全文获取类型
收费全文 | 2606篇 |
免费 | 219篇 |
国内免费 | 3篇 |
专业分类
2828篇 |
出版年
2021年 | 30篇 |
2019年 | 24篇 |
2017年 | 27篇 |
2016年 | 41篇 |
2015年 | 65篇 |
2014年 | 77篇 |
2013年 | 115篇 |
2012年 | 142篇 |
2011年 | 154篇 |
2010年 | 79篇 |
2009年 | 72篇 |
2008年 | 103篇 |
2007年 | 138篇 |
2006年 | 101篇 |
2005年 | 108篇 |
2004年 | 132篇 |
2003年 | 103篇 |
2002年 | 103篇 |
2001年 | 43篇 |
2000年 | 29篇 |
1999年 | 51篇 |
1998年 | 41篇 |
1997年 | 31篇 |
1996年 | 27篇 |
1995年 | 24篇 |
1994年 | 24篇 |
1993年 | 28篇 |
1992年 | 35篇 |
1991年 | 29篇 |
1990年 | 26篇 |
1989年 | 26篇 |
1988年 | 25篇 |
1987年 | 22篇 |
1985年 | 25篇 |
1984年 | 29篇 |
1982年 | 37篇 |
1981年 | 31篇 |
1980年 | 31篇 |
1979年 | 21篇 |
1978年 | 31篇 |
1977年 | 24篇 |
1976年 | 32篇 |
1975年 | 17篇 |
1974年 | 32篇 |
1973年 | 25篇 |
1972年 | 18篇 |
1969年 | 16篇 |
1964年 | 16篇 |
1961年 | 17篇 |
1957年 | 17篇 |
排序方式: 共有2828条查询结果,搜索用时 15 毫秒
71.
The soluble proanthocyanidins of the coloured seed coats of Vicia faba L. were isolated and separated by solvent partition. The chemical characteristics of the proanthocyanidins were elucidated by total oxidation and partial degradation in the presence of phloroglucinol followed by HPLC analysis. The native extract of proanthocyanidins contained (+)-gallocatechin, (-)-epigallocatechin, (+)-catechin and (-)-epicatechin units. Oligomeric procyanidins were purified by chromatography on Sephadex LH-20 and the accessible compounds were isolated by RP-HPLC using a Licrospher Li 100 Column. The structures of the purified oligomeric procyanidins were elucidated using a procedure involving TLC, UV spectroscopy, ESI-MS and HPLC analysis of the products from the phloroglucinol reaction. The major condensed tannins of Vicia faba comprise six compounds identified as two A-type procyanidin dimers, the procyanidin dimers B1, B2 and B3, and a procyanidin trimer. 相似文献
72.
Maurice S Coroller L Debaets S Vasseur V Le Floch G Barbier G 《Journal of applied microbiology》2011,111(6):1436-1446
Aims: To predict the risk factors for building infestation by Serpula lacrymans, which is one of the most destructive fungi causing timber decay in buildings. Methods and Results: The growth rate was assessed on malt extract agar media at temperatures between 1·5 and 45°C, at water activity (aw) over the range of 0·800–0·993 and at pH ranges from 1·5 to 11·0. The radial growth rate (μ) and the lag phase (λ) were estimated from the radial growth kinetics via the plots radius vs time. These parameters were then modelled as a function of the environmental factors tested. Models derived from the cardinal model (CM) were used to fit the experimental data and allowed an estimation of the optimal and limit values for fungal growth. Optimal growth rate occurred at 20°C, at high aw level (0·993) and at a pH range between 4·0 and 6·0. The strain effect on the temperature parameters was further evaluated using 14 strains of S. lacrymans. The robustness of the temperature model was validated on data sets measured in two different wood‐based media (Quercus robur L. and Picea abies). Conclusions: The two‐step procedure of exponential model with latency followed by the CM with inflection gives reliable predictions for the growth conditions of a filamentous fungus in our study. The procedure was validated for the study of abiotic factors on the growth rate of S. lacrymans. Significance and Impact of the Study: This work describes the usefulness of evaluating the effect of physico‐chemical factors on fungal growth in predictive building mycology. Consequently, the developed mathematical models for predicting fungal growth on a macroscopic scale can be used as a tool for risk assessment of timber decay in buildings. 相似文献
73.
In 2003, the invasive fruit fly Bactrocera invadens Drew, Tsuruta & White (Diptera: Tephritidae) (Drew et al. 2005), of possible Sri Lankan origin, has been detected in the East and about 1 yr later in West Africa. In regular surveys in Benin and Cameroon covering 4 yr, samples from 117 plant species across 43 families have been obtained. Incubation of field-collected fruits demonstrate that in West and Central Africa (WCA) B. invadens is highly polyphagous, infesting wild and cultivated fruits of at least 46 species from 23 plant families with guava (Psidium spp.), mango (Mangifera spp.), and citrus (spp.), and the wild hosts tropical almond (Terminalia catappa L.), African wild mango (Irvingia gabonensis (Aubry-Lecomte) Baill.), and sheanut (Vitellaria paradoxa C.F.Gaertn.) showing the highest infestation index. B. invadens occurs in 22 countries of WCA with new records for Angola, Central African Republic, the Congo, DR Congo, Equatorial Guinea, Gabon, Gambia, Guinea Bissau, Mali, Mauritania, Niger, and Sierra Leone. Overall, the pest has spread across a North-South distance of ?5,000 km representing a contiguous area of >8.3 million km(2) within WCA. B. invadens has adapted to a wide range of ecological and climatic conditions extending from low land rainforest to dry savanna. Because of its highly destructive and invasive potential, B. invadens poses a serious threat to horticulture in Africa if left uncontrolled. Moreover, the presence of this quarantine pest causes considerable restrictions on international trade of affected crops. 相似文献
74.
