全文获取类型
收费全文 | 4654篇 |
免费 | 673篇 |
国内免费 | 625篇 |
专业分类
化学 | 3642篇 |
晶体学 | 68篇 |
力学 | 195篇 |
综合类 | 55篇 |
数学 | 722篇 |
物理学 | 1270篇 |
出版年
2024年 | 7篇 |
2023年 | 44篇 |
2022年 | 91篇 |
2021年 | 123篇 |
2020年 | 150篇 |
2019年 | 191篇 |
2018年 | 163篇 |
2017年 | 118篇 |
2016年 | 232篇 |
2015年 | 235篇 |
2014年 | 262篇 |
2013年 | 350篇 |
2012年 | 335篇 |
2011年 | 370篇 |
2010年 | 283篇 |
2009年 | 277篇 |
2008年 | 358篇 |
2007年 | 320篇 |
2006年 | 275篇 |
2005年 | 240篇 |
2004年 | 216篇 |
2003年 | 213篇 |
2002年 | 284篇 |
2001年 | 229篇 |
2000年 | 126篇 |
1999年 | 95篇 |
1998年 | 62篇 |
1997年 | 36篇 |
1996年 | 27篇 |
1995年 | 25篇 |
1994年 | 23篇 |
1993年 | 23篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1982年 | 13篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1975年 | 3篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1971年 | 3篇 |
1936年 | 4篇 |
排序方式: 共有5952条查询结果,搜索用时 46 毫秒
31.
应用密度矩阵方程计算了四能级原子系统中三阶非线性极化率随信号光和探针光频率失谐的变化关系。结果表明,由于量子干涉对信号光强度的敏感性,使四能级原子介质的交叉Kerr非线性作用大大增强,与三能级系统相比,四能级原子介质的Kerr非线性系数可增强两个数量级。 相似文献
32.
Al-Cu-Fe thin films were prepared by laser induced arc (laser-arc) method from a single source—Al63Cu25Fe12 alloy, which was proved to consist of quasicrystalline phase together with approximant phase. The composition of the deposited films meets the requirement for formation of icosahedral symmetry phase. Quasicrystalline phase was obtained after annealing the amorphous as-deposit film samples. The optical properties of the samples were investigated. Thin film samples of Al, Cu and Fe deposited under the same condition were employed for comparison. The results showed specific reflective properties of Al-Cu-Fe quasicrystal thin film in some wavelength range. The optical conductivity of the films exhibited a negative peak, centered about 440 nm in range of 190 to 800 nm. The Al-Cu-Fe quasicrystal thin films could absorb almost all the ray in the wavelength range from 420nm to 450 nm. The ratio of absorption was greater than 99%. 相似文献
33.
34.
35.
Mitsunori Oda Yosuke Fukuchi Satoshi Ito Nguyen Chung Thanh Shigeyasu Kuroda 《Tetrahedron letters》2007,48(52):9159-9162
Reactions of pyrrolidine with 2 equiv of aldehydes without any catalyst in a pressurized vessel at 140–200 °C yielded 1,3-disubstituted pyrroles. -Branched aldehydes gave fairly good yields of the corresponding products by this method, which provides a facile non-oxidative procedure for synthesizing 1,3-dialkylpyrroles from inexpensive pyrrolidine and aldehydes. 相似文献
36.
ThefascinatingsbocturesandpropertiesoffullereneshaveoPeneduPanewfieldofchendstry.Inparticular,F.Wudletal.l'2haveshownthatwatersofubleC6ocomPoundsinhibittheHITVen-zymesprotease(HIVP)andreversetranscriPtase(HIVRT).IthasbeenafocusofstUdytoinvestigatethebiologicalactivitiesofthesenovelsubstances.Fortheirpossiblemedicaluses,tolinkC6omoleculetonaturalProductssuchassugars,pephdes,amioacides,andsoonisanimPortantmethodinthisfield.Vasella3reportedthefirstglucosidederivativeofC6o'InthispaPer,w… 相似文献
37.
Measurement of small-signal and large-signal responses of packaged laser modules at high temperature
Ning Hua Zhu Ji Min Wen Hai Peng Song Shang Jian Zhang Liang Xie 《Optical and Quantum Electronics》2006,38(15):1245-1257
In this paper, the pulsed injection method is extended to measure the chip temperature of various packaged laser modules,
such as the DFB laser modules, the FP laser modules, and the EML laser modules. An optimal injection condition is obtained
by investigating the dependence of the lasing wavelength on the width and period of the injection pulse in a relatively wide
temperature range. The small-signal frequency responses and large-signal performances of packaged laser modules at different
chip temperature are measured. The adiabatic small-signal modulation characteristics of packaged LD are first extracted. In
the large-signal measurement, the effects of chip temperature, bias current and driving signal on the performances of the
laser modules are discussed. It has been found that the large-signal performances of the EML modules depend on the different
red-shift speeds of the DFB and EAM sections as chip temperature varying, and the optimal characteristics may be achieved
at higher temperature. 相似文献
38.
39.
40.
Fa Jie Yang Da Ling Yang Shou Hai Zhang Xi Gao Jian 《中国化学快报》2007,18(8):966-968
A new interfacial polymerization (IP) procedure is developed in order to synthesize polypiperazine-amide thin-film membrane on the inner surface of poly(phthalazinone ether sulfone ketone) (PPESK) hollow fiber ultrafiltration (UF) membrane.A hollow fiber composite membrane with good performance was prepared and studied by FT-IR and scanning electron microscopy. 相似文献