全文获取类型
收费全文 | 19210篇 |
免费 | 1725篇 |
国内免费 | 844篇 |
出版年
2024年 | 33篇 |
2023年 | 209篇 |
2022年 | 389篇 |
2021年 | 657篇 |
2020年 | 453篇 |
2019年 | 573篇 |
2018年 | 602篇 |
2017年 | 578篇 |
2016年 | 768篇 |
2015年 | 1175篇 |
2014年 | 1276篇 |
2013年 | 1469篇 |
2012年 | 1775篇 |
2011年 | 1667篇 |
2010年 | 1057篇 |
2009年 | 983篇 |
2008年 | 1135篇 |
2007年 | 1029篇 |
2006年 | 989篇 |
2005年 | 832篇 |
2004年 | 774篇 |
2003年 | 661篇 |
2002年 | 622篇 |
2001年 | 199篇 |
2000年 | 135篇 |
1999年 | 154篇 |
1998年 | 175篇 |
1997年 | 146篇 |
1996年 | 103篇 |
1995年 | 101篇 |
1994年 | 86篇 |
1993年 | 96篇 |
1992年 | 82篇 |
1991年 | 78篇 |
1990年 | 63篇 |
1989年 | 46篇 |
1988年 | 49篇 |
1987年 | 42篇 |
1986年 | 36篇 |
1985年 | 65篇 |
1984年 | 50篇 |
1983年 | 35篇 |
1982年 | 34篇 |
1981年 | 40篇 |
1980年 | 32篇 |
1979年 | 22篇 |
1978年 | 23篇 |
1977年 | 25篇 |
1976年 | 20篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Josefa Salgado Jose Villalain Juan C. Gómez-Fernández 《European biophysics journal : EBJ》1993,22(2):151-155
-Tocopherol, ubiquinone-10 and ubiquinol-10 have been studied by high resolution magic angle samples spinning 13C-nuclear magnetic resonance in egg yolk phosphatidylcholine multilamellar vesicles model membranes in order to assess their location and the induced perturbations on this model system. -Tocopherol is placed in such a position that it is in close contact with the head group of the phospholipid and exposed to the solvent. In this position it significantly perturbs the phospholipid head group, the 5a-CH3 and the 7a-CH3 groups being the closest parts to the membrane surface. On the other hand, ubiquinol-10 perturbs the membrane surface more than ubiquinone-10, but neither compound significantly changed the phospholipid head group conformation. 相似文献
102.
The taxonomy of marine species of the genus Diphyllobothrium, particularly those parasitic in cetaceans, is rather confused. During parasitological investigations of long-finned pilot
whales Globicephala melas from waters off the Faroe Islands, five diphyllobothriid species were detected: Diphyllobothrium sp. (possibly D. polyrugosum), D. stemmacephalum, Diphyllobothrium sp. A, Diphyllobothrium sp. B and Diphyllobothriidae sp. D. stemmacephalum is reported for the first time from G. melas. The stituation regarding the taxonomy of Diphylobothrium species from cetaceans is briefly reviewed. It is concluded that the recent development of genetic techniques may be of great
value in relation to clarifying the taxonomy of this group. 相似文献
103.
Fernando Hiraldo Borja Heredia Juan Carlos Alonso 《Ethology : formerly Zeitschrift fur Tierpsychologie》1993,93(2):117-124
Social feeding strategies of wintering red kites are analyzed in relation to age, food, roost-sites and differences from kite residents. Whereas young and adult wintering kites gathered at roost sites almost daily, adult residents did not, and immature residents only occasionally. Kites using roost sites feed more often on prey prelocated by others, while lone roosters also forage and discover food alone. After finding food, kites tend to shift to a new roost site and foraging area. Two details of the ‘information centre’ hypothesis are confirmed in our study: carcasses are unpredictably found patches, divisible between several individuals. But carcasses disappeared fast in the study area, and no increase with time in the number of birds consuming a carcass was observed, so that information transmission was unconfirmed. When kites leave the roost in groups no leader is detectable. It seems that other types of social foraging are operating, and the model best matching our results is network foraging. 相似文献
104.
