全文获取类型
收费全文 | 584888篇 |
免费 | 57838篇 |
国内免费 | 217篇 |
专业分类
642943篇 |
出版年
2018年 | 6004篇 |
2017年 | 5860篇 |
2016年 | 7611篇 |
2015年 | 8831篇 |
2014年 | 10824篇 |
2013年 | 15939篇 |
2012年 | 18136篇 |
2011年 | 18787篇 |
2010年 | 12846篇 |
2009年 | 11604篇 |
2008年 | 16849篇 |
2007年 | 17315篇 |
2006年 | 16633篇 |
2005年 | 15731篇 |
2004年 | 15651篇 |
2003年 | 15123篇 |
2002年 | 14812篇 |
2001年 | 25795篇 |
2000年 | 25739篇 |
1999年 | 20634篇 |
1998年 | 7060篇 |
1997年 | 7242篇 |
1996年 | 6927篇 |
1995年 | 6291篇 |
1994年 | 6364篇 |
1993年 | 6183篇 |
1992年 | 17073篇 |
1991年 | 16734篇 |
1990年 | 16587篇 |
1989年 | 16589篇 |
1988年 | 15201篇 |
1987年 | 14405篇 |
1986年 | 13319篇 |
1985年 | 13553篇 |
1984年 | 10963篇 |
1983年 | 9372篇 |
1982年 | 6909篇 |
1981年 | 6076篇 |
1980年 | 5903篇 |
1979年 | 10317篇 |
1978年 | 8016篇 |
1977年 | 7237篇 |
1976年 | 7016篇 |
1975年 | 7832篇 |
1974年 | 8352篇 |
1973年 | 8248篇 |
1972年 | 7457篇 |
1971年 | 6687篇 |
1970年 | 5868篇 |
1969年 | 5558篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Characterization of sequential immune complexes in infective endocarditis by Western blot analysis 总被引:2,自引:0,他引:2
R D Inman R A Rosenberg P B Redecha C L Christian 《Journal of immunology (Baltimore, Md. : 1950)》1984,133(1):217-221
A patient with cutaneous vasculitis during infective endocarditis due to Lactobacillus casei was studied. Immune complexes (IC) were isolated from serum at the time of diagnosis and after 4 wk of therapy. Purification of IC used differential polyethylene glycol precipitation and competitive binding to staphylococcal protein A. In situ radioiodination of IC was performed, followed by SDS-polyacrylamide gel electrophoresis (PAGE). Anti-IC antisera were raised in rabbits by immunization with purified IC. IC were characterized by SDS-PAGE followed by electrophoretic transfer to nitrocellulose, incubation with antiserum and then with 125I protein A, and autoradiography. Although early and late IC differed quantitatively, there were no differentiating immunochemical features. Both IC contained a 60,000 dalton component that did not react with preimmune serum nor with anti-normal human serum. This component reacted with antiserum rendered specific for L. casei by affinity chromatography. The restricted antigen-antibody representation in IC contrasted with a wider panel of antibody activity in patient serum. The Western blot analysis proves to be an ideal method for the characterization of IC because of its sensitivity, dissociative capability, and preservation of immunoreactivity. IC isolated at a time removed from the original antigenic challenge may provide insight into the nature of the inciting antigen. 相似文献
942.
943.
Insulin-mediated modifications of myocardial lipoprotein lipase and lipoprotein metabolism 总被引:1,自引:0,他引:1
Recirculating organ perfusion in vitro was conducted with hearts from control rats, animals given a single dose of streptozotocin (65 mg/kg) 48 h earlier, and streptozotocin-treated rats administered insulin (5 units), 2 h prior to organ perfusion. During 45-min perfusions, the lipolysis of very low density lipoprotein (VLDL) triglyceride was significantly less in hearts from diabetics than in controls (41.9 +/- 7.3% of control). This was associated with significant reductions in heparin-releasable (functional) lipoprotein lipase and tissue lipoprotein lipase of perfused hearts. The decreases in VLDL triglyceride metabolism and the levels of myocardial lipoprotein lipase were completely reversed by treatment of diabetic rats with insulin 2 h prior to study. Similar improvement of VLDL triglyceride metabolism and increases in myocardial lipoprotein lipase activity were observed in hearts from diabetic rats by direct addition of 100 milliunits/ml of insulin to the recirculating perfusion media. Under these conditions, the increase in both fractions of lipoprotein lipase in response to insulin was completely inhibited, and utilization of VLDL triglyceride was partially inhibited by pre-perfusion with cycloheximide for 10 min. The data derived from either VLDL triglyceride lipolysis in organ perfusion or direct measurement of myocardial lipoprotein lipase demonstrate a direct effect of insulin on myocardial lipoprotein lipase activity, and suggest that the response to insulin may be due in part to effects on protein synthesis. 相似文献
944.
