全文获取类型
收费全文 | 73908篇 |
免费 | 5879篇 |
国内免费 | 8730篇 |
专业分类
化学 | 32243篇 |
晶体学 | 438篇 |
力学 | 6900篇 |
综合类 | 1322篇 |
数学 | 25281篇 |
物理学 | 22333篇 |
出版年
2023年 | 667篇 |
2022年 | 1313篇 |
2021年 | 1492篇 |
2020年 | 1612篇 |
2019年 | 1761篇 |
2018年 | 1462篇 |
2017年 | 1782篇 |
2016年 | 2070篇 |
2015年 | 1834篇 |
2014年 | 2557篇 |
2013年 | 4801篇 |
2012年 | 2998篇 |
2011年 | 3398篇 |
2010年 | 2946篇 |
2009年 | 4131篇 |
2008年 | 4574篇 |
2007年 | 4738篇 |
2006年 | 4453篇 |
2005年 | 3806篇 |
2004年 | 3536篇 |
2003年 | 3521篇 |
2002年 | 3202篇 |
2001年 | 2719篇 |
2000年 | 2688篇 |
1999年 | 2352篇 |
1998年 | 2252篇 |
1997年 | 1843篇 |
1996年 | 1634篇 |
1995年 | 1494篇 |
1994年 | 1403篇 |
1993年 | 1191篇 |
1992年 | 1147篇 |
1991年 | 866篇 |
1990年 | 720篇 |
1989年 | 621篇 |
1988年 | 572篇 |
1987年 | 447篇 |
1986年 | 371篇 |
1985年 | 442篇 |
1984年 | 439篇 |
1983年 | 220篇 |
1982年 | 349篇 |
1981年 | 403篇 |
1980年 | 300篇 |
1979年 | 292篇 |
1978年 | 220篇 |
1977年 | 206篇 |
1976年 | 154篇 |
1974年 | 109篇 |
1973年 | 105篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
961.
潘建敏 《浙江大学学报(理学版)》1997,24(2):108-114
本文探讨了随机删失场合半参数回归模型的参数估计问题.考虑半参数回归模型Y =X}}3 + g(T)十。,其中(X,T)’为取值于Kp X [0,1〕上的随机向量,月为1'维未知参数向量,8为定义于【0.1]上的未知函数,。为随机误差,Ee = 0 . Eez = az }。未知,且(X ,T)与。独立,).被一个与之独立的随机变量V所截.此时仅能观察到:Z=min(Y,V),o=1(Y簇V),参数I3,az的估计量禽及公 z可综合非参数的权函数估计法与参数的最小二乘估计方法得到.本文对核函数的情形得到了念及ar z的精确收敛速度即重对数律. 相似文献
962.
I.V. Kityk A. Ali Umar M. Oyama 《Physica E: Low-dimensional Systems and Nanostructures》2005,27(4):420-426
We have found that the gold nanoparticles on the ITO substrates might be considered promising materials for circularly polarized light-induced linear electrogyration (EG). The maximal achieved value of the EG susceptibility described by third-order axial tensor caused by probe circularly polarized light at a wavelength of 1060 nm was equal to about 13 deg/mm at pulsed electric field strength 30.0 V/cm with a duration of about 1 ms. We have revealed that the maximal EG coefficient is achieved for the samples possessing maximal resistivity. The investigated composites possess long-lived EG grating which decreases by not more than 12% after 120 min of laser treatment. Applying a non-circular pump light leads to the diminishing of the observed EG. 相似文献
963.
Conductive composite films of poly(styrene‐co‐n‐butylacrylate) copolymers filled with low‐density, Ni‐plated core‐shell polymeric particles were prepared and their behaviors of positive temperature coefficient of resistance (PTCR) were investigated. When the conductive fillers in the composite film were loaded beyond the critical volume, 10 up to 25 vol %, composite films exhibited a unique electrical resistant transition behavior, which the electrical resistance rapidly increased by several orders of magnitude at the critical temperature. The PTCR transition temperature, in general, occurred before the glass transition temperature of polymer matrix. Further increased the conductive filler loading to 30 vol %, the overpacked conduction paths were formed in the entire composite and the PTCR effects became blurred. While the composite film treated with thermal cycle several times from room temperature up to 120 °C, the electrical resistivity increased accompanied with the shift of the PTCR transition to lower temperature. The reason might have been caused by the formed interfacial cracks within the composite film. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 322–329, 2007 相似文献
964.
一、引 言 利用垂直场反馈控制等离子体位移是所有托卡马克装置运行的重要组成部分。对于中小型的托卡马克装置,人们曾倾向于用大功率晶闸管作反馈系统的调节器。它所遇到的主要困难有:第一需要有一个较大功率的中频电源。无论是中频发电机或者是逆变器都需要有较大的投资。另一方面受到中频电源的频率及晶闸管的关断时间的限制使反馈系统的时间响 相似文献
965.
A. L. Lapidus S. D. Pirozhkov A. R. Tumanova T. G. Koksharova N. V. Volkova V. A. Bakulev V. S. Mokrushin 《Russian Chemical Bulletin》1992,41(1):178-180
A new method has been developed for the synthesis of the ethyl ester of the mononitrile of malonic acid by the carbonylation of benzenesulfonyloxyacetonitrile in absolute ethanol in the presence of cobalt carbonyl. The yield of the desired product was 30% with 60–90% conversion of the starting compound. The effects of temperature, pressure, and reaction time were studied.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. S. M. Kirov Urals Polytechnical Institute, Ekaterinburg. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 215–216, January, 1992. 相似文献
966.
Martin van Gemmeren 《Transactions of the American Mathematical Society》1996,348(6):2413-2426
In the first part we prove an extension of the Chern-Lashof inequality for noncompact immersed manifolds with finitely many ends. For this we give a lower bound of the total absolute curvature in terms of topological invariants of the manifold. In the second part we discuss tightness properties for such immersions. Finally, we give an upper bound for the substantial codimension.
967.
Summary The relative X-ray fluorescence (XRF) intensities for annular source and various annular specimen are measured with a Ge-Li
detection system and calculated by the Monte Carlo numerical techniques (MCNT).Kα X-ray intensities of annular specimens with different radii prepared from a pure-molybdenum foil are measured and it is
seen that the measured values are in good agreement with the values calculated by MCNT. The variation of the fluorescence
intensity due to the collimator radius is also studied. The differences between the MCNT and experimental results are discussed
in terms of the possible sources of errors. 相似文献
968.
用ESR方法研究了红薯淀粉在γ射线预辐照下,产生的淀粉自由基特性及其室温下的自由基衰减动力学反应。结果表明在室温条件下,淀粉自由基的相对浓度随辐射剂量的增大而增加。自由基相对浓度的室温衰减用二级反应动力学处理,求得了衰减速率常数和淀粉自由基反应的半衰期。 相似文献
969.
970.
研究了在美国BNL/AGS上能量10.7AGeV的197Au离子诱发核作用,报告了EMU–01国际合作实验关于射弹核碎裂和产生粒子密度等最新实验结果. 相似文献