全文获取类型
收费全文 | 215438篇 |
免费 | 1564篇 |
国内免费 | 627篇 |
专业分类
化学 | 117923篇 |
晶体学 | 3270篇 |
力学 | 8349篇 |
综合类 | 6篇 |
数学 | 23305篇 |
物理学 | 64776篇 |
出版年
2020年 | 1970篇 |
2019年 | 2263篇 |
2018年 | 3205篇 |
2017年 | 3113篇 |
2016年 | 4267篇 |
2015年 | 2371篇 |
2014年 | 3818篇 |
2013年 | 9260篇 |
2012年 | 6891篇 |
2011年 | 8434篇 |
2010年 | 6071篇 |
2009年 | 5921篇 |
2008年 | 8136篇 |
2007年 | 8206篇 |
2006年 | 7630篇 |
2005年 | 6937篇 |
2004年 | 6166篇 |
2003年 | 5641篇 |
2002年 | 5497篇 |
2001年 | 5939篇 |
2000年 | 4684篇 |
1999年 | 3470篇 |
1998年 | 3007篇 |
1997年 | 3033篇 |
1996年 | 2823篇 |
1995年 | 2319篇 |
1994年 | 2419篇 |
1993年 | 2450篇 |
1992年 | 2595篇 |
1991年 | 2657篇 |
1990年 | 2559篇 |
1989年 | 2533篇 |
1988年 | 2463篇 |
1987年 | 2434篇 |
1986年 | 2357篇 |
1985年 | 3037篇 |
1984年 | 3194篇 |
1983年 | 2559篇 |
1982年 | 2827篇 |
1981年 | 2703篇 |
1980年 | 2503篇 |
1979年 | 2718篇 |
1978年 | 2833篇 |
1977年 | 2856篇 |
1976年 | 2832篇 |
1975年 | 2687篇 |
1974年 | 2665篇 |
1973年 | 2810篇 |
1972年 | 1875篇 |
1967年 | 1830篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The influence of thermal treatment on a (Li2OAl2O3 SiO2) glass ceramic is studied by laser spectroscopy. At temperatures above 800 °C a fluorescence of Cr3+ ions around 693 nm appears which indicates the growth of crystallites where the Cr3+ ions occupy sites similar to those in Al2O3. 相似文献
992.
S. I. Dolinsky V. P. Druzhinin M. S. Dubrovin V. B. Golubev V. N. Ivanchenko A. P. Lysenko A. A. Mikhailichenko E. V. Pakhtusova A. N. Peryshkin S. I. Serednyakov Yu. M. Shatunov V. A. Sidorov 《Zeitschrift fur Physik C Particles and Fields》1989,42(4):511-518
The results of the measurements of radiative decays of ρ and ω mesons with the Neutral Detector at thee + e ? collider VEPP-2M are presented. The branching ratio of the decay ω→π 0γ was measured with higher than in previous experiments accuracy: $${\rm B}(\omega \to \pi ^0 \gamma ) = 0.0888 \pm 0.0062$$ . The ρ0→π 0 γ branching ratio was measured for the first time: $$B(\rho ^0 \to \pi ^0 \gamma ) = (7.9 \pm 2.0) \cdot 10^{ - 4} $$ . The decays ρ, ω→ηγ were studied. Their branching ratios with the assumption of constructive ρ?ω interference are: $$\begin{gathered} B(\omega \to \eta \gamma ) = (7.3 \pm 2.9) \cdot 10^{ - 4} , \hfill \\ B(\rho \to \eta \gamma ) = (4.0 \pm 1.1) \cdot 10^{ - 4} \hfill \\ \end{gathered} $$ . The branching ratios of ρ, ω→ηγ and ω→e + e ? decays were also measured: $$\begin{gathered} B(\omega \to \pi ^ + \pi ^ - \pi ^0 ) = 0.8942 \pm 0.0062, \hfill \\ B(\omega \to e^ + e^ - ) = (7.14 \pm 0.36) \cdot 10^{ - 5} \hfill \\ \end{gathered} $$ . The upper limit for the ω→π 0 π 0 γ branching ratio was placed: B(ω→π 0 π 0 γ)<4·10?4 at 90% confidence level. 相似文献
993.
