全文获取类型
收费全文 | 23277篇 |
免费 | 3896篇 |
国内免费 | 3653篇 |
专业分类
化学 | 18113篇 |
晶体学 | 395篇 |
力学 | 1118篇 |
综合类 | 273篇 |
数学 | 2294篇 |
物理学 | 8633篇 |
出版年
2024年 | 55篇 |
2023年 | 454篇 |
2022年 | 656篇 |
2021年 | 847篇 |
2020年 | 1009篇 |
2019年 | 1010篇 |
2018年 | 860篇 |
2017年 | 877篇 |
2016年 | 1214篇 |
2015年 | 1256篇 |
2014年 | 1592篇 |
2013年 | 1929篇 |
2012年 | 2285篇 |
2011年 | 2362篇 |
2010年 | 1696篇 |
2009年 | 1507篇 |
2008年 | 1726篇 |
2007年 | 1528篇 |
2006年 | 1366篇 |
2005年 | 1050篇 |
2004年 | 741篇 |
2003年 | 626篇 |
2002年 | 622篇 |
2001年 | 543篇 |
2000年 | 436篇 |
1999年 | 423篇 |
1998年 | 292篇 |
1997年 | 264篇 |
1996年 | 248篇 |
1995年 | 205篇 |
1994年 | 177篇 |
1993年 | 168篇 |
1992年 | 131篇 |
1991年 | 110篇 |
1990年 | 92篇 |
1989年 | 84篇 |
1988年 | 67篇 |
1987年 | 59篇 |
1986年 | 54篇 |
1985年 | 38篇 |
1984年 | 26篇 |
1983年 | 19篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1975年 | 5篇 |
1974年 | 6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 46 毫秒
71.
The compression behaviour of Ni77P23 amorphous alloy is investigated at room temperature in a diamond-anvil cell instrument using in-situ high pressure energy dispersive x-ray diffraction with a synchrotron radiation source. The equation of state is determined by fitting the experimental data according to the Birch-Murnaghan equation. It is found that the structure of Ni77P23 amorphous alloy is stable under pressures up to 30.5 GPa. Within the pressure range from zero to the experimental one, the pressure-induced structural relaxation is reversible. 相似文献
72.
73.
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
74.
Jing Zhang Dan Shan Shaolin Mu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5573-5582
A copolymer, poly(aniline‐co‐o‐aminophenol), was prepared chemically by using ammonium peroxydisulfate as an oxidant. The monomer concentration ratio of o‐aminophenol to aniline strongly influences the copolymerization rate and properties of the copolymer. The optimum composition of a mixture for the chemical copolymerization consisted of 0.3 M aniline, 0.021 M o‐aminophenol, 0.42 M ammonium peroxydisulfate, and 2 M H2SO4. The result of cyclic voltammograms in a potential region of ?0.20 to 0.80 V (vs.SCE) indicates that the electrochemical activity of the copolymer prepared under the optimum condition is similar to that of polyaniline in more acid solutions. However, the copolymer still holds the good electrochemical activity until pH 11.0. Therefore, the pH dependence of the electrochemical property of the copolymer is improved, compared with poly(aniline‐co‐o‐aminophenol) prepared electrochemically, and is much better than that of polyaniline. The spectra of IR and 1H NMR confirm that o‐aminophenol units are included in the copolymer chain, which play a key role in extending the usable pH region of the copolymer. The visible spectra of the copolymers show that a high concentration ratio of o‐aminophenol to aniline in a mixture inhibits the chain growth. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5573–5582, 2007 相似文献
75.
Thermal Rate Constants of the N(^4S)+O2(X^3∑g^-) → NO(X^2Ⅱ) +O(^3P) Reaction on the ^2A′ Potential Energy Surface 下载免费PDF全文
A quasiclassical trajectory study with the sixth-order explicit symplectic algorithm for the N(^4S)+O2(X^3∑g^-) → NO(X^2Ⅱ) +O(^3P) reaction has been reported by employing a new ground potential energy surface. We have discussed the influence of the relative translational energy, the vibrational and rotational levels of O2 molecules on the total reaction cross section. Thermal rate constants at temperatures 300, 600, and 1000 K determined in this work for the reaction are 4.4 × 10^7, 1.8 × 10^10, and 3.1 × 10^11 cm^3mol^-1s^-1, respectively. It is found that they are in better agreement with the experimental data than previous theoretical values. 相似文献
76.
77.
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
78.
79.
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
80.
For vertical-cavity surface-emitting lasers (VCSELs) with polarization-rotated feedback, there exist several synchronization
types such as synchronizations between total powers and synchronizations between separate polarization modes. Based on the
two-mode rate equations, we study and compare numerically the performances of different synchronization types. Our results
show that three synchronization types exhibit good performances when their synchronization conditions are satisfied. They
are the complete synchronization between total powers, complete synchronization between x-polarized modes, and generalized synchronization between x-polarized and y-polarized modes. The former two types are sensitive to the injection rate and spontaneous emission, while the third type
is contrary. Synchronization type with the best performance may switch from one to another, with changing of injection rate
and spontaneous emission factor. 相似文献