全文获取类型
收费全文 | 37479篇 |
免费 | 1282篇 |
国内免费 | 7篇 |
专业分类
化学 | 21098篇 |
晶体学 | 165篇 |
力学 | 792篇 |
数学 | 6165篇 |
物理学 | 10548篇 |
出版年
2023年 | 205篇 |
2021年 | 301篇 |
2020年 | 487篇 |
2019年 | 317篇 |
2018年 | 440篇 |
2017年 | 426篇 |
2016年 | 963篇 |
2015年 | 824篇 |
2014年 | 914篇 |
2013年 | 2030篇 |
2012年 | 1578篇 |
2011年 | 1902篇 |
2010年 | 961篇 |
2009年 | 778篇 |
2008年 | 1816篇 |
2007年 | 1797篇 |
2006年 | 1573篇 |
2005年 | 1455篇 |
2004年 | 1168篇 |
2003年 | 987篇 |
2002年 | 893篇 |
2001年 | 751篇 |
2000年 | 665篇 |
1999年 | 451篇 |
1998年 | 404篇 |
1997年 | 400篇 |
1996年 | 508篇 |
1995年 | 454篇 |
1994年 | 473篇 |
1993年 | 557篇 |
1992年 | 461篇 |
1991年 | 342篇 |
1990年 | 379篇 |
1989年 | 311篇 |
1988年 | 324篇 |
1987年 | 335篇 |
1986年 | 299篇 |
1985年 | 474篇 |
1984年 | 457篇 |
1983年 | 423篇 |
1982年 | 434篇 |
1981年 | 443篇 |
1980年 | 401篇 |
1979年 | 362篇 |
1978年 | 408篇 |
1977年 | 388篇 |
1976年 | 340篇 |
1975年 | 322篇 |
1974年 | 309篇 |
1973年 | 316篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Söhnel T Brown R Kloo L Schwerdtfeger P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(14):3167-3173
The stability of gold iodides in the oxidation state +I and +III is investigated at the ab initio and density functional level using relativistic and nonrelativistic energy-adjusted pseudopotentials for gold and iodine. The calculations reveal that relativistic effects stabilize the higher oxidation state of gold as expected, that is Au2I6 is thermodynamically stable at the relativistic level, whilst at the nonrelativistic level the complex of two iodine molecules weakly bound to both gold atoms in Au2I2 is energetically preferred. The rather low stability of AuI3 with respect to dissociation into AuI and I2 will make it difficult to isolate this species in the solid state as (possibly) Au2I6 or detect it by matrix-isolation techniques. The monomer AuI3 is Jahn-Teller distorted from the ideal trigonal planar (D3h) form, but adopts a Y-shaped structure (in contrast to AuF3 and AuCl3), and in the nonrelativistic case can be described as I2 weakly bound to AuI. Relativistic effects turn AuI3 from a static Jahn-Teller system to a dynamic one. For the yet undetected gas-phase species AuI accurate coupled-cluster calculations for the potential energy curve are used to predict vibrational-rotational constants. Solid-state density functional calculations are performed for AuI and Au2I6 in order to predict cohesive energies. 相似文献
962.
H. Mocnik B. Arcimowicz W. Salmhofer L. Windholz G. H. Guthöhrlein 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,36(2):129-136
By investigating the hyperfine structure of 41 Ta I lines we could determine the magnetic hyperfine interaction constants A and the electric quadrupole interaction constants B of 25 even parity levels and 32 odd parity levels. Additionally, we could classify one line. With 78 dipole allowed transitions which we tried to excite by laser light we obtained neither optogalvanic nor fluorescence signals. Therefore we conclude that some of the Ta I levels, listed in commonly used tables [e.g. Moore, Ch.: Atomic energy levels. Vol. III. Natl. Bur. Stand. (U.S.) Circ. No. 467. Washington, D.C.: U.S. GPO 1949], do not exist. 相似文献
963.
It is possible to determine very high concentrations of nickel photometrically by means of ethylenediaminetetra-acetic acid, by working at a pH between 4.55 and 6.82. The absorption curves obtained for this complex are very reproducible; for these measurements an Elko II apparatus with filter S57E is used. High concentrations of ammoniacal salts hinder the measurement. The formation of the complex is not influenced by the anion of the compound of nickel used. The Lambert-Beer law is followed for strengths of nickel of 40 — 5000 mg/100 ml. This procedure is convenient for alloys rich in nickel. 相似文献
964.
