全文获取类型
收费全文 | 646篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
化学 | 488篇 |
晶体学 | 7篇 |
力学 | 9篇 |
数学 | 78篇 |
物理学 | 80篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 12篇 |
2020年 | 8篇 |
2019年 | 5篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 18篇 |
2013年 | 25篇 |
2012年 | 25篇 |
2011年 | 44篇 |
2010年 | 30篇 |
2009年 | 23篇 |
2008年 | 18篇 |
2007年 | 31篇 |
2006年 | 34篇 |
2005年 | 28篇 |
2004年 | 39篇 |
2003年 | 29篇 |
2002年 | 26篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1972年 | 3篇 |
1969年 | 4篇 |
排序方式: 共有662条查询结果,搜索用时 15 毫秒
71.
Livraghi S Corazzari I Paganini MC Ceccone G Giamello E Fubini B Fenoglio I 《Chemical communications (Cambridge, England)》2010,46(44):8478-8480
A safe UV filter may be obtained by inhibiting the photo-generation of free radicals through modification of the surface of TiO(2) nanoparticles with carbon. 相似文献
72.
73.
74.
The cerebral involvement of a 13-yr-old boy with Wilson's disease was serially evaluated during the first 18 mo of D-penicillamine treatment. An ultra-low-field magnetic resonance imaging (ULF MRI) system, operating at 0.02 T, with computerized image processing was used. The half-yr period prior to the clinical diagnosis was set, the patient had showed poor school performance, emotional lability, deteriorating handwriting, progressively slow, gross, and fine motor functions, and a fixed rigid smile. No overt signs of liver disease were found. With D-penicillamine treatment (1–1.5 g/d) a continuous improvement was seen. The pretreatment MRI investigation showed pronounced pathological transformation in the basal ganglia. However, changes were seen also in most other parts of the brain indicating diffuse involvement. During treatment the computerized MR images became gradually more normal. The current magnetic resonance imaging system with computerized image processing is a sensitive and simple method for evaluation of subtle parenchymal changes of the brain. 相似文献
75.
Carlos Camacho‐Camacho Monique Biesemans Ingrid Verbruggen Rudolph Willem 《应用有机金属化学》2005,19(3):343-346
The reactivity and catalytic potential of the tin salicylaldoximate cluster [(Me2Sn)2(Me2SnO)(OCH3) (HONZO)(ONZO)] ( 1 ), with HONZOH = o‐HON?CH? C6H4OH, on the acylation reaction of various alcohols with ethyl acetate is reported. The catalyst is active toward primary and unhindered secondary alcohols, but inefficient toward tertiary and secondary bulky alcohols and phenols. A possible mechanism for the transesterification reaction catalyzed by 1 , accounting for the influence of steric factors, is proposed. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
76.
77.
Helicobacter species have been isolated and cultured from both the gastric and enterohepatic niches of the gastrointestinal tract and
are associated with a wide spectrum of diseases. Some members of the enterohepatic Helicobacter species (EHS), which include Helicobacter bilis, Helicobacter hepaticus and Helicobacter pullorum, are associated with chronic inflammatory and proliferative bowel inflammation, hepatitis and in experimental murine studies
with hepatic cancer. The present study aimed to explore if polysulphated polysaccharides can prevent adhesion of EHS to the
murine macrophage cell line J774A.1. A competitive binding assay showed that heparin and heparan sulphate at a concentration
of 1.25 mg/ml reduced binding of H. hepaticus and H. pullorum to the host cells, but not H. bilis. Of the tested Helicobacter spp, the highest inhibition by heparin was demonstrated for H. pullorum (P < 0.01), the most hydrophilic strain. Partially or completely de-sulphated heparin derivatives lost the ability to inhibit
adherence of EHS, indicating the importance of sulphated groups of heparin. The most efficient inhibitor of EHS binding to
macrophages was fucoidan, which reduced bacterial adhesion of the three enterohepatic Helicobacter species to a greater extent than heparin, 60–90% inhibition vs 30–70% inhibition by heparin. Identification of receptors
that EHS ligands bind to is important for understanding the development of infection and may provide a rational target to
prevent infection and therapy. 相似文献
78.
Zou Y Wang D Wurst K Kühnel C Reinhardt I Decker U Gurram V Camadanli S Buchmeiser MR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(49):13832-13846
Two novel Zr(IV)- and Hf(IV)-based bisamido complexes bearing the 6-[2-(diethylboryl)phenyl]pyrid-2-yl motif, that is, [ZrCl(2){Me(2)Si(DbppN)(2)}(thf)] (9) and [HfCl(2){Me(2)Si(DbppN)(2)}(thf)(2)] (10) (DbppN=6-[2-(diethylboryl)phenyl]pyridine-2-amido) have been prepared. Their reactivities have been compared with that of a model precatalyst that does not bear the aminoborane motif. Upon activation with methylalumoxane, precatalysts 9 and 10 are active in the homopolymerization of ethylene (E) yielding high-density polyethylene (HDPE). In the copolymerization of E with cyclopentene (CPE), for example by the action of 9, the presence of CPE resulted in a dramatic increase in the polymerization activity of E, while CPE incorporation remained close to or at zero. In the vinyl-insertion copolymerization of norborn-2-ene (NBE) with E by the action of 9, statistical cyclic olefin copolymers of these two monomers were obtained. At higher NBE concentrations, however, 9 gave rise to reversible ring-opening metathesis (ROMP)/vinyl-insertion polymerization (VIP) of NBE with E, resulting in the formation of multi-block copolymers of the general formula poly(NBE)(ROMP)-co-poly(NBE)(VIP)-co-poly(E). This particular feature of precatalyst 9, that is, the ability to induce a reversible α-H elimination/α-H addition reaction, is attributed to the unique role of the 6-[2-(diethylboryl)phenyl]pyrid-2-yl ligand. Accordingly, a model precatalyst lacking this ligand does not have the ability to induce α-H elimination/α-H addition reactions. The different (11)B NMR shifts of various diethylborylphenylpyrid-2-ylamines and -amides permit a ranking of the strengths of the B-N bonds in these compounds. This strength of the B-N bond is correlated with the propensity of 9/MAO to produce poly(NBE)(ROMP)-co-poly(NBE)(VIP)-co-poly(E) at different temperatures. 相似文献
79.
Tietze LF Schmuck K Schuster HJ Müller M Schuberth I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(6):1922-1929
Chemotherapy of malign tumors is usually associated with serious side effects as common anticancer drugs lack selectivity. An approach to deal with this problem is the antibody-directed enzyme prodrug therapy (ADEPT) and the prodrug monotherapy (PMT). Herein, the synthesis and biological evaluation of new glycosidic prodrugs suitable for both concepts are described. All prodrugs but one are stable in human serum and show QIC(50) values (IC(50) of prodrug/IC(50) of prodrug in the presence of the appropriate glycohydrolase) of up to 6500. This is the best value found so far for compounds interacting with DNA. 相似文献
80.