全文获取类型
收费全文 | 809篇 |
免费 | 81篇 |
专业分类
890篇 |
出版年
2022年 | 3篇 |
2021年 | 12篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 12篇 |
2016年 | 11篇 |
2015年 | 31篇 |
2014年 | 24篇 |
2013年 | 42篇 |
2012年 | 54篇 |
2011年 | 74篇 |
2010年 | 42篇 |
2009年 | 37篇 |
2008年 | 49篇 |
2007年 | 52篇 |
2006年 | 47篇 |
2005年 | 47篇 |
2004年 | 42篇 |
2003年 | 60篇 |
2002年 | 51篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 16篇 |
1990年 | 10篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1977年 | 2篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1969年 | 4篇 |
1968年 | 3篇 |
排序方式: 共有890条查询结果,搜索用时 15 毫秒
881.
882.
A mechanistic model of competition on a single resource wastested experimentally with two freshwater rotifers, Brachionusrubens and B.calyciflorus, both grown on the alga Chlorellapyrenoidosa. Using open culture systems for each species wemeasured: (i) the resource-saturated exponential growth rate,µmax, and (ii) the relationship between specific growthrate, µ, at steady-state and the residual algal concentrationover a range of system turnover rates, or dilution rates, D.The µmax of B.calyciflorus was {small tilde}60% higherthan B. rubens. These results were then used to construct agraphical model for predicting the victor in interspecific competitionbetween the two rotifers. Since the two resource-dependent growthrates crossed, one species, B.calyciflorus, was predicted tobe the victor at a high D while B. rubens was predicted as thevictor at low D. Finally, the outcome of competition was determinedfor two turnover rates. As predicted by the graphical competitionmodels, B.calyciflorus was the dominant species at rapid D (0.029h1) and B.rubens was dominant at slow D (0.0044 h1).These studies support recent conclusions that mechanistic competitionmodels may be applied to predict dominant species from a prioriinformation on growth potential and resource levels, which isnot possible with traditional Lotka-Volterra models. 相似文献
883.
Nicholas Timmins 《BMJ (Clinical research ed.)》2008,336(7659):1464-1465
884.
The assembly zone is a morphologically distinct region in the insect integument that lies between the epidermis and its principal secretory product, the lamellate cuticle. Despite its central location in the process of cuticle formation, little is known about its structure or function. Using various antisera we have shown that in Drosophila melanogaster larvae and pupae the assembly zone is antigenically distinct from the overlying lamellate cuticle. This observation suggests that this region does not contain lamellae in the process of assembling but rather is a stable and permeable matrix through which lamellar components travel in the process of cuticle formation. Curiously an antigen present in the assembly zone was also contained in the moulting gel, indicating a heretofore unsuspected chemical relationship between these two materials. 相似文献
885.
Kenneth P. McNatty Dianne Moore Smith Anastasia Makris Rapin Osathanondh Kenneth J. Ryan 《Steroids》1980,35(6):643-651
The ability of the human oocyte-cumulus cell complex to synthesize progesterone, androgens and estrogens and to modify its endocrine environment in vitro was investigated. Germinal-vesicle stage oocytes with adhering layers of cumulus cells were recovered from human ovaries and maintained for 40–50 h in vitro in a culture medium with or without antral fluid.The results show that oocyte-cumulus (0-C) cell complexes were capable of synthesizing progesterone, androgens and estrogens. Oocytes with the capacity of resuming meiosis in vitro were part of an 0-C complex producing significantly more progesterone than those 0-C complexes containing oocytes incapable of resuming meiosis. Irrespective of the stage of oocyte maturation at the end of culture, testosterone and estrone were respectively the major androgen and estrogen produced.It is concluded that the oocyte-cumulus compartment of the antral follicle is a steroidogenically competent unit and that it has the capacity to modify the endocrine microenvironment of the follicle. 相似文献
886.
887.
B. J. Trask Heather Mefford Ger van den Engh Hillary F. Massa Ramesh C. Juyal Lorraine Potocki Brenda Finucane Dianne N. Abuelo David R. Witt Ellen Magenis Antonio Baldini Frank Greenberg James R. Lupski P. I. Patel 《Human genetics》1996,98(6):710-718
We have used bivariate flow karyotyping to quantify the deletions involving chromosome 17 in sixteen patients with Smith-Magenis
syndrome (SMS). The fluorescence intensities of mitotic chromosomes stained with Hoechst 33258 and chromomycin were quantified
in a dual-beam flow cytometer. For each patient, the position of the peak representing the deleted chromosome 17 was compared
to those of the normal homologs of an unaffected parent. The patients could be classified into four groups based on the size
of their deletions. The deletions ranged from ∼9–10 Mb (∼10–11% of the chromosome) to below the detection limit of the technique
(2 Mb). Different deletion sizes were detected among patients whose high-resolution banding results were similar. Some deletions
detected by banding were not detected by flow analyses. Deletion estimates are largely consistent with the results of molecular
analyses. Patients with larger deletions that extend into band 17p12 have abnormal electrophysiologic studies of peripheral
nerves. Deletion size does not appear to correlate with the degree of mental retardation, presence of behavioral abnormalities,
craniofacial anomalies or common skeletal findings in SMS. By identifying patients with varying deletion sizes, these data
will aid the construction of a long-range deletion-based map of 17p11.2 and identification of the genes involved in this syndrome.
Received: 19 March 1996 / Revised: 21 June 1996 相似文献
888.
889.
Fernando Larrea Cecilia Cari o Dianne O. Hardy Neal A. Musto James F. Catterall 《The Journal of steroid biochemistry and molecular biology》1995,53(1-6):553-559
The human testosterone-estradiol-binding globulin (hTeBG) is a plasma heterogeneous glycoprotein with high affinity for a number of circulating steroid hormones. The heterogeneity originates from differential glycosylation of a common protein precursor. Analysis of desialylated hTeBG by isoelectric focusing (IEF) has revealed that microheterogeneity could be partly attributed to variability in sialic acid content or rearrangement of amino acid composition. We have studied this possibility by the analysis of desialylated serum hTeBG by Western blotting of proteins previously separated on IEF-gels. Two distinct well-defined IEF patterns were identified. The most frequent consisted of two major IEF-bands of equal color intensity. The other pattern consisting of four IEF-bands was present in only 5.55% of the total serum samples analyzed. Family studies showed that these phenotypes were autosomally inherited with a simple Mendelian transmission and allele frequencies had an excellent agreement between the observed and expected phenotypes. Androgen affinity constants and serum concentrations of hTeBG variant were similar to those of normal hTeBG. Molecular analyses of each of the exons of hTeBG gene by denaturing gradient gel electrophoresis revealed the presence of a point mutation in exon 8. The studies presented herein confirm and extend previous reports on the existence of structural variants of hTeBG. In addition, the mutation reported in this study is probably the same as that recently identified within numerous ethnic groups throughout the world, thus further supporting the concept of a two allele gene worldwide concoding hTeBG. 相似文献
890.
Samples of fish larvae collected in 1983, 1984, and 1986 in two distributary channels of the St. Clair River delta were characteristically rich in species (a total of 48) and low in abundance (generally less than a mean of 5 100 m-3 of water filtered). Most species were residents of the delta; others apparently hatched in tributaries of the St. Clair River or in southern Lake Huron, and drifted into the delta. Highest species diversity was nearshore, although largest catches of larvae were of rainbow smelt, gizzard shad, and alewife, which were found mainly in mid-channel. Cyprinids (17 species) were better represented than other families. 相似文献