全文获取类型
收费全文 | 34043篇 |
免费 | 2307篇 |
国内免费 | 911篇 |
专业分类
化学 | 22576篇 |
晶体学 | 237篇 |
力学 | 1148篇 |
综合类 | 47篇 |
数学 | 4468篇 |
物理学 | 8785篇 |
出版年
2023年 | 314篇 |
2022年 | 323篇 |
2021年 | 471篇 |
2020年 | 659篇 |
2019年 | 616篇 |
2018年 | 507篇 |
2017年 | 455篇 |
2016年 | 952篇 |
2015年 | 1002篇 |
2014年 | 1152篇 |
2013年 | 1995篇 |
2012年 | 2267篇 |
2011年 | 2339篇 |
2010年 | 1447篇 |
2009年 | 1242篇 |
2008年 | 1969篇 |
2007年 | 1896篇 |
2006年 | 1896篇 |
2005年 | 1765篇 |
2004年 | 1459篇 |
2003年 | 1181篇 |
2002年 | 1057篇 |
2001年 | 776篇 |
2000年 | 683篇 |
1999年 | 467篇 |
1998年 | 404篇 |
1997年 | 414篇 |
1996年 | 495篇 |
1995年 | 403篇 |
1994年 | 379篇 |
1993年 | 418篇 |
1992年 | 350篇 |
1991年 | 315篇 |
1990年 | 274篇 |
1989年 | 255篇 |
1988年 | 269篇 |
1987年 | 241篇 |
1986年 | 229篇 |
1985年 | 291篇 |
1984年 | 257篇 |
1983年 | 184篇 |
1982年 | 234篇 |
1981年 | 214篇 |
1980年 | 214篇 |
1979年 | 199篇 |
1978年 | 207篇 |
1977年 | 158篇 |
1976年 | 187篇 |
1975年 | 131篇 |
1974年 | 147篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
81.
Máté Matolcsi 《Acta Mathematica Hungarica》2005,108(1-2):129-136
Summary He present work deals with estimations of the n-th linear polarization constant c(H)n of an n-dimensional real Hilbert space H. We provide some new lower bounds on the value of sup║y║=1 │1,y> ... n,y>│, where x1, ... ,xn are unit vectors in H. In particular, the results improve an earlier estimate of Marcus. However, the intriguing conjecture c(H) n= nn/2 remains open. 相似文献
82.
83.
A.M. van der Kraan 《Hyperfine Interactions》1998,111(1-4):23-34
In modern society the application of catalysts, and hence, research in the field of catalysis, is becoming more and more important. In the strongly increasing chemical industry most reaction processes are performed with the aid of catalysts. Knowledge about the structure of the active sites present at the surface of catalysts will facilitate the design of new catalysts with better performances. Such knowledge can be obtained by Mössbauer spectroscopy, which is an excellent in-situ characterization technique due to the high penetrating power of the γ-radiation used and the sensitivity of the spectral parameters for the chemical state and local environment of the Mössbauer atoms. 相似文献
84.
85.
Lizeng Wang Chengsong Ma Xiaoli Zhang Yibing Ren Yong Yu 《Fresenius' Journal of Analytical Chemistry》1995,351(7):689-691
The electrochemical behavior of the copper-tyrosine complex has been studied by linear-sweep adsorption voltammetry. In 0.02 mol/L Na2HPO4 buffer solution (pH=9.6), the complex can be adsorped on a hanging mercury drop electrode and reduced at a peak potential of about –0.42 V (vs. SCE). The secondary derivative peak height is linear proportional to the concentration of tyrosine in the range 1.0×10–7–5.0×10–5 mol/L. The detection limit is 5×10–8 mol/L.Project supported by the Provincial Science Foundation of Shandong Province 相似文献
86.
87.
Th. Gerrits H. A. M. van den Berg J. Hohlfeld O. Gielkens L. Br Th. Rasing 《Journal of magnetism and magnetic materials》2002,240(1-3):283-286
We have measured the response of a 20×10 μm, 8 nm thin NiFe (80:20) permalloy film due to excitation by short in-plane magnetic field pulses. We will show that using a two-pulse-technique a complete control of the precessional motion of the magnetisation can be achieved on picosecond timescales. Furthermore, we will present numerical calculations which show that a complete suppression of magnetisation ringing after switching can only be realised by a cascade of short field pulses. 相似文献
88.
We study the expected delay in cyclic polling models with general ‘branching-type’ service disciplines. For this class of
models, which contains models with exhaustive and gated service as special cases, we obtain closed-form expressions for the
expected delay under standard heavy-traffic scalings. We identify a single parameter associated with the service discipline
at each queue, which we call the ‘exhaustiveness’. We show that the scaled expected delay figures depend on the service policies
at the queues only through the exhaustiveness of each of the service disciplines. This implies that the influence of different
service disciplines, but with the same exhaustiveness, on the expected delays at the queues becomes the same when the system
reaches saturation. This observation leads to a new classification of the service disciplines. In addition, we show monotonicity
of the scaled expected delays with respect to the exhaustiveness of the service disciplines. This induces a complete ordering
in terms of efficiency of the service disciplines. The results also lead to new rules for optimization of the system performance
with respect to the service disciplines at the queues. Further, the exact asymptotic results suggest simple expected waiting-time
approximations for polling models in heavy traffic. Numerical experiments show that the accuracy of the approximations is
excellent for practical heavy-traffic scenarios.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
89.
Ralf Jäger Anatolij I. Saprykin J. Sabine Becker Hans -Joachim Dietze José A. C. Broekaert 《Mikrochimica acta》1997,125(1-4):41-44
The analytical capabilities of a high-resolution mass spectrometer in combination with a 13.56 MHz glow discharge ion source for the analysis of semiconducting materials (silicon carbide and gallium arsenide) were studied. It was shown that single positively charged ions of sample material have about 10 eV higher average energy than the ions of the discharge and residual gas. Therefore effective energy separation of the ions of analyte from the ions of the discharge and residual gas was achieved by adjusting the ion transfer optics (breadth and position of energy slit), which improves the analytical capabilities of the developed method.Some analytical applications are presented to illustrate the performance of r.f. GDMS for the bulk analysis of semiconducting materials. The results of the trace element analysis of gallium arsenide and silicon carbide samples are compared with data of independent methods (LIMS, ICP-AES, SIMS).Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthdayOn leave from the Institute of Inorganic Chemistry, 630090 Novosibirsk, Russia 相似文献
90.
Q. Gong R. N tzel P.J. van Veldhoven T.J. Eijkemans J.H. Wolter 《Journal of Crystal Growth》2005,280(3-4):413-418
We report on the shape transition from InAs quantum dashes to quantum dots (QDs) on lattice-matched GaInAsP on InP(3 1 1)A substrates. InAs quantum dashes develop during chemical-beam epitaxy of 3.2 monolayers InAs, which transform into round InAs QDs by introducing a growth interruption without arsenic flux after InAs deposition. The shape transition is solely attributed to surface properties, i.e., increase of the surface energy and symmetry under arsenic deficient conditions. The round QD shape is maintained during subsequent GaInAsP overgrowth because the reversed shape transition from dot to dash is kinetically hindered by the decreased ad-atom diffusion under arsenic flux. 相似文献