全文获取类型
收费全文 | 24459篇 |
免费 | 3938篇 |
国内免费 | 2637篇 |
专业分类
化学 | 17021篇 |
晶体学 | 307篇 |
力学 | 1461篇 |
综合类 | 249篇 |
数学 | 2722篇 |
物理学 | 9274篇 |
出版年
2024年 | 78篇 |
2023年 | 507篇 |
2022年 | 823篇 |
2021年 | 835篇 |
2020年 | 991篇 |
2019年 | 908篇 |
2018年 | 759篇 |
2017年 | 742篇 |
2016年 | 1115篇 |
2015年 | 1046篇 |
2014年 | 1308篇 |
2013年 | 1692篇 |
2012年 | 2111篇 |
2011年 | 2093篇 |
2010年 | 1456篇 |
2009年 | 1392篇 |
2008年 | 1556篇 |
2007年 | 1436篇 |
2006年 | 1364篇 |
2005年 | 1121篇 |
2004年 | 886篇 |
2003年 | 725篇 |
2002年 | 627篇 |
2001年 | 522篇 |
2000年 | 517篇 |
1999年 | 592篇 |
1998年 | 487篇 |
1997年 | 428篇 |
1996年 | 436篇 |
1995年 | 387篇 |
1994年 | 357篇 |
1993年 | 326篇 |
1992年 | 269篇 |
1991年 | 230篇 |
1990年 | 235篇 |
1989年 | 159篇 |
1988年 | 119篇 |
1987年 | 84篇 |
1986年 | 97篇 |
1985年 | 65篇 |
1984年 | 37篇 |
1983年 | 39篇 |
1982年 | 37篇 |
1981年 | 21篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1976年 | 1篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Shi Yao Zhu 《Optics Communications》1991,80(5-6):393-396
The degenerate parametric oscillator (DPO) is analyzed with the nonlinear material treated quantum mechanically. The source of squeezing in the DPO is the same as in the two-photon correlated-spontaneous-emission laser (CEL) — the level coherence. In this sense, they are similar. The amount of squeezing in DPO is the same as in the two-photon CEL at two-photon resonance, but the gain in DPO is usually much smaller than that in the two-photon CEL at two-photon resonance. 相似文献
142.
矩孔金属光栅矢量模式理论的数值计算 总被引:1,自引:0,他引:1
根据矩孔金属光栅的矢量模式理论,计算了不同入射方向,波长及偏振态情况下衍射场的分布,研究了不同光栅结构对衍射效率,偏振态变化的影响;同时,根据实际需要,加工制作了一批不同深度的矩孔光栅样品,进行了实验测量,并将计算值与实验值进行了比较,两者基本相符。 相似文献
143.
This paper reports the measurement of magnetic properties of the soft magnetic composite material SOMALOYTM 500 in a square sample under different patterns of flux density with 2D magnetic excitations. The test system, principle of measurement, magnetic power loss calculation, and methods of correction for misalignment of H surface sensing coils are presented. The experimental results show that although nominally isotropic, the SOMALOYTM 500 sample exhibits some anisotropy. The results are useful in the design and performance analysis of rotating electrical machines. 相似文献
144.
A set of experiments was carried out to validate an optimization procedure based on finite element method (FEM). The idea of the procedure, fully presented in previous edition of this journal [Zhu X, Zhu Z, Cheng J. Using optimized surface modifications to improve low frequency response in a room. Appl Acoust 2004;65:841-60], is to produce an optimal geometry modification on the wall for improving low frequency sound uniformity in small rooms. Four experimental models were set up with a scale of 1:5. One was modified according to the optimized result and the others were treated with no optimization consideration. Measured frequency responses of four rooms were compared with numerical results calculated by FEM models. The transient responses in these rooms were also measured and analyzed. The agreements between calculation and measurement are satisfactory though the discrepancies due to the uncertainty of acoustic behavior of the room boundaries remain. The optimization procedure has been supported by the results that the optimized room produces the flattest frequency response and also the most smooth energy decay within the frequency range studied. The reductions of response fluctuation have reached 4.3 dB for prediction and 2.6 dB for measurement, respectively. 相似文献
145.
146.
147.
148.
149.
In CZE, the adsorption of the proteins on the capillary wall is a common problem. This paper describes the simple method of utilizing zwitterionic buffer additives to improve the separation of proteins in untreated fused silica capillaries at neutral pH. Three kinds of zwitterion are evaluated in the separation of acidic, neutral, and basic proteins, including their effect on protein efficiency, mobility, separation, and resolution; the difference between the effects of the different additives are also highlighted. The method has proved to be a possible means of reducing protein adsorption, especially for basic proteins. 相似文献
150.
Crack initiation and stable crack growth under monotonic loading in steels has been studied using an elastic-plastic finite element analysis. The fracture criterion used for crack initiation and stable crack growth was the critical strain energy density. In addition the shift core method for the analysis of crack extension was used. In the shift core modelling method, crack advance is simulated by moving the coordinates of the core region which surrounds the crack tip, to obtain the stiffness reduction. Simultaneously the core itself geometrically undergoes a simple rigid-body motion or translation during the crack extension. The analytically calculated and experimentally measured load for crack initiation and the subsequent stable crack growth agreed well. 相似文献