全文获取类型
收费全文 | 98456篇 |
免费 | 5189篇 |
国内免费 | 5322篇 |
专业分类
化学 | 21803篇 |
晶体学 | 416篇 |
力学 | 3906篇 |
综合类 | 532篇 |
数学 | 11020篇 |
物理学 | 20967篇 |
综合类 | 50323篇 |
出版年
2024年 | 202篇 |
2023年 | 734篇 |
2022年 | 1477篇 |
2021年 | 1617篇 |
2020年 | 1663篇 |
2019年 | 1683篇 |
2018年 | 1515篇 |
2017年 | 1788篇 |
2016年 | 2007篇 |
2015年 | 2403篇 |
2014年 | 4366篇 |
2013年 | 5201篇 |
2012年 | 5097篇 |
2011年 | 5570篇 |
2010年 | 4441篇 |
2009年 | 5747篇 |
2008年 | 6049篇 |
2007年 | 7088篇 |
2006年 | 6300篇 |
2005年 | 5224篇 |
2004年 | 4527篇 |
2003年 | 4653篇 |
2002年 | 4787篇 |
2001年 | 3770篇 |
2000年 | 3281篇 |
1999年 | 2696篇 |
1998年 | 2320篇 |
1997年 | 1627篇 |
1996年 | 1519篇 |
1995年 | 1325篇 |
1994年 | 1268篇 |
1993年 | 980篇 |
1992年 | 1021篇 |
1991年 | 769篇 |
1990年 | 692篇 |
1989年 | 590篇 |
1988年 | 473篇 |
1987年 | 399篇 |
1986年 | 307篇 |
1985年 | 244篇 |
1984年 | 238篇 |
1983年 | 139篇 |
1982年 | 189篇 |
1981年 | 184篇 |
1980年 | 122篇 |
1979年 | 157篇 |
1978年 | 129篇 |
1977年 | 119篇 |
1976年 | 77篇 |
1973年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
第二讲合成孔径声纳成像及其研究进展 总被引:1,自引:0,他引:1
文章在介绍了图像声纳的特点、合成孔径声纳(synthetic aperture sonar,SAS)产生背景和发展过程的基础上,对合成孔径声纳的原理、技术难点、成像算法等问题进行了讨论.着重分析了合成孔径声纳成像过程中高分辨率的获取方法、水声信道对成像的影响、多子阵技术及其成像算法、稳定的声纳运动平台和运动监测问题、运动补偿与自聚焦方法等.文章还给出了国内外合成孔径声纳研究的最新进展情况,进而展望了合成孔径声纳的应用前景. 相似文献
892.
M K Parida Nita Sinha B Adhikary B Allanach A Alok K S Babu B Brahmachari D Choudhury E J Chun P K Das A Ghosal D Hitlin W S Hou S Kumar H N Li E Ma S K Majee G Majumdar B Mishra G Mohanty S Nandi H Pas M K Parida S D Rindani J P Saha N Sahu Y Sakai S Sen C Sharma C D Sharma S Shalgar N N Singh S Uma Sankar N Sinha R Sinha F Simonetto R Srikanth R Vaidya 《Pramana》2006,67(5):849-860
This is the report of flavor physics and model building working group at WHEPP-9. While activites in flavor physics have been
mainly focused on B-physics, those in model building have been primarily devoted to neutrino physics. We present summary of working group discussions
carried out during the workshop in the above fields, and also briefly review the progress made in some projects subsequently. 相似文献
893.
We consider a composite material composed of fibres included in a resin which becomes solid when it is heated up (reaction of reticulation). The mathematical modelling of the cure process is given by a kinetic equation describing the evolution of the reaction of reticulation coupled with the heat equation. In this paper, we are interested in the computation of approximate solutions. We propose a family of discretized problems depending on two parameters (β1, β2) ε [0, 1]2 which split the linear and non‐ linear terms in implicit and explicit parts. We prove the stability and convergence of the discretization for any (β1, β2) ε [½, 1 ] × [0, 1]. We present also some numerical results. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
894.
任鸣 《宁波大学学报(理工版)》2007,20(3):417-420
通过对浙江会展旅游现状的分析和研究,总结了浙江会展旅游业的现状与优势,指出了面临的问题,进而从政府与会展企业角度提出了发展浙江会展旅游业的对策. 相似文献
895.
896.
Summary Certain characteristics of a two-fiber sensor device, of the type proposed by Papaet al. for sea water turbidity monitorship, are examined. The extension of medium from which most of the received backscattered
power originates is investigated, together with possible effects of multiple scattering on the received power. Laboratory
measurements testing the results of the analysis are reported.
Riassunto Sono esaminate alcune caratteristiche di un sensore a due fibre, del tipo di quello proposto da Papaet al. per il monitoraggio della torbidità dell'acqua di mare. è stata studiata l'estensione della zona del mezzo da cui proviene la maggior parte della radiazione retrodiffusa ricevuta. Sono stati considerati effetti di diffusione multipla. I risultati dell'analisi sono stati controllati con misure in laboratorio.
Резюме Исследуются некоторые характеристики дву-qh-нитевого датчика, предложенного Папа и др. для мониторирования мутности морской воды. Исследуется расширение зоны в среде, из которой формируется основная часть рассеянного назад излучения. Также рассматриваются эффекты многократного рассеяния. На основе лабораторных измерений проводится проверка результатов анализа.相似文献
897.
J.D. Desai 《Applied Surface Science》2006,252(6):2251-2258
Iron oxide thin films have been obtained by spray pyrolysis using 100% methanolic and ethanolic solutions of iron tri-chloride. The films were deposited onto ITO-coated glass substrates. The preparative conditions have been optimized to obtain compact, pin-hole-free and smooth thin films which are adherent to the substrate. The structural, morphological and compositional characterizations have been carried out by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The films deposited using ethanolic solution results into pure hematite; α-Fe2O3 thin films, however, films deposited using methanolic solution consists of hematite and maghemite-c phases of iron oxide. The films are nanocrystalline with particle size of 30-40 nm. The optical absorbance of the film was of the order of 105 cm−1. The optical band gap of films was found to be 2.26 and 2.20 eV for the films deposited using methanolic and ethanolic solutions, respectively. 相似文献
898.
899.
氨基膦酸羧酸螯合树脂的合成及其对痕量镧系稀土富集分离性能的研究 总被引:3,自引:0,他引:3
简要叙述了氨基膦酸羧酸树脂的合成路线 ,用 ICP- AES对其富集分离痕量镧系稀土元素进行了研究 ,讨论了吸附酸度、洗脱、吸附流速以及共存离子干扰等的影响 ,并进行了实际样品的分析 ,获得了满意的结果 . 相似文献
900.
The K-shell X-ray fluorescence cross sections are determined experimentally for 10 elements such as Pb, Hg, Ir, W, Lu, Tm,
Dy, Tb, Gd and Nd at excitation energy of 661.6 keV associated with γ-rays of 137Cs radioisotope. The technique employed involves the measurement of total intensity of fluorescent K X-rays that follow the
photoeffect absorption of a known flux of γ-rays using a well type Nal(Tl) detector. The obtained results are compared with the available theoretical values and other
measured values. 相似文献