全文获取类型
收费全文 | 5063篇 |
免费 | 194篇 |
国内免费 | 1篇 |
出版年
2023年 | 18篇 |
2022年 | 19篇 |
2021年 | 42篇 |
2020年 | 22篇 |
2019年 | 33篇 |
2018年 | 91篇 |
2017年 | 80篇 |
2016年 | 106篇 |
2015年 | 88篇 |
2014年 | 120篇 |
2013年 | 210篇 |
2012年 | 435篇 |
2011年 | 651篇 |
2010年 | 287篇 |
2009年 | 89篇 |
2008年 | 435篇 |
2007年 | 404篇 |
2006年 | 343篇 |
2005年 | 311篇 |
2004年 | 239篇 |
2003年 | 237篇 |
2002年 | 176篇 |
2001年 | 67篇 |
2000年 | 146篇 |
1999年 | 75篇 |
1998年 | 53篇 |
1997年 | 17篇 |
1996年 | 12篇 |
1995年 | 17篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1987年 | 17篇 |
1985年 | 19篇 |
1984年 | 22篇 |
1982年 | 16篇 |
1981年 | 9篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 17篇 |
1975年 | 12篇 |
1974年 | 18篇 |
1973年 | 9篇 |
1971年 | 10篇 |
1967年 | 8篇 |
排序方式: 共有5258条查询结果,搜索用时 31 毫秒
81.
Martina Grdiša Sandra Babić Martina Periša Klaudija Carović‐Stanko Ivan Kolak Zlatko Liber Marija Jug‐Dujaković Zlatko Satovic 《化学与生物多样性》2013,10(3):460-472
Dalmatian pyrethrum (Tanacetum cinerariifolium (Trevir. ) Sch.Bip. ) is a plant species endemic to the east Adriatic coast. The bioactive substance of Dalmatian pyrethrum is a natural insecticide, pyrethrin, a mixture of six active components (pyrethrins I and II, cinerins I and II, and jasmolins I and II). The insecticidal potential of pyrethrin was recognized decades ago, and dried and ground flowers have traditionally been used in Croatian agriculture and households. A total of 25 Dalmatian pyrethrum populations from Croatia were studied to determine the pyrethrin content and composition, and to identify distinct chemotypes. The total pyrethrin content ranged from 0.36 to 1.30% (dry flower weight; DW) and the pyrethrin I/pyrethrin II ratio ranged from 0.64 to 3.33%. The statistical analyses revealed that the correlations between the percentage of pyrethrin I and of all the other components were significant and negative. The total pyrethrin content was positively correlated with the percentage of pyrethrin I and negatively correlated with cinerin II. The multivariate analysis of the chemical variability enabled the identification of five chemotypes among 25 Dalmatian pyrethrum populations. The chemical characterization of indigenous Dalmatian pyrethrum populations may serve as a good background for future breeding and agricultural exploitation. 相似文献
82.
Renata Jurišić Grubešić Goran Srečnik Dario Kremer Jadranka Vuković Rodríguez Toni Nikolić Sanda Vladimir‐Knežević 《化学与生物多样性》2013,10(7):1305-1316
A rapid reversed‐phase (RP) high‐performance liquid chromatography method was developed and applied for simultaneous separation, and determination of flavonoids and phenolic acids in eight Plantago L. taxa (P. altissima L., P. argentea Chaix , P. coronopus L., P. holosteum Scop . ssp. depauperata Pilger , P. holosteum ssp. holosteum, P. holosteum ssp. scopulorum (Degen) Horvati? , P. lagopus L., and P. maritima L.) growing in Croatia. Chromatographic separation was carried out on Zorbax Eclipse XDB‐C18 using gradient elution with a H2O (pH 2.5, adjusted with CF3COOH) and MeCN mixture at 30°. The contents of analyzed phenolic compounds (% of the dry weight of the leaves, dw) varied among examined species: rutin (max. 0.024%, P. argentea), hyperoside (max. 0.020%, P. lagopus), quercitrin (max. 0.013%, P. holosteum ssp. holosteum), quercetin (max. 0.028%, P. holosteum ssp. scopulorum), chlorogenic acid (max. 0.115%, P. lagopus), and caffeic acid (max. 0.046%, P. coronopus). Isoquercitrin was detected only in P. argentea (0.020%), while isochlorogenic acid content was below limit of quantification in all investigated species. Multivariate analyses (UPGMA and PCA) showed significant differences in contents of investigated polyphenolic compounds between different Plantago taxa. Accordingly, investigated substances might be employed as chemotaxonomic markers in the study of the complex genus Plantago. 相似文献
83.
