全文获取类型
收费全文 | 1354篇 |
免费 | 207篇 |
出版年
2022年 | 15篇 |
2021年 | 34篇 |
2019年 | 16篇 |
2018年 | 19篇 |
2017年 | 22篇 |
2016年 | 39篇 |
2015年 | 46篇 |
2014年 | 41篇 |
2013年 | 44篇 |
2012年 | 71篇 |
2011年 | 67篇 |
2010年 | 58篇 |
2009年 | 57篇 |
2008年 | 53篇 |
2007年 | 43篇 |
2006年 | 46篇 |
2005年 | 44篇 |
2004年 | 50篇 |
2003年 | 41篇 |
2002年 | 42篇 |
2001年 | 41篇 |
2000年 | 48篇 |
1999年 | 28篇 |
1998年 | 31篇 |
1997年 | 15篇 |
1994年 | 13篇 |
1993年 | 18篇 |
1992年 | 23篇 |
1991年 | 14篇 |
1990年 | 28篇 |
1989年 | 36篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 23篇 |
1985年 | 22篇 |
1984年 | 24篇 |
1983年 | 15篇 |
1982年 | 11篇 |
1981年 | 18篇 |
1979年 | 14篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1976年 | 16篇 |
1975年 | 16篇 |
1974年 | 18篇 |
1973年 | 23篇 |
1972年 | 17篇 |
1971年 | 18篇 |
1970年 | 14篇 |
1967年 | 15篇 |
排序方式: 共有1561条查询结果,搜索用时 15 毫秒
21.
The effect of the suspensor and gibberellic acid on Phaseolus vulgaris embryo protein content 总被引:2,自引:0,他引:2
The role of the suspensor in the early development of the dicot embryo has not yet been defined. It has been described as merely an anchor and also as the major route of nutrients into the embryo. In order to further elucidate the role of the suspensor, early 0.2-mm and late heart stage 0.5-mm Phaseolus vulgaris (var. Taylor's Horticultural) embryos have been examined in tissue culture. It is known that Phaseolus embryos in culture at low osmotic potential will germinate precociously and that embryos in culture at high osmotic potential will either fail to grow or form callus. Optimum sucrose concentrations for continued, normal embryonic development of 0.2 mm and 0.5 mm P. vulgaris in tissue culture with Gamborg B5 medium were determined to be 12 and 6%, respectively. Protein content was examined in embryos and suspensors. Results showed that both 0.2- and 0.5-mm embryos required an attached suspensor for maximum protein content. Protein levels were substantially decreased when the embryo was cultured detached from or without the suspensor. Gibberellic acid at 10(-6) to 10(-7) M restored the protein content to that of freshly excised embryos. 相似文献
22.
The effects of Ro 15-1788 and ethyl-beta-carboline-3-carboxylate (beta-CCE) were studied alone and in combination on the behavioral performances of squirrel monkeys. Under one procedure, performances maintained by food were suppressed by electric shock presentation (punishment or "conflict" procedure). Under a second procedure, responding was maintained either by food or electric shock delivery under a 5-min fixed-interval schedule. Doses of beta-CCE between 0.1 and 3.0 mg/kg, i.m., produced graded decreases in punished responding which were reversed by pretreatment with Ro 15-1788 (1.0 - 10.0 mg/kg, i.m.). Low doses of beta-CCE (0.03 - 0.3 mg/kg, i.m.) increased responding of monkeys maintained by shock presentation, but did not affect food-maintained responding; higher doses of beta-CCE decreased responding under both schedules. These effects of beta-CCE are opposite those produced by the benzodiazepines under this procedure. Ro 15-1788 (1.0 mg/kg i.m.) antagonized the effects of beta-CCE, producing a shift to the right in the dose-response curves. These findings provide further support for the view that beta-CCE and Ro 15-1788 produce effects mediated by the same benzodiazepine receptor recognition site. 相似文献
23.
