全文获取类型
收费全文 | 31721篇 |
免费 | 3443篇 |
国内免费 | 3304篇 |
专业分类
化学 | 26250篇 |
晶体学 | 808篇 |
力学 | 1855篇 |
综合类 | 263篇 |
数学 | 509篇 |
物理学 | 8783篇 |
出版年
2024年 | 35篇 |
2023年 | 273篇 |
2022年 | 600篇 |
2021年 | 707篇 |
2020年 | 924篇 |
2019年 | 946篇 |
2018年 | 1012篇 |
2017年 | 1389篇 |
2016年 | 1586篇 |
2015年 | 1228篇 |
2014年 | 1397篇 |
2013年 | 3140篇 |
2012年 | 2073篇 |
2011年 | 1835篇 |
2010年 | 1669篇 |
2009年 | 1944篇 |
2008年 | 1688篇 |
2007年 | 1823篇 |
2006年 | 1625篇 |
2005年 | 1427篇 |
2004年 | 1297篇 |
2003年 | 1143篇 |
2002年 | 963篇 |
2001年 | 835篇 |
2000年 | 863篇 |
1999年 | 793篇 |
1998年 | 661篇 |
1997年 | 575篇 |
1996年 | 536篇 |
1995年 | 517篇 |
1994年 | 427篇 |
1993年 | 380篇 |
1992年 | 321篇 |
1991年 | 244篇 |
1990年 | 229篇 |
1989年 | 209篇 |
1988年 | 250篇 |
1987年 | 227篇 |
1986年 | 142篇 |
1985年 | 101篇 |
1984年 | 108篇 |
1983年 | 36篇 |
1982年 | 84篇 |
1981年 | 49篇 |
1980年 | 35篇 |
1979年 | 45篇 |
1978年 | 21篇 |
1977年 | 14篇 |
1976年 | 8篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
Tensile impact experiments of EC8.0−24×7 glass fiber bundles at different low temperaturesT(14°C, −40°C and −10°C) and strain rates ɛ were carried out, and complete stress-strain curves were obtained. Within the range
of the experiment temperatures and strain rates, it is found that the initial modulusE, the ultimate strength σmax and the unstable strain ɛ
b
of the glass fiber bundles all increase with ɛ at an identicalT. At an identical ɛ, with the decrease ofT, E and σmax increase; but ɛ
b
increases when 10°C>T>−40°C and decreases when −40°C>T>−100°C. The strain-rate- and temperature-dependent bimodal Weibull statistical constitutive theory was adopted for the statistical
analysis of the experimental results, and the Weibull parameters of single fiber were obtained. The results show that the
bimodal Weibull distribution function is suitable to represent the strength distribution of the glass fiber at low temperature
and different strain rates. The differences in the mechanical properties between EC8.0−24×7 and EC5.5−12 ×14 glass fiber bundles
were also discussed.
Project supported by the National Natural Science Foundation of China (No. 19772058). 相似文献
92.
93.
简析"静止液体内部压强公式验证"实验的设计策略 总被引:1,自引:1,他引:0
“静止液体内部压强公式验证”在现行教材中有两种实验方法。通过分析实验的设计策略,说明其作用、效果及操作上的困难,指出合理的与不合理诸因素,从而提出改进实验的方法,化难为易,提高实验教学效果。 相似文献
94.
The stationary and the time-dependent homogeneous ordered states in convection may both become unstable against localized perturbations. Defects are then created and they may contribute to the disorganization of the homogeneous state. We present an experimental study of defects in some homogeneous stationary structures as well as in the traveling-wave states of convection of a nematic liquid crystal. We show that the core of the defects is a germ of the unstable state and it can become unstable under the external stress. Then, either fully homogeneous states with the symmetry of the core, or complex disordered states can develop from the local instability of defects in processes quite similar to displacive transitions in solids. Some of the main features are qualitatively similar to numerical simulations of an appropriate Landau-Ginzburg equation. 相似文献
95.
