全文获取类型
收费全文 | 19228篇 |
免费 | 877篇 |
国内免费 | 104篇 |
专业分类
化学 | 13221篇 |
晶体学 | 108篇 |
力学 | 423篇 |
数学 | 3018篇 |
物理学 | 3439篇 |
出版年
2023年 | 117篇 |
2022年 | 109篇 |
2021年 | 270篇 |
2020年 | 379篇 |
2019年 | 404篇 |
2018年 | 243篇 |
2017年 | 241篇 |
2016年 | 610篇 |
2015年 | 565篇 |
2014年 | 650篇 |
2013年 | 1045篇 |
2012年 | 1141篇 |
2011年 | 1267篇 |
2010年 | 755篇 |
2009年 | 662篇 |
2008年 | 1045篇 |
2007年 | 1037篇 |
2006年 | 970篇 |
2005年 | 886篇 |
2004年 | 779篇 |
2003年 | 648篇 |
2002年 | 611篇 |
2001年 | 315篇 |
2000年 | 297篇 |
1999年 | 278篇 |
1998年 | 250篇 |
1997年 | 235篇 |
1996年 | 271篇 |
1995年 | 252篇 |
1994年 | 223篇 |
1993年 | 219篇 |
1992年 | 201篇 |
1991年 | 172篇 |
1990年 | 174篇 |
1989年 | 171篇 |
1988年 | 156篇 |
1987年 | 126篇 |
1986年 | 118篇 |
1985年 | 171篇 |
1984年 | 167篇 |
1983年 | 129篇 |
1982年 | 159篇 |
1981年 | 157篇 |
1980年 | 136篇 |
1979年 | 139篇 |
1978年 | 164篇 |
1977年 | 116篇 |
1976年 | 105篇 |
1975年 | 123篇 |
1974年 | 93篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
Martin E. Schimpf J. Calvin Giddings 《Journal of Polymer Science.Polymer Physics》1989,27(6):1317-1332
The thermal diffusion coefficient DT has been obtained for 17 polymer-solvent combinations, each of them spanning a range of polymer molecular weights, using thermal field-flow fractionation. The polymers examined include polystyrene, poly(alpha-methyl)styrene, polymethylmethacrylate, and polysioprene. The solvents include benzene, toluene, ethylbenzene, tetrahydrofuran, methylethylketone, ethylacetate, and cyclohexane. Although DT was confirmed as essentially independent of polymer molecular weight, it was found to vary substantially with the chemical composition of polymer and solvent. The results were used to evaluate several thermal diffusion theories; the agreement with theory was generally found to be unsatisfactory. Attempts were then made to correlate the measured thermal diffusion coefficients with various physicochemical parameters of the polymers and solvent. A good correlation was found in which DT increases with the thermal conductivity difference of the polymer and solvent and varies inversely with the activation energy of viscous flow of the solvent. 相似文献
24.
Xiaojuan Hao Camilla Nilsson Martin Jesberger Martina H. Stenzel Eva Malmstrm Thomas P. Davis Emma
stmark Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2004,42(23):5877-5890
The synthesis and characterization of novel first‐ and second‐generation true dendritic reversible addition–fragmentation chain transfer (RAFT) agents carrying 6 or 12 pendant 3‐benzylsulfanylthiocarbonylsulfanylpropionic acid RAFT end groups with Z‐group architecture based on 1,1,1‐hydroxyphenyl ethane and trimethylolpropane cores are described in detail. The multifunctional dendritic RAFT agents have been used to prepare star polymers of poly(butyl acrylate) (PBA) and polystyrene (PS) of narrow polydispersities (1.4 < polydispersity index < 1.1 for PBA and 1.5 < polydispersity index < 1.3 for PS) via bulk free‐radical polymerization at 60 °C. The novel dendrimer‐based multifunctional RAFT agents effect an efficient living polymerization process, as evidenced by the linear evolution of the number‐average molecular weight (Mn) with the monomer–polymer conversion, yielding star polymers with molecular weights of up to Mn = 160,000 g mol?1 for PBA (based on a linear PBA calibration) and up to Mn = 70,000 g mol?1 for PS (based on a linear PS calibration). A structural change in the chemical nature of the dendritic core (i.e., 1,1,1‐hydroxyphenyl ethane vs trimethylolpropane) has no influence on the observed molecular weight distributions. The star‐shaped structure of the generated polymers has been confirmed through the cleavage of the pendant arms off the core of the star‐shaped polymeric materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5877–5890, 2004 相似文献
25.
