全文获取类型
收费全文 | 2618篇 |
免费 | 103篇 |
国内免费 | 15篇 |
专业分类
化学 | 1767篇 |
晶体学 | 30篇 |
力学 | 69篇 |
数学 | 151篇 |
物理学 | 452篇 |
无线电 | 267篇 |
出版年
2023年 | 16篇 |
2022年 | 48篇 |
2021年 | 71篇 |
2020年 | 69篇 |
2019年 | 67篇 |
2018年 | 70篇 |
2017年 | 48篇 |
2016年 | 113篇 |
2015年 | 74篇 |
2014年 | 132篇 |
2013年 | 205篇 |
2012年 | 170篇 |
2011年 | 195篇 |
2010年 | 107篇 |
2009年 | 90篇 |
2008年 | 143篇 |
2007年 | 145篇 |
2006年 | 123篇 |
2005年 | 125篇 |
2004年 | 74篇 |
2003年 | 80篇 |
2002年 | 68篇 |
2001年 | 28篇 |
2000年 | 30篇 |
1999年 | 13篇 |
1998年 | 32篇 |
1997年 | 20篇 |
1996年 | 22篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 17篇 |
1991年 | 24篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 17篇 |
1986年 | 7篇 |
1985年 | 22篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 23篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1975年 | 7篇 |
1974年 | 6篇 |
排序方式: 共有2736条查询结果,搜索用时 328 毫秒
761.
G.S. Ranganath S. Chandrasekhar U.D. Kini K.A. Suresh S. Ramaseshan 《Chemical physics letters》1973,19(4):556-560
A rigorous theory is developed of the optical properties of a mixture of right-handed and left-handed cholesteric liquid crystals, taking into account the effect of absorption. The dependence of the rotatory power and circular dichroism on pitch and on sample thickness is discussed. 相似文献
762.
Liquid crystals of disc-like molecules 总被引:2,自引:0,他引:2
Thermotropic mesomorphism has been observed in pure compounds consisting of simple disc-like molecules, viz., benzene-hexa-n-alkanoates. Thermodynamic, optical and x-ray studies indicate that the mesophase is a highly ordered lamellar type of liquid
crystal. Based on the x-ray data, a structure is proposed in which the discs are stacked one on top of the other in columns
that constitute a hexagonal arrangement, but the spacing between the discs in each column is irregular. Thus the structure
has translational periodicity in two dimensions and liquid-like disorder in the third. 相似文献
763.
An algorithm for optimum allocation of redundancies in a general system is presented. The method is applicable to problems having any number of constraints which need not be linear. For selecting the subsystem where redundancy is to be added, a heuristic criterion is introduced which takes into account the relative increment in reliability versus increments in constraints. The method is applicable for any system configuration where subsystems are composed of identical parallel elements. The algorithm is simple, requires little computation effort, and is easily programmed for a computer. An example of a nonseries system illustrates the procedure. 相似文献
764.
Our experiments show that the optical absorption from indirect transitions in Ge does not exhibit steps but consists of a series of absorption peaks at high magnetic fields. The measurements also indicate a strong Coulomb interaction in the absorption process. 相似文献
765.
766.
Monitoring health-related radiation damage is important for the future, and a system to detect chromosomal aberrations associated with radiation is extremely useful for monitoring populations exposed to radiation. In general, the most useful indicator of radiation damage at the cellular level is the occurrence of ring, dicentric, fragment, and fragment ring chromosomes. 相似文献
767.
Spraul BK Suresh S Glaser S Perahia D Ballato J Smith DW 《Journal of the American Chemical Society》2004,126(40):12772-12773
Hexa-peri-hexabenzocoronene (HBC) derivatives possess many interesting properties ranging from liquid crystallinity, to hole transport, to variable emission behavior, yet are plagued by insolubility and general accessibility of polymerizable substituents. The first synthesis of trifluorovinyl ether-substituted hexabenzocoronene and its polymerization to perfluorocyclobutyl (PFCB) polymers and copolymers is shown. Unlike hydrocarbon ethers, fluoro vinyl ethers are stable under HBC oxidation conditions. Discrete HBC units in PFCB polymers provide access to potentially processable HBC optical materials. 相似文献
768.
Mazumder UK Gupta M Karki SS Bhattacharya S Rathinasamy S Thangavel S 《Chemical & pharmaceutical bulletin》2004,52(2):178-185
In search of potential anticancer drug candidates in ruthenium complexes, a series of mononuclear ruthenium complexes of the type [Ru(phen)(2)(nmit)]Cl(2) (Ru1), [Ru(bpy)(2)(nmit)]Cl(2) (Ru2), [Ru(phen)(2)(icpl)]Cl(2) (Ru3), Ru(bpy)(2)(icpl)]Cl(2) (Ru4) (phen=1,10-phenanthroline; bpy=2,2'-bipyridine; nmit=N-methyl-isatin-3-thiosemicarbazone, icpl=isatin-3-(4-Cl-phenyl)thiosemicarbazone) and [Ru(phen)(2)(aze)]Cl(2) (Ru5), [Ru(bpy)(2)(aze)]Cl(2) (Ru6) (aze=acetazolamide) and [Ru(phen)(2)(R-tsc)](ClO(4))(2) (R=methyl (Ru7), ethyl (Ru8), cyclohexyl (Ru9), 4-Cl-phenyl (10), 4-Br-phenyl (Ru11), and 4-EtO-phenyl (Ru12), tsc=thiosemicarbazone) were prepared and characterized by elemental analysis, FTIR, (1)H-NMR and FAB-MS. Effect of these complexes on the growth of a transplantable murine tumor cell line (Ehrlich Ascites Carcinoma) and their antibacterial activity were studied. In cancer study the effect of hematological profile of the tumor hosts have also been studied. In the cancer study, the complexes Ru1-Ru4, Ru10 and Ru11 have remarkably decreased the tumor volume and viable ascitic cell count as indicated by trypan blue dye exclusion test (p<0.05). Treatment with the ruthenium complexes prolonged the lifespan of Ehrlich Ascites Carcinoma (EAC) bearing mice. Tumor inhibition by the ruthenium chelates was followed by improvements in hemoglobin, RBC and WBC values. All the complexes showed antibacterial activity, except Ru5 and Ru6. Thus, the results suggest that these ruthenium complexes have significant antitumor property and antibacterial activity. The results also reflect that the drug does not adversely affect the hematological profiles as compared to that of cisplatin on the host. 相似文献
769.
The nucleation and growth kinetics of highly ordered gold nanocrystal superlattices during the evaporation of nanocrystal colloidal droplets was elucidated by in situ time-resolved small-angle x-ray scattering. We demonstrated for the first time that the evaporation rate can affect the dimensionality of the superlattices. The formation of two-dimensional nanocrystal superlattices at the liquid-air interface of the droplet has exponential growth kinetics that originates from interface crushing. 相似文献
770.
Triphenylarsine catalyses the formation of epoxides from carbonyl compounds and tosylhydrazone salts. This convergent synthesis gives complete trans selectivity for all aldehyde and tosylhydrazone salt coupling partners. 相似文献