全文获取类型
收费全文 | 2813篇 |
免费 | 90篇 |
国内免费 | 169篇 |
出版年
2023年 | 15篇 |
2022年 | 25篇 |
2021年 | 67篇 |
2020年 | 37篇 |
2019年 | 45篇 |
2018年 | 38篇 |
2017年 | 45篇 |
2016年 | 48篇 |
2015年 | 68篇 |
2014年 | 88篇 |
2013年 | 108篇 |
2012年 | 91篇 |
2011年 | 102篇 |
2010年 | 73篇 |
2009年 | 123篇 |
2008年 | 152篇 |
2007年 | 139篇 |
2006年 | 148篇 |
2005年 | 112篇 |
2004年 | 113篇 |
2003年 | 95篇 |
2002年 | 81篇 |
2001年 | 97篇 |
2000年 | 80篇 |
1999年 | 109篇 |
1998年 | 65篇 |
1997年 | 80篇 |
1996年 | 84篇 |
1995年 | 94篇 |
1994年 | 45篇 |
1993年 | 45篇 |
1992年 | 51篇 |
1991年 | 60篇 |
1990年 | 55篇 |
1989年 | 43篇 |
1988年 | 40篇 |
1987年 | 51篇 |
1986年 | 29篇 |
1985年 | 32篇 |
1984年 | 43篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 24篇 |
1980年 | 30篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1974年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有3072条查询结果,搜索用时 15 毫秒
61.
Co-culture of rabbit 2-cell embryos with rabbit oviduct epithelial cells and other somatic cells 总被引:2,自引:0,他引:2
E W Carney C Tobback J E Ellington R H Foote 《Molecular reproduction and development》1990,27(3):209-215
Rabbit 2-cell embryos were co-cultured in Basel Synthetic Medium II + 10% fetal bovine serum with one of the following: primary cultures of rabbit oviduct epithelial cells (ROEC), a rabbit kidney epithelioid cell line (RK13), a rabbit epidermal epithelioid cell line (Sf1), or a rabbit skin fibroblast-like cell line (RAB9). Embryos cultured in medium alone served as controls. After 4 d of culture at 39 degrees C in 5% CO2 in air, 77-93% of the rabbit embryos which were co-cultured with somatic cells had reached the blastocyst stage, and 60-76% were hatching through their zonae pellucidae. These percentages, however, were not significantly different (P greater than .05) from those of embryos in medium alone, of which 90% had reached the blastocyst stage and 83% were hatching. Mean intrazonal embryo diameters also did not differ significantly among treatments (239-302 microns). Bovine 1-8-cell embryos were also co-cultured with ROEC. This stimulated 60% of these embryos to develop beyond the so-called "16-cell block" in vitro, whereas 0% of the embryos cultured in medium alone developed past this block. Evaluation of the ROEC cultures by light microscopy, immunocytochemistry, and gel electrophoretic analysis of conditioned medium, together with the positive results with bovine embryos, indicate that the ROEC culture partially simulates oviductal conditions in vivo. Therefore, our results suggest that oviduct epithelial cells may play a less pivotal role in regulating early development in the rabbit than in the cow.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
62.
T. C. Hsu Edward J. Shillitoe Lorraine M. Cherry Qi Lin Stimson P. Schantz Cynthia Furlong 《In vitro cellular & developmental biology. Plant》1990,26(1):80-84
Summary Forty lymphoblastoid (lymphoid) lines were established from 42 volunteer blood donors, including healthy individuals and patients
with head and neck carcinomas. Each peripheral blood sample was split into two portions, one for the establishment of a lymphoid
line and the other for short-term culture, which was used to estimate bleomycin sensitivity by cytogenetic procedures. Twenty
lymphoid lines were selected at random to compare bleomycin sensitivity with data obtained from short-term lymphocyte cultures.
In each set, bleomycin sensitivity of lymphoid cells was similar to that of the lymphocytes. The lymphoid lines, which can
be propagated for an unlimited supply of relatively homogeneous cellular material, will be useful for a variety of future
investigations.
This investigation was supported by grants from the John S. Dunn Foundation, Houston, TX, the Esther Knispel Fund administered
by The University of Texas M. D. Anderson Cancer Center, Houston, TX, and Department of Health and Human Services PHS grant
DE 07007. 相似文献
63.
