全文获取类型
收费全文 | 8630篇 |
免费 | 1559篇 |
国内免费 | 964篇 |
专业分类
化学 | 6365篇 |
晶体学 | 76篇 |
力学 | 512篇 |
综合类 | 45篇 |
数学 | 1057篇 |
物理学 | 3098篇 |
出版年
2024年 | 26篇 |
2023年 | 208篇 |
2022年 | 360篇 |
2021年 | 340篇 |
2020年 | 467篇 |
2019年 | 394篇 |
2018年 | 352篇 |
2017年 | 285篇 |
2016年 | 415篇 |
2015年 | 431篇 |
2014年 | 539篇 |
2013年 | 640篇 |
2012年 | 774篇 |
2011年 | 823篇 |
2010年 | 548篇 |
2009年 | 489篇 |
2008年 | 480篇 |
2007年 | 454篇 |
2006年 | 471篇 |
2005年 | 356篇 |
2004年 | 278篇 |
2003年 | 227篇 |
2002年 | 279篇 |
2001年 | 160篇 |
2000年 | 169篇 |
1999年 | 179篇 |
1998年 | 129篇 |
1997年 | 128篇 |
1996年 | 139篇 |
1995年 | 108篇 |
1994年 | 97篇 |
1993年 | 64篇 |
1992年 | 66篇 |
1991年 | 57篇 |
1990年 | 46篇 |
1989年 | 42篇 |
1988年 | 37篇 |
1987年 | 18篇 |
1986年 | 25篇 |
1985年 | 21篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1957年 | 3篇 |
1935年 | 1篇 |
1931年 | 1篇 |
1930年 | 3篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
为了便于模式变换器的设计,达到双频微波都能集中辐射的目的,提出一种轴向分区的双频磁绝缘线振荡器,该器件束波互作用区为中间隔开、两端不同周期、不同深度的慢波结构,使电子在上下游与不同频率特性的慢波结构进行束波互作用,得到稳定的双频微波输出。使用2.5维全电磁粒子模拟软件进行数值模拟,在工作电压450 kV,电流40 kA条件下输出微波功率为1.4 GW,功率效率约为7%,输出的微波频率分别为1.25 GHz和1.65 GHz,两者频谱幅度相差约为1.5 dB,模式为TEM模。 相似文献
902.
L. Liu J. J. Zheng S. L. Yuan Z. M. Tian C. H. Wang 《Journal of nanoparticle research》2011,13(6):2305-2310
Magnetic properties of La1−x
Ca
x
MnO3 (0.5 ≤ x ≤ 0.8) samples with an equivalent average particle size ~50 nm prepared by a sol–gel method were investigated. The charge
ordering (CO) transition that is observed in the bulks disappears and the ferromagnetic (FM) transition occurs in all the
prepared samples. For all the samples, the spontaneous magnetization (M
S) value is much lower than the corresponding theoretic value, which shows that the majority of the sample is antiferromagnetic
(AFM). However, the M
S value is much larger than the corresponding value reported by some other groups. The invisible of CO transition and the large
M
S value can be attributed to the good connection among the adjacent particles. Moreover, the exchange bias (EB) phenomenon
is observed except the x = 0.5 sample. With x increasing, the M
S value decreases and the EB field increases, which can be understood by considering the coexistence of FM phase with Mn3+–Mn4+ spin clusters in the shell and the AFM phase in the core of the nanoparticles. 相似文献
903.
Jiyeon Lee Dahye Im Yajie Liu Jing Fang Xibao Tian Minsu Kim Prof. Wen-Bin Zhang Prof. Jongcheol Seo 《Angewandte Chemie (International ed. in English)》2023,62(51):e202314980
A technique combining ion mobility spectrometry-mass spectrometry (IMS-MS) and supercharging electrospray ionization (ESI) has been demonstrated to differentiate protein chemical topology effectively. Incorporating as many charges as possible into proteins via supercharging ESI allows the protein chains to be largely unfolded and stretched, revealing their hidden chemical topology. Different chemical topologies result in differing geometrical sizes of the unfolded proteins due to constraints in torsional rotations in cyclic domains. By introducing new topological indices, such as the chain-length-normalized collision cross-section (CCS) and the maximum charge state (zM) in the extensively unfolded state, we were able to successfully differentiate various protein chemical topologies, including linear chains, ring-containing topologies (lasso, tadpole, multicyclics, etc.), and mechanically interlocked rings, like catenanes. 相似文献
904.
Superconductivities and structural properties of Ti-Zr-Ta ternary alloys are extensively investigated. The TiZrTa sample has a cubic structure (β -phase) and shows a sharp superconducting transition at a critical temperature (Tc) of about 7.3 K. In addition, two series of Ti-Zr-Ta alloys, with nominal compositions of Ti65-xZr35Tax and TixZr65-xTa35 respectively, are prepared, and their superconductivities and crystal structures change regularly with the chemical composition. Our experimental study also indicates that the annealing processing of this kind of material can cause the transition temperature to increase and the highest Tc is observed to be about 8.3 K in annealed samples. 相似文献
905.