Jos M Cuezva Ana I Flores Antonio Liras Juan F Santarn Agustín Alconada 《Biology of the cell / under the auspices of the European Cell Biology Organization》1993,77(1):47-62
Summary— A review of the proteinaceous machinery involved in protein sorting pathways and protein folding and assembly in mitochondria and peroxisomes is presented. After considering the various sorting pathways and targeting signals of mitochondrial and peroxisomal proteins, we make a comparative dissection of the protein factors involved in: i) the stabilization of cytosolic precursor proteins in a translocation competent conformation; ii) the membrane import apparatus of mitochondria and peroxisomes; iii) the processing of mitochondrial precursor proteins, and the eventual processing of certain peroxisomal precursor, in the interior of the organelles; and iv) the requirement of molecular chaperones for appropriate folding and assembly of imported proteins in the matrix of both organelles. Those aspects of mitochondrial biogenesis that have developed rapidly during the last few years, such as the requirement of molecular chaperones, are stressed in order to stimulate further parallel investigations aimed to understand the origin, biochemistry, molecular biology and pathology of peroxisomes. In this regard, a brief review of findings from our group and others is presented in which the role of the F1-ATPase α-subunit is pointed out as a molecular chaperone of mitochondria and chloroplasts. In addition, data are presented that could question our previous indication that the immunoreactive protein found in the rat liver peroxisomes is due to the presence of the F1-ATPase α-subunit. 相似文献
105.
Ethanol-hypersensitive strains (ets mutants), unable to grow on media containing 6% ethanol, were isolated from a sample of mutagenized Schizosaccharomyces pombe wild-type cells. Genetic analysis of these ets strains demonstrated that the ets phenotype is associated with mutations in a large set of genes, including cell division cycle (cdc) genes, largely non-overlapping with the set represented by the temperature conditional method; accordingly, we isolated some ets non-ts cdc ? mutants, which may identify novel essential genes required for regulation of the S. pombe cell cycle. Conversely, seven well characterized ts cdc ? mutants were tested for their ethanol sensitivity; among them, cdc1–7 and cdc13–117 exhibited a tight ets phenotype. Ethanol sensitivity was also tested in strains bearing different alleles of the cdc2 gene, and we found that some of them were ets, but others were non-ets; thus, ethanol hypersensitivity is an allele-specific phenotype. Based on the single base changes found in each particular allele of the cdc2 gene, it is shown that a single amino acid substitution in the p34cdc2 gene product can produce this ets phenotype, and that ethanol hypersensitivity is probably due to the influence of this alcohol on the secondary and/or tertiary structure of the target protein. Ethanol-dependent (etd) mutants were also identified as mutants that can only be propagated on ethanol-containing media. This novel type of conditional phenotype also covers many unrelated genes. One of these etd mutants, etd1-1, was further characterized because of the lethal cdc ? phenotype of the mutant cells under restrictive conditions (absence of ethanol). The isolation of extragenic suppressors of etd1-1, and the complementation cloning of a DNA fragment encompassing the etd1 + wild-type gene (or an extragenic multicopy suppressor) demonstrate that current genetic techniques may be applied to mutants isolated by using ethanol as a selective agent. 相似文献
106.
药敏药片经临床对金黄色葡萄球菌、大肠埃希氏菌、铜绿假单胞菌等235株考核.表明药片工艺研究先进,药片与培养基结合牢固,无断裂、崩解,不渗出颗粒,抑菌圈呈同心园扩散.边缘清楚。药物含量均匀,释放度好。药片抑菌差仅1~3mm;而纸片抑菌差为2~12mm。药片变黑系数CV为2.71~4.21;而纸片CV为3.82~14.36。表明纸片片间差大,药片精密度明显好于纸片。 相似文献
107.
