全文获取类型
收费全文 | 3772篇 |
免费 | 287篇 |
专业分类
4059篇 |
出版年
2022年 | 19篇 |
2021年 | 59篇 |
2020年 | 27篇 |
2019年 | 43篇 |
2018年 | 51篇 |
2017年 | 53篇 |
2016年 | 86篇 |
2015年 | 108篇 |
2014年 | 128篇 |
2013年 | 216篇 |
2012年 | 216篇 |
2011年 | 220篇 |
2010年 | 111篇 |
2009年 | 101篇 |
2008年 | 164篇 |
2007年 | 193篇 |
2006年 | 182篇 |
2005年 | 156篇 |
2004年 | 138篇 |
2003年 | 148篇 |
2002年 | 134篇 |
2001年 | 117篇 |
2000年 | 129篇 |
1999年 | 95篇 |
1998年 | 50篇 |
1997年 | 49篇 |
1996年 | 41篇 |
1995年 | 37篇 |
1994年 | 35篇 |
1993年 | 32篇 |
1992年 | 87篇 |
1991年 | 70篇 |
1990年 | 67篇 |
1989年 | 62篇 |
1988年 | 47篇 |
1987年 | 52篇 |
1986年 | 44篇 |
1985年 | 40篇 |
1984年 | 43篇 |
1983年 | 47篇 |
1982年 | 19篇 |
1981年 | 18篇 |
1979年 | 33篇 |
1978年 | 18篇 |
1975年 | 26篇 |
1974年 | 20篇 |
1973年 | 19篇 |
1971年 | 17篇 |
1970年 | 21篇 |
1967年 | 20篇 |
排序方式: 共有4059条查询结果,搜索用时 0 毫秒
71.
Amicucci Antonella Rossi Ismaela Potenza Lucia Agostini Deborah Stocchi Vilberto 《Biotechnology Techniques》1997,11(3):149-154
Isolates of white truffles were identified as Tuber magnatum Pico species using a pair of primers selected from a sequence characterised amplified region (SCAR) and a specific random amplified polymorphic DNA (RAPD) marker. The present study reveals that PCR-fragment-pattern polymorphisms, the construction of probes and couples of primers from one or more of these polymorphic fragments may provide a useful and rapid tool for identifying species of ectomycorrhizal fungi in addition to conventional methods (morphological parameters). 相似文献
72.
Thedei G. Nozawa S.R. Simoes A.L. Rossi A. 《World journal of microbiology & biotechnology》1997,13(6):609-611
The mycelial Pi-repressible alkaline phosphatase of the wild-type strain 74A of Neurospora crassa was separated into at least ten isoforms by isoelectric focusing. The components visualized by activity with sodium -naphthyl phosphate as the substrate were predominantly acidic proteins with isoelectric points ranging from pH 4.5 to 7.6. The number of these isoforms was a function of growth pH. Strain pho-2A did not produce active Pi-repressible alkaline phosphatase (the pho-2 gene codes for its amino acid sequence), which gives an indication that these isoforms are encoded by the same structural gene. 相似文献
73.
Evolution of human immunodeficiency virus type 1 in perinatally infected infants with rapid and slow progression to disease. 总被引:1,自引:1,他引:0 下载免费PDF全文
F Salvatori S Masiero C Giaquinto C M Wade A J Brown L Chieco-Bianchi A De Rossi 《Journal of virology》1997,71(6):4694-4706
We addressed the relationship between the origin and evolution of human immunodeficiency virus type 1 (HIV-1) variants and disease outcome in perinatally infected infants by studying the V3 regions of viral variants in samples obtained from five transmitting mothers at delivery and obtained sequentially over the first year of life from their infected infants, two of whom (rapid progressors) rapidly progressed to having AIDS. Phylogenetic analyses disclosed that the V3 sequences from each mother-infant pair clustered together and were clearly distinct from those of the other pairs. Within each pair, the child's sequences formed a monophyletic group, indicating that a single variant initiated the infection in both rapid and slow progressors. Plasma HIV-1 RNA levels increased in all five infants during their first months of life and then declined within the first semester of life only in the three slow progressors. V3 variability increased over time in all infants, but no differences in the pattern of V3 evolution in terms of potential viral phenotype were observed. The numbers of synonymous and nonsynonymous substitutions varied during the first semester of life regardless of viral load, CD4+-cell count, and disease progression. Conversely, during the second semester of life the rate of nonsynonymous substitutions was higher than that of synonymous substitutions in the slow progressors but not in the rapid progressors, thus suggesting a stronger host selective pressure in the former. In view of the proposal that V3 genetic evolution is driven mainly by host immune constraints, these findings suggest that while the immune response to V3 might contribute to regulating viral levels after the first semester of life, it is unlikely to play a determinant role in the initial viral decline soon after birth. 相似文献
74.
