全文获取类型
收费全文 | 5488篇 |
免费 | 597篇 |
国内免费 | 2篇 |
出版年
2021年 | 63篇 |
2019年 | 56篇 |
2018年 | 52篇 |
2017年 | 55篇 |
2016年 | 122篇 |
2015年 | 173篇 |
2014年 | 193篇 |
2013年 | 241篇 |
2012年 | 319篇 |
2011年 | 301篇 |
2010年 | 192篇 |
2009年 | 150篇 |
2008年 | 307篇 |
2007年 | 237篇 |
2006年 | 239篇 |
2005年 | 225篇 |
2004年 | 235篇 |
2003年 | 179篇 |
2002年 | 212篇 |
2001年 | 129篇 |
2000年 | 137篇 |
1999年 | 102篇 |
1998年 | 64篇 |
1997年 | 55篇 |
1996年 | 60篇 |
1995年 | 56篇 |
1994年 | 55篇 |
1993年 | 48篇 |
1992年 | 102篇 |
1991年 | 91篇 |
1990年 | 66篇 |
1989年 | 80篇 |
1988年 | 103篇 |
1987年 | 83篇 |
1986年 | 70篇 |
1985年 | 113篇 |
1984年 | 89篇 |
1983年 | 74篇 |
1982年 | 54篇 |
1981年 | 46篇 |
1980年 | 38篇 |
1979年 | 57篇 |
1978年 | 66篇 |
1977年 | 43篇 |
1976年 | 40篇 |
1975年 | 45篇 |
1974年 | 46篇 |
1973年 | 55篇 |
1971年 | 46篇 |
1969年 | 39篇 |
排序方式: 共有6087条查询结果,搜索用时 359 毫秒
11.
12.
R C Garcia C G Peterson A W Segal P Venge 《Biochemical and biophysical research communications》1985,132(3):1130-1136
Elastase in the human neutrophil is associated with various subpopulations of primary granules of different density. The proportion of this enzyme that is extracted with acetate pH 4.2 and cetyltrimethylammonium bromide varies in the different subpopulations. Nevertheless, the electrophoretic mobility and relative proportions of elastase isoenzymes is the same in both extracts from the different subpopulations. On stimulation of neutrophils with N-formylmethionylleucylphenylalanine, elastase is not released from the least dense subpopulation, whereas other two subpopulations do undergo degranulation to approximately the same extent. However, the release of elastase from these two denser granules differs after they are isolated and treated with calcium. 相似文献
13.
Aileen F. G. Bongat Rina Saksena Roberto Adamo Yukari Fujimoto Zenyu Shiokawa Dwight C. Peterson Koichi Fukase Willie F. Vann Pavol Kováč 《Glycoconjugate journal》2010,27(1):69-77
Using recombinant tetanus toxin HC fragment (rTT-HC) as carrier, we prepared multimeric bivalent immunogens featuring the synthetic hexasaccharide fragment of O-PS of Vibrio cholerae O:1, serotype Ogawa, in combination with either the synthetic hexasaccharide fragment of O-PS of Vibrio cholerae O:1, serotype Inaba, or a synthetic disaccharide tetrapeptide peptidoglycan fragment as adjuvant. The conjugation reaction
was effected by squaric acid chemistry and monitored in virtually real time by SELDI-TOF MS. In this way, we could prepare
well-defined immunogens with predictable carbohydrate–carrier ratio, whose molecular mass and the amount of each saccharide attached could be independently determined. The ability to prepare such neoglycoconjugates opens unprecedented possibilities
for preparation of conjugate vaccines for bacterial diseases from synthetic carbohydrates. 相似文献
14.
15.
P. Magnus 《Plant Systematics and Evolution》1905,55(6):225-227
Ohne Zusammenfassung 相似文献
16.
17.
18.
