全文获取类型
收费全文 | 19137篇 |
免费 | 1267篇 |
国内免费 | 688篇 |
专业分类
21092篇 |
出版年
2023年 | 203篇 |
2022年 | 368篇 |
2021年 | 653篇 |
2020年 | 424篇 |
2019年 | 516篇 |
2018年 | 804篇 |
2017年 | 675篇 |
2016年 | 780篇 |
2015年 | 897篇 |
2014年 | 1135篇 |
2013年 | 1461篇 |
2012年 | 1577篇 |
2011年 | 1534篇 |
2010年 | 973篇 |
2009年 | 744篇 |
2008年 | 759篇 |
2007年 | 628篇 |
2006年 | 570篇 |
2005年 | 374篇 |
2004年 | 311篇 |
2003年 | 310篇 |
2002年 | 253篇 |
2001年 | 288篇 |
2000年 | 270篇 |
1999年 | 261篇 |
1998年 | 182篇 |
1997年 | 190篇 |
1996年 | 189篇 |
1995年 | 183篇 |
1994年 | 150篇 |
1993年 | 127篇 |
1992年 | 167篇 |
1991年 | 168篇 |
1990年 | 119篇 |
1989年 | 116篇 |
1988年 | 124篇 |
1987年 | 119篇 |
1986年 | 105篇 |
1985年 | 149篇 |
1984年 | 129篇 |
1983年 | 119篇 |
1982年 | 112篇 |
1981年 | 119篇 |
1980年 | 83篇 |
1979年 | 107篇 |
1978年 | 91篇 |
1977年 | 83篇 |
1975年 | 85篇 |
1974年 | 94篇 |
1969年 | 92篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The effects of 41 benzothiazolium salts on Euglena gracilis were characterized with regard to the influence on growth and on chlorophyll synthesis, and to their ability to induce permanent loss of chloroplasts. Some salts induced white mutants of E. gracilis (the first benzothiazole derivatives with this activity). The relationship between the biological effect and chemical structure was confirmed and expressed quantitatively by means of Free - Wilson and Fujita - Ban analysis. 相似文献
22.
In submerged Claviceps cultures the activity of hydroxymethylglutaryl-CoA reductase preceded the increase of alkaloid production and of sterol content. During the first alkaloid phase, cell mevalonate was involved in the biosynthesis of both alkaloids and steroids. In the second production phase, it was predominantly used for alkaloid synthesis. Hydroxymethylglutaryl-CoA reductase appears to be a suitable target for physiological manipulation to increase clavine alkaloid yields. 相似文献
23.
Corynebacterium glutamicum CBII, in the stationary phase of growth, was found to produce spontaneously a substance resembling bacteriocins by its bactericidal properties. This substance designated glutamicin CBII was observed to exhibit bactericidal activity against coryneform bacteria (12 species tested) but not against unrelated gram-positive (3) and gram-negative (3) bacteria, while its action on bacteria with no quite known relatedness to the coryneform group (14) was found to be variable. Glutamicin CBII was partially purified by precipitation with ammonium sulphate (70% saturation), selective heat precipitation and gel chromatography on Sepadex G-50. The antibacterial substance diffused through cellophane membrane with an approximate cut-off of 10000 dalton and its sedimentation coefficient was determined to be 1.1. S by ultracentrifugation. Heating at 100°C for 30 min had no effect on its activity. Glutamicin CBII was proved to be resistant to chloroform, trypsin, chymotrypsin, pronase, and subtilisin. According to its staining behaviour and 1H NMR spectra it probably represents a glycoprotein containing only a minor protein component.
相似文献
相似文献
24.
Curves relating net photosynthetic rate to irradiance [P(I) curve relation] were estimated and analysed inMercurialis perennis L. plants stemming from three forest (spruce, beech and ash) stands with different tree leaf canopy development and different
light regime.
The saturating irradiance (Is) reached the highest values in plants of all three stands in spring (spruce forest: 438 W m−2, beech forest: 440 W m−2 and ash forest: 367 W m−2), it declined sharply in the middle of the growing season (283, 285 and 297 W m-2, respectively) and this Is level persisted until autumn. A pronounced dynamics in plants from spruce and beech forests made itself manifest also in
the adaptation (Ia) and compensating (Ic) irradiances, respectively. After a sudden decline in summer, values in autumn were close to those of the vernal season.
The most pronounced parameter, which optimally expressed the adaptation ofMercurialis perennis to various light conditions, was the photosynthetic efficiency (α) calculated as the slope of the linear part of the curve
relating net photosynthetic rate to irradiance.
At the time of the highest PN sat. value in course of the growing season (August) (spruce forest: 100, beech forest: 98.7 and ash forest: 85.8 μg CO2 m−2 s−1), RD was in its minimum; in autumn PN sat. reached the lowest values which corresponded to the most intensive RD.
It was found thatMercurialis perennis plants stemming from forest stands with different light conditions did not make use equally of the altering light conditions
in the course of the growing season. By the underlying analysis of P(I) curves this rhizomatous perennial herb (geophyte)
may be characterized as a shade tolerant species. 相似文献
25.
Formation of protoplasts and their reversion were followed in 7 strains of brevibacteria. The formation of protoplasts and
their reversion differed both between various species of brevibacteria and between various mutant strains of the same species. 相似文献
26.
27.
Vera Hadačová Květa Vacková Eva Klozová M. Kutáček Květa Pitterová 《Biologia Plantarum》1983,25(3):209-215
In partly purified protein complexes obtained from 22 species of theAllium genus and 6 cultivars ofAllium cepa the activity of cholinesterases was detected and measured using the method of Ellman et al. The degree of its inhibition with 10-4 M neostigmine was also tested. It was found that the activity of cholinesterase differed in individual species up to two hundred times, while the differences in the inhibitory activity of 10-4 M neostigmine occurred only in a few cases. Individual sections and cultivars could not be characterized on the basis of the differences in the activities of the cholinesterases. Of all the sections that ofPhyllodolon shows the highest average activity. In the case of the tested cultivars distinctly the lowest activity was observed in cv. Kastická. The values of the enzymatic activity measured by Ellman’s method in this plant material include the activity of specific and unspecific cholinesterases and the part uninhibitable by neostigmine. 相似文献
28.
29.
30.