全文获取类型
收费全文 | 11418篇 |
免费 | 1407篇 |
国内免费 | 963篇 |
专业分类
化学 | 5679篇 |
晶体学 | 132篇 |
力学 | 477篇 |
综合类 | 72篇 |
数学 | 791篇 |
物理学 | 2949篇 |
综合类 | 3688篇 |
出版年
2024年 | 39篇 |
2023年 | 222篇 |
2022年 | 329篇 |
2021年 | 388篇 |
2020年 | 434篇 |
2019年 | 374篇 |
2018年 | 331篇 |
2017年 | 315篇 |
2016年 | 469篇 |
2015年 | 493篇 |
2014年 | 671篇 |
2013年 | 722篇 |
2012年 | 807篇 |
2011年 | 836篇 |
2010年 | 561篇 |
2009年 | 510篇 |
2008年 | 668篇 |
2007年 | 556篇 |
2006年 | 523篇 |
2005年 | 432篇 |
2004年 | 310篇 |
2003年 | 307篇 |
2002年 | 239篇 |
2001年 | 204篇 |
2000年 | 239篇 |
1999年 | 313篇 |
1998年 | 284篇 |
1997年 | 284篇 |
1996年 | 293篇 |
1995年 | 244篇 |
1994年 | 207篇 |
1993年 | 171篇 |
1992年 | 161篇 |
1991年 | 151篇 |
1990年 | 141篇 |
1989年 | 125篇 |
1988年 | 108篇 |
1987年 | 78篇 |
1986年 | 61篇 |
1985年 | 41篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1970年 | 12篇 |
1937年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
21.
J.J. Pan Xiangdong Qiu Kejian Guan Liang Dong FengQing Zhou Wei Wang Mingjie Zhang James Guo Jun Yang Chunmeng Wu 《光学学报》2003,23(Z1)
A low cost, coolerless 980nm diode pumped, gain flattened L band EDFA with fast transient control, high pump efficiency and gain clamping effect was realized by using FBGs as C band seed generators. 相似文献
22.
Ivan Pan 《Comptes Rendus Mathematique》2005,341(7):439-443
We show that the first dynamical degree of a Cremona transformation stabilizing an irrational non elliptic curve is 1. Moreover, among these transformations, we characterize those which have finite order. To cite this article: I. Pan, C. R. Acad. Sci. Paris, Ser. I 341 (2005). 相似文献
23.
An experimental method is developed to examine the near tip deformation at the mesoscopic scale level. The differential interference contrast (DIC) method is used by application of the Nomarski prism in polarized microscope for measuring the out of surface deformation. The method is very sensitive to small height changes detected by different interference color. Discussed are results for the crack tip deformation field. 相似文献
24.
T. Brian Cavitt Brian Phillips Charles E. Hoyle Bo Pan Sukhendu B. Hait Kalyanaraman Viswanathan Sonny Jnsson 《Journal of polymer science. Part A, Polymer chemistry》2004,42(16):4009-4015
Three‐component photoinitiators comprised of an N‐arylphthalimide, a diarylketone, and a tertiary amine were investigated for their initiation efficiency of acrylate polymerization. The use of an electron‐deficient N‐arylphthalimide resulted in a greater acrylate polymerization rate than an electron‐rich N‐arylphthalimide. Triplet energies of each N‐arylphthalimide, determined from their phosphorescence spectra, and the respective rate constants for triplet quenching by the N‐arylphthalimide derivatives (acquired via laser flash photolysis) indicated that an electron–proton transfer from an intermediate radical species to the N‐arylphthalimide (not energy transfer from triplet sensitization) is responsible for generating the initiating radicals under the conditions and species concentrations used for polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4009–4015, 2004 相似文献
25.
Chun‐Yan Hong Ye‐Zi You Cai‐Yuan Pan 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4873-4881
Well‐defined diblock and triblock copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM) and poly(ethylene oxide) (PEO) were successfully synthesized through the reversible addition–fragmentation chain transfer polymerization of N‐isopropylacrylamide (NIPAM) with PEO capped with one or two dithiobenzoyl groups as a macrotransfer agent. 1H NMR, Fourier transform infrared, and gel permeation chromatography instruments were used to characterize the block copolymers obtained. The results showed that the diblock and triblock copolymers had well‐defined structures and narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight < 1.2), and the molecular weight of the PNIPAM block in the diblock and triblock copolymers could be controlled by the initial molar ratio of NIPAM to dithiobenzoate‐terminated PEO and the NIPAM conversion. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4873–4881, 2004 相似文献
26.
Xiao‐Dong Pan 《Journal of Polymer Science.Polymer Physics》2004,42(13):2467-2478
For properly chosen elastomer compounds, thermorheological characterization is combined with an examination of the variation of the wet sliding friction with temperature. A conceptual argument leads to the assumption that the wet sliding friction should maximize at the energy dissipation peak associated with the dynamic softening transition at a characteristic frequency determined by the sliding speed and the effective smallest surface asperity scale. The dynamic softening transition is characterized with the peak in tan δ/G′n, where tan δ is the loss tangent, G′ is the elastic modulus, and n is a constant between 0 and 1. The William–Landel–Ferry transform is uncritically applied for extrapolating the position of the peak in tan δ/G′n at high frequencies. Even based on the criterion of tan δ, the results obtained on a concrete surface indicate that the effective smallest asperity scale is of order of 100 μm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2467–2478, 2004 相似文献
27.
28.
29.
合成了一种新的手性β-二酮-(+)-乙酰-d-龙脑酰基甲烷[H(acm)],确证了结构,进一步将其制成Eu+3络合物,并研究了手性位移效果. 相似文献
30.
本文介绍了营业杠杆系数这一衡量企业经营风险的重要指标,对该指标的特性进行了较深入的分析和探讨。同时,还导出了利用该指标判断企业经营安全状态的方法。 相似文献