全文获取类型
收费全文 | 5877篇 |
免费 | 1463篇 |
国内免费 | 1649篇 |
专业分类
化学 | 1823篇 |
晶体学 | 40篇 |
力学 | 1161篇 |
综合类 | 211篇 |
数学 | 1525篇 |
物理学 | 4229篇 |
出版年
2024年 | 59篇 |
2023年 | 196篇 |
2022年 | 165篇 |
2021年 | 198篇 |
2020年 | 121篇 |
2019年 | 174篇 |
2018年 | 120篇 |
2017年 | 147篇 |
2016年 | 172篇 |
2015年 | 170篇 |
2014年 | 480篇 |
2013年 | 324篇 |
2012年 | 368篇 |
2011年 | 467篇 |
2010年 | 446篇 |
2009年 | 498篇 |
2008年 | 805篇 |
2007年 | 363篇 |
2006年 | 335篇 |
2005年 | 318篇 |
2004年 | 379篇 |
2003年 | 375篇 |
2002年 | 302篇 |
2001年 | 263篇 |
2000年 | 194篇 |
1999年 | 163篇 |
1998年 | 165篇 |
1997年 | 148篇 |
1996年 | 106篇 |
1995年 | 137篇 |
1994年 | 140篇 |
1993年 | 110篇 |
1992年 | 142篇 |
1991年 | 92篇 |
1990年 | 94篇 |
1989年 | 110篇 |
1988年 | 29篇 |
1987年 | 29篇 |
1986年 | 25篇 |
1985年 | 14篇 |
1984年 | 18篇 |
1983年 | 16篇 |
1982年 | 6篇 |
1980年 | 2篇 |
1979年 | 4篇 |
排序方式: 共有8989条查询结果,搜索用时 125 毫秒
961.
962.
以(E)-3-甲氧基-巴豆酸和1-羟基苯并三唑为原料合成了标题化合物,通过~1H NMR等进行了表征,并通过XRD衍射测定了晶体结构,晶体属于单斜晶系,P2_1/c空间群。晶胞参数为a=1.4001(3)nm,b=1.0014(2)nm,c=1.5699(3)nm,α=90°,β=100.13(3)°,γ=90°,D+x=1.429g/cm~3,Z=8,F(000)=976,μ=0.11mm~(-1),最终偏差因子R_1=0.063,ωR_2=0.141。使用Gaussian 03程序,用量子化学中的密度泛函理论(DFT),在B3LYP/6-311G(d,p)基组下计算了该化合物的优化结构参数、电荷分布、分子总能量。算得的键长键角数据和单晶衍射数据相符合。结果表明计算得到的分子几何优化结构可靠,所用的计算方法可靠。 相似文献
963.
本文以西藏大学为例,探索在民族地方高校新设"计算物理基础"课程的目的、做法及实施情况.以Matlab为平台,将计算机数值计算与模拟实验引入普通物理教学中,促进Matlab的数值计算及模拟功能与普通物理课程教学的整合,对学生进行科学计算教育,培养学生的科学计算能力,推进民族地区普通物理数字化教学改革. 相似文献
964.
<正>Phase mismatching for third-harmonic generation(THG) in barium metaborate(BBO) crystal is investigated in detail.Upon using BBO crystal in the TypeⅠ(oo→e) scheme,in the two independent planes (principal section of the crystal and the plane normal to principal section),when the input second-harmonic beam deviates from the expected direction,phase mismatching occurs and the angle deviation produces different effects on the conversion efficiency.We numerically simulate these two cases of phase mismatching and identify the relation between the conversion efficiency and the deviation angle in the air.The computational results indicate that the phase matching tolerance in the principal section is 0.2°(in the air),while the phase matching tolerance in the plane normal to principal section is 4.5°(in the air).After conducting a lab experiment,the results agree perfectly with the computational results,indicating that the deviation angle in the principal section has a greater effect on the conversion efficiency. 相似文献
965.
In this work, we analyze the positive parity of states of odd-A Eu isotopes within the framework of interacting boson fermion model (IBFM-1). The result of an IBFM-1 multilevel calculation with the 3s1/2, 2d3/2, 2d5/2, and 1g7/2 single panicle orbits is reported for the positive parity states of the odd-A Eu isotopes. A/so, an IBM-1 calculation is presented for the low-lying states in the even-even 152-154Sm core nucleus. The energy levels and B(E2) transition probabilities are calculated and compared with the experimental data. It is found that the calculated positive parity low spin state energy spectra of the odd-A Eu isotopes agree quite well with the experimental data. 相似文献
966.
The ground state properties of the spherical nucleus ^40Ca have been investigated by using constrained spherical Hartree Fock (CSHF) approximation at equilibrium and under high radial compression in a six major shells. The effective baryon-baryon interaction that includes the △(1236) resonance freedom degrees to calculate nuclear properties is used. The nucleon-nucleon (N-N) interaction is based on Reid soft core (RSC) potential. The results of calculations show that much of increase in the nuclear energy generated under compression is used to create the massive △ particles. The number of △ 's can be increased to about 2.1% of constituents of nucleus when nuclear density reaches about 1.34 times of normal density. The single particle energy levels are calculated and their behavior under compression is also examined. △ good agreement has been found between current calculations and phenomenological shell model for low lying single-particle spectra. The gap between shells is very clear and L-S coupling become stronger as increasing the static load on the nucleus. The results show a considerable reduction in compressibility when freedom degrees of △'s are taken into account. It has been found that the total nuclear radial density becomes denser in the interior and less dense in the exterior region of nucleus. The surface of nucleus becomes more and more responsive to compression than outer region. 相似文献
967.
The atomic and electronic structures of T1 and In on Si(111) surfaces are investigated using the firstprinciples total energy calculations. Total energy optimizations show that the energetically favored structure is 1/3 ML T1 adsorbed at the T4 sites on Si(111) surfaces. The adsorption energy difference of one T1 adatom between (√3 × √3) and (1 × 1) is less than that of each In adatom. The DOS indicates that TI 6p and Si 3p electrons play a very important role in the formation of the surface states. It is concluded that the bonding of TI adatoms on Si(111) surfaces is mainly polar covalent, which is weaker than that of In on Si(111). So T1 atom is more easy to be migrated than In atom in the same external electric field and the structures of T1 on Si(111) is prone to switch between (√3 × √3) and (1 × 1). 相似文献
968.
Radioactive decay of super heavy nuclei via the emission of α-particles has been studied theoretically in the preformed cluster model (PCM). The nucleus-nucleus (NN) potential is obtained by double folding the density distributions of the α-particle and the daughter nucleus with a realistic effective interaction. The M3Y effective interaction, supplemented by a zero-range pseudo-potential for exchange term, is used to calculate the NN potential. The α decay half-lives for 317 nuclei at Z=102 120 are performed in the PCM framework with the theoretical Q values extracted from the MSller-Nix-Kratz and Liran-Marinov-Zeldes mass tables and are compared with the experimental data. The calculated results are also compared with those obtained by using Q values from the Muntian-Hofmann-Patyk-Sobiczewski and Myers-Swiatecki mass estimates. 相似文献
969.
970.
The decay properties of the D and D s mesons are computed in a nonrelativistic phenomenological quark-antiquark potential of the type V (r) =-4 /3 α s /r+ Ar ν with different choices of ν.Numerical method to solve the Schrdinger equation has been used to obtain the spectroscopy of qQ mesons.The numerically obtained radial solutions are employed to obtain the decay constant and leptonic decay widths.It has been observed that predictions of the ground state masses and the decay widths are consistent with other model predictions as well as with the known experimental values. 相似文献