全文获取类型
收费全文 | 4285篇 |
免费 | 196篇 |
国内免费 | 20篇 |
专业分类
化学 | 3388篇 |
晶体学 | 37篇 |
力学 | 78篇 |
数学 | 411篇 |
物理学 | 587篇 |
出版年
2023年 | 26篇 |
2022年 | 42篇 |
2021年 | 70篇 |
2020年 | 91篇 |
2019年 | 88篇 |
2018年 | 56篇 |
2017年 | 56篇 |
2016年 | 128篇 |
2015年 | 127篇 |
2014年 | 141篇 |
2013年 | 193篇 |
2012年 | 314篇 |
2011年 | 376篇 |
2010年 | 205篇 |
2009年 | 192篇 |
2008年 | 349篇 |
2007年 | 307篇 |
2006年 | 277篇 |
2005年 | 279篇 |
2004年 | 241篇 |
2003年 | 187篇 |
2002年 | 181篇 |
2001年 | 54篇 |
2000年 | 62篇 |
1999年 | 52篇 |
1998年 | 42篇 |
1997年 | 29篇 |
1996年 | 37篇 |
1995年 | 23篇 |
1994年 | 18篇 |
1993年 | 29篇 |
1992年 | 26篇 |
1991年 | 17篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1969年 | 5篇 |
排序方式: 共有4501条查询结果,搜索用时 15 毫秒
1.
The Effect of the Spacer of Bis(biurea) Ligands on the Structure of A2L3‐type (A=anion) Phosphate Complexes
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof. Biao Wu Dr. Shaoguang Li Prof. Yibo Lei Prof. Huaiming Hu Dr. Nader de Sousa Amadeu Prof. Dr. Christoph Janiak Dr. Jennifer S. Mathieson Dr. De‐Liang Long Prof. Leroy Cronin Prof. Xiao‐Juan Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2588-2593
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes. 相似文献
2.
3.
4.
Ieva
Dauickait Amos S. Lawless Jennifer A. Scott Peter Jan van Leeuwen 《Numerical Linear Algebra with Applications》2020,27(5)
We consider the large sparse symmetric linear systems of equations that arise in the solution of weak constraint four‐dimensional variational data assimilation, a method of high interest for numerical weather prediction. These systems can be written as saddle point systems with a 3 × 3 block structure but block eliminations can be performed to reduce them to saddle point systems with a 2 × 2 block structure, or further to symmetric positive definite systems. In this article, we analyse how sensitive the spectra of these matrices are to the number of observations of the underlying dynamical system. We also obtain bounds on the eigenvalues of the matrices. Numerical experiments are used to confirm the theoretical analysis and bounds. 相似文献
5.
Homo-apioneplanocin A was efficiently synthesized via stereoselective hydroxymethylation, regio- and chemoselective hydroboration, and chemoselective oxidation as key steps from d-ribose. 相似文献
6.
7.
Christos Kravvaritis Marilena Mitrouli Jennifer Seberry 《Linear and Multilinear Algebra》2007,55(5):471-490
In the present article we concentrate our study on the growth problem for the weighing matrix W(12,11) and show that the unique W(12,11) has three pivot structures. An improved algorithm for extending a k × k (0,+,-) matrix to a W(n,n-1), if possible, has been developed to simplify the proof. For the implementation of the algorithm special emphasis is given to the notions of data structures and parallel processing. 相似文献
8.
Sang Hyun Kwon Yoshio Okamoto Chiyo Yamamoto Wonjo Cheong Myeonghee Moon Jung Hag Park 《Analytical sciences》2006,22(12):1525-1529
Porous zirconia particles are very robust material and have received considerable attention as a stationary phase support for HPLC. We prepared cellulose dimethylphenylcarbamate-bonded carbon-clad zirconia (CDMPCCZ) as a chiral stationary phase (CSP) for separation of enantiomers of a set of 14 racemic compounds in normal phase (NP) and reversed-phase (RP) liquid chromatography. Retention and enantioselectivity on CDMPCCZ were compared to those on CDMPC-coated zirconia (CDMPCZ) to see how the change in immobilization method of the chiral selector affects the retention and chiral selectivity. In NPLC, retention was longer and the number of resolved racemates was smaller on CDMPCCZ than on CDMPCZ. However, chiral selectivity factors for some resolved racemates were better on CDMPCCZ than on CDMPCZ. The longer retention on CDMPCCZ is likely due to strong, non-chiral discriminating interactions with the carbon layer on CDMPCZ. In RPLC only two racemates were resolved on CDMPCCZ, but retention times were shorter than, and resolutions were comparable to, those in NPLC, indicating a potential for improving chromatographic performance of the CDMPCCZ column in RPLC with optimized column preparation and separation conditions. 相似文献
9.
10.