全文获取类型
收费全文 | 36276篇 |
免费 | 9588篇 |
国内免费 | 1396篇 |
专业分类
化学 | 41754篇 |
晶体学 | 319篇 |
力学 | 441篇 |
数学 | 2302篇 |
物理学 | 2444篇 |
出版年
2021年 | 143篇 |
2020年 | 1223篇 |
2019年 | 2569篇 |
2018年 | 1004篇 |
2017年 | 643篇 |
2016年 | 3370篇 |
2015年 | 3518篇 |
2014年 | 3421篇 |
2013年 | 4082篇 |
2012年 | 2890篇 |
2011年 | 2095篇 |
2010年 | 2818篇 |
2009年 | 2781篇 |
2008年 | 2310篇 |
2007年 | 1702篇 |
2006年 | 1400篇 |
2005年 | 1608篇 |
2004年 | 1414篇 |
2003年 | 1306篇 |
2002年 | 1990篇 |
2001年 | 1374篇 |
2000年 | 1284篇 |
1999年 | 372篇 |
1998年 | 44篇 |
1997年 | 45篇 |
1995年 | 24篇 |
1994年 | 24篇 |
1993年 | 35篇 |
1992年 | 39篇 |
1991年 | 25篇 |
1990年 | 38篇 |
1989年 | 31篇 |
1988年 | 53篇 |
1987年 | 50篇 |
1986年 | 49篇 |
1985年 | 60篇 |
1984年 | 43篇 |
1983年 | 60篇 |
1982年 | 35篇 |
1981年 | 39篇 |
1980年 | 39篇 |
1979年 | 44篇 |
1978年 | 43篇 |
1977年 | 30篇 |
1976年 | 55篇 |
1975年 | 37篇 |
1974年 | 25篇 |
1928年 | 28篇 |
1924年 | 25篇 |
1885年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
This paper outlines the development and adaptation of a coupling strategy for transient temperature analysis in a solid via a conjugate heat transfer method. This study proposes a quasi‐dynamic coupling procedure to bridge the temporal disparities between the fluid and the solid. In this approach, dynamic thermal modeling in the solid is coupled with a sequence of steady states in the fluid. This quasi‐dynamic algorithm has been applied to the problem of convective heat transfer over, and transient conduction heat transfer within, a flat plate using the severe thermal conditions of a solid propellant rocket. Two different coupled thermal computations have been performed. In the first one—referred to as the reference computation—the coupling period is equal to the smallest solid time constant. In the second one, a very large coupling period is used. The results show that the procedure can predict accurate transient temperature fields at a reasonable computational cost. The simulation CPU time is approximately reduced by up to 90%, while maintaining a very good accuracy. All the details of the numerical test case are given in the paper. This application illustrates the capabilities and the overall efficiency of this coupled approach in a solid transient problem using long term simulations of time dependent flows. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
993.
994.
Yao‐Cheng Shi Huan‐Ren Cheng Da‐Cong Cheng 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(6):581-583
The title compound, hexadecacarbonylbis{μ3‐[(diphenylphosphanyl)methanediidyl]sulfanido}‐μ4‐disulfido(2−)‐hexairon(4 Fe—Fe), [Fe6(C13H10PS)2(S2)(CO)16], contains two inversion‐related [Fe3(Ph2PCS)(CO)8] subclusters linked by an equatorial disulfide bond [S—S = 2.1490 (9) Å]. Each Ph2PCS3− ligand is coordinated to a triiron core in a μ3‐κP:κ2C:κ2S fashion. 相似文献
995.
Zhenhui Qi Dr. Changzhu Wu Dr. Paula Malo de Molina Han Sun Andrea Schulz Prof. Christian Griesinger Prof. Michael Gradzielski Prof. Rainer Haag Prof. Marion B. Ansorge‐Schumacher Prof. Christoph A. Schalley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(31):10150-10159
A new and versatile, crown ether appended, chiral supergelator has been designed and synthesized based on the bis‐urea motif. The introduction of a stereogenic center improved its gelation ability significantly relative to its achiral analogue. This low‐molecular‐weight gelator forms supramolecular gels in a variety of organic solvents. It is sensitive to multiple chemical stimuli and the sol–gel phase transitions can be reversibly triggered by host–guest interactions. The gel can be used to trap enzymes and release them on demand by chemical stimuli. It stabilizes the microparticles in Pickering emulsions so that enzyme‐catalyzed organic reactions can take place in the polar phase inside the microparticles, the organic reactants diffusing through the biphasic interface from the surrounding organic phase. Because of the higher interface area between the organic and polar phases, enzyme activity is enhanced in comparison with simple biphasic systems. 相似文献
996.
997.
Markus Follmann Nils Griebenow Michael G. Hahn Ingo Hartung Franz‐Josef Mais Joachim Mittendorf Martina Schfer Hartmut Schirok Johannes‐Peter Stasch Friederike Stoll Alexander Straub Peter Jeschke Ralf Nauen Michael Edmund Beck Hans‐Wilhelm Engels Hans‐Georg Pirkl Reinhard Albers Rolf W. Albach Jens Krause Andreas Hoffmann Holger Casselmann Jeff Dormish 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2013,125(36):9503-9503
998.
Synthesis and Rearrangement of P‐Nitroxyl‐Substituted PIII and PV Phosphanes: A Combined Experimental and Theoretical Case Study
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tobias Heurich Dr. Zheng‐Wang Qu Dr. Senada Nožinović Dr. Gregor Schnakenburg Dr. Hideto Matsuoka Prof. Dr. Stefan Grimme Prof. Dr. Olav Schiemann Prof. Dr. Rainer Streubel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(29):10102-10110
Low‐temperature generation of P‐nitroxyl phosphane 2 (Ph2POTEMP), which was obtained by the reaction of Ph2PH ( 1 ) with two equivalents of TEMPO, is presented. Upon warming, phosphane 2 decomposed to give P‐nitroxyl phosphane P‐oxide 3 (Ph2P(O)OTEMP) as one of the final products. This facile synthetic protocol also enabled access to P‐sulfide and P‐borane derivatives 7 and 13 , respectively, by using Ph2P(S)H ( 6 ) or Ph2P(BH3)H ( 11 ) and TEMPO. Phosphane sulfide 7 revealed a rearrangement to phosphane oxide 8 (Ph2P(O)STEMP) in CDCl3 at ambient temperature, whereas in THF, thermal decomposition of sulfide 7 yielded salt 10 ([TEMP‐H2][Ph2P(S)O]). As well as EPR and detailed NMR kinetic studies, indepth theoretical studies provided an insight into the reaction pathways and spin‐density distributions of the reactive intermediates. 相似文献
999.
1000.
Synthesis of Some New Thiazole,Oxazole, Pyrimidine and Pyridazine Derivatives from 2‐cyano‐N‐octadecyl‐acetamide as Antimicrobial and Surface Active Agents
下载免费PDF全文
![点击此处可从《Journal of heterocyclic chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The motivation behind the present work is to synthesize some nonionic surfactants containing heterocyclic nucleus with intermediate fatty compounds for improving their surfactants properties. 2‐Cyano‐N‐octadecylacetamide was utilized as key intermediate for the synthesis of some new thiazole, pyrazole, oxazole, pyrimidine, 1,3‐dithiolane, thiophene, coumarin, oxazine and pyridazine derivatives. The newly synthesized compounds undergo propoxylation using propylene oxide to afford nonionic surface active agents. The antimicrobial and surface activities were evaluated and characterized through investigations of their spreading behavior in monolayer on water. 相似文献