全文获取类型
收费全文 | 7118篇 |
免费 | 523篇 |
出版年
2023年 | 33篇 |
2022年 | 91篇 |
2021年 | 192篇 |
2020年 | 104篇 |
2019年 | 132篇 |
2018年 | 195篇 |
2017年 | 178篇 |
2016年 | 271篇 |
2015年 | 386篇 |
2014年 | 435篇 |
2013年 | 544篇 |
2012年 | 718篇 |
2011年 | 661篇 |
2010年 | 387篇 |
2009年 | 353篇 |
2008年 | 459篇 |
2007年 | 427篇 |
2006年 | 382篇 |
2005年 | 357篇 |
2004年 | 297篇 |
2003年 | 266篇 |
2002年 | 239篇 |
2001年 | 40篇 |
2000年 | 42篇 |
1999年 | 48篇 |
1998年 | 54篇 |
1997年 | 31篇 |
1996年 | 31篇 |
1995年 | 31篇 |
1994年 | 27篇 |
1993年 | 20篇 |
1992年 | 24篇 |
1991年 | 15篇 |
1990年 | 15篇 |
1989年 | 19篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 11篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1966年 | 2篇 |
排序方式: 共有7641条查询结果,搜索用时 375 毫秒
171.
M. Soledad Vazquez Mariano A. Rodríguez-Cabal Daniela V. Gonzalez Gabriel S. Pacheco Guillermo C. Amico 《Bird Study》2013,60(4):478-483
Capsule: Studies of nest predation using artificial nests need to consider the effect of egg size on the types of predator that are detected.Aims: To estimate the nest predation rate in the Patagonian temperate forest and evaluate the influence of egg size on predator guild.Methods: On different plant species, we placed 108 nests each containing eggs of either Atlantic Canary Serinus canaria or Common Quail Coturnix coturnix, and a model clay egg of equal size to the real egg. Nest predators were identified from the marks left on the clay eggs or by videos recorded using camera traps.Results: 86% of the nests were predated. Birds, mainly Chimango Caracara Milvago chimango, were the main nest predators. A marsupial, the Monito del Monte Dromiciops gliroides, and rodents also contributed to nest predation. Nest predation rates were similar for both egg sizes but the nest predator guild was different. Birds and rodents preyed on both eggs but the Monito del Monte consumed mainly small eggs.Conclusion: Egg size did not influence the rate of nest predation but, instead, affected the nest predator guild. Consequently, in order to avoid underestimating the impacts of small predators, egg size should be considered in studies of nest predation. 相似文献
172.
The assays commonly used to determine ATP content in biological samples generally measure total cellular ATP content, but not the different subcellular pools. In this study a new simple method for measuring ATP content in a cytosol-enriched fraction (CEF) was developed, based on a rapid cytosolic ATP extraction (by an isotonic grinding medium that preserves organelle integrity) and its detection monitoring the NADPH fluorescence generated via hexokinase/glucose-6-phosphate dehydrogenase coupled reactions. Four protocols, differing for timing of NADPH generation and for either the presence or absence of some inhibitors of ATP and NADPH metabolism, were compared by determining CEF-ATP, as well as total ATP, in durum wheat (Triticum durum Desf.) etiolated seedlings. The best protocol was the one adopting both simultaneous NADPH generation and use of inhibitors during tissue homogenization. This protocol also showed higher performance than the classical trichloroacetic acid extraction. Using the new method, CEF-ATP content was assessed in control, salt- and osmotic-stressed seedlings, resulting 2.68 ± 0.04, 1.69 ± 0.12 (?40%) and 1.35 ± 0.16 (?50%) μmol/g dry weight, respectively. Finally, the effects of this stress-dependent decrease of cytosolic ATP were evaluated with respect to a possible modulation of two mitochondrial energy-dissipating systems, the uncoupling protein (PUCP) and the K+ channel (PmitoKATP), both inhibited by cytosolic ATP. Experiments carried out at different physiological ATP concentrations suggest that the decreased cytosolic ATP content occurring under hyperosmotic stress may contribute to attenuate inhibition of PmitoKATP, thus promoting its activity (up to about 90%), but not of PUCP, that appears to lose ATP sensitivity under stress condition. 相似文献
173.
