全文获取类型
收费全文 | 20403篇 |
免费 | 1296篇 |
国内免费 | 679篇 |
出版年
2023年 | 193篇 |
2022年 | 354篇 |
2021年 | 663篇 |
2020年 | 433篇 |
2019年 | 527篇 |
2018年 | 832篇 |
2017年 | 692篇 |
2016年 | 815篇 |
2015年 | 930篇 |
2014年 | 1170篇 |
2013年 | 1525篇 |
2012年 | 1633篇 |
2011年 | 1610篇 |
2010年 | 1036篇 |
2009年 | 776篇 |
2008年 | 830篇 |
2007年 | 689篇 |
2006年 | 639篇 |
2005年 | 422篇 |
2004年 | 351篇 |
2003年 | 355篇 |
2002年 | 289篇 |
2001年 | 314篇 |
2000年 | 300篇 |
1999年 | 279篇 |
1998年 | 196篇 |
1997年 | 195篇 |
1996年 | 199篇 |
1995年 | 188篇 |
1994年 | 154篇 |
1993年 | 130篇 |
1992年 | 193篇 |
1991年 | 203篇 |
1990年 | 145篇 |
1989年 | 146篇 |
1988年 | 149篇 |
1987年 | 140篇 |
1986年 | 118篇 |
1985年 | 176篇 |
1984年 | 151篇 |
1983年 | 132篇 |
1982年 | 120篇 |
1981年 | 123篇 |
1979年 | 123篇 |
1978年 | 96篇 |
1977年 | 89篇 |
1975年 | 92篇 |
1974年 | 107篇 |
1973年 | 91篇 |
1969年 | 101篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Zuzana Kossaczká Eva Machová Anna Vojtková-Lepšiková 《Applied microbiology and biotechnology》1991,36(3):375-378
Summary The yeast-like organism Aureobasidium pullulans efficiently converted abetd-xylose to cell mass (Y
X/S=0.45 g·g–1) with negligible production of polyols (Y
P/S=0.003 g·g–1) under aerobic conditions. A. pullulans grown semiaerobically exhibited different fermentation capacities in seven basal (vitaminless) medium and medium containing a mixture of seven vitamins. It was found that under semiaerobic conditions a mixture of vitamins significantly enhanced production of ethanol from abetd-xylose, resulting in a 15-fold higher yield coefficient of ethanol (Y
E/S=0.22 g·g–1) as compared to that achieved in vitaminless medium. This increase in ethanol production was accomplished at the expense of cell mass. A. pullulans produced extremely low amounts of polyols throughout all aerobic and semiaerobic experiments. A. pullulans displayed strictly NADPH-linked xylose reductase and NAD+-linked xylitol dehydrogenase activities. 相似文献
103.
J. Nešvera M. Pátek J. Hochmannová E. Chibisova I. Serebrijski Y. Tsygankov A. Netrusov 《Applied microbiology and biotechnology》1991,35(6):777-780
Summary
Brevibacterium methylicum is a newly isolated Gram-positive facultatively methylotrophic bacterium that uses the NAD+-dependent methanol dehydrogenase for methanol oxidation and assimilates its carbon via the ribulose monophosphate cycle. Protoplasts prepared by lysozyme treatment of B. methylicum cells grown in the presence of glycine were transformed by plasmid shuttle vectors pCEM500 (16.5 kb; Smr/Spr, Kmr/Gmr) and pEC71 (7.1 kb; Kmr/Nmr) constructed on the basis of B. lactofermentum plasmid pAM330 and replicating in Escherichia coli and in amino-acid-producing coryneform bacteria. The resistance markers were found to be expressed in B. methylicum and autonomous plasmid DNAs of various size were isolated from the transformants. The presence of the pAM330 replicon in these plasmids was demonstrated by DNA-DNA hybridization experiments.
Offprint requests to: J. Nevera 相似文献
104.
Conidia of the speciesFusarium culmorum /W.G.Sm./ Sacc. andFusarium graminearum Schwabe are characterized by variability in zearalenone production and dimensions depending on the substrate. The sporulation of isolates from some wheat eultivars have been deprived in vivo and in vitro in the first passage, but not their pathogenicity and toxic metabolites production. Nonsporulating strains produced lower quantités of zearalenone than sporulating ones. Liquid filtrates of such nonsporulating strains had a high phytotoxic effect on wheat caryopses. The crystalline toxin DAS /0,25 ug/ml/ had low phytotoxic effect on wheat caryopses. 相似文献
105.