We examine use of environmental information systems by ASG AB (hereafter ASG), an international logistics and transport firm headquartered in Stockholm, Sweden, as a case study to illustrate the role of information systems in life-cycle-oriented environmental management. This case provides an example of how a firm can use interorganizational information systems (IOISs) to move toward environmentally sustainable business practices. Through the use of IOISs, ASG has been able to improve its environmental performance and that of its suppliers. Further, this improved environmental performance has been a competitive advantage for ASG and enabled it to attract new business. As such, ASG's experiences illustrate how aggressive practices move environmental management beyond compliance and cost control, at which many firms have been successful, to revenue generation. The case also shows how environmentally sustainable business practices can be integrated into a firm's strategy. In addition to illustrating how ASG has used IOISs to improve environmental performance, we compare their use of environmental ISs with the expected evolution of environmental ISs presented in the Shaft and colleagues (1997) framework. Although some of ASG's experiences verify the expected progression of these types of systems, some developments are not as expected. These differences have implications for the framework. 相似文献
19.
Novel stabilization of phenylalanine ammonia-lyase catalyst during bioconversion of trans-cinnamic acid to l-phenylalanine 总被引:4,自引:0,他引:4
Christopher T. Evans Dayle Conrad Kim Hanna Wendy Peterson Christin Choma Masanaru Misawa 《Applied microbiology and biotechnology》1987,25(5):399-405
Summary Production of l-phenylalanine from trans-cinnamic acid using isolate SPA10 cells was reduced to 26% of that observed initially when cells were reacted a second time with fresh substrate mixture. The stability (reuseability) of Phenylalanine Ammonia-Lyase (PAL) containing cells was significantly influenced by both the trans-cinnamate concentration and initial reaction pH. Using 2% t-cinnamate, l-phenylalanine production was 7-fold greater after 3 successive runs at pH 9.0 than at the optimum of pH 10.2. Cells reacted in the presence of 5% t-cinnamate were relatively unstable. Permeabilising agents, such as toluene and xylene, stimulated l-phenylalanine production but also enhanced instability of the catalyst. Several effectors were shown to stimulate the initial rate of the PAL bioconversion, but only sorbitol, alginate, glutaraldehyde, polyethylene glycol and glycerol conferred any significant degree of stability. Sparging of cultures and bioreactors with various gases revealed that oxygen enhanced PAL inactivation, CO2 had little effect and nitrogen conferred remarkable stability on PAL activity for several weeks in culture medium. The presence of chloride ions (from HCl) and aeration of substrate mixtures resulted in poor reuseability of catalyst. A combination of H2SO4 substitution for HCl and N2-sparging resulted in excellent initial conversions and good catalyst stability at 26°C but less at 30°C. The inclusion of 1.5 M sorbitol in reaction mixtures maintained PAL stability over several successive incubations. 相似文献
20.
Quantitation of the O(2)-Dependent, CO(2)-Reversible Component of the Postillumination CO(2) Exchange Transient in Tobacco and Maize Leaves 总被引:2,自引:2,他引:0
Peterson RB 《Plant physiology》1987,84(3):862-867
The postillumination transient of CO2 exchange and its relation to photorespiration has been examined in leaf discs from tobacco (Nicotiana tabacum) and maize (Zea mays). Studies of the transients observed by infrared gas analysis at 1, 21, and 43% O2 in an open system were extended using the nonsteady state model described previously (Peterson and Ferrandino 1984 Plant Physiol 76: 976-978). Cumulative CO2 exchange equivalents (i.e. nanomoles CO2) versus time were derived from the analyzer responses of individual transients. In tobacco (C3), subtraction of the time course of cumulative CO2 exchange under photorespiratory conditions (21 or 43% O2) from that obtained under nonphotorespiratory conditions (1% O2) revealed the presence of an O2-dependent and CO2-reversible component within the first 60 seconds following darkening. This component was absent in maize (C4) and at low external O2:CO2 ratios (i.e. <100) in tobacco. The size of the component in tobacco increased with net photosynthesis as irradiance was increased and was positively associated with inhibition of net photosynthesis by O2. This relatively simple and rapid method of analysis of the transient is introduced to eliminate some uncertainties associated with estimation of photorespiration based on the maximal rate of postillumination CO2 evolution. This method also provides a useful and complementary tool for detecting variation in photorespiration. 相似文献