全文获取类型
收费全文 | 3533篇 |
免费 | 368篇 |
出版年
2022年 | 22篇 |
2021年 | 53篇 |
2020年 | 40篇 |
2019年 | 38篇 |
2018年 | 36篇 |
2017年 | 51篇 |
2016年 | 76篇 |
2015年 | 112篇 |
2014年 | 142篇 |
2013年 | 158篇 |
2012年 | 224篇 |
2011年 | 198篇 |
2010年 | 127篇 |
2009年 | 114篇 |
2008年 | 158篇 |
2007年 | 212篇 |
2006年 | 167篇 |
2005年 | 134篇 |
2004年 | 140篇 |
2003年 | 146篇 |
2002年 | 114篇 |
2001年 | 66篇 |
2000年 | 58篇 |
1999年 | 47篇 |
1998年 | 49篇 |
1997年 | 41篇 |
1996年 | 44篇 |
1995年 | 39篇 |
1994年 | 39篇 |
1993年 | 35篇 |
1992年 | 57篇 |
1991年 | 32篇 |
1990年 | 49篇 |
1989年 | 46篇 |
1988年 | 57篇 |
1987年 | 38篇 |
1986年 | 34篇 |
1985年 | 41篇 |
1984年 | 49篇 |
1983年 | 31篇 |
1982年 | 22篇 |
1981年 | 42篇 |
1980年 | 26篇 |
1979年 | 32篇 |
1978年 | 31篇 |
1977年 | 23篇 |
1976年 | 25篇 |
1975年 | 18篇 |
1974年 | 37篇 |
1972年 | 18篇 |
排序方式: 共有3901条查询结果,搜索用时 125 毫秒
71.
The representation and characterization of molecular surfaces are important in many areas of molecular modeling. Parametric representations of protein molecular surfaces are a compact way to describe a surface, and are useful for the evaluation of surface properties such as the normal vector, principal curvatures, and principal curvature directions. Simplified representations of molecular surfaces are useful for efficient rendering and for the display of large-scale surface features. Several techniques for representing surfaces by expansions of spherical harmonic functions have been reported, but these techniques require that the radius function is single valued, that is, each ray from an origin inside the surface intersects the surface at one and only one point. A new technique is described that removes this limitation and can be used to compute surface shape properties. © 1993 John Wiley & Sons, Inc. 相似文献
72.
A kinetic study of the activity of mushroom polyphenol oxidase in an organic system was carried out to obtain detailed enzyme kinetic data in relation to optimization of reaction conditions and substrate specificity. A simple method for consistent measurement of reaction rates in the heterogeneous enzyme/organic solvent system (consisting of immobilized polyphenol oxidase and a hydrated solution of the substrate in chloroform) was designed. The aqueous content of the system was optimized using p-cresol as the substrate. With this system, a crude extract of Agaricus bisporus was used to hydroxylate and oxidize a range of selected p-substituted phenolic substrates, yielding o-quinone products. Michaelis-Menten kinetics were used to obtain apparent K(M) and V(max) values with respect to each of these substrates. Results from this analysis indicated a correlation between the enzymic kinetic parameters obtained and the steric requirements of the substrates, which could be rationalized in terms of the restricted flexibility of the enzyme when it is in chloroform and also in terms of substrate and solvent hydrophobicity. In the course of the investigation UV molar absorption coefficients of several o-quinones were measured by a novel method: (1)H nuclear magnetic resonance (NMR) spectroscopy was employed to determine component concentrations in reaction mixtures resulting from the transformation of phenols by polyphenol oxidase in chloroform. Thus the UV molar absorption coefficients could be obtained directly, avoiding the necessity to isolate the water-sensitive, unstable o-quinones. (c) 1993 John Wiley & Sons, Inc. 相似文献
73.
Elnur Babayev Chanakarn Suebthawinkul Dilan Gokyer Wendena S. Parkes Felipe Rivas Mary Ellen Pavone Adam R. Hall Michele T. Pritchard Francesca E. Duncan 《Aging cell》2023,22(11):e14004
Reproductive aging is associated with ovulatory defects. Age-related ovarian fibrosis partially contributes to this phenotype as short-term treatment with anti-fibrotic compounds improves ovulation in reproductively old mice. However, age-dependent changes that are intrinsic to the follicle may also be relevant. In this study, we used a mouse model to demonstrate that reproductive aging is associated with impaired cumulus expansion which is accompanied by altered morphokinetic behavior of cumulus cells as assessed by time-lapse microscopy. The extracellular matrix integrity of expanded cumulus–oocyte complexes is compromised with advanced age as evidenced by increased penetration of fluorescent nanoparticles in a particle exclusion assay and larger open spaces on scanning electron microscopy. Reduced hyaluronan (HA) levels, decreased expression of genes encoding HA-associated proteins (e.g., Ptx3 and Tnfaip6), and increased expression of inflammatory genes and matrix metalloproteinases underlie this loss of matrix integrity. Importantly, HA levels are decreased with age in follicular fluid of women, indicative of conserved reproductive aging mechanisms. These findings provide novel mechanistic insights into how defects in cumulus expansion contribute to age-related infertility and may serve as a target to extend reproductive longevity. 相似文献
74.
