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21.
Rhizopus is a zygomycetous genus. Several species of this taxon may infect humans and lower animals. Seventeen isolates ofRhizopus species in three distinct morphological groups were studied: the stolonifer group (sporangiophores greater than 1 mm in height, sporangial diameters of 100–275 µm, branched rhizoids); the arrhizus group (sporangiophores greater than 1 mm in height, branched rhizoids, sporangial diameters of 100–240 µm); and the microsporus group (sporangiophores less than 0.8 mm in height, sporangial diameters less than 100 µm, simple rhizoids). Maximal growth temperatures were characteristic: the stolonifer group grew at 30°C, the arrhizus group grew at 36°C, and the microsporus group grew at 45°C. The DNA mol% G + C base composition of all isolates ranged from 34.9 to 40.2% Species within the three groups were grouped by DNA differences. The arrhizus group was most distinctive with a value of 34.9–36.3%; the stolonifer and microsporus groups had G + C values of 37.0–39.3% and 37.8–40.2%, respectively. Our research clarifies and defines the G-C values of the three important groups ofRhizopus species. 相似文献
22.
Phosphatidylcholine biosynthesis in celery cell suspension cultures with altered sterol compositions
Cell suspension cultures of celery were treated with the plant growth regulator, paclobutrazol. Lipid analysis revealed that use of this xenobiotic had little effect on the quantity or acyl quality of the major phospholipid classes or on the actual amounts of free sterol present in the cell. It did however, cause dramatic changes in the free sterol profile exhibited by treated cultures. In this respect, an increase in 14α-methylsterols was observed.
The synthesis of phosphatidylcholine in celery cell suspension cultures with altered free sterol compositions was studied using two radiolabelled biosynthetic precursors, [3 H-methyl]choline and [3 H-methyl]methionine. The studies showed that the rate of phosphatidylcholine biosynthesis via the CDP-base pathway proceeded at a slower rate in paclobutrazol treated cultures. Accumulation of label phosphocholine was observed arising from reduced CTP:cholinephosphatecytidylyltransferase activity. In contrast, phosphatidylcholine biosynthesis via the sequential methylation of ethanolamine derivatives appeared to be enhanced in cells that had an unusually high 14α-methylsterol content. From these investigations it may be postulated that the biosynthesis of phosphatidylcholine in Apium graveolens suspension cultures may be regulated by membrane sterol composition. 相似文献
The synthesis of phosphatidylcholine in celery cell suspension cultures with altered free sterol compositions was studied using two radiolabelled biosynthetic precursors, [
23.
Bernard Chapais Carole Gauthier Jean Prud’homme 《International journal of primatology》1995,16(3):521-536
It has been proposed that monkeys direct grooming to high-ranking individuals in an attempt to obtain agonistic support in
return. But whether these two categories of interactions are causally related has proven difficult to establish. Part of the
problem stems from the fact that in stable groups social relationships reflect an equilibrium state and that behaviors need
only be performed at low rates and long intervals to maintain the current social structure. In theory, however, if affiliative
and supportive interactions are indeed causally related, it should be possible to accentuate their temporal relation, hence
their causal dynamics. For example, destabilizing dominance relations can be expected to induce competition for status and
force individuals to deploy behavioral tactics for settling new rank relations. We experimentally induced rank reversals in
a captive group of Japanese macaques (Macaca fuscata) composed of three matrilines (A-B-C rank order). A reversed C-A-B order
composed of three individuals per matriline was maintained for 2 weeks. The results show the close temporal relation among
(i) asserting one’s rank, (ii) competing for access to dominants through affiliation and interferences in affiliation, (iii)
receiving support from dominants against lower-ranking individuals, and (iv) supporting dominants against subordinates. These
findings are compatible with one version of the affiliation-for-support hypothesis, namely that monkeys affiliate with dominants
as a way to assert their position in the hierarchy. In a functional perspective, mutual selfishness provides a better explanation
than reciprocal altruism because the possibility that both groomers and supporters derive immediate net benefits cannot be
excluded. 相似文献
24.
The Second Messenger, Cyclic AMP, Is Not Sufficient for Myelin Gene Induction in the Peripheral Nervous System 总被引:1,自引:0,他引:1
Joseph F. Poduslo Randall S. Walikonis Marie-Christine Domec Carole T. Berg Carrie J. Holtz-Heppelmann 《Journal of neurochemistry》1995,65(1):149-159
Abstract: The adenylyl cyclase-cyclic AMP (cAMP) second messenger pathway has been proposed to regulate myelin gene expression; however, a clear correlation between endogenous cAMP levels and myelin-specific mRNA levels has never been demonstrated during the induction or maintenance of differentiation by the myelinating Schwann cell. Endogenous cAMP levels decreased to 8–10% of normal nerve by 3 days after crush or permanent transection injury of adult rat sciatic nerve. Whereas levels remained low after transection injury, cAMP levels reached only 27% of the normal values by 35 days after crush injury. Because P0 mRNA levels were 60% of normal levels by 14 days and 100% by 21 days after crush injury, cAMP increased only well after P0 gene induction. cAMP, therefore, does not appear to trigger myelin gene induction but may be involved in myelin assembly or maintenance. Forskolin, an activator of adenylyl cyclase, increased endoneurial cAMP levels only in the normal nerve, and in the crushed nerve beginning at 16 days after injury, but at no time in the transected nerve. Only by treating transected nerve with 3-isobutyl-1-methylxanthine (IBMX), an inhibitor of cAMP phosphodiesterases, in combination with forskolin was it possible to increase cAMP levels. No induction of myelin genes, however, was observed with short- or long-term treatment with IBMX and forskolin in the transected nerve. A three-fold increase in phosphodiesterase activity was observed at 35 days after both injuries, and a nonmyelinated nerve was shown to have even higher activity. These experiments, therefore, suggest an important role for phosphodiesterase in the inactivation of this second messenger-dependent stimuli when Schwann cells are non-myelinating, such as after sciatic nerve injury or in the nonmyelinated nerve, which again implies that cAMP may be required for the maintenance of the myelin sheath. 相似文献
25.
