全文获取类型
收费全文 | 3887篇 |
免费 | 513篇 |
国内免费 | 301篇 |
出版年
2023年 | 17篇 |
2022年 | 15篇 |
2021年 | 23篇 |
2020年 | 15篇 |
2019年 | 22篇 |
2018年 | 32篇 |
2017年 | 20篇 |
2016年 | 36篇 |
2015年 | 28篇 |
2014年 | 54篇 |
2013年 | 15篇 |
2012年 | 337篇 |
2011年 | 408篇 |
2010年 | 69篇 |
2009年 | 54篇 |
2008年 | 275篇 |
2007年 | 303篇 |
2006年 | 325篇 |
2005年 | 363篇 |
2004年 | 309篇 |
2003年 | 304篇 |
2002年 | 247篇 |
2001年 | 200篇 |
2000年 | 292篇 |
1999年 | 137篇 |
1998年 | 37篇 |
1997年 | 46篇 |
1996年 | 29篇 |
1995年 | 29篇 |
1994年 | 28篇 |
1993年 | 24篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1990年 | 26篇 |
1989年 | 35篇 |
1988年 | 19篇 |
1987年 | 30篇 |
1985年 | 20篇 |
1983年 | 16篇 |
1959年 | 16篇 |
1958年 | 15篇 |
1957年 | 20篇 |
1956年 | 19篇 |
1955年 | 24篇 |
1954年 | 20篇 |
1953年 | 18篇 |
1952年 | 17篇 |
1951年 | 17篇 |
1950年 | 13篇 |
1949年 | 15篇 |
排序方式: 共有4701条查询结果,搜索用时 217 毫秒
1.
2.
3.
Oligomerization and the sensitivity of phosphoenolpyruvate carboxylase to inactivation by proteinases 总被引:3,自引:2,他引:1 下载免费PDF全文
Phosphenolpyruvate (PEP) carboxylase from leaves of Crassula argentea displays varying levels of sensitivity to inactivation by various proteolytic enzymes. In general, the native enzyme is sensitive to proteinases known to attack at the carbonyl end of lysine or arginine (trypsin, papain, or bromelain). The ineffective proteolytic enzymes are those which have low specificity or which attack at the N-terminal end of hydrophobic amino acids, or which cannot attack lysine. The lack of an effect of endoproteinase arginine C, which is specific for arginine, probably indicates that lysine is the critical residue. When the native enzyme, which is comprised of an equilibrium of dimers with tetramers in approximately equal quantities, is treated by preincubation with 5 millimolar PEP, the enzyme becomes much more resistant to proteolytic inactivation. When the preincubation is with 5 millimolar malate rather than buffer alone, the effect is to slightly increase (ca. 15%) the sensitivity of the enzyme to inactivation by trypsin as measured by estimates of the pseudo-first order rate constant for inactivation. PEP carboxylase from corn leaves appears to be relatively susceptible to inactivation by trypsin, but is unaffected by preincubation with malate or PEP. The sensitivity of this C4 enzyme to inhibition by malate is also unaffected by preincubation with these ligands. 相似文献
4.
Temperature Effects on Phosphoenolpyruvate Carboxylase from a CAM and a C(4) Plant : A Comparative Study 总被引:2,自引:2,他引:0 下载免费PDF全文
The effect of temperature in the range from 10 to 35°C on various characteristics of phosphoenolpyruvate carboxylase from the leaves of a CAM plant, Crassula argentea and a C4 plant Zea mays shows a number of different effects related to the environment in which these distinct types of metabolic specialization normally operate. The Arrhenius plot of Vmax for the two enzyme forms shows that the CAM enzyme has a linear increase with temperature while the C4 enzyme has an inflection at 27°C implying a conformational or aggregational change in the enzyme or a shift in reaction mechanism to one requiring a lower activation energy. The Arrhenius plot of Km for the two enzymes reveals the startling fact that at temperatures above 20°C an increasing temperature causes an increase in KmPEP for the CAM enzyme while the C4 enzyme displays a decreased Km as the temperature increases. The inhibitory effect of 5 millimolar malate also shows opposite trends for the two enzymes. For the CAM enzyme the percent inhibition by malate increases from essentially none at 15°C to 70% at 35°C. For the C4 enzyme the percent inhibition drops from about 60% at 20°C to 2% at 30°C. Similar opposite behavior of the two enzymes is found with the Ki for malate. Pretreatment at high temperatures for periods up to 2 hours was found to result in differences similar to those described above if the treated enzyme were subsequently assayed at 25°C. 相似文献
5.
K5株钩端螺旋体系1960年自昆明市郊高山姬鼠(Apodemus chevrieri)肾分离获得,经多次鉴定均属波摩那群新型,建议命名为昆明型钩端螺旋体(Leptospira interrogans serovarkuming)。 相似文献
7.
8.
9.
本文的二个新种是樱桃双羽爪瘿螨Diptacus pseudocerasis sp.nov.和三角枫双羽爪瘿螨Diptacus aceris sp.nov.它们均营自由生活,分别寄生于樱桃Prunus pseudocerasus和三角枫Acer buergerianus 相似文献
10.
国产磨芋属的染色体核型报道(1) 总被引:4,自引:0,他引:4
本文报道了磨芋属(Amorphophallus Blume)六个种的染色体数目和核型,其中5个种属于首次报道。其核型公式如下: 1.滇磨芋 K(2n)=2x=26=26m.2.磨芋 K(2n)=2x=26=26m.3.攸落磨芋K(2n)=2x=26=22m(2SAT)+4sm.(2SAT).4.西盟磨芋 K(2n)=2x=26=20m+4sm+2st.5.勐海磨芋 K(2n)=2x=26=22m+4sm.6.白磨芋 K(2n)=2x=26=20m(2SAT)+6sm。 相似文献