全文获取类型
收费全文 | 1045篇 |
免费 | 116篇 |
国内免费 | 86篇 |
出版年
2024年 | 5篇 |
2023年 | 35篇 |
2022年 | 42篇 |
2021年 | 67篇 |
2020年 | 65篇 |
2019年 | 63篇 |
2018年 | 52篇 |
2017年 | 56篇 |
2016年 | 42篇 |
2015年 | 48篇 |
2014年 | 47篇 |
2013年 | 64篇 |
2012年 | 44篇 |
2011年 | 50篇 |
2010年 | 34篇 |
2009年 | 37篇 |
2008年 | 59篇 |
2007年 | 65篇 |
2006年 | 56篇 |
2005年 | 44篇 |
2004年 | 36篇 |
2003年 | 36篇 |
2002年 | 18篇 |
2001年 | 17篇 |
2000年 | 19篇 |
1999年 | 14篇 |
1998年 | 11篇 |
1997年 | 17篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有1247条查询结果,搜索用时 265 毫秒
81.
与“全红”瓯江彩鲤体色相关的SRAP及SCAR分子标记 总被引:1,自引:0,他引:1
利用相关序列扩增多态性(Sequence Related Amplified Polymorphism,SRAP)技术分析"全红"和"粉玉"瓯江彩鲤,筛选与瓯江彩鲤体色相关的分子遗传标记。从88个SRAP引物组合筛选出的12个引物组合共获得扩增条带104个,并筛选出1个SRAP特异扩增带,即"全红"瓯江彩鲤家系SR2,7173 bp带。该条SRAP特异扩增条带经回收、克隆和测序,并将测序结果进行BLAST分析,发现该片段在GenBank中与斑马鱼的POl多蛋白基因和尿红素基因有较高的同源性。根据序列信息分别设计了4对正、反向引物(22—26 bp)。用4对引物分别在"全红"瓯江彩鲤F2和"粉玉"瓯江彩鲤F2群体中进行PCR扩增,仅发现SC-3(154 bp)能够在"全红"瓯江彩鲤群体中特异扩增,而且在"粉玉"瓯江彩鲤F2群体中未出现此扩增带。采用大样本对该SC-3标记进行验证,结果发现,在"全红"瓯江彩鲤群体中呈现阳性,而在"粉玉"瓯江彩鲤群体中为阴性,可以区分这两种群体。因此SC-3标记可以作为"全红"瓯江彩鲤群体一个重要的分子遗传特征指标,为进一步进行分子标记辅助育种奠定了基础。 相似文献
82.
哺乳动物毛色形成机制与影响因素 总被引:2,自引:0,他引:2
哺乳动物拥有丰富多彩的毛色,对于多种多样的动物毛色,影响其形成的可能原因较多,遗传物质与环境的相互作用不可忽视。本文针对调控黑色素细胞形成及褐黑色素、真黑色素合成的相关基因,分析了哺乳动物毛色形成的可能机制,并对研究不同毛色动物的同种动物遗传差异的方法进行了讨论。 相似文献
83.
Human hair melanins: what we have learned and have not learned from mouse coat color pigmentation 总被引:1,自引:0,他引:1
Hair pigmentation is one of the most conspicuous phenotypes in humans. Melanocytes produce two distinct types of melanin pigment: brown to black, indolic eumelanin and yellow to reddish brown, sulfur‐containing pheomelanin. Biochemically, the precursor tyrosine and the key enzyme tyrosinase and the tyrosinase‐related proteins are involved in eumelanogenesis, while only the additional presence of cysteine is necessary for pheomelanogenesis. Other important proteins involved in melanogenesis include P protein, MATP protein, α‐MSH, agouti signaling protein (ASIP), MC1R (the receptor for MSH and ASIP), and SLC7A11, a cystine transporter. Many studies have examined the effects of loss‐of‐function mutations of those proteins on mouse coat color pigmentation. In contrast, much less is known regarding the effects of mutations of the corresponding proteins on human hair pigmentation except for MC1R polymorphisms that lead to pheomelanogenesis. This perspective will discuss what we have/have not learned from mouse coat color pigmentation, with special emphasis on the significant roles of pH and the level of cysteine in melanosomes in controlling melanogenesis. Based on these data, a hypothesis is proposed to explain the diversity of human hair pigmentation. 相似文献
84.
