全文获取类型
收费全文 | 4802篇 |
免费 | 510篇 |
国内免费 | 633篇 |
专业分类
化学 | 1437篇 |
晶体学 | 26篇 |
力学 | 203篇 |
综合类 | 126篇 |
数学 | 3546篇 |
物理学 | 607篇 |
出版年
2024年 | 5篇 |
2023年 | 46篇 |
2022年 | 85篇 |
2021年 | 126篇 |
2020年 | 139篇 |
2019年 | 166篇 |
2018年 | 162篇 |
2017年 | 157篇 |
2016年 | 203篇 |
2015年 | 146篇 |
2014年 | 239篇 |
2013年 | 380篇 |
2012年 | 215篇 |
2011年 | 291篇 |
2010年 | 248篇 |
2009年 | 329篇 |
2008年 | 347篇 |
2007年 | 301篇 |
2006年 | 310篇 |
2005年 | 229篇 |
2004年 | 215篇 |
2003年 | 240篇 |
2002年 | 221篇 |
2001年 | 144篇 |
2000年 | 183篇 |
1999年 | 136篇 |
1998年 | 100篇 |
1997年 | 126篇 |
1996年 | 92篇 |
1995年 | 62篇 |
1994年 | 54篇 |
1993年 | 43篇 |
1992年 | 30篇 |
1991年 | 31篇 |
1990年 | 17篇 |
1989年 | 10篇 |
1988年 | 22篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1936年 | 3篇 |
排序方式: 共有5945条查询结果,搜索用时 25 毫秒
961.
使用密度泛函理论的离散变分方法(DFT-DVM)研究了双帽Keggin型杂多阴离子[PM12O40(VO)2]n--(M=Mo,n=5; M=V,n=9),即[PMo12O40(VO)2]5- (a)和[PV12O40(VO)2]9- (b)的电子结构,讨论了双帽的形成对Keggin型杂多阴离子的电子结构和催化性质的影响,并与其Keggin型杂多阴离子(PM12O40)n-(M=Mo,n=3; M=V,n=15)的计算结果进行了对比分析,计算结果表明,双帽的形成对Keggin型杂多阴离子的电子结构产生了很大的影响,因而它们在催化活性上可能会表现出较大的差异. 相似文献
962.
Masahiro Mitsuyama Koichi Kondo 《Journal of polymer science. Part A, Polymer chemistry》2001,39(6):913-917
11‐Dodecyn‐1‐ol as an achiral, aliphatic, monosubstituted acetylene was copolymerized with cholesteryl 3‐butynyl carbonate as a chiral, aliphatic, monosubstituted acetylene with Rh(nbd)[B(C6H5)4] (nbd = norbornadiene) in tetrahydrofuran. The main chain of the obtained copolymers seemed to be mainly composed of the cis‐type structure. The backbone π–π* transition of these copolymers showed significant circular dichroism (CD), indicating an excess of one‐handed helical conformation. These CD signals were varied with the contents of the cholesteryl units in the copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 913–917, 2001 相似文献
963.
Karim Nour 《Mathematical Logic Quarterly》2002,48(3):357-366
In this paper, we present an extension of λμ‐calculus called λμ++‐calculus which has the following properties: subject reduction, strong normalization, unicity of the representation of data and thus confluence only on data types. This calculus allows also to program the parallel‐or. 相似文献
964.
Let μ be a nonnegative Radon measure on R d which satisfies the growth condition μ(B(x,r)) ≤ C0rn for all x ∈Rd and r >0,where C0 is a fixed constant and 0相似文献
965.
966.
We study Tsirelson type spaces of the form T[(ℳ︁k, θk)lk=1] defined by a finite sequence (ℳ︁k)lk=1 of compact families of finite subsets of ℕ. Using an appropriate index, denoted by i(ℳ︁), to measure the complexity of a family ℳ︁, we prove the following: If i(ℳ︁k) < ω for all k = 1, …, l, then the space T[(ℳ︁k, θk)lk=1] contains isomorphically some lp, 1 < p < ∞, or c0. If i(ℳ︁) = ω, then the space T[ℳ︁, θ] contains a subspace isomorphic to a subspace of the original Tsirelson's space. 相似文献
967.
968.
969.
A series of chiral smectic C phase shish‐kebab type liquid crystal polymers was synthesized by low‐temperature solution condensation polymerization from 2,5‐bis[4‐((S)‐alkoxyl)benzoyloxy]hydroquinone and aliphatic diacylchloride. The monomers and their precursors were identified by using elemental analysis, infrared spectrum, nuclear magnetic resonance and mass spectrometry. The polymers were characterized by gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis, temperature‐variable X‐ray diffraction, polarimeter and polarizing microscope (POM) with a heating stage. All the polymers entered into liquid crystal phase when heated to above their melting temperature. The Schlieren texture and sanded texture were observed on POM. All the chiral compounds and polymers showed high optical activity. Temperature‐variable, X‐ray diffraction study together with the POM and polarimetric analysis revealed that the polymers synthesized are chiral smectic C phase. Thus, the present report provides examples of shish‐kebab type polymers that form a chiral smectic C phase. The change of the melting temperature and isotropization temperature with the variation in molecular structure was also discussed. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
970.
Hiroshi Seino Amane Mochizuki Osamu Haba Mitsuru Ueda 《Journal of polymer science. Part A, Polymer chemistry》1998,36(13):2261-2267
A positive-working photosensitive polyimide precursor based on fluorinated poly(amic acid) (FPAA) and 2,3,4-tris(1-oxo-2-diazonaphthoquinon-4-ylsulfonyloxy)benzophenone (D4SB) as a photosensitive compound has been developed. FPAA was prepared by ring-opening polyaddition of dianhydrides, pyromellitic dianhydride and biphenyltetracarboxylic dianhydride, with diamine, 2,2′-bis(trifluoromethyl)benzidine, in methanol. The FPAA film showed excellent transparency to UV light and good solubility in a wide range of organic solvents. The dissolution behavior of FPAA containing 30 wt % D4SB after exposure was studied, and it was found that the difference of dissolution rate between exposed and unexposed parts was enough to get high contrast due to the photochemical reaction of D4SB in the polymer film. The photosensitive fluorinated polyimide (FPI) precursor containing 30 wt % D4SB showed a sensitivity of 80 mJ cm−2 and a contrast of 7.8 with 365 nm light when it was developed with 0.3% aqueous tetramethyl ammonium hydroxide solution at room temperature. The FPI film cured up to 360°C had a low coefficient of thermal expansion of 10.3 ppm °C−1 and a low dielectric constant of 3.04. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2261–2267, 1998 相似文献