Growth responses of Pithophora oedogonia (Mont.) Wittr. and Spirogyra sp. to nine combinations of temperature (15°, 25°, and 35°C) and photon flux rate (50, 100, and 500 μmol·m?2·s?1) were determined using a three-factorial design. Maximum growth rates were measured at 35°C and 500 pmol·m?2·s?1 for P. oedogonia (0.247 d?1) and 25°C and 500 μmol·m?2·s?1 for Spirogyra sp. (0.224 d?1). Growth rates of P. oedogonia were strongly inhibited at 15°C (average decrease= 89%of maximum rate), indicating that this species is warm stenothermal. Growth rates of Spirogyra sp. were only moderately inhibited at 15° and 35°C (average decrease = 36 and 30%, respectively), suggesting that this species is eurythermal over the temperature range employed. Photon flux rate had a greater influence on growth of Spirogyra sp. (31% reduction at 50 pmol·m?2·s?1 and 25°C) than it did on growth of P. oedogonia (16% reduction at 50 μmol·m?2·s?1 and 35°C). Spirogyra sp. also exhibited much greater adjustments to its content of chlorophyll a (0.22–3.34 μg·mg fwt?1) than did P. oedogonia (1.35–3.08 μg·mg fwt?1). The chlorophyll a content of Spirogyra sp. increased in response to both reductions in photon flux rate and high temperatures (35°C). Observed species differences are discussed with respect to in situ patterns of seasonal abundance in Surrey Lake, Indiana, the effect of algal mat anatomy on the internal light environment, and the process of acclimation to changes in temperature and irradiance conditions. 相似文献
26.
Deborah L. Weissenborn Cynthia J. Denbow Marko Laine Saara S. Lång Zhenbiao Yang Xueshu Yu Carole L. Cramer 《Physiologia plantarum》1995,93(2):393-400
Terpenoid phytoalexins and other defense compounds play an important role in disease resistance in a variety of plant families but have been most widely studied in solanaceous species. The rate-limiting step in terpenoid phytoalexin production is mediated by 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), which catalyzes mevalonic acid synthesis. HMGRs are involved in the biosynthesis of a broad array of terpenoid compounds, and distinct isoforms of HMGR may be critical in directing the flux of pathway intermediates into specific end products. Plant HMGRs are encoded by a small gene family, and genomic or cDNA sequences encoding HMGR have been isolated from several plant species. In tomato, four genes encode HMGR; these genes are differentially activated during development and stress responses. One gene, hmg 2 , is activated in response to wounding and a variety of pathogenic agents suggesting a role in sesquiterpene phytoalexin biosynthesis. In contrast, expression patterns of tomato hmg l suggest a role in sterol biosynthesis and cell growth. Other plant species show an analogous separation of specific HMGR isoforms involved in growth and/or housekeeping function and inducible isoforms associated with biosynthesis of phytoalexins or other specialized "natural products". We are applying a variety of cell and molecular techniques to address whether subcellular localization and/or differential expression of these isoforms are key factors in determining end product accumulation during development and defense. 相似文献
27.
The male determinant of self-incompatibility in Brassica oleracea is located in the pollen coating 总被引:2,自引:0,他引:2
Andrew G. Stephenson James Doughty Suzanne Dixon Carole Elleman Simon Hiscock Hugh G. Dickinson 《The Plant journal : for cell and molecular biology》1997,12(6):1351-1359
An in vitro bioassay has been developed to explore the role of the pollen coating in the pollen/stigma interaction in Brassica oleracea . In the assay, coating is removed from pollen grains, supplemented with protein fractions isolated from coatings of different S (self incompatibility) haplotypes, and then—using micromanipulation—interposed between individual pollen grains and the stigmatic surface. Normally, the coating used is of the same haplotype as the pollen in the experiment—thus constituting an 'extension' of its own coat—but carrying the supplemented protein fractions. Initial experiments confirmed preliminary data that the pollen coating contained the male determinant of self incompatibility (SI); not only did the addition of 'self' coating (i.e. that with the same S -haplotype as the stigma) prevent the success of a compatible cross pollination, but a 'cross' coating (i.e. that with a different S -haplotype from the stigma) could induce the germination and growth of self pollen. Protein supplementation experiments demonstrated that the pollen-held determinant is contained within the water soluble component of the pollen coat, while further analysis revealed that the active molecular species possesses an Mr 10 kDa. More extensive fractionation by gel filtration and reverse phase HPLC was used to isolate a family of basic, cysteine-rich proteins (PCP-A: P ollen C oat P roteins-class A)—one of which is known to bind to stigmatically-expressed components of the S -locus in Brassica . Introduction of the PCP-A protein fraction into the bioassay confirmed the male determinant of SI as a protein, and probably a member of the PCP-A protein family. 相似文献
28.
Effect of Monensin on Growth and Methanogenesis of Methanobacterium formicicum 总被引:1,自引:0,他引:1 下载免费PDF全文
Monensin inhibited methanogenesis from formate but not from H2-CO2 by resting-cell suspensions of Methanobacterium formicicum. The antibiotic severely inhibited growth on formate. The lag phase of H2-CO2-grown cultures was prolonged by monensin, but these cultures recovered from the initial inhibition. The recovery did not result from the development of a monensin-resistant population or inactivation of the antibiotic. 相似文献
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