全文获取类型
收费全文 | 13134篇 |
免费 | 1344篇 |
国内免费 | 2篇 |
专业分类
14480篇 |
出版年
2022年 | 136篇 |
2021年 | 265篇 |
2020年 | 131篇 |
2019年 | 170篇 |
2018年 | 225篇 |
2017年 | 189篇 |
2016年 | 346篇 |
2015年 | 575篇 |
2014年 | 603篇 |
2013年 | 670篇 |
2012年 | 966篇 |
2011年 | 897篇 |
2010年 | 567篇 |
2009年 | 525篇 |
2008年 | 712篇 |
2007年 | 742篇 |
2006年 | 664篇 |
2005年 | 646篇 |
2004年 | 644篇 |
2003年 | 595篇 |
2002年 | 561篇 |
2001年 | 219篇 |
2000年 | 190篇 |
1999年 | 254篇 |
1998年 | 158篇 |
1997年 | 119篇 |
1996年 | 109篇 |
1995年 | 103篇 |
1994年 | 89篇 |
1993年 | 90篇 |
1992年 | 137篇 |
1991年 | 146篇 |
1990年 | 161篇 |
1989年 | 127篇 |
1988年 | 142篇 |
1987年 | 115篇 |
1986年 | 114篇 |
1985年 | 117篇 |
1984年 | 105篇 |
1983年 | 97篇 |
1982年 | 85篇 |
1981年 | 70篇 |
1980年 | 58篇 |
1979年 | 97篇 |
1978年 | 65篇 |
1977年 | 62篇 |
1976年 | 54篇 |
1975年 | 63篇 |
1974年 | 52篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Monoclonal antibody as a probe for structure and function of an Escherichia coli outer membrane protein 总被引:16,自引:0,他引:16
Eight independently derived monoclonal antibodies directed against the LamB protein were produced and characterized. By using these antibodies as probes, we identified four distinct topological and functional regions in the LamB molecule. Four monoclonal antibodies recognize antigenic determinants of the protein exposed on the outer side of the membrane. Two of these have their binding sites located in a region involved in maltose transport. One monoclonal antibody presumably binds to a determinant which is normally hidden in the membrane and three monoclonal antibodies recognize determinants facing the periplasmic space. 相似文献
3.
4.
Studies on the ecology of microbial parasites and their hosts are predicated on understanding the assemblage of and relationship among the species present. Changes in organismal morphology and physiology can have profound effects on host–parasite interactions and associated microbial community structure. The marine rickettsial organism, “Candidatus Xenohaliotis californiensis” (WS-RLO), that causes withering syndrome of abalones has had a consistent morphology based on light and electron microscopy. However, a morphological variant of the WS-RLO has recently been observed infecting red abalone from California. We used light and electron microscopy, in situ hybridization and16S rDNA sequence analysis to compare the WS-RLO and the morphologically distinct RLO variant (RLOv). The WS-RLO forms oblong inclusions within the abalone posterior esophagus (PE) and digestive gland (DG) tissues that contain small rod-shaped bacteria; individual bacteria within the light purple inclusions upon hematoxylin and eosin staining cannot be discerned by light microscopy. Like the WS-RLO, the RLOv forms oblong inclusions in the PE and DG but contain large, pleomorphic bacteria that stain dark navy blue with hematoxylin and eosin. Transmission electron microscopy (TEM) examination revealed that the large pleomorphic bacteria within RLOv inclusions were infected with a spherical to icosahedral-shaped putative phage hyperparasite. TEM also revealed the presence of rod-shaped bacteria along the periphery of the RLOv inclusions that were morphologically indistinguishable from the WS-RLO. Binding of the WS-RLO-specific in situ hybridization probe to the RLOv inclusions demonstrated sequence similarity between these RLOs. In addition, sequence analysis revealed 98.9–99.4 % similarity between 16S rDNA sequences of the WS-RLO and RLOv. Collectively, these data suggest that both of these RLOs infecting California abalone are “Candidatus Xenohaliotis californiensis,” and that the novel variant is infected by a putative phage hyperparasite that induced morphological variation of its RLO host. 相似文献
5.
6.
7.
Little is known regarding the role of androgenic hormones in the maintenance of myosin heavy chain (MHC) composition of rodent masticatory muscles. Because the masseter is the principal jaw closer in rodents, we felt it was important to characterize the influence of androgenic hormones on the MHC composition of the masseter. To determine the extent of sexual dimorphism in the phenotype of masseter muscle fibers of adult (10-mo-old) C57 mice, we stained tissue sections with antibodies specific to type IIa and IIb MHC isoforms. Females contain twice as many fibers containing the IIa MHC as males, and males contain twice as many fibers containing the IIb MHC as females. There is a modest amount of regionalization of MHC phenotypes in the mouse masseter. The rostral portions of the masseter are composed mostly of type IIa fibers, whereas the midsuperficial and caudal regions contain mostly type IIb fibers. Using immunoblots, we showed that castration results in an increase in the expression of type IIa MHC fibers in males. Ovariectomy has no effect on the fiber type composition in females. We conclude that testosterone plays a role in the maintenance of MHC expression in the adult male mouse masseter. 相似文献
8.
The specificity of the syngeneic mixed leukocyte response, a primary anti-I region T cell proliferative response, is determined intrathymically 总被引:6,自引:0,他引:6
L H Glimcher R H Schwartz D L Longo A Singer 《Journal of immunology (Baltimore, Md. : 1950)》1982,129(3):987-991
In previous studies, the syngeneic MLR of peripheral T cells was shown to be predominantly an I region-restricted function. In this report we show that adult thymocytes are also capable of responding to syngeneic irradiated stimulator cells in a syngeneic MLR, provided that TCGF is added to the culture system. Using this assay, it was possible for the first time to examine the pattern of I region restriction within the thymus itself. Analysis of the thymocyte syngeneic MLR in thymuses from radiation-induced bone marrow chimeras demonstrated that the MHC preference seen in the peripheral T cell population also existed in cells resident within the thymus. Experiments utilizing congenitally athymic mice transplanted with allogeneic thymic grafts demonstrated that both peripheral T cells and thymocytes from such animals displayed a strong preferential proliferation toward stimulator cells bearing thymic-type MHC determinants. The results in the nude model thus demonstrate that the thymus by itself is sufficient to impart such restriction specificity on a developing T cell repertoire. These results are consistent with the notion that the thymus exerts selective pressure on maturing T cell populations that results in a skewing of the T cell repertoire toward the recognition of thymic-type I region products, and that this MHC preference exists before expansion of T cells in the periphery. 相似文献
9.
10.
We present a fast, reliable and inexpensive restriction-free cloning method for seamless DNA insertion into any plasmid without sequence limitation. Exponential megapriming PCR (EMP) cloning requires two consecutive PCR steps and can be carried out in one day. We show that EMP cloning has a higher efficiency than restriction-free (RF) cloning, especially for long inserts above 2.5 kb. EMP further enables simultaneous cloning of multiple inserts. 相似文献