J. Carlsson P. Jönsson L. Sturesson 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1990,16(2):87-90
The lifetimes of the silver 5p 2 P states have been measured with high accuracy by time-resolved laser spectroscopy using the delayed coincidence technique. Also, the hyperfine structure of107Ag and109Ag in these two states has been studied by observing quantum beats. 相似文献
965.
HPLC-separation of cis and trans monounsaturated fatty acids 总被引:1,自引:0,他引:1
Summary The chromatography of monounsaturated fatty acids as their methyl esters on silver nitrate-loaded HPLC-columns has been studied. The separation of cis- and trans-isomers was easily achieved even with columns of low performance. High-performance small-particle-columns treated with silver nitrate separated a large variety of monounsaturated cis and trans positional isomers. The influence of variable silver-loads on the selectivity of the system was studied and a survey of the distribution of positional trans C181 isomers in commercial margarines is given. 相似文献
966.
M. Trömel 《Journal of solid state chemistry》1980,35(1):90-98
The strong variability of bond length between Sb(III) or Te(IV) and oxygen is correlated with distances to more distant oxygen atoms in the trans position. Closer approach of the trans-oxygen atom leads to lengthening of the bond in question. Hyperbolic functions represent suitable approximations for the correlations and give the bond lengths on the average within 0.04 Å. The distance relations are discussed for various limiting coordinations corresponding to 3, 4, and 5. 相似文献
967.
W. Fleischhacker H. Markut F. Vieböck 《Monatshefte für Chemie / Chemical Monthly》1972,103(4):1066-1077
Zusammenfassung Beim Erhitzen von 14-Brom-codeinon-dimethylacetal (1) in absol. Methanol mit einer äquivalenten Menge Na2CO3 entstehen die drei isomeren Methoxycodeinon-acetale3, 4 und5 sowie die beiden Indolino-codeinonderivate6 und7. Die Strukturen und Konfigurationen der Verbindungen3–6 werden auf Grund der NMR- und IR-Spektren sowie durch Umwandlung in bekannte Verbindungen bewiesen.
Herrn Prof.E. Ziegler mit den besten Wünschen zum 60. Geburtstag gewidmet. 相似文献
The methanolysis of 14-bromo-codeinone dimethyl acetal
14-Bromocodeinone dimethyl acetal (1) reacts in methanol containing sodium carbonate (0.5 moles) to give the three isomeric methoxycodeinone acetals3, 4, and5 besides the indolino-codeinones6 and7. The structures and configurations of3–6 were established on the basis of NMR- and IR-spectroscopy and by conversion to known compounds.
Herrn Prof.E. Ziegler mit den besten Wünschen zum 60. Geburtstag gewidmet. 相似文献
968.
The complex generated from 1/2[Ir(OMe)(cod)]2 and 4,4'-di-tert-butyl-2,2'-bipyridine catalyzes the regioselective borylation of ferrocenes, CpMn(CO)3 and CpMo(CO)3CH3 with a stoichiometric amount of B2pin2. 相似文献
969.
The determination of quaternary ammonium ions by capillary electrophoresis (CE) is reviewed. The analytes include tetraalkylammonium and alkylbenzyldimethylammonium compounds frequently used as antiseptic and antibacterial agents as well as in various household products, several plant growth regulators and herbicides, by-products in bile acid sequestrants, and a range of anticholinergic drugs. Besides direct and indirect UV detection, hyphenation with electrospray mass spectrometry is particularly suited for quaternary ammonium ions and may lower the detection limits by two orders of magnitude. In comparison with established liquid chromatographic techniques, CE may exhibits superior separation efficiency. Applications in routine analysis have demonstrated that CE is reliable and robust enough to represent a real alternative to chromatography. 相似文献
970.
Klika KD Imrich J Danihel I Böhm S Kristian P Hamul'aková S Pihlaja K Koch A Kleinpeter E 《Magnetic resonance in chemistry : MRC》2005,43(5):380-388
The configuration and dynamic behavior of O-allyl-S-methyl-N-(acridin-9-yl)iminothiocarbonate (1) and its S-allyl-O-methyl regioisomer (2) were studied using quantum chemical calculations and by applying a novel graphical method to scatter maps obtained from MD simulations for evaluation of an NOE-weighted internuclear distance (r(NOE)). Energy calculations indicated that the Z configuration was predominant for each compound and, further, this was supported both by the calculated chemical shifts and the r(NOE). Both N-inversion- and rotation-type transition-state structures were also calculated for the E/Z isomerization process, the results indicating that the preferred interconversion mechanism for 1 is N-inversion, but contrastingly, interconversion via rotation is equally as probable as N-inversion for 2. This supports the notion that one or the other or both pathways can be active and each system needs to be assessed on a case-by-case basis. 相似文献