全文获取类型
收费全文 | 233564篇 |
免费 | 13088篇 |
国内免费 | 9245篇 |
专业分类
化学 | 114436篇 |
晶体学 | 2640篇 |
力学 | 9405篇 |
综合类 | 520篇 |
数学 | 20418篇 |
物理学 | 63337篇 |
无线电 | 45141篇 |
出版年
2023年 | 2326篇 |
2022年 | 2989篇 |
2021年 | 3793篇 |
2020年 | 3761篇 |
2019年 | 3604篇 |
2018年 | 3254篇 |
2017年 | 3036篇 |
2016年 | 4885篇 |
2015年 | 4872篇 |
2014年 | 6007篇 |
2013年 | 10965篇 |
2012年 | 10526篇 |
2011年 | 11655篇 |
2010年 | 8051篇 |
2009年 | 8115篇 |
2008年 | 9908篇 |
2007年 | 9704篇 |
2006年 | 9467篇 |
2005年 | 8788篇 |
2004年 | 7313篇 |
2003年 | 6387篇 |
2002年 | 6015篇 |
2001年 | 6229篇 |
2000年 | 5365篇 |
1999年 | 4964篇 |
1998年 | 4432篇 |
1997年 | 4138篇 |
1996年 | 4057篇 |
1995年 | 3875篇 |
1994年 | 3523篇 |
1993年 | 3364篇 |
1992年 | 3453篇 |
1991年 | 3238篇 |
1990年 | 2990篇 |
1989年 | 2823篇 |
1988年 | 2632篇 |
1987年 | 2329篇 |
1986年 | 2153篇 |
1985年 | 2723篇 |
1984年 | 2721篇 |
1983年 | 2315篇 |
1982年 | 2566篇 |
1981年 | 2316篇 |
1980年 | 2335篇 |
1979年 | 2284篇 |
1978年 | 2392篇 |
1977年 | 2312篇 |
1976年 | 2331篇 |
1975年 | 2254篇 |
1973年 | 2346篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
Ferdinand P. Ferragu O. Lechien J.L. Lescop B. Magne S. Marty V. Rougeault S. Kotrotsios G. Neuman V. Depeursinge Y. Michel J.B. Van Uffelen M. Varelas D. Berthou H. Pierre G. Renouf C. Jarret B. Verbandt Y. Stevens W. Voet M.R.H. Toscano D. 《Lightwave Technology, Journal of》1995,13(7):1303-1313
Recent developments of stability control in mines, essentially based on Ge-doped fiber Bragg gratings (FBG) are reported including results about the different aspects of the system: accurate characterizations of FBG, sensor network topology and multiplexing method, user interface design and sensor packaging 相似文献
152.
Composite chiral materials are realized by embedding large numbers of handed inclusions within a host material. A computational methodology is presented whereby the effective constitutive parameters of artificial chiral materials are computed while accounting for all self and mutual interactions among the inclusions. This technique combines a full-wave, Monte-Carlo scattering solution for randomly oriented inclusions together with an analytical solution for the scattering by a canonically-shaped body having a properly chosen constitutive model. It is believed that the effective constitutive parameters shown in this paper are the first full-wave computation of these quantities to appear in the literature 相似文献
153.
This paper describes a soft switching active snubber for an IGBT operating in a single switch unity power factor three-phase diode rectifier. The soft switching snubber circuit provides zero-voltage turn-off for the main switch. The high turn-off losses of the IGBT due to current tailing are reduced by zero-voltage switching. This allows the circuit to be operated at very high switching frequencies with regulated DC output voltage, high quality input current and unity input power factor. Simulation and experimental results are included 相似文献
154.
Chen L.R. Benjamin S.D. Smith P.W.E. Sipe J.E. 《Quantum Electronics, IEEE Journal of》1998,34(11):2117-2129
We discuss theoretical and experimental studies on the propagation of ultrashort pulses through fiber Bragg gratings. We also consider several applications in optical communications to be found by combining ultrashort pulses and fiber Bragg gratings: a multiwavelength source for wavelength-division-multiplexed systems and a means for implementing optical code-division multiple access 相似文献
155.
Low-temperature-grown GaAs (LT-GaAs) is a promising material for all-optical switching devices due to its outstanding optical characteristics. In this paper, we outline a simplified model we have developed to describe the dynamics of the carriers in this material. We also report the results of a series of measurements that we have performed to characterize the optical properties of the material. Specifically, we present the first measurements of the two-photon absorption coefficient and the refractive index changes as a function of the growth and annealing temperatures in LT-GaAs. Finally, we show how our model can be used to optimize the material for applications in all-optical switching 相似文献
156.
157.
W. Knoll W. Hickel M. Sawodny J. Stumpe H. Knobloch 《Fresenius' Journal of Analytical Chemistry》1991,341(3-4):272-278
Summary We report on novel optical techniques, based on evanescent waves, for the characterization of polymer surfaces and thin films. We first describe photo-ablation studies with polysilane films investigated by surface plasmon microscopy, a technique which is particularly well-suited for ultrathin samples. Thicker films that are homogeneous enough to carry optical waveguide modes can be characterized with high lateral resolution by the recently developed waveguide microscopy. We demonstrate this for a thin film of a solid polyelectrolyte. Finally, we report on surface plasmon field-enhanced Raman-spectroscopic and -imaging investigations of ultrathin Langmuir-Blodgett-Kuhn-layers of cadmium arachidate.W. Hickel is now with HOECHST AG, Angewandte Physik, W-6230 Frankfurt 80 相似文献
158.
The equations describing the behaviour of temperature/flow microsensorsemploy-ing polysilicon thermistors form a degenerate nonlinearparabolic system. One special feature is that different equationsof this system are to be satisfied on different domains. Bymeans of supersolutions and subsolutions, the maximum principle,and fixed point arguments, the authors show the existence ofsolutions to the equations. 相似文献
159.
160.
This contribution discusses the phenomena of retrograde condensation of one or two liquids. It w1 be shown that both phenomena can be well understood. Also the relation of retrograde condensation of one liquid phase with the condensation behavior of natural gas will be discussed. Similarly that of two liquid phases with multiple phase behavior occurring in low temperature reservoir fluids will be pointed out. 相似文献