全文获取类型
收费全文 | 974篇 |
免费 | 84篇 |
出版年
2021年 | 9篇 |
2019年 | 8篇 |
2018年 | 11篇 |
2017年 | 14篇 |
2016年 | 15篇 |
2015年 | 23篇 |
2014年 | 25篇 |
2013年 | 37篇 |
2012年 | 57篇 |
2011年 | 41篇 |
2010年 | 25篇 |
2009年 | 18篇 |
2008年 | 37篇 |
2007年 | 32篇 |
2006年 | 28篇 |
2005年 | 29篇 |
2004年 | 34篇 |
2003年 | 35篇 |
2002年 | 39篇 |
2001年 | 27篇 |
2000年 | 28篇 |
1999年 | 26篇 |
1998年 | 20篇 |
1997年 | 13篇 |
1996年 | 14篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 16篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 18篇 |
1988年 | 18篇 |
1987年 | 15篇 |
1986年 | 18篇 |
1985年 | 26篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1977年 | 11篇 |
1975年 | 8篇 |
1973年 | 13篇 |
1972年 | 10篇 |
1971年 | 16篇 |
1970年 | 19篇 |
1969年 | 7篇 |
1967年 | 7篇 |
1966年 | 9篇 |
排序方式: 共有1058条查询结果,搜索用时 15 毫秒
1.
Rabbit alveolar macrophages exhibit a chemiluminescent response which is associated with phagocytosis of zymosan and polystyrene-butadiene particles. The chemiluminescence reaches a peak in 15 to 25 minutes and then gradually diminishes over the next 1 to 3 hours. During the time of maximal light emission there appears to be no actual uptake of particles, but the response is dependent upon the particle concentration. The metabolic inhibitor, DNP (2,4-dinitrophenol), causes a rapid inhibition of the chemiluminescent response. The addition of ATP to the medium prior to exposure of the cells to particles causes the chemiluminescent response to be greatly diminished, i.e., 0.3mM ATP virtually abolishes the response. These experiments suggest that some metabolic response of the cell to phagocytosis is responsible for the chemiluminescence. 相似文献
2.
3.
M. D. Furones † D. J. Alderman D. Bucke T. C. Fletcher ‡§ D. Knox ‡ A. White ‡§ 《Journal of fish biology》1992,41(6):1037-1041
Rainbow trout fed diets containing 7, 86 or 806 mg vitamin E kg−1 for 22 weeks were exposed to virulent Yersinia ruckeri by bath or injection. Mortalities were always least among those fed the highest concentration of vitamin E but serum antibody production was not affected by vitamin E levels. 相似文献
4.
5.
Role of plasminogen, plasmin, and plasminogen activators in the migration of fibroblasts into plasma clots 总被引:2,自引:0,他引:2
Human diploid fibroblasts were seeded onto or into plasma clots and different aspects of cell adhesion and migration were measured. The roles of plasminogen activators and plasmin were studied by either the removal of plasminogen from plasma prior to clotting or by the addition of 10 mM epsilon-aminocaproic acid, which brings about an inhibition of plasmin in this system. When cells were seeded onto the surface of plasma clots, rates of attachment, spreading, and migration were unaffected by plasminogen depletion or plasmin inhibition. In contrast, when cells were seeded into plasma clots, then, although the rates of cells spreading were unaffected, cell migration was abolished by plasminogen depletion or by plasmin inhibition. When cells were seeded onto the surface of plasma clots and the rate of migration into the clots was measured, there was an absolute requirement for plasmin activity; while fibroblasts migrated rapidly into the fibrin lattice of control clots, in the case of plasminogen-depleted clots, cells failed to penetrate the lattice. Focussing through a plasma clot revealed that fibroblasts do not migrate through the fibrin lattice but instead, localized areas of fibrinolysis are generated and cells migrate over the surface of the area of lysis. 相似文献
6.
R J Knox D A Lydall F Friedlos C Basham J J Roberts 《Biochimica et biophysica acta》1987,908(3):214-223
The effects of introducing various DNA damage into pSV2gpt DNA on the subsequent expression of xanthine guanine phosphoribosyltransferase (XGPRT), after its transfection into two Walker 256 cell lines, one which is inherently sensitive only to difunctional agents while the other shows a normal sensitivity, have been examined. Both the sensitive (WS) and the relatively resistant (WR) cell lines were shown to be equally capable of both ligation of DNA double-strand breaks (although the efficiency varied with the actual site of the break) introduced into pSV2gpt and homologous recombination of pSV2gpt fragments (recombination events are thought to be important in the repair of DNA-DNA interstrand crosslinks). Reacting the plasmid with either the difunctional platinum compound, Cisplatin, or the monofunctional reacting Pt(Dien) caused a dose-dependent decrease in the subsequent expression of XGPRT. This decrease was about the same with either agent in either cell line when expressed as a function of dose of drug. However, when the actual binding of platinum to DNA by these compounds was measured, a large difference (due to the higher specific binding of Pt(Dien) to DNA) in the effects of the difunctional, as opposed to the monofunctional agent, was apparent and this was a reflection of the relative cytotoxicities of these compounds towards mammalian cells. Although at doses of Cisplatin equitoxic to WS and WR cells 20-fold less Pt is bound to the DNA of WS cells, no significant difference was seen on the expression of pSV2gpt, reacted with this agent, between WS or WR cells. Based upon a knowledge of the proportions of adducts formed in DNA reacted with Cisplatin, the lesion that inactivates expression of XGPRT was probably the intrastrand crosslink and it was calculated that due to the size of the plasmid, the interstrand crosslink was unlikely to be present at these inactivating doses. It is suggested that the inherent sensitivity of WS cells only to difunctional agents is due to their response to such relatively rare lesions such as a DNA-DNA interstrand crosslink. 相似文献
7.