Jeffrey A. Harvey Daniela Weber Patrick De Clercq Rieta Gols 《Entomologia Experimentalis et Applicata》2013,149(3):219-228
In some parasitic Hymenoptera the dying caterpillars remain attached or close to the parasitoid cocoons. It has been suggested that the caterpillars act as ‘bodyguards’ for the vulnerable cocoons and therefore protect them against predators and/or hyperparasitoids (the ‘usurpation hypothesis’). This hypothesis has been demonstrated in associations where the caterpillars remain active and/or aggressive after parasitism. However, in other associations the caterpillars are so physiologically depleted after parasitism that they are unable to physically defend the cocoons and instead sit atop them in a moribund state. In this study a generalist predator, the spined soldier bug, Podisus maculiventris Say (Hemiptera: Pentatomidae), was provided with cocoons of the gregarious endoparasitoid Cotesia glomerata L. and the solitary endoparasitoid Microplitis mediator Haliday (both Hymenoptera: Braconidae), in turn attended by their hosts, Pieris brassicae L. (Lepidoptera: Pieridae) and Mamestra brassicae L. (Lepidoptera: Noctuidae), respectively. Cotesia glomerata produces broods of up to 40 cocoons and the dying caterpillars sit atop the cocoons where they exhibit little response to physical stimuli. Previous studies reported that dying P. brassicae caterpillars were ineffective bodyguards against two species of hyperparasitoids. In both associations, the dying host caterpillars were significantly preferred as food by P. maculiventris over the parasitoid cocoons. However, in absence of caterpillars, the bugs readily attacked the C. glomerata cocoons. Alternatively, the survival of M. mediator was very low, irrespective of whether a caterpillar was present or not. Caterpillars attacked by M. mediator are several times smaller than those attacked by C. glomerata. Consequently, the predators ran out of food much more quickly in the former and switched from one prey to the other. We show that in some host–parasitoid associations the dying caterpillars provide more visually apparent or nutritionally superior prey, rather than acting as bodyguards. 相似文献
174.
Daniela Morick Michaela Schatz Raphael Hubrich Helen Hoffmeister Anya Krefft Ralph Witzgall Claudia Steinem 《Biochemical and biophysical research communications》2013
Polycystin-2 (PC2) trafficking has been proposed to be a result of the interaction of PIGEA14 with PC2 as a function of the phosphorylation state of PC2. Here, we investigated the interaction of PIGEA14 with the C-terminal part of polycystin-2 wild type (cPC2wt) and the pseudophosphorylated mutant (cPC2S812D) to first, quantify the binding affinity between cPC2 and PIGEA14 and second, to elucidate the influence of PC2 phosphorylation on PIGEA14 binding. Solid supported membranes composed of octanethiol/1,2-dioleoyl-sn-glycero-3-phosphocholine doped with the receptor lipid DOGS–NTA–Ni were used to attach PIGEA14 to the membrane via its hexahistidine tag. By means of the quartz crystal microbalance technique, binding affinities as well as kinetic constants of the interaction were extracted in a label-free manner by applying the scaled particle theory. The results show that the dissociation constant of cPC2 to PIGEA14 is in the 10 nM regime providing strong evidence of a very specific interaction of cPC2 with PIGEA14. The interaction of cPC2wt is twofold larger than that of cPC2S812D. The moderate higher binding affinity of cPC2wt to PIGEA14 is discussed in light of PC2 trafficking to the plasma membrane. 相似文献
175.
176.
