全文获取类型
收费全文 | 1010篇 |
免费 | 86篇 |
学科分类
生物科学 | 1096篇 |
出版年
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 21篇 |
2018年 | 8篇 |
2017年 | 19篇 |
2016年 | 13篇 |
2015年 | 22篇 |
2014年 | 32篇 |
2013年 | 43篇 |
2012年 | 49篇 |
2011年 | 45篇 |
2010年 | 26篇 |
2009年 | 26篇 |
2008年 | 30篇 |
2007年 | 50篇 |
2006年 | 28篇 |
2005年 | 31篇 |
2004年 | 24篇 |
2003年 | 32篇 |
2002年 | 27篇 |
2001年 | 30篇 |
2000年 | 30篇 |
1999年 | 37篇 |
1998年 | 21篇 |
1997年 | 20篇 |
1996年 | 16篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 15篇 |
1992年 | 19篇 |
1991年 | 6篇 |
1990年 | 26篇 |
1989年 | 20篇 |
1988年 | 25篇 |
1987年 | 21篇 |
1986年 | 14篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1969年 | 11篇 |
1912年 | 7篇 |
1911年 | 13篇 |
排序方式: 共有1096条查询结果,搜索用时 32 毫秒
1.
Anna E. Goodroe Casey Fitz Michael L. Power Ricki J. Colman Saverio Capuano III Toni E. Ziegler 《American journal of primatology》2020,82(6):e23131
Vitamin D3 (cholecalciferol) is endogenously produced in the skin of primates when exposed to the appropriate wavelengths of ultraviolet light (UV-B). Common marmosets (Callithrix jacchus) maintained indoors require dietary provision of vitamin D3 due to lack of sunlight exposure. The minimum dietary vitamin D3 requirement and the maximum amount of vitamin D3 that can be metabolized by marmosets is unknown. Observations of metabolic bone disease and gastrointestinal malabsorption have led to wide variation in dietary vitamin D3 provision amongst research institutions, with resulting variation in circulating 25-hydroxyvitamin D3 (25(OH)D3), the accepted marker for vitamin D sufficiency/deficiency. Multiple studies have reported serum 25(OH)D3 in captive marmosets, but 25(OH)D3 is not the final product of vitamin D3 metabolism. In addition to serum 25(OH)D3, we measured the most physiologically active metabolite, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), and the less well understood metabolite, 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) to characterize the marmoset's ability to metabolize dietary vitamin D3. We present vitamin D3 metabolite and related serum chemistry value colony reference ranges in marmosets provided diets with 26,367 (Colony A, N = 113) or 8,888 (Colony B, N = 52) international units (IU) of dietary vitamin D3 per kilogram of dry matter. Colony A marmosets had higher serum 25(OH)D3 (426 ng/ml [SD 200] vs. 215 ng/ml [SD 113]) and 24,25(OH)2D3 (53 ng/ml [SD 35] vs. 7 ng/ml [SD 5]). There was no difference in serum 1,25(OH)2D3 between the colonies. Serum 1,25(OH)2D3 increased and 25(OH)D3 decreased with age, but the effect was weak. Marmosets tightly regulate metabolism of dietary vitamin D3 into the active metabolite 1,25(OH)2D3; excess 25(OH)D3 is metabolized into 24,25(OH)2D3. This ability explains the tolerance of high levels of dietary vitamin D3 by marmosets, however, our data suggest that these high dietary levels are not required. 相似文献
2.
Plant Ecology - In forests, the majority of fine roots are located within the upper soil horizons, and fine root biomass decreases with depth. We evaluated spatial patterns in the distribution of... 相似文献
3.
4.
Strategies for signal amplification in nucleic acid detection 总被引:3,自引:0,他引:3
S. Calin Andras J. Brian Power Edward C. Cocking Michael R. Davey 《Molecular biotechnology》2001,19(1):29-44
Many aspects of molecular genetics necessitate the detection of nucleic acid sequences. Current approaches involving target
amplification (in situ PCR, Primed in situ Labeling, Self-Sustained Sequence Replication, Strand Displacement Amplification), probe amplification (Ligase Chain Reaction,
Padlock Probes, Rolling Circle Amplification) and signal amplification (Tyramide Signal Amplification, Branched DNA Amplification)
are summarized in the present review, together with their advantages and limitations. 相似文献
5.
M M Power 《Cytogenetics and cell genetics》1987,45(3-4):163-168
Two unrelated chromosome abnormalities were found in equine half sibs. The proposita, Case 1, which was short in stature and infertile, had a de novo unbalanced X;15 translocation involving loss of Xp. Replication studies indicated that the translocated X was preferentially late replicating and that this late replication spread variably into the autosomal segment. Case 2, a half brother of the proposita, was short in stature, had cryptorchidism, and was trisomic for chromosome 28. Cytogenetic analysis of the dam, the sire of Case 1, and two other phenotypically normal half sibs revealed normal chromosome complements. Five further normal pregnancies were reported. The finding of two unrelated chromosome abnormalities is therefore probably fortuitous in this family. This is the first case of an unbalanced X-autosome translocation and the first case of an autosome trisomy to be reported in the horse. 相似文献
6.
7.
Recent studies point to the need for improved understanding of environmental management frameworks designed to combine qualitative public and quantitative technical inputs in decision-making processes. Flux in public perception and concern about risks imply frameworks must be iterative in nature and incorporate a variety of assessment triggers in the form of decision points. A conceptual model is proposed here to explain the de facto operation of standard risk analytic frameworks within the broader sociopolitical milieu of public policy. The model is presented as a decision flow diagram that emphasizes setting environmental management goals based on societal input and the formulation of decision criteria for selecting management actions to achieve those goals. Prospective and retrospective decision control points operate to select management options that, respectively, avoid or reduce actual or predicted effects. Feedback loops that modify risk management outcomes are identified. Technical and scientific inputs (i.e., risk analysis) are assigned an essential information role within the framework and are responsible for informing the management process with the results of appropriately conducted and reviewed investigations. The proposed model is intended primarily to indicate how environmental risk management decision-making and associated technical assessments may be influenced by social pressures. It is hoped this understanding will lead to analytical transparency and better public communication of the environmental implications of policy options. 相似文献
8.
9.
K Guven R S Power S Avramides R Allender D I de Pomerai 《Journal of biochemical and molecular toxicology》1999,13(6):324-333
The dithiocarbamate fungicides maneb and mancozeb induce a short-term stress response in a transgenic Caenorhabditis elegans strain (PC72) carrying a reporter lacZ gene under the control of a homologous heat shock (hsp16) promoter. This response can be readily monitored as induced beta-galactosidase activity, either by in situ staining or by a quantitative fluorometric enzyme assay. Particularly strong responses are induced by mancozeb (three- to fivefold above controls at 500 microg mL(-1)), causing acute toxicity at concentrations comparable to those recommended for field application (2 mg mL(-1)). Although much of this fungicide is adsorbed by soil, sufficient (ca. 6%) enters the soil water compartment to cause mild stress in the transgenic worm assay. Among possible metabolites from mancozeb breakdown, neither Mn2+ nor ethylenethiourea (ETU) is particularly toxic even at 10% of the optimum mancozeb dosage. Stress responses to a range of other pesticides are also reported, and in several cases it is clear that a nontarget soil species (here, transgenic C. elegans) may be sensitive to low-level contamination. 相似文献
10.