全文获取类型
收费全文 | 4565篇 |
免费 | 386篇 |
国内免费 | 23篇 |
出版年
2023年 | 37篇 |
2022年 | 28篇 |
2021年 | 63篇 |
2020年 | 58篇 |
2019年 | 55篇 |
2018年 | 121篇 |
2017年 | 108篇 |
2016年 | 136篇 |
2015年 | 138篇 |
2014年 | 151篇 |
2013年 | 273篇 |
2012年 | 383篇 |
2011年 | 355篇 |
2010年 | 180篇 |
2009年 | 196篇 |
2008年 | 313篇 |
2007年 | 285篇 |
2006年 | 249篇 |
2005年 | 239篇 |
2004年 | 204篇 |
2003年 | 156篇 |
2002年 | 166篇 |
2001年 | 120篇 |
2000年 | 116篇 |
1999年 | 76篇 |
1998年 | 39篇 |
1997年 | 26篇 |
1996年 | 38篇 |
1995年 | 30篇 |
1994年 | 28篇 |
1993年 | 22篇 |
1992年 | 46篇 |
1991年 | 46篇 |
1990年 | 55篇 |
1989年 | 25篇 |
1988年 | 37篇 |
1987年 | 31篇 |
1986年 | 30篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 23篇 |
1982年 | 23篇 |
1981年 | 18篇 |
1980年 | 18篇 |
1979年 | 29篇 |
1978年 | 19篇 |
1977年 | 12篇 |
1976年 | 12篇 |
1974年 | 15篇 |
1968年 | 12篇 |
排序方式: 共有4974条查询结果,搜索用时 31 毫秒
991.
Layal Fahed Didier Stien Naïm Ouaini Véronique Eparvier Marc El Beyrouthy 《化学与生物多样性》2016,13(5):591-595
The chemical compositions and antimicrobial activities of the essential oils (EOs) of aerial parts of Salvia multicaulis Vahl , collected during the same week from two different Lebanese regions, were investigated. The EOs were obtained by hydrodistillation using a Clevenger‐type apparatus and characterized by GC and GC/MS analyses. The minimum inhibitory concentrations of these EOs were determined against one Gram‐negative and two Gram‐positive bacteria, one yeast, and five dermatophytes using the broth microdilution technique. One EO was notably active against Staphylococcus aureus, methicillin‐resistant S. aureus, and all of the Trichophyton species tested. Nerolidol was found to be the major compound in the active oil; nerolidol was also absent from the inactive oil. This study demonstrated that nerolidol shows antimicrobial activity and therefore significantly contributes to the antimicrobial potential of the oil. The chemical diversity of worldwide S. multicaulis EOs was analyzed, revealing that the EOs of this study belong to two different chemotypes found in the literature. The nerolidol chemotype appears to be restricted to Lebanon, and it can be used as antimicrobial agent against external bacterial and fungal infections. 相似文献
992.
993.
Christoffer Høyvik Hilde Christophe Pélabon Loreleï Guéry Geir Wing Gabrielsen Sébastien Descamps 《Ecology and evolution》2016,6(7):1914-1921
The energetic costs of reproduction in birds strongly depend on the climate experienced during incubation. Climate change and increasing frequency of extreme weather events may severely affect these costs, especially for species incubating in extreme environments. In this 3‐year study, we used an experimental approach to investigate the effects of microclimate and nest shelter on the incubation effort of female common eiders (Somateria mollissima) in a wild Arctic population. We added artificial shelters to a random selection of nesting females, and compared incubation effort, measured as body mass loss during incubation, between females with and without shelter. Nonsheltered females had a higher incubation effort than females with artificial shelters. In nonsheltered females, higher wind speeds increased the incubation effort, while artificially sheltered females experienced no effect of wind. Although increasing ambient temperatures tended to decrease incubation effort, this effect was negligible in the absence of wind. Humidity had no marked effect on incubation effort. This study clearly displays the direct effect of a climatic variable on an important aspect of avian life‐history. By showing that increasing wind speed counteracts the energetic benefits of a rising ambient temperature, we were able to demonstrate that a climatic variable other than temperature may also affect wild populations and need to be taken into account when predicting the effects of climate change. 相似文献
994.
