全文获取类型
收费全文 | 751篇 |
免费 | 25篇 |
出版年
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 13篇 |
2014年 | 15篇 |
2013年 | 50篇 |
2012年 | 32篇 |
2011年 | 30篇 |
2010年 | 25篇 |
2009年 | 27篇 |
2008年 | 47篇 |
2007年 | 45篇 |
2006年 | 51篇 |
2005年 | 29篇 |
2004年 | 40篇 |
2003年 | 36篇 |
2002年 | 29篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 16篇 |
1998年 | 13篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 10篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1970年 | 3篇 |
1968年 | 4篇 |
排序方式: 共有776条查询结果,搜索用时 31 毫秒
111.
Fukami H Chen CA Budd AF Collins A Wallace C Chuang YY Chen C Dai CF Iwao K Sheppard C Knowlton N 《PloS one》2008,3(9):e3222
Modern hard corals (Class Hexacorallia; Order Scleractinia) are widely studied because of their fundamental role in reef building and their superb fossil record extending back to the Triassic. Nevertheless, interpretations of their evolutionary relationships have been in flux for over a decade. Recent analyses undermine the legitimacy of traditional suborders, families and genera, and suggest that a non-skeletal sister clade (Order Corallimorpharia) might be imbedded within the stony corals. However, these studies either sampled a relatively limited array of taxa or assembled trees from heterogeneous data sets. Here we provide a more comprehensive analysis of Scleractinia (127 species, 75 genera, 17 families) and various outgroups, based on two mitochondrial genes (cytochrome oxidase I, cytochrome b), with analyses of nuclear genes (ss-tubulin, ribosomal DNA) of a subset of taxa to test unexpected relationships. Eleven of 16 families were found to be polyphyletic. Strikingly, over one third of all families as conventionally defined contain representatives from the highly divergent "robust" and "complex" clades. However, the recent suggestion that corallimorpharians are true corals that have lost their skeletons was not upheld. Relationships were supported not only by mitochondrial and nuclear genes, but also often by morphological characters which had been ignored or never noted previously. The concordance of molecular characters and more carefully examined morphological characters suggests a future of greater taxonomic stability, as well as the potential to trace the evolutionary history of this ecologically important group using fossils. 相似文献
112.
113.
We conducted a 3-year study of a natural population of the willow leaf beetle Plagiodera versicolora (Coleoptera: Chrysomelidae) on a river bank of the Inukami River, Shiga, central Japan, where four willow species (Salix chaenomeloides, S. eriocarpa, S. integra, and S. serissaefolia) occur sympatrically. Our survey showed that: (1) at the study site, the abundance of P. versicolora greatly varied among years and among willow species; (2) adult abundance changed seasonally with species-specific patterns on different willow species; and (3) the dispersal-settlement of adults had the most pronounced effects on the seasonal population growth rate of P. versicolora. Factors affecting these results were discussed. 相似文献
114.
Yoshida Y Sakai N Masuda H Furuichi M Nishikawa F Nishikawa S Mizuno H Waga I 《Analytical biochemistry》2008,375(2):217-222
Antibody-based detection systems are widely used, but in the cases of immunoprecipitations and enzyme-linked immunoassays, they can be laborious. These techniques require the preparation of at least two kinds of non-cross-reactive immunoglobulin Gs (IgGs), usually made from different species against the single target molecule. Aptamers composed of nucleic acids possess strict recognition ability for the target molecule's three-dimensional structure and, thus, are considered to act like IgG. In this study, experimental trials were designed to combine the advantages of IgG and aptamers. For this purpose, aptamers against rabbit IgG were identified by in vitro selection. One of the obtained aptamers had a dissociation constant lower than 15 pM to the rabbit IgG. It bound specifically to the constant region of the rabbit IgG, and no binding was observed with mouse or goat IgG. Moreover, this aptamer recognized only the native form of rabbit IgG and could not bind the sodium dodecyl sulfate (SDS)-denatured form. These features show the advantage of using the aptamer as a secondary probing agent rather than the usual secondary antibodies. 相似文献
115.
Satoshi Iwao Nobuko Iwao Denis C. Muller Dariush Elahi Hiroshi Shimokata Reubin Andres 《Obesity (Silver Spring, Md.)》2001,9(11):685-695
Objectives: To examine the power of the combined measurements of body mass index (BMI) and waist circumference (WC) for the prediction of abnormality in coronary heart disease risk factors and to determine whether the additional measurement of WC is predictive in older men and women. Research Methods and Procedures: 1190 men and 751 women of the Baltimore Longitudinal Study of Aging were dichotomized into younger (<65 years) and older (65+ years) age groups. Coronary risk factors in the realms of glucose/insulin metabolism, blood pressure, and plasma lipids were assessed. The relationship of BMI and WC, singly and combined, to 10 risk factors for coronary heart disease was examined. Results: In younger and older men and women, BMI and WC are highly correlated (0.84 to 0.88). BMI and WC are also significantly correlated to all 10 coronary risk factors in younger men and women and to 8 of the 10 in the older men and women. Both partial correlation and logistic regression analyses revealed a modest but significant improvement in the prediction of coronary risk in younger men and women by WC after controlling for the level of BMI. There was no improvement in the older subjects. Discussion: WC adds only modestly to the prediction of coronary risk in younger subjects once BMI is known, and adds nothing to the production of risk in older subjects. 相似文献
116.