Abstract This paper deals with the karyotype of green peach aphid, Myzus persicae (Sulzer), with three different life cycles in different regions of China. The results showed that four types of karyotype were found in the natural populations of red form and brown form aphids. Four types of karyotype are as follows: 2n = 12 with autosomes 1, 3 translocated (T1–3); 3n = 18 normal triploid; 3n = 18 with T1–3 translocation; and 2n = 11. However, in the yellowish‐green aphids there were only two types of karyotype, normal karyotype 2n= 12 (NK) and 2n = 12 with T1–3 translocation. There was no significant difference in the relative lengths of chromosomes in 2n = 12 karyotype among different color forms and groups from different regions. 相似文献
85.
R M Christie 《Biotechnic & histochemistry》2007,82(2):51-56
Although the color of indigo is strongly dependent on its environment, it is blue in most commonly encountered situations. Indigo's absorption at such long wavelengths for such a small molecule is unique, and I provide here an overview of the concepts advanced to account for this feature. A traditional valence-bond approach may be used to provide a reasonable qualitative explanation. A more rigorous, quantitative explanation is provided by molecular orbital methods of varying degrees of sophistication and several explanations have been proposed based on these models. Commonly, it is suggested that the important structural unit in determining color is based on the cross-conjugated “H-chromophore” concept. A second closely related explanation describes it as two symmetrically coupled merocyanine chains. Another proposal suggests that the basic chromophore may be interpreted as the aza analogue of two coupled anti aromatic-cyclopentadienyl ions. PiSYSTEM, a commercially available quantum mechanics program, has been used to provide a successful quantitative account of the colors of indigo and indirubin, a red isomer. 相似文献
86.
Honda T Tatsuzawa F Kobayashi N Kasai H Nagumo S Shigihara A Saito N 《Phytochemistry》2005,66(15):1844-1851
Three acylated cyanidin 3-sambubioside-5-glucosides (1-3) were isolated from the violet-blue flowers of Orychophragonus violaceus, and their structures were determined by chemical and spectroscopic methods. Two of those acylated anthocyanins (1 and 3) were cyanidin 3-O-[2-O-(2-O-(4-O-(6-O-(4-O-(beta-D-glucopyranosyl)-trans-caffeoyl)-beta-D-glucopyranosyl)-trans-caffeoyl)-beta-D-xylopyranosyl)-6-O-(4-O-(beta-D-glucopyranosyl)-trans-acyl)-beta-D-glucopyranoside]-5-O-(6-O-malonyl-beta-D-glucopyranoside)s, in which the acyl groups were p-coumaric acid for 1, and sinapic acid for 3, respectively. The last anthocyanin 2 was cyanidin 3-O-[2-O-(2-O-(4-O-(6-O-(4-O-(beta-D-glucopyranosyl)-trans-caffeoyl)-beta-D-glucopyranosyl)-trans-caffeoyl)-beta-D-xylopyranosyl)-6-O-(4-O-(beta-D-glucopyranosyl)-trans-feruloyl)-beta-D-glucopyranoside]-5-O-beta-D-glucopyranoside. In these flowers, the anthocyanins 2 and 3 were present as dominant pigments, and 1 was obtained in rather small amounts. 相似文献
87.
Daniel?M.?A.?Pessoa Eduardo?S.?Perini Lívia?S.?Carvalho Carlos?Tomaz Valdir?F.?PessoaEmail author 《International journal of primatology》2005,26(1):147-158
We assessed the color discriminations by golden-headed lion tamarins (Leontopithecus chrysomelas) via a series of tasks involving a behavioral paradigm that maximizes the naturalness of the stimuli. The stimuli were pairs of Munsell color chips used in earlier experiments with human dichromats. We tested 3 male and 3 female monkeys with stimuli of random brightness values in order to assure that discriminations were based on color rather than brightness cues. Results indicate that each male and one female presented random performances for stimuli resembling hue conditions under which tamarins forage: oranges vs. greens. Two females exhibited discriminations consistent with allelic trichromacy. Findings indicate the presence of an M/L cone opsin polymorphism, a condition of most platyrrhines that is characterized by dichromatic and/or trichromatic females and dichromatic males. Interspecific differences in allelic frequency among lion tamarins raises the possibility that habitat fragmentation is affecting heterozygous frequencies, a trend that could impact tamarin foraging efficiency. 相似文献
88.