Nemanja Rajčević Peđa Janaćković Srđan Bojović Vele Tešević Petar D. Marin 《化学与生物多样性》2013,10(1):144-156
The essential‐oil compositions of one Croatian and three Serbian populations of Juniperus deltoides R.P.Adams have been determined by GC/MS analysis. In total, 147 compounds were identified, representing 97.3–98.3% of the oil composition. The oils were dominated by monoterpenes, which are characteristic components for the species of the section Juniperus. Two monoterpenes, α‐pinene and limonene, were the dominant constituents, with a summed‐up average content of 49.45%. Statistical methods were used to determine the diversity of the terpene classes and the common terpenes between the newly described J. deltoides populations from Serbia and Croatia. Only reports on several specimens from this species have been reported so far, and there are no studies that treat population diversity. Cluster analysis of the oil contents of 21 terpenes showed high correlation with the geographical distribution of the populations, separating the Croatian from the Serbian populations. The comparison of the essential‐oil compositions obtained in the present study with literature data, showed the separation of J. deltoides and J. oxycedrus ssp. oxycedrus from the western Mediterranean region. 相似文献
84.
Tina Kamčeva Maja Radisavljević Iva Vukićević Jürgen Arnhold Marijana Petković 《化学与生物多样性》2013,10(11):1972-1986
Phospholipase A2 is involved in propagation of inflammatory processes and carcinogenesis through its role in phospholipid metabolism, and release of arachidonic acid and lysophospholipids. Recent findings on correlation between elevated PLA2 activity and metastatic cancer render this enzyme an attractive target for cancer therapy. On the other hand, due to a broad range of oxidation states under physiological conditions and a high affinity for protein binding, platinum and ruthenium coordination complexes are promising candidates for PLA2 inhibitors. In this article, we discuss the interactions of Pt and Ru coordination complexes with PLA2 and phospholipids, as well as the application of MALDI‐TOF mass spectrometry for screening PLA2 inhibitors. Owing to the ability of this technique to simultaneously detect and monitor changes in substrate and product concentrations, the inhibitor mechanisms of both Pt and Ru complexes with various ligands were determined. 相似文献
85.
86.
Ana Vrsalović Presečki Zvjezdana Findrik Blažević Đurđa Vasić-Rački 《Bioprocess and biosystems engineering》2013,36(1):117-126
The first step of starch hydrolysis, i.e. liquefaction has been studied in this work. Two commercial α-amylases from Bacilllus licheniformis, known as Termamyl and Liquozyme have been used for this purpose. Using starch as the substrate, kinetics of both enzymes has been determined at optimal pH and temperature (pH 7, T = 80 °C) and at 65 °C and pH 5.5. Michaelis–Menten model with uncompetitive product inhibition was used to describe enzyme kinetics. Mathematical models were developed and validated in the repetitive batch and fed-batch reactor. Enzyme inactivation was described by the two-step inactivation model. All experiments were performed with and without calcium ions. The activities of both tested amylases are approximately one hundred times higher at 80 °C than at 65 °C. Lower inactivation rates of enzymes were noticed in the experiments performed at 65 °C without the addition of calcium than in the experiments at 80 °C. Calcium ions in the reaction medium significantly enhance amylase stability at 80 °C and pH 7. At other process conditions (65 °C and pH 5.5) a weaker calcium stabilizing effect was detected. 相似文献
87.