75.
76.
Maurice Campbell 《BMJ (Clinical research ed.)》1958,2(5106):1175-1184
77.
78.
van den Hoff MJ Kruithof BP Moorman AF 《BioEssays : news and reviews in molecular, cellular and developmental biology》2004,26(3):248-261
Postnatally, heart muscle cells almost completely lose their ability to divide, which makes their loss after trauma irreversible. Potential repair by cell grafting or mobilizing endogenous cells is of particular interest for possible treatments for heart disease, where the poor capacity for cardiomyocyte proliferation probably contributes to the irreversibility of heart failure. Knowledge of the molecular mechanisms that underly formation of heart muscle cells might provide opportunities to repair the diseased heart by induction of (trans) differentiation of endogenous or exogenous cells into heart muscle cells. We briefly review the molecular mechanisms involved in early development of the linear heart tube by differentiation of mesodermal cells into heart muscle cells. Because the initial heart tube does not comprise all the cardiac compartments present in the adult heart, heart muscle cells are added to the distal borders of the tube and within the tube. At both distal borders, mesodermal cell are recruited into the cardiac lineage and, within the heart tube, muscular septa are formed. In this review, the relative late additions of heart muscle cells to the linear heart tube are described and the potential underlying molecular mechanisms are discussed. 相似文献
79.
Eric Giraud Alain Brauman Simon Keleke Bertrand Lelong Maurice Raimbault 《Applied microbiology and biotechnology》1991,36(3):379-383
Summary An amylolytic lactic acid bacterium identified as Lactobacillus plantarum was isolated from cassava roots (Manihot esculenta var. Ngansa) during reting. The amylolytic enzyme synthesized was an extracellular -amylase with an optimum pH of 5.0 and an optimum temperature of 55° C. Cultured on starch, the strain displayed a growth rate of 0.43 h–1, a biomass yield of 0.19 g·g–1 and a lactate yield of 0.81 g·g–1. The growth kinetics were similar on starch and glucose. Sufficient enzyme was synthesized and starch hydrolysis was not a limiting factor for growth. Biosynthesis of the enzyme was observed when the glucose concentration was less than 6.7 g·l–1 and reached up to 4 IU·ml–1 at the end of the fermentation.
Offprint requests to: M. Raimbault 相似文献
80.
Sophie J. Bernelot Moens Hans L. Mooij H . Carlijne Hassing Janine K. Kruit Julia J. Witjes Michiel A. J. van de Sande Aart J. Nederveen Ding Xu Geesje M. Dallinga-Thie Jeffrey D. Esko Erik S. G. Stroes Max Nieuwdorp 《PloS one》2014,9(12)
Exotosin (EXT) proteins are involved in the chain elongation step of heparan sulfate (HS) biosynthesis, which is intricately involved in organ development. Loss of function mutations (LOF) in EXT1 and EXT2 result in hereditary exostoses (HME). Interestingly, HS plays a role in pancreas development and beta-cell function, and genetic variations in EXT2 are associated with an increased risk for type 2 diabetes mellitus. We hypothesized that loss of function of EXT1 or EXT2 in subjects with hereditary multiple exostoses (HME) affects pancreatic insulin secretion capacity and development. We performed an oral glucose tolerance test (OGTT) followed by hyperglycemic clamps to investigate first-phase glucose-stimulated insulin secretion (GSIS) in HME patients and age and gender matched non-affected relatives. Pancreas volume was assessed with magnetic resonance imaging (MRI). OGTT did not reveal significant differences in glucose disposal, but there was a markedly lower GSIS in HME subjects during hyperglycemic clamp (iAUC HME: 0.72 [0.46–1.16] vs. controls 1.53 [0.69–3.36] nmol·l−1·min−1, p<0.05). Maximal insulin response following arginine challenge was also significantly attenuated (iAUC HME: 7.14 [4.22–10.5] vs. controls 10.2 [7.91–12.70] nmol·l−1·min−1 p<0.05), indicative of an impaired beta-cell reserve. MRI revealed a significantly smaller pancreatic volume in HME subjects (HME: 72.0±15.8 vs. controls 96.5±26.0 cm3 p = 0.04). In conclusion, loss of function of EXT proteins may affect beta-cell mass and insulin secretion capacity in humans, and render subjects at a higher risk of developing type 2 diabetes when exposed to environmental risk factors. 相似文献