全文获取类型
收费全文 | 4195篇 |
免费 | 132篇 |
国内免费 | 10篇 |
专业分类
化学 | 2270篇 |
晶体学 | 42篇 |
力学 | 127篇 |
数学 | 456篇 |
物理学 | 1442篇 |
出版年
2022年 | 63篇 |
2021年 | 65篇 |
2020年 | 75篇 |
2019年 | 75篇 |
2018年 | 86篇 |
2017年 | 59篇 |
2016年 | 109篇 |
2015年 | 80篇 |
2014年 | 104篇 |
2013年 | 253篇 |
2012年 | 225篇 |
2011年 | 263篇 |
2010年 | 161篇 |
2009年 | 148篇 |
2008年 | 210篇 |
2007年 | 206篇 |
2006年 | 217篇 |
2005年 | 183篇 |
2004年 | 127篇 |
2003年 | 115篇 |
2002年 | 102篇 |
2001年 | 75篇 |
2000年 | 76篇 |
1999年 | 53篇 |
1998年 | 42篇 |
1997年 | 40篇 |
1996年 | 50篇 |
1995年 | 49篇 |
1994年 | 43篇 |
1993年 | 57篇 |
1992年 | 45篇 |
1991年 | 34篇 |
1990年 | 49篇 |
1989年 | 40篇 |
1988年 | 40篇 |
1987年 | 39篇 |
1986年 | 29篇 |
1985年 | 45篇 |
1984年 | 38篇 |
1983年 | 40篇 |
1982年 | 36篇 |
1981年 | 37篇 |
1980年 | 41篇 |
1979年 | 33篇 |
1978年 | 38篇 |
1977年 | 33篇 |
1976年 | 37篇 |
1975年 | 31篇 |
1974年 | 35篇 |
1973年 | 37篇 |
排序方式: 共有4337条查询结果,搜索用时 15 毫秒
151.
Abstract In recent years attention has been directed toward the synthesis of modified sugars wherein the oxygen atom in the sugar ring is replaced by sulfur, selenium or phosphorus. Synthesis of sugar analogs with phosphorus as the ring heteroatom is interesting from the point of view of their possible biological activity. 相似文献
152.
Prof. Dr. Steven Stevenson Amanda J. Rothgeb Katelyn R. Tepper Prof. Dr. James Duchamp Prof. Dr. Harry C. Dorn Xian B. Powers Mrittika Roy Prof. Dr. Marilyn M. Olmstead Prof. Dr. Alan L. Balch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(54):12545-12551
Purified samples of Ho3N@C2(22010)-C78 and Tb3N@C2(22010)-C78 have been isolated by two distinct processes from the rich array of fullerenes and endohedral fullerenes present in carbon soot from graphite rods doped with Ho2O3 or Tb4O7. Crystallographic analysis of the endohedral fullerenes as cocrystals with Ni(OEP) (in which OEP is the dianion of octaethylporphyrin) shows that both molecules contain the chiral C2(22010)-C78 cage. This cage does not obey the isolated pentagon rule (IPR) but has two sites where two pentagons share a common C−C bond. These pentalene units bind two of the metal ions, whereas the third metal resides near a hexagon of the cage. Inside the cages, the Ho3N or Tb3N unit is planar. Ho3N@C2(22010)-C78 and Tb3N@C2(22010)-C78 use the same cage previously found for Gd3N@C2(22010)-C78 rather than the IPR-obeying cage found in Sc3N@D3h-C78. 相似文献
153.
2-Phenylquinoline derivatives have been synthesized through the thermolysis of suitable enaminoimine hydrochiorides. 相似文献
154.
S. N. Hardrict R. Gurarslan C. J. Galvin H. Gracz D. Roy B. S. Sumerlin J. Genzer A. E. Tonelli 《Journal of Polymer Science.Polymer Physics》2013,51(9):735-741
In this brief report, we demonstrate that Kerr effect measurements, which determine the excess birefringence contributed by polymer solutes in dilute solutions observed under a strong electric field, are highly sensitive to and capable of determining their microstructures, as well as their locations along the macromolecular backbone. Specifically, using atactic triblock copolymers with the same overall composition of styrene (S) and p-bromostyrene (pBrS) units, but with two different block arrangements, that is, pBrS90-b-S120-b-pBrS90 (I) and S60-b-pBrS180-b-S60 (II), which are indistinguishable by NMR, we detected a dramatic difference in their molar Kerr constants (mK), in agreement with those previously estimated. Although similar in magnitude, their Kerr constants differ in sign, with mK(II) positive and mK(I) negative. In addition, S/pBrS random and gradient copolymers synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization exhibit a heretofore unexpected enhanced enchainment of racemic (r) pBrS-pBrS diads. Comparison of their observed and calculated mKs suggests that the gradient S/pBrS copolymers possess an unanticipated additional gradient in stereosequence that parallels their comonomer gradient, that is, as the concentration of pBrs units decreases from one end of the copolymer chain to the other, so does the content of r diads. This conclusion could only be reached by comparison of observed and calculated Kerr effects, which access the global properties of macromolecules, and not NMR, which is only sensitive to local polymer structural environments, but not to their locations on the copolymer chains. Molar Kerr constants are characteristic of entire polymer chains and are highly sensitive to their constituent microstructures and their distribution along the chain. They may be used to both identify constituent microstructures and locate them along the polymer chain, thereby enabling, for the first time, characterization of their complete macrostructures. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 相似文献
155.
Debayan Roy Dr. Beeraiah Baire 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(12):4009-4015
Design and development of a domino cyclative approach for the synthesis of new polycyclic γ-butenolides from β-aryl-Z-enoate propargylic alcohols, through the interception of an intermediate of the Z-enoate-assisted Meyer–Schuster rearrangement, has been reported. A systematic NMR analysis of various derivatives of this class revealed and supported the potential atropisomerism associated with them. These molecules represent first examples of butenolide ring-based atropisomeric compounds in organic chemistry. The synthetic process involves a synchronous construction of both rings with concurrent creation of the potential stereogenic rotational axis. 相似文献
156.
157.
158.
Sujoy Biswas V. H. Rupawate S. B. Roy M. Sahu 《Journal of Radioanalytical and Nuclear Chemistry》2014,300(2):853-858
In this paper a quaternary ammonium based room temperature ionic liquid (IL) trioctylmethylammonium hydrogen phthalate has been reported as promising extractant for separation of U(VI) from other metal ions from aqueous media. The IL was synthesized via metathesis route and characterized using various techniques such as hydrogen nuclear magnetic resonance, electron spray ionization mass spectrometry and infra red etc. The newly synthesized IL was evaluated for extraction of U(VI), Th(IV), La(III), Y(III), Nd(III) and Fe(III) from aqueous solutions and follow the order: U(VI) > Th(IV) > Fe(III) > Y(III) >> Nd(III) ~ La(III). 相似文献
159.
160.