全文获取类型
收费全文 | 2574篇 |
免费 | 224篇 |
出版年
2023年 | 7篇 |
2022年 | 21篇 |
2021年 | 43篇 |
2020年 | 27篇 |
2019年 | 33篇 |
2018年 | 37篇 |
2017年 | 32篇 |
2016年 | 79篇 |
2015年 | 110篇 |
2014年 | 146篇 |
2013年 | 176篇 |
2012年 | 217篇 |
2011年 | 208篇 |
2010年 | 150篇 |
2009年 | 106篇 |
2008年 | 183篇 |
2007年 | 150篇 |
2006年 | 155篇 |
2005年 | 138篇 |
2004年 | 110篇 |
2003年 | 102篇 |
2002年 | 104篇 |
2001年 | 29篇 |
2000年 | 31篇 |
1999年 | 29篇 |
1998年 | 33篇 |
1997年 | 28篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 20篇 |
1991年 | 22篇 |
1990年 | 17篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1977年 | 6篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 7篇 |
排序方式: 共有2798条查询结果,搜索用时 31 毫秒
1.
H Vaer?y F Nyberg H Franzén L Terenius 《Biochemical and biophysical research communications》1987,148(1):24-30
Enzyme activity capable of converting the glycine-extended substance P precursor, substance P-Gly12, into substance P was purified from human cerebrospinal fluid. The conversion reaction was monitored by radioimmunoassay measurement of substance P formation. The chemical identity of the product was verified by reversed-phase HPLC. The enzyme reaction was stimulated by Cu(II) ion and ascorbic acid and inhibited by the presence of diethyldithiocarbamate. By HPLC molecular sieving, the major enzyme activity appeared as a protein of 26,000 molecular weight. 相似文献
2.
J. Dierschke T. Krüger F. Hüttmann F. Bairlein Kerstin Müller G. Scheiffarth H. -W. Helb W. Irsch W. Lantermann B. Haubitz W. Winkel und J. Haffer 《Journal of Ornithology》2003,144(4):484-498
Ohne Zusammenfassung 相似文献
3.
Anna Nilsson Thomas E. Fehniger Lena Gustavsson Malin Andersson Kerstin Kenne Gy?rgy Marko-Varga Per E. Andrén 《PloS one》2010,5(7)
Readouts that define the physiological distributions of drugs in tissues are an unmet challenge and at best imprecise, but are needed in order to understand both the pharmacokinetic and pharmacodynamic properties associated with efficacy. Here we demonstrate that it is feasible to follow the in vivo transport of unlabeled drugs within specific organ and tissue compartments on a platform that applies MALDI imaging mass spectrometry to tissue sections characterized with high definition histology. We have tracked and quantified the distribution of an inhaled reference compound, tiotropium, within the lungs of dosed rats, using systematic point by point MS and MS/MS sampling at 200 µm intervals. By comparing drug ion distribution patterns in adjacent tissue sections, we observed that within 15 min following exposure, tiotropium parent MS ions (mass-to-charge; m/z 392.1) and fragmented daughter MS/MS ions (m/z 170.1 and 152.1) were dispersed in a concentration gradient (80 fmol-5 pmol) away from the central airways into the lung parenchyma and pleura. These drug levels agreed well with amounts detected in lung compartments by chemical extraction. Moreover, the simultaneous global definition of molecular ion signatures localized within 2-D tissue space provides accurate assignment of ion identities within histological landmarks, providing context to dynamic biological processes occurring at sites of drug presence. Our results highlight an important emerging technology allowing specific high resolution identification of unlabeled drugs at sites of in vivo uptake and retention. 相似文献
4.
5.