Contrasting patterns of floral and molecular variation across a cline in Mimulus aurantiacus 总被引:1,自引:0,他引:1
Abstract Steep clines in ecologically important traits may be caused by divergent natural selection. However, processes that do not necessarily invoke ongoing selection, such as secondary contact or restricted gene flow, can also cause patterns of phenotypic differentiation over short spatial scales. Distinguishing among all possible scenarios is difficult, but an attainable goal is to establish whether scenarios that imply selection need to be invoked. We compared the extent of morphological and genetic differentiation between geographically structured red and yellow floral races of Mimulus aurantiacus (bush monkeyflower; Phrymacea). Flower color was assessed in a common garden as well as in the field to determine whether variation was genetic and to quantify the extent of geographical differentiation. Population genetic differentiation at marker loci was measured for both chloroplast and nuclear genomes, and the degree of population structure within and among the floral races was evaluated. Flower color shows both a strong genetic basis and a sharp geographic transition, with pure red-flowered populations in western San Diego County and pure yellow-flowered populations to the east. In the zone of contact, both pure and intermediate phenotypes occur. Patterns of genetic differentiation at marker loci are far less pronounced, as little of the variation is partitioned according to the differences in flower color. Phenotypic differentiation (QST ) between populations with different flower colors is much greater than neutral genetic differentiation (FST ). When comparisons are made between populations of the same flower color, the opposite trend is evident. Limited neutral genetic structure between the floral races, combined with sharp differentiation in flower color, is consistent with the hypothesis that current or recent natural selection maintains the cline in flower color. 相似文献
89.
Nilsson P Paavilainen L Larsson K Odling J Sundberg M Andersson AC Kampf C Persson A Al-Khalili Szigyarto C Ottosson J Björling E Hober S Wernérus H Wester K Pontén F Uhlen M 《Proteomics》2005,5(17):4327-4337
A great need exists for the systematic generation of specific antibodies to explore the human proteome. Here, we show that antibodies specific to human proteins can be generated in a high-throughput manner involving stringent affinity purification using recombinant protein epitope signature tags (PrESTs) as immunogens and affinity-ligands. The specificity of the generated affinity reagents, here called mono-specific antibodies (msAb), were validated with a novel protein microarray assay. The success rate for 464 antibodies generated towards human proteins was more than 90% as judged by the protein array assay. The antibodies were used for parallel profiling of patient biopsies using tissue microarrays generated from 48 human tissues. Comparative analysis with well-characterized monoclonal antibodies showed identical or similar specificity and expression patterns. The results suggest that a comprehensive atlas containing extensive protein expression and subcellular localization data of the human proteome can be generated in an efficient manner with mono-specific antibodies. 相似文献
90.
dos Santos AB Traverse J Cervantes FJ van Lier JB 《Biotechnology and bioengineering》2005,89(1):42-52
The effect of temperature, hydraulic retention time (HRT) and the redox mediator anthraquinone-2,6-disulfonate (AQDS), on electron transfer and subsequent color removal from textile wastewater was assessed in mesophilic and thermophilic anaerobic bioreactors. The results clearly show that compared with mesophilic anaerobic treatment, thermophilic treatment at 55 degrees C is an effective approach for increasing the electron transfer capacity in bioreactors, and thus improving the decolorization rates. Furthermore, similar color removals were found at 55 degrees C between the AQDS-free and AQDS-supplemented reactors, whereas a significant difference (up to 3.6-fold) on decolorization rates occurred at 30 degrees C. For instance, at an HRT of 2.5 h and in the absence of AQDS, the color removal was 5.3-fold higher at 55 degrees C compared with 30 degrees C. The impact of a mix of mediators with different redox potentials on the decolorization rate was investigated with both industrial textile wastewater and the azo dye Reactive Red 2 (RR2). Color removal of RR2 in the presence of anthraquinone-2-sulfonate (AQS) (standard redox potential E(0)' of -225 mV) was 3.8-fold and 2.3-fold higher at 30 degrees C and 55 degrees C, respectively, than the values found in the absence of AQS. Furthermore, when the mediators 1,4-benzoquinone (BQ) (E(0)' of +280 mV), and AQS were incubated together, there was no improvement on the decolorization rates compared with the bottles solely supplemented with AQS. Results imply that the use of mixed redox mediators with positive and negative E(0)' under anaerobic conditions is not an efficient approach to improve color removal in textile wastewaters. 相似文献