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1.
黄酮类化合物药理作用的研究进展   总被引:124,自引:1,他引:123  
总结黄酮类化合物在药理作用方面的研究近况,在阐述黄酮类化合物的生物活性、药理作用的同时,结合结构分析和作用机制,揭示与其部分活性相关的构效关系,并对黄酮类化合物药理作用的研究提出进一步的展望。  相似文献
2.
脂肪酶催化合成生物柴油的研究   总被引:77,自引:0,他引:77       下载免费PDF全文
生物柴油是用动植物油脂或长链脂肪酸与甲醇等低碳醇合成的脂肪酸甲酯,是一种替代能源。这里探讨了生物法制备生物柴油的过程,采用脂肪酶酯化和酯交换两条工艺路线进行催化合成。深入研究制备过程中,不同脂肪酶、酶的用量和纯度、有机溶剂、低碳醇的抑制作用、吸水剂的作用、反应时间和进程、底物的特异性和底物摩尔比等参数对酯化过程的影响。试验结果表明,采用最佳酯化反应参数和分批加入甲醇并用硅胶作脱水剂的工艺过程,酯化率可以达到92%,经分离纯化后的产品GC分析的纯度可达98%以上,固定化酶的使用半衰期可达到360h。同时对酯交换制备生物柴油过程中,甲醇的用量和甲醇的加入方式对脂肪酶催化过程的影响作了初步研究,优化后的酯交换率可达到83%。  相似文献
3.
In most soils, inorganic phosphorus occurs at fairly low concentrations in the soil solution whilst a large proportion of it is more or less strongly held by diverse soil minerals. Phosphate ions can indeed be adsorbed onto positively charged minerals such as Fe and Al oxides. Phosphate (P) ions can also form a range of minerals in combination with metals such as Ca, Fe and Al. These adsorption/desorption and precipitation/dissolution equilibria control the concentration of P in the soil solution and, thereby, both its chemical mobility and bioavailability. Apart from the concentration of P ions, the major factors that determine those equilibria as well as the speciation of soil P are (i) the pH, (ii) the concentrations of anions that compete with P ions for ligand exchange reactions and (iii) the concentrations of metals (Ca, Fe and Al) that can coprecipitate with P ions. The chemical conditions of the rhizosphere are known to considerably differ from those of the bulk soil, as a consequence of a range of processes that are induced either directly by the activity of plant roots or by the activity of rhizosphere microflora. The aim of this paper is to give an overview of those chemical processes that are directly induced by plant roots and which can affect the concentration of P in the soil solution and, ultimately, the bioavailability of soil inorganic P to plants. Amongst these, the uptake activity of plant roots should be taken into account in the first place. A second group of activities which is of major concern with respect to P bioavailability are those processes that can affect soil pH, such as proton/bicarbonate release (anion/cation balance) and gaseous (O2/CO2) exchanges. Thirdly, the release of root exudates such as organic ligands is another activity of the root that can alter the concentration of P in the soil solution. These various processes and their relative contributions to the changes in the bioavailability of soil inorganic P that can occur in the rhizosphere can considerably vary with (i) plant species, (ii) plant nutritional status and (iii) ambient soil conditions, as will be stressed in this paper. Their possible implications for the understanding and management of P nutrition of plants will be briefly addressed and discussed.  相似文献
4.
14种微藻总脂含量和脂肪酸组成研究   总被引:54,自引:4,他引:50  
比较分析了14种微藻的总脂含量和脂肪酸组成,结果表明:除小球藻、亚心形扁藻、极微小环藻、微绿球藻外,其他微藻的总脂含量均超过其干重的10%。每一纲的微藻脂肪酸组成都有各自特点,绿藻纲中16:0、16:1(n-7)、18:1(n-9)含量较高,但微绿球藻中16:1(n-7)、20:5(n-3)(EPA)含量远高于其他绿藻;金藻纲中含大量14:0、16:0、18:3(n-3)、22:6(n-3)(DHA);硅藻纲中14:0、16:0、16:1(n-7)、EPA含量较高;黄藻纲的异胶藻富含16:0、16:1(n-7)和EPA。  相似文献
5.
Structure-antioxidant activity relationships of flavonoids and phenolic acids   总被引:51,自引:0,他引:51  
The recent explosion of interest in the bioactivity of the the flavonoids of higher plants is due, at least in part, to the potential health benefits of these polyphenolic components of major dietary constituents. This review article discusses the biological properties of the flavonoids and focuses on the relationship between their antioxidant activity, as hydrogen donating free radical scavengers, and their chemical structures. This culminates in a proposed hierarchy of antioxidant activity in the aqueous phase. The cumulative findings concerning structure-antioxidant activity relationships in the lipophilic phase derive from studies on fatty acids, liposomes, and low-density lipoproteins; the factors underlying the influence of the different classes of polyphenols in enhancing their resistance to oxidation are discussed and support the contention that the partition coefficients of the flavonoids as well as their rates of reaction with the relevant radicals define the antioxidant activities in the lipophilic phase.  相似文献
6.
