全文获取类型
收费全文 | 1668篇 |
免费 | 111篇 |
专业分类
1779篇 |
出版年
2023年 | 17篇 |
2022年 | 18篇 |
2021年 | 28篇 |
2020年 | 21篇 |
2019年 | 30篇 |
2018年 | 42篇 |
2017年 | 42篇 |
2016年 | 42篇 |
2015年 | 69篇 |
2014年 | 85篇 |
2013年 | 84篇 |
2012年 | 109篇 |
2011年 | 115篇 |
2010年 | 77篇 |
2009年 | 52篇 |
2008年 | 93篇 |
2007年 | 89篇 |
2006年 | 98篇 |
2005年 | 95篇 |
2004年 | 94篇 |
2003年 | 68篇 |
2002年 | 60篇 |
2001年 | 24篇 |
2000年 | 15篇 |
1999年 | 27篇 |
1998年 | 16篇 |
1997年 | 22篇 |
1996年 | 17篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 6篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1973年 | 7篇 |
1967年 | 7篇 |
1966年 | 5篇 |
1965年 | 5篇 |
排序方式: 共有1779条查询结果,搜索用时 15 毫秒
81.
82.
Jan Moncol Barbora Kalinakova Miroslava Kleinova Daniela Hudecova Milan Mazur 《Inorganica chimica acta》2004,357(11):3211-3222
New copper(II) clofibriates (clof, {2-(4-chlorophenoxy)-2-methylpropionic or 2-(4-chlorophenoxy)isobutyric acid}) of composition Cu(clof)2L2 (where L=2-pyridylmethanol (2-pymeth) (1), N-methylnicotinamide (Menia) (4), N,N-diethylnicotinamide (Et2nia) (5), isonicotinamide (isonia) (7) or methyl-3-pyridylcarbamate (mpc) (8)), [Cu(clof)2(4-pymeth)2(H2O)] · 2H2O (4-pymeth=4-pyridylmethanol) (2 · 2H2O) and Cu(clof)2L (where L=4-pymeth (3) or Et2nia (6)) have been prepared and spectroscopically characterized. All the Cu(clof)2L2 compounds seem to possess distorted octahedral copper(II) stereochemistry with differing tetragonal distortions. An X-ray analysis of 1 was carried out and it featured a tetragonal-bipyramidal geometry around the copper(II) atom. X-ray analysis of 2 · 2H2O featured a square-pyramidal geometry around copper(II) atom. Both the Cu(clof)2L compounds seem to consist of a binuclear unit of tetracarboxylate type bridging. An X-ray analysis of 6 revealed typical binuclear paddle-wheel type structure, consisting of two copper(II) atoms in square-pyramidal geometry bridged by four carboxylate anions in the xy-plane. All complexes under study were characterized by EPR and electronic spectroscopy. The antimicrobial effects have been tested on various strains of bacteria, yeasts and filamentous fungi. 相似文献
83.
84.
The antioxidant activity and contents of various polyphenol classes in the seeds of 20 soybean hybrids were evaluated. Total polyphenols, tannins and proanthocyanidins were determined after extraction of plant material with 70% aqueous acetone. In addition, flavonoid content was determined. Antioxidant activity of seed extracts was evaluated by DPPH free radical scavenging activity assay. A positive linear correlation between antioxidant activity and contents of total phenols, tannins and proanthocyanidins was established. The highest antioxidant activity was observed in the extracts of hybrids which have higher levels of all polyphenol classes examined. The most of the single-cross hybrids were poor in tannins which recommend them as good source for ensiled livestock feed. Results suggested that polyphenol content should be considered as an important feature of the soybean seed. 相似文献
85.
Irena Axmanová Milan Chytrý Jiří Danihelka Pavel Lustyk Martin Kočí Svatava Kubešová Michal Horsák Mikhail M. Cherosov Paraskovia A. Gogoleva 《Plant Ecology》2013,214(2):207-219
Local species richness–productivity (SR–P) relationship is usually reported as unimodal if long productivity gradients are sampled. However, it tends to be monotonically increasing in low-productive environments due to the decreasing part of the SR–P curve being truncated. Previous work indicated that this can hold true for forest herb layers, because of an upper bound on productivity caused mainly by canopy shading. Here, we ask whether the same pattern exists in a region with an upper bound on productivity caused by a harsh climate. We sampled herbaceous vegetation of boreal forests and grasslands in a low-productive region of central Yakutia (NE Siberia) with dry and winter-cool continental climate. We collected data on species composition, herb-layer productivity (aboveground herbaceous biomass), soil chemistry and light availability. We applied regression models to discriminate between monotonically increasing, decreasing and unimodal responses of herb-layer species richness to measured variables and analysed trends in the species-pool size and beta diversity along the productivity gradient. Our expectation of the monotonically increasing SR–P relationship was confirmed for neither forest herb layers nor grasslands. In the forest herb layers, no relationship was detected. In grasslands, the relationship was unimodal with species richness decline starting at much lower productivity levels than in more productive temperate grasslands. Potential causes for this decline are either limitation of local species richness by the species pool, which contains few species adapted to more productive habitats, or competitive exclusion, which can become an important control of species richness under lower levels of productivity than is the case in temperate grasslands. 相似文献
86.
Allison Jones Andrew E. Teschendorff Quanxi Li Jane D. Hayward Athilakshmi Kannan Tim Mould James West Michal Zikan David Cibula Heidi Fiegl Shih-Han Lee Elisabeth Wik Richard Hadwin Rupali Arora Charlotte Lemech Henna Turunen P?ivi Pakarinen Ian J. Jacobs Helga B. Salvesen Milan K. Bagchi Indrani C. Bagchi Martin Widschwendter 《PLoS medicine》2013,10(11)
87.
Ivan Soldatovic Rade Vukovic Djordje Culafic Milan Gajic Vesna Dimitrijevic-Sreckovic 《PloS one》2016,11(1)
Objective
To evaluate siMS score and siMS risk score, novel continuous metabolic syndrome scores as methods for quantification of metabolic status and risk.Materials and Methods
Developed siMS score was calculated using formula: siMS score = 2*Waist/Height + Gly/5.6 + Tg/1.7 + TAsystolic/130—HDL/1.02 or 1.28 (for male or female subjects, respectively). siMS risk score was calculated using formula: siMS risk score = siMS score * age/45 or 50 (for male or female subjects, respectively) * family history of cardio/cerebro-vascular events (event = 1.2, no event = 1). A sample of 528 obese and non-obese participants was used to validate siMS score and siMS risk score. Scores calculated as sum of z-scores (each component of metabolic syndrome regressed with age and gender) and sum of scores derived from principal component analysis (PCA) were used for evaluation of siMS score. Variants were made by replacing glucose with HOMA in calculations. Framingham score was used for evaluation of siMS risk score.Results
Correlation between siMS score with sum of z-scores and weighted sum of factors of PCA was high (r = 0.866 and r = 0.822, respectively). Correlation between siMS risk score and log transformed Framingham score was medium to high for age groups 18+,30+ and 35+ (0.835, 0.707 and 0.667, respectively).Conclusions
siMS score and siMS risk score showed high correlation with more complex scores. Demonstrated accuracy together with superior simplicity and the ability to evaluate and follow-up individual patients makes siMS and siMS risk scores very convenient for use in clinical practice and research as well. 相似文献88.
89.
90.