Mitsuhiro Nishisaka Naoaki Yokoyama Xuenan Xuan Noboru Inoue Hideyuki Nagasawa Kozo Fujisaki Takeshi Mikami Ikuo Igarashi 《International journal for parasitology》2001,31(14):1673-1679
Passive immunisations with a monoclonal antibody termed 1-5H showed a partial but significant inhibition of parasitaemia against Babesia microti challenge infection. By immunoscreening with 1-5H, a clone (termed p58 gene) was obtained from a cDNA expression library of B. microti and the complete nucleotide sequence was determined. A protein homology search showed significant amino acid identities to the η subunit of the chaperonin containing T-complex protein 1 (CCT) of human (59%), mouse (58%) and Plasmodium falciparum (62%). Genomic analyses indicated that the p58 gene is present as a single copy gene and contains a total of approximately 400-bp introns in the genome of B. microti. The mAb 1-5H recognised a 58-kDa protein of B. microti and was found to cross-react with a 60-kDa protein of Babesia rodhaini. These results suggest the possibility that the p58 protein is the CCT η subunit of B. microti and functions as a chaperonin. 相似文献
117.
118.
119.
Satoshi Nasu Kenji Yamaguchi Shigeki Sakakibara Hideto Imai Iwao Ueda 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,677(1):109-119
The intraperitoneal or oral administration of pyrazinamide and pyrazinoic acid (pyrazine 2-carboxylic acid) resulted in a marked increase of the NAD content in rat liver. The injections of pyrazine and pyrazine 2,3-dicarboxylic acid exhibited no significant effect on the hepatic NAD content. The boiled extract obtained from liver and kidney of rat injected with either pyrazinamide or pyrazinoic acid exhibited a potent inhibitory effect on the aminocarboxymuconate-semialdehyde decarboxylase (EC 4.1.1.45) activity in either liver or kidney, although pyrazinamide or pyrazinoic acid per se did not inhibit the enzyme activity. The unknown inhibitor of aminocarboxymuconate-semialdehyde decarboxylase was dialysable and heat-stable, and mostly excreted in urine by 6 and 12 h after injection of pyrazinoic acid and pyrazinamide, respectively. Pyrazine 2,3-dicarboxylic acid, pyrazine, nicotinamide, nicotinic acid, tryptophan, anthranilic acid, 5-hydroxyanthranilic acid and quinolinic acid exhibited no significant effect on the aminocarboxymuconate-semialdehyde decarboxylase activity in liver and kidney at the concentration of 1 mM in the reaction mixture. The expired 14CO2 from l-[benzen ring-U-14C]tryptophan was markedly decreased by the pyrazinamide injection, while the urinary excretion of 14C-labeled metabolites from l-tryptophan, mainly quinolinic acid, was markedly increased. These results suggest that the glutarate pathway of l-tryptophan was strongly inhibited by the inhibitor produced after the administration of pyrazinoic acid and pyrazinamide. Pyrazinamide but not pyrazinoic acid also exhibited a significant inhibition of the nuclear enzyme poly(ADP-ribose) synthetase in rat liver. 相似文献
120.
Ikuko Fujisaki Kenneth G. Rice Leonard G. Pearlstine Frank J. Mazzotti 《Hydrobiologia》2009,635(1):329-338
Feeding opportunities of American alligators (Alligator mississippiensis) in freshwater wetlands in south Florida are closely linked to hydrologic conditions. In the Everglades, seasonally and annually
fluctuating surface water levels affect populations of aquatic organisms that alligators consume. Since prey becomes more
concentrated when water depth decreases, we hypothesized an inverse relationship between body condition and water depth in
the Everglades. On average, condition of adult alligators in the dry season was significantly higher than in the wet season,
but this was not the case for juveniles/subadults. The correlation between body condition and measured water depth at capture
locations was weak; however, there was a significant negative correlation between the condition and predicted water depth
prior to capture for all animals except for spring juveniles/subadults which had a weak positive condition–water depth relationship.
Overall, a relatively strong inverse correlation occurred at 10–49 days prior to the capture day, suggesting that current
body condition of alligators may depend on feeding opportunities during that period. Fitted regression of body condition on
water depth (mean depth of 10 days when condition-water depth correlation was greatest) resulted in a significantly negative
slope, except for spring adult females and spring juveniles/subadults for which slopes were not significantly different from
zero. Our results imply that water management practices may be critical for alligators in the Everglades since water depth
can affect animal condition in a relatively short period of time. 相似文献