M. Sari-Gorla L. Rampoldi G. Binelli C. Frova M. E. Pè 《Molecular & general genetics : MGG》1996,251(5):551-555
Genetic factors controlling tolerance to the herbicide Alachlor in maize were localised by means of two different strategies. In the first approach, backcross (BC) plants, derived from pollen which had been subjected to selective pressure for resistance to the herbicide, were analysed for segregation distortion at 47 RFLP loci and compared to BC plants obtained from non-selected pollen. Preferential transmission of five chromosomal regions where putative QTLs (Quantitative Trait Loci) are localised was revealed in the BC plants from selected pollen. A second approach was based on a classical linkage analysis for segregation of the same set of RFLPs and factors controlling the trait, in a BC population of 210 individuals, by means of regression analysis. This study detected seven significant loci in four genomic regions. Overall, two loci revealed both segregation distortion and association with the expression of the trait, indicating linkage to genes expressed in both gametophytic and sporophytic phase. Three chromosomal regions appeared to carry factors involved in plant tolerance to Alachlor which are not expressed in pollen. Conversely, three loci were linked to factors selectable in pollen, but did not reveal significant association with tolerance in the plant in the segregating populations. 相似文献
64.
Maize is a cereal particularly lacking in tryptophan, which is the precursor of serotonin, an important neurotransmitter.
Altough complementary foods may eliminate tryptophan deficiency, serotonin deficiency may often continue to exist because
of competition made by other Large Neutral Amino Acids (LNAA) against tryptophan for neuron access, since they use the same
carrier to cross the blood-brain barrier. Thus serotonin synthesis depends on two variables: the amount of tryptophan and
the trp/LNAA ratio (R). “R” is lowest for common maize, low for beans and, as a rule, for most vegetable foods, higher for
meat. So, when maize is the preponderant food in the meal, the “R” value lowers and so in parallel serotonin synthesis does.
Serotonin deficiency involves several behavioural consequences, such as the tendency towards aggressive behaviour or the religious
fanaticism. Among native american populations, these consequences appear, as a rule, positively correlated with maize alimentary
dependence (Aztecs appear as those who greatly suffered from serotonin deficiency). In the world these are thinkable for some
african populations (i.e. Zulu) or european (i.e. Balkan peoples). 相似文献
65.
小麦×玉米杂交后代的蛋白质及酯酶同工酶分析 总被引:9,自引:0,他引:9
以8 个普通小麦(Triticum aestivum L.)品种为母本,2 个栽培玉米(Zea m ays L.)品种为父本杂交所获得的F2 代在形态上出现了明显变异。对其籽粒进行蛋白质电泳分析,得到了如下主要结果:杂交后代的蛋白质谱带较母本有了很大的变异,主要集中在高分子量麦谷蛋白(HMW-Glu)区域。杂交后代的蛋白质谱带由5 种类型构成:1.母本型,占全部测试籽粒的22.6% ;2.附加型,占14.3% ;3.互补型,占15.5% ;4.杂种型,占30.9% ;5.缺失型,占16.7% 。对“矮杆早”ד紫粘”的F2 代籽粒进行酯酶同工酶电泳分析发现,变异主要发生在EST-1 区。由此看来,小麦×玉米的杂合子中玉米染色体在被排除前后,可以诱发小麦染色体组发生遗传变异 相似文献
66.
五种野生稻叶绿体DNA多态性研究 总被引:7,自引:0,他引:7
对野生稻 5个种的18个材料的叶绿体DNA(cpDNA)进行了EcoRI的RFLP分析。
结果显示,共有10种酶切模式,不同种野生稻的cpDNA的RFLP类型都不同,而且在其中一些
种内也有变化,尤以O.rufipogon的种内多态性最为显著,并主要与地理来源有关。本研究还在O.punctata的材料中发现一种以往的分析都不曾描述过的多态性模式。通过对结果的分析,探讨了不同种类野生稻的叶绿体基因组之间以及它们与核基因组之间的进化关系。
Abstract:The polymorphisms of chloroplast DNA from 18 materials of 5 wild rice species were investigated using RFLP analysis.10 restriction patterns were obtained from the analysis of these materials.Different species had different of its RFLP patterns chloroplast DNA,and the polymorphisms existed even with species,especially in O.rufipogon varieties of different geographical origins.In O.punctata a new type of rice chloroplast DNA restriction pattern was discovered which had not been reported before.According to the results obtained,the evolutionary relationships among chlorplast genomes,and between chloroplast and nuclear genomes in different wild rice are discussed. 相似文献
67.
