全文获取类型
收费全文 | 11520篇 |
免费 | 2460篇 |
国内免费 | 1282篇 |
专业分类
化学 | 6015篇 |
晶体学 | 195篇 |
力学 | 494篇 |
综合类 | 83篇 |
数学 | 1444篇 |
物理学 | 7031篇 |
出版年
2024年 | 16篇 |
2023年 | 153篇 |
2022年 | 333篇 |
2021年 | 384篇 |
2020年 | 534篇 |
2019年 | 477篇 |
2018年 | 454篇 |
2017年 | 497篇 |
2016年 | 567篇 |
2015年 | 468篇 |
2014年 | 594篇 |
2013年 | 1011篇 |
2012年 | 778篇 |
2011年 | 837篇 |
2010年 | 699篇 |
2009年 | 724篇 |
2008年 | 732篇 |
2007年 | 702篇 |
2006年 | 671篇 |
2005年 | 584篇 |
2004年 | 555篇 |
2003年 | 480篇 |
2002年 | 561篇 |
2001年 | 406篇 |
2000年 | 359篇 |
1999年 | 271篇 |
1998年 | 237篇 |
1997年 | 177篇 |
1996年 | 148篇 |
1995年 | 112篇 |
1994年 | 114篇 |
1993年 | 71篇 |
1992年 | 86篇 |
1991年 | 62篇 |
1990年 | 48篇 |
1989年 | 46篇 |
1988年 | 45篇 |
1987年 | 30篇 |
1986年 | 31篇 |
1985年 | 37篇 |
1984年 | 39篇 |
1983年 | 17篇 |
1982年 | 23篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1978年 | 18篇 |
1977年 | 6篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
In this paper we compute the number of curves of genus 2 defined over a finite field k of odd characteristic up to isomorphisms defined over k; the even characteristic case is treated in an ongoing work (G. Cardona, E. Nart, J. Pujolàs, Curves of genus 2 over field of even characteristic, 2003, submitted for publication). To this end, we first give a parametrization of all points in
, the moduli variety that classifies genus 2 curves up to isomorphism, defined over an arbitrary perfect field (of zero or odd characteristic) and corresponding to curves with non-trivial reduced group of automorphisms; we also give an explicit representative defined over that field for each of these points. Then, we use cohomological methods to compute the number of k-isomorphism classes for each point in
. 相似文献
132.
对轴线起爆式螺线管型爆磁压缩发生器进行了理论模型研究,建立了爆炸管的一维爆轰驱动模型、螺线管内空间磁场强度分布模型、爆炸管外表面磁压力模型和发生器系统的等效电路模型等,对此类发生器的物理过程进行系统描述。在此基础上,编制了相应的零维数值模拟程序CEMG 1.0,利用该程序分别对四种不同模型参数的发生器进行了理论计算和参数优化,并对其中一模型发生器爆炸管外表面的磁压力及其引起的剩余电感进行了计算,给出了剩余电感与初始输入条件及负载电感的关系,从而得到该模型的输出性能极限。对理论模型的正确性进行了实例验算证明。 相似文献
133.
134.
We consider the asymptotic dynamics of the Einstein-Maxwell field equations for the class of non-tilted Bianchi cosmologies with a barotropic perfect fluid and a pure homogeneous source-free magnetic field, with emphasis on models of Bianchi type VII0, which have not been previously studied. Using the orthonormal frame formalism and Hubble-normalized variables, we show that, as is the case for the previously studied class A magnetic Bianchi models, the magnetic Bianchi VII0 cosmologies also exhibit an oscillatory approach to the initial singularity. However, in contrast to the other magnetic Bianchi models, we rigorously establish that typical magnetic Bianchi VII0 cosmologies exhibit the phenomena of asymptotic self-similarity breaking and Weyl curvature dominance in the late-time regime. 相似文献
135.
P. Tekely V. G rardy P. Palmas D. Canet A. Retournard 《Solid state nuclear magnetic resonance》1995,4(6):361-367
A simple modification of the standard cross-polarization method designed for quenching the proton T1ρ dependence when studying polarization transfer is presented. It is demonstrated that by using this simple procedure, new and subtle details of cross-polarization dynamics, previously hidden by the T1ρ(1H) effect, can be observed in dipolar-coupled spin systems. 相似文献
136.
Seventeen 1-aryl-2,2-dichlorocyclopropanes were examined by using IR, 13C NMR, and mass spectrometry. The data obtained from IR and 13C NMR spectra indicate that the bond strength of carbon-chlorine on the cyclopropane ring and the electron density of that carbon depend on the substituent. The mass fragmentation patterns of compounds in this series resemble those of the dibromo analogues. The fragmentation mechanism is proposed to involve the formation of indenium ion through an electrocyclization. 相似文献
137.
A special two-sided condition for the incremental magnetic reluctivity is introduced which guarantees the unique existence of both the weak and the approximate solutions of the nonlinear stationary magnetic field distributed on a region composed of different media, as well as a certain estimate of the error between the two solutions. The condition, being discussed from the physical as well as the mathematical point of view, can be easily verified and is fulfilled for various magnetic reluctivity models used in electrotechnical practice. 相似文献
138.
关于正形置换多项式的注记 总被引:5,自引:1,他引:4
n为正整数,m为大于1的正整数,本文证明了当n≡0,1(mod m)时,F2^n上不存在2^m-1次正形置换多项式,并给出了该结果的几个推论:F2^n上不存在次数为3的正形置换多项式;n〉2时,F2^n上的4次正形置换多项式都是仿射多项式. 相似文献
139.
Electronic structure spin-polarized calculations were performed for 79-atoms embedded clusters representing the ordered intermetallic compound FeNi, the fcc Fe-rich disordered alloy Fe85Ni15 in an antiferromagnetic (AFM) configuration, and the ferromagnetic (FM) disordered alloy Fe50Ni50. The spin-polarized discrete variational method (DVM) in Density Functional theory was employed. Spin magnetic moments, as well as the 57Fe Mössbauer hyperfine parameters isomer shift and magnetic hyperfine fields, were obtained from the calculations. For FM Fe50Ni50, the effect of pressure on the hyperfine field and on the isomer shift was investigated, for three different local atomic configurations surrounding the 57Fe probe atom. In the case of the isomer shift, the calculated values were compared to reported experimental data. 相似文献
140.
Li Zhang James A. Bain Jian-Gang Zhu Leon Abelmann Takahiro Onoue 《Journal of magnetism and magnetic materials》2006
A method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. In this work, field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2–7 V were applied to a CoNi/Pt multilayered film fabricated on either bare silicon or oxidized silicon substrates. Different types of Ir/Pt and W STM tips were used in the experiment. The results show that thermally recorded magnetic marks are formed with a nearly uniform mark size of 170 nm on the film fabricated on bare silicon substrate when the pulse voltage is above a threshold voltage. The mark size becomes 260 nm when they are written on the identical film fabricated on an oxidized silicon substrate. The threshold voltage depends on the material work function of the tip, with W having a threshold voltage about 1 V lower than Pt. A synthesized model, which contains the calculation of the emission current, the simulation of heat transfer during heating, and the study of magnetic domain formation, was introduced to explain experimental results. The simulation agrees well with the experiments. 相似文献