全文获取类型
收费全文 | 7273篇 |
免费 | 532篇 |
国内免费 | 2篇 |
出版年
2023年 | 60篇 |
2022年 | 128篇 |
2021年 | 203篇 |
2020年 | 152篇 |
2019年 | 221篇 |
2018年 | 243篇 |
2017年 | 230篇 |
2016年 | 289篇 |
2015年 | 416篇 |
2014年 | 400篇 |
2013年 | 539篇 |
2012年 | 576篇 |
2011年 | 628篇 |
2010年 | 388篇 |
2009年 | 321篇 |
2008年 | 428篇 |
2007年 | 403篇 |
2006年 | 354篇 |
2005年 | 317篇 |
2004年 | 290篇 |
2003年 | 260篇 |
2002年 | 234篇 |
2001年 | 73篇 |
2000年 | 53篇 |
1999年 | 54篇 |
1998年 | 51篇 |
1997年 | 52篇 |
1996年 | 41篇 |
1995年 | 36篇 |
1994年 | 21篇 |
1993年 | 28篇 |
1992年 | 33篇 |
1991年 | 24篇 |
1990年 | 21篇 |
1989年 | 15篇 |
1988年 | 23篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1982年 | 12篇 |
1981年 | 18篇 |
1980年 | 14篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1975年 | 10篇 |
1974年 | 7篇 |
排序方式: 共有7807条查询结果,搜索用时 93 毫秒
991.
Igual José M Velázquez Encarna Mateos Pedro F. Rodríguez-Barrueco Claudino Cervantes Emilio Martínez-Molina Eustoquio 《Plant and Soil》2001,229(1):35-39
Carboxymethyl cellulase activities were evaluated in eight strains of Frankia from diverse host specificity groups and geographical origins. Cellulase activity was detected in culture supernatants of all strains in the absence of CMC (Carboxymethylcellulose) as an inducer using both double-layer plate and reducing sugar assays, indicating a constitutive production of CM-cellulases by Frankia. CM-cellulase isoenzyme profiles were visualized using activity gel electrophoresis of concentrated culture supernatants. Different electrophoretic profiles were observed among the eight strains tested, which correlate with the host specificity and taxonomic grouping of Frankia. 相似文献
992.
Characterization of Rhizobial Isolates of Phaseolus vulgaris by Staircase Electrophoresis of Low-Molecular-Weight RNA
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Encarna Velzquez Esperanza Martínez-Romero Dulce Nombre Rodríguez-Navarro Martha E. Trujillo Antonio Daza Pedro F. Mateos Eustoquio Martínez-Molina Peter van Berkum 《Applied microbiology》2001,67(2):1008-1010
Low-molecular-weight (LMW) RNA molecules were analyzed to characterize rhizobial isolates that nodulate the common bean growing in Spain. Since LMW RNA profiles, determined by staircase electrophoresis, varied across the rhizobial species nodulating beans, we demonstrated that bean isolates recovered from Spanish soils presumptively could be characterized as Rhizobium etli, Rhizobium gallicum, Rhizobium giardinii, Rhizobium leguminosarum bv. viciae and bv. trifolii, and Sinorhizobium fredii. 相似文献
993.
Igual José M. Valverde Angel Rivas Raúl Mateos Pedro F. Rodríguez-Barrueco C. Martínez-Molina Eustoquio Cervantes Emilio Velázquez Encarna 《Plant and Soil》2003,254(1):115-123
Submergence stimulates elongation of the leaves of Rumex palustris and under laboratory conditions the maximum final leaf length (of plants up to 7 weeks old) was obtained within a 9 day period. This elongation response, mainly determined by petiole elongation, depends on the availability of storage compounds and developmental stage of a leaf. A starch accumulating tap root and mature leaves and petioles were found to supply elongating leaves with substrates for polysaccharide synthesis in expanding cell walls. Changes in the composition of cell wall polysaccharides of elongated petioles suggest a substantial cell wall metabolism during cell extension. Reduced starch levels or removal of mature leaves caused a substantial limitation of submerged leaf growth. From the 5th leaf onward enough reserves were available to perform submerged leaf growth from early developmental stages. Very young petioles had a limited capacity to elongate. In slightly older petioles submergence resulted in the longest final leaf lengths and these values gradually decreased when submergence was started at more mature developmental stages. Submerged leaf growth is mainly a matter of petiole elongation in which cell elongation has a concurrent synthesis of xylem elements in the vascular tissue. Mature petioles still elongated (when submerged) by cell and tissue elongation only: the annular tracheary elements stretched enabling up to 70% petiole elongation. 相似文献
994.