V. V. Aivazyan I. V. Ajinenko Yu. A. Belokopytov P. C. Bosetti H. B?ttcher F. Botterweck P. V. Chliapnikov F. Crijns A. De Roeck E. A. De Wolf Th. Driever K. Dziunikowska A. Eskreys W. Friebel Z. C. Garutchava V. G. Gavrjusev H. Graessler P. van Hal T. Haupt W. Kittel S. S. Megrabyan F. Meijers A. B. Micha?owska V. I. Nikolaenko L. C. S. Oliveira K. Olkiewicz L. P. Petrovikh E. Riipinen V. M. Ronjin A. M. Rybin H. M. T. Saarikko W. Schmitz L. Scholten R. Schulte O. G. Tchikilev L. A. Tikhonova A. G. Tomaradze V. A. Uvarov F. Verbeure R. Wischnewski A. Wróblewski S. A. Zotkin NA Collaboration 《Zeitschrift fur Physik C Particles and Fields》1989,42(4):533-542
Forward-backward multiplicity correlations in σ+,K + p andpp collisions at 250 GeV/c ( \(\sqrt s \) =22 GeV) are given for all charges and for the different charge combinations. The correlations are found to be caused predominantly by centrally produced particles. It is demonstrated that this result is an agreement with observations at the ISR and the CERNp \(\bar p\) -Collider. The results are compared to expectations from LUND, DPM and FRITIOF Monte Carlo models and a geometrical picture relating correlations in hadron-hadron collisions toe + e ? data in terms of impact parameters is tested. 相似文献
994.
The parton distributions of the nucleon are evaluated dynamically using the assumption that at some low resolution scale the nucleon consists entirely of valence quarks. A simple parametrization of the resulting gluon distribution is presented, forx? 10?5 up toQ 2?106 GeV2. This gluon distribution is predicted dicted to be much steeper and larger in the very smallx region (x<10?2) than usually assumed. Applications to deep inelastic scaling violations and heavy quark (c, b, t) contribution are discussed and presented as well as hadronic heavy quark production at SSC/LHC energies. For example, the \(b\bar b\) production rate at 40 TeV is predicted to be about an order of magnitude larger than that estimated with other gluon distributions so far. 相似文献
995.
K. D. Duch M. Heel H. Kalinowsky F. Kayser E. Klempt B. May O. Schreiber P. Weidenauer M. Ziegler D. Bailey S. Barlag J. M. Butler U. Gastaldi R. Landua C. Sabev W. Dahme F. Feld-Dahme U. Schaefer W. R. Wodrich J. C. Bizot B. Delcourt J. Jeanjean H. Nguyen E. G. Auld D. A. Axen K. L. Erdman B. Howard R. Howard B. L. White S. Ahmad M. Comyn G. M. Marshall G. Beer L. P. Robertson M. Botlo C. Laa H. Vonach C. Amsler M. Doser J. Riedlberger U. Straumann P. Truöl ASTERIX Collaboration 《Zeitschrift fur Physik C Particles and Fields》1989,45(2):223-234
Antiproton-proton annihilation at rest in a gaseous H2 target at NTP into the final state π+ π? K ± π? (K 0) with an undetectedK 0 or \(\bar K^0 \) has been investigated. We observe theE(1420) resonance in the invariant mass spectrum (K 0)miss K ± π? with massM E =1413±8 MeV/c2 and widthГ E =62 ± 16MeV/c2 and find evidence for the production of thef 1(1285). The absolute branching ratio of \(\bar p\) p → π+ π? E 0,E 0 →K 0 L K ± π ? at (61±6)%P wave annihilation is (3.0±0.9)·10?4 of all annihilations. The observed suppression of theE production fromP wave with respect to theS wave together with some simple selection rules suggest that the quantum numbers of theE(1420) areJ pc=0?+ and not I++. 相似文献
996.
