全文获取类型
收费全文 | 573篇 |
免费 | 47篇 |
出版年
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 17篇 |
2020年 | 11篇 |
2019年 | 21篇 |
2018年 | 15篇 |
2017年 | 15篇 |
2016年 | 26篇 |
2015年 | 23篇 |
2014年 | 19篇 |
2013年 | 39篇 |
2012年 | 37篇 |
2011年 | 42篇 |
2010年 | 20篇 |
2009年 | 23篇 |
2008年 | 28篇 |
2007年 | 29篇 |
2006年 | 23篇 |
2005年 | 38篇 |
2004年 | 32篇 |
2003年 | 18篇 |
2002年 | 17篇 |
2001年 | 16篇 |
2000年 | 20篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有620条查询结果,搜索用时 15 毫秒
41.
Three anthracene derivatives, auxenone, oncocalyxonol and auxemim, were isolated from Auxemma ontocalyx. The structures of these compounds as 1,4,8-trihydroxy-2-methoxy-5-methyl-9,10-anthraquinone, rel-9alpha,11alpha-epoxy-1,4,8alpha,11alpha-tetrahydroxy-2-methoxy-8a beta-methyl-5,6,7,8,8a,9, 10,10a beta-octahydro-10-anthracenone and rel-8alpha,11beta-epoxy-2,11-dimethoxy-8a beta-methyl-5,6,7,8,8a,9-hexahydro-1,4-anthracenedione were determined by analysis of spectral data (1D and 2D NMR, IR, HREIMS and UV). 相似文献
42.
Amino acid changes S180A (S-->A at site 180), H197Y, Y277F, T285A, and
A308S are known to shift the maximum wavelength of absorption (lambda max)
of red and green visual pigments toward blue, essentially in an additive
fashion. To test the generality of this "five-sites" rule, we have
determined the partial amino acid sequences of red and green pigments from
five mammalian orders (Artiodactyla, Carnivora, Lagomorpha, Perissodactyla,
and Rodentia). The result suggests that cat (Felis catus), dog (Canis
familiaris), and goat (Capra hircus) pigments all with AHYTA at the five
critical sites have lambda max values of approximately 530 nm, whereas rat
(Rattus norvegicus) pigment with AYYTS has a lambda max value of
approximately 510 nm, which is accurately predicted by the five-sites rule.
However, the observed lambda max values of the orthologous pigments of
European rabbit (Oryctolagus cuniculus), white-tailed deer (Odocoileus
virginianus), gray squirrel (Sciurus carolinensis), and guinea pig (Cavia
procellus) are consistently more than 10 nm higher than the predicted
values, suggesting the existence of additional molecular mechanisms for red
and green color vision. The inferred amino acid sequences of ancestral
organisms suggest that the extant mammalian red and green pigments appear
to have evolved from a single ancestral green-red hybrid pigment by
directed amino acid substitutions.
相似文献
43.
Adventitious shoot regeneration from internodal explants of mature plants of Annona muricata L. was obtained on Nitsch media. Meristems were induced with sorbitol as the sole carbon source supplemented with 2 mg l–1 of benzylaminopurine and 0.5 mg l–1 naphthaleneacetic acid. Adventitious shoots were developed only when the explants were transferred onto growth regulator-free media containing sucrose, galactose, or glucose. A hypothesis is proposed for the involvement of sorbitol in the induction and development of de novo shoots from internodal explants of mature trees of A. muricata. 相似文献
44.
45.
Ana Sílvia Franco Pinheiro Moreira José Pires de Lemos Filho Gerhard Zotz Rosy Mary dos Santos Isaias 《Flora》2009,204(8):604-611
This study compares photosynthetic and structural features of Dichaea cogniauxiana and Epidendrum secundum leaves and roots. The diurnal titratable acidity fluctuations indicated crassulacean acid metabolism (CAM) in E. secundum leaves, associated with anatomical features like thick cuticle, large and vacuolated cells, and reduced stomata size and frequency. Roots of both species had chloroplasts in their cortical parenchyma. However, neither the roots nor D. cogniauxiana leaves did show tissue sap acidity fluctuations. This indicates C3 metabolism in these organs. This lack of oscillation of organic acids in Epidendrum roots was at odds with a CAM-like 13C ratio, suggesting that in spite of active CO2 fixation in roots during the day, the bulk of carbon is imported from the leaves. Roots of both species showed Fv/Fm, ΔF/Fm′, ETR values similar to reports from other non-foliar photosynthetic organs. Besides reducing root carbon cost, root photosynthesis may also be important by alleviating potential hypoxia, since water-saturated velamen severely impedes the gas exchange between radicular cortex. 相似文献
46.
