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81.
Marrs BL 《Photosynthesis research》2002,73(1-3):55-58
The development of genetics as a tool for the study of photosynthesis is recounted, beginning in the period when no genetic
exchange mechanism was known for any photosynthetic microorganism, and ending with the sequencing of the key genes for photosynthesis.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
82.
83.
Christopher?T.?WalshEmail author Sarah?E.?O'Connor Tanya?L.?Schneider 《Journal of industrial microbiology & biotechnology》2003,30(8):448-455
The epothilones are a family of macrolactone natural products from the myxobacterial species Sorangium cellulosum. Similar to taxol, they are of current clinical interest as anticancer agents. Sequence analysis of the epothilone gene cluster
allowed the identification of polyketide synthase and nonribosomal peptide synthetase modules involved in catalyzing epothilone
biosynthesis. Given this information, it has been possible to test the predicted functions of several modules to date. EpoA
ACP, EpoB, and EpoC have been overproduced in Escherichia coli, allowing in vitro reconstitution of the EpoA/B/C interface and production of the expected epothilone precursor. Further
experiments probed the tolerance of EpoB and EpoC for unnatural substrates. These studies of the first three modules of the
epothilone biosynthetic cluster suggest that combinatorial biosynthesis may lead to the production of a variety of epothilone
analogs that incorporate diversity into the heterocycle starter unit. Additional efforts with the remaining modules, coupled
with increased understanding of the macrocyclizing thioesterase domain, may lead to the production of epothilone variants
with improved clinical properties. 相似文献
84.
Tarka-Leeds DK Herr DW Klinefelter GR Rogers JM 《Birth defects research. Part B, Developmental and reproductive toxicology》2003,68(4):383-390
BACKGROUND: Microtia is a reduction in pinna size, usually seen in humans in conjunction with other medical conditions. We report microtia in CD‐1 mice after gestational exposure to ethane dimethanesulfonate (EDS), an alkylating agent and adult rat Leydig cell toxicant. METHODS: Time‐pregnant CD‐1 mice were administered 0, 80, or 160 mg EDS/kg on gestation days (GD) 11–17, or 0 or 160 mg EDS/kg on GD 11–13, GD 13–15 or GD 15–17. Pinnae were measured on postnatal days (PND) 4, 8, 18, and 28; and were observed for detachment from birth through PND 8. Branchial‐arch derived skeletal structures and histology of the pinna was examined on PND 4 and 24. Brainstem auditory evoked response (BAER) tests were carried out at approximately PND 160 to determine possible effects on hearing. RESULTS: All offspring of EDS‐treated dams exhibited bilateral, dose‐related decreases in pinna size. Gestational exposure during GD 11–13 produced smaller ears than during GD 13–15 or 15–17, but not as small as the GD 11–17 regimen. Ossification of other pharyngeal arch derivatives was delayed whereas histology was unremarkable. BAER analysis showed a decrease in the proportion of adult offspring producing a quantifiable response to varied auditory stimuli among EDS‐treated litters. CONCLUSIONS: Gestational exposure to EDS affects pinna development in the mouse, with a broad period of sensitivity during the second half of gestation. Microtia induced by EDS may be associated with hearing deficits, suggesting functional importance of pinna size or additional effects of EDS on ear development not detected by morphological examination. Birth Defects Res B68:383–390, 2003. © 2003 Wiley‐Liss, Inc. 相似文献
85.
EDDHA added in an optimal concentration (20.5 mumol.L-1) to a modified Pirson-Seidel nutrient solution induces flowering in some clones of the species Lemna minor, Lemna gibba and Spirodela polyrrhiza, which in the absence of EDDHA in the same nutrient solution do not flower. By adding EDDHA (20.5 mumol.L-1), floral induction under LD conditions is optimally promoted in the long-day (LD) species Lemna minor. After adding EDDHA to the nutrient solution, before floral induction and during flowering, Zn, Mn and Cu content is significantly increased in plants. Zn-EDDHA (0.86 mumol.L-1), Mn-EDDHA (1.51 mumol.L-1) and Cu-EDDHA (0.12 mumol.L-1), when used individually, greatly promote flowering under LD conditions as compared to flowering in the same nutrient solution with an equivalent quantity of Zn, Mn or Cu in the nonchelate form. If, on the other hand, Zn-EDDHA and Mn-EDDHA are added to the nutrient solution together (instead of Zn and Mn in nonchelate form), their effect on the promotion of flowering is less than in the case of their individual use. This shows that there is antagonism between Zn-EDDHA and Mn-EDDHA that is eliminated by adding EDDHA to the nutrient solution. We obtained the highest percentage of flowering plants (i.e. 74%) if we added EDDHA (20.5 mumol.L-1) to the nutrient solution containing Mn, Zn and Cu in chelate form. 74% of flowering plants actually means that flowering was achieved in all physiologically mature plants. Our results show that EDDHA promotes floral induction in Lemna minor under LD conditions, especially through chelating Zn, Mn and Cu, and, in addition, through eliminating the antagonism between Mn and Zn chelates EDDHA. Zn-EDDHA (0.86 mumol.L-1) also promote floral differentiation, especially cell division of microspore mother cells into dyads and those into microspore tetrads, which can be seen in microphotographs. When investigating possible pathways through which Mn-EDDHA, Zn-EDDHA and Cu-EDDHA promote flowering, we studied the effects of various concentrations of IAA and sucrose added to the nutrient solution as well. The results support the hypothesis that one of the possible pathways in which Mn-EDDHA promotes floral induction is through auxin oxidase, whereas Zn-EDDHA and Cu-EDDHA probably promote it through the enhancement of the photosynthesis and synthesis of sucrose. 相似文献
86.
