全文获取类型
收费全文 | 11208篇 |
免费 | 1235篇 |
国内免费 | 2篇 |
出版年
2022年 | 67篇 |
2021年 | 165篇 |
2020年 | 95篇 |
2019年 | 120篇 |
2018年 | 170篇 |
2017年 | 186篇 |
2016年 | 260篇 |
2015年 | 396篇 |
2014年 | 449篇 |
2013年 | 598篇 |
2012年 | 715篇 |
2011年 | 684篇 |
2010年 | 436篇 |
2009年 | 372篇 |
2008年 | 574篇 |
2007年 | 562篇 |
2006年 | 504篇 |
2005年 | 478篇 |
2004年 | 515篇 |
2003年 | 437篇 |
2002年 | 453篇 |
2001年 | 280篇 |
2000年 | 278篇 |
1999年 | 238篇 |
1998年 | 160篇 |
1997年 | 111篇 |
1996年 | 121篇 |
1995年 | 108篇 |
1994年 | 111篇 |
1993年 | 94篇 |
1992年 | 178篇 |
1991年 | 170篇 |
1990年 | 172篇 |
1989年 | 171篇 |
1988年 | 151篇 |
1987年 | 136篇 |
1986年 | 126篇 |
1985年 | 97篇 |
1984年 | 109篇 |
1983年 | 97篇 |
1982年 | 82篇 |
1981年 | 76篇 |
1979年 | 96篇 |
1978年 | 78篇 |
1977年 | 81篇 |
1976年 | 83篇 |
1975年 | 80篇 |
1974年 | 63篇 |
1973年 | 61篇 |
1971年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Keith Nelson Dennis Hedgecock Bruce Heyer Thomas Nunn 《Journal of experimental marine biology and ecology》1983,72(1):83-98
By means of compartmental analysis of two experiments manipulating flow rate, short-range density-dependent growth inhibition in juvenile lobsters (Homarus) was shown to implicate a rapidlydecaying or ephemeral substance. Pulsed production of a long-lived inhibitor was ruled out as a sole explanation of the effect. Behavioral observations eliminated the hypothesis that reduced growth of inhibited animals was causally related to their increased locomotory activity. Implications for chemical ecology of the effects of ephemeral agents upon growth and behavior are discussed. 相似文献
993.
The mechanism of the inhibitory action of glucocorticoids on glucose uptake is incompletely understood. Treatment with corticosteroids of cells in which glucose uptake is stimulated at insulin postbinding and postreceptor sites may clarify the site of the steroid inhibitory action. Hydrogen peroxide, which has been shown to stimulate the insulin receptor tyrosine kinase, and phorbol myristate acetate (PMA) which stimulates protein kinase C were, therefore, used as stimulators of glucose transport in this study. These studies demonstrate that dexamethasone and the sphingoid bases, sphinganine and sphingosine, inhibit glucose uptake that has been stimulated at either the receptor kinase or protein kinase C level in both 3T3-L1 and 3T3-C2 cells. These data confirm glucocorticoid inhibitory action at a post binding level and support the suggestion that some corticosteroid inhibitory effects may be mediated by an action on sphingolipid metabolism. 相似文献
994.
995.
996.
Bacterial Diversity and Distribution in the Holocene Sediments of a Northern Temperate Lake 总被引:1,自引:0,他引:1
Sediments contain an abundance of microorganisms. However, the diversity and distribution of microorganisms associated with
sediments are poorly understood, particularly in lacustrine environments. We used banding patterns from denaturing gradient
gel electrophoresis (DGGE) and 16S rDNA sequences to assess the structure of bacterial communities in the Holocene sediments
of a meromictic lake in Minnesota. Cluster analysis of the DGGE banding patterns indicates that the early- and middle-Holocene
samples group separately from the late-Holocene samples. About 79% of the recovered bacterial sequences cluster with the α-,
β-, δ-, ɛ-, and γ- Proteobacteriaceae and Firmicutes. The remaining ∼21% lack cultured representatives. The taxonomic lineages
of bacteria differ statistically among the early-, middle-, and late-Holocene samples, although the difference is smallest
between early- and middle-Holocene samples. Early- and middle-Holocene samples are dominated by ɛ-Proteobacteriaceae, and
late-Holocene samples are dominated by sequences from uncultured subphyla. We only recovered δ-Proteobacteriaceae in late-Holocene
sediments and α- and γ- Proteobacteriaceae in late- and middle-Holocene sediments. Diversity estimates derived from early-,
middle-, and late-Holocene clone libraries indicate that the youngest (late-Holocene) samples had significantly greater bacterial
diversity than the oldest (early-Holocene) samples, and the middle-Holocene samples contained intermediate levels of diversity.
