首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1473篇
  免费   81篇
  国内免费   40篇
  1594篇
  2024年   2篇
  2023年   29篇
  2022年   24篇
  2021年   36篇
  2020年   35篇
  2019年   47篇
  2018年   48篇
  2017年   57篇
  2016年   40篇
  2015年   44篇
  2014年   121篇
  2013年   248篇
  2012年   88篇
  2011年   61篇
  2010年   34篇
  2009年   53篇
  2008年   59篇
  2007年   78篇
  2006年   74篇
  2005年   63篇
  2004年   53篇
  2003年   39篇
  2002年   29篇
  2001年   27篇
  2000年   23篇
  1999年   13篇
  1998年   19篇
  1997年   18篇
  1996年   13篇
  1995年   14篇
  1994年   8篇
  1993年   10篇
  1992年   9篇
  1991年   11篇
  1990年   4篇
  1989年   9篇
  1988年   5篇
  1987年   8篇
  1986年   10篇
  1985年   4篇
  1983年   3篇
  1982年   2篇
  1981年   4篇
  1980年   4篇
  1979年   6篇
  1978年   2篇
  1975年   1篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
排序方式: 共有1594条查询结果,搜索用时 15 毫秒
71.
CD36 is a fatty acid translocase in striated muscle cells and cardiomyocytes. Some study suggested that alterations in CD36 gene may be associated with coronary artery disease (CAD) risk. The aim of the current study was to compare the frequency of CD36 variants in region encoding lipid-binding domain in Caucasian patients with early-onset CAD, no-CAD adult controls and neonates. The study group comprised 100 patients with early onset CAD. The genetic control groups were 306 infants and 40 no-CAD adults aged over 70 years. Exons 4, 5 and 6 including fragments of flanking introns were studied using the denaturing high-performance liquid chromatography technique and direct sequencing. Changes detected in analyzed fragment of CD36: IVS3-6 T/C (rs3173798), IVS4-10 G/A (rs3211892), C311T (Thr104Ile, not described so far) in exon 5, G550A (Asp184Asn, rs138897347), C572T (Pro191Leu, rs143150225), G573A (Pro191Pro, rs5956) and A591T (Thr197Thr, rs141680676) in exon 6. No significant differences in the CD36 genotype, allele and haplotype frequencies were found between the three groups. Only borderline differences (p = 0.066) were found between early onset CAD patients and newborns in the frequencies of 591T allele (2.00% vs 0.50%) and CGCGCGT haplotype (2.00% vs 0.50%) with both IVS3-6C and 591T variant alleles. In conclusion, CD36 variants: rs3173798, rs3211892, rs138897347, rs5956, rs143150225 rs141680676 and C311T do not seem to be involved in the risk of early-onset CAD in Caucasian population.  相似文献   
72.
利用从126个RAPD(RandomAmplifiedPolymorphicDNAs)随机引物中筛选到的可扩增出清晰条带、主带明显、稳定的8条引物,对采集自江苏、安徽和江西不同寄主的45个Phytophthoraboehmeriae菌株进行全基因组DNARAPD标记遗传多样性分析。选用引物共标出DNA指纹图带68条,其中多态性条带20条,多态性检测率为29.4%,表明该种内不同地区和寄主来源的菌株间变异较小。利用Popgene软件计算供试菌株间的遗传距离并绘制聚类树状图,供试菌株被划分为2个遗传聚类组。菌株间的遗传相似性与菌株的寄主来源有一定的相关性,来自江苏、江西和安徽棉花上的27个菌株被划分在同一遗传聚类组内,而分离自构树、枫杨和苎麻的18个菌株被划分在另一个遗传聚类组。结果还表明菌株间遗传相似性与其地区来源无直接相关性。  相似文献   
73.
细胞分裂素对拟南芥(Arabidopsis thaliana)花分生组织细胞的分裂和分化具有重要作用。本研究利用APETALA1(AP1)特异启动子在花分生组织和第1、2轮花器官中表达细胞分裂素合成酶(isopentyl transferase,IPT)基因IPT4,研究细胞分裂素对花和花器官发育的影响。在pAP1∷IPT4转基因植株中出现了花密集和花器官数目增多等现象。原位杂交和GUS组织染色结果发现,在pAP1∷IPT4转基因植株中,花分生组织特征决定基因LEAFY(LFY)与花器官特征决定基因AP1、PISTILLATA(PI)和AGAMOUS(AG)的表达量均有不同程度的提高。研究结果表明在拟南芥中表达pAP1∷IPT4影响其花和花器官的正常发育。  相似文献   
74.
This study was conducted to establish the contribution of genetic host factors in the susceptibility to community acquired pneumonia (CAP) in the Russian population. Patients with CAP (n = 334), volunteers without a previous history of CAP, constantly exposed to infectious agents, control A group (n = 141) and a second control group B consisted of healthy persons (n = 314) were included in the study. All subjects were genotyped for 13 polymorphic variants in the genes of xenobiotics detoxification CYP1A1 (rs2606345, rs4646903, and rs1048943), GSTM1 (Ins/del), GSTT1 (Ins/del), ABCB1 rs1045642); immune and inflammation response IL-6 (rs1800795), TNF-a (rs1800629), MBL2 (rs7096206), CCR5 (rs333), NOS3 (rs1799983), angiotensin-converting enzyme ACE (rs4340), and occlusive vascular disease/hyperhomocysteinemia MTHFR (rs1801133). Seven polymorphic variants in genes CYP1A1, GSTM1, ABCB1, NOS3, IL6, CCR5 and ACE were associated with CAP. For two genes CYP1A1 and GSTM1 associations remained significant after correction for multiple comparisons. Multiple analysis by the number of all risk genotypes showed a highly significant association with CAP (P = 2.4 × 10− 7, OR = 3.03, 95% CI 1.98–4.64) with the threshold for three risk genotypes. Using the ROC-analysis, the AUC value for multi-locus model was estimated as 68.38.  相似文献   
75.