Rat hepatic zinc thionein levels can be modulated by a variety of external and internal stimuli. Metals, such as zinc or copper, induce levels 20 to 50 fold over controls. Catecholamines can increase levels 10 to 20 fold, while glucocorticoids, such as dexamethasone, can increase levels modestly by 2-6 fold. We have investigated the ability of additional hormones, which have receptors on hepatocytes, to modulate the levels of hepatic zinc thionein. Glucagon, angiotensin II, and Arg-vasopressin were administered intravenously and intraperitoneally, one time and three times, over an 11 hour period. Zinc thionein levels in rat liver were increased 1.7 to 5.6 fold by glucagon and 1.7 to 3.6 fold by angiotensin II, but not at all by Arg-vasopressin, as compared to appropriate controls. Glucagon and angiotensin II, when administered in vivo, can modulate zinc thionein levels in rat liver to an extent similar to glucocorticoids. Hepatic zinc thionein levels must now be recognized to be affected in vivo by metals, glucocorticoids, catecholamines, and polypeptide hormones. 相似文献
24.
25.
Monoclonal antibodies against human beta-glucocerebrosidase 总被引:5,自引:0,他引:5
R A Barneveld F P Tegelaers E I Ginns P Visser E A Laanen R O Brady H Galjaard J A Barranger A J Reuser J M Tager 《European journal of biochemistry》1983,134(3):585-589
Monoclonal antibodies were obtained against the membrane-bound lysosomal enzyme beta-glucocerebrosidase (acid beta-glucosidase), which is deficient in Gaucher's disease. BALB/c mice were immunized with homogeneous enzyme protein extracted from a sodium dodecyl sulphate/polyacrylamide gel. The mice were subsequently hyperimmunized with partially purified enzyme prior to fusion of spleen cells with myeloma cells. After fusion, 32 primary hybrid cell populations were obtained which continued to produce antibodies against beta-glucocerebrosidase after prolonged time of culture. All antibodies reacted with both native and denatured enzyme. Four primary cell populations were subcloned and the antibodies produced were characterized. The antibodies were all four of the IgG1 subclass. Three of these antibodies bind to protein A whereas one does not. The results of binding assays indicated that three of the antibodies react with the same antigenic domain (epitope 1), but the fourth with a different one (epitope 2). Probably two antigenic determinants are present in epitope 1 since one of the antibodies with specificity for epitope 1 is inactivated after iodination by the chloramine-T procedure whereas a second one is not. 相似文献
26.
Frank O. Brady 《Life sciences》1983,32(26):2981-2987
In a continuing study of the importance of metallothionein (MT) in the growth and development of neonates, zinc and copper metabolism in rat brain, heart, lung, spleen, and thymus has been analyzed in 5, 10, 15, 20 and 25 day old rats. Total, cytosol, and MT zinc and copper concentrations and organ contents were determined. Zinc, but very little, if any copper was associated with MT in these organs. Concentrations ranged from 0.03 to 3.3 μg Zn in MT/g; organ contents ranged from 0.003 to 2.2 μg Zn in MT/organ. Brain exhibited the highest concentrations and contents of zinc in MT, approaching the levels found in kidneys. Rank order of organ contents of zinc in MT was brain > lung > heart, spleen, thymus, during this neonatal growth period. When organ growth was rapid, a large percentage (20–95%) of the cytosolic zinc present in these organs was associated with MT, as has been previously observed with liver, kidneys, and testes. None of these organs undergoes the dramatic changes in zinc and copper metabolism previously observed in neonatal rat liver and gastrointestinal tract, and in maturing testes. They are more comparable to kidneys in their concentrations of zinc in MT. Like testes, little copper is found in these organs. 相似文献
27.
A method has been described for the measurement of apoB concentration and specific activity in very low density lipoprotein (VLDL) and low density lipoprotein (LDL) during metabolic studies. For measurement of specific activity, apoB was separated from other apolipoproteins and lipids by precipitation in, and subsequent washing with, isopropanol. For determination of apoB concentration, equal volumes of lipoprotein and isopropanol were mixed, and the protein content of the apoB precipitate was measured by the difference between total lipoprotein protein and the protein measured in the supernatant. Evidence that there was no apoB solubilization in isopropanol and that precipitated apoB was virtually free of soluble apolipoproteins was obtained by electrophoresis. Lipid contamination of the apoB precipitate was less than 1%. The methods were applicable to VLDL, intermediate density lipoprotein (IDL), and LDL from normolipemic patients with protein concentrations between 187 micrograms/ml and 1898 micrograms/ml. The data obtained using isopropanol were highly correlated with those using tetramethylurea, and recoveries of apoB were similar. Furthermore, the isopropanol method has been demonstrated to yield consistent data for apoB specific activities in a study of VLDL, IDL, and LDL metabolism. 相似文献
28.
29.
30.