全文获取类型
收费全文 | 2117篇 |
免费 | 53篇 |
国内免费 | 223篇 |
专业分类
2393篇 |
出版年
2023年 | 14篇 |
2022年 | 17篇 |
2021年 | 33篇 |
2020年 | 37篇 |
2019年 | 26篇 |
2018年 | 25篇 |
2017年 | 25篇 |
2016年 | 28篇 |
2015年 | 53篇 |
2014年 | 61篇 |
2013年 | 98篇 |
2012年 | 83篇 |
2011年 | 78篇 |
2010年 | 74篇 |
2009年 | 107篇 |
2008年 | 91篇 |
2007年 | 113篇 |
2006年 | 99篇 |
2005年 | 93篇 |
2004年 | 94篇 |
2003年 | 111篇 |
2002年 | 81篇 |
2001年 | 88篇 |
2000年 | 69篇 |
1999年 | 51篇 |
1998年 | 58篇 |
1997年 | 59篇 |
1996年 | 79篇 |
1995年 | 61篇 |
1994年 | 62篇 |
1993年 | 53篇 |
1992年 | 48篇 |
1991年 | 40篇 |
1990年 | 32篇 |
1989年 | 27篇 |
1988年 | 20篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 22篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1977年 | 16篇 |
1976年 | 10篇 |
1975年 | 14篇 |
1974年 | 15篇 |
1973年 | 9篇 |
排序方式: 共有2393条查询结果,搜索用时 15 毫秒
61.
62.
63.
Previously we have demonstrated the dynamic change of microtubules (MTs) during cell cycle progression using highly synchronized tobacco BY-2 cells and characterized the specific transition points of MT organization (Hasezawa and Nagata, 1991). In this study the effect of okadaic acid (OA), a specific inhibitor of protein phosphatase 1 and 2A, on such changes of MTs during cell cycle was examined. These experiments revealed that cell cycle was arrested before the formation of the preprophase band (PPB), at anaphase and at the border of M/G1. Although the block at the anaphase seemed to be analogous to that observed in animal cells (Yamashita et al., 1990), the other two blocks were specific to plant cells. It is interesting that these two blocks coincided with the transition points of MT organization, as revealed in the previous study (Hasezawa and Nagata, 1991). Thus it is proposed that phosphorylation is involved in MT organization, although the effect of OA has been shown mainly to be the activation of cdc-2/histone H1 kinase in animal cells. Another inhibitor of protein phosphatase 1 and 2A, calyculin A (CLA), showed very similar effects on the cell cycle progression. The use of such inhibitors to dissect the cell cycle progression of plant cells is discussed. 相似文献
64.
Genetically uniform burley tobacco (Nicotiana tabacum) was grown under field and various controlled-environment conditions to determine whether environment influenced epicuticular alkane, fatty acid, and fatty-alcohol composition of the leaves. Quantity and quality of alkanes, fatty acids, and fatty alcohols were greatly influenced by environmental conditions. Highest light intensity did not result in the largest total long aliphatic carbon-chain production. Generally, long photoperiod and cool temperature were associated with highest long aliphatic carbon-chain production on a leaf area basis. Quantity of the individual alkane, fatty acid, or fatty alcohol classes present under the different growth conditions varied in relation to the leaf metabolic status and not leaf size. 相似文献
65.
66.
67.
Heat shock induced proteins in plant cells 总被引:1,自引:0,他引:1
Thomas Barnett Mitchell Altschuler Carl N. McDaniel Joseph P. Mascarenhas 《Genesis (New York, N.Y. : 2000)》1979,1(4):331-340
Tobacco (Nicotiana tabacum) and soybean (Glycine max) tissue culture cells were exposed to a heat shock and protein synthesis studied by SDS-polyacrylamide gel electrophoresis after labeling with radioactive amino acids. A new pattern of protein synthesis is observed in heat-shocked cells compared to that in control cells. About 12 protein bands, some newly appearing, others synthesized in greatly increased quantities in heat-shock cells, are seen. Several of the heat-shock proteins (HSPs) in both tobacco and soybean are similar in size. One of the HSPs in soybean (76K) shares peptide homology with its presumptive 25°C counterpart, indicating that the synthesis of at least some HSPs may not be due to activation of new genes. The optimum temperature for maximal induction of most HSPs is 39–40°C. Total protein synthesis decreases as heat-shock temperature is increased and is barely detectable at 45°C. The heat-shock response is maintained for a relatively short time in tobacco cells. After 3 hr at 39°C, a decrease is seen in the synthesis of the HSPs, and after 4 hr practically no HSPs are synthesized. After exposure to 39°C for 1 hr, followed by a return of tobacco cells to 26°C, recovery to the control pattern of synthesis requires greater than 6 hours. These results indicate that cells of flowering plants exhibit a heat-shock response similar to that observed in animal cells. 相似文献
68.
