全文获取类型
收费全文 | 24943篇 |
免费 | 1789篇 |
国内免费 | 2篇 |
出版年
2023年 | 202篇 |
2022年 | 308篇 |
2021年 | 719篇 |
2020年 | 461篇 |
2019年 | 582篇 |
2018年 | 716篇 |
2017年 | 649篇 |
2016年 | 999篇 |
2015年 | 1487篇 |
2014年 | 1584篇 |
2013年 | 1958篇 |
2012年 | 2292篇 |
2011年 | 2114篇 |
2010年 | 1280篇 |
2009年 | 1192篇 |
2008年 | 1470篇 |
2007年 | 1350篇 |
2006年 | 1285篇 |
2005年 | 1098篇 |
2004年 | 1046篇 |
2003年 | 915篇 |
2002年 | 783篇 |
2001年 | 226篇 |
2000年 | 158篇 |
1999年 | 194篇 |
1998年 | 182篇 |
1997年 | 164篇 |
1996年 | 131篇 |
1995年 | 109篇 |
1994年 | 104篇 |
1993年 | 94篇 |
1992年 | 77篇 |
1991年 | 62篇 |
1990年 | 62篇 |
1989年 | 62篇 |
1988年 | 40篇 |
1987年 | 54篇 |
1986年 | 30篇 |
1985年 | 45篇 |
1984年 | 49篇 |
1983年 | 42篇 |
1982年 | 32篇 |
1981年 | 37篇 |
1980年 | 29篇 |
1979年 | 21篇 |
1978年 | 27篇 |
1977年 | 37篇 |
1975年 | 20篇 |
1974年 | 23篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Isolation of yeast with killer activity and its breeding with an industrial baking strain by protoplast fusion 总被引:5,自引:0,他引:5
Adela Bortol Clara Nudel Elda Fraile Ramon de Torres Ana Giulietti J. F. T. Spencer Dorothy Spencer 《Applied microbiology and biotechnology》1986,24(5):414-416
Summary Wild strains of Saccharomyces cerevisiae were isolated from dairy products, bakery goods, fresh fruit and vegetables, and tested for killer activity. Four isolates out of 238 strains possessed killer activity. The best of these was converted to the petite form and hybridized with an industrial strain of Saccharomyces cerevisiae by protoplast fusion. Thirty-eight out of 104 isolates had killer activity, and some of these had good dough-raising activity as well. 相似文献
92.
The rate of photosynthetic nitrate utilization in Anacystis nidulans is strongly influenced by the availability of carbon dioxide. This dependence can be relieved by inhibiting the metabolism of the ammonium derived from nitrate reduction. Nitrate uptake seems to be modulated through a sensitive regulatory system integrating the photosynthetic metabolism of carbon and nitrogen, with CO2 fixation products antagonizing the inhibitory effect of ammonium derivatives. 相似文献
93.
José Fayos Aurea Perales Mariano Pinar Manuel Rico Benjamín Rodríguez 《Phytochemistry》1983,22(9):1983-1984
The structure and absolute configuration of desangeloylshairidin, a guaianolide isolated from Guillonea scabra, have been established by X-ray diffraction analysis. No conformational change was observed in its seven-membered ring between the crystal and deuterochloroform solution states. 相似文献
94.
Heritable fragile sites on human chromosomes. X. New folate-sensitive fragile sites: 6p23, 9p21, 9q32, and 11q23 总被引:3,自引:1,他引:2
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Four new folate-sensitive fragile sites are documented at 6p23, 9p21, 9q32, and 11q23. These have all been shown to be heritable except for the one at 9p21, which has been seen only in a single individual. As with the other autosomal fragile sites, these appear to be innocuous in heterozygotes. 相似文献
95.
Jorgina Satrustegui Juan Bautista Alberto Machado 《Molecular and cellular biochemistry》1983,51(2):123-127
Summary The utilization by yeast of two carbon sources is carried out through the operation of the glyoxylic acid cycle. Kinetic data from the isocitrate transforming enzymes suggest that the flow of isocitrate through the glyoxylic acid cycle depends upon the inhibition of the isocitrate decarboxylating enzymes. Both isocitrate dehydrogenases are inhibited by a mixture of glyoxylate + oxaloacetate, but for the reasons described in the text we consider that this inhibition is of no physiological significance. On the other hand, we have found that NADPH is a competitive inhibitor of NADP-isocitrate dehydrogenase with respect to NADP+, with a KI similar to its KM. It also produces an additive effect on the NADH-produced inhibition of NAD-isocitrate dehydrogenase. We propose NADPH as the compound that channels the utilization of isocitrate into the glyoxylic acid cycle. This is supported by the finding of an increased NADPH/NADP+ ratio in acetate grown yeast with respect to glucose grown cells. 相似文献
96.
