全文获取类型
收费全文 | 20100篇 |
免费 | 2406篇 |
国内免费 | 1966篇 |
专业分类
化学 | 10034篇 |
晶体学 | 130篇 |
力学 | 914篇 |
综合类 | 105篇 |
数学 | 1567篇 |
物理学 | 5000篇 |
综合类 | 6722篇 |
出版年
2024年 | 64篇 |
2023年 | 349篇 |
2022年 | 475篇 |
2021年 | 588篇 |
2020年 | 579篇 |
2019年 | 516篇 |
2018年 | 466篇 |
2017年 | 428篇 |
2016年 | 728篇 |
2015年 | 672篇 |
2014年 | 971篇 |
2013年 | 1153篇 |
2012年 | 1384篇 |
2011年 | 1455篇 |
2010年 | 1051篇 |
2009年 | 1063篇 |
2008年 | 1194篇 |
2007年 | 1062篇 |
2006年 | 919篇 |
2005年 | 911篇 |
2004年 | 720篇 |
2003年 | 704篇 |
2002年 | 741篇 |
2001年 | 697篇 |
2000年 | 596篇 |
1999年 | 650篇 |
1998年 | 546篇 |
1997年 | 538篇 |
1996年 | 523篇 |
1995年 | 433篇 |
1994年 | 413篇 |
1993年 | 334篇 |
1992年 | 288篇 |
1991年 | 261篇 |
1990年 | 232篇 |
1989年 | 213篇 |
1988年 | 146篇 |
1987年 | 106篇 |
1986年 | 76篇 |
1985年 | 50篇 |
1984年 | 27篇 |
1983年 | 29篇 |
1982年 | 22篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
LD泵浦固体激光器基模振荡光的场分布噪音 总被引:3,自引:3,他引:0
通过调整泵浦光直径,使得LD端面泵浦固体激光器的振荡光工作于基模.在排除高阶横模的条件下,测量了由于热透镜的不稳定引起的光场场分布的噪音.实验发现,基模振荡光的高斯半径、光束指向角都在波动,而且光斑存在畸变波动.对一个未采取抑制措施的2W连续LD端面泵浦Nd:YAG固体激光器进行了测量.结果表明,在总功率不变的情况下,激光束峰值点附近的光强波动达到6.3%;激光的高斯半径波动达到5.8%;激光的指向角波动达到0.3mrad. 相似文献
72.
73.
74.
Chirped fiber grating was used in dispersion compensator. We tried to use the same phase mask to write fiber grating of different wavelength with two methods to reduce the price of the fiber grating. 相似文献
75.
Huimin Xie Biao Li Robert Geer Bai Xu James Castracane 《Optics and Lasers in Engineering》2003,40(3):163-177
A focused ion beam (FIB) Moiré method is proposed to measure the in-plane deformation of object in a micrometer scale. The FIB Moiré is generated by the interference between a prepared specimen grating and FIB raster scan lines. The principle of the FIB Moiré is described. The sensitivity and accuracy of deformation measurement are discussed in detail. Several specimen gratings with 0.14 and 0.20 μm spacing are used to generate FIB Moiré patterns. The FIB Moiré method is successfully used to measure the residual deformation in a micro-electro-mechanical system structure after removing the SiO2 sacrificial layer with a 5000 lines/mm grating. The results demonstrate the feasibility of this method. 相似文献
76.
Tetraalkyltin complexes, SnR4 (R = Me, Et, Pr, Bu) could react with Pt/HY at 193, 243, 273 and 333 K, respectively. The reactions occurred on the surface of the zeolite and the organotin grafted zeolites were characterized in detail. The framework and the microporous structure of the grafted Pt/HY zeolites were retained. However, the modified zeolites showed better size selectivity in the absorption of hydrocarbons. 相似文献
77.
矩阵的弱相似性及其应用 总被引:1,自引:0,他引:1
胡付高 《信阳师范学院学报(自然科学版)》2003,16(1):4-6
推广了矩阵环Mn(F)中相似性概念,提出了矩阵的弱相似概念,研究了它的基本性质,获得一些有趣结果,此外,指出了文[3]的一个错误,给出了Laffey-Choi一个关键引理的矩阵式的证明。 相似文献
78.
The growth mechanism of the peritectic η phase involving the peritectic reaction and peritectic transformation in Cu-70%Sn alloy was investigated under directional
solidification. The results show that a major growth mechanism in thickening of the peritectic η-layer is not the peritectic reaction but the peritectic transformation. The transformation temperature and isothermal time
play crucial roles in determining the volume fraction and the thickness of the peritectic η phase. With the increase of the temperature and isothermal time, the volume fraction of the peritectic η phase increases. The regressed data show that the relationship between the thickness of η phase (Δx) and the transformation temperature (T) meets the following equation In Δx=6.5−1673 1 / T. Additionally, there exists a relationship between the thickness of the η phase (Δx) and the isothermal time (t) at the 9 mm solidification distance below the peritectic reaction interface, Δx=0.72t
1/2, which is consistent with the theoretical model.
Supported by the National Science Foundation of China (Grant No. 50395102) 相似文献
79.
论国有经济的核心地位 总被引:2,自引:0,他引:2
国有经济在社会主义初级阶段多种经济成分组成的市场经济中居于核心地位。国有经济在国民经济中发挥主导作用,是其核心地位的外在表现形式。国有经济的核心地位,是由国家代表全社会占有的社会主义国有制的性质和其产业分布决定的。核心地位的巩固,有赖主导作用的充分发挥,整体推进国有企业改革和良好的外部运行环境的形成。 相似文献
80.
This paper deals with the optimal control of a one-machine two-product manufacturing system with setup changes, operating in a continuous time dynamic environment. The system is deterministic. When production is switched from one product to the other, a known constant setup time and a setup cost are incurred. Each product has specified constant processing time and constant demand rate, as well as an infinite supply of raw material. The problem is formulated as a feedback control problem. The objective is to minimize the total backlog, inventory and setup costs incurred over a finite horizon. The optimal solution provides the optimal production rate and setup switching epochs as a function of the state of the system (backlog and inventory levels). For the steady state, the optimal cyclic schedule is determined. To solve the transient case, the system's state space is partitioned into mutually exclusive regions such that with each region, the optimal control policy is determined analytically. 相似文献