全文获取类型
收费全文 | 1067853篇 |
免费 | 113891篇 |
国内免费 | 755篇 |
专业分类
1182499篇 |
出版年
2018年 | 9597篇 |
2016年 | 14356篇 |
2015年 | 21613篇 |
2014年 | 24096篇 |
2013年 | 32422篇 |
2012年 | 35226篇 |
2011年 | 33635篇 |
2010年 | 23358篇 |
2009年 | 21589篇 |
2008年 | 28904篇 |
2007年 | 29604篇 |
2006年 | 28032篇 |
2005年 | 32260篇 |
2004年 | 30975篇 |
2003年 | 28654篇 |
2002年 | 25717篇 |
2001年 | 44931篇 |
2000年 | 44828篇 |
1999年 | 36407篇 |
1998年 | 13254篇 |
1997年 | 13647篇 |
1996年 | 12961篇 |
1995年 | 12115篇 |
1994年 | 11920篇 |
1993年 | 11697篇 |
1992年 | 30705篇 |
1991年 | 29919篇 |
1990年 | 29370篇 |
1989年 | 28778篇 |
1988年 | 26849篇 |
1987年 | 25434篇 |
1986年 | 23596篇 |
1985年 | 23620篇 |
1984年 | 19522篇 |
1983年 | 16622篇 |
1982年 | 12746篇 |
1981年 | 11634篇 |
1980年 | 10772篇 |
1979年 | 18319篇 |
1978年 | 14358篇 |
1977年 | 13163篇 |
1976年 | 12165篇 |
1975年 | 13538篇 |
1974年 | 14604篇 |
1973年 | 14531篇 |
1972年 | 13133篇 |
1971年 | 12014篇 |
1970年 | 10469篇 |
1969年 | 10245篇 |
1968年 | 9237篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
J. Dierschke T. Krüger F. Hüttmann F. Bairlein Kerstin Müller G. Scheiffarth H. -W. Helb W. Irsch W. Lantermann B. Haubitz W. Winkel und J. Haffer 《Journal of Ornithology》2003,144(4):484-498
Ohne Zusammenfassung 相似文献
992.
A rapid, sensitive, assay for enzymes that degrade heparin is described. The procedure is based on the interference of heparin with color development during the interaction of protein with the dye Coomassie brilliant blue. The loss of this property when the glycosaminoglycan is degraded by heparinase can be used to quantify activity of the enzyme in pure form, or in complex biological samples such as tissue homogenates or serum. The assay is also suitable for studying dependence of heparinase activity under conditions such as varying pH and temperature. 相似文献
993.
Conventional amperometric alcohol electrodes were constructed with oxygen- and hydrogen peroxide-base sensors and a much improved electrode was designed by placing a hydrophobic, gas-permeable membrane over the conventional hydrogen peroxide-based alcohol electrode. The immobilization of alcohol oxidase with glutaraldehyde was also studied and optimized. The upper linear ranges of the conventional and newly designed alcohol electrodes were 0.02 and 0.5% ethanol, respectively. The hydrophobic membrane of the new design eliminated the classical electrochemical interferences of hydrogen peroxide-based electrodes and the typical pH dependence of enzymatic systems. 相似文献
994.
K Scheuch W D Pietruschka E Hentschel P Winiecki G Gruber 《Activitas nervosa superior》1988,30(3):169-173
Biochemical and immunological parameters, physical and mental performance, subjective complaints and behavioural characteristics were compared before and after 14 final examinations undertaken by 64 students during a three-month examination period. A decrease in cholesterol, triglycerides, HDL-cholesterol, physical performance and an increase in LDL/HDL cholesterol quotient, lactate level, mental performance were accompanied by a lower frequency of mental complaints and higher frequency of physical complaints. From the multidimensional variance and discriminant analysis 17 of the 44 variables discriminated between the state prior to and after the examination period. The results are interpreted in terms of the psychophysiological adaptation to adequate mental stress. 相似文献
995.
Procedure and Analysis of a Useful Method in Determining Mycelial Dry Weights from Agar Plates 下载免费PDF全文
The evaluation of growth by dry weight determination of fungus mycelium for agar plates was examined. The data obtained were statistically analyzed. This method was shown to be sufficiently accurate to be used as an investigative tool. 相似文献
996.
997.
998.
999.
Heat treatment results in a loss of transgene-encoded activities in several tobacco lines. 总被引:1,自引:0,他引:1 下载免费PDF全文
Heat treatment (37 degrees C) of transgenic tobacco (Nicotiana tabacum) plants led to a reversible reduction or complete loss of transgene-encoded activities in about 40% of 10 independent transformants carrying the luciferase-coding region fused to the 355 cauliflower mosaic virus or the soybean small subunit promoter and the nopaline synthase promoter driving the neomycin phosphotransferase gene, whereas the other lines had temperature-tolerant activities. Temperature sensitivity or tolerance of transgene-encoded activities was heritable. In some of the lines, temperature sensitivity of the transgene-encoded activities depended on the stage of development, occurring in either seedlings (40% luciferase and 50% neomycin phosphotransferase) or adult plants (both 40%). The phenomenon did not correlate with copy numbers or the homo- or hemizygous state of the transgenes. In lines harboring a temperature-sensitive luciferase activity, reduction of bioluminescence was observed after 2 to 3 h at 37 degrees C. Activity was regained after 2 h of subsequent cultivation at 25 degrees C. Irrespective of the reaction to the heat treatment, the level of luciferase RNA was slightly increased at 37 degrees C. Only in lines showing temperature sensitivity of transgene-encoded activities was the amount of luciferase and neomycin phosphotransferase strongly reduced. In sterile culture, heat treatment for 15 d did not cause visible damage or changes in plant morphology. In all plants tested a slight induction of the heat-shock response was observed at 37 degrees C. 相似文献