全文获取类型
收费全文 | 34108篇 |
免费 | 1913篇 |
国内免费 | 1541篇 |
专业分类
37562篇 |
出版年
2023年 | 568篇 |
2022年 | 810篇 |
2021年 | 1037篇 |
2020年 | 952篇 |
2019年 | 1407篇 |
2018年 | 1202篇 |
2017年 | 793篇 |
2016年 | 828篇 |
2015年 | 1063篇 |
2014年 | 2254篇 |
2013年 | 2631篇 |
2012年 | 1631篇 |
2011年 | 2149篇 |
2010年 | 1662篇 |
2009年 | 1533篇 |
2008年 | 1734篇 |
2007年 | 1690篇 |
2006年 | 1432篇 |
2005年 | 1273篇 |
2004年 | 1142篇 |
2003年 | 925篇 |
2002年 | 816篇 |
2001年 | 515篇 |
2000年 | 479篇 |
1999年 | 514篇 |
1998年 | 431篇 |
1997年 | 381篇 |
1996年 | 405篇 |
1995年 | 400篇 |
1994年 | 371篇 |
1993年 | 283篇 |
1992年 | 306篇 |
1991年 | 274篇 |
1990年 | 225篇 |
1989年 | 216篇 |
1988年 | 169篇 |
1987年 | 163篇 |
1986年 | 137篇 |
1985年 | 282篇 |
1984年 | 356篇 |
1983年 | 279篇 |
1982年 | 309篇 |
1981年 | 246篇 |
1980年 | 261篇 |
1979年 | 194篇 |
1978年 | 154篇 |
1977年 | 157篇 |
1976年 | 159篇 |
1975年 | 106篇 |
1974年 | 102篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
L. O. Greenfield 《Human Evolution》1993,8(3):187-204
A tooth at the border between two morphogenetic fields (mandibular canine and honing premolar) may become morphologically
similar to and/or functionally incorporated with the teeth of either field. In light of this, observations of the morphology
and occlusion of female anthropoid C1s from 58 extant species are presented to assess whether and to what extent they exhibit incisor-like form and function. Female
C1s in 74% of the taxa observed exhibit well developed incisor-like traits which may reflect field border phenomena. In another
9%, incisor traits are present but they are not examples of field border phenomena. Interspecies variation in female C1 morphology is related to behavior, function, natural selection and phyletic inertia. A selection model, derived from the
data, is used to explain C1 sexual dimorphism and the evolution of male and female human canines. The data's relevance to the field vs clone theory debate
is also discussed. 相似文献
72.
73.
Backgroundobesity is a major risk factor for many metabolic diseases such as diabetes and cardiometabolic diseases. This study aimed to evaluate the association of plasma and urinary barium concentrations, CYP19A1 gene polymorphisms, and their interaction with central obesity in a rural Chinese population.Methodsrestricted cubic spline model was used to explore the dose-response relationship between barium and the risk of developing central obesity and waist circumference; logistic regression model was used to assess the association between barium, CYP19A1 gene polymorphisms and their interaction with central obesity.Resultsthe results of the restricted cubic spline model showed that plasma barium concentration was linearly associated with the risk of developing central obesity and non-linearly associated with waist circumference. Logistic regression analysis showed that participants with Q4 plasma barium concentration exhibited a higher risk of central obesity compared to participants with Q1 barium concentration; participants carrying the rs10046-AA gene exhibited a lower risk of central obesity than those carrying the rs10046-G(GG+GA) gene; participants carrying the rs10046-GA genotype showed 1.754 times higher risk of central obesity than those carrying rs10046-GG+AA genotype. There was a significant interaction between plasma barium and CYP19A1 gene polymorphism on central obesity.Conclusionthe development of central obesity was associated with plasma barium and CYP19A1. 相似文献
74.
75.
