全文获取类型
收费全文 | 7898篇 |
免费 | 537篇 |
专业分类
8435篇 |
出版年
2023年 | 85篇 |
2022年 | 65篇 |
2021年 | 145篇 |
2020年 | 116篇 |
2019年 | 118篇 |
2018年 | 354篇 |
2017年 | 283篇 |
2016年 | 344篇 |
2015年 | 286篇 |
2014年 | 348篇 |
2013年 | 584篇 |
2012年 | 640篇 |
2011年 | 672篇 |
2010年 | 420篇 |
2009年 | 276篇 |
2008年 | 246篇 |
2007年 | 211篇 |
2006年 | 248篇 |
2005年 | 114篇 |
2004年 | 145篇 |
2003年 | 116篇 |
2002年 | 86篇 |
2001年 | 102篇 |
2000年 | 106篇 |
1999年 | 116篇 |
1998年 | 85篇 |
1997年 | 78篇 |
1996年 | 77篇 |
1995年 | 87篇 |
1994年 | 71篇 |
1993年 | 65篇 |
1992年 | 80篇 |
1991年 | 70篇 |
1990年 | 56篇 |
1989年 | 73篇 |
1987年 | 66篇 |
1986年 | 58篇 |
1985年 | 75篇 |
1984年 | 61篇 |
1983年 | 66篇 |
1982年 | 59篇 |
1981年 | 69篇 |
1980年 | 57篇 |
1979年 | 80篇 |
1978年 | 57篇 |
1977年 | 62篇 |
1975年 | 52篇 |
1974年 | 59篇 |
1973年 | 52篇 |
1969年 | 56篇 |
排序方式: 共有8435条查询结果,搜索用时 15 毫秒
31.
The microbial community in the soil was analyzed during four weeks of a continuous enrichment of structural chernozem soil samples with a 0.1% solution of carboxymethyl cellulose (CMC) under aerobic and semianaerobic conditions. During the first 14 d, the total amount of the aerobic and anaerobic, cellulose-degrading microorganisms increased significantly. Various metabolic pathways were u‘ed te decompose the substrate: diverse metabolic systems were activated and different groups of microorganisms preferred in dependence on the presence of oxygen or the source of mineral nitrogen. In the later phases of cultivation, a decrease in the concentration of zymogenous microflora and in the level of substrate mineralization was observed ovon though CM-cellulase activity remained high. During the fourth week of cultivation, a conspicuous increase in the numbers of oligothropic bacteria occurring in the colcnies of the microorganisms degrading cellulose was found. The representatives of prosthecobacteria (Caulobacter, Hyphomicrobium, Prosthecomicrobium spp.) andSeliberia sp. were thus identified. This “microflora of dispersion” attends the zymogenous microbes degrading CMC and indicates later phases of the process of decomposition. 相似文献
32.
The effect of twelve detergents on aspartate ammonia-lyase activity of Escherichia alcalescens used for the production of L-aspartic acid was tested. Best permeabilization was found with Triton X-100, Slovafol 910 and Corona, a mixed commercial preparation. In contrast to Triton X-100 and Slovafol 910, a much narrower range of suitable concentrations was observed with Corona. 相似文献
33.
Jana Pospíšilová 《Biologia Plantarum》1988,30(5):393-396
UsingNicotiana tabacum L. plantlets cultivatedin vitro as a model system it was proved that osmotic adjustment may be caused by a decrease in water potential of substrate as well
as by a decrease in air humidity. 相似文献
34.
Phenolic acids were separated into three fractions and determined by HPLC inMedicago sativa callus culture at the age of two, three and four weeks. The contents of free and especially of predominating ester-bound
phenolic acids decreased with callus age to approx. 80 % while the content of phenolic acids nonextractable by methanol increased
byca. 90 %. The proportion of benzoic acid derivatives rose from 15 to 21 % within four weeks. The determined difference in the
contents of phenolic acids in the upper and lower parts of callus diminished with age. The content of bound forms was higher
in the lower part regardless of the callus age. The content of free acids in two weeks old callus was half as high as in the
upper part. 相似文献
35.
36.
37.
38.
Biosynthesis of monensins a and b: the role of isoleucine 总被引:3,自引:0,他引:3
Isoleucine added to the cultivation medium of Streptomyces cinnamonensis C-100-5 induced a relative increase of the production of monensin B at the expense of monensin A. U-14C-Isoleucine was found not to be a specific monensin B precursor. The incorporation of 1-13C-2-methylbutyrate into monensins A and B showed the label to be evenly incorporated in both products at carbon atoms originating from C(1) of propionate. In regulatory mutants insensitive to 2-amino-3-chlorobutyrate isoleucine influenced the production of monensins only slightly but strains resistant to 2-aminobutyrate and norleucine decreased their total production by 2-12% in the presence of isoleucine which was associated with a decrease of monensin A content by 14-52%. The inhibitory effect of isoleucine on the biosynthesis of valine, a specific precursor of the butyrate unit of monensin A, is discussed. 相似文献
39.
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
40.
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