全文获取类型
收费全文 | 11454篇 |
免费 | 1831篇 |
国内免费 | 2178篇 |
专业分类
化学 | 8822篇 |
晶体学 | 128篇 |
力学 | 696篇 |
综合类 | 168篇 |
数学 | 1457篇 |
物理学 | 4192篇 |
出版年
2024年 | 37篇 |
2023年 | 265篇 |
2022年 | 473篇 |
2021年 | 447篇 |
2020年 | 527篇 |
2019年 | 530篇 |
2018年 | 418篇 |
2017年 | 456篇 |
2016年 | 620篇 |
2015年 | 631篇 |
2014年 | 672篇 |
2013年 | 924篇 |
2012年 | 891篇 |
2011年 | 984篇 |
2010年 | 720篇 |
2009年 | 679篇 |
2008年 | 767篇 |
2007年 | 643篇 |
2006年 | 614篇 |
2005年 | 558篇 |
2004年 | 462篇 |
2003年 | 379篇 |
2002年 | 421篇 |
2001年 | 332篇 |
2000年 | 290篇 |
1999年 | 266篇 |
1998年 | 212篇 |
1997年 | 152篇 |
1996年 | 175篇 |
1995年 | 122篇 |
1994年 | 141篇 |
1993年 | 108篇 |
1992年 | 82篇 |
1991年 | 102篇 |
1990年 | 96篇 |
1989年 | 51篇 |
1988年 | 47篇 |
1987年 | 30篇 |
1986年 | 34篇 |
1985年 | 39篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1971年 | 1篇 |
1959年 | 1篇 |
1957年 | 3篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Pure aluminum films were deposited on B270 glass by electron beam evaporation technique. The aluminum films, which were used as anode, were placed in phosphoric acid to prepare porous alumina films using a two-step anodization method. They were subsequently annealed in high temperature to improve transmission. The microstructure, transmitted spectrum and laser damage characteristics of the alumina films were then tested. Their microstructure formed in phosphoric acid was retiform. The transmissivity can be increased efficiently if the annealing temperature is adequately high. The laser-damaged spots of the porous films were formed by innumerable small damaged pits with no mutual effect. In contrast, the laser-damaged spots of the compact films were formed by several larger damaged pits which acted together toward expansion. The damage process of the porous films comprised heat ablation and stress fracture. 相似文献
992.
993.
Dr. Qi Wei Jia‐Jia Wang Dr. Chao He Prof. Dr. Jian‐Wen Cheng Prof. Dr. Guo‐Yu Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(31):10759-10762
A new borate LiBa3(OH)[B9O16][B(OH)4], which combines the uniform porosity of open‐frameworks with the extraordinary NLO properties of borates, has been obtained under hydrothermal conditions by using mixed lithium and barium ions as templates. The framework displays an acs‐type net with large 21‐ring channels. The second harmonic generation (SHG) measurement shows that it is a type I phase‐matchable material with a strong SHG signal intensity about 3.1 times that of KDP (KH2PO4). UV/Vis–NIR diffuse reflectance analysis indicates that the compound has a wide transparency range with the short‐wavelength absorption edge below 200 nm. These characteristics reveal that the compound is a promising deep‐UV nonlinear optical material. 相似文献
994.
995.
Ag3PW12O40 and Ag4SiW12O40 showed high activity and stability in the synthesis of diethylene glycol ethyl ether with diethylene glycol and ethanol, on which the conversion is 80.2% and 78.4%, respectively, and the selectivity of diethylene glycol ether is 75.4% and 80.6%, respectively. After the third reaction cycle, Ag3PW12O40 and Ag4SiW12O40) still showed higher activity and selectivity, on which the conversion is 72. 6% and 77.5% respectively. But the activity of Ag3PMo12O40 is lower, the conversion is only 21.0%. IR, XRD, TG and n‐butylamine titrimetry showed that the catalysis may be connected with two kinds of acidic centers owned by heteropoly acidic salt. 相似文献
996.
Nonlinear optical properties of stimulated Brillouin scattering process in submerged object detection 总被引:2,自引:0,他引:2
Yuelan Lü 《中国光学快报(英文版)》2008,6(2)
Nonlinear optical properties of stimulated Brillouin scattering(SBS)to signal detection in water are analyzed.With the threshold characteristics,SBS only occnrs when the high power laser is focused in the SBS cell.When there is an object present in front of the focus,it leads to lower incident intensity and then SBS does not occur.The backward SBS signal depends on the focusing location.The nonlinear optical properties of SBS process in the focusing regime axe analyzed theoretically.With the object coming near to the focusing center,the backward Stokes signal rises up from zero to a maximum,and then grows to saturation.The delay time of the echo signal to pump signal can give the object location.In experiment,the peak position of varying rate of energy can give object location. 相似文献
997.
In a capillary discharge experiment for the neon-like argon lasing, we have proposed an experimental scheme to verify that the multi-spike of X-ray diode (XRD) signal is a multi-pulse laser or is a reflection of the laser pulse in the XRD.The ceramic capillary has an inner diameter of 3mm and a length of 200mm.At the gas pressure of 28Pa and discharge current of 27kA, stable lasing has been realized.The experimental results prove that the multi-spike of XRD signal is a reflection of the electromagnetic signal produced by the laser pulse in the XRD.The improved electrocircuit scheme of the XRD to minimize the reflection phenomena is also found. 相似文献
998.
During the design process of Blu-ray disc optical pick-up (BD OPU), the optical system and the collimator lens design is especially important. This paper designs an optical system and some lenses for the BD OPU, including collimator lens, beam shaping lens for laser beam shaping, and cylinder lens for signal detecting. In this OPU, we use a triplet lens to collimate the laser beam. At the same time, we build a series of assembly jigs to make sure that each lens can be put into the OPU basement properly. At last, we get the reading spot image and S-curve photo of OPU, which can be used to read Blu-ray disc (BD). 相似文献
999.
Using front face-pumped compact active mirror laser (CAMIL) structure, we have demonstrated an Yb:YAG/YAG composite ceramic disk laser with pumping wavelength at 970 nm. The laser has been operated in both continuous-wave (CW) and Q-switching modes. Under CW operation, laser output power of 1.05 W with 2% transmission output coupler was achieved at the wavelength of 1031 nm. Q- switched laser output was gotten by using an acousto-optic Q-switch. The repetition rate ranged from 1 to 30 kHz and the pulse width varied from 166 to 700 ns. 相似文献
1000.
For linear combinations of Gamma operators, if 0<a<2r, 1/2-1/2r≤λ≤l, or 0≤λ<1/2-1/2r(r≥2),0<a<r+10<a<(r+1)/1-λ, we obtain an equivalent theorem with ωuλρ(f ,t) instead of ωrλφ(f,t), where ωuφ(f,t) is theDitzian-Totik moduli of smoothness. 相似文献