全文获取类型
收费全文 | 2741篇 |
免费 | 163篇 |
出版年
2022年 | 27篇 |
2021年 | 36篇 |
2020年 | 25篇 |
2019年 | 24篇 |
2018年 | 36篇 |
2017年 | 24篇 |
2016年 | 72篇 |
2015年 | 125篇 |
2014年 | 117篇 |
2013年 | 145篇 |
2012年 | 202篇 |
2011年 | 203篇 |
2010年 | 120篇 |
2009年 | 114篇 |
2008年 | 122篇 |
2007年 | 142篇 |
2006年 | 111篇 |
2005年 | 124篇 |
2004年 | 139篇 |
2003年 | 116篇 |
2002年 | 114篇 |
2001年 | 86篇 |
2000年 | 78篇 |
1999年 | 63篇 |
1998年 | 38篇 |
1997年 | 23篇 |
1996年 | 24篇 |
1995年 | 19篇 |
1994年 | 11篇 |
1993年 | 21篇 |
1992年 | 37篇 |
1991年 | 30篇 |
1990年 | 35篇 |
1989年 | 29篇 |
1988年 | 26篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1981年 | 7篇 |
1979年 | 13篇 |
1978年 | 10篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1975年 | 13篇 |
1974年 | 18篇 |
1973年 | 9篇 |
1971年 | 8篇 |
1969年 | 8篇 |
排序方式: 共有2904条查询结果,搜索用时 296 毫秒
1.
2.
Human chorionic gonadotropins (hCGs) highly purified from the urine of patients with trophoblastic diseases and of healthy pregnant women contain approximately four mucin-type sugar chains in one molecule. The structures of these sugar chains were studied comparatively by using a new sensitive method to obtain mucin-type sugar chains quantitatively as radioactive oligosaccharides from a small amount of glycoproteins. The mucin-type sugar chains of all hCGs include sialylated and nonsialylated Gal beta 1----3GalNAc and Gal beta 1----4GlcNAc beta 1----6(Gal beta 1----3)GalNAc. In the case of normal hCG and hydatidiform mole hCG, oligosaccharides containing the tetrasaccharide core occupy approximately 10% of the total mucin-type sugar chains. The ratio of the tetrasaccharide containing oligosaccharides is increased prominently to approximately 60% in choriocarcinoma hCG. The proportion in invasive mole hCG was also increased, but less than the proportion of choriocarcinoma hCG. 相似文献
3.
The effects of estrogen on the uridine uptake into cells were examined in primary cultures of liver parenchymal cells from Xenopus laevis. The total uptake of [3H]uridine into the estrogen-treated cells and its incorporation into RNA were about 1.5 times higher than the values for control cells. The uptake of [3H]adenosine and its incorporation into RNA were not affected by estrogen. An experiment in which liver parenchymal cells were double labeled with [3H]uridine and [3H]adenosine showed that estrogen elevated the specific radioactivity of the UTP pool 1.4-fold the value found for the control cells, but that of the ATP pool was not altered by estrogen. Short term labeling revealed that estrogen did not significantly alter the rate of the initial uptake of [3H]uridine into the cells, but it did stimulate [3H]uridine phosphorylation about 1.7-fold. Uridine kinase activity measured in cell-free extracts of hepatocytes treated with estrogen had a value 1.6 times that of the control cells. These data indicate that the stimulation of [3H]uridine uptake and phosphorylation in Xenopus laevis hepatocytes in the presence of estrogen is caused by the enhancement of uridine kinase activity. 相似文献
4.
Ultrastructural changes of the midgut epithelial cells in feeding and moulting nymphs of the tick Haemaphysalis longicornis 总被引:1,自引:0,他引:1
The midgut epithelial cells in nymphs fed on laboratory rabbits were examined during feeding and after detachment. The midgut epithelium at the unfed stage consisted of digestive cells of lower activity, containing such nutritive substances as protein, lipid and glycogen. As feeding proceeded, the cells became active in intracellular digestion. At the middle of the feeding stage, the spent digestive cells derived from the active digestive cells began to be replaced by the new digestive cells of lower activity. After detachment, the pinocytotic activity of the above cells increased greatly, and the digestive activity increased to some extent. As a result, many large endosomes were formed by fusion of numerous pinosomes. Thereafter, endosomes decreased in size as digestion proceeded and there was an increase of haematin granules. On day 7 after detachment, the new digestive cells of lower activity, belonging to the 'nutritional reserve' type, appeared adjacent to the spent digestive cells which had almost exhausted all endosomes, and these new cells had completely replaced the spent cells by day 3 after moulting. 相似文献
5.