Temperature effects on deposition rate of silicon nitride films were characterized by building a neural network prediction model. The silicon nitride films were deposited by using a plasma enhanced chemical vapor deposition system and process parameter effects were systematically characterized by 26−1 fractional factorial experiment. The process parameters involved include a radio frequency power, pressure, temperature, SiH4, N2, and NH3 flow rates. The prediction performance of generalized regression neural network was drastically improved by optimizing multi-valued training factors using a genetic algorithm. Several 3D plots were generated to investigate parameter effects at various temperatures. Predicted variations were experimentally validated. The temperature effect on the deposition rate was a complex function of parameters but N2 flow rate. Larger decreases in the deposition rate with the temperature were only noticed at lower SiH4 (or higher NH3) flow rates. Typical effects of SiH4 or NH3 flow rate were only observed at higher or lower temperatures. A comparison with the refractive index model facilitated a selective choice of either SiH4 or NH3 for process optimization. 相似文献
96.
利用有效液滴模型计算了偶偶超重核的α衰变半衰期,计算过程中采用了保持碎片体积守恒的不对称形状描述以及有效惯性系数计算Gamow势垒穿透因子.首先在质子数Z为88—98的区域检验了有效液滴模型,发现计算结果与实验符合得比较好.随后将此模型推广到Z≥100的情况,虽然只用了两个模型参数,计算结果与实验数据符合,说明有效液滴模型是计算偶偶超重核素α衰变半衰期的一个成功模型. 相似文献
97.
Tunable properties of light propagation in photonic crystal fibers filled with liquid crystals, called photonic liquid crystal
fibers (PLCFs) are presented. The propagation properties of PLCFs strongly depend on contrast between refractive indices of
the solid core (pure silica glass) and liquid crystals (LCs) filing the holes of the fiber. Due to relatively strong thermo-optical
effect, we can change the refractive index of the LC by changing its temperature. Numerical analysis of light propagation
in PLCF, based on two simulation methods, such as finite difference (FD) and multipole method (MM) is presented. The numerical
results obtained are in good agreement with our earlier experimental results presented elsewhere [1]. 相似文献
98.
从D触发器激励表入手,分别给出了采用单边沿D触发器和双边沿D触发器的2^n进制异步加法计数器、减法计数器的设计方法.在此基础上,采用逻辑函数修改技术,通过实例讨论了基于单边沿D触发器和双边沿D触发器的异步任意进制计数器的设计.该设计方法方便,快速,具有一定的实用意义. 相似文献
99.
G. Gargaro F. Gasparrini D. Misiti G. Palmieri M. Pierini C. Villani 《Chromatographia》1987,24(1):505-509
Summary Enantiomers of several sulfoxides and some selenoxides can be easily separated by using a new chiral stationary phase (CSP-DACH-DNB)
containing the 3,5-dinitrobenzoyl derivative of R,R-(-)1,2-diamino-cyclohexane as selector, covalently bonded to the siliceous
matrix. The easy operative conditions and the high enantioselectivity values (α) allow a direct transfer of the analytical
separations to a semi-preparative and preparative scale. 相似文献
100.
Curved Ferroelectric Liquid Crystal Matrix Displays Driven by Field-Sequential-Color and Active-Matrix Techniques 总被引:1,自引:0,他引:1
Hideo Fujikake Hiroto Sato Takeshi Murashige Yoshihide Fujisaki Taiichiro Kurita Tadahiro Furukawa Fumio Sato 《Optical Review》2006,13(1):14-19
This paper describes a curved field-sequential-color matrix display using fast-response ferroelectric liquid crystal. Black
matrix and transparent electrode patterns were formed on a thin plastic substrate by a transfer method from a glass substrate.
While a composite film of liquid crystal and micro-polymers of walls and fibers was formed between the flexible substrates
by printing, laminating and curing processes of a solution of monomers and liquid crystal, the mechanical stability was enhanced
by use of multi-functional monomers to form large display panels. The image pixels of the matrix panel were driven by an active
matrix scheme using an external switch transistor array at a frequency of 180 Hz for intermittent three-primary-color backlight
illumination. The flexible A4-paper-sized color display with 24 × 16 pixels and 60 Hz field frequency was demonstrated by
illuminating it with sequential three-primary-color lights from light-emitting diodes of the backlight. Our display system
is useful in various information displays because of its freedom of setting and location. 相似文献