全文获取类型
收费全文 | 1944篇 |
免费 | 186篇 |
国内免费 | 2篇 |
出版年
2022年 | 15篇 |
2021年 | 29篇 |
2020年 | 15篇 |
2019年 | 18篇 |
2018年 | 23篇 |
2017年 | 14篇 |
2016年 | 42篇 |
2015年 | 55篇 |
2014年 | 60篇 |
2013年 | 98篇 |
2012年 | 110篇 |
2011年 | 77篇 |
2010年 | 59篇 |
2009年 | 64篇 |
2008年 | 87篇 |
2007年 | 103篇 |
2006年 | 88篇 |
2005年 | 77篇 |
2004年 | 78篇 |
2003年 | 78篇 |
2002年 | 69篇 |
2001年 | 43篇 |
2000年 | 44篇 |
1999年 | 37篇 |
1998年 | 29篇 |
1997年 | 23篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 37篇 |
1991年 | 41篇 |
1990年 | 44篇 |
1989年 | 33篇 |
1988年 | 40篇 |
1987年 | 25篇 |
1986年 | 31篇 |
1985年 | 33篇 |
1984年 | 23篇 |
1983年 | 24篇 |
1982年 | 25篇 |
1981年 | 18篇 |
1980年 | 18篇 |
1978年 | 17篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1974年 | 18篇 |
1973年 | 13篇 |
1971年 | 15篇 |
1970年 | 13篇 |
排序方式: 共有2132条查询结果,搜索用时 31 毫秒
61.
Exposure to acidified PBS (pH 3) for 60 sec removed swine zonae pellucidae from 70.4% of 27 swine morulae, and 73.7% of these formed blastocysts in culture. Further investigations revealed that treating embryos with 0.5% pronase and acidified PBS (pH 3) for 30 sec each was more effective. Zonae were removed in 90.6% of 85 embryos (four-cell to morulae) treated. A total of 76.9% of 65 zona-free embryos and 81.6% of 38 untreated embryos formed blastocysts (P > 0.05). An additional 57 untreated and 49 zona-free embryos (morulae to blastocysts) were transferred to seven recipient sows. Four sows returned to estrus (18 to 27 days), but three others were pregnant when slaughtered at 38 to 42 days. One pregnant sow had received a combination of five zona-free and six untreated embryos and demonstrated the potential for further development of treated embryos in vivo. 相似文献
62.
Somatic cell genetic mapping of marsupial and monotreme species will greatly extend the power of comparative gene mapping to detect ancient mammalian gene arrangements. The use of eutherian-marsupial cell hybrids for such mapping is complicated by the frequent retention of deleted and rearranged marsupial chromosomes. We used staining techniques, involving the fluorochromes Hoechst 33258 and chromomycin A3, to facilitate rapid and unequivocal identification of marsupial chromosomes and chromosome segments and to make chromosome assignment and regional localization of marsupial genes possible. Chromosome segregation in rodent-macropod hybrids was consistent with preferential loss of the marsupial complement. The extent of loss was very variable. Some hybrids retained 30% of the marsupial complement; some retained small centric fragments; and some, no cytologically identifiable marsupial material. We examined the chromosomes and gene products of a number of rodent-grey kangaroo Macropus giganteus hybrids, and have assigned the genes Pgk-A (phosphoglycerate kinase-A), Hpt (Hypoxanthine phosphoribosyl transferase), and Gpd (Glucose-6-phosphate dehydrogenase) to the long arm of the kangaroo X chromosome, and provisionally established the gene order Pgk-A -Hpt -Gpd. 相似文献
63.
Target antigens in malaria transmission blocking immunity 总被引:7,自引:0,他引:7
R Carter L H Miller J Rener D C Kaushal N Kumar P M Graves C A Grotendorst R W Gwadz C French D Wirth 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1984,307(1131):201-213
Malaria transmission blocking immunity has been found to operate against two distinct phases of development of malaria parasites in the mosquito midgut: (i) against the extracellular gametes and newly fertilized zygotes shortly after ingestion by a mosquito of parasitized blood and (ii) against the zygotes during their subsequent development into ookinetes. Immunity is antibody-mediated and stage-specific. A set of three proteins, synthesized in the gametocytes, expressed on the surface of the gametes and newly fertilized zygotes and subsequently shed during later transformation of the zygotes, has been identified as the target antigens of anti-gamete fertilization blocking antibodies. A single protein, synthesized and expressed on the zygote surface during its development to ookinetes, has been identified as the target of antibodies which block the development of the fertilized parasites in the mosquito. Immunization of human populations against gamete or zygote antigens, while not directly protecting an immunized individual from inflection, would reduce the transfer of malaria within the population. Such immunity, in addition to reducing the overall rate of malaria transmission, would, if combined with a vaccine against the asexual (disease-causing) stages, reduce the chance of selection of parasites that are resistant to the asexual vaccine by preventing their entry into the mosquito population. 相似文献
64.
