全文获取类型
收费全文 | 25055篇 |
免费 | 2033篇 |
国内免费 | 1098篇 |
专业分类
化学 | 12427篇 |
晶体学 | 434篇 |
力学 | 1549篇 |
综合类 | 55篇 |
数学 | 2509篇 |
物理学 | 11212篇 |
出版年
2024年 | 33篇 |
2023年 | 279篇 |
2022年 | 485篇 |
2021年 | 519篇 |
2020年 | 479篇 |
2019年 | 473篇 |
2018年 | 554篇 |
2017年 | 458篇 |
2016年 | 786篇 |
2015年 | 631篇 |
2014年 | 886篇 |
2013年 | 1436篇 |
2012年 | 1774篇 |
2011年 | 2015篇 |
2010年 | 1419篇 |
2009年 | 1382篇 |
2008年 | 1511篇 |
2007年 | 1435篇 |
2006年 | 1418篇 |
2005年 | 1132篇 |
2004年 | 962篇 |
2003年 | 739篇 |
2002年 | 678篇 |
2001年 | 1059篇 |
2000年 | 790篇 |
1999年 | 703篇 |
1998年 | 500篇 |
1997年 | 500篇 |
1996年 | 443篇 |
1995年 | 357篇 |
1994年 | 326篇 |
1993年 | 252篇 |
1992年 | 274篇 |
1991年 | 211篇 |
1990年 | 217篇 |
1989年 | 175篇 |
1988年 | 122篇 |
1987年 | 113篇 |
1986年 | 108篇 |
1985年 | 115篇 |
1984年 | 70篇 |
1983年 | 53篇 |
1982年 | 35篇 |
1981年 | 32篇 |
1980年 | 23篇 |
1977年 | 19篇 |
1976年 | 29篇 |
1975年 | 27篇 |
1974年 | 21篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
101.
102.
Fabrication of bamboo-shaped GaN nanorods 总被引:1,自引:0,他引:1
H. Li J.Y. Li M. He X.L. Chen Z. Zhang 《Applied Physics A: Materials Science & Processing》2002,74(4):561-562
Bamboo-shaped GaN nanorods were formed through a simple sublimation method. They were characterized by means of X-ray powder
diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected-area
electron diffraction (SAED). The TEM image showed that the nanorods were bamboo-like. XRD, HRTEM and SAED patterns indicated
that the nanorods were single-crystal wurtzite GaN.
Received: 8 January 2001 / Accepted: 28 April 2001 / Published online: 20 December 2001 相似文献
103.
104.
By introducing an imaginary space transform curvature ρs, a complex space called Riemannian space is constructed, in which the light propagating in free space has the trajectory
of straight line while propagating. Moreover, this curvature couples with that of the wave front of the paraxial beam ρw, and therefore a complex curvature ρc is constructed, which can be employed to investigate the behavior of the light transmission and to generalize the ABCD law.
Project supported by the National Hi-Tech Inertial Confinement Fusion Committee, the Guangdong Natural Science Foundation
the Postdoctoral Foundation of Guangdong and National Postdoctoral Foundation of China. 相似文献
105.
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
106.
Experiments for the determination of mono-, di and tri-butyltin (MBT, DBT and TBT) by hydride generation/gas chromatography/atomic absorption spectrometry in various matrices (sediment, suspended matter, mussel, algae and water) have revealed that poor butyltin recoveries are obtained in sediments displaying high sulphur and hydrocarbon contents; very poor recoveries were also observed for TBT in sediments with high chlorophyll pigment contents as well as in algal samples. It was however not clear whether the hydride generatin was inhibited by these infering compounds, as was previously assumed in the case of hydrocarbons, or whether interferences affected the atomization rate. Further studies were performed to solve this problem in order to validate this method in the case of analyses of, for example, oil-contaminated sediment and algae. This paper presents the results obtained. It is concluded here that the poor recoveries were due to an inhibition of hydride generation rather than to interference at the atomization stage. 相似文献
107.
本文主要研究了 Banach 空间上交换算子组的张量积以及 Banach 代数的张量积中交换元组的 Taylor 联合谱,推广了 Vasilescu,F.H.及 Wrobel,V.等人结果。 相似文献
108.
L. B. Sjogren H. -X. L. Liu X. -H. Qin C. W. Domier N. C. Luhmann 《International Journal of Infrared and Millimeter Waves》1993,14(6):1201-1216
Device alternatives for millimeter-wave beam control arrays are examined. For the control function, a wide range of semiconductor device as well as bulk material alternatives are considered. In addition, alternatives to the traditional metal strip are considered for the passive electromagnetic array element. This work should provide a broader perspective regarding the choices available for the optimized design of new beam control arrays. 相似文献
109.
The gravitational interaction between grooves machined in a hollow cylindrical mass of uniform density, and an external point mass, is derived in terms of the Associated Legendre functions, and the parametric form of the coupling coefficients is presented. The cross-sections of the grooves, which are regularly spaced in azimuth, are in the form of truncated sectors of the cylinder's end-faces. This theory is applied to the test-masses for the Satellite Test of the Equivalence Principle (STEP) experiment, for which four grooves have been assumed, and an expression for the axialforce is derived which is more than 104 times faster to compute than a Monte-Carlo integration of similar accuracy. Following this analysis it is suggested that the STEP test-masses should carry at least 6 grooves. This theory has wider application to gravitational problems involving general sectored cylindrical bodies. 相似文献
110.
单模光纤中皮秒啁啾脉冲压缩 总被引:11,自引:2,他引:9
对单模光纤正群速色散区秒啁啾脉冲的非线性传进行了近似的解析分析和定量的数值计算。结果表明,负啁啾脉冲在传输过程中能得到有效压缩。压缩比与脉冲初始峰值功率和初始啁啾程度有关。初始峰值功率一定的脉冲,其压缩比随初始啁啾程度的增大面大,初始啁啾程度一定的脉冲,压缩比随初始峰值功率的增大而减小,表明自相位调制效应导致脉冲压缩效果变差。计算结果还表明,在脉冲时域宽度得到压缩的同时,光谱宽度也能得到同步压缩。 相似文献