A convenient method for determining the absolute configuration of chiral secondary alcohols using the racemic NMR anisotropy reagent, (+/-)-2-methoxy-2-(1-naphthyl)propionic acid [(+/-)-M(alpha)NP acid], and an HPLC-CD detector was developed. The method was successfully applied to some chiral alcohols derived from (-)-alpha-santonin. 相似文献
87.
Matthew?J.?Allen Thomas?J.?MeadeEmail author 《Journal of biological inorganic chemistry》2003,8(7):746-750
The study of in vivo developmental events has undergone significant advances with the advent of biological molecular imaging techniques such as computer enhanced light microscopy imaging, positron emission tomography (PET), micro-CT, and magnetic resonance imaging (MRI). MRI has proven to be a particularly powerful tool in clinical and biological settings. Images can be acquired of opaque living animals, with the benefit of tracking events of extended periods of time on the same specimen. Contrast agents are routinely used to enhance regions, tissues, and cells that are magnetically similar but histologically distinct. A principal barrier to the development of MR contrast agents for investigating developmental biological questions is the ability to deliver the agent across cellular membranes. As part of our research, we are investigating a number of small molecules that facilitate transport of charged and uncharged species across cell membranes. Here we describe the synthesis and testing of a Gd(III)-based MR contrast agent conjugated to polyarginine that is able to permeate cell membranes. We confirmed cellular uptake of the agent using two-photon laser microscopy to visualize a Eu(III) derivative of the contrast agent in cell culture, and verified this uptake by T1
analysis of the Gd(III) agent in cells.Abbreviations DOTA
1,4,7,10-tetraazacyclododecane-N,N,N,N-tetraacetic acid
- DOTA(tris-t-Bu ester)
1,4,7,10-tetraazacyclododecane-1,4,7-tris(acetic acid-tert-butyl ester)-10-acetic acid
- DO3A(tris-t-Bu ester)
1,4,7-tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane
- MRI
magnetic resonance imaging
- PET
positron emission tomography
- TPLM
two-photon laser microscopy 相似文献
88.
Enzymes and chelating agent in cotton pretreatment 总被引:6,自引:0,他引:6
Csiszár E Losonczi A Szakács G Rusznák I Bezúr L Reicher J 《Journal of biotechnology》2001,89(2-3):271-279
Desized cotton fabric and cotton seed-coat fragments (impurities) have been treated with commercial cellulase (Celluclast 1.5 L), hemicellulase–pectinase (Viscozyme 120 L) and xylanase (Pulpzyme HC) enzymes. Seed-coat fragments hydrolyzed much faster than the cotton fabric itself. This relative difference in hydrolysis rates makes possible a direct enzymatic removal of seed-coat fragments from desized cotton fabric. Addition of chelating agents such as ethylenediamine-tetra-acetic acid (EDTA) markedly enhanced the directed enzyme action. Pretreatments carried out in acidic solution at pH 5 increased the lightness of seed-coat fragments, contrary to the samples treated in neutral medium at pH 7. Alkaline scouring resulted in darker seed-coat fragments except for the samples pretreated with Pulpzyme HC plus EDTA. This effect is similar to that observed in the biobleaching process in pulp and paper industry. 相似文献
89.
The rate of expansion of bacterial colonies of S. liquefaciens is investigated in terms of a mathematical model that combines biological as well as hydrodynamic processes. The relative
importance of cell differentiation and production of an extracellular wetting agent to bacterial swarming is explored using
a continuum representation. The model incorporates aspects of thin film flow with variable suspension viscosity, wetting,
and cell differentiation. Experimental evidence suggests that the bacterial colony is highly sensitive to its environment
and that a variety of mechanisms are exploited in order to proliferate on a variety of surfaces. It is found that a combination
of effects are required to reproduce the variation of bacterial colony motility over a large range of nutrient availability
and medium hardness.
Received: 29 April 1999 相似文献
90.
Susanna Sánchez deViala Bill B. Brodie Eloy Rodriguez Donna M. Gibson 《Journal of nematology》1998,30(2):192-200
Thiarubrine C, a polyacetylenic 1,2-dithiin isolated from the roots of Rudbeckia hirta (Asteraceae), exhibited strong nematicidal activity in in vitro and growth chamber assays. Thiarubrine C was toxic, in the absence of light, to the plant-parasitic nematodes Meloidogyne incognita and Pratylenchus penetrans at LC₅₀s of 12.4 ppm and 23.5 ppm, respectively. A minimum exposure time between 12 and 24 hours was the critical period for nematode mortality due to thiarubrine C. Although thiarubrine C was not totally dependent on light for toxicity, activity was enhanced in the presence of light, especially with the microbivorous nematode, Teratorhabditis dentifera. Upon exposure of M. incognita juveniles to 20 ppm thiarubrine C for 1 hour, infection of tomato plants was greatly reduced compared to untreated checks. Thiarubrine C was also effective in reducing plant infection when mixed with soil 24 hours prior to or at planting, unlike other related compounds such as δ-terthienyl. 相似文献