全文获取类型
收费全文 | 63645篇 |
免费 | 4025篇 |
国内免费 | 10篇 |
出版年
2023年 | 457篇 |
2022年 | 407篇 |
2021年 | 859篇 |
2020年 | 796篇 |
2019年 | 764篇 |
2018年 | 2001篇 |
2017年 | 1859篇 |
2016年 | 2436篇 |
2015年 | 3175篇 |
2014年 | 3127篇 |
2013年 | 4263篇 |
2012年 | 5063篇 |
2011年 | 4543篇 |
2010年 | 2839篇 |
2009年 | 2162篇 |
2008年 | 3537篇 |
2007年 | 3321篇 |
2006年 | 3128篇 |
2005年 | 2681篇 |
2004年 | 2579篇 |
2003年 | 2335篇 |
2002年 | 2134篇 |
2001年 | 1400篇 |
2000年 | 1395篇 |
1999年 | 1073篇 |
1998年 | 461篇 |
1997年 | 334篇 |
1996年 | 336篇 |
1995年 | 325篇 |
1994年 | 259篇 |
1993年 | 229篇 |
1992年 | 535篇 |
1991年 | 458篇 |
1990年 | 420篇 |
1989年 | 412篇 |
1988年 | 403篇 |
1987年 | 358篇 |
1986年 | 341篇 |
1985年 | 345篇 |
1984年 | 355篇 |
1983年 | 242篇 |
1982年 | 228篇 |
1981年 | 178篇 |
1980年 | 181篇 |
1979年 | 220篇 |
1978年 | 213篇 |
1975年 | 200篇 |
1974年 | 218篇 |
1973年 | 224篇 |
1972年 | 185篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
The role and source of gibberellins (GAs) involved in the development of parthenocarpic fruits of Pisum sativum L. has been investigated. Gibberellins applied to the leaf adjacent to an emasculated ovary induced parthenocarpic fruit development on intact plants. The application of gibberellic acid (GA3) had to be done within 1 d of anthesis to be fully effective and the response was concentration-dependent. Gibberellin A1 and GA3 worked equally well and GA20 was less efficient. [3H]Gibberellin A1 applied to the leaf accumulated in the ovary and the accumulation was related to the growth response. These experiments show that GA applied to the leaf in high enough concentration is translocated to the ovary. Emasculated ovaries on decapitated pea plants develop without application of growth hormones. When [3H] GA1 was applied to the leaf adjacent to the ovary a substantial amount of radioactivity accumulated in the growing shoot of intact plants. In decapitated plants, however, this radioactivity was mainly found in the ovary. There it caused growth proportional to the accumulation of CA1. Application of LAB 150978, an inhibitor of GA biosynthesis, to decapitated plants inhibited parthenocarpic fruit development and this inhibition was counteracted by the application of GA3 (either to the fruit, or the leaf adjacent to the ovary, or through the lower cut end of the stem). All evidence taken together supports the view that parthenocarpic pea fruit development on topped plants depends on the import of gibberellins or their precursors, probably from the vegetative aerial parts of the plant.Abbreviations FW
flesh weight
- GAn
gibberellin An
- HPLC
high-performance liquid chromatography 相似文献
262.
Effects of social isolation and crowding upon adrenocortical reactivity and behavior in the rat 总被引:2,自引:0,他引:2
The effects of social isolation and crowding on adrenocortical function and upon behavioral responsiveness to electric shock have been studied in male and female rats. All female experimental groups showed higher corticosterone levels and heavier adrenals than their male counterparts. The major effect of housing condition concerned the corticosterone response to stress, while basal hormone concentration was not modified. Socially housed rats showed a more intense adrenocortical response and also a greater behavioral reactivity to electric shock than the isolates. 相似文献
263.
D Barettino G Morcillo J L Díez M T Carretero M J Carmona 《Biochimie et biologie cellulaire》1988,66(11):1177-1185
264.
