全文获取类型
收费全文 | 3293篇 |
免费 | 191篇 |
国内免费 | 279篇 |
出版年
2023年 | 26篇 |
2022年 | 37篇 |
2021年 | 78篇 |
2020年 | 71篇 |
2019年 | 92篇 |
2018年 | 82篇 |
2017年 | 74篇 |
2016年 | 76篇 |
2015年 | 77篇 |
2014年 | 158篇 |
2013年 | 184篇 |
2012年 | 114篇 |
2011年 | 164篇 |
2010年 | 139篇 |
2009年 | 165篇 |
2008年 | 165篇 |
2007年 | 174篇 |
2006年 | 177篇 |
2005年 | 168篇 |
2004年 | 157篇 |
2003年 | 136篇 |
2002年 | 117篇 |
2001年 | 128篇 |
2000年 | 59篇 |
1999年 | 107篇 |
1998年 | 80篇 |
1997年 | 82篇 |
1996年 | 71篇 |
1995年 | 74篇 |
1994年 | 57篇 |
1993年 | 44篇 |
1992年 | 49篇 |
1991年 | 52篇 |
1990年 | 38篇 |
1989年 | 34篇 |
1988年 | 25篇 |
1987年 | 29篇 |
1986年 | 18篇 |
1985年 | 37篇 |
1984年 | 31篇 |
1983年 | 15篇 |
1982年 | 23篇 |
1981年 | 11篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 7篇 |
1976年 | 12篇 |
1975年 | 3篇 |
1973年 | 6篇 |
排序方式: 共有3763条查询结果,搜索用时 436 毫秒
51.
H. Miura S. Tanii T. Nakamura N. Watanabe 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,89(2-3):276-280
The endosperm starch of the wheat grain is composed of amylose and amylopectin. Genetic manipulation of the ratio of amylose to amylopectin or the amylose content could bring about improved texture and quality of wheat flour. The chromosomal locations of genes affecting amylose content were investigated using a monosomic series of Chinese Spring (CS) and a set of Cheyenne (CNN) chromosome substitution lines in the CS genetic background. Trials over three seasons revealed that a decrease in amylose content occurred in monosomic 4A and an increase in monosomic 7B. Allelic variation between CS and CNN was suggested for the genes on chromosomes 4A and 7B. To examine the effects of three Waxy (Wx) genes which encode a granule-bound starch synthase (Wx protein), the Wx proteins from CS monosomics of interest were analyzed using SDS-PAGE. The amount of the Wx protein coded by the Wx-B1 gene on chromosome arm 4AL was reduced in monosomic 4A, and thus accounted for its decreased amylose content. The amounts of two other Wx proteins coded by the Wx-A1 and Wx-D1 genes on chromosome arms 7AS and 7DS, respectively, showed low levels of protein in the monosomics but no effect on amylose content. The effect of chromosome 7B on the level of amylose suggested the presence of a regulator gene which suppresses the activities of the Wx genes. 相似文献
52.
Konieczny and Ausubel have described a technique whereby Arabidopsis thaliana loci can be rapidly mapped to one of the ten chromosome arms using a small number of F2 progeny from crosses between the ecotypes Landsberg erecta and Columbia. The technique involves the use of 18 co-dominant, cleaved amplified polymorphic sequence (CAPS) markers which are evenly distributed throughout the Arabidopsis genome. We have mapped these 18 markers using recombinant inbred (RI) lines generated in our laboratory. These data enable a better integration of loci mapped relative to the CAPS markers into the restriction fragment length polymorphism (RFLP) map generated using Arabidopsis RI lines. 相似文献
53.
54.
近年来研究表明组胺及其受体在正常造血调控中起着重要作用。本研究用琼脂半固体培养技术观察了特异性组胺H2受体激动剂英普咪定和拮抗剂西咪替丁对髓系粒-单核细胞白血病干细胞株WEHI3细胞生长的影响。结果表明不同浓度的英普咪定(10-8─10-4mol/L)对集落数呈明显剂量依赖性抑制,与对照组比较p<0.01。10-10─10-9mol/L英普咪定对集落数无明显影响。10-4─6×10-4mol/L的英普咪定对集落产率的抑制作用趋于饱和。最大抑制效能为对照组的54%(p<0.01)。10-4mol/L西咪替丁能完全阻断10-8mol/L英普咪定的集落抑制作用。对≥10-6mol/L英普咪定的作用西咪替丁均有部分阻断作用,与对照组比较P<0.01。单用西咪替丁对WEHI3细胞无明显直接作用。这提示WEHI3细胞株上存在有组胺H2受体,激动H2受体可抑制细胞增殖。 相似文献
55.
