全文获取类型
收费全文 | 3913篇 |
免费 | 77篇 |
国内免费 | 32篇 |
专业分类
化学 | 3105篇 |
晶体学 | 63篇 |
力学 | 62篇 |
数学 | 184篇 |
物理学 | 608篇 |
出版年
2022年 | 25篇 |
2021年 | 30篇 |
2020年 | 33篇 |
2019年 | 37篇 |
2018年 | 25篇 |
2017年 | 34篇 |
2016年 | 46篇 |
2015年 | 72篇 |
2014年 | 82篇 |
2013年 | 273篇 |
2012年 | 173篇 |
2011年 | 231篇 |
2010年 | 134篇 |
2009年 | 109篇 |
2008年 | 202篇 |
2007年 | 206篇 |
2006年 | 222篇 |
2005年 | 208篇 |
2004年 | 195篇 |
2003年 | 206篇 |
2002年 | 201篇 |
2001年 | 52篇 |
2000年 | 59篇 |
1999年 | 60篇 |
1998年 | 49篇 |
1997年 | 42篇 |
1996年 | 56篇 |
1995年 | 54篇 |
1994年 | 46篇 |
1993年 | 30篇 |
1992年 | 34篇 |
1991年 | 31篇 |
1990年 | 32篇 |
1989年 | 36篇 |
1988年 | 41篇 |
1987年 | 30篇 |
1986年 | 26篇 |
1985年 | 53篇 |
1984年 | 52篇 |
1983年 | 29篇 |
1982年 | 57篇 |
1981年 | 43篇 |
1980年 | 58篇 |
1979年 | 59篇 |
1978年 | 45篇 |
1977年 | 31篇 |
1976年 | 24篇 |
1975年 | 28篇 |
1974年 | 29篇 |
1973年 | 19篇 |
排序方式: 共有4022条查询结果,搜索用时 0 毫秒
251.
Alexander A. Kaminskii Ladislav Bohatý Oliver Lux Hanjo Rhee Hans Joachim Eichler Eugen Libowitzky Reiner Kleinschrodt Hitoki Yoneda Akira Shirakawa Petra Becker 《Laser \u0026amp; Photonics Reviews》2016,10(5):814-825
Hexagonal Ca5(PO4)3F, known as natural crystal fluorapatite and oldest host‐crystal for Ln3+‐lasant ions, is presented as a Raman‐active material. High‐order Raman‐induced χ(3)‐nonlinear processes are discovered in natural crystals of fluorapatite under picosecond pumping at 1.064 μm and 0.532 μm wavelength. A multitude of Stokes and anti‐Stokes components is generated in the ultraviolet, visible and near‐infrared spectral region by stimulated Raman scattering (SRS) and Raman four‐wave mixing (FWHM), resulting in a frequency comb with a width of 520 THz. The spectral lines are identified and attributed to the ν1(Ag) vibration mode of the tetrahedral [PO4] units which is related to a Raman shift of ωSRS ≈ 965 cm−1. The first Stokes steady‐state Raman gain coefficient in the near‐infrared spectral range is estimated to be >0.38 cm·GW−1. Finally, a short review of SRS‐promoting vibration modes and observed χ(3)‐ nonlinear interactions in all known SRS‐active natural crystals (minerals) is given.
252.
Akira Saito 《Combinatorica》1996,16(3):433-437
A graphG is said to bek-path-connected if every pair of distinct vertices inG are joined by a path of length at leastk. We prove that if max{deg
G
x
, deg
G
y
}k for every pair of verticesx,y withd
G
(x,y)=2 in a 2-connected graphG, whered
G
(x,y) is the distance betweenx andy inG, thenG isk-path-connected. 相似文献
253.
Kimura H Nakayama Y Tsuchida A Okubo T 《Colloids and surfaces. B, Biointerfaces》2007,56(1-2):236-Optics
Rheological properties for Chinese ink in exhaustively deionized aqueous media were carefully examined. In the steady shear measurement, the shear viscosities of the ink could be well explained by considering the “effective” volume fraction of the particles in the ink including the electrical double layers and by using Einstein's equation for dilute suspension viscosity, when the particle volume fraction was substantially low. In the case that the volume fraction was higher, the shear viscosities showed extremely higher than those from Einstein's prediction, though the ink remained a Newtonian liquid. In the stress-strain measurement, the shear moduli were observed at strain smaller than 0.2. The “weak” aggregation among the particles in the ink under no shear or low shear rates was supported. It should be noted that the glue in the suspension plays an important role for the good liquidity of the ink and for the “weak” bridges among the particles resulting its good dispersion stability. 相似文献
254.
255.
Magnetic field has been applied to a copper vapor laser with an intention of improving the laser characteristics by inner gas convection. The convection induced by the J×B cross-field discharge (the Lorentz force) is used for partially replacing or mixing the laser medium in a highly heated discharged region with relatively cold gas surrounding the region. It is observed that the output power increases with the increase of the magnetic field. A 23% increase in the output power is obtained with a magnetic field of 150 gauss. The cross-field discharge causes an increase in the peak discharge voltage and a reduction in the initial part of discharge current (Phantom current). Based on the results observed, the possible mechanisms for increasing the power are discussed. 相似文献
256.
The structure of the 1,3,4,6-tetrakis(isopropylthio)thieno[3,4-c]thiophene dication ( 2 ) prepared from 1,3,4,6-tetrakis(isopropylthio)thieno[3,4-c]thiophene ( 1 ) by two-electron oxidation was investigated by X-ray crystallographic analysis. The results revealed that the positive charges are largely delocalized on the two i-PrS-C-C-C-SPr-i moieties. 相似文献
257.
Cyclic and acyclic ethers are regioselectively cleaved at less substituted α-carbon-oxygen bond in the absence of Lewis acid by the reagent system of sodium iodide and acyl chlorides. 相似文献
258.
Ichikawa S Minakawa N Shuto S Tanaka M Sasaki T Matsuda A 《Organic & biomolecular chemistry》2006,4(7):1284-1296
3'-beta-Carbamoylmethylcytidine (CAMC) and its derivatives were synthesized using an intramolecular Reformatsky-type reaction promoted by SmI2 as the key step. In vitro tumor cell growth inhibitory activity was evaluated and CAMC was found to exhibit potent cytotoxicity against various human tumor cell lines. From a structure-activity relationship study it was postulated that the cytotoxic mechanism of action of CAMC did not require phosphorylation at the 5'-hydroxyl group. This study provides a novel strategy for the development of a new type of antitumor nucleoside. 相似文献
259.
Yamashita M Ueda K Sakaguchi K Tokuda H Iida A 《Chemical & pharmaceutical bulletin》2011,59(10):1289-1293
In this paper, a concise one-pot method for the construction of benzo[f]indole-4,9-dione motifs is described. These transformations proceed via a sequential palladium- and copper-catalyzed coupling reaction of 1,4-naphthoquinones with terminal acetylenes, followed by a copper-catalyzed intramolecular cyclization reaction of the resulting coupling product. 相似文献
260.
Selective solvation can be crucial in phase separation in polar binary mixtures (water–oil) with a small amount of hydrophilic ions or hydrophobic particles. They are preferentially attracted to one of the solvent components, leading to a number of intriguing effects coupled to phase separation. For example, if cations and anions interact differently with the two components, an electric double layer emerges at a liquid–liquid interface. The main aim of this paper is to show that a strongly hydrophilic (hydrophobic) solute induces precipitation of water-rich (oil-rich) domains above a critical solute density np outside the solvent coexistence curve. 相似文献