从每公斤萌发24h的玉米胚丙酮粉中可提纯得63mg的钙调素(CaM),这是目前从每公斤植物材料中所提纯得CaM的最高记录。对其理化性质的研究表明,玉米胚CaM 有较高的生物学活性,能较好地激活磷酸二酯酶,其紫色吸收光谱,SDS-PAGE电泳行为及氨基酸组成与其它的植物CaM相似。上述结果表明玉米胚是1个提取植物CaM相似。上述结果表明玉米胚是1个提取植物CaM的适宜材料。 相似文献
68.
69.
Summary The orientation of cortical microtubules in plant cells has been extensively studied, in part because of their influence on the expansion of most plant cell types. Cortical microtubules are often arranged in helical arrays, which are well known to occur with a specific pitch as a function of development or experimental treatment; however, it is not known if the handedness of helical arrays can also be specified. We have studied the handedness of helical arrays by using Vibratome sectioning of maize primary roots and confocal microscopy of Arabidopsis primary roots. In cortical cells of maize roots, the helical array was found to have the same handedness at a given position, not only for the cells of a single root, but also for the cells of more than one hundred roots examined. Quantification of angular distribution of apparent individual microtubules showed that defined regions of the root were composed of cells with highly uniform microtubule orientation. In the region between transverse and longitudinal microtubules (5–10.5 mm from the tip), the array formed a right-handed helix, and basal of cells with longitudinal microtubules (11.5–15 mm from the tip), the array formed a left-handed helix. Similarly, in epidermal cells of Arabidopsis roots right-handed helical arrays were found in the region between transverse and longitudinal microtubules. These results suggest that, in addition to the orientation of microtubules, the handedness of helical microtubule arrays is under cellular control.Abbreviations Cy3
indocarbocyanine
- PBS
phosphate-buffered saline
- PIPES
piperazine-N,N-bis-[2-ethanesulfonic acid] 相似文献
70.
S. Saisingtong J. E. Schmid P. Stamp B. Büter 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,92(8):1017-1023
Efficient methods of chromosome doubling are critical for the production of microspore-derived, doubled-haploid (=DH) plants, especially if, as in maize anther culture, spontaneous chromosome doubling occurs infrequently. In the present study, colchicine (5–1000 mg/l) was added to the induction medium and maize anthers were incubated in the colchicine-containing medium for different durations (1–7 days). In order to improve overall anther culture response, the culture temperature was adjusted to 14°C during the first 7 days. Colchicine applied at low concentration, i.e. 5 mg/l (7 days), or for short duration, i.e. 1–3 days (250 mg/l), showed beneficial effects on the formation of embryolike structures (=ES) and thus led to increased plant production, but was comparatively ineffective regarding chromosome doubling. Optimal doubling effects were observed when anthers had been exposed to culture medium containing 250 and 1000 mg/l of colchicine (7 days); in these treatments the doubling index (=DI), defined as the quotient of the number of DH plants and the number of totally regenerated plants in a specific treatment, rose to 0.56 and 0.53, respectively, compared to 0.20 in the untreated control. However, colchicine administered at concentrations higher than 250 mg/l seemed to be detrimental to general plant production; thus, in spite of a high DI, the overall DH plant production was even lower than in the control treatment. Maximum DH plant production for three different genotypes was accomplished with culture medium containing 250 mg/l of colchicine (7 days). With the best-responding genotype (ETH-M 36) a DH plant production of 9.9 DH plants/100 anthers was accomplished, i.e. a 7-fold increase compared to the non-treated anthers. This is the first report on efficient chromosome doubling in anther culture by subjecting anthers to colchicinecontaining induction medium during a post-plating cold treatment. Chromosome doubling as described here becomes an integral part of the maize anther culture protocol and thus represents a rapid and economical way to produce DH plants. 相似文献