全文获取类型
收费全文 | 4944篇 |
免费 | 374篇 |
出版年
2022年 | 62篇 |
2021年 | 105篇 |
2020年 | 56篇 |
2019年 | 61篇 |
2018年 | 109篇 |
2017年 | 94篇 |
2016年 | 131篇 |
2015年 | 167篇 |
2014年 | 250篇 |
2013年 | 297篇 |
2012年 | 334篇 |
2011年 | 312篇 |
2010年 | 202篇 |
2009年 | 166篇 |
2008年 | 247篇 |
2007年 | 226篇 |
2006年 | 230篇 |
2005年 | 199篇 |
2004年 | 186篇 |
2003年 | 155篇 |
2002年 | 125篇 |
2001年 | 138篇 |
2000年 | 101篇 |
1999年 | 97篇 |
1998年 | 50篇 |
1997年 | 34篇 |
1996年 | 37篇 |
1995年 | 33篇 |
1994年 | 39篇 |
1993年 | 38篇 |
1992年 | 76篇 |
1991年 | 67篇 |
1990年 | 68篇 |
1989年 | 56篇 |
1988年 | 45篇 |
1987年 | 53篇 |
1986年 | 47篇 |
1985年 | 52篇 |
1984年 | 47篇 |
1983年 | 38篇 |
1982年 | 41篇 |
1981年 | 28篇 |
1979年 | 33篇 |
1978年 | 27篇 |
1977年 | 33篇 |
1975年 | 27篇 |
1974年 | 21篇 |
1973年 | 25篇 |
1972年 | 24篇 |
1969年 | 32篇 |
排序方式: 共有5318条查询结果,搜索用时 15 毫秒
131.
Purification and characterisation of a beta-glucosidase (cellobiase) from a mushroom Termitomyces clypeatus 总被引:1,自引:0,他引:1
A beta-glucosidase with cellobiase activity was purified to homogeneity from the culture filtrate of the mushroom Termtomyces clypeatus. The enzyme had optimum activity at pH 5.0 and temperature 65 degrees C and was stable up to 60 degrees C and within pH 2-10. Among the substrates tested, p-nitrophenyl-beta-D-glucopyranoside and cellobiose were hydrolysed best by the enzyme. Km and Vm values for these substrates were 0.5, 1.25 mM and 95, 91 mumol/min per mg, respectively. The enzyme had low activity towards gentiobiose, salicin and beta-methyl-D-glucoside. Glucose and cellobiose inhibited the beta-D-glucosidase (PNPGase) activity competitively with Ki of 1.7 and 1.9 mM, respectively. Molecular mass of the native enzyme was approximated to be 450 kDa by HPLC, whereas sodium dodecyl sulphate polyacrylamide gel electrophoresis indicated a molecular mass of 110 kDa. The high molecular weight enzyme protein was present both intracellularly and extracellularly from the very early growth phase. The enzyme had a pI of 4.5 and appeared to be a glycoprotein. 相似文献
132.
Summary X-Ray radiography was employed to monitor the diffusion of sucrose into plaster of Paris matrix containing 20% yeast cells. It was observed that the depth of penetration of tracer Pb detected by radiography matched with the substrate penetration detected by chemical test. However electron probe microanalysis (EPMA) did not yield any conclusive evidence regarding the movements of tracer Pb and substrate to the same extent. 相似文献
133.
N.A. Chowdhury M. Moniruzzaman N. Nahar N. Choudhury 《World journal of microbiology & biotechnology》1991,7(6):603-606
A locally isolated strain of Micromonospora sp. when grown on different natural cellulosic substrates gave the highest activity of carboxymethylcellulase (34 U/ml) and Avicelase (0.9 U/ml) on rice straw. Sugar cane bagasse was also a good substrate for growth and cellulase production. With commercial cellulosic substrates, highest carboxymethylcellulase (90 U/ml) and Avicelase (2.8 U/ml) activities were when the organism grew on xylan. Saccharification of sugar cane bagasse and rice straw by enzyme preparations of the organism grown on the respective substrates released 5.6 and 5.8 mg reducing sugar/ml. With all enzyme preparations, bagasse was more easily saccharified than rice straw.The authors are with the Atomic Energy Research Establishment, GPO Box 3787, Dhaka 1000, Bangladesh; N.A. Chowdhury, M. Moniruzzaman, and N. Choudhury in the Institute of Food and Radiation Biology, and N. Nahar in the Institute of Nuclear Science and Technology. 相似文献
134.
