全文获取类型
收费全文 | 553篇 |
免费 | 43篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 32篇 |
2020年 | 6篇 |
2019年 | 13篇 |
2018年 | 20篇 |
2017年 | 13篇 |
2016年 | 17篇 |
2015年 | 21篇 |
2014年 | 24篇 |
2013年 | 40篇 |
2012年 | 42篇 |
2011年 | 49篇 |
2010年 | 28篇 |
2009年 | 29篇 |
2008年 | 38篇 |
2007年 | 30篇 |
2006年 | 18篇 |
2005年 | 21篇 |
2004年 | 18篇 |
2003年 | 23篇 |
2002年 | 21篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1949年 | 1篇 |
排序方式: 共有596条查询结果,搜索用时 62 毫秒
91.
Urszula Krzemińska Robyn Wilson Beng Kah Song Sampath Seneviratne Sharif Akhteruzzaman Joanna Gruszczyńska Wiesław Świderek Teh Ser Huy Christopher M. Austin Sadequr Rahman 《Biological invasions》2016,18(7):1867-1881
The common house crow (Corvus splendens) is one of the best known and most wide spread species of the family Corvidae. It is a successful invasive species able to exploit urban environments, well removed from its natural distribution. It is considered a pest as it attains high population densities, can cause serious economic losses and has many adverse effects on native fauna and flora, including predation, competitive displacement and disease transmission. Little genetic research on the house crow has been undertaken so we have only a limited understanding of its natural genetic population structure and invasion history. In this study, we employ microsatellite and mitochondrial DNA markers to assess genetic diversity, phylogeography and population structure of C. splendens within its native range represented by Sri Lanka and Bangladesh and introduced range represented by Malaysia, Singapore, Kenya and South Africa. We found high levels of genetic diversity in some of the invasive populations for which multiple invasions are proposed. The lowest genetic diversity was found for the intentionally introduced population in Selangor, Malaysia. Sri Lanka is a possible source population for Malaysia Selangor consistent with a documented introduction over 100 years ago, with port cities within the introduced range revealing possible presence of migrants from other unsampled locations. We demonstrate the power of the approach of using multiple molecular markers to untangle patterns of invasion, provide insights into population structure and phylogeographic relationships and illustrate how historical processes may have contributed to making this species such a successful invader. 相似文献
92.
Analyses of isoamylase gene activity in wild-type barley indicate its involvement in starch synthesis 总被引:5,自引:0,他引:5
Sun Chuanxin Sathish P. Ahlandsberg Staffan Jansson Christer 《Plant molecular biology》1999,40(3):431-443
The notion of debranching enzyme activity as a participant in starch synthesis is gaining acceptance. Inconsistent reports from mutant analyses implicate either isoamylase or pullulanase as a determinant in amylopectin formation and whether wild-type plants utilize one or the other, or both, of these debranching enzymes in starch synthesis is unclear. Recent results on the su1 mutant in maize suggest that both forms of debranching enzymes might be involved in amylopectin formation. We wished to find out if isoamylase takes part in starch synthesis by comparing isoamylase gene activity under three conditions: (1) during starch accumulation in developing sink tissues; (2) during starch degradation in germinating seeds; (3) in ectopic expression after applying sucrose, a starch precursor. We isolated the gene for barley isoamylase, iso1, and analysed its expression and regulation in germinating seeds, developing endosperm and vegetative tissues, and compared the isoamylase gene expression in sink tissues from three different species. Our results indicate that isoamylase gene activity is involved in starch synthesis in wild-type plants and is modulated by sucrose. 相似文献
93.
In this paper, a new systematic sampling scheme with Markovian behaviour which yields positive first order inclusion probabilities for all units and positive second order inclusion probabilities for all pairs of units is introduced. The suggested method has been compared with sample random sampling, stratified random sampling, linear systematic sampling and systematic sampling with two random starts for the populations exhibiting exponential trend, autocorrelatedness and randomness. Throughout the discussion, the sample size is assumed to be even and the population size is a multiple of the sample size. The suggested method works well for estimating a finite population total for the population exhibiting exponential trend. 相似文献
94.
95.
Zhuang Jin Hua Lin Sathish Srinivasan Jerome C. Nwachukwu Nelson Bruno Patrick R. Griffin Kendall W. Nettles Theodore M. Kamenecka 《Bioorganic & medicinal chemistry letters》2017,27(2):347-353
Adverse effects of glucocorticoids could be limited by developing new compounds that selectively modulate anti-inflammatory activity of the glucocorticoid receptor (GR). We have synthesized a novel series of steroidal GR ligands, including potent agonists, partial agonists and antagonists with a wide range of effects on inhibiting secretion of interleukin-6. Some of these new ligands were designed to directly impact conformational stability of helix-12, in the GR ligand-binding domain (LBD). These compounds modulated GR activity and glucocorticoid-induced gene expression in a manner that was inversely correlated to the degree of inflammatory response. In contrast, compounds designed to directly modulate LBD epitopes outside helix-12, led to dissociated levels of GR-mediated gene expression and inflammatory response. Therefore, these new series of compounds and their derivatives will be useful to dissect the ligand-dependent features of GR signaling specificity. 相似文献
96.
