全文获取类型
收费全文 | 6547篇 |
免费 | 165篇 |
国内免费 | 43篇 |
专业分类
化学 | 4481篇 |
晶体学 | 56篇 |
力学 | 159篇 |
数学 | 779篇 |
物理学 | 1280篇 |
出版年
2022年 | 39篇 |
2021年 | 75篇 |
2020年 | 109篇 |
2019年 | 96篇 |
2018年 | 65篇 |
2017年 | 65篇 |
2016年 | 122篇 |
2015年 | 113篇 |
2014年 | 127篇 |
2013年 | 265篇 |
2012年 | 378篇 |
2011年 | 458篇 |
2010年 | 197篇 |
2009年 | 188篇 |
2008年 | 362篇 |
2007年 | 401篇 |
2006年 | 377篇 |
2005年 | 363篇 |
2004年 | 332篇 |
2003年 | 287篇 |
2002年 | 272篇 |
2001年 | 136篇 |
2000年 | 132篇 |
1999年 | 79篇 |
1998年 | 61篇 |
1997年 | 60篇 |
1996年 | 77篇 |
1995年 | 75篇 |
1994年 | 69篇 |
1993年 | 73篇 |
1992年 | 67篇 |
1991年 | 50篇 |
1990年 | 54篇 |
1989年 | 59篇 |
1988年 | 59篇 |
1987年 | 47篇 |
1986年 | 39篇 |
1985年 | 62篇 |
1984年 | 51篇 |
1983年 | 52篇 |
1982年 | 75篇 |
1981年 | 48篇 |
1980年 | 53篇 |
1979年 | 42篇 |
1978年 | 48篇 |
1977年 | 38篇 |
1976年 | 49篇 |
1975年 | 61篇 |
1974年 | 38篇 |
1973年 | 46篇 |
排序方式: 共有6755条查询结果,搜索用时 15 毫秒
11.
12.
Stacy J. Taylor Robson F. Storey 《Journal of polymer science. Part A, Polymer chemistry》2004,42(23):5942-5953
3,3′,5,5′‐Tetrakis(2‐chloro‐2‐propyl)biphenyl (biphenyl tetracumyl chloride, BPTCC) and 1,3‐bis[3,5‐bis(2‐chloro‐2‐propyl)phenoxy]propane (diphenoxypropane tetracumyl chloride, DPPTCC) were synthesized as initiators for quasiliving cationic polymerization of isobutylene (IB). In the synthesis of BPTCC, tetrafunctionality was achieved via the coupling of dimethyl 5‐bromoisophthalate (DMBI) using nickel dibromide bis(triphenylphosphine) and zinc in the presence of a base; in the synthesis of DPPTCC, two equivalents of dimethyl 5‐hydroxyisophthalate were linked via reaction with 1,3‐dibromopropane in the presence of potassium carbonate. Both initiators were used to initiate the polymerization of IB under quasiliving cationic polymerization conditions. PIB initiated from BPTCC revealed a chain end/molecule value (as determined by 1H‐NMR) of 3.85, verifying the nearly exclusive production of 4‐arm polyisobutylene (PIB). GPC analysis revealed a narrow peak representing the target four‐arm PIB, with a slight shoulder at high elution volumes (low molecular weights). GPC analysis of the PIB initiated by DPPTCC revealed multimodal distributions, suggesting the formation of two‐, three‐, and four‐arm star polymers during the polymerization. This behavior was attributed to Friedel–Crafts alkylation of the initiator core after the addition of one IB unit, which was activated by the electron‐donating oxytrimethyleneoxy linking moiety. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5942–5953, 2004 相似文献
13.
In his curriculum vitae, John Hawkes lists his research interestsas geometric measure theory, probability (Lévy processes),and potential theory (probabilistic). In fact, he made significantcontributions to all three areas, and there are strong relationshipsbetween them. He used both geometric measure theory and potentialtheory as tools for his study of the trajectories of particularLévy processes, but in many cases he needed to developthe tool before it was ready to be used. We will summarise hisresearch later, but first we discuss what is known of his lifehistory. 相似文献
14.
A polymer-supported diphenylphosphoryl azide was prepared. This polymer-supported version of DPPA is useful due to its lower toxicity, moisture tolerance and ease of workup after reaction. The synthetic application of this solid-phase reagent was explored by conversion of a variety of carboxylic acids to urethanes and ureas through Curtius rearrangement reactions. Carboxylic acids bearing different functional groups (aromatic, aliphatic and heterocyclic carboxylic acids) were subjected to the reaction. The corresponding products were isolated with satisfactory yields. 相似文献
15.
Summary It is shown that the outer automorphism group of a Coxeter groupW of finite rank is finite if the Coxeter graph contains no infinite bonds. A key step in the proof is to show that if the
group is irreducible andΠ
1 andΠ
2 any two bases of the root system ofW, thenΠ
2 = ±ωΠ
1 for some ω εW. The proof of this latter fact employs some properties of the dominance order on the root system introduced by Brink and
Howlett.
This article was processed by the author using the Springer-Verlag TEX PJour1g macro package 1991. 相似文献
16.
17.
18.
19.
The stannous chloride dihydrate-mediated deprotection-bicyclisation of a range of amides possessing a pendant acetal group is reported. These mild reaction conditions have been used to prepare a number of ring-fused heterocyclic compounds, some in enantiomerically pure form, which should be of interest both in their own right and as building blocks for the production of more complex target molecules. 相似文献
20.