全文获取类型
收费全文 | 17137篇 |
免费 | 800篇 |
国内免费 | 153篇 |
专业分类
化学 | 11868篇 |
晶体学 | 163篇 |
力学 | 529篇 |
综合类 | 1篇 |
数学 | 1591篇 |
物理学 | 3938篇 |
出版年
2023年 | 81篇 |
2022年 | 253篇 |
2021年 | 345篇 |
2020年 | 314篇 |
2019年 | 314篇 |
2018年 | 280篇 |
2017年 | 241篇 |
2016年 | 507篇 |
2015年 | 468篇 |
2014年 | 621篇 |
2013年 | 1056篇 |
2012年 | 1247篇 |
2011年 | 1403篇 |
2010年 | 853篇 |
2009年 | 754篇 |
2008年 | 1103篇 |
2007年 | 968篇 |
2006年 | 921篇 |
2005年 | 867篇 |
2004年 | 745篇 |
2003年 | 642篇 |
2002年 | 630篇 |
2001年 | 416篇 |
2000年 | 376篇 |
1999年 | 229篇 |
1998年 | 158篇 |
1997年 | 168篇 |
1996年 | 217篇 |
1995年 | 169篇 |
1994年 | 160篇 |
1993年 | 156篇 |
1992年 | 133篇 |
1991年 | 112篇 |
1990年 | 113篇 |
1989年 | 112篇 |
1988年 | 69篇 |
1987年 | 63篇 |
1986年 | 66篇 |
1985年 | 87篇 |
1984年 | 66篇 |
1983年 | 62篇 |
1982年 | 53篇 |
1981年 | 63篇 |
1980年 | 39篇 |
1979年 | 43篇 |
1978年 | 39篇 |
1977年 | 44篇 |
1976年 | 52篇 |
1975年 | 37篇 |
1974年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Yu-Soo Lee Hyun-Ju Chung Jong-Han Joung Eung-Jo Kim Hee-Je Kim 《Optics & Laser Technology》2004,36(1):461-61
We describe the pulse forming of pulsed CO2 laser using multi-pulse superposition technique. Various pulse shapes, high duty cycle pulse forming network (PFN) are constructed by time sequence. This study shows a technology that makes it possible to make various long pulse shapes by activating SCRs of three PFN modules consecutively at a desirable delay time with the aid of a PIC one-chip microprocessor. The power supply for this experiment consists of three PFN modules. Each PFN module uses a capacitor, a pulse forming inductor, a SCR, a high voltage pulse transformer, and a bridge rectifier on each transformer secondary. The PFN modules operate at low voltage by driving the primary of HV pulse transformer. The secondary of the transformer has a full-wave rectifier, which passes the pulse energy to the load in a continuous sequence.We investigated various long pulse shapes as different trigger time intervals of SCRs among three PFN modules. As a result, we could obtain laser beam with various pulse shapes and durations from about 250 to 1000 μs. 相似文献
22.
Jong Chan Lee Jin Young Park So Young Yoon Yong Hun Bae Seung Jun Lee 《Tetrahedron letters》2004,45(1):191-193
A novel and direct method for the synthesis of α-halocarbonyl compounds using sequential treatment of carbonyl compounds with [hydroxy(tosyloxy)iodo]benzene followed by magnesium halides under solvent-free microwave irradiation conditions is described. 相似文献
23.
Myungjin Jeon Dongsoong Han Kyeongsu Park Gundon Choi 《Journal of Applied Mathematics and Computing》2005,18(1-2):235-246
We present an interpolating, univariate subdivision scheme which preserves the discrete curvature and tangent direction at each step of subdivision. Since the polygon have a geometric information of some original (in some sense) curve as a discrete curvature, we can expect that the limit curve has the same curvature at each vertex as the control polygon. We estimate the curvature bound of odd vertices and give an error estimate for restoring a curve from sampled vertices on curves. 相似文献
24.
We have rigorously calculated for the first time all the inter-electrode and pixel capacitances of Thin-Film Transistor Liquid Crystal Displays using the electrical energy distribution inside a liquid crystal cell. The energy distribution is obtained from the three-dimensional profiles of potential distribution and molecular director. The dynamic equation of continuum theory for liquid crystals is described in a tensorial form in order to maintain the equivalence of n and -n . The effects of lateral fields generated by multiple electrodes of finite sizes are taken into account in the simulation. As a numerical technique, we used a finite difference method which is suitable for the highly non-linear equations. As a result, we confirmed that the pixel capacitance for our pixel structure is about 40% larger than that of the conventional approach. It is also revealed that the gate-common and gate-data inter-electrode capacitances are not negligible. 相似文献
25.
S. H. Park J. H. Chang M. Yang H. S. Ahn S. N. Yi K. Goto M. W. Cho T. Yao J. S. Song 《Current Applied Physics》2004,4(6):607-610
Photoluminescence (PL) linewidth broadening of CdxZn1 − xSe/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced. 相似文献
26.
27.
Solid state nuclear track detectors are commonly used for measurements of concentrations of radon gas and/or radon progeny. All these measurements depend critically on the thickness of the removed layer during etching. However, the thickness of removed layer calculated using the etching period does not necessarily provide a sufficiently accurate measure of the thickness. For example, the bulk etch rate depends on the strength of stirring during etching for the LR 115 detector. We propose here to measure the thickness of the removed layer by using energy-dispersive X-ray fluorescence spectrometry. In the present work, a reference silver nitrate pellet is placed beneath the LR 115 detector, and the fluorescence X-ray intensity for silver is then measured. We have found a linear relationship between the X-ray intensity and the thickness of the removed layer for LR 115 detector. This provides a fast method to measure the thickness of removed layer from etching of LR 115 detector. However, this method was found to be inapplicable for the CR-39 detector. Therefore, alternative methods have yet to be explored for the CR-39 detector. 相似文献
28.
29.
30.
The glow curve structures for LiF:Mg,Cu,Na,Si TL detectors with various dopant concentrations and sintering temperatures were investigated for the improvement of the glow curve structure and sensitivity of the TL detector. The dopant concentrations were varied over the following ranges: Mg (0–0.25 mol%), Cu (0–0.07 mol%), Na and Si (0–1.5 mol%). With increasing Cu concentration, the intensity of the main peak was intensified and reached a maximum at a concentration of 0.05 mol%. The high-temperature peak was reduced. The dependency of the main peak intensity on the Mg concentration exhibits a sharp maximum at 0.2 mol%. The intensity of the high-temperature peak tends to rise slightly with increasing Mg concentration. It was found that the optimum concentrations of the dopants in the LiF:Mg,Cu,Na,Si TL material are Mg: 0.2 mol%, Cu: 0.05 mol%, Na and Si: 0.9 mol%. The dependency of the main peak intensity on sintering temperature exhibits a very sharp maximum at 830°C. The high-temperature peak was rapidly reduced after 825°C. 相似文献