The role of organic acids in the mobilization of plant nutrients from the rhizosphere was assessed in seven contrasting soil types. The results indicated that malate was poor at mobilizing micronutrients from all the test soils, whilst citrate was capable of mobilizing significant quantities. Citrate was also capable of mobilizing P from one soil which possessed a large Ca-P fraction. This mobilization of P was due to both the complexing action of the citrate anion and due to the dissolution properties of the protons released from citric acid upon equilibrium with the soil solution. The reaction of citrate with cations was found to be near instantaneous with significant absorption to the solid phase in some soils at low concentrations. Soil decomposition studies indicated that citrate was rapidly broken down in organic soils but was more resistant to degradation in subsoil horizons. It was concluded that organic acids can be expected to be of little consequence in nutrient mobilization from high pH soils, whilst in acid soils they may be involved both in a more general mechanism for micronutrient uptake or as a potential Al detoxification mechanism.Abbreviations C6H8O7 Citric acid and H-citrate indicates - C6H5O7Na3 whilst Na-citrate indicates  相似文献
7.
Oxidative stress-induced apoptosis prevented by trolox   总被引:45,自引:0,他引:45  
The ability of oxidative stress to induce apoptosis (programmed cell death), and the effect of Trolox, a water soluble vitamin E analog, on this induction were studied in vitro in mouse thymocytes. Cells were exposed to oxidative stress by treating them with 0.5–10 μM hydrogen peroxide (H2O2) for 10 min, in phosphate-buffered saline supplemented with 0.1 mM ferrous sulfate. Cells were resuspended in RPMI 1640 medium with 10% serum and incubated at 37°C under 5% CO2 in air. Electron microscopic studies revealed morphological changes characteritic of apoptosis in H2O2-treated fragmented the DNA in a manner typical of apoptotic cells, producing a ladder pattern of 200 base pair increments upon agarose gel electrophoresis. The percentage of DNA fragmentation (determined fluorometrically) increased with increasing doses of H2O2 and postexposure incubation times. Pre- or posttreatment of cells with Trolox reduced H2O2-induced DNA fragmentation to control levels and below. The results indicate that oxidative stress induces apoptosis in thymocytes, and this induction can be prevented by Trolox, a powerful inhibitor of membrane damage.  相似文献
8.
Regulation of auxin transport by aminopeptidases and endogenous flavonoids   总被引:45,自引:0,他引:45  
Murphy A  Peer WA  Taiz L 《Planta》2000,211(3):315-324
 The 1-N-naphthylphthalamic acid (NPA)-binding protein is a putative negative regulator of polar auxin transport that has been shown to block auxin efflux from both whole plant tissues and microsomal membrane vesicles. We previously showed that NPA is hydrolyzed by plasma-membrane amidohydrolases that co-localize with tyrosine, proline, and tryptophan-specific aminopeptidases (APs) in the cotyledonary node, hypocotyl-root transition zone and root distal elongation zone of Arabidopsisthaliana (L.) Heynh. seedlings. Moreover, amino acyl-β-naphthylamide (aa-NA) conjugates resembling NPA in structure have NPA-like inhibitory activity on growth, suggesting a possible role of APs in NPA action. Here we report that the same aa-NA conjugates and the AP inhibitor bestatin also block auxin efflux from seedling tissue. Bestatin and, to a lesser extent, some aa-NA conjugates were more effective inhibitors of low-affinity specific [3H]NPA-binding than were the flavonoids quercetin and kaempferol but had no effect on high-affinity binding. Since the APs are inhibited by flavonoids, we compared the localization of endogenous flavonoids and APs in seedling tissue. A correlation between AP and flavonoid localization was found in 5- to 6-d-old seedlings. Evidence that these flavonoids regulate auxin accumulation in vivo was obtained using the flavonoid-deficient mutant, tt4. In whole-seedling [14C]indole-3-acetic acid transport studies, the pattern of auxin distribution in the tt4 mutant was shown to be altered. The defect appeared to be in auxin accumulation, as a considerable amount of auxin escaped from the roots. Treatment of the tt4 mutant with the missing intermediate naringenin restored normal auxin distribution and accumulation by the root. These results implicate APs and endogenous flavonoids in the regulation of auxin efflux. Received: 2 December 1999 / Accepted: 16 January 2000  相似文献
9.
杂交稻幼苗经聚乙二醇(PGE4000)渗透胁迫(-0.95MPa)处理,幼苗含水量及相对含水量下降,游离脯氨酸和膜脂过氧化产物丙二醛(MDA)含量上升,质膜透性增大。随PEG渗透胁迫时间延长,幼苗膜脂饱和脂肪酸含量逐渐增加,不饱和脂肪酸含量降低,不饱和脂肪酸指数(IUFA)减少。脯氨酸累积与MDA增长及膜透性加大呈正相关性,与膜脂脂肪酸不饱和度呈负相关性。讨论了游离脯氨酸累积与细胞透性的相关性,以  相似文献
10.
不同阶段中华绒螯蟹肝胰腺的脂类及脂肪酸组成   总被引:43,自引:2,他引:41  
成永旭  堵南山 《动物学报》1998,44(4):420-429
研究了不同发育阶段中华绒螯蟹肝胰腺脂类及脂肪酸组成。结果表明:在卵巢快速发育阶段,肝胰腺数显著下降总脂的含量也略有降低,致使肝胰腺脂类的绝对量有显著的降低。未成熟和成熟中华绒螯的肝胰腺总分别为34.37%和28.13%。  相似文献
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