Stochastic multiscale modelling of cortical bone elasticity based on high-resolution imaging 总被引:1,自引:0,他引:1
995.
Gustavo Ponce Iram P. Sanchez Selene M. García Jose M. Torrado Saúl Lozano‐Fuentes Beatriz Lopez‐Monroy Adriana E. Flores 《Insect Science》2016,23(6):829-834
The L1014F mutation in the voltage‐sodium channel gene has been associated with resistance to DDT and pyrethroids in various arthropod species including mosquitoes. We determined the frequency of the L1014F kdr mutation in 16 field populations of Culex quinquefasciatus from Northeastern Mexico collected between 2008 and 2013. The L1014F was present in all populations analyzed with the lowest frequency (3.33%) corresponding to the population from Monclova collected in 2012, and the highest frequency (63.63%) from the Monterrey population collected in 2012. The presence of a kdr mutation in populations of Cx. quinquefasciatus from northeastern Mexico provides evidence of pyrethroid resistance. This requires a special attention, considering that pyrethroid‐based insecticides are commonly used in vector‐control campaigns, especially against Aedes aegypti (L.). 相似文献
996.
R Gentile V Sciscioli G Petrosino A di Summa M Lenti G Passantino 《Bollettino della Società italiana di biologia sperimentale》1989,65(12):1107-1114
The authors report the variable number of pyloric caeca of some species of fish and describe their macroanatomy. They also describe and compare the microanatomy of pyloric caeca in three species; in particular they point out the thickness of tunica muscularis, the shape and length of villi which protrude into the lumen and the variable number of goblet cells. The tunica muscularis is very strong in Uranoscopus and consists of three strata: external and inner longitudinal strata, middle circular stratum. The tunica muscularis is less thick in Diplodus and in Scorpaena. The lamina propria and epithelium form villi which protrude into the lumen. They are covered with columnar epithelium and goblet cells which are more numerous in Uranoscopus and Scorpaena and less numerous in Diplodus. At last the authors describe in pyloric caeca of Scorpaena the presence of a network which engages all the lumen; it consists of connective tissue septa which directly derive from the lamina propria and is covered with the same columnar epithelium and goblet cells. 相似文献
997.
Calcium phosphate deposits in domes of human pancreatic adenocarcinoma (Capan-1) cell cultures 总被引:2,自引:0,他引:2
E Hollande J H Levrat di Donato M Fanjul C Palevody M Daumas J Puech G Ratovo 《Biology of the cell / under the auspices of the European Cell Biology Organization》1990,69(3):191-203
Human pancreatic cells of the Capan-1 line form domes in culture during the stationary growth stage. The domes are thought to be a result of the transport of water and electrolytes by the Capan-1 cells. In older Capan-1 cultures, the epithelial sheets formed thickenings from several layers of cells of which the outermost ones were joined by tight type junctions. In the intracellular space, deposits of insoluble calcium salts were observed. Culture of Capan-1 cells in the presence of fibroblasts prolonged survival of the cultures with intact domes for more than 80 days. The Capan-1 cells proliferated forming multilayers and closed cavities which we called super-domes. X-ray spectrometry and electron diffraction analysis showed that the abundant deposits inside these cavities consisted of calcium phosphate in an apatite structure. The number of these deposits increased with time in culture, and they appeared to be formed at the sites of contact with an extracellular matrix consisting of cell debris. Deposits were not observed within the culture medium. Cells from domes were stained cytochemically for ATPases and alkaline phosphatases and examined by light and electron microscopy. The Capan-1 cells surrounding the domes were differentiated, polarized cells containing placental type alkaline phosphatases on their apical membranes and Ca2(+)-ATPases on their basolateral membranes. These enzymes were thought to play a role in the accumulation of phosphate and Ca2+ ions in the dome cavities, which then formed crystals in the presence of organic compounds produced by lysis of cells of the deepest layers of the super-domes. The crystals of hydroxyapatite observed in standard Capan-1 cell cultures and those cocultured with fibroblasts were assumed to be a result of transepithelial transport of Ca2+ and phosphate ions by these cells. 相似文献
998.
