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981.
Christensen Steen; Tokuoka Yoko; Silverthorne Jane; Wada Masamitsu 《Plant & cell physiology》1998,39(6):647-654
Light regulates development in the fern Adiantum capillus-venerisduring both the haploid gametophyte and diploid sporophyte phases.In this study, we have investigated the role of the photoreceptorphytochrome in haploid spore germination and regulation of expressionof mRNA encoding the major light-harvesting polypeptides ofphotosystem II {Lhcb mRNAs). Both of these responses appearto be induced by phytochrome and inhibited by blue light, acting.throughseparate photoreceptor(s). Characteristics of phytochrome actionwere similar for both responses, showing no induction in thevery low fluence range and an escape from far-redreversal for 50% of the response by 6 h. Overall, these resultsshow that phytochrome regulates both a morphological and a molecularprocess in haploid fern spores, and that these processes mayshare a common signal transduction pathway. (Received February 4, 1998; Accepted April 8, 1998) 相似文献
982.
A field study of nitrogen dynamics and spring barley growth as affected by the quality of incorporated residues from white clover and ryegrass 总被引:7,自引:0,他引:7
Hauggaard-Nielsen H. de Neergaard A. Jensen L.S. Høgh-Jensen H. Magid J. 《Plant and Soil》1998,203(1):91-101
Biofumigation refers to the suppression of soil-borne pests and pathogens by biocidal compounds released by Brassicaceous green manure and rotation crops when glucosinolates (GSLs) in their tissues are hydrolysed. We investigated the effect of environment and ontogeny on the GSL production, and thus biofumigation potential, of eight entries from five Brassica species. The environments included autumn and spring sown field plots (FA and FS) and potted plants grown under ambient conditions (PAM) or in a temperature controlled glasshouse at 20 °C/12 °C (PTC). GSL concentration was measured in the root and shoot tissue at buds-raised, flowering and maturity. Of particular interest was the suitability of the pot-grown plants for screening large numbers of brassicas for GSL production. The type of GSLs present in the tissues and their relative proportions remained relatively constant across environments and at different growth stages, with the exception of an increase in indolyl GSLs in the FS environment suspected of being induced by insect attack. Total GSL concentration generally declined from buds-raised to flowering in all environments, and was lowest at maturity. The exceptions were B. campestris, which had higher GSL concentration at flowering than at buds-raised, and the PTC environment in which most species also showed an increase at flowering. Despite GSL types and their proportions remaining relatively constant, the total GSL concentration in the root and shoot tissue of all entries varied significantly with environment (3–10-fold) and was generally ranked FS>PAM>FA>PTC. Interactions between species and environments meant that the ranking of the Brassica entries for total shoot and root GSL concentration changed with environment. However within three entries from B. napus, the ranking was consistent across the environments. The added effect of environment on phenological development and biomass production further influenced GSL production (the product of GSL concentration and biomass) on a ground area basis. The results suggest that glasshouse environments can be used to determine the types and proportions of GSLs present, and to rank entries within, but not between species for the total concentration in the tissues. However the influence of the environment on both GSL concentration and biomass production suggests that an accurate estimate of GSL production on a ground area basis to assess biofumigation potential will require measurement in the target environment. 相似文献
983.
William A. Jensen 《Sexual plant reproduction》1998,11(1):1-5
This year marks the 100th anniversary of the discovery of double fertilization by Nawaschin in St. Petersburg, Russia and,
independently, Guignard in France. This discovery came at the end of a period of controversy about fertilization in angiosperms
and ushered in a new period of intense research. Still, by 1950, there were many unanswered questions about double fertilization
because of limitations of the light microscope. The introduction of the electron microscope stimulated new research and helped
resolve some of the questions. My own research with the electron microscope and that of people who worked in my laboratory
is recounted and some of the still unanswered questions raised.
Received: 30 October 1997 / Accepted: 5 December 1997 相似文献
984.
985.
Annette Bruun Jensen Andrea Gargas Jørgen Eilenberg Søren Rosendahl 《Fungal genetics and biology : FG & B》1998,24(3):325-334
We sequenced the nuclear small subunit of ribosomal DNA (SSU rDNA) from seven species within the insect-pathogenic order Entomophthorales. These sequences were aligned with other published SSU rDNA sequences and phylogenies were inferred using phenetic and cladistic methods. Based on three different phylogenetic methods the Entomophthorales (excludingBasidiobolus ranarum) is monophyletic;B. ranarumwas more closely related to chytrids from Chytridiales and Neocallimasticales than to Entomophthorales, as was proposed by Nagahamaet al.(Mycologia87:203–209, 1995). Nuclear characters (large nuclei containing conspicuous condensed chromatin and lack of a prominent nucleolus) were of predictive value for the monophyly of the family Entomophthoraceae. Conidial characters separate the Entomophthoraceae, which only includes obligate pathogens, into at least two lineages: one lineage with uninucleate conidia and another with multinucleate conidia. The two species ofConidiobolusstudied were paraphyletic in our analyses and only distantly related to each other. This information may prove to be important in the use of these fungi as biocontrol agents. 相似文献
986.