A polyclonal antiserum and monoclonal antibodies have been prepared to purified pollen exines of Calocedrus decurrens Florin. The location of the antigen is in the exine, as shown by light-and electron-microscopic immunocytochemistry. The greatest reduction in antibody binding follows treatment of the exine with chemicals known to alter sporopollenin. These results provide evidence that sporopollenin is antigenic. Exines of ten species of gymnosperms and angiosperms also bound the polyclonal antiserum, indicating similarity of sporopollenin structure. 相似文献
8.
When human diploid fibroblasts were seeded onto the surface of blood clots, lysis of the clot occurred as a result of the release of cellular plasminogen activator. A number of aspects of this lysis were studied. 1. There was no significant difference in rates of lysis of whole blood clots, platelet-rich plasma clots, and platelet-poor plasma clots brought about by the same number of fibroblasts. 2. Clot lysis was promoted by nondividing cells and by proliferating cells. 3. Using cycloheximide to block protein synthesis it was found that the plasminogen activator released by fibroblasts had an active half-life of less than an hour. 4. When clots were washed prior to the addition of cells then lysis occurred at an increased rate. This was probably due to the removal of alpha 2-antiplasmin from the clots, since when antisera to alpha 2-antiplasmin was added to clots, lysis also proceeded at an increased rate. 5. Medium conditioned by fibroblasts did not promote clot lysis even when antiplasmin was removed by washing or by addition of antisera. 6. Cells had to be in direct contact with the clot in order to bring about lysis; when cells were separated from clots by permeable membranes there was no lysis. 7. When cross-linking of fibrin was reduced by the inhibition of transglutaminase, the rate of clot lysis was increased. 相似文献
9.
Summary Cytological changes associated with the final maturation, and dehiscence of the 16-grain compound pollen (polyads) have been followed in anthers at female and male phase of flowering. InAcacia retinodes, the transition from female to male phase takes approximately 24 h. The spherical generative cell at female phase is connected with the vegetative cell plasma membrane by a junction zone. This is sited adjacent to a germinal aperture, comprising wall ingrowths and membrane labyrinths. By male phase, the generative cell has elongated into a spindle-shape, and its surface is characteristically scalloped. The membrane labyrinths, especially those at the apertures, now contain masses of coated vesicles, implicated in the transport and secretion of proteins. Two-dimensional projections indicate that the generative cell and vegetative nucleus are closely associated forming a male germ unit. 相似文献
10.
R J Knox D A Lydall F Friedlos C Basham C J Rawlings J J Roberts 《Mutation research》1991,255(3):227-240
The Walker 256 rat tumour has been maintained in vivo for over 60 years and until recently was used as a primary screen for new antitumour agents. This screen was particularly useful in identifying difunctional alkylating agents as potentially useful anticancer agents and it would seem that the Walker tumour is composed of cells sensitive towards this type of agent. A cell line (WS) established from the Walker tumour retained the sensitivity of the tumour towards difunctional agents and we have examined its phenotype in comparison to a derived, resistant, cell line (WR). The response of WR cells to a range of cytotoxic agents was similar to other established cell lines whilst WS cells were much more sensitive only towards difunctional reacting agents. There were no significant differences in the binding of these agents to the DNA of WS or WR cells. All the agents towards which WS cells showed sensitivity were, without exception, capable of reacting with DNA in Walker cells and forming DNA-DNA interstrand crosslinks. WS cells were not sensitive to busulphan, BCNU, CCNU or Me-CCNU but these agents did not produce interstrand crosslinks in the DNA of either WS or WR cells. Thus WS cells are intrinsically sensitive to specific DNA damage and this is probably a DNA interstrand crosslink. Hybrid cells produced by fusion of WS with WR cells lacked the inherent sensitivity of the WS cells towards cisplatin; sensitivity was therefore a recessive characteristic. Transfection of WS cells with human DNA also gave rise to 2 cisplatin-resistant clones, although it could not be ascertained if these clones were true transfectants or revertants. The survival of these resistant clones, after treatment with cisplatin, was about the same as WR cells a finding which would be consistent with complementation by a transferred gene or reversion of a single gene defect in WS cells. In their sensitivity only to difunctional compounds and lack of an apparent DNA excision repair defect the phenotype of Walker cells strongly resembles those cells from human patients suffering from Fanconi's anaemia and also of yeast snm1 mutant cells. The mechanisms giving rise to this failure to tolerate specific DNA damage (which seems to involve the inability to recover from the initial inhibition of DNA synthesis and may involve a single defect of a gene involved in the late steps of crosslink repair), do not involve drug uptake, drug binding to DNA, cell size, cell doubling time or DNA excision repair. 相似文献