全文获取类型
收费全文 | 66138篇 |
免费 | 6405篇 |
国内免费 | 4296篇 |
专业分类
化学 | 22156篇 |
晶体学 | 584篇 |
力学 | 6908篇 |
综合类 | 705篇 |
数学 | 18748篇 |
物理学 | 27738篇 |
出版年
2024年 | 92篇 |
2023年 | 555篇 |
2022年 | 1110篇 |
2021年 | 1293篇 |
2020年 | 1550篇 |
2019年 | 1528篇 |
2018年 | 1421篇 |
2017年 | 1629篇 |
2016年 | 1819篇 |
2015年 | 1426篇 |
2014年 | 2449篇 |
2013年 | 4387篇 |
2012年 | 2814篇 |
2011年 | 3239篇 |
2010年 | 2748篇 |
2009年 | 3872篇 |
2008年 | 4246篇 |
2007年 | 4581篇 |
2006年 | 3918篇 |
2005年 | 3279篇 |
2004年 | 2792篇 |
2003年 | 3034篇 |
2002年 | 3291篇 |
2001年 | 2573篇 |
2000年 | 2365篇 |
1999年 | 2010篇 |
1998年 | 1919篇 |
1997年 | 1240篇 |
1996年 | 1146篇 |
1995年 | 999篇 |
1994年 | 1009篇 |
1993年 | 790篇 |
1992年 | 837篇 |
1991年 | 593篇 |
1990年 | 543篇 |
1989年 | 424篇 |
1988年 | 385篇 |
1987年 | 347篇 |
1986年 | 319篇 |
1985年 | 295篇 |
1984年 | 303篇 |
1983年 | 188篇 |
1982年 | 255篇 |
1981年 | 236篇 |
1980年 | 166篇 |
1979年 | 200篇 |
1978年 | 155篇 |
1977年 | 137篇 |
1976年 | 94篇 |
1973年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
Gas-phase 21Ne nuclear magnetic resonance spectra were measured at the natural abundance of 21Ne isotope for samples consisting of pressurized neon up to 60 bar at room temperature and applying the magnetic field of the strength B0 = 11.7574 T. It showed that the nuclear magnetic resonance frequency is linearly dependent on the density of gaseous neon. The resonance frequency was extrapolated to the zero-density point, and it permitted the determination of the 21Ne nuclear magnetic moment, μ(21Ne) = 0.6617774(10) μN. The present value of μ(21Ne) is not influenced by the bulk magnetic susceptibility of neon and interactions between neon atoms; therefore, it is more precise and reliable than the previous result obtained for μ(21Ne). 相似文献
42.
43.
《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2020,37(2):417-456
We study the energy-critical nonlinear wave equation in the presence of an inverse-square potential in dimensions three and four. In the defocussing case, we prove that arbitrary initial data in the energy space lead to global solutions that scatter. In the focusing case, we prove scattering below the ground state threshold. 相似文献
44.
Activated carbon production from almond shells using phosphoric acid activation agent was achieved by applying both conventional heating and microwave heating in succession. The morphology and surface properties of activated carbon were studied using thermogravimetric and differential gravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, and Brunauer–Emmett–Teller analysis. A surface area of 1128 m2/g was achieved by optimizing the microwave power (500?W), microwave application time (15?minutes), conventional heating time (45?minutes), conventional heating temperature (500?°C), and the phosphoric acid:sample ratio (0.7:1). An adsorption capacity of methylene blue of 148?mg/g and an iodine value of 791?mg/g was obtained for the prepared activated carbon. 相似文献
45.
In this paper, we consider a viscoelastic wave equation of variable coefficients in the presence of past history with nonlinear damping and delay in the internal feedback and dynamic boundary conditions. Under suitable assumptions, we establish an explicit and general decay rate result without imposing restrictive assumption on the behavior of the relaxation function at infinity by Riemannian geometry method and Lyapunov functional method. 相似文献
46.
Two novel 2′-hydroxychalcone derivatives (i.e., M1 and M2) are explored in this work. We mainly focus on investigating the effects of photoexcitation on hydrogen bonds and on the excited-state intramolecular proton transfer (ESIPT) process. On the basis of calculations of electrostatic potential surface and intramolecular interactions, we verify the formation of hydrogen bond O1 H2···O3 in both S0 and S1 states. Exploring the ultraviolet–visible spectra in the liquid phase, our simulated results reappear in the experimental phenomenon. Analyzing molecular geometry and infrared stretching vibrational spectra, we confirm O1 H2···O3 is strengthened for both M1 and M2 in the S1 state. We further confirm that charge redistribution facilitates ESIPT tendency. Constructing potential energy curves, we find the ultrafast ESIPT behavior for M1, which is because of the deficiency of side hydroxyl moiety comparing with M2. This work makes a reasonable affiliation of the ESIPT mechanism for M1 and M2. We wish this paper could facilitate understanding these two novel systems and promote their applications. 相似文献
47.
48.
49.
Padavattan Govindaswamy Patrick J. Carroll Yurij A. Mozharivskyj Mohan Rao Kollipara 《Journal of Chemical Sciences》2006,118(4):319-326
The reaction of [{(η5-C5Me5)M(μ-Cl)Cl}2] {where M = Rh (1), Ir (2)} with functionalized phosphine viz., diphenyl-2-pyridylphosphine (PPh2Py) in dichloromethane solvent yield neutral ϰ1-P-coordinated rhodium and iridium complexes [(η5-C5Me5)RhCl2(κ1-P-PPh2Py)]3 and [(η5-C5Me5) IrCl2(ϰ1-P-PPh2Py)]4. Reaction of complexes 1 and 2 with the ligand PPh2Py in methanol under reflux give bis-substituted complexes such as [(η5-C5Me5)RhCl(ϰ1-P-PPh2Py)2]+
5 and [(η5-C5Me5)IrCl(ϰ1-P-PPh2Py)2]+
6, whereas stirring in methanol at room temperature gives P-, N-chelating complexes of the type [(η5-C5Me5)RhCl(ϰ2-P-N-PPh2Py)]+ 7 and [(η5-C5Me5)IrCl(ϰ2-P-N-PPh2Py)]+
8. Neutral ϰ1-P-coordinated complexes [(η5-C5Me5)RhCl2(ϰ1-P-PPh2Py)]3 and [(η5-C5Me5)IrCl2(ϰ1-P-PPh2Py)]4 easily undergo conversion to the cationic P-, N-chelating complexes [(η5-C5Me5)RhCl(ϰ2-P-N-PPh2Py)]+
7 and [(η5-C5Me5) IrCl(ϰ2-P, N-PPh2Py)]+
8 on stirring in methanol at room temperature. These complexes are characterized by FT-IR and FT-NMR spectroscopy as well as
analytical methods. The molecular structures of the representative complexes [(η5-C5Me5)RhCl2(ϰ1-P-PPh2Py)]3, [(η5-C5Me5)IrCl2(ϰ1-P-PPh2Py)]4 and hexafluorophosphate salt of complex [(η5-C5Me5)IrCl(ϰ2-P-PPh2Py)2]+
6 are established by single-crystal X-ray diffraction methods 相似文献
50.