M Kedra-Luboínska E Zamecka Z Porembska 《Biochemical medicine and metabolic biology》1988,39(3):247-257
1. Two forms of arginase were isolated from human erythrocytes; the main form adsorbed on CM-cellulose and the second form, occurring in much smaller amount, adsorbed on DEAE-cellulose. 2. The molecular weight of either arginase was 120,000 +/- 5000. 3. The erythrocyte arginases are similar in immunological properties to arginase A4 from human kidney and A2 from human liver, respectively. 4. Despite the literature data stating that human erythrocyte arginase and human liver arginase are identical, it was found that the main forms of arginase of these tissues A4 from erythrocytes and A5 from liver differ in immunological properties. 相似文献
265.
N-Succinyl-glycyl-leucyl-cystein(S-benzyl) p-nitroanilide and N-succinyl-leucyl-leucyl-cystein(S-benzyl) p-nitroanilide were found to be very sensitive substrates for the assay of papain, ficin, and bromelain. These p-nitroanilides were hydrolyzed only very slightly by chymotrypsin, but not detectably by trypsin. 相似文献
266.
Summary Phenotypic analyses of genetic combinations involving the gene extramacrochaetae (emc) reveal its participation in the differentiation of both sensory elements and wing veins. The study of near-amorphic alleles of emc in mitotitc recombination clones indicates that it also affects cell proliferation. These clones show abnormal sizes, shapes and spatial distribution. They differentiate extra sensory elements as well as extra veins. A gain of function mutation in the gene causes opposite phenotypes in both differentiation systems. The effects of the mutant on proliferation and patterning are consistent with the emc gene being involved in the transfer of information between neighbouring cells, which leads to the spatial expression of the achaetescute gene complex and genes involved in vein formation. 相似文献
267.
J. Šťovíčková J. Turková B. Urbánek V. Bažant J. Kavalírová 《Biotechnology Techniques》1988,2(2):121-126
Summary The effect was studied of the method of drying chymotrypsin attached to bead cellulose on its chemical and physical characteristics. These characteristics are not deteriorated when replacing the commonly used lyophilisation by fluid drying in the air stream. The preparations saved essentially the same proteolytic activity as well as stability even when increasing the drying air temperature to 70°C. 相似文献
268.
In order to improve the interpretation of the results of pollen analyses concerning mediaeval anthropogenous sediments a set of recent seeds of the principal cereals was pollenanalytically elaborated. The aim was to find out whether pollen grains can be preserved on mature seeds. The pollen spectra obtained from the material of mediaeval anthropogenous sediments include, in most cases, a large amount of pollen of certain plants including cereals. It is suggested that part of the pollen spectra from anthropogenous sediments need not come from air transport, i.e. from the surrounding vegetation; it could get into waste pits in another way. Above all, some foodstuffs were considered to be the sources of pollen grains. The origin of some grains coming from honey and from plant infusions has, at least partly, been demonstrated (Jankovská 1987). As the next step, attention was paid to other products, mainly those of cereals. An experimental pollen analysis of recent seeds of selected cereals showed that pollen grains are preserved on their surface, often in high concentrations. This is due, above all, to the cleistogamy of most cereals. The highest values of pollen grains have so far been found inAvena sativa andPanicum milliaceum. Triticum aestivum andHordeum vulgare showed lower values of pollen grains. The lowest amounts were found in heterogamousSecale cereale. Simultaneously, the pollen of plants growing in a neighbourhood, above all the pollen of field weeds, was found sticking to the seeds. 相似文献
269.
270.
Ivo Šafařík 《Journal of industrial microbiology & biotechnology》1988,3(4):259-261
Summary A new insoluble chromogenic substrate for the determination of proteolytic activity was developed. This substrate was prepared by incorporating black drawing ink into casein and heating this complex at 200°C for 4 h. It is especially suitable for determining the activity of alkaline bacterial proteinases. 相似文献