Pedro Daleo 《Journal of experimental marine biology and ecology》2003,291(2):255-267
In this paper, we address the question of whether the presence of the burrowing crab Chasmagnathus granulatus affects the habitat use of the fiddler crab Uca uruguayensis. Field samples showed that the species have a disjoint spatial distribution. Male fiddler crab density decreased in zones with C. granulatus, however, female density increased. Male fiddler crabs avoided feeding on sediment affected by C. granulatus and were more preyed. Predation was higher during the fiddler crab reproductive season and, probably due to predation risk, males showed lower reproductive display in shared zones. Field experiments shows that when C. granulatus were excluded, densities of U. uruguayensis increased mainly due to an increase in density of males. Habitat differentiation of these species may be because C. granulatus affects U. uruguayensis in several ways, including direct predation, disturbance and behavioural changes associated to predation risk. Males and females are affected differentially probably because of the extreme sexual dimorphism of this crab species. Coloration on enlarged claw and waving activities are all factors that increase predation risk for male and the presence of only one feeding claw may increase sediment-mediated effects. 相似文献
995.
Margarida Castro Pedro EncarnaçãoOliver Tully 《Journal of experimental marine biology and ecology》2002,269(1):53-64
Lipofuscin accumulation is associated with ageing at the subcellular level. A strong correlation between lipofuscin and age has been found in crustaceans using histological techniques. This association has been proposed as the basis for a methodology to age crustaceans and in some cases lipofuscin levels were found to be better correlated with age than size. The experiment presented here was designed to test the potential effect of diet, in particular dietary antioxidants, on lipofuscin accumulation and age estimation.The shrimp, Penaeus japonicus, was reared in an aquaculture facility and fed commercial pellets with modified vitamins C and E contents. One group was fed with levels of vitamins C and E of 1000 and 150 mg/kg, respectively, and another group with 2500 and 5000 mg/kg, respectively. The experiment started when the shrimp were 19 weeks old. Samples were obtained at this point and at ages 33 and 43 weeks. Lipofuscin was measured in the nerve cords (antennal neuropils and oesophageal connectives) in an area adjacent to the brain.Dietary antioxidants significantly affected lipofuscin levels. High vitamin content in the diet resulted in lower percentage of the observed area covered with lipofuscin, lower lipofuscin granule density and lower average granule size. Gender had no effect on any of these variables and granule size did not significantly change within each treatment. Lipofuscin area and granule density increased with age in both vitamin treatments.These results suggest that age estimation using lipofuscin indices may be biased when: (1) wild populations are dispersed over diverse environments; (2) the age estimation of wild individuals is based on the results obtained using laboratory-reared individuals. 相似文献
996.
Functional avidity of tumor antigen-specific CTL recognition directly correlates with the stability of MHC/peptide multimer binding to TCR. 总被引:4,自引:0,他引:4
Valérie Dutoit Verena Rubio-Godoy Marie-Agnès Doucey Pascal Batard Danielle Liénard Donata Rimoldi Daniel Speiser Philippe Guillaume Jean-Charles Cerottini Pedro Romero Danila Valmori 《Journal of immunology (Baltimore, Md. : 1950)》2002,168(3):1167-1171
Avidity of Ag recognition by tumor-specific T cells is one of the main parameters that determines the potency of a tumor rejection Ag. In this study we show that the relative efficiency of staining of tumor Ag-specific T lymphocytes with the corresponding fluorescent MHC class I/peptide multimeric complexes can considerably vary with staining conditions and does not necessarily correlate with avidity of Ag recognition. Instead, we found a clear correlation between avidity of Ag recognition and the stability of MHC class I/peptide multimeric complexes interaction with TCR as measured in dissociation kinetic experiments. These findings are relevant for both identification and isolation of tumor-reactive CTL. 相似文献
997.
