全文获取类型
收费全文 | 5384篇 |
免费 | 142篇 |
国内免费 | 20篇 |
专业分类
化学 | 3726篇 |
晶体学 | 71篇 |
力学 | 74篇 |
数学 | 235篇 |
物理学 | 1440篇 |
出版年
2022年 | 29篇 |
2021年 | 35篇 |
2020年 | 55篇 |
2019年 | 65篇 |
2018年 | 53篇 |
2017年 | 34篇 |
2016年 | 85篇 |
2015年 | 87篇 |
2014年 | 116篇 |
2013年 | 255篇 |
2012年 | 250篇 |
2011年 | 264篇 |
2010年 | 151篇 |
2009年 | 160篇 |
2008年 | 285篇 |
2007年 | 239篇 |
2006年 | 260篇 |
2005年 | 245篇 |
2004年 | 243篇 |
2003年 | 190篇 |
2002年 | 197篇 |
2001年 | 149篇 |
2000年 | 161篇 |
1999年 | 86篇 |
1998年 | 62篇 |
1997年 | 63篇 |
1996年 | 62篇 |
1995年 | 44篇 |
1994年 | 67篇 |
1993年 | 89篇 |
1992年 | 94篇 |
1991年 | 74篇 |
1990年 | 63篇 |
1989年 | 55篇 |
1988年 | 72篇 |
1987年 | 73篇 |
1986年 | 74篇 |
1985年 | 105篇 |
1984年 | 96篇 |
1983年 | 39篇 |
1982年 | 69篇 |
1981年 | 74篇 |
1980年 | 67篇 |
1979年 | 60篇 |
1978年 | 52篇 |
1977年 | 64篇 |
1976年 | 56篇 |
1975年 | 40篇 |
1974年 | 49篇 |
1973年 | 30篇 |
排序方式: 共有5546条查询结果,搜索用时 15 毫秒
11.
Takaaki Kakitsuka Shinji Matsuo Seok–Hwan Jeong Toru Segawa Hiroshi Okamoto Yoshihiro Kawaguchi Yasuhiro Kondo Yuzo Yoshikuni Hiroyuki Suzuki 《Optical and Quantum Electronics》2006,38(12-14):1053-1060
We theoretically investigated a digitally tunable laser with a chirped ladder filter and a ring resonator to obtain a wide wavelength tuning range covering the whole C- or L- band. The clear relation between the tuning range and laser structure, especially the ladder filter, is described analytically. The introduction of a chirped structure into a ladder filter is effective in achieving both wide tunability and a stable lasing mode. A numerical simulation based on multimode rate equations shows that a tuning range of over 40 nm and a mode suppression ratio over 40 dB can be achieved by introducing a chirped ladder filter. 相似文献
12.
In this article a stability result for the Falk model system is proven. The Falk model system describes the martensitic phase transitions in shape memory alloys. In our setting, the steady state is a nonlocal elliptic problem. We show the dynamical stability for the linearized stable critical point of the corresponding functional. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
13.
14.
Corrosion-related defects of pure iron were investigated by measuring Doppler broadening energy spectra (DBES) of positron annihilation and positron annihilation lifetime (PAL). Defect profiles of the S-parameter from DBES as a function of positron incident energy up to 30 keV (i.e. ∼1 μm depth) were analyzed. The DBES data show that S-parameter increases as a function of positron incident energy (mean depth) after corrosion, and the increase in the S-parameter is larger near the surface than in the bulk due to corrosion. Furthermore, information on defect size from PAL data as a function of positron incident energy up to 10 keV (i.e. ∼0.2 μm depth) was analyzed. In the two-state trapping model, the lifetime τ2 = 500 ps is ascribed to annihilation of positrons in voids with a size of the order of nanometer. τ1, which decreases with depth from the surface to the bulk, is ascribed to the annihilation of positrons in dislocations and three-dimensional vacancy clusters. The corroded samples show a significant increase in τ1 and the intensity I2, and near the surface the corroded iron introduces both voids and large-size three-dimensional vacancy clusters. The size of vacancy clusters decreases with depth. 相似文献
15.
Adsorption structures of the pentacene (C22H14) molecule on the clean Si(0 0 1)-2 × 1 surface were investigated by scanning tunneling microscopy (STM) in conjunction with density functional theory calculations and STM image simulations. The pentacene molecules were found to adsorb on four major sites and four minor sites. The adsorption structures of the pentacene molecules at the four major sites were determined by comparison between the experimental and the simulated STM images. Three out of the four theoretically identified adsorption structures are different from the previously proposed adsorption structures. They involve six to eight Si-C covalent chemical bonds. The adsorption energies of the major four structures are calculated to be in the range 67-128 kcal/mol. It was also found that the pentacene molecule hardly hopped on the surface when applying pulse bias voltages on the molecule, but was mostly decomposed. 相似文献
16.
Kentaro Suzuya Tomoaki Kamiyama Takemi Yamamura Kiyohito Okamura Kenji Suzuki 《Journal of Non》1992,150(1-3):167-171
A small-angle X-ray scattering (SAXS) study was performed to reveal the nanometer scale hybrid structure of Si---Ti---C---O fibers prepared by the pyrolysis of polytitanocarbosilane. The SAXS profile for Si---Ti---C---O fibers is attributed to two different types of scattering entities: an anisotropic contribution from long filaments with diameters hundreds to thousands of Ångströms and an isotropic contribution from β-SiC fine clusters of about a nanometer in diameter. A drastic degradation in the tensile strength of the fibers is correlated to the characteristic variations in their long-and medium-range structure. 相似文献
17.
18.
19.
The anti-tumor agent, tamoxifen, is easily synthesized by the successive allylation of benzaldehyde and the Friedel-Crafts alkylation reaction of anisole with the intermediary homoallyl silyl ethers, followed by the migration of the double bond to form the desired tetra-substituted ethylenes. Several derivatives of tamoxifen are also produced according to a similar synthetic strategy. 相似文献
20.
K. Suzuki S. Miyashita K. Takashina Y. Hirayama 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):232
We investigate the quantum Hall effect (QHE) in the InAs/GaSb hybridized electron–hole system grown on a conductive InAs substrate which act as a back-gate. In these samples, the electron density is constant and the hole density is controlled by the gate-voltage. Under a magnetic field perpendicular to the sample plane, the QHE appears along integer Landau-level (LL) filling factors of the net-carriers, where the net-carrier density is the difference between the electron and hole densities. In addition, longitudinal resistance maxima corresponding to the crossing of the extended states of the original electron and hole LLs make the QHE regions along integer-νnet discontinuous. Under tilted magnetic fields, these Rxx maxima disappear in the high magnetic field region. The results show that the in-plane magnetic field component enhances the electron–hole hybridization and the formation of minigaps at LL crossings. 相似文献