全文获取类型
收费全文 | 62460篇 |
免费 | 4027篇 |
国内免费 | 6篇 |
专业分类
66493篇 |
出版年
2023年 | 450篇 |
2022年 | 391篇 |
2021年 | 840篇 |
2020年 | 761篇 |
2019年 | 753篇 |
2018年 | 1969篇 |
2017年 | 1830篇 |
2016年 | 2390篇 |
2015年 | 3137篇 |
2014年 | 3087篇 |
2013年 | 4147篇 |
2012年 | 5006篇 |
2011年 | 4462篇 |
2010年 | 2785篇 |
2009年 | 2134篇 |
2008年 | 3455篇 |
2007年 | 3255篇 |
2006年 | 3053篇 |
2005年 | 2618篇 |
2004年 | 2538篇 |
2003年 | 2266篇 |
2002年 | 2087篇 |
2001年 | 1415篇 |
2000年 | 1391篇 |
1999年 | 1066篇 |
1998年 | 445篇 |
1997年 | 323篇 |
1996年 | 333篇 |
1995年 | 312篇 |
1994年 | 238篇 |
1993年 | 227篇 |
1992年 | 537篇 |
1991年 | 464篇 |
1990年 | 417篇 |
1989年 | 412篇 |
1988年 | 409篇 |
1987年 | 355篇 |
1986年 | 345篇 |
1985年 | 346篇 |
1984年 | 352篇 |
1983年 | 236篇 |
1982年 | 216篇 |
1980年 | 178篇 |
1979年 | 219篇 |
1978年 | 208篇 |
1975年 | 197篇 |
1974年 | 221篇 |
1973年 | 224篇 |
1972年 | 185篇 |
1969年 | 172篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
841.
Phospholipid turnover during phagocytosis in human polymorphonuclear leucocytes 总被引:1,自引:0,他引:1 下载免费PDF全文
Merche García Gil Fernando Alonso Vicente Alvarez Chiva Mariano Sánchez Crespo José M. Mato 《The Biochemical journal》1982,206(1):67-72
We have previously observed that the phagocytosis of zymosan particles coated with complement by human polymorphonuclear leucocytes is accompanied by a time- and dose-dependent inhibition of phosphatidylcholine synthesis by transmethylation [García Gil, Alonso, Sánchez Crespo & Mato (1981) Biochem. Biophys. Res. Commun. 101, 740–748]. The present studies show that phosphatidylcholine synthesis by a cholinephosphotransferase reaction is enhanced, up to 3-fold, during phagocytosis by polymorphonuclear cells. This effect was tested by both measuring the incorporation of radioactivity into phosphatidylcholine in cells labelled with [Me-14C]choline, and by assaying the activity of CDP-choline:diacylglycerol cholinephosphotransferase. The time course of CDP-choline:diacylglycerol cholinephosphotransferase activation by zymosan mirrors the inhibition of phospholipid methyltransferase activity previously reported. The extent of incorporation of radioactivity into phosphatidylcholine induced by various doses of zymosan correlates with the physiological response of the cells to this stimulus. This effect was specific for phosphatidylcholine, and phosphatidyl-ethanolamine turnover was not affected by zymosan. The purpose of this enhanced phosphatidylcholine synthesis is not to provide phospholipid molecules rich in arachidonic acid. The present studies show that about 80% of the arachidonic acid generated in response to zymosan derives from phosphatidylinositol. A transient accumulation of arachidonoyldiacylglycerol has also been observed, which indicates that a phospholipase C is responsible, at least in part, for the generation of arachidonic acid. Finally, isobutylmethylxanthine and quinacrine, inhibitors of phosphatidylinositol turnover, inhibit both arachidonic acid generation and phagocytosis, indicating a function for this pathway during this process. 相似文献
842.
