全文获取类型
收费全文 | 3741篇 |
免费 | 293篇 |
国内免费 | 6篇 |
专业分类
化学 | 2880篇 |
晶体学 | 9篇 |
力学 | 303篇 |
数学 | 472篇 |
物理学 | 376篇 |
出版年
2021年 | 33篇 |
2020年 | 58篇 |
2019年 | 58篇 |
2018年 | 34篇 |
2017年 | 35篇 |
2016年 | 109篇 |
2015年 | 150篇 |
2014年 | 189篇 |
2013年 | 283篇 |
2012年 | 231篇 |
2011年 | 195篇 |
2010年 | 231篇 |
2009年 | 207篇 |
2008年 | 166篇 |
2007年 | 169篇 |
2006年 | 128篇 |
2005年 | 131篇 |
2004年 | 114篇 |
2003年 | 86篇 |
2002年 | 93篇 |
2001年 | 47篇 |
2000年 | 47篇 |
1999年 | 36篇 |
1998年 | 48篇 |
1997年 | 38篇 |
1996年 | 38篇 |
1995年 | 56篇 |
1994年 | 53篇 |
1993年 | 106篇 |
1992年 | 36篇 |
1991年 | 40篇 |
1990年 | 24篇 |
1989年 | 27篇 |
1988年 | 25篇 |
1987年 | 25篇 |
1985年 | 37篇 |
1984年 | 36篇 |
1983年 | 24篇 |
1982年 | 22篇 |
1981年 | 29篇 |
1980年 | 33篇 |
1979年 | 26篇 |
1977年 | 29篇 |
1976年 | 27篇 |
1975年 | 25篇 |
1974年 | 32篇 |
1973年 | 30篇 |
1972年 | 23篇 |
1970年 | 57篇 |
1969年 | 34篇 |
排序方式: 共有4040条查询结果,搜索用时 0 毫秒
101.
A stereocontrolled route to the deschloro cyclopentyl core of the palau'amines and styloguanidines has been developed. This strategy makes use of the intramolecular Pauson-Khand cyclization of an enyne with a "transient N-O tether" to construct a five-membered carbocycle in a diastereoselective fashion. [reaction: see text] 相似文献
102.
Dr. David Wifling Dr. Christopher Pfleger Jonas Kaindl Passainte Ibrahim Dr. Ralf C. Kling Prof. Dr. Armin Buschauer Prof. Dr. Holger Gohlke Prof. Dr. Timothy Clark 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(64):14613-14624
Histamine H4 receptor (H4R) orthologues are G-protein-coupled receptors (GPCRs) that exhibit species-dependent basal activity. In contrast to the basally inactive mouse H4R (mH4R), human H4R (hH4R) shows a high degree of basal activity. We have performed long-timescale molecular dynamics simulations and rigidity analyses on wild-type hH4R, the experimentally characterized hH4R variants S179M, F169V, F169V+S179M, F168A, and on mH4R to investigate the molecular nature of the differential basal activity. H4R variant-dependent differences between essential motifs of GPCR activation and structural stabilities correlate with experimentally determined basal activities and provide a molecular explanation for the differences in basal activation. Strikingly, during the MD simulations, F16945.55 dips into the orthosteric binding pocket only in the case of hH4R, thus adopting the role of an agonist and contributing to the stabilization of the active state. The results shed new light on the molecular mechanism of basal H4R activation that are of importance for other GPCRs. 相似文献
103.
Dr. Jakob-Jonathan Maudrich Max Widemann Fatima Diab Ralf H. Kern Dr. Peter Sirsch Dr. Christian P. Sindlinger Dr. Hartmut Schubert Prof. Dr. Lars Wesemann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(70):16081-16087
Organodihydridoelement anions of germanium and tin were reacted with metallocene dichlorides of Group 4 metals Ti, Zr and Hf. The germate anion [Ar*GeH2]− reacts with hafnocene dichloride under formation of the substitution product [Cp2Hf(GeH2Ar*)2]. Reaction of the organodihydridostannate with metallocene dichlorides affords the reduction products [Cp2M(SnHAr*)2] (M=Ti, Zr, Hf). Abstraction of a hydride substituent from the titanium bis(hydridoorganostannylene) complex results in formation of cation [Cp2M(SnAr*)(SnHAr*)]+ exhibiting a short Ti–Sn interaction. (Ar*=2,6-Trip2C6H3, Trip=2,4,6-triisopropylphenyl). 相似文献
104.
Jiawang Liu Ji Yang Francesco Ferretti Ralf Jackstell Matthias Beller 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(14):4738-4742
The first catalyst for the alkoxycarbonylation of gem‐difluoroalkenes is described. This novel catalytic transformation proceeds in the presence of Pd(acac)2/1,2‐bis((di‐tert‐butylphosphan‐yl)methyl)benzene (btbpx) ( L4 ) and allows for an efficient and straightforward access to a range of difluoromethylated esters in high yields and regioselectivities. The synthetic utility of the protocol is showcased in the practical synthesis of a Cyclandelate analogue using this methodology as the key step. 相似文献
105.
106.
107.
Glycation (or non-enzymatic glycosylation) is a common non-enzymatic covalent modification of human proteins. Glucose, the highest concentrated monosaccharide in blood, can reversibly react with amino groups of proteins to form Schiff bases that can rearrange to form relatively stable Amadori products. These can be further oxidized to advanced glycation end products (AGEs). Here, we analyzed the glycation patterns of human serum albumin (HSA) in plasma samples obtained from five patients with type 2 diabetes mellitus. Therefore, glycated peptides from a tryptic digest of plasma were enriched with m-aminophenylboronic acid (mAPBA) affinity chromatography. The glycated peptides were then further separated in the second dimension by RP-HPLC coupled on-line to an electrospray ionization (ESI) tandem mass spectrometer (MS/MS). Altogether, 18 Amadori peptides, encompassing 40% of the HSA sequence, were identified. The majority of the peptides were detected and relatively quantified in all five samples with a high reproducibility among the replicas. Eleven Lys-residues were glycated at similar quantities in all samples, with glycation site Lys549 (KAm(Glc)QTALVELVK) being the most abundant. In conclusion, the established mAPBA/nanoRP-HPLC-ESI-MS/MS approach could reproducibly identify and quantify glycation sites in plasma samples, potentially useful in diagnosis and therapeutic control. 相似文献
108.
109.
Zapf A Jackstell R Rataboul F Riermeier T Monsees A Fuhrmann C Shaikh N Dingerdissen U Beller M 《Chemical communications (Cambridge, England)》2004,(1):38-39
A practical synthesis of a novel class of phosphine ligands, phosphino substituted N-aryl pyrroles (PAP ligands), has been developed. These ligands are applied in the palladium-catalyzed coupling of a variety of aryl and heteroaryl chlorides with phenylboronic acid showing exceedingly high turnover numbers at mild reaction temperatures and even at room temperature. 相似文献