Vasopressin activates Akt/mTOR pathway in smooth muscle cells cultured in high glucose concentration
Daniela K. Montes Marianne Brenet Vanessa C. Muñoz Patricia V. Burgos Carolina I. Villanueva Carlos D. Figueroa Carlos B. González 《Biochemical and biophysical research communications》2013
Mammalian target of rapamycin (mTOR) complex is a key regulator of autophagy, cell growth and proliferation. Here, we studied the effects of arginine vasopressin (AVP) on mTOR activation in vascular smooth muscle cells cultured in high glucose concentration. 相似文献
177.
178.
Simona Maria Monti Giuseppina De Simone Nina A. Dathan Martha Ludwig Daniela Vullo Andrea Scozzafava Clemente Capasso Claudiu T. Supuran 《Bioorganic & medicinal chemistry letters》2013,23(6):1626-1630
Several β-carbonic anhydrases (CAs, EC 4.2.1.1) are present in all land plants examined thus far. Here we report the first detailed biochemical characterization of one such isoform, FbiCA 1, from the C4 plant Flaveria bidentis, which was cloned, purified and characterized as recombinant protein. FbiCA 1 has an interesting CO2 hydrase catalytic activity (kcat of 1.2 × 105 and kcat/Km of 7.5 × 106 M?1 × s?1) and was moderately inhibited by most simple/complex inorganic anions. Potent FbiCA 1 inhibitors were also detected, such as trithiocarbonate, diethyldithiocarbamate, sulfamide, sulfamic acid, phenylboronic acid and phenylarsonic acid (KIs in the range of 4–60 μM). Such inhibitors may be used as tools to better understand the role of various β-CA isoforms in photosynthesis. 相似文献
179.
Atilla Akdemir Daniela Vullo Viviana De Luca Andrea Scozzafava Vincenzo Carginale Mosè Rossi Claudiu T. Supuran Clemente Capasso 《Bioorganic & medicinal chemistry letters》2013,23(4):1087-1090
The α-carbonic anhydrase (CA, EC 4.2.1.1) from the extremophilic bacterium Sulfurihydrogenibium azorense (SazCA) was recently shown to be the fastest CA known. Here we investigated this enzyme for its activation with a series of amino acids and amines. The best SazCA activators were d-Phe, l-DOPA, l- and d-Trp, dopamine and serotonin, which showed activation constants in the range of 3–23 nM. l- and d-His, l-Phe, l-Tyr, 2-pyridyl-methylamine and L-adrenaline were also effective activators (KAs in the range of 62–90 nM), whereas d-Dopa, d-Tyr and several heterocyclic amines showed activity in the micromolar range. The good thermal stability, robustness, very high catalytic activity and propensity to be activated by simple amino acids and amines, make SazCA a very interesting candidate for biomimetic CO2 capture processes. 相似文献
180.
Ahmed M. Alafeefy Semra Isik Nabila A. Al-Jaber Daniela Vullo Hatem A. Abdel-Aziz Abdelkader E. Ashour Amani S. Awaad Clemente Capasso Claudiu T. Supuran 《Bioorganic & medicinal chemistry letters》2013,23(12):3570-3575
A series of benzenesulfonamides incorporating cyanoacrylamide moieties (tyrphostine analogs) were assayed as inhibitors of the β-carbonic anhydrase (CA, EC 4.2.1.1) from Saccharomyces cerevisiae, ScCA. Some of these compounds were low nanomolar or subnanomolar ScCA inhibitors and showed selectivity ratios in the range of 4.91–69.86 for inhibiting the yeast enzyme over the offtarget human (h) isoforms hCA I and of 6.46–13.52 for inhibiting ScCA over hCA II. The model organism S. cerevisiae and this particular enzyme may be useful for detecting antifungals with a novel mechanism of action compared to the classical azole drugs to which significant drug resistance emerged. Indeed, some of these sulfonamides inhibited the growth of the yeast with CC50-s in the range of 0.73–6.54 μM. 相似文献