Anne Buschmann Ute Ziegler Martin H. Groschup 《Accreditation and quality assurance》2004,9(4-5):191-197
The accumulation of pathological prion protein is used as a diagnostic marker for transmissible spongiform encephalopathies. According to European Union (EU) regulations cattle older than 30 months of age (Germany, France, Italy, and Spain by national law >24 months) and slaughtered for human consumption must be tested by using rapid tests for bovine spongiform encephalopathy (BSE). Likewise fallen stock and clinically affected animals must be tested. This article gives a short overview of the incidence of BSE in Europe. The diagnostic hierarchy, i.e., the officially approved methodology for the confirmation of suspect rapid test cases, and the organization of the numerous laboratories involved in this large-scale testing for BSE are described. Special emphasis is given to necessary quality control measures currently in place for BSE rapid testing laboratories and to measures intended to assure a consistent performance of the commercially available rapid test kits.Presented at BERM-9—Ninth International Symposium on Biological and Environmental Reference Materials, 15–19 June 2003, Berlin, Germany. 相似文献
26.
Ionel Rosenthal Joe Z. Sostaric Peter Riesz 《Research on Chemical Intermediates》2004,30(7-8):685-701
Sonochemistry and photochemistry are initiated by high-energy transient species, which may be prone to mutual interaction. Electronic excitation of solutes by energy transfer from high energy species generated in collapsing bubbles is already supported by experimental evidence. The rates of photochemical reactions can be affected by ultrasound-induced mixing of liquids caused by microstreaming near pulsating cavitation bubbles and shockwaves due to bubble collapse. This may not only improve light absorption but also modify the pathway of reaction by increasing the contact between reagents. Finally, one may speculate about a potentially new chemistry of photoexcited solutes under the extreme conditions inside cavitation microreactors. This work reviews research on the excitation of solutes by sonoluminescence, the combined effects of ultrasound and light on liquid systems and the effect of ultrasound on photocatalytic reactions. 相似文献
27.
Periodica Mathematica Hungarica - In our paper we study the usage of partially defined Boolean functions (PDBFs) for generating cryptographically strong Boolean functions. A PDBF can be considered... 相似文献
28.
Dmitri V Sevenard Vyacheslav Ya SosnovskikhAlexander A Kolomeitsev Martin H KönigsmannGerd-Volker Röschenthaler 《Tetrahedron letters》2003,44(41):7623-7627
In a convenient and efficient procedure, the nucleophilic 1,4-trifluoromethylation of several α,β-enones using (trifluoromethyl)trimethylsilane was achieved. The high regioselectivity of the reaction has been reached by blocking the carbonyl moiety of the electrophile with a bulky aluminum-centered Lewis acid. 相似文献
29.
Matrix extensions and eigenvalue completions, the generic case 总被引:2,自引:0,他引:2
William Helton Joachim Rosenthal Xiaochang Wang 《Transactions of the American Mathematical Society》1997,349(8):3401-3408
In this paper we provide new necessary and sufficient conditions for the so-called eigenvalue completion problem.
30.
The quantum defect orbital (QDO ) method and its relativistic (RQDO ) counterpart have been employed in this work to compute oscillator strengths for several fine-structure transitions in members of the copper isoelectronic sequence up to Z = 92. The RQDO results are found to be in quite good agreement with the best estimates derived from other sources, whenever the comparison is possible. © 1994 John Wiley & Sons, Inc. 相似文献