Interaction of Insulin-Like Growth Factor-Binding Protein 2 with α2-Macroglobulin in the Circulation
Insulin-like growth factors (IGFs) play active role in mitogenic and metabolic processes. In the peripheral circulation, they are mostly bound to specific IGF-binding proteins (IGFBPs). Proteolysis of IGFBPs releases free, active IGFs. IGFBP-2 is the second most abundant of the six binding proteins and its concentration increases in catabolic states. The possible interaction between IGFBP-2 and other proteins in the circulation was investigated in this study. Our results showed that IGFBP-2 associates with α2-macroglobulin (α2M), a protease inhibitor. Formation of IGFBP-2/α2M complexes most likely contributes to the regulation of IGFBP-2 proteolysis and, thus, the activity of IGFs. 相似文献
88.
The most commonly preserved soft tissues associated with ornithischian dinosaurs are skin remains. The apparent resistance of hadrosaur skin to decay, and its abundance in the fossil record relative to that of other tetrapods, has been attributed to factors such as thickness and composition. Here we report additional intrinsic factors within hadrosaur skin: 3D-preserved eumelanin-bearing bodies, dermal cells and blood vessel fragments in an organic matrix composed of protein fossilization products. The skin is much thinner than that of living mammals of similar size. It is likely that the preservation of hadrosaur skin is related to the arrangement of the layers composing it. 相似文献
89.
Sherpa Ang D. Guilfoyle David N. Naik Aditi A. Isakovic Jasmina Irie Fumitoshi Yamaguchi Yu Hrabe Jan Aoki Chiye Hrabetova Sabina 《Neurochemical research》2020,45(1):53-67
Neurochemical Research - Brain white matter is the means of efficient signal propagation in brain and its dysfunction is associated with many neurological disorders. We studied the effect of... 相似文献
90.
Milana Trifunović-Momčilov Danijela Paunović Snežana Milošević Marija Marković Slađana Jevremović Ivana Č Dragićević Angelina Subotić 《The Annals of applied biology》2020,177(1):74-89
Common centaury (Centaurium erythraea Rafn.) is a plant species that can inhabit saline soils. It is known as a plant with high spontaneous regeneration potential in vitro. In the present work we evaluated shoots and roots salinity tolerance of non-transformed and three AtCKX transgenic centaury lines to graded NaCl concentrations (0, 50, 100, 150, 200 mM) in vitro. Overexpression of AtCKX genes in transgenic centaury plants resulted in an altered cytokinins (CKs) profile leading to a decline of bioactive CK levels and, at the same time, increased contents of storage CK forms, inactive CK forms and/or CK nucleotides. Significant increment of fresh shoot weight was obtained in shoots of non-transformed and AtCKX1 transgenic line only on medium supplemented with 50 mM NaCl. However two analysed AtCKX2 transgenic lines reduced shoot growth at all NaCl concentrations. In general, centaury roots showed higher tolerance to salinity than shoots. Non-transformed and AtCKX1 transgenic lines tolerated up to 100 mM NaCl without change in frequency of regeneration and number of regenerated plants. Roots of two analysed AtCKX2 transgenic lines showed different regeneration potential under salt stress. Regeneration of transgenic AtCKX2-26 shoots even at 200 mM NaCl was recorded. Salinity stress response of centaury shoots and roots was also evaluated at biochemical level. Free proline, malondialdehyde and hydrogen peroxide content as well as antioxidative enzymes activities were investigated in shoots and roots after 1, 2, 4 and 8 weeks. In general, adition of NaCl in culture medium elevated all biochemical parameters in centaury shoots and in roots. Considering that all analysed AtCKX transgenic centaury lines showed altered salt tolerance to graded NaCl concentrations in vitro it can be assumed that CKs might be involved in plant defence to salt stress conditions. 相似文献