全文获取类型
收费全文 | 20505篇 |
免费 | 1475篇 |
国内免费 | 1篇 |
出版年
2024年 | 9篇 |
2023年 | 146篇 |
2022年 | 276篇 |
2021年 | 611篇 |
2020年 | 381篇 |
2019年 | 456篇 |
2018年 | 591篇 |
2017年 | 543篇 |
2016年 | 807篇 |
2015年 | 1248篇 |
2014年 | 1309篇 |
2013年 | 1656篇 |
2012年 | 1990篇 |
2011年 | 1779篇 |
2010年 | 1104篇 |
2009年 | 957篇 |
2008年 | 1192篇 |
2007年 | 1155篇 |
2006年 | 1050篇 |
2005年 | 908篇 |
2004年 | 861篇 |
2003年 | 763篇 |
2002年 | 657篇 |
2001年 | 142篇 |
2000年 | 97篇 |
1999年 | 141篇 |
1998年 | 149篇 |
1997年 | 114篇 |
1996年 | 107篇 |
1995年 | 83篇 |
1994年 | 76篇 |
1993年 | 55篇 |
1992年 | 48篇 |
1991年 | 38篇 |
1990年 | 69篇 |
1989年 | 28篇 |
1988年 | 24篇 |
1987年 | 32篇 |
1986年 | 21篇 |
1985年 | 23篇 |
1984年 | 38篇 |
1983年 | 34篇 |
1982年 | 19篇 |
1981年 | 30篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1975年 | 12篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
851.
DNA extraction and PCR amplification method suitable for fresh, herbarium-stored, lichenized, and other fungi 总被引:6,自引:0,他引:6
Oscar F. Cubero Ana Crespo Jamshid Fatehi Paul D. Bridge 《Plant Systematics and Evolution》1999,216(3-4):243-249
This paper presents a DNA extraction method suitable for fresh, herbarium-stored, lichenized and other fungal specimens. The method is fast and reliable, comparatively inexpensive and is suitable for obtaining PCR amplification quality DNA from large numbers of samples in a short time. The method has been tested with over 300 samples ofAscochyta, Phyllosticta, Ramalina, Parmelia andPhysconia. Amplifiable fungal DNA was extracted from pure cultures, leaf lesions, whole thalli and dissected only-fungal sections of lichenized fungi. In addition, the method has proved suitable for use with herbarium specimens of both lichenized and non-lichenized fungi, stored as dried pure cultures or dried infected plant material. 相似文献
852.
853.
854.
855.
856.
Salazar AM Calderón-Aranda E Cebrián ME Sordo M Bendesky A Gómez-Muñoz A Acosta-Saavedra L Ostrosky-Wegman P 《Molecular and cellular biochemistry》2004,255(1-2):25-31
Arsenic is a common environmental toxicant and epidemiological studies associate arsenic exposure with various pathologic disorders and several types of cancer. Skin cancers are the most common arsenic-induced neoplasias and the prevalence of skin lesions has been reported to be significantly elevated in individuals exposed to arsenic via drinking water in Mexico. Being lymphocytes the main cells used for human monitoring, we evaluated the expression of p53 protein in the lymphocytes from 44 healthy individuals and 19 samples from individuals living in a chronic arsenicism endemic region. Of the latter group, 12 individuals had non-melanoma skin cancer and 9 of them expressed p53 in the circulating lymphocytes, whereas only one of the 7 non-cancer arsenic exposed individuals expressed it. In the healthy non-arsenic exposed group only one from 44 individuals expressed the protein. These results suggest a clear relationship between non-melanoma skin cancer and p53 expression in circulating lymphocytes. p53 expression in circulating lymphocytes should be evaluated as a potential biomarker of effect or susceptibility. 相似文献
857.