97.
Meghann Ryan Peter Kochunov Laura M. Rowland Braxton D. Mitchell S. Andrea Wijtenburg Els Fieremans Jelle Veraart Dmitry S. Novikov Xiaoming Du Bhim Adhikari Feven Fisseha Heather Bruce Joshua Chiappelli Hemalatha Sampath Seth Ament Jeffrey O'Connell Alan R. Shuldiner L. Elliot Hong 《Obesity (Silver Spring, Md.)》2017,25(11):1876-1880
98.
Edward H. Miller Sampath S. Seneviratne Ian L. Jones Gregory J. Robertson Sabina I. Wilhelm 《Journal of Ornithology》2008,149(4):545-554
Species and sexual differences in vocalizations and the vocal tract are widespread. We studied the vocal tract of Common (Uria aalge) and Thick-billed (U. lomvia) Murres. We predicted anatomical or allometric differences in adults between species and sexes due to vocal differences related
to social behavior (Common Murres nest at higher densities; males are the more aggressive sex, etc.). The vocal tract was
anatomically simple and similar between species and sexes. The trachea was mainly cartilage, but the posteriormost 4–6 tracheal
rings were calcified and fused as the tympanum, as part of the syrinx. The syrinx included the (unfused) first bronchial semirings,
which were enlarged and calcified beneath the insertion of M. tracheolateralis. Weak bilateral asymmetry (right side larger) occurred in widths of M. tracheolateralis and M. sternotrachealis. The trachea was ∼10% longer in Common Murres; the tympanum and M. sternotrachealis width were relatively larger in Thick-billed Murres. Vocal-tract morphology and size did not differ between the sexes in
either species. In allometric analyses on adults, isometry characterized (1) tympanum size in relation to head + bill length,
and to humerus length (respectively), in Thick-billed Murres, and (2) M. sternotrachealis width in relation to tarsometatarsal length in both species. Comparative field studies on species and sexes are needed to
clarify the functional significance of our findings in relation to vocalization. 相似文献
99.
The objectives of the study were to propose a two-stage microfluidization combined with an ultrafiltration (UF) treatment for chitosan mass production and the manipulation of molecular weight and its distribution. The proposed methods are based on the degradation rate and rate constant of various process variables studied. Results obtained were that the rate constants were faster during the earlier reaction period, were higher for those operating at a higher pressure, were better for using concurrent UF treatment to remove small degraded fragments, and the degradation rate constants were faster for 30 °C solutions than that for 50 or 0 °C. A two-stage microfluidization process is proposed. The first stage constitutes of the highest possible concentration solution with concurrent UF treatment at 50 °C, and recycled 5 times. The second stage consists of the highest possible concentration of solutions with concurrent UF treatment at 30 °C, and recycled 5 times. 相似文献
100.
Sampath Amutha Krishnan Kathiravan Sima Singer Liana Jashi Ilan Shomer Benjamin Steinitz Victor Gaba 《In vitro cellular & developmental biology. Plant》2009,45(6):758-768
Regeneration of new shoots in plant tissue culture is often associated with appearance of abnormally shaped leaves. We used
the adventitious shoot regeneration response induced by decapitation (removal of all preformed shoot apical meristems, leaving
a single cotyledon) of greenhouse-grown cotyledon-stage seedlings to test the hypothesis that such abnormal leaf formation
is a normal regeneration progression following wounding and is not conditioned by tissue culture. To understand why shoot
regeneration starts with defective organogenesis, the regeneration response was characterized by morphology and scanning electron
and light microscopy in decapitated cotyledon-stage Cucurbita pepo seedlings. Several leaf primordia were observed to regenerate prior to differentiation of a de novo shoot apical meristem from dividing cells on the wound surface. Early regenerating primordia have a greatly distorted structure
with dramatically altered dorsoventrality. Aberrant leaf morphogenesis in C. pepo gradually disappears as leaves eventually originate from a de novo adventitious shoot apical meristem, recovering normal phyllotaxis. Similarly, following comparable decapitation of seedlings
from a number of families (Chenopodiaceae, Compositae, Convolvulaceae, Cucurbitaceae, Cruciferae, Fabaceae, Malvaceae, Papaveraceae,
and Solanaceae) of several dicotyledonous clades (Ranunculales, Caryophyllales, Asterids, and Rosids), stems are regenerated
bearing abnormal leaves; the normal leaf shape is gradually recovered. Some of the transient leaf developmental defects observed
are similar to responses to mutations in leaf shape or shoot apical meristem function. Many species temporarily express this
leaf development pathway, which is manifest in exceptional circumstances such as during recovery from excision of all preformed
shoot meristems of a seedling. 相似文献