全文获取类型
收费全文 | 24729篇 |
免费 | 1967篇 |
国内免费 | 1659篇 |
出版年
2024年 | 42篇 |
2023年 | 178篇 |
2022年 | 333篇 |
2021年 | 751篇 |
2020年 | 560篇 |
2019年 | 749篇 |
2018年 | 820篇 |
2017年 | 674篇 |
2016年 | 1019篇 |
2015年 | 1420篇 |
2014年 | 1733篇 |
2013年 | 1836篇 |
2012年 | 2249篇 |
2011年 | 2147篇 |
2010年 | 1429篇 |
2009年 | 1167篇 |
2008年 | 1558篇 |
2007年 | 1383篇 |
2006年 | 1241篇 |
2005年 | 1167篇 |
2004年 | 1108篇 |
2003年 | 961篇 |
2002年 | 816篇 |
2001年 | 594篇 |
2000年 | 510篇 |
1999年 | 385篇 |
1998年 | 230篇 |
1997年 | 188篇 |
1996年 | 133篇 |
1995年 | 105篇 |
1994年 | 85篇 |
1993年 | 63篇 |
1992年 | 116篇 |
1991年 | 85篇 |
1990年 | 65篇 |
1989年 | 70篇 |
1988年 | 48篇 |
1987年 | 38篇 |
1986年 | 27篇 |
1985年 | 32篇 |
1984年 | 22篇 |
1983年 | 23篇 |
1982年 | 21篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1979年 | 17篇 |
1978年 | 18篇 |
1975年 | 15篇 |
1974年 | 13篇 |
1970年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
131.
132.
Alterations in the amount of fibronectin and in the number of its receptors during myoblast differentiation of chicken embryo were investigated. The amount of fibronectin in the cell surface pool as measured by immunoblotting decreased during myogenesis To identify and characterize the fibronectin receptors on the myoblasts, the interactions of the 28,000 dalton (28 kDa) amino terminal fragment and 85,000 dalton (85 kDa) cell-binding fragment of fibronectin with my-oblasts were examined. The binding of the 28 kDa fragment was found to be time-dependent and reached a maximum level within 60 min. The unlabeled 28 kDa fragment inhibited the binding of the radioiodinated 28 kDa fragment, whereas the unlabeled 85 kDa fragment and antibody to integrin did not inhibit it, suggesting that the 28 kDa fragment interacts with the matrix assembly receptors but not with the cell adhesion receptors. There was a single class of 3.4 × 105 binding sites per cell with an apparent dissociation constant of 1.4 × 10?7 M on 30 hr old myoblasts. The specific binding of the radioiodinated 28 kDa fragment to myoblasts decreased as the fusion proceeded. This decrease of binding was consistent with the decrease in the amount of fibronectin. Furthermore, the levels of fibronectin and binding of the radioiodinated 28 kDa fragment in the fusion-blocked myoblasts by EGTA treatment appeared to remain constant. These results suggest that the decrease and/or loss of fibronectin during myoblast fusion is closely correlated with the alteration of fibronectin receptors and with the fusion of myoblasts. 相似文献
133.
Total 2,829 persons consisted of 1,019 general patients and 1,030 asthma-suspected patients who visited Kangnam St. Mary's Hospital and 780 general patients who visited Cheju Medical Center were examined for the antibody titers of Toxoplasma by indirect latex agglutination (ILA) test. Nineteen out of 1,019(1.86%) cases in general patients group, 11 out of 1,030(1.07%) cases in asthma patients group, and 45 out of 780(5.77%) cases in Cheju patients group showed positive ILA titers. Concerned with the age and ILA positive cases, general and asthma patients expressed more cases at thirties to sixties while Cheju patients showed high incidence at children and adolescents in addition to the above mentioned ages. Frequencies of ILA positive titers were highest in 1:32 and 1:64, and some cases showed 1:2,048 or higher titers. 相似文献
134.
Byoung K. Choi Kwan H. Han Tea Y. Park 《Flexible Services and Manufacturing Journal》1996,8(2):159-182
Presented in the article is a method for constructing a graphical model of an FMS by using a new modeling tool called JR-net (Job Resource relation-net). JR-net is an object-oriented graphical tool for modeling automated manufacturing systems (AMSs), such as FMSs, FASs, and AS/RSs. As with the object-oriented modeling paradigm of Rumbaugh et al. (1991), the JR-net modeling framework supports the three stages of models: static layout model (object model); job flow model (functional model); and supervisory control model (dynamic model). In this article, the existing JR-net structure (Park 1992, Han et al., 1995) is extended further to make it a graphical tool for FMS modeling. Using the extended JR-net, a step-by-step procedure for constructing a graphical model of FMSs is presented. Also addressed are issues of classifying FMSs in terms of their generic functions and of utilizing the JR-net model of FMSs. 相似文献
135.
