全文获取类型
收费全文 | 2400篇 |
免费 | 46篇 |
国内免费 | 1篇 |
专业分类
化学 | 1333篇 |
晶体学 | 16篇 |
力学 | 32篇 |
数学 | 154篇 |
物理学 | 912篇 |
出版年
2020年 | 28篇 |
2019年 | 22篇 |
2016年 | 37篇 |
2015年 | 24篇 |
2014年 | 34篇 |
2013年 | 93篇 |
2012年 | 84篇 |
2011年 | 76篇 |
2010年 | 56篇 |
2009年 | 51篇 |
2008年 | 111篇 |
2007年 | 92篇 |
2006年 | 105篇 |
2005年 | 97篇 |
2004年 | 82篇 |
2003年 | 51篇 |
2002年 | 48篇 |
2001年 | 53篇 |
2000年 | 43篇 |
1999年 | 24篇 |
1998年 | 27篇 |
1997年 | 34篇 |
1996年 | 40篇 |
1995年 | 32篇 |
1994年 | 42篇 |
1993年 | 56篇 |
1992年 | 49篇 |
1991年 | 25篇 |
1990年 | 36篇 |
1989年 | 25篇 |
1988年 | 25篇 |
1987年 | 40篇 |
1986年 | 34篇 |
1985年 | 36篇 |
1984年 | 39篇 |
1983年 | 23篇 |
1981年 | 21篇 |
1980年 | 24篇 |
1979年 | 17篇 |
1978年 | 30篇 |
1977年 | 40篇 |
1976年 | 33篇 |
1975年 | 28篇 |
1974年 | 22篇 |
1973年 | 35篇 |
1970年 | 20篇 |
1957年 | 30篇 |
1956年 | 16篇 |
1955年 | 29篇 |
1954年 | 21篇 |
排序方式: 共有2447条查询结果,搜索用时 15 毫秒
121.
The known CEPA variants CEPA (v) withv = 0,1,2,3 and two new ones withv = 4, 5 are compared both formally and for various numerical examples with CP-MET. The main conclusions are: 1. In those situations
where both CP-MET and the CEPA variants are justified (i.e. for “good” closed shell states) the correlation energies obtained
with the 7 different schemes differ very little (by something like ±2%), with CEPA (1) closest to CP-MET (difference usually
a fraction of 1%) and CEPA (4) nearly as close; this is rather insensitive to whether one uses canonical or localized orbitals.
Even CEPA (3) is not too far from CP-MET, which confirms an earlier suggestion of Kelly. 2. In those cases where one of the
7 schemes fails (e.g. due to near degeneracy as in covalent molecules at large internuclear distances) the other 6 usually
fail as well, though CEPA (0) is then somewhat poorer than the other schemes. Then no longer CEPA (1) but rather CEPA (3)
is closest to CP-MET and then all schemes converge much better in a localized representation. 3. CEPA (2) usually leads to
best agreement with experiment since it simulates to some extent triple substitutions. In none of the studied examples does
CP-MET show a significant superiority as compared to the other schemes. Possible improvements to extend the domain of applicability
of these methods are discussed. 相似文献
122.
R.C. Greenwood C.W. Reich H.A. Baader H.R. Koch D. Breitig O.W.B. Schult B. Fogelberg A. B?cklin W. Mampe T. Von Egdy K. Schreckenbach 《Nuclear Physics A》1978,304(2):327-428
The level structure of 158Gd has been studied using the prompt γ-rays and conversion electrons emitted following neutron capture in 157Gd. The γ-ray energy and intensity measurements were made using both Ge(Li) detectors and a curved-crystal spectrometer. Conversion-electron energy and intensity measurements were made using two separate magnetic spectrometers: one to measure the primary electron spectrum and the other to measure the lower energy secondary electron spectrum. Some γ-γ coincidence measurements were also made among the secondary γ-rays. From these data, a neutron separation energy of 7937.1 ± 0.5 keV has been determined for 158Gd. A level scheme containing 59 excited states with energies < 2.25 MeV, for which de-excitation modes have been identified, is proposed for 158Gd. Many of these states have been grouped into rotational bands. A total of thirteen excited rotational bands with band-head energies below 2.0 MeV are contained in the level scheme. Features of the proposed level scheme include: the Kπ = 0?, 1? and 2? octupole-vibrational bands with band-head energies of 1263, 977 and 1793 keV, respectively; the γ-vibrational band at 1187 keV; three excited Kπ = 0+ bands with band-head energies of 1196, 1452 and 1743 keV; several two-quasiparticle bands with band-head energies in keV (and Kπ assignments) of 1380 (4+), 1636 (4?), 1847 (1+), 1856 (1?), 1920 (4+) and 1930 (1+). An analysis of (d, p) reaction data is presented which permits definite two-quasiparticle configuration assignments to be made to most of these latter bands. Evidence is presented which suggests strong mixing of some two-neutron and two-proton bands. A phenomenological four-band mixing analysis is made of the energy and E2 transition-probability data for the ground-state band and the three lowest-lying excited collective positive-parity bands. Good agreement with experiment is obtained. A Coriolis-mixing analysis of the octupole bands has been carried out and good agreement with the data on level energies and E1 transition probabilities to the ground-state band has been achieved. Values of Z, the ratio of the E1 transition matrix element with ΔK = 1 to that with ΔK = 0, involving the octupole bands and the first four 0+ bands are derived. For three of these 0+ bands, absolute values of these matrix elements are deduced. An interesting alternation in the sign of Z is observed for these four 0+ bands. 相似文献
123.
