全文获取类型
收费全文 | 3230篇 |
免费 | 218篇 |
专业分类
3448篇 |
出版年
2023年 | 15篇 |
2022年 | 30篇 |
2021年 | 52篇 |
2020年 | 39篇 |
2019年 | 58篇 |
2018年 | 81篇 |
2017年 | 55篇 |
2016年 | 83篇 |
2015年 | 135篇 |
2014年 | 144篇 |
2013年 | 230篇 |
2012年 | 246篇 |
2011年 | 251篇 |
2010年 | 154篇 |
2009年 | 123篇 |
2008年 | 215篇 |
2007年 | 219篇 |
2006年 | 180篇 |
2005年 | 153篇 |
2004年 | 151篇 |
2003年 | 159篇 |
2002年 | 159篇 |
2001年 | 27篇 |
2000年 | 16篇 |
1999年 | 26篇 |
1998年 | 26篇 |
1997年 | 34篇 |
1996年 | 20篇 |
1995年 | 30篇 |
1994年 | 22篇 |
1993年 | 23篇 |
1992年 | 27篇 |
1991年 | 23篇 |
1990年 | 26篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1971年 | 4篇 |
排序方式: 共有3448条查询结果,搜索用时 15 毫秒
181.
Franzoni L Lücke C Pérez C Cavazzini D Rademacher M Ludwig C Spisni A Rossi GL Rüterjans H 《The Journal of biological chemistry》2002,277(24):21983-21997
Retinoid-binding proteins play an important role in regulating transport, storage, and metabolism of vitamin A and its derivatives. The solution structure and backbone dynamics of rat cellular retinol-binding protein type I (CRBP) in the apo- and holo-form have been determined and compared using multidimensional high resolution NMR spectroscopy. The global fold of the protein is consistent with the common motif described for members of the intracellular lipid-binding protein family. The most relevant difference between the NMR structure ensembles of apo- and holoCRBP is the higher backbone disorder, in the ligand-free form, of some segments that frame the putative entrance to the ligand-binding site. These comprise alpha-helix II, the subsequent linker to beta-strand B, the hairpin turn between beta-strands C and D, and the betaE-betaF turn. The internal backbone dynamics, obtained from 15N relaxation data (T1, T2, and heteronuclear nuclear Overhauser effect) at two different fields, indicate several regions with significantly higher backbone mobility in the apoprotein, including the betaC-betaD and betaE-betaF turns. Although apoCRBP contains a binding cavity more shielded than that of any other retinoid carrier, conformational flexibility in the portal region may assist retinol uptake. The stiffening of the backbone in the holoprotein guarantees the stability of the complex during retinol transport and suggests that targeted retinol release requires a transiently open state that is likely to be promoted by the acceptor or the local environment. 相似文献
182.
183.
In the search for increasingly accurate protein structures, technological advances are opening up new possibilities. In the last few years the wide accessibility of intense synchrotron sources, the availability of efficient 2D-detectors, and the routine use of cryo-crystallography techniques have yielded a significant number of atomic resolution protein structures. Here we review the most interesting results achieved in this field with a particular emphasis to the biological implications and to the correlation between protein geometry and conformation. 相似文献
184.
Russo MV Campanella L Avino P 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2002,780(2):431-441
We describe an analytical method that allows the determination of organophosphorus pesticides (OPs) in different human tissues. It involves an extraction procedure with ethanol-ethyl acetate, followed by gel permeation chromatography clean-up step and analysis by capillary gas chromatography-negative chemical ionization mass spectrometry in the selected ion monitoring mode. The method was tested for 37 OPs and the recoveries obtained vary between 60 and 106% with standard deviations ranging between +/-2 and +/-10. These values are independent of the analyzed tissue. Peak area repeatability as RSD for some OPs was < or =4.8% while a good linear relationship in the range 1.0-500 pg microl(-1) with r(2)> or =0.9878 was obtained. The limit of detection for the 37 OPs falls between 0.01 and 0.09 ng g(-1) with an RSD< or =9.5%. The analytical set up in this paper has been used to analyze different samples of human tissues (liver, healthy kidney, cancer kidney and adipose tissue) of 24 patients. The number of the identified OPs in the tissue samples is different (max. 20) according to the sample while their concentration ranges between the limit of detection and 28.0 ng g(-1). The highest concentrations have been determined in liver samples without any pathology (0.4-28.0 ng g(-1)) while the lowest concentrations have been determined in healthy kidney samples (0.01-1.50 ng g(-1)). In the cancer kidney samples OP concentrations vary between 0.03 and 4.6 ng g(-1): these concentrations are more elevated than those determined in healthy kidney samples. The comparison between the concentration of OPs determined in the healthy part, when possible, and those determined in the cancer part of the same kidney sample are very interesting: in fact, in the latter the OP concentration is generally 1-2-times higher than that in the former, an index of lower enzymatic activity in the cancer tissue. 相似文献
185.
186.
187.
