcyclohexanone ( 1 ), a new technical synthesis of (3R,3′R)-zeaxanthin is described. According to a 2(C9 + C6) + C10 = C40 construction scheme, the ketone 1 was first transformed with (E)-3-methylpent-2-en-4-yn-1-ol ( 5 ) into a C15-intermediate which, by a three-step sequence, could be converted into the known olefinic C15-Wittig salt 4 . Optimized conditions for the final Wittig reaction of 4 with the C10-dialdehyde 3 are discussed. Based on 1 , the overall yield of the entire technical process is ca. 40%. 相似文献
45.
Milan Milosević 《Mikrochimica acta》1988,95(1-6):137-139
Effect of front surface reflectance is incorporated into standard Kubelka-Munk theory of diffuse reflection. A method of obtaining the absorption coefficient independent of scattering coefficient is presented. 相似文献
46.
The catalytic efficiency of adenylyl cyclase activity of edema factor (EF) from Bacillus anthracis is enhanced by approximately 1000-fold upon its binding to mammalian protein calmodulin (CaM). A tandem cell-based and protein binding-based screen of a 10,000 member library identified a molecule that inhibits the EF-CaM interaction and therefore the adenylyl cyclase activity. A combination of fluorescence spectroscopy and photolabeling studies showed that the molecule targets the CaM binding region of EF. A series of related compounds were synthesized and evaluated to identify one compound, 4-[4-(4-nitrophenyl)-thiazolylamino]-benzenesulfonamide, that maintained activity against EF but showed minimal toxicity to two cultured cell lines. This compound represents an important reagent to study the role of EF in anthrax pathology and may represent a drug lead against anthrax infection. 相似文献
47.
Milan Melník Peter Mikuš 《Phosphorus, sulfur, and silicon and the related elements》2020,195(5):367-370
AbstractIn this review, the structural data of monomeric platinum(II) complexes with inner coordination spheres of Pt(η2-P2L)(SiL)2, Pt(η2-P2L)(η2-Si2L) and Pt(η2-P,SiL)2 are classified and analyzed. These complexes crystallize in three crystal systems: monoclinic (8 examples), triclinic (4 examples) and orthorhombic (4 examples). Distorted square-planar environments about the Pt(II) atoms are built up by combination of homobi-P,P with two monodentate Si donor ligands; homobi-PP with homo-Si,Si donor ligands, or heterobi-P,Si donor ligands. The chelating ligands create metallacycles with the following angles: 65.0° (SiOSi) < 83.1° (SiC2Si) < 85.2° (PC2P) < 88.8° (SiSi2Si)). The mean Pt-P and Pt-Si bond distances in Pt(η2-P2L)·(SiL)2 complexes are 2.319 and 2.365?Å; in Pt(η2-P2L)(η2-Si2L) the values are 2.316 and 2.360?Å. The complex [Pt{η2-Me2P(C2B10H10)SiMe2}2] exists in two isomeric forms, a monoclinic cis- and a triclinic trans-isomer. The structural data are compared and discussed with the complexes of inner coordination spheres: Pt(η2-P2L)(XL)2 (X?=?O, N, CN, BL, Cl, SL, SeL, Br, or I) and Pt(η2-P2L)(η2-X2L) (X?=?OL, NL, SL or SeL). 相似文献
48.
Coppens P Vorontsov II Graber T Kovalevsky AY Chen YS Wu G Gembicky M Novozhilova IV 《Journal of the American Chemical Society》2004,126(19):5980-5981
Using a stroboscopic technique, in which the molecule is repeatedly excited and the structural change is probed more than 5000 times per second immediately after excitation, we performed a 16 K time-resolved single-crystal study of the microsecond lifetime triplet state of the Cu(I)phenanthroline derivative[Cu(I)(dmp)(dppe)][PF6] (dppe = 1,2-bis(diphenylphosphino)ethane). The geometry changes on excitation differ for the two symmetry-independent molecules, but are in the same direction as calculated for an isolated reference molecule, although the flattening distortion in the crystal is significantly smaller, implying that the reorganization energy is greatly affected by the confining medium. 相似文献
49.
In this paper the 4-state latch bridge model proposed by Rembold and Murphy is expanded; first by incorporation of the analytical expression of Ca2+ dependent MLCK activation from the work of Kato et al. and second, by inclusion of the myosin dephosphorylation based on the Michaelis-Menten kinetics. The analysis of the proposed model and the comparison with the original model results as well as with the experimental data is presented. The model is able to predict the steady-state isometric stress and the myosin phosphorylation in dependence on steady cytosolic [Ca2+] as well as the temporal evolution of the system in dependence on the input Ca2+ signal in the form of biphasic transient, whereby our model results are in several aspects in better agreement with experimental observations. 相似文献
50.
Jan Vorlíek Milan Fara Frantiek Vydra 《Fresenius' Journal of Analytical Chemistry》1968,241(5):314-318
Summary Conditions for the magnesium determination in alkaline solution by EDTA titration with biamperometric indication were examined. The most preferable pH range was found to be above 9.6. A reliable determination can be carried out in the presence of Ca, Ni, Cu and Co up to the ratio of 11. In the case of higher concentrations of Cu and Ni masking with potassium cyanide can be used. In this case, however, a change of the titration curves occurs.A new method for the determination of water-hardness by biamperometric indication is proposed. It is rapid and accurate and meets the requirements of routine and research work (error: ±1%).
Part XV: Vorlíek, J., and P. Peták: Microchem. J. 12, 466–471 (1967). 相似文献
Zusammenfassung Die Bedingungen für die Magnesiumbestimmung in alkalischer Lösung durch Titration mit ÄDTA bei biamperometrischer Endpunktsanzeige wurden untersucht. Der günstigste pH-Bereich liegt über 9,6. Zuverlässige Bestimmungen können in Gegenwart von Ca, Ni, Cu und Co bis zum Verhältnis 11 ausgeführt werden. Höhere Konzentrationen an Cu oder Ni können mit KCN maskiert werden, wobei allerdings eine Umkehrung der Kurven auftritt.Ein Verfahren zur Wasserhärtebestimmung mit biamperometrischer Indikation wird vorgeschlagen, das schnell durchzuführen ist und genaue Werte liefert (Fehler ±1%).
Part XV: Vorlíek, J., and P. Peták: Microchem. J. 12, 466–471 (1967). 相似文献