D. Grunenberg D. Sommer und K. H. Koch 《Fresenius' Journal of Analytical Chemistry》1984,319(6-7):665-669
Zusammenfassung Die Emissionsspektrometrie mit Grimmanregungsquelle (GDOS) liefert rationell und einfach zu interpretierende Tiefenprofile. Es können sowohl dünnste Schichten von 2 nm als auch aufgebrachte Metallbeläge bis zu 100 m untersucht werden. Art und Verteilung der Elemente in den Schichten werden innerhalb weniger Minuten nachgewiesen und durch Vergleich mit Standardreferenzmaterialien quantifiziert.Damit stellt die Oberflächenanalytik mittels GDOS ein wichtiges, in vielen Anwendungsfällen unentbehrliches Hilfsmittel bei der Verfahrensentwicklung und Produktcharakterisierung metallischer Werkstoffe dar.
Examples for the characterisation of coated metal surfaces by a GDOS-rapid method
Summary The glow discharge optical spectrometry (GDOS) produces depth profiles in a simple and economical way. Thinnest layers of about 2 nm as well as metal coatings up to 100 m can be analysed. Type and distribution of the elements in coatings are identified and determined within a few minutes by comparing the signals obtained with those of standard reference samples.Hence, the GDOS-surface analysis method proves to be an important and in many cases an undispensable auxiliary means in connection with the improvement of production processes and the characterisation of the metallic products.相似文献
124.
J.A. Pinston W. Mampe R. Roussille K. Schreckenbach D. Heck H.G. Börner H.R. Koch S. Andre D. Barneoud 《Nuclear Physics A》1979,321(1):25-44
Gamma and electron spectra following thermal neutron capture on 99Tc have been studied with a bent-crystal spectrometer, Ge(Li) and Si(Li) detectors and a magnetic spectrometer. Prompt and delayed γ-γ coincidences with Ge(Li) detectors have been performed. A level scheme is proposed for 100Tc comprising 21 excited states up to 640 keV. The binding energy of the last neutron in 100Tc was deduced. For most levels, spin and parity values were assigned. Two isometric transitions of respective half-lives 10.2 and 4.6 μs have been identified using the 100Mo(d, 2n)100Tc reaction with a pulsed beam of deuterons. From the comparison of the present (n, γ) study and the collaborative study of the 99Tc(d, p) reaction, several members of the multiplets , , and have been identified. 相似文献
125.
Professor Dr.-Ing. R. Hackstein F. Koch 《Mathematical Methods of Operations Research》1980,24(8):B221-B238
Zusammenfassung Bei deterministischen Netzplantechnik-Modellen erfolgt die Terminierung der einzelnen Vorgänge in der Regel unter der Annahme, da\ die vorgegebenen Vorgangsdauern konstant sind. Fa\t man dagegen diese Dauern als minimale Zeitabstände auf, so lassen sich zusätzliche Aussagen über die Auswirkungen von Vorgangsdehnungen bzw. -unterbrechungen ermitteln. Darüber hinaus können höhere Pufferzeiten bzw. kürzere Projektdauern erzielt werden.
Dr.-Ing., Dipl.-Wirtsch.-Ing.Friedhelm Koch war zur Zeit der Erstellung dieses Manuskripts Mitarbeiter im selben Institut; er ist heute Mitarbeiter der NETRONIC GmbH in Aachen-Walheim. 相似文献
Summary In deterministic network models the given durations of activities are usually assumed to be constant for time analysis. If those durations are interpreted as minimal durations, additional assertions about expanding resp. interrupting activities are possible. Moreover, greater floats resp. shorter project durations can be achieved.