Ross H. Hall 《In vitro cellular & developmental biology. Plant》1976,12(3):216-224
Summary Cells possess extraordinary powers to organize their molecular processes not only to maintain a cell in a given steady state
but also to recognize that state during differentiation. Regulation of these organizational forces appears to be under the
control of chemical factors, and a hormonal concept of regulation has evolved. Hormones have been considered to act by reacting
with a specific target site. This may be part of their mode of action, but I would like to suggest that a hormone enters and
becomes part of a total molecular resonance system. In so doing, the entire molecular system of the cell is modified.
Of the known plant hormones, the cytokinins, because of their role in experimentally induced cell division and differentiation,
serve as a probe of hormonal involvement in differentiation. Cultured somatic cells of tobacco plants can be induced to undergo
differentiation by addition of cytokinin and auxin to the medium. Studies of the cytokinin hormones show a series of diverse
molecular involvements. The archetype cytokinin, N6-(Δ2-isopentenyl) adenosine (i6Ado), occurs in some molecular species of tRNA where it plays a vital role in the codon-anticodon interaction of tRNA and
m-RNA. i6Ado under-goes extensive metabolism in the tobacco tissue. It is either degraded to adenosine or converted to derivatives
that possess biological activity. It is perhaps, therefore, more correct to consider the hormone function as being derived
from this total metabolic web.
The normal somatic cells of tobacco cultures spontaneously change occasionally into an autonomous form that requires no external
growth factors. This line of cells synthesizes i6Ado. The metabolic web of the hormone-dependent strain can be perturbed by added auxin but such is not the case in the autonomous
strain. These data provide some insight into the altered state of cytokinin activity in which a cell line changes into an
autonomous form. Curiously, in become independent of the requirement for exogenous cytokinin, the autonomous tissue becomes
sensitive to added cytokinin. i6Ado also inhibits the growth of lines of mammalian cancer cells grown in culture.
Presented in the formal symposium on Information Transfer in Eukaryotic Cells, at the 26th Annual Meeting of the Tissue Culture
Association, Montreal, Quebec, June 2–5, 1975. 相似文献
69.
Bernard L. Powell Jerry W. Pickering Simon H. Wender Eddie C. Smith 《Phytochemistry》1975,14(8):1715-1717
Two anodic isoperoxidases (A1 and A2) from tobacco tissue culture W-38 and two cathodic isoperoxidases (C3 and C4) from tobacco suspension culture WR-132 have been separated and characterized. Molecular weights for each of the isoperoxidases have been determined by two different methods. Only C4 contained a carbohydrate component. The substrate specificity and the pH optima for the four enzymes with each of five substrates were determined. 相似文献
70.
转金属硫蛋白基因(MT1)烟草耐NaCl胁迫能力 总被引:1,自引:0,他引:1
为明确柽柳(Tamarix sp.)金属硫蛋白(MT1)基因过量表达对提高植物耐NaCl能力的作用,对转MT1因烟草进行分子检测和生理特性分析,结果表明具有卡那霉素抗性的转基因植株经RT-PCR Southern杂交均表现为阳性,说明外源MT1基因已整合到烟草基因组,并且得到了表达。金属硫蛋白基因的过量表达提高了转基因烟草植株的耐NaCl能力,表现为在含有150mmol/L和300mmol/L NaCl的MS培养基上,转基因植株的株高和鲜重均明显优于非转基因株系;在生理性状上表现为转基因植株丙二醛(MDA)含量明显低于非转基因株系,而超氧化物歧化酶(SOD)、过氧化物酶(POD)活性比非转基因株系明显增加。 相似文献