核糖核酸(RNA)与稀土铽离子在pH5.0~6.5条件下能形成具有较强荧光的络合物,其激发峰在288nm处,发射峰为494nm及545nm处.RNA在0.1~10mg/L范围内与其荧光强度呈线性关系,其检出限为6.0×10 ̄(-8)mol/L.腺苷酸,尿苷酸,胞苷酸对RNA的干扰比较小,因此可在其存在下选择性地测定RNA. 相似文献
76.
Jacqueline S. Knight Francisco Madueño Simon A. Barnes John C. Gray 《Molecular biotechnology》1996,6(3):335-345
The levels of individual photosynthetic proteins can be independently decreased by theAgrobacterium-mediated transformation of plants with antisens RNA constructs. Protocols for the introduction of such constructs intoAgrobacterium, theAgrobacterium-mediated transformation of tobacco leaf disks, and the screening and analysis of the transgenic plants produced are described. 相似文献
77.
用σ ̄(70)或σ ̄(38)和核心酶(E)组成的大肠杆菌RNA聚合酶全酶(Eσ)对四种启动子进行了体外转录。结果表明:lacUV5,rplJ主要被Eσ ̄(70)识别,katE主要被Eσ ̄(38)识别,fic在低盐浓度时被Eσ ̄(70)识别,在高浓度盐时被Eσ ̄(38)识别;Eσ ̄(38)转录特异性启动子所需酶量大于Eσ ̄(70)转录特异性启动子的酶量;在含有分别对σ ̄(70)或σ ̄(38)亲和性大的混和启动子的体外转录中,启动子之间不存在干扰和竞争,转录水平与启动子浓度成正相关。 相似文献
78.
Enzymatic labeling of nucleic acids is a fundamental tool in molecular biology with virtually every aspect of nucleic acid
hybridization technique involving the use of labeled probes. Different methods for enzymatic labeling of DNA, RNA and oligonucleotide
probes are available today. In this review, we will describe both radioactive and nonradioactive labeling methods, yet the
choice of system for labeling the probe depends on the application under study. 相似文献
79.
Absorption and imagery locate immune responses in the body 总被引:2,自引:0,他引:2
M. Banks Gregerson Ingram M. Roberts Michael M. Amiri 《Applied psychophysiology and biofeedback》1996,21(2):149-165
Imagery instructions specifying mucosal immunity should alter mucosal immunoglobulin A (m-IgA) levels in high absorbers, whose intent concentration evokes intense physiological responses. After screening for health status, 121 high or low absorbers were randomly assigned to either Relaxation Alone (R), Relaxation with Mucosal Immune Imagery (RI), or Vigilance Task control (VT). Before and after one 60-min intervention, subjects reported theory-relevant psychological variables and provided 5ml whole saliva, which was immediately frozen and assayed lateren masse with enzyme-linked immunoabsorbence (ELISA). MANOVA analysis of psychological variables replicated past research. ANOVA on residualized m-IgA found Time × Absorption interaction and Condition main effects. High more than low absorbers responded to relaxation with mucosal immune imagery by producing higher m-IgA. High absorbers appear able to locate where their immune systems will respond. Individual differences like absorption level need to be emphasized in diagnosis and treatment responsiveness.National Institutes of HealthM. Banks (Jasnoski) Gregerson, Department of Psychology, The George Washington University, changed to The Family Therapy Institute; Ingram M. Roberts, The George Washington University Medical Center, changed to Department of Medicine, Bridgeport Hospital; and Michael M. Amiri, The George Washington University Medical Center, changed to the Department of Neuroscience, NINDS Branch, National Institutes of Health. This research supported by an intra-mural BioMedical Research Grant from The George Washington University, was presented at the 1992 Annual Meeting of the Eastern Psychological Association, Boston, Massachusetts. Special thanks are extended to the following students who assisted instrumentally at various stages: undergraduates Lina Alathari, S. Theodor King, Beth Lieberman, Parisa Lotfi, Anita McClenon, and Karen Siscoe, and graduate student Mariken Hasert. 相似文献
80.