Analysis of mannose selection used for transformation of sugar beet 总被引:39,自引:0,他引:39
Joersbo Morten Donaldson Iain Kreiberg Jette Petersen Steen Guldager Brunstedt Janne Okkels Finn T. 《Molecular breeding : new strategies in plant improvement》1998,4(2):111-117
Various factors affecting mannose selection for the production of transgenic plants were studied using Agrobacterium tumefaciens-mediated transformation of sugar beet (Beta vulgaris L.) cotyledonary explants. The selection system is based on the Escherichia coli phosphomannose isomerase (PMI) gene as selectable gene and mannose as selective agent. Transformation frequencies were about 10-fold higher than for kanamycin selection but were only obtained at low selection pressures (1.0–1.5 g/l mannose) where 20–30% of the explants produced shoots. The non-transgenic shoots were eliminated during the selection procedure by a stepwise increase in the mannose concentration up to 10 g/l. Analysis of the transformed shoots showed that the PMI activity varied from 2.4 mU/mg to 350 mU/mg but the expression level was independent of the selection pressure. Complete resistance to mannose of transformed shoots was observed already at low PMI activities (7.5 mU/mg). Genomic DNA blot analysis confirmed the presence of the PMI gene in all transformants analysed. The possible mode of action of mannose selection compared to other selection methods is discussed. 相似文献
987.
Biomanipulation as an Application of Food-Chain Theory: Constraints, Synthesis, and Recommendations for Temperate Lakes 总被引:25,自引:2,他引:23
Lars-Anders Hansson Helene Annadotter Eva Bergman Stellan F. Hamrin Erik Jeppesen Timo Kairesalo Eira Luokkanen Per-Åke Nilsson Martin Søndergaard John Strand 《Ecosystems》1998,1(6):558-574
The aim of this review is to identify problems, find general patterns, and extract recommendations for successful biomanipulation.
An important conclusion is that the pelagic food chain from fish to algae may not be the only process affected by a biomanipulation.
Instead, this process should be viewed as the “trigger” for secondary processes, such as establishment of submerged macrophytes,
reduced internal loading of nutrients, and reduced resuspension of particles from the sediment. However, fish reduction also
leads to a high recruitment of young-of-the-year (YOY) fish, which feed extensively on zooplankton. This expansion of YOY
the first years after fish reduction is probably a major reason for less successful biomanipulations. Recent, large-scale
biomanipulations have made it possible to update earlier recommendations regarding when, where, and how biomanipulation should
be performed. More applicable recommendations include (1) the reduction in the biomass of planktivorous fish should be 75%
or more; (2) the fish reduction should be performed efficiently and rapidly (within 1–3 years); (3) efforts should be made
to reduce the number of benthic feeding fish; (4) the recruitment of YOY fish should be reduced; (5) the conditions for establishment
of submerged macrophytes should be improved; and (6) the external input of nutrients (phosphorus and nitrogen) should be reduced
as much as possible before the biomanipulation. Recent biomanipulations have shown that, correctly performed, the method also
achieves results in large, relatively deep and eutrophic lakes, at least in a 5-year perspective. Although repeated measures
may be necessary, the general conclusion is that biomanipulation is not only possible, but also a relatively inexpensive and
attractive method for management of eutrophic lakes, and in particular as a follow-up measure to reduced nutrient load.
Received 14 April 1998; accepted 31 August 1998 相似文献
988.
Erik Bechgaard Karsten Lindhardt Lise Martinsen 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1998,712(1-2)
This paper describes the development of a simple and sensitive analytical method for the quantification of melatonin in human plasma and rabbit serum, using standard analytical equipment and on-line column enrichment without prior extraction, clean-up or derivatization. The analytical procedure was found to be accurate, precise and linear. For human plasma, the accuracy was 101% (range 89–106%), and the mean precision was 5% (range 2–9%) for all concentrations (0, 2, 10, 50 and 200 ng/ml) tested (n=6). The accuracy in rabbit serum was 101% (range 90–112%), and the mean precision was 13% (range 8–19%) for all concentrations (0, 2, 10, 50, 200 and 500 ng/ml) tested (n=6). The retention time of melatonin was about 8 min and the total recoveries were found to be approximately 65 and 85%, respectively, for human plasma and rabbit serum. The limit of detection was found to be lower than 1 ng/ml for human plasma and around 2 ng/ml for rabbit serum. The method is, therefore, found to be suitable for melatonin bioavailability studies in rabbits and presumably also in humans. 相似文献
989.
Zhu Genhai Bohnert Hans J. Jensen Richard G. Wildner Günter F. 《Photosynthesis research》1998,55(1):67-74
Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) (EC 4.1.1.39) not only catalyzes carboxylation and oxygenation of ribulose-1,5-bisphosphate (RuBP), but it can also act either as an epimerase or isomerase converting RuBP into xylulose-1,5-bisphosphate (XuBP) or 3-ketoarabinitol-1,5-bisphosphate (KABP), respectively, a process called misfire. XuBP is formed as a result of misprotonation at C3 of the RuBP-enediol. It is released from Rubisco active sites and accumulates in the reaction mixture. Increasing the amounts of CO2 or O2 decreases XuBP production. However, KABP synthesis, which has been proposed to be only a product due to C2 misprotonation of the RuBP-endiol, is dependent upon the presence of O2. KABP remains tightly bound to Rubisco active sites after its formation, causing the loss of Rubisco activity (fallover). The results suggest that the non-stabilized form of the peroxy-intermediate in the oxygenase reaction can be converted in a backreaction to KABP and molecular oxygen. The stabilization of the peroxy-intermediate due to the presence of Mn2+ instead of Mg2+ eliminates the formation of KABP. 相似文献
990.