Stolf-Moreira R Medri ME Neumaier N Lemos NG Pimenta JA Tobita S Brogin RL Marcelino-Guimarães FC Oliveira MC Farias JR Abdelnoor RV Nepomuceno AL 《Genetics and molecular research : GMR》2010,9(4):1946-1956
Soybean genotypes MG/BR46 (Conquista) and BR16, drought-tolerant and -sensitive, respectively, were compared in terms of morphophysiological and gene-expression responses to water stress during two stages of development. Gene-expression analysis showed differential responses in Gmdreb1a and Gmpip1b mRNA expression within 30 days of water-deficit initiation in MG/BR46 (Conquista) plants. Within 45 days of initiating stress, Gmp5cs and Gmpip1b had relatively higher expression. Initially, BR16 showed increased expression only for Gmdreb1a, and later (45 days) for Gmp5cs, Gmdefensin and Gmpip1b. Only BR16 presented down-regulated expression of genes, such as Gmp5cs and Gmpip1b, 30 days after the onset of moisture stress, and Gmgols after 45 days of stress. The faster perception of water stress in MG/BR46 (Conquista) and the better maintenance of up-regulated gene expression than in the sensitive BR16 genotype imply mechanisms by which the former is better adapted to tolerate moisture deficiency. 相似文献
47.
Claudia NCD Lemos Fernando M Reis Guilherme N Pena Laila C Silveira Aroldo F Camargos 《Reproductive biology and endocrinology : RB&E》2010,8(1):51
Background
Reproductive function following chemotherapy is of increasing importance given that survival rates are improving. We assessed whether a gonadotropin-releasing hormone antagonist (GnRHant; cetrorelix) could promote ovarian protection against damage due to chemotherapy. 相似文献48.
Furlan Lopes Cassiane Lemos Costa Alice Dionísio Jaqueline Fernanda Delgado Cañedo Andres da Rosa Renata Del Valle Garnero Analia Inacio Ribeiro José Ricardo Gunski Ricardo José 《Genetica》2022,150(5):235-246
Genetica - Known as "electric-light bugs", belostomatids potentially act as agents of biological control. The Belostoma genus has holokinetic chromosomes, interspecific variation in... 相似文献
49.
Beres C de Nazaré FV de Souza NC Miguel MA Werneck MM 《Biosensors & bioelectronics》2011,30(1):328-332
Cells detection is crucial in microbiological analysis of clinical, food, water or environmental samples. However, currently employed methods are time consuming. Plastic optical fiber (POF) biosensors consist in a viable alternative for rapid and inexpensive scheme for detection. In order to study the sensitivity of tapers for microbiological detection, geometric parameters are studied, such as the taper waist diameter since the formation of taper regions are the key sensing element in this particular type of sensors. In this study, a series of POF taper sensors were prepared using a specially developed tapering machine, and the dispersion of geometric dimensions is evaluated, aiming to achieve the best tapering characteristics which will provide a better sensitivity on the sensor response. The fiber tapers that presented the finest results were those constructed in U-shaped (bended) configurations, with taper waist diameters ranging from 0.40 mm up to 0.50 mm. These fiber tapers were used as the main section of the monitoring device, and when chemically treated as immunosensors for the detection of bacteria, yeast and erythrocytes. 相似文献
50.
Glutaraldehyde (GLUT) was evaluated for control of single and dual species biofilms of Bacillus cereus and Pseudomonas fluorescens on stainless steel surfaces using a chemostat system. The biofilms were characterized in terms of mass, cell density, total and matrix proteins and polysaccharides. The control action of GLUT was assessed in terms of inactivation and removal of biofilm. Post-biocide action was characterized 3, 7, 12, 24, 48 and 72 h after treatment. Tests with planktonic cells were also performed for comparison. The results demonstrated that in dual species biofilms the metabolic activity, cell density and the content of matrix proteins were higher than those of either single species. Planktonic B. cereus was more susceptible to GLUT than P. fluorescens. The biocide susceptibility of dual species planktonic cultures was an average of each single species. Planktonic cells were more susceptible to GLUT than their biofilm counterparts. Biofilm inactivation was similar for both of the single biofilms while dual biofilms were more resistant than single species biofilms. GLUT at 200 mg l(-1) caused low biofilm removal (<10%). Analysis of the post-biocide treatment data revealed the ability of biofilms to recover their activity over time. However, 12 h after biocide application, sloughing events were detected for both single and dual species biofilms, but were more marked for those formed by P. fluorescens (removal >40% of the total biofilm). The overall results suggest that GLUT exerts significant antimicrobial activity against planktonic bacteria and a partial and reversible activity against B. cereus and P. fluorescens single and dual species biofilms. The biocide had low antifouling effects when analysed immediately after treatment. However, GLUT had significant long-term effects on biofilm removal, inducing significant sloughing events (recovery in terms of mass 72 h after treatment for single biofilms and 42 h later for dual biofilms). In general, dual species biofilms demonstrated higher resistance and resilience to GLUT exposure than either of the single species biofilms. P. fluorescens biofilms were more susceptible to the biocide than B. cereus biofilms. 相似文献