The observed patterns of diversity may be caused by increased bacterial niche-partitioning in younger sediments that contain
a greater abundance of labile organic matter than older sediments.
D. M. Nelson and S. Ohene-Adjei contributed equally to this work 相似文献
997.
Smither SJ Hill J van Baar BL Hulst AG de Jong AL Titball RW 《Journal of microbiological methods》2007,68(1):26-31
The outer membrane of Gram-negative bacteria contains proteins that might be good targets for vaccines, antimicrobials or detection systems. The identification of surface located proteins using traditional methods is often difficult. Yersinia pestis, the causative agent of plague, was labelled with biotin. Tagged proteins were visualised through streptavidin probing of Western blots. Seven biotinylated proteins of Y. pestis were identified including two porins and the putative virulence factor catalase peroxidase. 相似文献
998.
999.
Silvia Flores-Benítez Juan F. Jiménez-Bremont Sergio Rosales-Mendoza Gerardo R. Argüello-Astorga Rosalba Castillo-Collazo Ángel Gabriel Alpuche-Solís 《Plant Cell, Tissue and Organ Culture》2007,91(3):215-224
Agave salmiana was transformed using two different protocols: co-cultivation with Agrobacterium tumefaciens and particle bombardment. The uidA (β-glucuronidase) gene was used as a reporter gene for both methods whereas the nptII and bar genes were used as selectable markers for A. tumefaciens and biolistic transformation respectively. Previous reports for in vitro regeneration of A. salmiana have not been published; therefore the conditions for both shoot regeneration and rooting were optimized using leaves and
embryogenic calli of Agave salmiana. The transgenes were detected by Polymerase Chain Reaction (PCR) in 11 month old plants. The transgenic nature of the plants
was also confirmed using GUS histochemical assays. Transformation via co-cultivation of explants with Agrobacterium harbouring the pBI121 binary vector was the most effective method of transformation, producing 32 transgenic plants and giving
a transformation efficiency of 2.7%. On the other hand, the biolistic method produced transgenic calli that tested positive
with the GUS assay after 14 months on selective medium while still undergoing regeneration. 相似文献
1000.
Lacadena J Alvarez-García E Carreras-Sangrà N Herrero-Galán E Alegre-Cebollada J García-Ortega L Oñaderra M Gavilanes JG Martínez del Pozo A 《FEMS microbiology reviews》2007,31(2):212-237
RNase T1 is the best known representative of a large family of ribonucleolytic proteins secreted by fungi, mostly Aspergillus and Penicillium species. Ribotoxins stand out among them by their cytotoxic character. They exert their toxic action by first entering the cells and then cleaving a single phosphodiester bond located within a universally conserved sequence of the large rRNA gene, known as the sarcin-ricin loop. This cleavage leads to inhibition of protein biosynthesis, followed by cellular death by apoptosis. Although no protein receptor has been found for ribotoxins, they preferentially kill cells showing altered membrane permeability, such as those that are infected with virus or transformed. Many steps of the cytotoxic process have been elucidated at the molecular level by means of a variety of methodological approaches and the construction and purification of different mutant versions of these ribotoxins. Ribotoxins have been used for the construction of immunotoxins, because of their cytotoxicity. Besides this activity, Aspf1, a ribotoxin produced by Aspergillus fumigatus, has been shown to be one of the major allergens involved in allergic aspergillosis-related pathologies. Protein engineering and peptide synthesis have been used in order to understand the basis of these pathogenic mechanisms as well as to produce hypoallergenic proteins with potential diagnostic and immunotherapeutic applications. 相似文献