S Graves 《BMJ (Clinical research ed.)》1978,2(6151):1572-1573
65.
66.
Hilary Glover 《Journal of phycology》1977,13(3):208-212
Cultures of Isochrysis galbana Parks and Phaeodactylum tricornutum Bohlin were grown in iron-limited chemostats. With increasing iron deficiency, photosynthetic rate per cell and assimilation number decreased. The pattern of photosynthesis was also altered; in Fe deficient cells the proportion of 14C fixed in glycine and serine decreased with an accompanying increase into alanine after 3 min assimilation. Although there was no significant effect of Fe deficiency on the proportion of 14C incorporated into total amino acids and amides, the percentage of total 14C fixed in protein increased with increasing Fe deficiency. Cellular levels of chlorophyll a, carotenoids, cytochromes and protein also decreased with increasing Fe deficiency. However, the reduction in chlorophyll a/cell was not as great as that of cytochrorne f1 and Fe deficient cells therefore showed a marked increase in chlorophyll a:cytochrorne f1 ratio. 相似文献
67.
Glycoprotein was isolated from a purified thymocyte membrane preparation by two methods: lithium diiodosalicylate-phenol extraction and hot 75% ethanol extraction. A higher yield of membrane sialic acid was obtained by the latter method. The preparations had similar apparent molecular weights on sodium dodecyl sulfate gel electrophoresis. Both had similar receptor activities against a panel of hemagglutinins, although the 75% ethanol extract was more active on a weight basis. However, there were significant differences in carbohydrate and amino acid compositions of the two thymocyte extracts. The lithium diiodosalicylate-extracted material had much more glucose, ribose, and glycine than the ethanol extract. The glycoprotein preparations from thymocytes were quite distinct from the glycoprotein of bovine erythrocytes in both composition and receptor properties. 相似文献
68.
C A Breitenberger M C Graves L L Spremulli 《Archives of biochemistry and biophysics》1979,194(1):265-270
The chloroplast protein synthesis factor responsible for the translocation step of polypeptide synthesis on chloroplast ribosomes (chloroplast elongation factor G [EF-G]) has been detected in whole cell extracts and in isolated chloroplasts from Euglena gracilis. This factor can be detected by its ability to catalyze translocation on 70 S prokaryotic ribosomes such as those from E. coli. Chloroplast EF-G is present in low levels when Euglena is grown in the dark and can be induced more than 20-fold when the organism is grown in the light. The induction of this factor by light is inhibited by cycloheximide, a specific inhibitor of protein synthesis on cytoplasmic ribosomes. However, inhibitors of chloroplast protein synthesis such as streptomycin or spectinomycin have no effect on the induction of this factor by light. Furthermore, chloroplast EF-G can be partially induced by light in an aplastidic mutant (strain W3BUL) which has neither significant plastid structure nor detectable chloroplast DNA. These data strongly suggest that the genetic information for chloroplast EF-G resides in the nuclear genome, and that this protein is synthesized on cytoplasmic ribosomes prior to compartmentalization within the chloroplasts. 相似文献
69.
70.
The activity of glycogen phosphorylase is controlled by two nucleotide sites. We have found that organic solvents affect the regulatory properties of phosphorylase by altering the binding at these two sites. At the activator site, the Ka for AMP is lowered 10-fold in the presence of 10% 1,2-dimethoxyethane while, at the inhibitor site, the Ki for caffeine is increased 6-fold. The stimulation of activity by organic solvents is highly dependent on the enzyme's activity state. Phosphorylase b, which has a requirement for a nucleotide activator, loses this requirement in the presence of organic solvents, while the active form of the enzyme, phosphorylase a, is only slightly stimulated by organic solvents. The activation profile obtained with rabbit liver phosphorylase suggests that differences in the properties of this enzyme from rabbit muscle phosphorylase might be explained by a change in the relative affinity for AMP at the two nucleotide sites. The results also suggest that 1,2-dimethoxyethane may be useful to determine accurately the activities of different forms of liver phosphorylase. 相似文献