Lars Svennerholm Pam Fredman Birgitta Jungbjer Jan-Eric Månsson Britt-Marie Rynmark Kerstin Boström Bengt Hagberg Lars Norén Pirkko Santavuori 《Journal of neurochemistry》1987,49(6):1772-1783
Lipid composition was studied on cerebral tissue from nine children who had died of a progressive encephalopathy called the infantile form of neuronal ceroid lipofuscinosis (INCL) or polyunsaturated fatty acid lipidosis (PFAL). In the terminal stage of the disease, the concentrations of all lipid classes were found to be significantly reduced in the cerebral and cerebellar cortex and white matter. The concentration of gangliosides of the cerebral cortex was 15% and that of cerebrosides (galactosylceramide) in white matter 0.2-5% of the normal values for the children's ages. The reduction of gangliosides mainly affected those of the gangliotetraose series, particularly GD1a. The fatty acids of the linolenic acid series were strongly reduced in ethanolamine and serine phosphoglycerides. A very large increase up to 100-fold of oligoglycosphingolipids of the globo series and two fucose-containing lipids of the neolacto series was found in the forebrain of the three advanced cases examined. The brain tissue also contained very high concentrations of mono-, di-, and trisialogangliosides of the lacto and neolacto series, gangliosides with type 1 chain dominating. The structures of the gangliosides were tentatively identified by gas chromatography-mass spectrometry and monoclonal antibodies with carefully determined epitope specificity. The gangliosides and neutral glycosphingolipids had very similar fatty acid composition, consisting of about 40% stearic acid and 40% C24-acids. 相似文献
6.
Summary The lipid and sterol content and composition of three lipid fractions (free fatty acids/ sterols, triacylglycerols and sterol/triterpenoid esters) extracted from three stem discs of Pinus sylvestris were assessed to investigate metabolic changes related to heartwood formation. The wood was separated into (1) cambial zone, (2) outer sapwood, (3) inner sapwood, (4) transition zone, (5) outer heartwood and 6) inner heart-wood. The fractions were separated by thin-layer chromatography (TLC) and analysed by gas-liquid chromatography (GLC). The amount of fatty acids of sapwood triacylglycerols was about 1.5% (dry wt.) but a large reduction occurred in the transition zone. In contrast, noticeable amounts of free fatty acids were present only in the heart-wood. The most important fatty acids in the sapwood fractions were 16:0, 18:0, 18:1, 18:2 (the dominant fatty acid in all fractions), 18:3 and 20:3. Together 18:1 and 18:2 formed about 70% of the total triacylglycerol fatty acids. Of the sterol/ triterpenoid esters, 18:2 and 18:3 were predominant. The fatty acid composition of all fractions changed in the transition zone. The sterols found were sitosterol, stigmastanol, campesterol and campestanol. The amount of sterol esters increased towards the heartwood, and the amount of free sterols was lowest in the inner sapwood. Sitosterol was the dominant sterol in both free sterols and sterol esters. 相似文献
7.
8.
The energetics of complementary packing of nonpolar side chains in the hydrophobic core of a protein were analyzed by protein engineering experiments. We have made the mutations Ile----Val, Ile----Ala, and Leu----Ala in a region of the small bacterial ribonuclease barnase where the major alpha-helix packs onto the central beta-sheet. The destabilization resulting from the creation of cavities was determined by measuring the decrease in free energy of folding from reversible denaturation induced by urea, guanidinium chloride, or heat. The different methods give consistent and reproducible results. The loss in free energy of folding for the mutant proteins is 1.0-1.6 kcal/mol per methylene group removed. This exceeds by severalfold the values obtained from model experiments of the partitioning of relevant side chains between aqueous and nonpolar solvents. Much of this discrepancy arises because two surfaces are buried when a protein folds--both the amino acid side chain in question and the portions of the protein into which it packs. These experiments directly demonstrate that the interior packing of a protein is crucial in stabilizing its three-dimensional structure: the conversion of leucine or isoleucine to alanine in the hydrophobic core loses half the net free energy of folding of barnase with a concomitant decrease in yield of the expressed recombinant protein. 相似文献
9.
Replication of bovine papillomavirus vectors in murine cells 总被引:2,自引:0,他引:2
Margareta Waldenstrm Kerstin Schenstrm Kerstin Sollerbrant Lennart Hansson 《Gene》1992,120(2):175-181
10.
A dynorphin B converting enzyme previously purified from bovine spinal cord was subjected to column electrophoresis in agarose suspension. By this technique combined with HPLC gel filtration it was possible to resolve and recover several isoforms of the proteinase. All these isoenzymes were associated with a similar molecular size but apparently they differed with regard to their net charges. No significant difference between their inhibitory profiles or their Km values for the release of Leu-enkephalin-Arg6 from dynorphin B was observed. 相似文献