Alexander V. Kirdyanov Eugene A. Vaganov Malcolm K. Hughes 《Trees - Structure and Function》2007,21(1):37-44
We propose a technique for separating the climatic signal which is contained in two tree-ring parameters widely used in dendroclimatology.
The method is based on the removal of the relationship between tree-ring width (TRW) and maximum latewood density (MXD) observed
for narrow tree rings from high latitudes. The new technique is tested on data from three larch stands located along the northern
timberline in Eurasia. Correlations were calculated between the temperatures of pentads (five consecutive days), TRW chronologies
and MXD chronologies calculated according to the standard and proposed methods. The analysis confirms the great importance
of summer temperature for tree radial growth and tree-ring formation. TRW is positively correlated with the temperature of
four to eight pentads (depending on the region) at the beginning of the growth season, but MXD as obtained by the standard
technique is correlated with temperature over a much longer period. For maximum density series from which the relationship
between MXD and TRW has been removed (MXD′), there is a clear correlation with temperatures in the second part of the growing
season. These results are consistent with the known dynamics of tree-ring growth in high latitudes and mechanisms of tree-ring
formation. 相似文献
945.
946.
947.
948.
The critical weed-free period in organically-grown winter wheat 总被引:1,自引:0,他引:1
J P WELSH H A J BULSON C E STOPES R J FROUD-WILLIAMS A J MURDOCH 《The Annals of applied biology》1999,134(3):315-320
Two experiments were conducted in central southern England between September 1994 and August 1996 to identify the critical weed-free period in organically grown winter wheat (Triticum aestivum, cv. Mercia). In competition with a mixed weed infestation of predominately Alopecurus myosuroides and Tripleurospermum inodorum it was found that wheat yield decreased as the duration of the weed-infested period increased and that the crop needed to be kept free of weeds from sowing in order to completely avoid any yield loss. Also, weeds emerging in the wheat crop (predominately T. inodorum) during the growing season had a significant and detrimental effect on yield. The existence of the critical period, therefore, depends on the imposition of an acceptable yield loss. If a 5% yield loss gives a marginal benefit compared with the cost of weed control, the critical period will begin at 506°C days after sowing (November) and end at 1023°C days after sowing (February). This information could be used by farmers to target mechanical weeding operations to control weeds at a time that will have maximum benefit to the crop. 相似文献
949.
V. Selvakumar P. R. Anbudurai T. Balakumar 《In vitro cellular & developmental biology. Plant》2001,37(2):280-284
Summary A protocol for rapid in vitro propagation using nodal explants obtained from 2-yr-old, field-grown medicinal plants of Plumbago zeylanica L. belonging to the family Plumbaginaceae is described. High frequency bud break and fast development of shoots were induced
on Murashige and Skoog's basal medium supplemented with 27.2 μM adenine sulfate +2.46 μM indole-3-butyric acid (IBA). Induction of rooting was achieved by transferring the shoots to the same basal medium containing
4.92 μM IBA. Using our protocol from one twig of P. zeylanica (eight responsive nodes per explant shoot) within a period of 5 mo., eight plantlets could be raised. After a hardening period
of 4 wk, there was a 90% transplantation success in the field compared to the 60–65% survival of plantlets recorded in the
experiments of previous workers. The plantlets derived through in vitro propagation mimic the growth and morphological characteristics of the donor plants. 相似文献
950.