全文获取类型
收费全文 | 2058篇 |
免费 | 76篇 |
国内免费 | 55篇 |
专业分类
2189篇 |
出版年
2023年 | 21篇 |
2022年 | 36篇 |
2021年 | 41篇 |
2020年 | 31篇 |
2019年 | 43篇 |
2018年 | 50篇 |
2017年 | 39篇 |
2016年 | 37篇 |
2015年 | 52篇 |
2014年 | 139篇 |
2013年 | 138篇 |
2012年 | 103篇 |
2011年 | 134篇 |
2010年 | 149篇 |
2009年 | 98篇 |
2008年 | 91篇 |
2007年 | 111篇 |
2006年 | 89篇 |
2005年 | 76篇 |
2004年 | 55篇 |
2003年 | 49篇 |
2002年 | 54篇 |
2001年 | 39篇 |
2000年 | 36篇 |
1999年 | 25篇 |
1998年 | 31篇 |
1997年 | 24篇 |
1996年 | 25篇 |
1995年 | 31篇 |
1994年 | 40篇 |
1993年 | 22篇 |
1992年 | 28篇 |
1991年 | 24篇 |
1990年 | 20篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 18篇 |
1986年 | 24篇 |
1985年 | 12篇 |
1984年 | 30篇 |
1983年 | 20篇 |
1982年 | 32篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有2189条查询结果,搜索用时 0 毫秒
1.
Papers on the mechanisms of translation initiation in mammals studied by reconstruction of initiation complexes from individual components are reviewed. The author points to the constraints of this approach and to the pitfalls ignoring which one might come to erroneous conclusions and even artifacts. In addition, some methods employed in the field as well as some technical problems are discussed in the paper, together with the means of obviating them. The review could be a guidebook for newcomers into this quite labor-consuming field. 相似文献
2.
RegB is involved in the control of the phage T4 life cycle. It inactivates the phage early mRNAs when their translation is
no more required. We determined its structure and identified residues involved in substrate binding. For this, all backbone
and 90% of side-chain resonance frequencies were assigned. 相似文献
3.
The involvement of gibberellins in the control of flowering of sunflower was studied by direct application of GA3 to the apex of the plants, analysis of the endogenous levels of gibberellin-like substances at different plant ages, and indirectly by the application of paclobutrazol, an inhibitor of gibberellin synthesis. GA3 speeded-up flower initiation and floral apex development. The time of GA3 application was more critical than the amount of GA3 applied. The endogenous levels of gibberellin-like compounds increased significantly by day 15 after sowing. The application of paclobutrazol markedly delayed floral initiation and this effect was also depedent on plant age. Both GA3 and paclobutrazol had their greatest effects between 10 and 20 days after sowing suggesting that an increase in gibberellins in that time period plays a role in floral initiation. 相似文献
4.
5.
6.
7.
8.
9.
Aqueous extracts of smoke, derived from Themeda triandra, a fire-climax grass, and Passerina vulgaris, a fynbos plant, stimulated the growth of primary root sections of tomato roots in suspension culture. The optimal dilution for both extracts was 1:2000. Several of the fractions obtained from TLC separation of the Themeda and the Passerina extracts significantly promoted primary root growth. The auxins naphthaleneacetic acid (NAA), indolebutyric acid (IBA) and indoleacetic acid (IAA) were found to stimulate the growth of the primary root axis, with IAA and NAA significantly promoting lateral root number. Similarly, the naturally occurring cytokinins, zeatin and its derivatives (zeatin-O-glucoside; dihydrozeatin and zeatin riboside) stimulated primary root length. Zeatin and dihydrozeatin promoted secondary root growth, but only at very low concentrations. 相似文献
10.
A. Schulz 《Protoplasma》1986,130(1):12-26
Summary 48 hours after interrupting the root stele ofPisum, wound phloem initiated (proximally or distally to the wound) to reconnect the vascular stumps was found to contain some nucleate wound-sieve elements. At the elongating end of an incomplete wound-sieve tube these elements exhibit a sequence of ultrastructural changes as known from protophloem-sieve tubes. Elongation occurs by the addition of newly divided (wound-) sieve-element/companion-cell complexes. In order to dedifferentiate and assume a new specialization formerly quiescent stelar or cortical cells require at least one (mostly more) preliminary division. Companion cells are consequently obligatory sister cells to wound-sieve elements.By reconstruction using serial sections it could be shown that wound-sieve tubes elongate bidirectionally, starting in an early activated procambial cell of the stele. The elongation is directed by the existence of plasmodesmata, preferably when lying in primary pit fields, and by the plane of preceding divisions. Thus, the developing wound-sieve tube can deviate from the damaged bundle and radiate into the cortex as soon as the plane of the preceding divisions is favourable. In the opposite direction, elongating wound-sieve tubes run parallel to pre-existing phloem traces, thus broading their base at the bundle for the deviating part of the wound-sieve tube. Frequently an individual wound-sieve tube is supplemented at the bundle by a further wound-sieve tube which is partly running parallel to it. Both sieve tubes are interlinked with sieve plates by three-poled sieve elements.Ultrastructurally, the developmental changes of nucleate wound-sieve elements follow the known pattern. In spite of its contrasting origin and odd shape a mature wound-sieve element eventually has the same contents as regular sieve elements: sieve-element plastids, mitochondria, stacked ER and small amounts of P-protein within an electronlucent cytoplasm. 相似文献