全文获取类型
收费全文 | 19777篇 |
免费 | 3576篇 |
国内免费 | 2720篇 |
专业分类
化学 | 14209篇 |
晶体学 | 340篇 |
力学 | 1224篇 |
综合类 | 220篇 |
数学 | 2100篇 |
物理学 | 7980篇 |
出版年
2024年 | 51篇 |
2023年 | 388篇 |
2022年 | 723篇 |
2021年 | 706篇 |
2020年 | 927篇 |
2019年 | 875篇 |
2018年 | 771篇 |
2017年 | 693篇 |
2016年 | 1035篇 |
2015年 | 1012篇 |
2014年 | 1257篇 |
2013年 | 1533篇 |
2012年 | 1876篇 |
2011年 | 1887篇 |
2010年 | 1341篇 |
2009年 | 1242篇 |
2008年 | 1451篇 |
2007年 | 1233篇 |
2006年 | 1052篇 |
2005年 | 880篇 |
2004年 | 654篇 |
2003年 | 558篇 |
2002年 | 509篇 |
2001年 | 413篇 |
2000年 | 390篇 |
1999年 | 356篇 |
1998年 | 267篇 |
1997年 | 245篇 |
1996年 | 261篇 |
1995年 | 192篇 |
1994年 | 198篇 |
1993年 | 153篇 |
1992年 | 145篇 |
1991年 | 127篇 |
1990年 | 129篇 |
1989年 | 84篇 |
1988年 | 78篇 |
1987年 | 54篇 |
1986年 | 58篇 |
1985年 | 50篇 |
1984年 | 42篇 |
1983年 | 30篇 |
1982年 | 30篇 |
1981年 | 23篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1970年 | 12篇 |
1937年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
A New Triterpene from the Orchid Pholidota yunnanensis 总被引:2,自引:0,他引:2
ZhiMingBI ZhengTaoWANG LuoShanXU 《中国化学快报》2004,15(10):1179-1181
A new triterpene, 25-methylenecyclopholidonyl p-hydroxy-trans-cinnamate, was isolated from a orchid Pholidota yunnanensis. The structure elucidation and ^1H, ^13C-NMR assignments were achieved by spectral and chemical method. 相似文献
53.
54.
Let f be a smooth map between unit spheres of possibly different dimensions. We prove the global existence and convergence of the mean curvature flow of the graph of f under various conditions. A corollary is that any area‐decreasing map between unit spheres (of possibly different dimensions) is isotopic to a constant map. © 2004 Wiley Periodicals, Inc. 相似文献
55.
Tao Liu Zuxiong Xu Zhongtao Zhao Ruzhang Ma Tiandou Hu Yaning Xie Yinghuan Guo 《中国科学A辑(英文版)》1997,40(4):395-399
The role of magnetoelastic coupling effects in nanocrystalline ferromagnets is investigated by means of high-field magnetization and Doppler-broadening spectrum measurements. For the nanocrystalline Fe73 5Cu1Nb3Si13.5B9 alloy, the results show that the pinning effects resulting from the quasidislocation dipole intensely influence the movement of domain wall; by coupling with the magnetostriction the defects-induced stress fields determine the magnetic properties at the early stage of crystallization. In view of the effective anisotropy and magnetoelastic coupling energy the optimal annealing conditions of alloys are discussed. 相似文献
56.
High-level ab initio calculations are carried out to study the relative stability of the two hydrogen bonded structures of water-hydrogen sulfide complex, one with water as the proton donor (A) and the other with hydrogen sulfide as the proton donor (B). The results show that structure A is considerably more stable than B at the correlated level, which is in contrast with previous results obtained from Hartree-Fock calculations. 相似文献
57.
罗尔定理证明一类存在性问题 总被引:1,自引:0,他引:1
提出罗尔定理证明一类存在性问题的方法,采用拉格朗日中值定理或柯西中值定理来证明这类问题往往需要构造精巧的辅助函数,我们还指出了这种方法的一般性. 相似文献
58.
研制出了用于计算氚投料量在FEB聚变堆各个子系统中的分布及其随时间变化的数值模拟程序包SWITRIM。通过近5年的使用,表明其运行良好、计算结果可靠。用SWITRIM数值模拟研究了聚变堆起动过程中的“氚坑深度和氚坑时间”新现象。简单介绍了SWITRIM程序包的组成和用户使用说明以及最新的运用等。 相似文献
59.
For approximate wave functions, we prove the theorem that there is a one‐to‐one correspondence between the constraints of normalization and of the Fermi–Coulomb and Coulomb hole charge sum rules at each electron position. This correspondence is surprising in light of the fact that normalization depends on the probability of finding an electron at some position. In contrast, the Fermi–Coulomb hole sum rule depends on the probability of two electrons staying apart because of correlations due to the Pauli exclusion principle and Coulomb repulsion, while the Coulomb hole sum rule depends on Coulomb repulsion. We demonstrate the theorem for the ground state of the He atom by the use of two different approximate wave functions that are functionals rather than functions. The first of these wave function functionals is constructed to satisfy the constraint of normalization, and the second that of the Coulomb hole sum rule for each electron position. Each is then shown to satisfy the other corresponding sum rule. The significance of the theorem for the construction of approximate “exchange‐correlation” and “correlation” energy functionals of density functional theory is also discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
60.
We present a semimonolithic frequency-doubler from 1080 to 540 nm with 80% doubling efficiency and up to 849-mW output power of green light. 相似文献