全文获取类型
收费全文 | 4071篇 |
免费 | 239篇 |
国内免费 | 312篇 |
出版年
2023年 | 58篇 |
2022年 | 74篇 |
2021年 | 94篇 |
2020年 | 101篇 |
2019年 | 109篇 |
2018年 | 109篇 |
2017年 | 114篇 |
2016年 | 115篇 |
2015年 | 106篇 |
2014年 | 157篇 |
2013年 | 335篇 |
2012年 | 132篇 |
2011年 | 138篇 |
2010年 | 106篇 |
2009年 | 185篇 |
2008年 | 239篇 |
2007年 | 239篇 |
2006年 | 177篇 |
2005年 | 174篇 |
2004年 | 172篇 |
2003年 | 146篇 |
2002年 | 118篇 |
2001年 | 106篇 |
2000年 | 67篇 |
1999年 | 71篇 |
1998年 | 80篇 |
1997年 | 61篇 |
1996年 | 65篇 |
1995年 | 74篇 |
1994年 | 61篇 |
1993年 | 59篇 |
1992年 | 60篇 |
1991年 | 50篇 |
1990年 | 40篇 |
1989年 | 56篇 |
1988年 | 54篇 |
1987年 | 43篇 |
1986年 | 39篇 |
1985年 | 59篇 |
1984年 | 74篇 |
1983年 | 39篇 |
1982年 | 53篇 |
1981年 | 37篇 |
1980年 | 36篇 |
1979年 | 35篇 |
1978年 | 28篇 |
1977年 | 22篇 |
1976年 | 16篇 |
1974年 | 13篇 |
1973年 | 11篇 |
排序方式: 共有4622条查询结果,搜索用时 78 毫秒
51.
Kate Swift Natalie Moltschaniwskyj 《Journal of experimental marine biology and ecology》2005,315(2):177-186
The cephalopod digestive gland plays an important role in the efficient assimilation of nutrients and therefore the fast growth of the animal. The histological and enzymatic structure of Euprymna tasmanica was studied and used in this experiment to determine the dynamics of the gland in response to feeding. The major roles of the digestive gland were secretion of digestive enzymes in spherical inclusions (boules) and excretion of metabolic wastes in brown body vacuoles. High levels of trypsin, chymotrypsin and α-amylase, low levels of α-glucosidase and negligible carboxypeptidase activity were produced by the gland. There was no evidence of secretion of digestive enzymes in other organs of the digestive tract. Within 60 min of a feeding event, the gland produced increasing numbers of boules to replace those lost from the stomach during the feeding event. Initially, small boules were seen in the digestive cells, they increased in size until they are released into the lumen of the gland where they are transported to the stomach. There was no evidence of an increase in activity of digestive enzymes following a feeding event, despite structural changes in the gland. However, there was large variation among individuals in the level of digestive enzyme activity. A negative correlation between boule and brown body vacuole density suggested that the large variation in enzyme activity may be due to the digestive gland alternating between enzyme production and excretion. 相似文献
52.
真菌源激发子对采后葡萄果皮抗性产生的诱导 总被引:2,自引:2,他引:0
利用细胞壁提取法从葡萄采后致病菌Alternaria alternate(Fr.)Keissl中提取出激发子。在采前一周用激发子处理葡萄,研究激发子诱导葡萄采后抗病效果。结果表明:葡萄经激发子处理后,果皮内与抗病有关的过氧化物酶(POD)、多酚氧化酶(PPO)和苯丙氨酸解氨酶(PAL)活性显著增强,酚类物质和木质素含量也显著提高,贮藏期自然发病率和发病指数降低,其中以125μg·mL-1处理效果最好,果实发病率和发病指数比对照降低500%左右。 相似文献
53.
Carlos E. Aragón Maritza Escalona Iris Capote Danilo Pina Inaudis Cejas Roberto Rodriguez Maria Jesus Cañal Jorge Sandoval Sophe Roels Pierre Debergh Justo Gonzalez-Olmedo 《In vitro cellular & developmental biology. Plant》2005,41(4):550-554
Summary The photosynthetic capacity changes and the main enzymatic systems related to carbon metabolism were investigated during the
in vitro culture of plantain shoots (Musa AAB cv. CEMSA 3/4) in temporary immersion bioreactors (TIB) and their subsequent acclimatization.
The maximal rate of photosynthesis (Pn), transpiration, and the activity of the carbon metabolism enzymes phosphoenolpyruvate
carboxylase (PEPC), acid invertase (AI), pyruvate kinase (PK) and sucrose phosphate synthase (SPS) were measured every 7 d
during the 21 d of elongation in TIB, and the following 42 d of acclimatization. Sucrose content in the liquid medium and
in the leaves was also determined. The most significant changes in plant growth were observed during acclimatization. During
the in vitro stage photosynthesis was limited (4–6 μmol CO2m−2s−1); the photosynthetic rate however increases rapidly and significantly as soon as in vitro culture is over during acclimatization. PEPC activity increased during the whole evaluation period. The highest levels were
achieved around days 42 and 56. PK and SPS activities were optimal during the first weeks in acclimatization (28–35 d), while
AI increased at the beginning of the elongation phase (7 d), and later at the end of the acclimatization (49–63 d). The relationships
between morphological parameters, photosynthetic capacity of the plantlets and the carbon metabolism enzymes during both phases
of the culture are discussed. 相似文献
54.