九种蹄盖蕨科植物配子体的酯酶同工酶分析 总被引:5,自引:1,他引:4
本文培养了蹄盖蕨科9个种即中华蹄盖蕨(Athyriumsinense)带岭蹄盖蕨(A.dalingense)、多齿蹄盖蕨(A.multidentatum)(包括青柄和紫柄2种带岭蹄蕨类型)、东北蛾眉蕨(Lunathyriumpycnosorum)、朝鲜介蕨(Dryoathyriumcoreanum)、山冷蕨(Cystopterissudetica)、假冷蕨(Pseudocystopterisspinulosa)、欧洲羽节蕨(Gymnocarpiumdryopteris)和黑鳞短肠蕨(Alantodiacrenata)的配子体为材料,进行酯酶同工酶的分析,以表明它们的种间差异,其中多齿蹄盖蕨的青柄和紫柄两种类型的酶谱存在明显差异,应考虑紫柄为多齿蹄盖蕨的变型。 相似文献
136.
Construction and characterization of two rice bacterial artificial chromosome libraries from the parents of a permanent recombinant inbred mapping population 总被引:13,自引:0,他引:13
Hong-Bin Zhang Sangdun Choi Sung-Sick Woo Zhikang Li Rod A. Wing 《Molecular breeding : new strategies in plant improvement》1996,2(1):11-24
Rice is a leading grain crop and the staple food for over half of the world population. Rice is also an ideal species for genetic and biological studies of cereal crops and other monocotyledonous plants because of its small genome and well developed genetic system. To facilitate rice genome analysis leading to physical mapping, the identification of molecular markers closely linked to economic traits, and map-based cloning, we have constructed two rice bacterial artificial chromosome (BAC) libraries from the parents of a permanent mapping population (Lemont and Teqing) consisting of 400 F9 recombinant inbred lines (RILs). Lemont (japonica) and Teqing (indica) represent the two major genomes of cultivated rice, both are leading commercial varieties and widely used germplasm in rice breeding programs. The Lemont library contains 7296 clones with an average insert size of 150 kb, which represents 2.6 rice haploid genome equivalents. The Teqing library contains 14208 clones with an average insert size of 130 kb, which represents 4.4. rice haploid genome equivalents. Three single-copy DNA probes were used to screen the libraries and at least two overlapping BAC clones were isolated with each probe from each library, ranging from 45 to 260 kb in insert size. Hybridization of BAC clones with chloroplast DNA probes and fluorescent in situ hybridization using BAC DNA as probes demonstrated that both libraries contain very few clones of chloroplast DNA origin and are likely free of chimeric clones. These data indicate that both BAC libraries should be suitable for map-based cloning of rice genes and physical mapping of the rice genome. 相似文献
137.
利用改进的kar交配法,将一个含有340kb人基因组DNA的YAC片段的供体酵母菌株YAC23与受体菌株YLB504进行交配,以选择平板对所形成的候选YAC导入菌进行筛选。经PCR分析,候选YAC导入菌在404bp处有一个扩增带,即具有受体菌株的交配型(MAT α)。进一步用脉冲电泳进行核型鉴定,证实YACs己成功地进入受体,实现了YACs从一个宿主到另一个宿主之间的转移。 相似文献
138.
抗人肺腺癌单克隆抗体重,轻链可变区基因的分离克隆和序列测定 总被引:6,自引:1,他引:5
根据鼠免疫球蛋白重。轻链可变区基因FR1和FR4的序列保守性,化学合成了适于体外扩增Ig重、轻链可变区基因(V_H和V_L)的数对引物。以分泌抗人肺腺癌单抗的杂交瘤细胞株WLA-2C4的基因组DNA为模板,PCR扩增V_H和V_L基因,分别克隆人pUC19载体。转化子经蓝、白斑筛选,酶切鉴定,双脱氧测序证实确为鼠单抗可变区基因,其中V_H基因全长为348bp,编码116aa,属重链ⅡB亚类;V_L基因全长318bp,编码106aa,属K轻链Ⅵ亚类。 相似文献
139.
140.