全文获取类型
收费全文 | 405446篇 |
免费 | 160856篇 |
国内免费 | 29616篇 |
出版年
2018年 | 5582篇 |
2017年 | 5172篇 |
2016年 | 6773篇 |
2015年 | 8820篇 |
2014年 | 9870篇 |
2013年 | 12655篇 |
2012年 | 14452篇 |
2011年 | 15109篇 |
2010年 | 12343篇 |
2009年 | 16125篇 |
2008年 | 13976篇 |
2007年 | 14256篇 |
2006年 | 12578篇 |
2005年 | 12072篇 |
2004年 | 12129篇 |
2003年 | 11282篇 |
2002年 | 11859篇 |
2001年 | 18433篇 |
2000年 | 16268篇 |
1999年 | 17708篇 |
1998年 | 12178篇 |
1997年 | 12074篇 |
1996年 | 11277篇 |
1995年 | 11402篇 |
1994年 | 10849篇 |
1993年 | 10426篇 |
1992年 | 16438篇 |
1991年 | 16028篇 |
1990年 | 16631篇 |
1989年 | 15704篇 |
1988年 | 14480篇 |
1987年 | 13328篇 |
1986年 | 12184篇 |
1985年 | 11825篇 |
1984年 | 9538篇 |
1983年 | 8158篇 |
1982年 | 7328篇 |
1981年 | 6563篇 |
1980年 | 6302篇 |
1979年 | 8925篇 |
1978年 | 7157篇 |
1977年 | 6817篇 |
1976年 | 6355篇 |
1975年 | 6338篇 |
1974年 | 6921篇 |
1973年 | 6944篇 |
1972年 | 6828篇 |
1971年 | 6344篇 |
1970年 | 5530篇 |
1969年 | 5463篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Subnuclear localization and antitransforming activity of N-myc:beta-galactosidase fusion proteins. 总被引:3,自引:2,他引:1
N-myc expression is under stage- and tissue-specific regulation in mammalian development, but its function is totally unknown. We sought agents to block N-myc activity in order to infer from the effect the possible function of N-myc in the apparently complex processes. As candidates for such agents, we tested fusion genes encoding N-myc:beta-galactosidase fusion proteins for their effects on the formation of transformed foci of rat embryo primary fibroblasts as the result of transfection with N-myc and activated H-ras. One of the gene constructs very efficiently antagonized N-myc activity, as assessed by its effect on focus formation, but did not appreciably affect cell viability. The product of this gene was not only targeted to the nucleus but also accumulated in subnuclear loci which may represent the sites where normal N-myc proteins reside. The occurrence of antagonistic effect at a low stoichiometric ratio suggested that the fusion protein gene competed with the N-myc gene in a fashion analogous to a dominant negative mutation. 相似文献
992.
B E Cohen 《Plastic and reconstructive surgery》1984,74(5):650-656
Reconstruction of normal shoulder contour is possible utilizing a latissimus dorsi musculocutaneous flap at the end of a long neurovascular pedicle. The thoracodorsal vessels and their lateral divisions form the basis of the pedicle. The nerve in the pedicle is left intact if maintenance of muscle bulk is desired and sectioned if atrophy is preferred. The amount of muscle taken in conjunction with the skin island is determined by the nature of the defect to be corrected. The twin goals of a single-stage reconstruction and a satisfactory aesthetic result are achieved with this method. 相似文献
993.
Using a slide culture technique, it was determined unequivocally that the chlamydospore of Candida albicans does germinate. The germination was by way of a multiple-budding process which was associated mostly with young spores following their transfer to a fresh environment. It is concluded the chlamydospore of C. albicans is a reproductive cell with a transient viability. 相似文献
994.
995.
Isolation of Temperature-Sensitive Membrane Mutants of Escherichia coli K-12 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Johan F. Steenbakkers J. H. F. F. Broekman A. Kerkenaar P. G. De Haan 《Journal of bacteriology》1973,116(2):535-540
Mutants with impaired biosynthesis of unsaturated fatty acids or altered metabolism of the phospholipids were isolated at a rather high frequency from a set of temperature-sensitive lysis mutants. It is suggested that preselection for the lysis phenotype makes it possible to isolate several kinds of mutants affected in the integrity of the cytoplasmic membrane. 相似文献
996.
Sporadic (less than regular weekly) coital activity is associated with a particular type of infertility—the short hyperthermic (luteal) phase. This preliminary report is the first suggestion that a reduced frequency of human sexual activity might, itself, be associated with subfertile reproductive function. 相似文献
997.
P Salgame A S Varadhachary L L Primiano J E Fincke S Muller M Monestier 《Nucleic acids research》1997,25(3):680-681
We describe a simple and convenient enzyme-linked immunosorbent assay (ELISA) for the detection of apoptosis in tissue culture. An early event in apoptosis is DNA fragmentation followed by release of nucleosomes into the cytoplasm. Our sandwich assay uses a pair of monoclonal antibodies specific for two nucleosomal epitopes to capture and detect cytoplasmic nucleosomes onto the ELISA plate. Our assay is about 500 times more sensitive than the detection of apoptotic DNA ladder by agarose electrophoresis and is especially suited for the testing of large numbers of samples. 相似文献
998.
A mutant of Aspergillus nidulans, designated nuv11, has been isolated as hypersensitive to the monofunctional alkylating agent MNNG and the quasi-UV-mimetic mutagen 4-NQO. The mutation was recessive, resulting from mutation of a single gene which mapped to chromosome IV, and was non-allelic to the previously characterised repair-deficient mutations uvsB and uvsH which are also located on this linkage group. The nuv11 mutation results in slow growth, deficient intragenic and intergenic meiotic recombination, increased spontaneous chromosome instability, and increased intragenic and intergenic mitotic recombination in homozygous diploids. By screening a wild-type gene bank of A nidulans, a clone (pNUV11A40) has been isolated which complements the nuv11 mutation, restoring wild-type responses to both MNNG and 4-NQO. 相似文献
999.
In 2009 through 2011, among 730 individuals of kaluga and Amur sturgeon collected in the lower reaches of the Amur River and the Amursky Liman, 17 morphologically intermediate individuals (hybrids) with the body length of 56 to 202 cm (median, 81 cm) were identified, including 11 individuals (4.6%) found in 2009, three individuals (1.6%) found in 2010, and three individuals (1.1%), in 2011. In 16 hybrids, 819 bp of the mtDNA control regions were sequences and 11 haplotypes were identified. Since all these haplotypes were from the mtDNA lineages of kaluga, it was concluded that hybridization occurred in one direction, kaluga (♀) × Amur sturgeon (♂). This asymmetry could be caused by the large size differences between these species. Since the earlier examined morphologically typical Amur sturgeons showed the absence of alien haplotypes (Shedko et al., 2015), the absence of the mtDNA introgression is claimed. This can be caused by low viability or sterility of the backcross females (kaluga (♀) × Amur sturgeon (♂)) × Amur sturgeon (♂). The samples of hybrids and typical kaluga individuals demonstrated no differences in the frequency spectra of the mtDNA haplotypes. However, haplotype and nucleotide diversity in the first sample was somewhat higher than in the second one (0.950 versus 0.927 and 0.0054 versus 0.0044, respectively). The data obtained will be useful for population monitoring of kaluga and Amur sturgeon, Amur River endemics, which are classified as critically endangered by the IUCN Red List of Threatened Species. 相似文献
1000.