55.
Jacek Patykowski 《Acta Physiologiae Plantarum》2006,28(6):589-598
The aim of the research was to estimate the sensitivity of tomato tissue and spore from necrotrophic isolate of B. cinerea on H2O2. The influence of exogenic H2O2 and B. cinerea on plant tissue and on the activity of peroxidases (PO), catalase (CAT) and superoxide dismutase (SOD) in apoplastic tomato
leaves fraction were investigated.
It was proved that 40 mM H2O2 damaged the cells of a host, and inhibited in vitro germination of B.cinerea spores. Complete inhibition of germination was observed after the use 100 mM H2O2. In the presence of spores H2O2 was decomposed to H2O and O2. Trace activity of catalase was observed in a solution of spores used for inoculation. Necrosis which appeared on the leaves
after 40 mM H2O2 treatment resembled hypersensitive response. On the leaves pretreated at this concentration the development of infection
was observed. The H2O2 concentration harmful for the tissues, stimulated the PO activity measured with NADH — responsible for generation of ·O
2
−
, as well as with syringaldazine (S) and ferulic acid (FA), substrates characteristics of forms lignifying and strengthening
the cell wall. Clear increase in CAT activity, resulting from infection and early pretreatment with H2O2 was observed in apoplast. No effect on SOD activity was observed.
A hypothesis may be put forward, that germinating spores produce enzymes which allow them to decompose H2O2 generated in apoplast, so there is little likelihood that B. cinerea can be directly inhibited by reactive oxygen forms (ROS) during initial stages of infection. Necrotic lesions resembling
HR generated by exogenous H2O2 as well as induction of activity of apoplastic plant enzymes, particularly PO connected with strengthening and lignification
of cell wall, were not sufficient factors to inhibit fungal expansion. 相似文献
56.
Céline Faugeron Jean-Claude Mollet Yannis Karamanos Henri Morvan 《Acta Physiologiae Plantarum》2006,28(6):557-565
Activities of two de-N-glycosylation enzymes, PNGase (peptide N
4(N-acetyl-glucosaminyl)asparagine amidase) and ENGase (endo N-acetyl-β-D-glucosaminidase), involved in the release of N-glycans from N-glycoproteins, were monitored in several organs of tomato plants (Lycopersicon esculentum, Mill., cv. Dombito) with a fluorescence-HPLC procedure using a resofurin-labelled N-glycopeptide substrate. PNGase and ENGase
activities were detected in every organ assayed but with quantitative differences. The highest activities were found in the
youngest parts of the plant, i.e. apical buds, flowers and leaf blades. PNGase activities were consistently higher than ENGase
activities (three-fold in average). Both de-N-glycosylation activities were associated with high levels of proteins and protease activities. During fruit growth and ripening,
these three parameters decreased notably. The ubiquitous detection of these enzyme activities in the different organs is probably
associated with the previously characterized unconjugated N-glycans in tomato. The possible role of PNGase and ENGase degradation
products (i.e. unconjugated N-glycans) are discussed in relation with their biological functions in plant development. 相似文献
57.
细菌群体感应淬灭酶的研究进展 总被引:11,自引:1,他引:10
细菌的群体感应系统(Quorum sensing,QS)参与许多生物学功能的调控,其中包括动植物病原细菌致病因子的生成以及人类某些病原细菌生物膜的形成。酰基高丝氨酸内酯(N—acylhomoserine laetone,AHL)是调控群体感应系统的关键信号分子。近年的研究表明,不同生物体包括细菌和真核生物中都存在类别不同的能够降解AHL的群体感应淬灭酶(Quorum—quenching enzyme)。在AHL依赖型致病菌和转基因植物中表达AHL降解酶能有效地抑制QS信号分子的积累,从而阻断了病原细菌的发病机制,提高了植物的抗病性。这些新颖的群体感应淬灭酶的发现,不仅为防治细菌侵染提供了可行的途径,也对研究它们在宿主中的功能和对生态系统的潜在影响提出挑战。 相似文献
58.
Zorica Knezevic Nenad Milosavic Dejan Bezbradica Zivana Jakovljevic Radivoje Prodanovic 《Biochemical Engineering Journal》2006,30(3):269-278
The present study compares the results of three different covalent immobilization methods employed for immobilization of lipase from Candida rugosa on Eupergit® C supports with respect to enzyme loadings, activities and coupling yields. It seems that method yielding the highest activity retention of 43.3% is based on coupling lipase via its carbohydrate moiety previously modified by periodate oxidation. Study of thermal deactivation kinetics at three temperatures (37, 50 and 75 °C) revealed that the immobilization method also produces an appreciable stabilization of the biocatalyst, changing its thermal deactivation profile. By comparison of the t1/2 values obtained at 75 °C, it can be concluded that the lipase immobilized via carbohydrate moiety was almost 2-fold more stable than conventionally immobilized one and 18-fold than free lipase. The immobilization procedure developed is quite simple, and easily reproduced, and provides a promising solution for application of lipase in aqueous and microaqueous reaction system. 相似文献
59.