This study is the first report of an algal disease, developed in close association with an endophytic organism, documented for the southeastern Pacific. We describe a disease affecting wild populations of the red alga Iridaea laminarioides Bory in central Chile, characterized by gall development on the surface of sporophytic, cystocarpic, and immature thalli. These abnormal growths result in severe morphological alterations of the affected thalli. Diseased fronds display an aggregated spatial distribution and occur throughout the year, with a maximum in summer followed by a decline in winter. The presence of galls was not associated with broken or torn fronds. Although causality has not been unequivocally demonstrated, our field and laboratory observations indicate a strong association of the galls with infections by an endophytic cyanobacterium, probably belonging to the genus Pleurocapsa. 相似文献
108.
Jesús Jimnez-Barbero Manuel Bernab Juan Antonio Leal Alicia Prieto Begoa Gmez-Miranda 《Carbohydrate research》1993,250(2):289-299
The structures of cell-wall mannans isolated from Aphamoascus mephitalus, A. Fulvescens, A. verrucosus, and A. reticulisporus have been investigated by chemical analyses and 1D and 2D 1H and 13C NMR techniques. It was found that all of them consists of a relatively simple comb-like structure of the disaccharide repeating block {→ 6)-[-Man p-(1 → 2)]--Man p-(1 →}. The conformations around the -(1 → 2) and -(1 → 6) linkages in thes kinds of polymers were also studied by using molecular mechanics and dynamics calculations, together with NOE data. The results are similar to those found within the oligosaccharide chains of glycoproteins, with a well-defined conformation for the -(1 → 2) linkage and a certain restriction around the -(1 → 6) bonding imposed by the 2-substitution. 相似文献
109.
Trinidad Hernández-Caselles José Villalaín Juan C. Gómez-Fernández 《Molecular and cellular biochemistry》1993,121(2):119-126
The roles of sulfhydryl and disulfide groups in the specific binding of synthetic cannabinoid CP-55,940 to the cannabinoid receptor in membrane preparations from the rat cerebral cortex have been examined. Various sulfhydryl blocking reagents including p-chloromercuribenzoic acid (p-CMB), N-ethylmaleimide (NEM), o-iodosobenzoic acid (o-ISB), and methyl methanethiosulfonate (MMTS) inhibited the specific binding of [3H]CP-55,940 to the cannabinoid receptor in a dose-dependent manner. About 80–95% inhibition was obtained at a 0.1 mM concentration of these reagents. Scatchard analysis of saturation experiments indicates that most of these sulfhydryl modifying reagents reduce both the binding affinity (Kd) and capacity (Bmax). On the other hand, DL-dithiothreitol (DTT), a disulfide reducing agent, also irreversibly inhibited the specific binding of [3H]CP-55,940 to the receptor and about 50% inhibition was obtained at a 5 mM concentration. Furthermore, 5mM DTT was abelt to dissociate 50% of the bound ligand from the ligand-receptor complex. The marked inhibition of [3H]CP-55,940 binding by sulfhydryl reagents suggests that at least one free sulfhydryl group is essential to the binding of the ligand to the receptor. In addition, the inhibition of the binding by DTT implies that besides free sulfhydryl group(s), the integrity of a disulfide bridge is also important for [3H]CP-55,940 binding to the cannabinoid receptor. 相似文献
110.
Estaras Matias Ortiz-Placin Candido Castillejo-Rufo Alba Fernandez-Bermejo Miguel Blanco Gerardo Mateos Jose M. Vara Daniel Gonzalez-Cordero Pedro L. Chamizo Sandra Lopez Diego Rojas Adela Jaen Isabel de Armas Noelia Salido Gines M. Iovanna Juan L. Santofimia-Castaño Patricia Gonzalez Antonio 《Journal of physiology and biochemistry》2023,79(1):235-249
Journal of Physiology and Biochemistry - We have investigated the effects of melatonin on major pathways related with cellular proliferation and energetic metabolism in pancreatic stellate cells.... 相似文献