Santucci D Francia N Aloe L Alleva E 《Journal of gravitational physiology : a journal of the International Society for Gravitational Physiology》2002,9(1):P39-P40
Behavioural responses of CD-1 mice exposed to 2 g hypergravity (HG; 60 or 120 min) were investigated during adolescence and at adulthood. To characterise motion sickness (MS), pica behaviour, a reliable MS index measured through kaolin consumption, and spontaneous activity were evaluated before, during and after HG exposure. Short- and/or long-lasting effects on emotional responses, exploratory behaviour and spatial learning performances were also investigated and brain levels of nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) assessed. An increased pica behaviour during post rotational days and a reduction in spontaneous activity during rotation indicated a mild sickness associated with HG, and susceptibility to MS was sex and age related. Short- and long-lasting effects of exposure were also observed, rotated mice showing altered emotional/anxiety behavioural profiles and impaired spatial learning performances. Moreover, central NGF levels were markedly increased after rotation, while minor changes were observed in BDNF levels. 相似文献
188.
Recently, increasing importance has been attached to the role of estrogens and their receptors in male reproduction, since they have been found to be abundant in the male reproductive tract. In the lizard, Podarcis sicula, a seasonal breeder, estrogens seem to be involved in the regulation of testicular activity. Particularly, it has been hypothesized that the block of spermatogenesis and the complete regression of the epididymis and other secondary sexual characters (SSCs) in autumn might be due to high estrogen levels. To investigate the role of estrogens in the reproductive process of male lizards, we utilized Fadrozole ((AI) [4-(5,6,7,8-tetrahydroimidazole [1,5-a] pyridin-5-yl)-benzonitrile monohydrochloride] (CGS 16949A)), a nonsteroidal inhibitor of aromatase, the enzyme involved in the aromatization of androgens to estrogens, evaluating its effects on plasma sex-hormone release, spermatogenesis and epididymis morphology. For this purpose, adult male lizards, captured during the autumnal recrudescence, were intraperitoneally injected with 0.5 microg and 5 microg/g/body weight of AI for 15 and 30 days. In the animals treated with the higher AI dose, estrogen levels decreased if compared to the control groups, whereas androgen levels increased. Furthermore, histologic sections of testes and epididymes showed that the 30-day treatment with AI-induced spermatogenesis resumption with release of sperms into the large lumen of the seminiferous tubules, and the epididymes appeared more developed with moderately secreting columnar canal cells. Therefore, it is proposed that failure of spermatogenesis in autumn might be due to high estrogen levels. 相似文献
189.
Mutations in the Dof zinc finger genes DAG2 and DAG1 influence with opposite effects the germination of Arabidopsis seeds 总被引:4,自引:0,他引:4
下载免费PDF全文
![点击此处可从《The Plant cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Gualberti G Papi M Bellucci L Ricci I Bouchez D Camilleri C Costantino P Vittorioso P 《The Plant cell》2002,14(6):1253-1263
We describe the Arabidopsis gene DAG2 encoding a Dof zinc finger protein and show that it is involved in the control of seed germination. An Arabidopsis mutant line with a T-DNA insertion in DAG2 isolated by reverse genetics produces seeds that are substantially more dependent than the wild type on the physical stimuli-light and cold treatment-that promote germination. Mutant dag2 seeds also are less sensitive to the germination-promotive effect of gibberellins, because a 10-fold higher amount of gibberellins is needed to restore germination when endogenous gibberellin biosynthesis is blocked. The seed germination characteristics of the dag2 mutant are opposite to those of dag1, a knockout mutant of another Dof gene (DAG1) that we showed previously to be involved in the control of seed germination, and are similar to those of plants that overexpress DAG1. The promoter of the DAG2 gene is active specifically in the vascular system of the mother plant but not in the embryo, and segregation analysis indicates that the effect of the dag2 mutation is maternal. Both characteristics are in common with DAG1; additionally, the DAG1 and DAG2 proteins share high sequence homology and an identical zinc finger domain. These data suggest, and the germination phenotype of the double mutant is compatible with, a model whereby the zinc finger proteins DAG1 and DAG2 act on a maternal switch that controls seed germination, possibly by regulating the same gene(s). 相似文献
190.
Human chromosomes 9, 12, and 15 contain the nucleation sites of stress-induced nuclear bodies
下载免费PDF全文
![点击此处可从《Molecular biology of the cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Denegri M Moralli D Rocchi M Biggiogera M Raimondi E Cobianchi F De Carli L Riva S Biamonti G 《Molecular biology of the cell》2002,13(6):2069-2079
We previously reported the identification of a novel nuclear compartment detectable in heat-shocked HeLa cells that we termed stress-induced Src-activated during mitosis nuclear body (SNB). This structure is the recruitment center for heat shock factor 1 and for a number of RNA processing factors, among a subset of Serine-Arginine splicing factors. In this article, we show that stress-induced SNBs are detectable in human but not in hamster cells. By means of hamster>human cell hybrids, we have identified three human chromosomes (9, 12, and 15) that are individually able to direct the formation of stress bodies in hamster cells. Similarly to stress-induced SNB, these bodies are sites of accumulation of hnRNP A1-interacting protein and heat shock factor 1, are usually associated to nucleoli, and consist of clusters of perichromatin granules. We show that the p13-q13 region of human chromosome 9 is sufficient to direct the formation of stress bodies in hamster>human cell hybrids. Fluorescence in situ hybridization experiments demonstrate that the pericentromeric heterochromatic q12 band of chromosome 9 and the centromeric regions of chromosomes 12 and 15 colocalize with stress-induced SNBs in human cells. Our data indicate that human chromosomes 9, 12, and 15 contain the nucleation sites of stress bodies in heat-shocked HeLa cells. 相似文献