A high affinity Ca2(+)-ATPase on the surface membrane of Leishmania donovani promastigote 总被引:2,自引:0,他引:2
A Ca2(+)-dependent ATP-hydrolytic activity was detected in the crude membrane ghost of the promastigote or vector form of the protozoal parasite Leishmania donovani, the pathogen responsible for kala azar. The Ca2(+)-ATPase was purified to apparent homogeneity after solubilization with deoxycholate. The enzyme consists of two subunits of Mr = 51,000 and 57,000 and has an apparent molecular weight of 215,000 +/- 12,000. The enzyme activity is exclusively dependent on Ca2+, and the pure enzyme can hydrolyze 1.6 mumol of ATP/min/mg of protein. The apparent Km for Ca2+ is 35 nM, which is further reduced to 12 nM in the presence of heterologous calmodulin. The enzyme is sensitive to vanadate, but is insensitive to oligomycin and ouabain. The enzyme is strongly associated with the plasma membrane and has its catalytic site oriented toward the cytoplasmic face. The enzyme spans across the plasma membrane as surface labeling with radioiodine shows considerable radioactivity in the completely purified enzyme. The localization and orientation of this high affinity, calmodulin-sensitive Ca2(+)-ATPase suggest some role of this enzyme in Ca2+ movement in the life cycle of this protozoal parasite. 相似文献
135.
Post-transfusion malaria in thalassaemia patients 总被引:1,自引:0,他引:1
A total of 125 beta-thalassaemia patients receiving repeated blood transfusions were screened by Giemsa stain, Acridine-orange stain and antigen detection for evidence of malaria infection on each visit. A total of 8 (6.4%) of the patients developed post-transfusion malaria (PMT) as confirmed by tracing the infected blood donors. A high incidence of PTM in thalassaemia patients appears to be due to the use of fresh blood and the high frequency of blood transfusions required by these patients. Antigen detection using monoclonal antibody was found to be more sensitive for diagnosis of PTM and for screening suspected donors than the conventional blood smear examination methods and is therefore recommended for routine blood donor screening to rule out malaria infection. 相似文献
136.
Enveloped animal viruses enter host cells either by direct fusion at neutral pH or by endocytosis. Herpes simplex virus (HSV) is believed to fuse with the plasma membrane of cells at neutral pH, and the glycoproteins gB and gD have been implicated in virus entry and cell fusion. Using cloned gB or gD genes, we show that cells expressing HSV-1 glycoproteins gB or gD can undergo fusion to form polykaryons by exposure only to acidic pH. The low pH-induced cell fusion was blocked in the presence of monoclonal antibodies specific to the glycoproteins. Infection of cells expressing gB or gD glycoproteins with HSV-1 inhibited the low pH-induced cell fusion. The results suggest that although the glycoproteins gB and gD possess fusogenic activity at acidic pH, other HSV proteins may regulate it such that in the virus-infected cell, this fusion activity is blocked. 相似文献
137.
Despite convincing physiological evidences for vasopressin (VP) autoregulation in the supraoptic (SON) and paraventricular (PVN) nuclei, the morphological demonstration of VP synapses has lagged behind. The present work investigates the possible existence of such synapses in the SON and PVN of the rat. Electron microscopy of sections immunostained with VP antibody (1:5,000) and conjugated with avidin-biotin demonstrated presynaptic terminals containing neurosecretory granule (NSG)-like bodies, 80-100 nm in diameter. The terminals formed axodendritic, axosomatic and axoaxonic synapses, though the postsynaptic elements remained largely unidentified. Other ultrastructural features of synaptic specialization were evident. The NSG-like bodies exhibited a varying and dynamic relationship to the presynaptic membrane, suggesting their involvement in synaptic mechanisms. 相似文献
138.
139.
140.
Shedding of vesicular stomatitis virus soluble glycoprotein by removal of carboxy-terminal peptide. 总被引:9,自引:5,他引:4
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A comparison of partial NH2-terminal sequences of vesicular stomatitis viral glycoprotein G (molecular weight, 69,000) and the soluble extracellular glycoprotein antigen Gs (molecular weight, 57,000) shows that both of the sequences are identical. Tryptic fingerprint analyses show that Gs lacks the carboxy-terminal region containing the membrane-anchoring hydrophobic domain of G. These results suggest that Gs is formed by cleavage in the carboxy-terminal region of G. 相似文献