全文获取类型
收费全文 | 11821篇 |
免费 | 1101篇 |
国内免费 | 956篇 |
专业分类
化学 | 3537篇 |
晶体学 | 28篇 |
力学 | 497篇 |
综合类 | 99篇 |
数学 | 8314篇 |
物理学 | 1403篇 |
出版年
2023年 | 121篇 |
2022年 | 86篇 |
2021年 | 135篇 |
2020年 | 305篇 |
2019年 | 278篇 |
2018年 | 304篇 |
2017年 | 290篇 |
2016年 | 450篇 |
2015年 | 362篇 |
2014年 | 546篇 |
2013年 | 901篇 |
2012年 | 592篇 |
2011年 | 644篇 |
2010年 | 557篇 |
2009年 | 792篇 |
2008年 | 872篇 |
2007年 | 774篇 |
2006年 | 724篇 |
2005年 | 627篇 |
2004年 | 504篇 |
2003年 | 575篇 |
2002年 | 483篇 |
2001年 | 302篇 |
2000年 | 316篇 |
1999年 | 341篇 |
1998年 | 267篇 |
1997年 | 312篇 |
1996年 | 168篇 |
1995年 | 144篇 |
1994年 | 127篇 |
1993年 | 91篇 |
1992年 | 75篇 |
1991年 | 70篇 |
1990年 | 78篇 |
1989年 | 55篇 |
1988年 | 58篇 |
1987年 | 45篇 |
1986年 | 48篇 |
1985年 | 60篇 |
1984年 | 65篇 |
1983年 | 21篇 |
1982年 | 40篇 |
1981年 | 36篇 |
1980年 | 42篇 |
1979年 | 30篇 |
1978年 | 32篇 |
1977年 | 41篇 |
1976年 | 25篇 |
1975年 | 15篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Tingrui Li Yilitabaier Julaiti Xiaopeng Wu Jie Han Dr. Jin Xie 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(71):e202202851
The gold-catalyzed ring-opening rearrangement of cyclopropenes affords an efficient route to either polysubstituted naphthols or aryl-substituted furans. Owing to the unique dichotomy of gold−carbenes, this protocol provides a switchable reaction selectivity between naphthols and furans enabled by the use of TFP−Au(MeCN)SbF6 (tri(2-furyl) phosphine) or PNP(AuNTf2)2 (bis(diphenylphosphino)(isopropyl) amine) as catalysts respectively. It is proposed that the gold−carbene intermediate might be involved in the cyclopropene→naphthol rearrangement while the gold-carbocation is more likely to be involved in the cyclopropene→furan rearrangement. 相似文献
4.
Hasan Kara Muhammad Aamir Ali Hüseyin Budak 《Mathematical Methods in the Applied Sciences》2021,44(1):104-123
In this paper, we define interval‐valued left‐sided and right‐sided generalized fractional double integrals. We establish inequalities of Hermite‐Hadamard like for coordinated interval‐valued convex functions by applying our newly defined integrals. 相似文献
5.
This work is concerned with the extension of the Jacobi spectral Galerkin method to a class of nonlinear fractional pantograph differential equations. First, the fractional differential equation is converted to a nonlinear Volterra integral equation with weakly singular kernel. Second, we analyze the existence and uniqueness of solutions for the obtained integral equation. Then, the Galerkin method is used for solving the equivalent integral equation. The error estimates for the proposed method are also investigated. Finally, illustrative examples are presented to confirm our theoretical analysis. 相似文献
6.
8.
9.
Kevin Salzmann Dr. Candela Segarra Prof. Dr. Martin Albrecht 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9017-9021
An exceptionally efficient ruthenium-based catalyst for olefin oxidation has been designed by exploiting N,N′-bis(pyridylidene)oxalamide (bisPYA) as a donor-flexible ligand. The dynamic donor ability of the bisPYA ligand, imparted by variable zwitterionic and neutral resonance structure contributions, paired with the redox activity of ruthenium provided catalytic activity for Lemieux–Johnson-type oxidative cleavage of olefins to efficiently prepare ketones and aldehydes. The ruthenium bisPYA complex significantly outperforms state-of-the-art systems and displays extraordinary catalytic activity in this oxidation, reaching turnover frequencies of 650 000 h−1 and turnover numbers of several millions. 相似文献
10.
Chase A. Salazar Joseph J. Gair Kaylin N. Flesch Ilia A. Guzei Jared C. Lewis Shannon S. Stahl 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(27):10965-10969
Mono-N-protected amino acids (MPAAs) are increasingly common ligands in Pd-catalyzed C−H functionalization reactions. Previous studies have shown how these ligands accelerate catalytic turnover by facilitating the C−H activation step. Here, it is shown that MPAA ligands exhibit a second property commonly associated with ligand-accelerated catalysis: the ability to support catalytic turnover at substoichiometric ligand-to-metal ratios. This catalytic role of the MPAA ligand is characterized in stoichiometric C−H activation and catalytic C−H functionalization reactions. Palladacycle formation with substrates bearing carboxylate and pyridine directing groups exhibit a 50–100-fold increase in rate when only 0.05 equivalents of MPAA are present relative to PdII. These and other mechanistic data indicate that facile exchange between MPAAs and anionic ligands coordinated to PdII enables a single MPAA to support C−H activation at multiple PdII centers. 相似文献