全文获取类型
收费全文 | 12695篇 |
免费 | 1745篇 |
国内免费 | 1611篇 |
专业分类
化学 | 7174篇 |
晶体学 | 80篇 |
力学 | 1023篇 |
综合类 | 51篇 |
数学 | 2137篇 |
物理学 | 5586篇 |
出版年
2025年 | 43篇 |
2024年 | 218篇 |
2023年 | 362篇 |
2022年 | 433篇 |
2021年 | 413篇 |
2020年 | 497篇 |
2019年 | 397篇 |
2018年 | 483篇 |
2017年 | 422篇 |
2016年 | 442篇 |
2015年 | 461篇 |
2014年 | 618篇 |
2013年 | 969篇 |
2012年 | 926篇 |
2011年 | 995篇 |
2010年 | 825篇 |
2009年 | 846篇 |
2008年 | 712篇 |
2007年 | 747篇 |
2006年 | 667篇 |
2005年 | 464篇 |
2004年 | 372篇 |
2003年 | 318篇 |
2002年 | 254篇 |
2001年 | 251篇 |
2000年 | 189篇 |
1999年 | 219篇 |
1998年 | 178篇 |
1997年 | 139篇 |
1996年 | 99篇 |
1995年 | 87篇 |
1994年 | 74篇 |
1993年 | 90篇 |
1992年 | 112篇 |
1991年 | 104篇 |
1990年 | 87篇 |
1989年 | 86篇 |
1988年 | 186篇 |
1987年 | 247篇 |
1986年 | 209篇 |
1985年 | 63篇 |
1984年 | 34篇 |
1981年 | 31篇 |
1972年 | 47篇 |
1971年 | 62篇 |
1970年 | 30篇 |
1968年 | 55篇 |
1967年 | 104篇 |
1966年 | 47篇 |
1965年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
《Communications in Nonlinear Science & Numerical Simulation》2007,12(6):920-927
The formally variable separation approach is used for handling the dust-acoustic solitary waves in a dusty plasma, including consideration of dust charge variation. New analytical solutions of nonlinear waves are formally derived for the governing equation of the system. We have triumphantly derived the exact analytical expressions and some approximate expressions of the nonlinear dust-acoustic waves in a dusty plasma under some special cases. The work introduces entirely new solutions and emphasizes the power of the newly developed method that can be used in problems with identical nonlinearities. 相似文献
2.
《Physics letters. A》2006,358(1):74-79
The evolution of Bose–Einstein condensates (BECs) loaded into a periodic ring optical lattices (OL) trap is studied. By means of the variational method and direct numerical simulations of the Gross–Pitaevskii (GP) equation, the ground state properties and the vortex stabilities of the condensates for both repulsive and attractive cases are investigated. The results show that the bound states exist for determinate OL strength and interatomic interaction. However, the ground states of BECs undergo delocalizing–localizing transition for both attractive and repulsive cases as the strength of the OL or the interatomic interaction is decreased below the critical value. The ring OL can suppress the delocalizing transition efficiently. 相似文献
3.
《Tetrahedron: Asymmetry》2006,17(19):2781-2792
We herein report an asymmetric synthesis of α,α-disubstituted α-amino alcohol derivatives 3, key intermediates of a novel immunomodulator, using enzymatic desymmetrization of 2-alkyl-2-tert-butoxycarbonylamino-1,3-propanediols 1a and 1b. This method makes it possible to prepare a chiral analogue of FTY720 4. These synthetic procedures allow for a broad structure variation in order to evaluate structure–activity relationships and the mechanism of action for sphingosine 1-phosphate-1 (S1P1) receptor agonist. 相似文献
4.
LIZHIBIN SHIHE 《高校应用数学学报(英文版)》1996,11(1):1-6
Abstract. We consider the following simplified model for the Belousou-Zhabotinskii(B-Z)reaction: 相似文献
5.
Zi-Zhong Li Qing-Xiang Guo Tan Ren Xiao-Qing Zhu You-Cheng Liu 《Journal of inclusion phenomena and macrocyclic chemistry》1993,15(1):37-42
Tetramethylsilane (TMS) can be included by -cyclodextrin (-CD), and sodium 2,2-dimethylsilapentane-5-sulphonate (DSS) can form inclusion complexes with - and -CD. The NMR chemical shifts are changed considerably as a result of the strong interaction between CD and the guest compound in the inclusion complexes. A downfield shift of as much as 0.63 ppm shift downfield has been observed for the protons of external TMS in CD aqueous solution. In view of this, the question arises of whether TMS and DSS can be used as internal references. DSS in D2O is suggested as an external reference for aqueous cyclodextrin solution in NMR measurements. 相似文献
6.
Lizeng PengHuawei Liu Tao ZhangFengzhi Zhang Tiansheng MeiYi Li Yulin Li 《Tetrahedron letters》2003,44(27):5107-5108
A stereoselective synthesis of brassinolide, which involves construction of the side chain by a highly stereoselective aldol reaction between 20S-6β-methoxy-3α,5-cyclo-5α-pregnane-20-carboxaldehyde 2 and ketone 3 or 4 catalyzed by l-proline, is described. 相似文献
7.
The dynamic compressive deformation of frozen soil was investigated by conduct-ing the split-Hopkinson pressure bar (SHPB) experiments at three temperatures and... 相似文献
8.
In the framework of the Skyrme-Hartree-Fock approach with 36 sets of the TI J parameterizations,the tensor force effect on the evolution of the single-proton states in the calcium isotopes is systematically investigated.It is shown that the single-proton states with higher angular momenta are influenced significantly by the tensor force and the trend in the evolution of somesingle-particle energy differences with the mass number of the isotopes depends sensitively on a parameter βT associated with the intensity of the tensor force.To understand this phenomenon,we analyze the spin-orbit potentials and the radial wave functions of relevant single-proton orbits in detail.In addition,it is found that some TI J interactions could cause the 2s1/21d3/2 energy level inversion in 48Ca. 相似文献
9.
In this work we present a study of growth and characterization of ZnS/carbon nanotube (CNT) composites. The composites were prepared with a chemical mix technique and characterized by SEM analysis, Auger Electron Spectroscopy (AES) and Cathodoluminescence (CL) spectroscopy. The analyses show that the sample is formed by a direct contact between CNT and zinc sulfide. In particular, SEM images show CNTs wrapped around ZnS micrometer particles. Furthermore, AES spectroscopy shows the absence of chemical bonds between ZnS and CNT and that the sample homogeneity increases with the CNT amount in the composite.Finally CL studies show that our composites present a visible luminescence signal centered at about 500 nm, with a shift of luminescence emission peak linked to the amount of CNT in the sample. 相似文献
10.
The particle-number conserving (PNC) method for treating the cranked shell model with monopole and quadrupole pairing correlations is used to study the superdeformed (SD) bands observed in odd–odd nuclei in the A190 mass region. Spins are assigned to the levels in these bands. The microscopic mechanism of the ω evolution of the dynamic moment of inertia J(2) for these SD bands are analyzed. In particular, the major roles of the j15/2 neutron and i13/2 proton orbitals played in the SD bands are investigated in detail by contributions to J(2) from each cranked orbital and interference terms between two cranked orbitals. Additivity in the A190 mass region is investigated. The experimental evidence for additivity of alignments in 192Tl can be reproduced by our calculations. 相似文献