全文获取类型
收费全文 | 488篇 |
免费 | 3篇 |
国内免费 | 3篇 |
专业分类
系统科学 | 10篇 |
教育与普及 | 1篇 |
理论与方法论 | 5篇 |
现状及发展 | 199篇 |
研究方法 | 90篇 |
综合类 | 179篇 |
自然研究 | 10篇 |
出版年
2018年 | 15篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 11篇 |
2014年 | 9篇 |
2013年 | 14篇 |
2012年 | 46篇 |
2011年 | 54篇 |
2010年 | 22篇 |
2009年 | 10篇 |
2008年 | 32篇 |
2007年 | 22篇 |
2006年 | 33篇 |
2005年 | 24篇 |
2004年 | 30篇 |
2003年 | 23篇 |
2002年 | 24篇 |
1999年 | 3篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 8篇 |
1972年 | 6篇 |
1971年 | 6篇 |
1970年 | 4篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1966年 | 3篇 |
1965年 | 2篇 |
1964年 | 3篇 |
1962年 | 1篇 |
1960年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1956年 | 1篇 |
1955年 | 5篇 |
1954年 | 1篇 |
1947年 | 1篇 |
排序方式: 共有494条查询结果,搜索用时 0 毫秒
401.
402.
Phenolic lipids are a very diversified group of compounds derived from mono and dihydroxyphenols, i.e., phenol, catechol,
resorcinol, and hydroquinone. Due to their strong amphiphilic character, these compounds can incorporate into erythrocytes
and liposomal membranes. In this review, the antioxidant, antigenotoxic, and cytostatic activities of resorcinolic and other
phenolic lipids are described. The ability of these compounds to inhibit bacterial, fungal, protozoan and parasite growth
seems to depend on their interaction with proteins and/or on their membrane-disturbing properties. 相似文献
403.
Maria J. Marcaida Inés G. Muñoz Francisco J. Blanco Jesús Prieto Guillermo Montoya 《Cellular and molecular life sciences : CMLS》2010,67(5):727-748
Homing endonucleases (HE) are double-stranded DNAses that target large recognition sites (12–40 bp). HE-encoding sequences
are usually embedded in either introns or inteins. Their recognition sites are extremely rare, with none or only a few of
these sites present in a mammalian-sized genome. However, these enzymes, unlike standard restriction endonucleases, tolerate
some sequence degeneracy within their recognition sequence. Several members of this enzyme family have been used as templates
to engineer tools to cleave DNA sequences that differ from their original wild-type targets. These custom HEs can be used
to stimulate double-strand break homologous recombination in cells, to induce the repair of defective genes with very low
toxicity levels. The use of tailored HEs opens up new possibilities for gene therapy in patients with monogenic diseases that
can be treated ex vivo. This review provides an overview of recent advances in this field. 相似文献
404.
405.
406.
Rodrigo Macip-Ríos Maria de Lourdes Arias Cisneros Xochitl S. Aguilar-Miguel Gustavo Casas-Andreu 《西北部美国博物学家》2011,69(4)
Ecological data directly from the field are important in understanding the life history strategies of kinosternid species in the tropics. Herein we summarize the basic population ecology and life history of Kinosternon integrum in the municipality of Tonatico (southeastern Estado de México, México). From October 2003 to November 2004, we marked a total of 204 turtles and recaptured 118 of them. Mean population size using the Jolly-Seber model was 197 (95% CI 128–416) individuals, with a sex ratio of 1:1.7, biased to females. Males were larger than females in carapace length and plastron length. The reproductive season starts in late June and finishes in late October. The smallest female with oviductal eggs was 122 mm in carapace length. Mean clutch size was 4 eggs ( s = 1.77, range 1–8) and was significantly and positively related to body size. Mean egg length was 30.43 mm ( s = 2.24, range 23.92–35.96), mean width was 16.35 mm ( s = 1.01, range 12.99–18.30), and mean weight was 5.14 g ( s = 0.60, range 3.41–6.57). Mean egg length was significantly and inversely related to clutch size. Relative clutch mass (reproductive effort) was 0.043 ( s = 0.017, range 0.017–0.071), which is the smallest value reported for the genus Kinosternon. Additionally, there was no evidence of a pelvic restriction on egg size in this population. This is the first study that documents basic population ecology and reproductive characteristics for a single population of the most widespread freshwater turtle in Mexico. 相似文献
407.
