全文获取类型
收费全文 | 15947篇 |
免费 | 2223篇 |
国内免费 | 2065篇 |
专业分类
化学 | 8904篇 |
晶体学 | 91篇 |
力学 | 687篇 |
综合类 | 97篇 |
数学 | 1319篇 |
物理学 | 4082篇 |
无线电 | 5055篇 |
出版年
2024年 | 65篇 |
2023年 | 393篇 |
2022年 | 465篇 |
2021年 | 658篇 |
2020年 | 610篇 |
2019年 | 590篇 |
2018年 | 483篇 |
2017年 | 474篇 |
2016年 | 651篇 |
2015年 | 696篇 |
2014年 | 830篇 |
2013年 | 1108篇 |
2012年 | 1301篇 |
2011年 | 1312篇 |
2010年 | 1007篇 |
2009年 | 927篇 |
2008年 | 1037篇 |
2007年 | 919篇 |
2006年 | 893篇 |
2005年 | 765篇 |
2004年 | 520篇 |
2003年 | 516篇 |
2002年 | 485篇 |
2001年 | 496篇 |
2000年 | 395篇 |
1999年 | 378篇 |
1998年 | 296篇 |
1997年 | 237篇 |
1996年 | 232篇 |
1995年 | 241篇 |
1994年 | 176篇 |
1993年 | 145篇 |
1992年 | 149篇 |
1991年 | 138篇 |
1990年 | 127篇 |
1989年 | 90篇 |
1988年 | 63篇 |
1987年 | 49篇 |
1986年 | 40篇 |
1985年 | 34篇 |
1984年 | 26篇 |
1983年 | 34篇 |
1982年 | 27篇 |
1981年 | 17篇 |
1979年 | 25篇 |
1978年 | 22篇 |
1977年 | 15篇 |
1976年 | 10篇 |
1975年 | 14篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Stopped-flow was used to evaluate the methylation and reduction kinetics of the isolated alpha subunit of acetyl-Coenzyme A synthase from Moorella thermoacetica. This catalytically active subunit contains a novel Ni-X-Fe4S4 cluster and a putative unidentified n = 2 redox site called D. The D-site must be reduced for a methyl group to transfer from a corrinoid-iron-sulfur protein, a key step in the catalytic synthesis of acetyl-CoA. The Fe4S4 component of this cluster is also redox active, raising the possibility that it is the D-site or a portion thereof. Results presented demonstrate that the D-site reduces far faster than the Fe4S4 component, effectively eliminating this possibility. Rather, this component may alter catalytically important properties of the Ni center. The D-site is reduced through a pathway that probably does not involve the Fe4S4 component of this active-site cluster. 相似文献
32.
The photoelectron branching ratios and the partial oscillator strengths (cross sections) for photoionisation of the valence orbitals of N2O and CO2 have been obtained in the energy range 20–60 eV using the magic angle dipole (e, 2e) method. In addition to single electron ionization processes there is a large contribution from multiple electron transitions at higher energies in agreement with recent theoretical predictions. The photoionization efficiency and the dipole oscillator strenght for total photoabsorption have also been measured. 相似文献
33.
Zi-Zhong Li Qing-Xiang Guo Tan Ren Xiao-Qing Zhu You-Cheng Liu 《Journal of inclusion phenomena and macrocyclic chemistry》1993,15(1):37-42
Tetramethylsilane (TMS) can be included by -cyclodextrin (-CD), and sodium 2,2-dimethylsilapentane-5-sulphonate (DSS) can form inclusion complexes with - and -CD. The NMR chemical shifts are changed considerably as a result of the strong interaction between CD and the guest compound in the inclusion complexes. A downfield shift of as much as 0.63 ppm shift downfield has been observed for the protons of external TMS in CD aqueous solution. In view of this, the question arises of whether TMS and DSS can be used as internal references. DSS in D2O is suggested as an external reference for aqueous cyclodextrin solution in NMR measurements. 相似文献
34.
A new series of MR-IPN polyacrylamide—poly(vinyl-ethylenediamine)chelatesorbents were prepared by the reaction of ethylenediamine with MR-IPN matrixes.The newchelate sorbent showed good sorption properties for auric and platinic ions. 相似文献
35.
A previous method for the determination of penicillins by direct titration with potassium iodate under strongly acidic conditions has been extended to the assay of some selected cephalosporins. Results are presented, including error and precision analyses, for the determination of cephaloridine, cephalothin and cephalexin. The appropriate stoichiometries are 1 mol cephalosporin to 3 mol iodate for cephalothin and cephaloridine; 1 mol to 2 mol iodate for cephalexin. An irreversible aqueous end-point technique has been compared with the chloroform layer method; the latter gives more precise results for the determination of cephaloridine and cephalothin (0.8% and 1.3% r.s.d. respectively). Comparable precision was obtained by either technique for the determination of cephalexin (1.39% r.s.d.). 相似文献
36.
37.
Zhen-Lin Qiu Dandan Chen Zeying Deng Ke-Shan Chu Yuan-Zhi Tan Jun Zhu 《中国科学:化学(英文版)》2021,(6):1004-1008
Carbon nanohoop,a class of constrained molecular architecture consisting of linked arene units,has attracted considerable interest from both experimental and th... 相似文献
38.
In this paper, the authors study the global regularity of the 3D magnetohydrodynamics system in terms of one velocity component. In particular, they establish a new
Prodi-Serrin type regularity criterion in the framework of weak Lebesgue spaces both in
time and space variables. 相似文献
39.
40.