全文获取类型
收费全文 | 305270篇 |
免费 | 5094篇 |
国内免费 | 2877篇 |
专业分类
化学 | 140919篇 |
晶体学 | 4476篇 |
力学 | 17421篇 |
综合类 | 105篇 |
数学 | 55964篇 |
物理学 | 94356篇 |
出版年
2022年 | 1812篇 |
2021年 | 2336篇 |
2020年 | 2513篇 |
2019年 | 2725篇 |
2018年 | 13445篇 |
2017年 | 13053篇 |
2016年 | 10580篇 |
2015年 | 3975篇 |
2014年 | 5003篇 |
2013年 | 11084篇 |
2012年 | 12809篇 |
2011年 | 20862篇 |
2010年 | 12957篇 |
2009年 | 13212篇 |
2008年 | 15908篇 |
2007年 | 17963篇 |
2006年 | 9432篇 |
2005年 | 9382篇 |
2004年 | 8925篇 |
2003年 | 8417篇 |
2002年 | 7376篇 |
2001年 | 7720篇 |
2000年 | 5943篇 |
1999年 | 4620篇 |
1998年 | 3724篇 |
1997年 | 3666篇 |
1996年 | 3377篇 |
1995年 | 3061篇 |
1994年 | 2847篇 |
1993年 | 2663篇 |
1992年 | 2992篇 |
1991年 | 2951篇 |
1990年 | 2835篇 |
1989年 | 2606篇 |
1988年 | 2626篇 |
1987年 | 2611篇 |
1986年 | 2429篇 |
1985年 | 3106篇 |
1984年 | 3328篇 |
1983年 | 2715篇 |
1982年 | 2874篇 |
1981年 | 2852篇 |
1980年 | 2706篇 |
1979年 | 2784篇 |
1978年 | 2868篇 |
1977年 | 2851篇 |
1976年 | 2926篇 |
1975年 | 2711篇 |
1974年 | 2675篇 |
1973年 | 2817篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Phase Relations and Sodium Ion Conductivity within the Quasi-binary System Na2SiF6/Na2AIF6 . The phase diagram of the Na2SiF6/Na3AlF6 system has been determined by means of x-ray powder diffraction, thermal analysis and conductivity measurements in the sub-solidus region. Na3AlF6 accomodates up to 73 mol.-% Na2SiF6 maintaining the crystal structure type. The sodium ion conductivity increases by about five orders of magnitude upon doping Na3AlF6 with Na2SiF6. 相似文献
72.
A. J. Maroulis P. D. Akrivos C. P. Hadjiantoniou-Maroulis 《Journal of heterocyclic chemistry》1993,30(4):913-916
Oxidation of the title compounds yields, besides the reported isoimides 3 and/or the amides 4 , also the imides 5 . The observed product dichotomy is considered as the result of an intramolecular nucleophilic attack on the aroyl group, of the pressumed zwitterionic intermediate 2 , by O or N present in the ambident N-aroylimine site of 2 . The results of AM1 calculations agree with the product studies and both permit the formulation of a set of rules correlating structure and selectivity. 相似文献
73.
A forecasting model is developed for the number of daily applications for loans at a financial services telephone call centre. The purpose of the forecasts and the associated prediction intervals is to provide effective staffing policies within the call centre. The model building process is constrained by the availability of only 2 years and 7 months of data. The distinctive feature of the data is that demand is driven in the main by advertising. The analysis given focuses on applications stimulated by press advertising. Unlike previous analyses of broadly similar data, where ARIMA models were used, a model with a dynamic level, multiplicative calendar effects and a multiplicative advertising response is developed and shown to be effective. 相似文献
74.
V. Palyok I.A. Szabó D.L. Beke A. Kikineshi 《Applied Physics A: Materials Science & Processing》2002,74(5):683-687
Surface relief formation at holographic recording on amorphous selenium films was demonstrated and investigated. The presence
of this optical phase modulation component is essential for ensuring significant, stable and erasable optical recording in
a-Se films at 290–320 K temperatures, where conventional photodarkening was known as insignificant and unstable. Photocrystallization
can only be observed in super-exposed a-Se films at the given experimental conditions of hologram recording. Erasing behavior
of surface relief gratings under heat treatment was also investigated in order to reveal further details of the mechanism.
Photoinduced structural transformations within the amorphous phase, connected to local ordering under the condition of light-induced
fluidity, are proposed as an explanation for the relief formation and erasing. The observed reversible optical recording process
may be useful for the various optoelectronic applications of photoconductive a-Se layers.
Received: 12 June 2000 / Accepted: 6 June 2001 / Published online: 30 August 2001 相似文献
75.
D. V. Vyalykh A. M. Shikin G. V. Prudnikova A. Yu. Grigor’ev A. G. Starodubov V. K. Adamchuk 《Physics of the Solid State》2002,44(1):164-170
This paper reports on the first experimental observation of quantum-well states and sp-type resonances in thin single-crystal gold, silver, and copper layers formed on single-crystal W(110) surfaces, which result from spatial localization of Bloch-type electronic wave functions in a quantum well with potential barriers at the vacuum/metal and metal/W(110) interfaces. The quantization of the valence-band electronic structure in Au/W(110), Ag/W(110), and Cu/W(110) systems was studied experimentally using angle-resolved photoelectron spectroscopy. 相似文献
76.
We present a stratification by “normal flatness” associated to an analytic mapping, analogous to Hironaka's classical result for analytic spaces. Our construction is based on a generic normal flatness theorem for mappings, proved using techniques concerning the variation of modules of meromorphically parametrized formal power series [1]. The existence of such a stratification was announced by Hironaka [13], but the other claims made in [13] are false. Counterexamples are also presented here. 相似文献
77.
In this paper, the authors studied certain properties of the estimate of Liang and Krishnaiah (1985, J. Multivariate Anal. 16, 162–172) for multivariate binary density. An alternative shrinkage estimate is also obtained. The above results are generalized to general orthonormal systems. 相似文献
78.
We consider the growth of a spherical crystal in a supersaturatedsolution. In the first part, existence and uniqueness resultsfor radially symmetric growth are obtained, provided that thesupersaturation is not too large; conversely, when the far-fieldsupersaturation exceeds a critical value, it is shown that theradially symmetric solution ceases to exist in finite time.In the second part, we examine the linear stability of a radiallysymmetric similarity solution (in which the radius grows ast?) to shape perturbations. The results are compared with previousquasi-static analyses, and, in particular, the critical radiusat which the crystal becomes unstable is found to be largerfor small supersaturations, but smaller for large supersaturations,than those predicted by the quasi-static analysis 相似文献
79.
采用密度泛函方法(B3P86)对 Fe_2分子结构进行了优化.计算结果中未观察到自旋污染,基态波函数与高态波函数并未混杂,结果表明,Fe_2中有8个未配对电子,这些电子空间分布不同和自旋平行产生的自旋极化效应,使 Fe_2能量最低.计算结果表明,Fe_2分子的基态是~9∑_g~ ,并非~7Δ_u,进而表明 Fe_2的自旋平行效应比电子自旋配对效应要强.计算得到该分子基态的二阶、三阶和四阶力常数分别为1.4115×10~(-2)aJ/nm~2、-37.1751×10~3aJ/nm~3和 98.7596×10~4aJ/nm~4;光谱数据ω_eχ_e、B_e、α_e分别为0.3522、0.0345、 0.4963×10~(-4)cm~(-1);离解能为3.5522eV,平衡键长为0.2137nm,振动频率为292.914cm~(-1);并得到了 Murrel-Sorbie 函数. 相似文献
80.