Michael P. Jennings Peter van der Ley Kathy E. Wilks Duncan J. Maskell † Jan T. Poolman E. Richard Moxon 《Molecular microbiology》1993,10(2):361-369
The galE gene from Haemophilus influenzae was used as a hybridization probe for the galE gene of Neisseria meningitidis Group B, identifying two different homologous loci. Each of the loci was cloned and nucleotide sequence analysis revealed that both loci contained sequences similar to galE. One contained a functional galE gene and mapped to the capsule biosynthetic locus. The second contained only a partial galE-coding sequence, which did not express a functional gene product. A galE mutant meningococcal strain was constructed by transformation with an inactivated galE gene. Analysis of the LPS from the galE mutant strain revealed an apparent reduction in molecular weight and a loss of reactivity with monoclonal antibodies specific for structures known to contain galactose. These results are consistent with an essential role for galE in the incorporation of galactose into meningococcal lipopolysaccharide. 相似文献
75.
Roberto de la Herrán Miguel Hermida Juan Andres Rubiolo Jèssica Gómez-Garrido Fernando Cruz Francisca Robles Rafael Navajas-Pérez Andres Blanco Paula Rodriguez Villamayor Dorinda Torres Pablo Sánchez-Quinteiro Daniel Ramirez Maria Esther Rodríguez Alberto Arias-Pérez Ismael Cross Neil Duncan Teresa Martínez-Peña Ana Riaza Adrian Millán M. Cristina De Rosa Davide Pirolli Marta Gut Carmen Bouza Diego Robledo Laureana Rebordinos Tyler Alioto Carmelo Ruíz-Rejón Paulino Martínez 《Molecular ecology resources》2023,23(4):886-904
Sex determination (SD) shows huge variation among fish and a high evolutionary rate, as illustrated by the Pleuronectiformes (flatfishes). This order is characterized by its adaptation to demersal life, compact genomes and diversity of SD mechanisms. Here, we assembled the Solea senegalensis genome, a flatfish of great commercial value, into 82 contigs (614 Mb) combining long- and short-read sequencing, which were next scaffolded using a highly dense genetic map (28,838 markers, 21 linkage groups), representing 98.9% of the assembly. Further, we established the correspondence between the assembly and the 21 chromosomes by using BAC-FISH. Whole genome resequencing of six males and six females enabled the identification of 41 single nucleotide polymorphism variants in the follicle stimulating hormone receptor (fshr) consistent with an XX/XY SD system. The observed sex association was validated in a broader independent sample, providing a novel molecular sexing tool. The fshr gene displayed differential expression between male and female gonads from 86 days post-fertilization, when the gonad is still an undifferentiated primordium, concomitant with the activation of amh and cyp19a1a, testis and ovary marker genes, respectively, in males and females. The Y-linked fshr allele, which included 24 nonsynonymous variants and showed a highly divergent 3D protein structure, was overexpressed in males compared to the X-linked allele at all stages of gonadal differentiation. We hypothesize a mechanism hampering the action of the follicle stimulating hormone driving the undifferentiated gonad toward testis. 相似文献
76.
77.
78.
Infection of broad mites, Polyphagotarsonemus latus, by conidia of Beauveria bassiana, Hirsutella thompsonii, and Paecilomyces fumosoroseus conidia was investigated in the laboratory under controlled temperature and moisture conditions. Infection of P. latus by the fungus (LC50) was related positively to the 1.16 × 106 B. bassiana conidia per ml, 2.39 × 103 H. thompsonii conidia per ml, and 1.29 × 105 P. fumosoroseus conidia per ml. Mortality caused by B. bassiana occurred the fastest among densities fluctuating between 65 and 125 mites per leaf. The pathogens B. bassiana and P. fumosoroseus, adjuvants (oil and molasses), and the acaricide ABG6364, a microbial insecticide containing the Beta-exotoxin of Bacillus thuringiensis were evaluated for efficacy against P. latus in a greenhouse test. The B. bassiana treated plants had the greatest and most persistent effect on percentage mortality of total broad mites present per leaf (88 %) followed by the acaricide ABG6364. Use of adjuvants (oil and molasses) did not increase infection of P. latus. 相似文献
79.
A. Chisholm J. Mann W. Sutherland A. Duncan M. Skeaff C. Frampton 《BMJ (Clinical research ed.)》1996,312(7036):931-934
OBJECTIVE--To examine the effect on lipid and lipoprotein concentrations when butter or an unsaturated margarine is used for cooking or spreading in a reduced fat diet. DESIGN--Randomised crossover study with two intervention periods of six weeks'' duration separated by a five week washout. SETTING--Community setting in New Zealand. SUBJECTS--49 volunteers with polygenic hypercholesterolaemia and baseline total cholesterol concentration in the range 5.5-7.9 mmol/l. MAIN OUTCOME MEASURES--Concentrations of total and low density lipoprotein, Lp(a) lipoprotein, high density lipoprotein, apolipoprotein B 100, and apolipoprotein A I. RESULTS--Concentrations of low density lipoprotein cholesterol and apolipoprotein B were about 10% lower with margarine than with butter. Lp(a) lipoprotein and high density lipoprotein cholesterol concentrations were similar with the two diets. CONCLUSION--Despite concerns about adverse effects on lipoproteins of trans fatty acids in margarines, the use of unsaturated margarine rather than butter by hypercholesterolaemic people is associated with a lipoprotein profile that would be expected to reduce cardiovascular risk. 相似文献
80.