S. Pelleschi A. Leonardi J. -P. Rocher G. Cornic D. de Vienne C. Thévenot J. -L. Prioul 《Molecular breeding : new strategies in plant improvement》2006,17(1):21-39
One hundred to 120 maize recombinant inbred lines at the mature fourth leaf stage derived from F-2 and Io parental lines were
grown in a glasshouse and were deprived of water for 9 days in order to detect pertinent markers of the physiological response
to water stress which may be used for breeding. Carbohydrate metabolism QTLs were compared to photosynthesis gas exchange
QTLs. The locations of these QTLs were further compared with those of morphological trait QTLs when water availability varied.
The traits ranged from three enzyme activities (invertase, sucrose-P synthase, ADP glucose pyrophosphorylase) and hexose,
sucrose, starch content to CO2 uptake and stomatal conductance, water status, leaf size, root/shoot ratio, and ABA (leaf, root and xylem sap). Four main
results were obtained (1) only 14 % of QTLs were common to both drought and watered treatments, confirming the existence of
stress specific chromosome regions, (2) the QTLs tended to form clusters, frequently consisting of QTLs from different classes
(growth, photosynthesis, water status, carbohydrate metabolism and ABA), (3) carbohydrate metabolism trait QTLs were more
frequently co-located with growth trait QTLs than photosynthesis related ones, especially in control conditions, (4) one co-location
was observed between the three enzyme activities implied in sucrose and starch metabolism and a corresponding structural gene,
which can be considered as a candidate gene for explaining part of the variability of each enzymatic trait (invertase, sucrose-P
synthase, ADPglucose pyrophosphorylase). It is concluded that, carbohydrate metabolism provides valuable traits for understanding
and improving maize responses to water stress. 相似文献
60.
S.N. Lavanya S. Niranjan Raj A.C. Udayashankar K.R. Kini K.N. Amruthesh S.R. Niranjana 《Archives Of Phytopathology And Plant Protection》2013,46(11):1252-1272
Pearl millet [Pennisetum glaucum (L.) R. Br.] has the seventh largest annual production in the world giving it significant economic importance. Although generally well adapted to the growing conditions in arid and semi-arid regions, major constraints to yields are susceptibility to downy mildew disease caused by the oomycete Sclerospora graminicola (Sacc.) Schroet. Induction of resistance against downy mildew disease of pearl millet has been well established using various biotic and abiotic inducers. The present study demonstrated the comparative analysis of the involvement of the important defence enzymes like β-1,3-Glucanase, chitinase, phenylalanine ammonia-lyase (PAL), peroxidase (POX), polyphenol oxidase (PPO) and lipoxygenase (LOX) during induced systemic resistance (ISR) mediated by inducers like Benzo(1,2,3)-thiadiazole-7-carbothionic acid-S-methyl ester (BTH), Beta amino butyric acid (BABA), Chitosan and Cerebroside against pearl millet downy mildew disease. Native-PAGE showed six POX isozymes in all categories of uninoculated pearl millet seedlings and maximum intensity of bands was noticed in resistant seedlings. After inoculation in Cerebroside-treated seedlings, there were seven isoforms, POX-4 was not present in any other seedlings. Native-PAGE analysis showed the presence of five PPO isozymes in all categories of uninoculated pearl millet seedlings and after inoculation seven isoforms of PPO-7 were noticed, and the intensity of banding was more in resistant and Cerebroside-treated seedlings. The isoforms PPO-3 were present as an extra band after inoculation in all seedlings. Isoform PPO-7, though found in all seedlings, was very prominent in Chitosan- and Cerebroside-treated seedlings. β-1,3-Glucanase Native-PAGE analysis showed the presence of only one isozyme in all categories of uninoculated/inoculated pearl millet seedlings. Glu-1 isozyme was very prominent in all seedlings including resistant and susceptible seedlings. Among the induced resistant seedlings, highest intensity was observed in Cerebroside-treated seedlings. Native-PAGE analysis showed the presence of three LOX isozymes in all categories of uninoculated pearl millet seedlings, and the intensity of banding pattern was very low in BTH-treated seedlings. LOX-1 and LOX-2 were very prominent in resistant, Chitosan- and Cerebroside-treated seedlings. Upon inoculation, one extra band, LOX-3, was exclusively noticed in Cerebroside-treated seedlings. In inoculated seedlings, LOX-1, LOX-2 and LOX-4 were very prominent in Chitosan Cerebroside-treated seedlings compared to other seedlings. 相似文献