Dr.-Ing., Dipl.-Wirtsch.-Ing.Friedhelm Koch war zur Zeit der Erstellung dieses Manuskripts Mitarbeiter im selben Institut; er ist heute Mitarbeiter der NETRONIC GmbH in Aachen-Walheim. 相似文献
126.
127.
Abstract The question of the emission of pseudoscalar bosons (axions) in nuclear deexcitation processes and their decay into two photons was studied with a rotatable multi detector system at the power reactor Biblis A. Assuming an axion mass of 250 keV and the standard model decay rate we obtain (1.0 ± 1.0) × 1O?10 for the ratio of the numbers of axions and Ml γ- ray transitions in the reactor core. This is ~ 10?5 of the model prediction. 相似文献
128.
S. Meyer und O. G. Koch 《Fresenius' Journal of Analytical Chemistry》1957,158(6):434-438
Zusammenfassung Es wird ein Schnellverfahren zur maßanalytischen Bestimmung des Arsens beschrieben. Das Arsen wird als Chinolinarsenmolybdat gefällt, der Niederschlag in 0,1 n Natronlauge gelöst und der NaOH-überschuß mit 0,1 n Salzsäure zurücktitriert. Das Verfahren eignet sich für Arsenmengen bis herab zu 0,01 mg As. Die Reproduzierbarkeit beträgt im Mittel ±0,010 mg As bei einem Zeitbedarf von 20 min für eine Einzelbestimmung.An dieser Stelle möchten wir Herrn R. Seiler für die gewissenhafte Durchführung der Versuche unseren Dank aussprechen. 相似文献
129.
Ondeykal JG Herath KB Jayasuriya H Polishook JD Bills GF Dombrowski AW Mojena M Koch G DiSalvo J DeMartino J Guan Z Nanakorn W Morenberg CM Balick MJ Stevenson DW Slattery M Borris RP Singh SB 《Molecular diversity》2005,9(1-3):123-129
The chemokines (CXCL9, CXCL10 and CXCL11) and associated CXCR3 receptor are expressed during the inflammatory process from multiple sclerosis, atherosclerosis or organ transplantation resulting in the recruitment of lymphocytes leading to tissue damage. It is hypothesized that blocking of the ligand/CXCR3 receptor interaction has potential to provide opportunity for development of agents that would block tissue rejection. In this paper, four classes of natural product inhibitors (IC50 ranging 0.1–41 M) have been described that block the CXCR3 receptor interaction of IP-10 ligand. These include a cyclic thiopeptide (duramycin), polyketide glycosides (roselipins), steroidal glycosides (hypoglausin A and dioscin) and a novel alkyl pyridinium alkaloid that were isolated by bioassay-guided fractionation of the organic extracts derived from actinomycete, fungal, plant and marine sources and discovered using 125 I IP-10/CXCR3 binding assay. Duramycin was the most potent with an IC50 of 0.1 M. Roselipins 2A, 2B and 1A showed IC50 values of 14.6, 23.5, and 41 M, respectively. Diosgenin glycosides dioscin, hypoglaucin A and kallstroemin D exhibited IC50 values of 2.1, 0.47 and 3 M, respectively. A novel cyclic 3-alkyl pyridinium salt isolated from a sponge displayed a binding IC50 of 0.67 M. 相似文献
130.
Aubert B Barate R Boutigny D Couderc F Karyotakis Y Lees JP Poireau V Tisserand V Zghiche A Grauges E Palano A Pappagallo M Pompili A Chen JC Qi ND Rong G Wang P Zhu YS Eigen G Ofte I Stugu B Abrams GS Borgland AW Breon AB Brown DN Button-Shafer J Cahn RN Charles E Day CT Gill MS Gritsan AV Groysman Y Jacobsen RG Kadel RW Kadyk J Kerth LT Kolomensky YG Kukartsev G Lynch G Mir LM Oddone PJ Orimoto TJ Pripstein M Roe NA Ronan MT Wenzel WA Barrett M Ford KE Harrison TJ Hart AJ Hawkes CM Morgan SE 《Physical review letters》2005,95(4):041805
We present results from an analysis of B(0)B(0)--> rho(+)rho(-) using 232 x 10(6) Gamma (4S) --> BB decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. We measure the longitudinal polarization fraction f(L) = 0.978 +/- 0.014(stat) + 0.021 / -0.029(syst) and the CP-violating parameters S(L)= -0.33 +/- 0.24(stat) + 0.08 / -0.14(syst) and C(L)= -0.03 +/- 0.18(stat) +/- 0.09(syst). Using an isospin analysis of B --> rhorho decays, we determine the unitarity triangle parameter alpha. The solution compatible with the standard model is alpha = (100 +/- 13) degrees. 相似文献