全文获取类型
收费全文 | 1439051篇 |
免费 | 135270篇 |
国内免费 | 1662篇 |
专业分类
1575983篇 |
出版年
2021年 | 18031篇 |
2019年 | 18059篇 |
2018年 | 20077篇 |
2017年 | 18895篇 |
2016年 | 30256篇 |
2015年 | 44253篇 |
2014年 | 52120篇 |
2013年 | 78480篇 |
2012年 | 39131篇 |
2011年 | 28355篇 |
2010年 | 45938篇 |
2009年 | 46594篇 |
2008年 | 26356篇 |
2007年 | 24329篇 |
2006年 | 29010篇 |
2005年 | 30559篇 |
2004年 | 29361篇 |
2003年 | 27088篇 |
2002年 | 25041篇 |
2001年 | 37359篇 |
2000年 | 34896篇 |
1999年 | 34041篇 |
1998年 | 25800篇 |
1997年 | 25604篇 |
1996年 | 25137篇 |
1995年 | 23244篇 |
1994年 | 23039篇 |
1993年 | 22178篇 |
1992年 | 29628篇 |
1991年 | 28015篇 |
1990年 | 26860篇 |
1989年 | 27578篇 |
1988年 | 25442篇 |
1987年 | 24405篇 |
1986年 | 22920篇 |
1985年 | 24977篇 |
1984年 | 24196篇 |
1983年 | 21470篇 |
1982年 | 21281篇 |
1981年 | 20538篇 |
1980年 | 19198篇 |
1979年 | 20637篇 |
1978年 | 19091篇 |
1977年 | 18226篇 |
1976年 | 17551篇 |
1975年 | 17321篇 |
1974年 | 18079篇 |
1973年 | 18354篇 |
1972年 | 15683篇 |
1971年 | 14388篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
761.
762.
Paul D. Bonnitcha Simon R. Bayly Mark B.M. Theobald Helen M. Betts Jason S. Lewis Jonathan R. Dilworth 《Journal of inorganic biochemistry》2010,104(2):126-9888
Combination agents comprising two different pharmacophores with the same biological target have the potential to show additive or synergistic activity. Bis(thiosemicarbazonato)copper(II) complexes (e.g. 64Cu-ATSM) and nitroimidazoles (e.g. 18F-MISO) are classes of tracer used for the delineation of tumor hypoxia by positron emission tomography (PET). Three nitroimidazole-bis(thiosemicarbazonato)copper(II) conjugates were produced in order to investigate their potential as combination hypoxia imaging agents. Two were derived from the known bifunctional bis(thiosemicarbazone) H2ATSM/A and the third from the new precursor diacetyl-2-(4-N-methyl-3-thiosemicarbazone)-3-(4-N-ethylamino-3-thiosemicarbazone) - H2ATSM/en. Oxygen-dependent uptake studies were performed using the 64Cu radiolabelled complexes in EMT6 carcinoma cells. All the complexes displayed appreciable hypoxia selectivity, with the nitroimidazole conjugates displaying greater selectivity than a simple propyl derivative used as a control. Participation of the nitroimidazole group in the trapping mechanism is indicated by the increased hypoxic uptake of the 2- vs. the 4-substituted 64Cu-ATSM/A derivatives. The 2-nitroimidazole derivative of 64Cu-ATSM/en demonstrated superior hypoxia selectivity to 64Cu-ATSM over the range of oxygen concentrations tested. Biodistribution of the radiolabelled 2-nitroimidazole conjugates was carried out in EMT6 tumor-bearing mice. The complexes showed significantly different uptake trends in comparison to each other and previously studied Cu-ATSM derivatives. Uptake of the Cu-ATSM/en conjugate in non-target organs was considerably lower than for derivatives based on Cu-ATSM/A. 相似文献
763.
