全文获取类型
收费全文 | 432篇 |
免费 | 14篇 |
专业分类
化学 | 347篇 |
晶体学 | 7篇 |
力学 | 2篇 |
数学 | 29篇 |
物理学 | 61篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 14篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 14篇 |
2014年 | 14篇 |
2013年 | 18篇 |
2012年 | 31篇 |
2011年 | 28篇 |
2010年 | 10篇 |
2009年 | 11篇 |
2008年 | 27篇 |
2007年 | 11篇 |
2006年 | 20篇 |
2005年 | 20篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 18篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 11篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1963年 | 2篇 |
1962年 | 4篇 |
1960年 | 2篇 |
1956年 | 2篇 |
1955年 | 2篇 |
1952年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有446条查询结果,搜索用时 15 毫秒
71.
Kirsten Knape Anton Beyer Anna Stary Gerhard Buchbauer Peter Wolschann 《Monatshefte für Chemie / Chemical Monthly》2008,454(5):1537-1544
Single nucleotide polymorphisms (SNPs) in odorant receptor genes may influence the protein sequence and consequently also
the function of the receptors. An analysis of the HapMap data for human OR3A1 was performed and provided evidence that genetic
differences subject to ancestry and gender can be recognized. A genomic comparison of individuals shows the diversity of odorant
receptor genes and therefore potentially the variety of the sense of smell. At this time, two complete human genomes are available
in public domain, which we used for this purpose. 相似文献
72.
73.
Robinson NE Zabrouskov V Zhang J Lampi KJ Robinson AB 《Rapid communications in mass spectrometry : RCM》2006,20(23):3535-3541
After synthesis and folding, proteins undergo many post-synthetic modifications, including cleavage, oxidation, glycosylation, methylation, racemization, phosphorylation, and deamidation. Of these modifications, non-enymatic deamidation is the most prevalent. Each asparaginyl and glutaminyl residue in a protein is a miniature molecular clock that deamidates with a genetically determined half-time. These half-times vary from a few hours to more than a century, depending on a primary, secondary, tertiary, and quaternary structure near the amide residue. It has been suggested that these clocks regulate many biological processes. A few such processes have been discovered. These discoveries have been difficult because deamidation is inconvenient to measure. While most post-synthetic changes are easily measured by mass spectrometry, deamidation increases molecular mass by only one nominal Dalton, so the deamidated isotopic envelope overlaps the undeamidated isotopic envelope. While peptide deamidation rate determination through deconvolution of these envelopes has been accomplished for several hundred peptides, deconvolution becomes more difficult as the molecular weight increases. In high-resolution mass spectrometers, this deconvolution is possible for larger molecules and an alternative method based on the 19 mDa mass defect between the deamidated envelope and the isotopic envelope of protein fragments can also be utilized. We herein report a comparison of the envelope deconvolution and the mass defect methods for measurement of deamidation in human eye lens crystallins, with special emphasis on betaB2 crystallin and gammaS crystallin. Measurement of extent of deamidation of betaB2 crystallin in a 7 Tesla ion cyclotron resonance Fourier transform mass spectrometer is found to be accurate to a relative standard deviation in a single measurement of about 4% for each method. The envelope deconvolution method is further illustrated by detection of deamidation in intact gammaS crystallin, a 20 904 Da protein, and discovery of the principal gammaS deamidation site. 相似文献
74.
Harvey P Chalmers KH De Luca E Mishra A Parker D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(28):8748-8757
Paramagnetic magnetic resonance chemical shift probes containing a proximal CF(3) group have been characterised. Different systems have been created that report reversible changes in calcium ion concentrations in the millimolar regime, signal the presence of citrate selectively in competitive aqueous media and allow the monitoring of remote ester/amide hydrolysis in relayed, irreversible transformations. Chemical shift non-equivalence is amplified by the presence of the proximate lanthanide ion, with a mean separation between the CF(3) group and the metal ion of 6.4 ? found for a thulium complex, in an X-ray structure of the metal complex aqua adduct. The enhanced rate of longitudinal relaxation of the (19)F nucleus allows faster data acquisition. 相似文献
75.
76.
Taft F Harmrolfs K Nickeleit I Heutling A Kiene M Malek N Sasse F Kirschning A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(3):880-886
Access of four new tumor specific folic acid/ansamitocin conjugates is reported that relies on a synthetic strategy based on the combination of mutasynthesis and semisynthesis. Two bromo‐ansamitocin derivatives were prepared by mutasynthesis or by a modified fermentation protocol, respectively, that served as starting point for the semisynthetic introduction of an allyl amine linker under Stille conditions. A sequence of standard coupling steps introduced the pteroic acid/glutamic acid/cysteine unit to the modified ansamitocins. All new derivatives, including those that are expected to be generated after internalization of the folic acid/ansamitocin conjugates into the cancer cell and reductive cleavage of the disulfide linkage showed good to strong antiproliferative activity (IC50 <10 nM ) for different cancer cell lines. Finally, the four conjugates were exposed to two cancer cell lines [cervix carcinoma, KB‐3‐1 (FR+) and lung carcinoma, A‐459 (FR?)], the latter devoid of the membrane‐bound folic acid receptor (FR?). All four conjugates showed strong antiproliferative activity for the FR+ cancer cell line but were inactive against the FR? cell line. The synthetic strategy pursued is based on the combination of mutasynthesis and semisynthesis and proved to be powerful for accessing new ansamitocin derivatives that are difficult to prepare by total synthesis. 相似文献
77.
CAS SCF and CCI calculations have been performed in order to establish the existence or non-existence of the HO3 radical. The potential surface for the dissociation reaction, HO3 → O2(3Σ) + OH, along one chosen coordinate has been calculated. The calculations show that although the wavefunctions describing the short-distance and long-distance states are of different character, the energies are the same and the curve connecting the states is very flat. There is probably no barrier towards dissociation of the radical. However, the existence of HO3 can still not be excluded. 相似文献
78.
79.
Let P be an operator of Dirac type and let D=P
2 be the associated operator of Laplace type. We impose spectral boundary conditions and study the leading heat content coefficients for D. 相似文献
80.