Basic electrophysiological parameters and frequency sensitivity of the ventricular myocardium of human embryos 总被引:1,自引:0,他引:1
The basic electrophysiological manifestations of the ventricular myocardium of twelve 7- to 12-week human embryos were measured with a glass electrode and a programmed stimulation technique. The resting membrane potential value was 79.37 +/- 0.34 mV and the overshoot 32.7 +/- 0.57 mV; the action potential (AP) duration at 1 Hz stimulation frequency was 120.0 +/- 5.7 ms at AP plateau phase levels and 258 +/- 17 ms at the level corresponding to 95% repolarization. The duration of the AP was a function of the stimulation frequency. i.e. it altered in correlation to the stimulation programme fully developed frequency sensitivity). In stimulation with different frequencies the duration of the steady state AP was in an inverse relation to the stimulation frequency, the maximum changes being found in the terminal repolarization zone. An interpolated extrasystole mainly affected the duration of the plateau phase. 相似文献
843.
In the present work the effects of the hypophysis hormones on oviduct mucoprotein components distribution patterns were studied. Remarkable changes after treating the toad with hypophysis injections were apparent. The distribution pattern for hexose, sialic acid, hexosamine and phosphate from 18 hours hypophysis treated toads were found to be identical with those obtained from preovulatory period animals. On the other hand, the levels for mucoprotein components from hypophysis treated animals were found to be approximately one-half or more higher than those obtained from postovulatory period toads. Otherwise, hypophysis treatment of the toads in preovulatory period had not effect on the levels and distribution patterns of mucoprotein components. These results suggest that hypophysis hormones are involved in the increase of the oviduct secretory activity. 相似文献
844.
Phosphatidylcholine is one of the most frequent phospholipid components of the inner mitochondrial membrane ofNeurospora crassa. Quantitative analysis of phospholipids of the wild strain ofNeurospora crassa and of its twocho mutants showed that these strains did not significantly differ in the content of phosphatidylcholine. Mutants cultivated
in a medium without choline contained, as compared with the wild strain, an increased amount of phosphatidylserine and a decreased
quantity of phosphatidic acid. Respiratory activity increased and sensitivity to inhibitors of respiration changed. It is
likely that the presence of choline in the growth medium exerts a regulatory effect on the cell metabolism of these mutants. 相似文献
845.
846.
Cultivation ofAspergillus niger 97A in baffled flasks on a shaker brings about metabolic changes demonstrated in increased citric acid biosynthesis, morphological
changes and alterations in the mycelial cell wall. 相似文献
847.
K. Lívanský 《Folia microbiologica》1982,27(6):455-459
The buffering capacity of solutions of KH2PO4 and NaHCO3 increases with their concentration, the behaviour being describable by mathematical expressions. Solutions of KH2PO4 prepared from tap water exhibit a buffering capacity higher by an order of magnitude than those prepared from distilled water.
However, there is no difference between the buffering capacities of solutions of NaHCO3 prepared from tap and distilled water. Urea and NH4NO3 have almost no effect on the buffering capacities of sol utions. 相似文献
848.
849.
Dagmar Jičínská Eduard Brabec Marcel Rejmánek Jan Jeník Joří Haager Josef Holub Věroslav Samek Hana Rambousková Josef Holub Marie Naděžda Končalová Robert Neuhäusl Josev Kyncl František Krahuleo Jaroslav Dobrý Blanka Úlehlová Jiří Úlehla Eliška Rybníčková Kamil Rybníček 《Folia Geobotanica》1982,17(4):431-448
850.
Evidence for sedative effects of low doses of morphine in mice involving receptors insensitive to naloxone 总被引:1,自引:0,他引:1
Low doses of morphine (0.30–2.5 mg/kg) decrease in a dose-dependent manner spontaneous climbing behaviour in mice. This effect is not modified by administration of naloxone at doses up to 1.25 mg/kg. These morphine doses do not modify the locomotor activity but, when they are associated with naloxone (0.5 mg/kg), an obvious inhibition occurs. In rats, a hyperactivity follows the akinesia produced by a morphine administration (10 mg/kg). This hyperactivity is changed into a significant hypokinesia when the animals are treated with naloxone (0.05 mg/kg). These results might reveal a dual effect of low doses of morphine, the excitatory effect of morphine being antagonized by naloxone whereas no action on the sedative effect is observed. 相似文献