全文获取类型
收费全文 | 436415篇 |
免费 | 49299篇 |
国内免费 | 182篇 |
出版年
2018年 | 3919篇 |
2017年 | 3874篇 |
2016年 | 5356篇 |
2015年 | 7527篇 |
2014年 | 8520篇 |
2013年 | 12496篇 |
2012年 | 13987篇 |
2011年 | 13897篇 |
2010年 | 9365篇 |
2009年 | 8715篇 |
2008年 | 12559篇 |
2007年 | 12716篇 |
2006年 | 12129篇 |
2005年 | 11486篇 |
2004年 | 11330篇 |
2003年 | 10825篇 |
2002年 | 10606篇 |
2001年 | 19712篇 |
2000年 | 19933篇 |
1999年 | 16227篇 |
1998年 | 5873篇 |
1997年 | 6087篇 |
1996年 | 5919篇 |
1995年 | 5396篇 |
1994年 | 5469篇 |
1993年 | 5366篇 |
1992年 | 13602篇 |
1991年 | 12829篇 |
1990年 | 12775篇 |
1989年 | 12737篇 |
1988年 | 11567篇 |
1987年 | 10990篇 |
1986年 | 10229篇 |
1985年 | 10344篇 |
1984年 | 8359篇 |
1983年 | 7236篇 |
1982年 | 5540篇 |
1981年 | 4888篇 |
1980年 | 4725篇 |
1979年 | 7927篇 |
1978年 | 6174篇 |
1977年 | 5464篇 |
1976年 | 5286篇 |
1975年 | 5672篇 |
1974年 | 5996篇 |
1973年 | 5880篇 |
1972年 | 5305篇 |
1971年 | 4657篇 |
1970年 | 4102篇 |
1969年 | 3821篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
761.
762.
Sequences related to the major subunit gene fedA of F107 fimbriae in porcine Escherichia coli strains that express adhesive fimbriae 总被引:1,自引:0,他引:1
Abstract Porcine Escherichia coli strains isolated from cases fo postweaning diarrhea or edema disease were analysed for the presence of fedA , the major subunit gene of F107 fimbriae. The E. coli isolates were known to contain colonisation factor '8813', or to express F107, 2134P or other fimbriae, different from F4, F5, F6, and F41. PCR with fedA -specific primers, restriction enzyme digestion of the PCR product, and nucleotide sequence analysis demonstrated that 2134P pili, colonisation factor '8813' and fimbriae identified on Australian strains of the O141 serotype belong to one family of F107 fimbrial antigens. 相似文献
763.
D. G. Zamolodchikov V. I. Grabovskii P. P. Shulyak O. V. Chestnykh 《Doklady biological sciences》2017,476(1):200-202
Regional Evaluation of Carbon Budget of Forests (RECBF), was used to study the dynamics of carbon balance in Russian forests in 1988–2015. The carbon sink (excess of absorption over losses) to forests was minimal in 1988. Since the first half of the 1990s, its increase has started. This increase was associated with the reduction of logging volume in connection with socioeconomic reforms. Since 2008, the carbon sink was gradually reduced due to increasing losses in logging operations, forest fires, and decreased carbon absorption. 相似文献
764.
765.
766.
Are all plant populations metapopulations? 总被引:2,自引:1,他引:1
767.
P Sinibaldi R Muraro M Centanni M G Giganti 《Bollettino della Società italiana di biologia sperimentale》1983,59(1):112-116
The behaviour of Na+/K+ ATPase during cell growth has been studied. Human cultured fibroblasts were used in the presence or absence of EGF. Sample and control cultures were stopped by gathering and washing the cells with tris buffer. Homogenates were tested for Na+/K+ ATPase activity by the method of incubating and for the -SH groups content (Ellman). Na+/K+ ATPase activity that slightly increases in the controls is strongly reduced by the addition of EGF. The behaviour shows evidence for a double mechanism of action: I) involvement of the cAMP system 2) decrease of the -SH group availability. 相似文献
768.
P Gysen G Heynen P Franchimont 《Comptes rendus des séances de la Société de biologie et de ses filiales》1980,174(5):867-877
Proteoglycans (PG) have been purified by classical methods from human articular cartilage in order to set up a radioimmunoassay. Conditions of labelling, purification of labelled PG, and optimal conditions of buffer, temperature, duration of incubations and dilution of antiserum are described. Separation of free and bound PG is performed by immunoprecipitation. It is demonstrated that human articular PG can be assayed quantitatively by RIA procedure, with the sensitivity of +/- 2 femto-moles (+/- 5 ng) per tube. 相似文献
769.
770.
—The distribution of choline acetyltransferase, aromatic l -amino acid decarboxylase and acetylcholinesterase in the nervous system of Helix aspersa has been studied using homogenates of whole ganglia, microdissection from freeze-dried sections and dissection of single neurons from fresh tissue. Choline acetyltransferase was found in both the cell body and neuropil layers of all the Helix ganglia. The enzyme was not specifically localized to any ganglion or region of ganglion. Between 10 and 30 per cent of the isolated single cell bodies contained the enzyme. The enzymic activity corresponded to 50–200 mmol ACh/1 cell bodies/h. Choline acetyltransferase is probably a specific marker for cholinergic cells in this species. Aromatic l -amino acid decarboxylase was more selectivity localized and its distribution corresponded well with that of monoamine containing cells as visualized by the fluorescence histochemical technique. A large proportion of cell bodies were localized in the boundary between the visceral and right parietal ganglia and in the pedal ganglion. The other ganglia contained few such cells. The activity of aromatic l -amino acid decarboxylase corresponded 10–50 mmol dopamine/1 cell bodies/h. A method was developed to measure the enzyme activity towards 5-hydroxytryptophan and DOPA in single cells simultaneously. The ratio between the activity towards both substrates did not vary significantly for the different cells. The enzyme is probably a specific marker for monoamine cells, but cannot be used to differentiate between the different monoamine cells. Acetylcholinesterase was uniformly distributed in the ganglia and was probably present in all nerve cells. 相似文献