The fluorescence of the voltage sensitive dye, diS-C3-(5), has been analyzed by means of synchronous excitation spectroscopy. Using this rather rare fluorescence technique we have been able to distinguish between the slightly shifted spectra of diS-C3-(5) fluorescence from cells and from the supernatant. It has been found that diS-C3-(5) fluorescence in the supernatant can be selectively monitored at exc = 630 nm and em= 650 nm, while the cell associated fluorescence can be observed at exc= 690 nm and em = 710 nm. A modified theory for the diSC3-(5) fluorescence response to the membrane potential is presented, according to which a linear relationship exists between the logarithmic increment of the dye fluorescence intensity in the supernatant, In I/I°, and the underlying change in the plasma membrane potential, p=p-°p. The theory has been tested on human myeloid leukemia cells (line ML-1) in which membrane potential changes were induced by valinomycin clamping in various K+ gradients. It has been demonstrated that the membrane potential change, p,can be measured on an absolute scale.
Offprint requests to: J. Plasek 相似文献
106.
I A Malanicheva L I Koz'mian Iu V Dudnik M Iu Novozhenov A V La?ko N P Potapova 《Antibiotiki i khimioterapii͡a》1991,36(5):5-8
Strain 344 synthesizing an antibiotic complex was isolated after fusion of the protoplasts of Streptomyces monomycini producing monomycin and Streptomyces kanamyceticus producing kanamycin. The major component of the complex was identified with albofungin and the minor one was suggested to be chloralbofungin. In the cultures of strain 344 variants forming monomycin were detected. After regeneration of the protoplasts of the parent strains there were isolated no stable clones synthesizing antibiotics differing from monomycin and kanamycin. 相似文献
107.
M. Kovačič 《Biological cybernetics》1991,64(4):337-342
The neural network that efficiently and nearly optimally solves difficult optimization problems is defined. The convergence proof for the Markovian neural network that asynchronously updates its neurons' states is also presented. The comparison of the performance of the Markovian neural network with various combinatorial optimization methods in two domains is described. The Markovian neural network is shown to be an efficient tool for solving optimization problems. 相似文献
108.
Malgorzata Schmidt Desirée Du Sart Paul Kalitsis Margaret Leversha Sue Dale Leslie Sheffield Daniela Toniolo 《Human genetics》1991,86(5):519-521
Summary We have analysed two duplications of the X chromosome in male patients using chromosome replication and DNA methylation patterns as determinants of the functional status of the duplicated segments. In both cases, the large duplicated regions, Xq12-q22 and Xq26.3-qter, were not inactivated. A review of previously reported male cases revealed that these duplications were also not subject to inactivation. Taken together, the examined duplications cover almost the entire X chromosome except the pericentromeric region and Xq25–26. Thus, most regions of the X chromosome can be present in two functional copies without lethal consequences. 相似文献
109.
Palmar flexion creases have been studied in schizophrenics with a family history of schizophrenia or other psychiatric disorders
and without such a background, and compared to a control population. Palmar flexion creases have been analyzed according to
the method suggested byBali & Chaube (1971). When compared to controls, differences in the DRBC and TRBC frequencies are significant in the subgroup with no family
history, supporting the existence of biological heterogeneity in schizophrenia, and of congenital factors when there is no
known genetic background. 相似文献
110.
M. Mačor 《Folia microbiologica》1988,33(6):466-473
Streptomycin and N-methyl-N’-nitro-N-nitrosoguanidine (MNNG) cause a 100% hereditary bleaching ofEuglena gracilis. In spite of the outcomes being the same, the corresponding mechanisms differ. By investigating the incorporation of the14C-labelled precursors of macromolecule synthesis we showed streptomycin to inhibit the synthesis of nucleic acids and proteins to the same extent (56%), whereas in the case of MNNG a 66% inhibition of nucleic acid synthesis and a 24% one of protein synthesis were observed. 相似文献