Dellias JM Onofre GR Werneck CC Landeira-Fernandez AM Melo FR Farias WR Silva LC 《Biochimie》2004,86(9-10):677-683
We compared the disaccharide composition of dermatan sulfate (DS) purified from the ventral skin of three species of rays from the Brazilian seacoast, Dasyatis americana, Dasyatis gutatta, Aetobatus narinari and of Potamotrygon motoro, a fresh water species that habits the Amazon River. DS obtained from the four species were composed of non-sulfated, mono-sulfated disaccharides bearing esterified sulfate groups at positions C-4 or C-6 of N-acetyl galactosamine (GalNAc), and disulfated disaccharides bearing esterified sulfate groups at positions C-2 of the uronic acid and at position C-4 or C-6 of GalNAc. However, DS from the skin of P. motoro presented a very low content of the disulfated disaccharides. The anticoagulant actions of ray skin DS, measured by both APTT clotting and HCII-mediated inhibition of thrombin assays, were compared to that of mammalian DS. DS from D. americana had both high APTT and HCII activities, whereas DS from D. gutatta showed activity profiles similar to those of mammalian DS. In contrast, DS from both A. narinari and P. motoro had no measurable activity in the APTT assay. Thus, the anticoagulant activity of ray skin DS is not merely a consequence of their charge density. We speculate that the differences among the anticoagulant activities of these three DS may be related to both different composition and arrangements of the disulfated disaccharide units within their polysaccharide chains. 相似文献
858.
Ruiz JF Lucas D García-Palomero E Saez AI González MA Piris MA Bernad A Blanco L 《Nucleic acids research》2004,32(19):5861-5873
DNA polymerase μ (Pol μ) is a DNA-dependent DNA polymerase closely related to terminal deoxynucleotidyl transferase (TdT), and prone to induce template/primer misalignments and misincorporation. In addition to a proposed general role in non-homologous end joining of double-strand breaks, its mutagenic potential and preferential expression in secondary lymphoid tissues support a role in somatic hypermutation (SHM) of immunoglobulin genes. Here, we show that human Pol μ protein is expressed in the nucleus of centroblasts obtained from human tonsils, forming a characteristic foci pattern resembling that of other DNA repair proteins in response to DNA damage. Overexpression of human Pol μ in Ramos cells, in which the SHM process is constitutive, augmented the somatic mutations specifically at the variable (V) region of the immunoglobulin genes. The nature of the mutations introduced, mostly base substitutions, supports the contribution of Pol μ to mutation of G and C residues during SHM. In vitro analysis of Pol μ misincorporation on specific templates, that mimic DNA repair intermediates and correspond to mutational hotspots, indicated that many of the mutations observed in vivo can be explained by the capacity of Pol μ to induce transient template/primer misalignments. 相似文献
859.
de la Hoz AB Pratto F Misselwitz R Speck C Weihofen W Welfle K Saenger W Welfle H Alonso JC 《Nucleic acids research》2004,32(10):3136-3147
860.
Beta-carotene storage, conversion to retinoic acid, and induction of the lipocyte phenotype in hepatic stellate cells 总被引:1,自引:0,他引:1
Martucci RB Ziulkoski AL Fortuna VA Guaragna RM Guma FC Trugo LC Borojevic R 《Journal of cellular biochemistry》2004,92(2):414-423
Hepatic stellate cells (HSCs) are the major site of retinol (ROH) metabolism and storage. GRX is a permanent murine myofibroblastic cell line, derived from HSCs, which can be induced to display the fat-storing phenotype by treatment with retinoids. Little is known about hepatic or serum homeostasis of beta-carotene and retinoic acid (RA), although the direct biogenesis of RA from beta-carotene has been described in enterocytes. The aim of this study was to identify the uptake, metabolism, storage, and release of beta-carotene in HSCs. GRX cells were plated in 25 cm(2) tissue culture flasks, treated during 10 days with 3 micromol/L beta-carotene and subsequently transferred into the standard culture medium. beta-Carotene induced a full cell conversion into the fat-storing phenotype after 10 days. The total cell extracts, cell fractions, and culture medium were analyzed by reverse phase high-performance liquid chromatography for beta-carotene and retinoids. Cells accumulated 27.48 +/- 6.5 pmol/L beta-carotene/10(6) cells, but could not convert it to ROH nor produced retinyl esters (RE). beta-Carotene was directly converted to RA, which was found in total cell extracts and in the nuclear fraction (10.15 +/- 1.23 pmol/L/10(6) cells), promoting the phenotype conversion. After 24-h chase, cells contained 20.15 +/- 1.12 pmol/L beta-carotene/10(6) cells and steadily released beta-carotene into the medium (6.69 +/- 1.75 pmol/ml). We conclude that HSC are the site of the liver beta-carotene storage and release, which can be used for RA production as well as for maintenance of the homeostasis of circulating carotenoids in periods of low dietary uptake. 相似文献