We investigate the structural, electronic and adsorption properties of one single CO molecule adsorbed on RhN (N = 2-19) clusters, using the density-functional theory in the spin-polarized generalized gradient approximation. It is found that the structural growth model of the RhN clusters transforms from double layers (N = 12-16) to three layers (N = 17-19). Three different adsorption types are the atop site adsorption for N = 6, 8, 9, 11, 12, the bridge site adsorption for N = 2-5, 7, 10, 13-15, 17 and the face adsorption for N = 16, 18, 19. The adsorption abilities of RhN clusters are related to C-O bond length, vibrational frequency, adsorption energy and the charge transfer between CO and Rh clusters as well as the electronic density of state. With the increase of Rh cluster size, the adsorption energy of CO adsorbed on RhN clusters tends to be 2.2 eV-2.3 eV, which is 0.2 eV-0.3 eV larger than the theoretical value (about 2.0 eV) of CO molecule adsorption on clean Rh (111) surface. 相似文献
906.
The low-lying electric dipole strengths in proton-rich nuclei 17F and 17Ne, which can be produced at HIRFL-CSR in Lanzhou, are investigated. In the framework of the covariant density functional theory the self-consistent relativistic Hartree Bogoliubov model and the relativistic quasiparticle random phase approximation with the NL3 parameter set and Gogny pairing interaction are adopted in the calculations. A pronounced dipole peak appears below 10 MeV in 17Ne, but does not occur in 17F. The properties of this low-lying E1 excitation in 17Ne are studied, which may correspond to a proton pygmy resonance with different characteristics from those of giant dipole resonance. 相似文献
907.
Andrew K. Johnson Jozef Kaczor Hongmei Han Maninder Kaur Guoxin Tian Linfeng Rao You Qiang Andrzej J. Paszczynski 《Journal of nanoparticle research》2011,13(10):4881-4895
The creation of multifunctional nanomaterials by combining organic and inorganic components is a growing trend in nanoscience. The unique size-dependent properties of magnetic nanoparticles (MNPs) make them amenable to numerous applications such as carriers of expensive biological catalysts, in magnetically assisted chemical separation of heavy metals and radionuclides from contaminated water sources. The separation of minor actinides from high-level radionuclide waste requires a sorbent stable in acidic pH, with ease of surface functionalization, and a high capacity for binding the molecules of interest. For the described experiments, the MNPs with 50 nm average size were used (size distribution from 20 to 100 nm and an iron content of 80–90 w/w%). The MNPs that have been double coated with an initial silica coating for protection against iron solubilization and oxidation in nitric acid solution (pH 1) and a second silica/polymer composite coating incorporating partially imbedded poly(allylamine) (PA). The final product is magnetic, highly swelling, containing >95% water, with >0.5 mmol amines g?1 available for functionalization. The amine groups of the magnetic resin were functionalized with the chelating molecules diethylenetriaminepentaacetic acid (DTPA) and N,N-dimethyl-3-oxa-glutaramic acid (DMOGA) for separation of minor actinides from used nuclear fuel. 相似文献
908.
W. Yang K. Nelissen M. H. Kong Y. T. Li Y. M. Tian 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,83(4):499-505
The angular and radial melting properties of two-dimensional classical systems consisting
of different types of particles confined in a parabolic trap are studied through modified
Monte Carlo simulations. A universal behavior of the angular melting process is found,
which occurs in multiple steps due to shell depended melting temperatures. The melting
sequence of the different shells is determined by two major factors: (1) the confinement
strength which each shell is subjected to, and (2) the specific structure of each shell.
Further, a continuous radial disordering of the particle types forming a single circular
shell is found and analyzed. This phenomenon has never been observed before in
two-dimensional mono-dispersive systems. This continuous radial disordering results from
the high energy barrier between different particle types in multi-species systems. 相似文献
909.
We investigate the diffusion interaction and quantitative analysis of zinc dialkyldithiophosphate (ZDDP) mixed with lube base oil (LBO) at different concentrations using terahertz time-domain spectroscopy (THzTDS).When the concentration exceeds 6.78%,the characteristic absorption peaks exhibit significantly shift,and the absorption coefficient peak value is nonlinear against concentration.Moreover,the absorption coefficients of mixed samples follow the Beer’s law at a concentration below 6.78%.The quantitative analysis enables a strategy for monitoring the formulation of lubricating oil in real time. 相似文献
910.
Youyi Sun Guizheng GuoBinhua Yang Wei CaiYe Tian Minghong HeYaqing Liu 《Physica B: Condensed Matter》2011,406(4):1013-1016
A new synthesis method of α-Fe2O3 nanoparticles was developed, in which the ferrous and ferric salts as well as polyaniline acted as the precursor and dispersant, respectively. From the investigation of X-ray diffraction and FT-IR spectra, the α-Fe2O3 nanoparticles can be directly prepared by the co-precipitation method without high-temperature calcining. Transmission electron microscope (TEM) and scanning electron microscope (SEM) observation revealed that the α-Fe2O3 nanoparticles had average diameters ranging from 30.0 to 75.0 nm. Compared with previous methods, this present method shows an easy processing and can be applied on the large-scale produce of α-Fe2O3 nanoparticles in one step. 相似文献