全文获取类型
收费全文 | 15426篇 |
免费 | 2571篇 |
国内免费 | 1907篇 |
专业分类
化学 | 11314篇 |
晶体学 | 227篇 |
力学 | 860篇 |
综合类 | 130篇 |
数学 | 1605篇 |
物理学 | 5768篇 |
出版年
2024年 | 62篇 |
2023年 | 317篇 |
2022年 | 562篇 |
2021年 | 574篇 |
2020年 | 586篇 |
2019年 | 650篇 |
2018年 | 526篇 |
2017年 | 509篇 |
2016年 | 719篇 |
2015年 | 733篇 |
2014年 | 929篇 |
2013年 | 1226篇 |
2012年 | 1426篇 |
2011年 | 1546篇 |
2010年 | 1033篇 |
2009年 | 1008篇 |
2008年 | 1013篇 |
2007年 | 990篇 |
2006年 | 796篇 |
2005年 | 683篇 |
2004年 | 580篇 |
2003年 | 443篇 |
2002年 | 414篇 |
2001年 | 350篇 |
2000年 | 328篇 |
1999年 | 251篇 |
1998年 | 212篇 |
1997年 | 168篇 |
1996年 | 185篇 |
1995年 | 147篇 |
1994年 | 154篇 |
1993年 | 118篇 |
1992年 | 115篇 |
1991年 | 93篇 |
1990年 | 87篇 |
1989年 | 77篇 |
1988年 | 44篇 |
1987年 | 41篇 |
1986年 | 42篇 |
1985年 | 40篇 |
1984年 | 29篇 |
1983年 | 16篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
G.B. Song C.Q. Han J.K. Liang Q.L. Liu F.S. Liu G.H. Rao 《Journal of solid state chemistry》2004,177(7):2394-2403
The subsolidus phase relations of the PrOx-CaO-CuO pseudo-ternary system sintered at 950-1000°C have been investigated by X-ray powder diffraction. In this system, there exist one compound Ca10Pr4Cu24O41, one Ca2Pr2Cu5O10-based solid solution, seven three-phase regions and two two-phase regions. The crystal structures of Ca10Pr4Cu24O41 and Ca2Pr2Cu5O10-based solid solution have been determined. Compound Ca10Pr4Cu24O41 crystallizes in an orthorhombic cell with space group D2h20−Cccm, Z=4. Its lattice parameters are a=11.278(2) Å, b=12.448(3) Å and c=27.486(8) Å. The crystal structure of Ca2Pr2Cu5O10-based solid solution is an incommensurate phase based on the orthorhombic NaCuO2 type subcell. The lattice parameters of the subcell of the Ca2.4Pr1.6Cu5O10 are a0=2.8246(7) Å, b0=6.3693(5) Å, c0=10.679(1) Å, and those of the orthorhombic superstructure are with a=5a0, b=b0, c=5c0. The Ca2.4Pr1.6Cu5O10 structure can also be determined by using a monoclinic supercell with space group C2h5−P21/c, Z=4, a=5a0, b=b0, and β=104.79(1)° or 136.60(1)°, V=5a0b0c0. 相似文献
52.
53.
M. Liang H. Ohm B. De Sutter K. Sistemich 《Zeitschrift für Physik A Hadrons and Nuclei》1992,344(3):357-358
Tie half-lives of 8 low lying levels of103Nb have been determined at the fission-product separator JOSEF. A B-- triple-coincidence method was used which consists in a measurement of the time delay between the feeding of the levels through the B– decay of103Zr and their decay, in coincidence with a tagging ray, with plastic, BaF2 and Ge detectors, respectively. Most of the investigated levels are members of the three known rotational bands based on the ground state and the 164 and 248 keV levels. The deformation Bq=0.31(3) of103Nb could be deduced from the half-life data. The half-lives are well reproduced through calculations in the frame of the Nilsson model.The authors thank Dr. T. Seo for valuable advise in connection with the Nilsson-model calculations. 相似文献
54.
55.