Christian Feißt Carlo Pergola Marija Rakonjac Antonietta Rossi Andreas Koeberle Gabriele Dodt Marika Hoffmann Christina Hoernig Lutz Fischer Dieter Steinhilber Lutz Franke Gisbert Schneider Olof Rådmark Lidia Sautebin Oliver Werz 《Cellular and molecular life sciences : CMLS》2009,66(16):2759-2771
We previously showed that, in vitro, hyperforin from St. John’s wort (Hypericum perforatum) inhibits 5-lipoxygenase (5-LO), the key enzyme in leukotriene biosynthesis. Here, we demonstrate that hyperforin possesses
a novel and unique molecular pharmacological profile as a 5-LO inhibitor with remarkable efficacy in vivo. Hyperforin (4 mg/kg, i.p.) significantly suppressed leukotriene B4 formation in pleural exudates of carrageenan-treated rats associated with potent anti-inflammatory effectiveness. Inhibition
of 5-LO by hyperforin, but not by the iron-ligand type 5-LO inhibitor BWA4C or the nonredox-type inhibitor ZM230487, was abolished
in the presence of phosphatidylcholine and strongly reduced by mutation (W13A-W75A-W102A) of the 5-LO C2-like domain. Moreover,
hyperforin impaired the interaction of 5-LO with coactosin-like protein and abrogated 5-LO nuclear membrane translocation
in ionomycin-stimulated neutrophils, processes that are typically mediated via the regulatory 5-LO C2-like domain. Together,
hyperforin is a novel type of 5-LO inhibitor apparently acting by interference with the C2-like domain, with high effectiveness
in vivo. 相似文献
408.
The aim of this paper is to propose a new methodology that allows forecasting, through Vasicek and CIR models, of future expected interest rates based on rolling windows from observed financial market data. The novelty, apart from the use of those models not for pricing but for forecasting the expected rates at a given maturity, consists in an appropriate partitioning of the data sample. This allows capturing all the statistically significant time changes in volatility of interest rates, thus giving an account of jumps in market dynamics. The new approach is applied to different term structures and is tested for both models. It is shown how the proposed methodology overcomes both the usual challenges (e.g., simulating regime switching, volatility clustering, skewed tails) as well as the new ones added by the current market environment characterized by low to negative interest rates. 相似文献
409.
410.
C. Rocca F. Scavello M. C. Granieri T. Pasqua N. Amodio S. Imbrogno A. Gattuso R. Mazza Maria Carmela Cerra Tommaso Angelone 《Cellular and molecular life sciences : CMLS》2018,75(4):743-756
Phoenixin-14 (PNX) is a newly identified peptide co-expressed in the hypothalamus with the anorexic and cardioactive Nesfatin-1. Like Nesfatin-1, PNX is able to cross the blood–brain barrier and this suggests a role in peripheral modulation. Preliminary mass spectrography data indicate that, in addition to the hypothalamus, PNX is present in the mammalian heart. This study aimed to quantify PNX expression in the rat heart, and to evaluate whether the peptide influences the myocardial function under basal condition and in the presence of ischemia/reperfusion (I/R). By ELISA the presence of PNX was detected in both hypothalamus and heart. In plasma of normal, but not of obese rats, the peptide concentrations increased after meal. Exposure of the isolated and Langendorff perfused rat heart to exogenous PNX induces a reduction of contractility and relaxation, without effects on coronary pressure and heart rate. As revealed by immunoblotting, these effects were accompanied by an increase of Erk1/2, Akt and eNOS phosphorylation. PNX (EC50 dose), administered after ischemia, induced post-conditioning-like cardioprotection. This was revealed by a smaller infarct size and a better systolic recovery with respect to those detected on hearts exposed to I/R alone. The peptide also activates the cardioprotective RISK and SAFE cascades and inhibits apoptosis. These effects were also observed in the heart of obese rats. Our data provide a first evidence on the peripheral activity of PNX and on its direct cardiomodulatory and cardioprotective role under both normal conditions and in the presence of metabolic disorders. 相似文献