E. Matsinos J. Guy E. Simopoulou W. Venus P. Allport M. Berggren M. Calicchio T. Coghen A. M. Cooper-Sarkar O. Erriquez N. Giannakopoulos G. T. Jones P. Marage M. M. Mobayyen D. R. O. Morrison S. O'Neale M. A. Parker J. Sacton R. A. Sansum N. Schmitz G. W. Van Apeldoorn K. Varvell A. Vayaki H. Wachsmuth W. Wittek BEBC WA Collaboration 《Zeitschrift fur Physik C Particles and Fields》1989,44(1):79-87
Backward proton and pion production is studied in ν and \(\bar v\) charged current interactions in neon. The results are compared with other experiments and theory. The complete backward proton data is compatible with protons produced by reinteractions in the nucleus. However in events with only one proton, muon variables appear correlated to those for the backward proton, as expected by the two-nucleon correlation model. 相似文献
997.
Franklin E. Schroeck Jr. 《International Journal of Theoretical Physics》1989,28(3):247-262
Recent results in the theory of integration of complex-valued functions with respect to a positive operator-valued measure are used to generalize the usual notion of coexistent observables. This leads to a connection between effects as observables and the quantization scheme of stochastic quantum mechanics. It also leads to a new viewpoint for the concept of a classical apparatus for quantum measurement which does not require a classical mechanical treatment of the apparatus from the outset. 相似文献
998.
C. Papatriantafillou C. E. Paraskevaidis C. Krikos P. Panagopoulos 《Journal of statistical physics》1989,54(1-2):191-200
We study a generalized Ising system consisting of a Bethe lattice on every site of which two spin-1/2 and two isospin-1/2 (or atomic species A) states can be realized, the spin-species interacting with appropriate nearest neighbor couplings. The system is equivalent to that of four states per site and we obtain its exact thermodynamic behavior. The case of a fixed concentration of species is the annealed or liquid magnetic binary alloy. The temperature dependence of the short-range-order (SRO) parameter of such systems is obtained as an application of the theory and discussed in connection with relevant material from the literature. When fixing both the concentration and the nearest neighbor spatial correlation of the species, we obtain Eggarter's formulas for the frozen-in species problem, which therefore are only approximately valid even on the Bethe lattice. 相似文献
999.
Büttiker and Landauer studied scattering off an oscillating rectangular barrier in order to shed light on the time aspects of tunneling. The expression for the traversal time resulting from this study is controversial. In addition, doubts have recently been expressed on technical aspects of their work. In an attempt to clarify these issues, we investigate a generalization of their model to arbitrary oscillating barriers,V(x, t)=V
0(x)+V
1(x)cos t. In the process, we confirm that Büttiker and Landauer's work is technically sound. However, we show, by several examples, that no direct general relation exists between the characteristic frequency of an oscillating barrier and the duration of the tunneling process. For a wide range of realistic parameters this characteristic frequency does not even exist.This paper is dedicated to E. G. D. Cohen. 相似文献
1000.
We have set up a laser system which simultaneously provides synchronized picosecond pulses in the visible and at a wavelength of 1.06 m with a repetition rate of 76 MHz. The set-up consists of a dye laser synchronously pumped by the second harmonic of a cw mode-locked Nd:YAG laser and a fiber-grating compressor for the fundamental wavelength of the Nd;YAG laser. Crosscorrelation measurments reveal the time jitter between the two pulse trains to be less than 10 ps. As a first application we have performed non-degenerate transient grating experiments in semiconductors. The non-degenerate technique allows to use excitation energies well above the bandgap energy and to separate non-linear refractive index effects from photoinduced absorption or transmission changes. 相似文献