Ana Rosa Santa Cruza Luis A. Quesada Allue Alberto Baldi 《Molecular and cellular biochemistry》1983,56(1):55-66
Microsomal preparations from malignant human breast tumors catalyzed the transfer of mannose and glucose from GDP-[14C]-Man and UDP-[14C]-Glc into lipid-linked sugars and glycoprotein-like substances. As judged by several criteria the obtained lipid-linked monosaccharides behaved as dolichyl phosphate mannose and dolichyl phosphate glucose whereas lipid-linked oligosaccharides behaved as polyprenyl diphosphate derivatives. The optimum conditions for mannosyl- and glucosyl-transfer reactions and the effect of dolichyl phosphate, detergent and EDTA on incubation mixture were described. 相似文献
97.
M. Bewick C. S. Ogg V. Parsons S. A. Snowdon L. Manuel 《BMJ (Clinical research ed.)》1972,3(5825):491-494
The rosette inhibition test was used in the clinical management of organ allografts to estimate the amount of immunosuppressive drugs necessary to prevent rejection. In patients surviving more than three months renal function appeared to be better than in a similar group of patients managed without the test. It is suggested that this was due to a reduction in the number of clinical or subclinical rejection episodes. On the other hand, the test indicates that in many cases the level of immunosuppression should be much higher, and if this advice is followed the patients become increasingly exposed to the risk of infection. In other words, those patients with good renal function remained well, whereas those who might otherwise have rejected their kidney and survived had in fact died of sepsis. 相似文献
98.
Human IgM (immunoglobulin M) was reduced with 24mm-mercaptoethylamine. This atreatment resulted in complete dissociation to IgMs subunits and free J chain. Intr-subunit interchain disulphide bonds remained intact. The mixture then was encouraged to reoxidize. The schlieren pattern of the reoxidized mixture showed the presence of a considerable quantity of IgM in addition to residual IgMs. The isolated reassembled IgM did not dissociate in 5m-guanidinium hydrochloride. It apparently contained the same amount of covalently attached J chain as did native IgM. The J chain was a part of the high-molecular-weight Fc fragment obtained from the reassembled IgM. 相似文献
99.
100.
A comparative study was done on some of the chemical changes occurring during autolysis of cultures ofAspergillus flavus in both physiologically acid and alkaline media. The mycelium ofA. flavus lost during autolysis 44 % of its maximum dry weight in the physiologically alkaline medium, whereas this loss was apparently nil in the physiologically acid medium. Nitrogen containing compounds seemed not to be affected by autolysis either in the physiologically acid or alkaline media. The disappearance of P-containing compounds in mycelium ofA. flavus autolysed in both conditions (NO
3
–
and NH
4
+
as N source) amounted to 64 % in the alkaline autolysis and to nearly 77 % in the acid autolysis. The results we have obtained for the acid autolysis strongly suggest that very little activity is shown by autolytic enzymes in the interval 10–133 days of incubation, when measuring autolysis by the loss in mycelial dry weight.
Zusammenfassung Eine vergleichende Untersuchung war unternommen an einigen der chemischen Veränderungen, die während der Autolyse der Kulturen vonAspergillus flavus in physiologischen sauren und alkalischen Medien vorkommen. Die Myzelien vonA. flavus haben während der Autolyse 44 % ihres größten Trockengewichtes in physiologisch alkalischem Medium verloren, während dieser Verlust in physiologisch saurem Medium anscheinend Null gewesen ist. Stickstoff enthaltende Substanzen erschienen während der Autolyse weder in physiologisch saueren noch in alkalischen Medien beeinflußt zu sein. Das Verschwinden von P-enthaltenden Substanzen in Myzelien vonA. flavus in Autolyse unter beiden Bedingungen (NO 3 – und NH 4 + als Stickstoffquelle) erreichte 64 % in alkalischer Autolyse und beinahe 77 % in der saueren Autolyse. Die Ergebnisse, die wir in der saueren Autolyse erhalten haben legen es sehr nahe, daß autolytische Enzyme eine sehr geringe Aktivität in der Zeitspanne von 10–133 Tagen der Inkubazion zeigen, wenn die Autolyse an dem Verlust des mycelialen Trockengewichtes gemessen wird.相似文献