Comparative study on glucocerebrosidase in spleens from patients with Gaucher disease. 总被引:1,自引:0,他引:1 下载免费PDF全文
J M Aerts W E Donker-Koopman S Brul S Van Weely M C Sa Miranda J A Barranger J M Tager A W Schram 《The Biochemical journal》1990,269(1):93-100
In Gaucher disease (glucosylceramide lipidosis), deficiency of glucocerebrosidase causes pathological storage of glucosylceramide, particularly in the spleen. A comparative biochemical and immunological analysis has therefore been made of glucocerebrosidase in spleens from normal subjects (n = 4) and from Gaucher disease patients with non-neuronopathic (n = 5) and neuronopathic (n = 5) phenotypes. The spleens from all Gaucher disease patients showed markedly decreased glucocerebrosidase activity. Discrimination of different phenotypes of Gaucher disease was not possible on the basis of the level of residual enzyme activity, or by measurements, using the immunopurified enzyme, of kinetic constants, pI or molecular mass forms. A severe decrease was found in the specific activity of glucocerebrosidase purified to homogeneity from the spleen of a patient with the non-neuronopathic phenotype of Gaucher disease, as compared with that of the enzyme purified from the spleen of a normal subject. This finding was confirmed by an immunological method developed for accurate assessment of the relative enzyme activity per molecule of glucocerebrosidase protein. The method revealed that the residual enzyme in the spleens of all investigated patients with a non-neuronopathic course of Gaucher disease had a more than 7-fold decreased activity of glucocerebrosidase (measured in the presence of taurocholate) per molecule of enzyme, and that the concentration of glucocerebrosidase molecules in the spleens of these patients was near normal. Observations made with immunoblotting experiments were consistent with these findings. In contrast, in the spleens of patients with neuronopathic phenotypes of Gaucher disease, the concentration of glucocerebrosidase molecules was severely decreased. 相似文献
999.
Anna Pelet Agnès Rotig Catherine Bonaïti-Pellié Daniel Rabier Valérie Cormier Elias Toumas Danièle Hentzen Jean-Marie Saudubray Arnold Munnich 《Human genetics》1990,84(2):167-171
Summary Ornithine transcarbamylase (OTC) deficiency is an X-linked disease responsible for lethal neonatal hyperammonemia in males. Partial OTC deficiency also occurs in females and can be responsible for life-threatening hyperammonemic comas in heterozygotes (15%). Increased orotic acid excretion occurs in both symptomatic and asymptomatic carriers, especially under protein loading tests. The disease is therefore partially dominant with neonatal lethality in the hemizygous male; the fraction of new mutations has previously been estimated to be low in males (point estimation = 0, upper bound of the confidence interval = 0.16) and 57% in females. Genetic counseling in this disease is difficult because it is not clear whether a negative protein loading test rules out carrier status. In an attempt to determine how reliable the test is for carrier detection, we investigated ten obligate carriers for orotic acid excretion; considering all data available, we concluded that the test is rarely negative in obligate carriers (8%). Consequently, a negative test in a mother decreases the minimum risk of being a carrier from 84% a priori to 30% if she had an affected son and from 43% a priori to 5% if she had a heterozygous daughter. Finally, the diagnosis of a new mutation in the germ cells of the maternal grandfather in one particular family could be ascertained by extensive DNA analysis. 相似文献
1000.