Marc Mercken Ursula Lübke Marc Vandermeeren Jan Gheuens A. Beate Oestreicher 《Developmental neurobiology》1992,23(3):309-321
The growth-associated protein B-50 also termed GAP-43, F1, pp46, P-57 and neuromodulin is a nervous tissuespecific protein kinase C (PKC) substrate that is considered to play a major role in neurite formation, regeneration, and neuroplasticity. We describe the isolation of seven mouse monoclonal antibodies (Mabs) directed against B-50. The Mabs are produced against the bovine B-50, selected by ELISA for cross-reactivity with its human counterpart, and evaluated on Western blots in comparison with the well-characterized affinity-purified rabbit polyclonal antibodies to rat-B-50. The Western blots show that the Mabs NM1, NM4, and NM6 recognize specifically the B-50 of bovine, human, and rat brain extract and the purified PKC phosphorylated and unphosphorylated rat B-50 isoforms. The Mabs NM2 and NM3 cross-react with bovine B-50 immunoreactive c-kinase substrate (BICKS), a protein sharing a 17 amino acid sequence homology with B-50. Two Mabs are useful for the detection of B-50 immunoreactivity in formalin-fixed human and rat brain tissues. In human specimen of the hippocampus, a characteristic neuropil distribution of B-50 is detected by the Mabs. In human muscle, Mabs reveal B-50 in nerve bundles and in axons at motor end plates. Thus, these Mabs are useful in investigating the function and localization of the B-50 protein. 相似文献
764.
J.T. Bonner 《FEMS microbiology letters》1994,120(1-2):1-7
Abstract Glycoproteins are providing to be quite common in prokaryotes. Those is S-layers are the best understood in terms of structure. Numerous eubacteria produce non-S-layer glycoproteins about which relatively little is known. The glycans on such protein and the nature and sites of their linkages to protein are novel in those glycoproteins which have been examined in any detail. The possible functions of the glycans are mostly not understood. Eubacterial non-S-layer glycoproteins and the glycosylation systems producing them observe more attention. 相似文献
765.
In a patient with the Zollinger-Ellison syndrome who had undergone vagotomy, pyloroplasty and, later, gastrojejunostomy, epigastric pain and stomal ulceration recurred despite the use of high doses (2700 mg/d) of cimetidine. Ranitidine, a new histamine H2-receptor antagonist, reversed all symptoms and healed the stomal ulcer without side effects, thus obviating the need for further surgery. Ranitidine may prove to be the drug of choice in the medical management of patients with the Zollinger-Ellison syndrome. 相似文献
766.
767.
D G Astaf'ev I V Maianskaia A K Akatov A N Maianski? 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1986,(7):48-51
In investigations based on the use of a highly sensitive test system permitting the detection of normal human antibodies to S. aureus peptidoglycan, the antigenic relationships between the peptidoglycans of S. aureus and other representatives of the genus Staphylococcus have been studied. Among other staphylococcal species, S. simulans, S. xylosus, S. hyicus, S. cohnii, S. hyicus s. s. chromogenes have been found to possess peptidoglycans most closely related to S. aureus peptidoglycans, while S. warneri and S. epidermidis peptidoglycans have proved to be least closely related to it. 相似文献
768.
769.
The influence of age, weaning, season of the year and body weight on the peripheral levels of progesterone, oestradiol-17β and luteinizing hormone (LH) were studied during neonatal, perinatal and peripubertal periods in buffalo heifers. The buffalo heifers exhibited oestrus only after 30 months of age and had higher levels of LH and oestradiol-17β and a lower level of progesterone on the day of oestrus. The progesterone concentration was affected significantly (P < 0.01) by different seasons, by weaning (P < 0.05) and varied between pubertal and neonatal periods (P < 0.01), whereas the oestradiol-17β level was affected significantly (P < 0.01) by weaning and varied at different seasons and with body weight. However, the LH concentration was greater during the neonatal period than the pre- and peripubertal periods and changed significantly (P < 0.01) between groups of ages and body weights. The results suggest that increases in the levels of oestradiol-17β and progesterone after 30 months of age are probably indicative of the onset of puberty in buffalo heifers. However, a further increase in oestradiol-17β, LH, and a decrease in progesterone are essential for oestrus and cyclicity to be exhibited in buffalo heifers. 相似文献
770.