Action spectra for the inhibition by light of the accumulationof photosynthetic pigments during the aerobic growth of a photosyntheticbacterium, Rhodobacter sphaeroides, and an aerobic photosyntheticbacterium, Erythrobacter sp. strain OCh 114, were determinedover the range of wavelengths from 380 to 870 nm. The actionspectra for the inhibition of accumulation of bacteriochlorophyllin both R. sphaeroides and Erythrobacter sp. strain OCh 114indicated that the maximum inhibition occurred at approximately400 nm and a low level of inhibition occurred at 575 and 770nm. In R. sphaeroides, the action spectrum for the inhibitionof accumulation of carotenoid paralleled that for the inhibitionof accumulation of bacteriochlorophyll over the same range ofwavelengths. These results indicate that in both species, grownunder aerobic conditions, the same photoreceptor is involvedin the inhibition. One possible candidate for the relevant photoreceptormay be the precursor(s) to bacteriochlorophyll. It is possiblethat the photoreceptor is decomposed by light absorbed by itselfor by an unidentified photoreceptor that absorbs blue light(a photo-sensitizer). It is suggested that the accumulationof carotenoid is dependent on the stability of the bacteriochlorophyll. (Received September 16, 1988; Accepted March 2, 1989) 相似文献
6.
R Morita S Morimoto E Koh K Fukuo S Kim K Itoh K Taniguchi T Onishi T Ogihara 《Biochemistry international》1989,18(3):647-653
Low density lipoprotein (LDL), a major cholesterol-carrying lipoprotein in the plasma, binds to its receptor through apoprotein B (Apo-B). The addition of LDL and Apo-B induced rapid (5 s), but transient increase in the inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) level with K0.5 values of 1.1 and 0.07 microgram/ml, accompanied by increases of cytosolic free Ca2+ concentration [( Ca2+]i), in vascular smooth muscle cells (VSMC). The increases by LDL and Apo-B were both reduced by pretreatment of the VSMC with pertussis toxin. The early change in Ins-1,4,5-P3 involving a GTP-binding protein may function as an initial signal for the action of LDL in VSMC. 相似文献
7.
S Morimoto S Imanaka E Koh T Shiraishi T Nabata S Kitano Y Miyashita Y Nishii T Ogihara 《Biochemistry international》1989,19(5):1143-1149
The inhibitory effects of 1 alpha,25-(OH)2D3 and synthetic oxa-derivatives of vitamin D3 on growth of normal and psoriatic fibroblasts in culture were compared. Proliferation of normal fibroblasts was strongly inhibited by these new compounds in the following order: 22-oxa-1 alpha,25-(OH)2D3 greater than 22-oxa-1 alpha-(OH)D3 greater than 1 alpha,25-(OH)2D3 greater than 20-oxa-1 alpha,25-(OH)2D3. 22-Oxa-1 alpha,25-(OH)2D3 was about 10-times more inhibitory than 1 alpha,25-(OH)2D3. Proliferation of psoriatic fibroblasts was not inhibited by 1 alpha,25-(OH)2D3 at concentrations of up to 10(-6) M, but was suppressed by 10(-8)-10(-6) M 22-oxa-1 alpha,25-(OH)2D3 and 10(-6) M 22-oxa-1 alpha-(OH)D3. These results suggest that oxa-derivatives of vitamin D3, especially 22-oxa-1 alpha,25-(OH)2D3, should be useful in further studies on the cause and treatment of psoriasis. 相似文献
8.
Kazuo Nakamura Yoshifumi Amano Ooki Nakayama 《Applied microbiology and biotechnology》1989,31(4):351-354
Summary A microbial sensor of immobilized Thiobacillus thiooxidans S3 cells was assembled to determine free sulphite in wine. Sulphite oxidation activity of the immobilized cells was sufficiently high for use even after 3 months storage at 4° C. The sensitivity of this sensor was 116 nA·1·mg-1 for sulphur dioxide. The relationship between the current decrease and the sulphur dioxide concentration was linear up to 17 mg·1-1. The sampling rate achieved was 10 min per sample including washing time. This sensor method needed no pretreatment of wine samples, and wines diluted with 5 mM sulphuric acid solution could be directly introduced in the computer-aided analysis system. The pigments in red wine did not disturbed the analysis. 相似文献
9.
S Kim S Morimoto E Koh Y Miyashita T Ogihara 《Biochemical and biophysical research communications》1989,164(3):1003-1008
The effects of a potassium (K+) channel opener BRL34915 and a specific K+ ionophore valinomycin on vasoconstriction induced by endothelin (ET) were compared with those of calcium (Ca2+) channel blockers, nicardipine and verapamil, using helical strips from rat thoracic aorta. ET induced potent and persistent contraction in control solution and similar but smaller contraction in Ca2+-free solution. BRL34915 and valinomycin inhibited the ET-induced contraction dose-dependently in control solution, but not in Ca2+-free solution. The ET-induced contraction was also inhibited by nicardipine and verapamil, though less strongly. On the other hand, high K+ (35 mM)-induced vasoconstriction was strongly inhibited by nicardipine and verapamil, but not by BRL34915 or valinomycin. These results support the idea that the extracellular Ca2+-dependent component of the ET-induced contraction may be mediated by Ca2+ influx by a route other than voltage-dependent Ca2+-channels. 相似文献