998.
Lise P S Labéjof Pierre Galle Pedro A O Mangabeira Amo H de Oliveira Maria I G Severo 《Cellular and molecular biology, including cyto-enzymology》2002,48(5):537-545
In order to understand the mechanisms of intestinal injuries due to ionizing radiation, various groups of rats have been whole-body irradiated by gamma-rays at two dose rates (1 Gy/min and 1 Gy/hr), three doses (1, 2 and 4 Gy) and two post-irradiation times (24 and 48 hr). Duodenum samples of the animals were prepared for light microscopy, according to classical methods for histology and TUNEL reaction. A small number of morphological differences were observed within the mucosa between the two dose rates used. The extent and the number of lesions were more important at the slower dose rate (1 Gy/hr) and increased with the total dose. Clear cavities were seen inside the lamina propria which appeared like capillaries free of blood cells. The mitotic index calculated from crypt cells showed a regular decrease with the dose, which was exacerbated at 48 hr post-irradiation. On the other hand, the apoptotic index increased with the dose and the postirradiation time. Our results lead to hypothesize another mechanism of intestinal mucosa renewal allowing to explain mucosa denudations observed after radiotherapy. Thus we propose a new concept in which the duodenal mucosa renewal may occur by whole villi shedding into the duodenal lumen. 相似文献
999.
Alternative pathway respiration is associated with ammonium ion sensitivity in spinach and pea plants 总被引:5,自引:0,他引:5
Berta Lasa Silvia Frechilla Pedro. M. Aparicio-Tejo Carmen Lamsfus 《Plant Growth Regulation》2002,37(1):49-55
Spinach and pea plants were grown in hydroponic culture with nitrate orammonium salts as the nitrogen source. Dry matter accumulation andphotosynthetic rate declined in spinach plants fed with ammonium salts, whereasthey did not change in pea plants compared with nitrate-fed plants. Measurementof organic nitrogen and free amino acid content showed that ammonium ions wereassimilated in shoots in spinach plants and in roots in pea plants. Ammoniumionnutrition led to a decline in starch content in both species. Organic acidsincreased in roots of pea plants fed with ammonium ions whereas they declinedinspinach plants. In both species ammonium ions increased root respiration ratebut the contribution of both routes (cytochromic and alternative pathway) tothis increase was different depending on the species. In spinach plants,ammonium ions increased the cytochromic path and decreased the alternativepathway, whereas in pea plants both routes were stimulated mainly through thealternative pathway. The differences in the sensitivity to ammonium ionsbetweenboth species are discussed in terms of differences in the availability of Cskeletons and energy, which could be due in part to differences in the capacityto stimulate the alternative pathway. 相似文献
1000.
Antonio Domínguez Alfonso Hermoso de Mendoza José Guerri Mariano Cambra Luis Navarro Pedro Moreno Leandro Peña 《Molecular breeding : new strategies in plant improvement》2002,10(1-2):1-10
The p25 coat protein (CP) gene of Citrustristezavirus (CTV) was incorporated to Mexican lime plants and forty-twotransgeniclines were produced, 25 containing the p25 CP gene of thesevere CTV strain T-305 and 17 with that of the mild strain T-317. When plantspropagated from each transgenic line were graft-inoculated with CTV T-305 oraphidinoculated with T-300, two types of response to viral challenge wereobserved: some lines developed CTV symptoms similar to those of non-transgeniccontrols, whereas others exhibited protection against the virus. Thisprotectionconsisted of a proportion of plants, ranging from 10 to 33%, that wereresistantto CTV, and the rest of them that showed a significant delay in virusaccumulation and symptom onset. Protection was efficient against non-homologousCTV strains and was generally accompanied by high accumulation of p25 CP in theprotected lines, which suggest a CP-mediated protection mechanism in mostcases.This is the first report demonstrating pathogen-derived resistance intransgenicplants against a Closterovirus member in its natural host. 相似文献