喹诺酮类药物抗乙型肝炎病毒体外实验研究 总被引:4,自引:0,他引:4
本文以2.2.15细胞株为模型,以HBsAg、HBeAg、HBVDNA、细胞存活率为观察指标,综合评价了喹诺酮类药物吡哌酸(PipemidicAcid)、氟哌酸(Norfloxacin)、环丙氟哌酸(Ciproflosxacin)、氟嗪酸(Ofloxacin)体外抗HBV效果。结果表明:吡哌酸、氟哌酸、环丙氟哌酸、氟嗪酸对HBsAg、HBeAg50%抑制浓度(ID_(50))分别为11μg/ml、64μg/ml、93μg/ml、105μg/ml和199μg/ml、111μg/ml、24μg/ml、217μg/ml,细胞存活率为50%时的药物浓度(CD_(50))分别为219μg/ml、90μg/ml、181μg/ml、169μg/ml,在所选定的用药浓度范围内不同程度抑制培养上清液及细胞内HBVDNA及其复制中间体的产生。尤其对超螺旋结构DNA(scDNA)有不完全抑制作用。 相似文献
56.
P. J. Hatt M. Moriniere H. Oberlander P. Porcheron 《In vitro cellular & developmental biology. Animal》1994,30(10):717-720
Summary During postembryonic development of insects, molting cycles affect epidermal cells with alternate periods of proliferation
and differentiation. Cells of the cell line established from imaginal discs of the Indian meal moth (IAL-PID2) differentiate
under the action of the molting hormone, 20-hydroxyecdysone, in a manner that is meaningful in terms of the development of
the tissue from which they were derived. In particular, the hormone caused an accumulation of the cells in the G2 phase of
their cycle and induced the formation of epithelial-like aggregates and the synthesis of specific proteoglycans. Recent discovery
of members of the insulin superfamily in insects and the role of growth factors played by this family of molecules in vertebrates
led us to check for their potential effects on IAL-PID2 cell cycle regulation. On the one hand, our results showed that insulin
was involved in partial resumption of the cell cycle after an arrest caused by serum deprivation, but that other growth factors
present in fetal calf serum were needed for full completion of mitosis. On the other hand, the cytostatic effect of 20-hydroxyecdysone
was reversible, and, prior exposure of the cells to the hormone allowed the cells to complete one cell cycle in serum-free
medium. These results suggest that the production of autocrine growth factors induced by ecdysteroids could circumvent the
absence of serum. This cell culture model provides potential for further study of interactions between ecdysteroids and growth
factor homologs during differentiation of insect epidermal cells. 相似文献
57.
58.
59.
Lines of wheat with the 6Mv chromosome from Aegilops ventricosa display partial resistance to both pathotypes Hal2 and Ha41 of Heterodera avenae. With either pathotype, the effect of this alien chromosome on cyst production, size, and fecundity was expressed in resistance tests. Partial resistance of five 6Mv(6D) substitution lines varied according to the intrinsic cyst-forming capacity of the nematode pathotypes and the recipient germplasms. Such partial resistance can be utilized in wheat breeding lines for integrated management of the cereal cyst nematode. 相似文献
60.
S. CARRÉ J. N. TASEI J. Le GUEN J. MESQUIDA G. MORIN 《The Annals of applied biology》1993,122(3):555-568
A simplified and non-destructive method using starch gel electrophoresis has been developed on seeds to identify inbred lines of Vicia faba and assess outcrossing rates and gene dispersal in pollination experiments. Six enzyme systems (Alcohol dehydrogenase, Aspartate aminotransferase, Glucose-6-phosphate isomerase, Isocitrate dehydrogenase, Phosphogluconate dehydrogenase and Shikimate dehydrogenase) were analysed from parental lines, crosses performed between lines bearing dissimilar isozyme patterns in pollination cages with Bombus and F2 progenies obtained from manual selfing of F1 hybrids. The allozymes at each of the seven studied loci segregated in the expected Mendelian fashion and behaved in a co-dominant manner except for the Adh-2 locus where the only variant was a null allele. No evidence of genetic linkage was observed between at least 13 of the 15 pairs of the studied loci. Percentage of cross fertilisation by Bombus between seven pairs of inbred lines ranged between 1.7% and 28.3%. Pollen transfer between a donor line and a recipient line by two species of Bombus did not lead to differences in outcrossing rates (both about 8%). The new PGD marker with two loci at three alleles each is particularly discriminating and valuable in pollination studies and breeding of V. faba. 相似文献