M. Liang H. Ohm B. De Sutter K. Sistemich B. Fazekas G. Molnär 《Zeitschrift für Physik A Hadrons and Nuclei》1991,340(2):223-224
The half-lives of low-lying levels of the neutron-rich isotopes102Mo and104Mo have been measured at the fission product separator Josef with the ß-- triple coincidence technique. Values of t1/2= 126(4)ps and 0.72(4)ns have been obtained for the 21
+ levels at 296 keV and 192 keV in102Mo and104Mo, respectively. Deformation parameters of ßq=0.28(1) and 0.31(1), respectively, are deduced, which are smaller than those of the isotones of Sr and Zr. The interacting boson model accounts well for the trend of 2+ energies in the Mo isotopes but slightly overpredicts the B(E2) values at saturation. A smooth dependence of 21
+ vs. E 21
+ is found for the A 100 region in agreement with the hydrodynamical model.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday 相似文献
56.
Hydrogen peroxide (HOOH) in ice and snow is an important chemical tracer for the oxidative capacities of past atmospheres. However, photolysis in ice and snow will destroy HOOH and form the hydroxyl radical (*OH), which can react with snowpack trace species. Reactions of *OH in snow and ice will affect the composition of both the overlying atmosphere (e.g., by the release of volatile species such as formaldehyde to the boundary layer) and the snow and ice (e.g., by the *OH-mediated destruction of trace organics). To help understand these impacts, we have measured the quantum yield of *OH from the photolysis of HOOH on ice. Our measured quantum yields (Phi(HOOH --> *OH)) are independent of ionic strength, pH, and wavelength, but are dependent upon temperature. This temperature dependence for both solution and ice data is best described by the relationship ln(Phi(HOOH --> *OH)) = -(684 +/- 17)(1/T) + (2.27 +/- 0.064) (where errors represent 1 standard error). The corresponding activation energy (Ea) for HOOH (5.7 kJ mol(-1)) is much smaller than that for nitrate photolysis, indicating that the photochemistry of HOOH is less affected by changes in temperature. Using our measured quantum yields, we calculate that the photolytic lifetimes of HOOH in surface snow grains under midday, summer solstice sunlight are approximately 140 h at representative sites on the Greenland and Antarctic ice sheets. In addition, our calculations reveal that the majority of *OH radicals formed on polar snow grains are from HOOH photolysis, while nitrate photolysis is only a minor contributor. Similarly, HOOH appears to be much more important than nitrate as a photochemical source of *OH on cirrus ice clouds, where reactions of the photochemically formed hydroxyl radical could lead to the release of oxygenated volatile organic compounds to the upper troposphere. 相似文献
57.
58.
59.
In this paper, the authors give some sufficient conditions for an amalgamated
3-manifold along a compact connected surface F with boundary to be ?-irreducible in
terms of distances between some kinds of vertex subsets of the curve complex and the arc
complex of F. 相似文献
60.
Tian-Yang Wu Juan Liang Jing-Ya Ai Jing-Long Cui Wei-Dong Huang Yi-Lin You Ji-Cheng Zhan 《Molecules (Basel, Switzerland)》2022,27(13)
Mulberry extract has been proven to have the effect of resisting alcohol damage, but its mechanism is still unclear. In this study, the composition of mulberry ethanol extract (MBE) was identified by LC-MS/MS and the main components of MBE were ascertained by measuring. Gastric mucosal epithelial (GES-1) cells were used to elucidate the mechanism of MBE and rutin (the central part of MBE) helped protect against alcohol damage. The results revealed that phenolics accounted for the majority of MBE, accounting for 308.6 mg/g gallic acid equivalents and 108 substances were identified, including 37 flavonoids and 50 non-flavonoids. The treatment of 400 μg/mL MBE and 320 μM rutin reduced early cell apoptosis and the content of intracellular reactive oxygen species, malondialdehyde and increased glutathione. The qPCR results indicated that the MBE inhibits the expression of genes in the mitogen-activated protein kinase (MAPK) pathway, including p38, JNK, ERK and caspase-3; rutin inhibits the expression of p38 and caspase-3. Overall, MBE was able to reduce the oxidative stress of GES-1 cells and regulated apoptosis-related genes of the MAPK pathway. This study provides information for developing anti-ethanol injury drugs or functional foods. 相似文献