全文获取类型
收费全文 | 13447篇 |
免费 | 1144篇 |
国内免费 | 6篇 |
出版年
2022年 | 75篇 |
2021年 | 226篇 |
2020年 | 146篇 |
2019年 | 195篇 |
2018年 | 206篇 |
2017年 | 193篇 |
2016年 | 335篇 |
2015年 | 487篇 |
2014年 | 633篇 |
2013年 | 759篇 |
2012年 | 921篇 |
2011年 | 953篇 |
2010年 | 602篇 |
2009年 | 586篇 |
2008年 | 766篇 |
2007年 | 777篇 |
2006年 | 746篇 |
2005年 | 690篇 |
2004年 | 656篇 |
2003年 | 625篇 |
2002年 | 616篇 |
2001年 | 183篇 |
2000年 | 132篇 |
1999年 | 150篇 |
1998年 | 147篇 |
1997年 | 124篇 |
1996年 | 119篇 |
1995年 | 128篇 |
1994年 | 96篇 |
1993年 | 124篇 |
1992年 | 120篇 |
1991年 | 87篇 |
1990年 | 108篇 |
1989年 | 80篇 |
1988年 | 71篇 |
1987年 | 75篇 |
1986年 | 64篇 |
1985年 | 82篇 |
1984年 | 105篇 |
1983年 | 82篇 |
1982年 | 107篇 |
1981年 | 93篇 |
1980年 | 78篇 |
1979年 | 64篇 |
1978年 | 64篇 |
1977年 | 51篇 |
1975年 | 48篇 |
1974年 | 82篇 |
1973年 | 57篇 |
1972年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
51.
Receptor-mediated internalization of epidermal growth factor (EGF) occurs by a process involving initially clathrin-coated pits on the cell surface and the subsequent formation of ligand-containing endosomes. Using a modified acid wash technique, cell surface-bound EGF was removed. Utilizing sucrose density centrifugation, the residual cell-associated EGF was separated into plasma membrane-associated and intracellular vesicle-associated forms. Using these procedures we have identified a transient form of cell-associated EGF that is still attached to the plasma membrane but not accessible to the extracellular fluid. This form of EGF appears to be the precursor for endosomic EGF. We suggest that this intermediate form represents the receptor-ligand complex shown by electronmicroscopy to be located in narrow-necked plasma membrane invaginations (Willingham, M. C., and Pastan, I. (1980) Cell 21, 67-77). 相似文献
52.
Selective elimination of non-lpr lymphoid cells in mice undergoing lpr-mediated graft-vs-host disease 总被引:2,自引:0,他引:2
D L Perkins J Michaelson R M Glaser A Marshak-Rothstein 《Journal of immunology (Baltimore, Md. : 1950)》1987,139(5):1406-1413
The transfer of lpr BM stem cells into lethally irradiated non-lpr recipients (including the congenic MRL/+ differing only at the lpr locus) causes GVHD characterized by a wasting syndrome. In this study we investigated the interaction between the autoimmune (lpr) and normal (A-Thy) B, T, and RBC cell lineages in two types of radiation chimeras: MRL/lpr plus A-Thy----(MRL/lpr X A-Thy)F1 and MRL/+ plus A-Thy----(MRL/lpr X A-Thy)F1. Analysis of B cell repopulation by competitive RIA of serum Igh-1 allotype showed that both the MRL and the A-Thy donor cells initially engrafted. However, by 2 to 4 mo post-transplantation the normal A-Thy allotype was barely detectable (reduced greater than 2 orders of magnitude), whereas the autoimmune MRL/lpr allotype persisted at normal levels. Similarly, investigation of the donor origin of peripheral blood T cells by two-color flow cytometry showed that by 8 mo post-transplantation normal A-Thy T cells had been eliminated and only MRL/lpr T cells were present in the circulation. In contrast, erythrocytes from both the MRL/lpr and A-Thy donor strains successfully engrafted the F1 recipients and persisted until the termination of the study. Control chimeras transplanted with a mixture of MRL/+ plus A-Thy BM were stably engrafted with both donor strains in both the erythroid and lymphoid populations. Additional experiments in which either B6/lpr or MRL/lpr (and B6/+ or MRL/+ control) BM cells were transferred into (MRL/lpr X B6/+)F1 and (MRL/lpr X B6/lpr)F1 recipients demonstrated that the development of GVHD was not simply due to increased alloreactivity by the lpr donor cells. In these chimeras only the recipients heterozygous (but not homozygous) for the lpr gene developed lpr-GVHD, although both types of recipients had identical genotypes except at the lpr locus. 相似文献
53.