传递不平衡检验其实质是边缘齐性检验,需同时考察家系中两个亲代向受累子代的传递情形.但是,其零假设成立时,同一家系中父亲的传递与母亲的传递并不一定相互独立.本文探讨了父母传递的独立性条件对检验统计量的影响.结果表明,即使父母传递不独立时,边缘齐性检验仍然适合.  相似文献   
76.
77.
Partially purified preparations of the hepatic glucokinase from C3H/He and C58 inbred mice have been used to explore the molecular basis for the observed twofold difference in activity between the strains. The single codominant gene that appears to regulate activity, the alleles of which are designated Gka and Gkb, respectively, for the two strains, could represent a structural gene change. This now seems unlikely because the mouse enzyme, although showing small differences from rat glucokinase, appeared to be identical in the two strains with respect to thermal stability, electrophoretic mobility in agarose gels, and kinetic properties such as the apparent K m values for MgATP2– and glucose and the unique cooperative interaction with the latter substrate. The enzymes also reacted identically in a range of immunological tests (double-diffusion, immunoelectrophoresis, immune precipitation and immune inhibition assays) and ELISA immune inhibition assays indicated that the twofold difference in activity was due to a similar difference in antigenically active enzyme. Genetic control over the physiologically significant regulation of enzyme amount is therefore probable.This work has been supported in part by a grant from the British Diabetic Association and a Training Studentship to PAJ from the Medical Research Council (U.K.).  相似文献   
78.
《Ethnic and racial studies》2012,35(8):1427-1446
Abstract

The national census is often seen as a site of struggle for minorities seeking recognition and equality. Much less is known about the conditions under which ethnic majorities are galvanized to stake identity claims in the census. This article examines recent trends in New Zealand where an increasing number of people from the dominant New Zealand European group are redefining themselves as ethnic New Zealanders. Drawing from the literature on ethnic boundaries, we theorize the factors underlying the surge in New Zealander identification, and present census data to demonstrate its selective appeal. We also review patterns of national naming in North America and Australia to show that the New Zealander phenomenon reflects a broader shift by settler state majorities to reimagine their identities. The implications for ethnic counting in other contexts are briefly considered.  相似文献   
79.
Durum wheat (Triticum turgidum subsp. durum) is a key crop worldwide, and yet, its improvement and adaptation to emerging environmental threats is made difficult by the limited amount of allelic variation included in its elite pool. New allelic diversity may provide novel loci to international crop breeding through quantitative trait loci (QTL) mapping in unexplored material. Here, we report the extensive molecular and phenotypic characterization of hundreds of Ethiopian durum wheat landraces and several Ethiopian improved lines. We test 81 587 markers scoring 30 155 single nucleotide polymorphisms and use them to survey the diversity, structure, and genome‐specific variation in the panel. We show the uniqueness of Ethiopian germplasm using a siding collection of Mediterranean durum wheat accessions. We phenotype the Ethiopian panel for ten agronomic traits in two highly diversified Ethiopian environments for two consecutive years and use this information to conduct a genome‐wide association study. We identify several loci underpinning agronomic traits of interest, both confirming loci already reported and describing new promising genomic regions. These loci may be efficiently targeted with molecular markers already available to conduct marker‐assisted selection in Ethiopian and international wheat. We show that Ethiopian durum wheat represents an important and mostly unexplored source of durum wheat diversity. The panel analysed in this study allows the accumulation of QTL mapping experiments, providing the initial step for a quantitative, methodical exploitation of untapped diversity in producing a better wheat.  相似文献   
80.
1. Recent biodiversity studies have addressed various community-level effects of biodiversity change, but the number of studies on specific biotic interactions is still rather limited. An open question in the context of plant-insect-herbivore relationships is how diversity impacts the population ecology of individual species. 2. In the present study, we explored the relationship between plant species diversity and the performance and fitness of a generalist herbivore, the meadow grasshopper Chorthippus parallelus Zetterstedt (Orthoptera, Gomphocerinae). A total of 1620 fourth-instar nymphs of this insect were captured and transferred to cages (10 females and 10 males per cage) on 81 experimental grassland communities in plots containing one to 60 plant species within the Jena biodiversity experiment. 3. Median survival of grasshoppers in the experiment was 14.5 days. Survival was independent of plant species richness and number of plant functional groups in the communities, but increased if plant communities contained grasses. Plant species richness and plant functional group richness had no effect on the number of oothecae laid by females or the number of hatchlings in the next generation. 4. Functional group composition of the plant communities affected most fitness measures. Grass presence increased the number of oothecae laid by females from 0.78 +/- 0.21 to 3.7 +/- 0.41 per female, and the number of hatchlings in the next generation from 4.0 +/- 1.3 to 16.6 +/- 2.4. Certain combinations of plant functional groups increased grasshopper survival. 5. The findings indicate that the fitness of C. parallelus is influenced more by plant functional group identity than by plant species richness. In the absence of grasses, grasshoppers performed better if more than just one functional group of plants was present. We call this a 'rescue effect' of plant functional group richness.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号