Isolation from neutrophil membranes of a complex containing active NADPH oxidase and cytochrome b-245 总被引:1,自引:0,他引:1
M C Serra P Bellavite A Davoli J V Bannister F Rossi 《Biochimica et biophysica acta》1984,788(1):138-146
The lipid composition and fluidity of basolateral membranes prepared from the mucosa of the proximal, middle and distal thirds of the rat small intestine were determined. Fluidity, as assessed by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene and a series of anthroyloxy fatty acid derivatives, is decreased in the distal third as compared to the proximal segments. This pattern is similar to that described previously for microvillus membranes. The decrease in fluidity of the distal as compared to the proximal membranes results from an increase in cholesterol content, cholesterol/phospholipid molar ratio and degree of saturation of the fatty acid residues. In the middle and distal thirds of the gut, the degree of saturation of the fatty acid residues is higher in microvillus as compared to basolateral membranes, accounting in part for the characteristically lower fluidity of the luminal membranes. The specific activity of the basolateral membrane (Na+ + K+)-dependent adenosine triphosphatase is significantly lower in the distal as compared to the proximal and middle thirds of the intestinal mucosa. Studies of the binding of [3H]ouabain indicate that this pattern results from fewer enzyme sites in the distal membranes. 相似文献
75.
S Ronca-Testoni S Hrelia G Hakim G Ronca C A Rossi 《Bollettino della Società italiana di biologia sperimentale》1984,60(4):713-719
Some smooth muscle relaxant drugs devoid of anticholinergic action have been tested for their interaction with calmodulin, calmodulin-stimulated cyclic nucleotide phosphodiesterase activity, and uterine membrane binding sites for nitrendipine and adenosine. The myolytic activity of octylonium bromide and pinaverium bromide may be due to their interaction with calmodulin-dependent systems. Trimebutine maleate does not bind either to calmodulin or to nitrendipine and adenosine receptors. Tiropramide has no effect on calmodulin-dependent systems and on Ca2+ channels but it shows a competition for the A2-type adenosine receptors. 相似文献
76.
A. M. Iorio M. Neri P. Enrico F. Titti G. B. Rossi E. Bonmassar 《Cancer immunology, immunotherapy : CII》1984,18(1):35-40
Summary The influence of in vivo infection with the polycythemic substrain of Friend leukemia virus on noninducible (natural) resistance against allogeneic normal or malignant grafts was studied in lethally irradiated mice. Parallel studies were performed on the NK system in the same experimental conditions. The results indicate that FLV-P infection of mice with full (DBA/2) vs partial (BALB/c and CD2F1) susceptibility did not suppress their in vivo natural resistance against bone marrow or El-4 leukemia cells. On the other hand, a decline in NK activity paralleled the progression of leukemic disease in the more susceptible DBA/2 hosts.
Abbreviations used: FLV-P, N-tropic polycythemic substrain of Friend Leukemia Virus Complex; NR, natural resistance; NR in vivo, natural resistance against normal or malignant hemopoietic grafts occurring in vivo in lethally irradiated mice; NK, natural killer; (125I)IUdR, 125I-labeled 5-iodio-2-deoxyuridine; IV, intravenous 相似文献
77.
In an attempt to deduce the physiological basis of proline excretion in argD
– strains of Escherichia coli K12, several properties of an argD
+ (nonexcreting) and an argD
– (excreting) derivative were compared. No difference was found in the transport or in the utilization of either proline or its immediate precursor, 1-pyrroline-5-carboxylate (PCA). Furthermore, no differences were found in the physical or kinetic properties of partially purified preparations of the enzyme mediating the final step in proline biosynthesis, PCA reductase. The specific activity of PCA reductase was, however, consistently higher in crude extracts prepared from the argD
– mutant.This work was supported by grants from the National Institutes of Allergy and Infectious Diseases (Public Health Service No. AI-10862) and The University of Connecticut Research Foundation (to C. M. B.). J. J. R. was supported by an NDEA Predoctoral Fellowship. 相似文献
78.
Francesca Clementi Jone Rossi Lucia Costamagna Jolanda Rosi 《Antonie van Leeuwenhoek》1980,46(4):399-405
Schwanniomyces castellii and Endomycopsis fibuligera Produced extracellular amylase(s) when grown on various carbon sources and at different pH values. Both yeast species showed significant amylase synthesis in the presence of either maltose or soluble starch. On the other substrates tested (glucose, cellobiose, sucrose, trehalose, melezitose, raffinose, ethanol, glycerol) differences were found regarding growth and amylase production. Free glucose in the culture medium apparently inhibited enzyme synthesis. The pH range allowing maximal growth and amylase production was 4.5–6.0 for E. fibuligera and 5.5–7.0 for S. castellii. 相似文献
79.
A patient with the phenotype of trisomy 21 and increased activity of superoxide dismutase A is reported with partial trisomy for the distal portion of 21q. The exceptional feature in this case is a 45-chromosome karyotype due to the translocation of two chromosomes 21 onto the distal end of 14q. 相似文献
80.