Michael Melkonian Geoffrey Ian McFadden Ingo Botho Reize Hans Rudolf Preisig 《Plant Systematics and Evolution》1987,158(1):47-61
The green flagellateSpermatozopsis exsultans
Korshikov has been studied in culture by light and electron microscopy. The organism is naked, bears four flagella and is conspicuously spirally twisted. The ultrastructure and location of cell organelles (except the flagellar apparatus) has been investigated in detail using an absolute configuration analysis. With the exception of a doubling of the flagella and of the secondary cytoskeletal microtubule system,S. exsultans has the exact same complement of organelles occupying the same relative positions as has been described forS. similis. The two species are therefore correctly placed in the same genus. The usefulness of absolute orientations of cell organelles for green algal taxonomy and phylogeny is stressed.Dedicated to Prof.M. Mix on the occasion of her 60th birthday. 相似文献
54.
The P-M Hybrid Dysgenesis Cline in Eastern Australian Drosophila melanogaster: Discrete P, Q and M Regions Are Nearly Contiguous 总被引:4,自引:2,他引:2
The dramatic latitudinal cline in P-M hybrid dysgenesis characteristics along the east coast of Australia is not smooth. Tests of recent collections of Drosophila melanogaster from the southeastern coast define the previously described cline as comprising three discrete, apparently contiguous regions of P, Q and M phenotypes, respectively. Northern populations from Cairns (16.9°SLat) to Ourimbah (33.4°SLat) are phenotypically P; populations from Wollongong (34.4°SLat) to Eden (37.1°SLat) are Q; and populations from Genoa (37.5°SLat) to Cygnet (43.2°SLat) are M. The decline in P activity from northern Queensland (55-60% gonadal dysgenesis (GD) in cross A) to mid-New South Wales (20-30% GD in cross A) is gradual; proceeding south, there then is a sharp drop to Q populations (<10% GD in crosses A and A*). This drop in P activity occurs in only 150 km, across the urban and suburban area of Sydney. Q populations are then found south to Eden, but Genoa, only about 50 km further southeast, is clearly M (48% GD in cross A*), as are two populations further south. The two discontinuities in the P-M cline do not correspond to obvious climatic differences along the coast, nor to obvious barriers to dispersal of D. melanogaster. The cline has apparently not moved between 1983 and 1985-1986. 相似文献
55.
Summary Adult mice were found to show regional variation in the epithelial expression of some molecules of the blood-group antigen series. To investigate connective tissue influences on such differences, heterotypic recombinants of epithelia and connective tissues from various regions were prepared and examined using monoclonal antibodies directed against bloodgroup antigens H and Ley. The results indicate that epithelia may maintain a preexisting regionally specific pattern following recombination but that, in some recombinant matches, the connective tissue is capable of signalling redirection of the pattern of expression towards that typical of the epithelium with which it is normally associated.This work was supported by NIH-NIDR RO1-DEO-5190 相似文献
56.
57.
58.
Summary The interior of Bowman's capsules of rat kidneys has been examined by scanning electron microscopy, and a distinctive population of cells around the exposed vascular poles of glomerular tufts were identified. The cells were situated in the annular groove at the root of the glomerulus, between the parietal epithelial cells and the podocytes. These peripolar cells were dendritic cells with long processes embracing the glomerular arterioles. Up to three peripolar cells were present at each vascular pole and they were mainly distributed in the glomeruli of the outer third of the renal cortex. This first detailed study of the surface morphology of the glomerular peripolar cell supports the suggestion that changes in the diameter of the polar region of the glomerular tuft may cause variations in stretching of the cuff of peripolar cells, and hence modulation of their secretory activity. 相似文献
59.
60.
Summary The distribution of FMRFamide-like immunoreactive neurons in the nervous system of the slug Limax maximus was studied using immunohistochemical methods. Approximately one thousand FMRFamide-like immunoreactive cell bodies were found in the central nervous system. Ranging between 15 m and 200 m in diameter, they were found in all 11 ganglia of the central nervous system. FMRFamide-like immunoreactive cell bodies were also found at peripheral locations on buccal nerve roots. FMRFamide-like immunoreactive nerve fibres were present in peripheral nerve roots and were distributed extensively throughout the neuropil and cell body regions of the central ganglia. They were also present in the connective tissue of the perineurium, forming an extensive network of varicose fibres. The large number, extensive distribution and great range in size of FMRFamide-like immunoreactive cell bodies and the wide distribution of immunoreactive fibres suggest that FMRFamide-like peptides might serve several different functions in the nervous system of the slug. 相似文献