全文获取类型
收费全文 | 2536篇 |
免费 | 256篇 |
国内免费 | 1篇 |
出版年
2021年 | 31篇 |
2019年 | 20篇 |
2018年 | 21篇 |
2017年 | 28篇 |
2016年 | 20篇 |
2015年 | 57篇 |
2014年 | 90篇 |
2013年 | 106篇 |
2012年 | 111篇 |
2011年 | 105篇 |
2010年 | 79篇 |
2009年 | 64篇 |
2008年 | 100篇 |
2007年 | 96篇 |
2006年 | 100篇 |
2005年 | 79篇 |
2004年 | 85篇 |
2003年 | 79篇 |
2002年 | 88篇 |
2001年 | 65篇 |
2000年 | 86篇 |
1999年 | 61篇 |
1998年 | 43篇 |
1997年 | 34篇 |
1996年 | 36篇 |
1995年 | 24篇 |
1994年 | 21篇 |
1993年 | 31篇 |
1992年 | 63篇 |
1991年 | 70篇 |
1990年 | 52篇 |
1989年 | 56篇 |
1988年 | 44篇 |
1987年 | 61篇 |
1986年 | 56篇 |
1985年 | 45篇 |
1984年 | 38篇 |
1983年 | 42篇 |
1982年 | 36篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 37篇 |
1978年 | 31篇 |
1977年 | 27篇 |
1976年 | 18篇 |
1974年 | 19篇 |
1973年 | 29篇 |
1970年 | 24篇 |
1969年 | 18篇 |
1968年 | 17篇 |
排序方式: 共有2793条查询结果,搜索用时 15 毫秒
51.
The protoplasting and transformation techniques described by Chang and Cohen [5] have been modified by the inclusion of mutanolysin and these techniques have been used to prepare protoplasts of a number ofBacillus spp. Cells of some, however, remained resistant to cell wall hydrolysis by both mutanolysin and lysozyme. Protoplasts were prepared from sixBacillus species, including a strain ofB. subtilis, and transformed with the plasmid pUB110. Transformation with the shuttle vector pHV33 was, however, less successful and antibiotic-resistant protoplasts, although detected, either failed to regenerate their osmotic stability or rapidly lost their antibiotic resistance. 相似文献
52.
Stability of tissue culture medium pH as a function of autoclaving,time, and cultured plant material
Robert M. Skirvin Mel C. Chu Mary L. Mann Heather Young Joseph Sullivan Thomas Fermanian 《Plant cell reports》1986,5(4):292-294
Autoclaving is a standard procedure for sterilizing nutrient media for plant tissue cultures. Most tissue cultures are grown at pH 5.2 to 5.8 with pH adjustments being made prior to autoclaving. This paper reports that there are significant differences between initial pH levels and pH levels following autoclaving, particularly in the pH range of 5.7 to 8.5. This effect is noted with and without agar. In addition, we report that with time the pH of the medium drifts into the acid range. When Cucumis callus was added to the medium, the pH was changed significantly within 48 hours. The amount and direction (increase or decrease of pH) was significantly correlated with the original pH. This suggests that researchers should be wary of the true pH situation in their medium. In addition, in publications authors should specify whether their medium pH value was determined before or after autoclaving. 相似文献
53.
54.
Conformational changes in Sindbis virus envelope proteins accompanying exposure to low pH. 总被引:22,自引:16,他引:6
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The attachment of high multiplicities of Sindbis virus to tissue-cultured cells followed by brief treatment at low pH has been shown to produce cell fusion (fusion from without). In this report, experiments to determine the effects of low pH on the physical and biological properties of Sindbis virus are described. Exposure of purified Sindbis virions to mildly acidic conditions resulted in a rapid and irreversible alteration in particle density and sedimentation characteristics, followed by a slower loss of infectivity. Infectivity was not restored by a return to neutral pH; rather, the loss of virus infectivity seemed to be initiated by exposure to low pH but continued at neutral pH. The formation of a virus-cell complex in which virions were attached to the cell surface protected the particles from low-pH inactivation, although low pH could still expose virus functions responsible for cell fusion. Low pH was found to induce a conformational change in the E2 polypeptide of the intact virion. These results are discussed with respect to the process of Sindbis virus infection of tissue-cultured cells. 相似文献
55.
56.
Structural alterations in fibronectin correlated with morphological changes in smooth muscle cells 总被引:2,自引:0,他引:2
Nontransformed cultures of vascular smooth muscle cells proliferate until they form a confluent sheet of cells. Subsequently, the cells become reorganized to form multicellular nodules that are loosely attached to the substrate. The formation of nodules is facilitated by the addition of medium conditioned by nodular cultures. Nodulation is inhibited by the addition of fibronectin. Fibronectins derived from monolayer culture conditioned medium or from plasma are maximally effective while fibronectin isolated from nodular cell conditioned medium is inactive. Analysis by NaDodSO4-polyacrylamide gel electrophoresis reveals that the nodular cell fibronectin has a molecular weight that is about 20-30 kd less than that of monolayer cell fibronectin. Further, nodular cell conditioned medium contains an activity that can convert both plasma fibronectin and monolayer cell fibronectin to the lower molecular weight correlated with the loss of biological activity. 相似文献
57.
A paired-tracer dilution method for characterizing membrane transport in the perfused rat hindlimb. Effects of insulin, feeding and fasting on the kinetics of sugar transport.
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M J Rennie J P Idstr?m G E Mann T Scherstén A C Bylund-Fellenius 《The Biochemical journal》1983,214(3):737-743
We have applied the paired-tracer dilution method to the study of transport processes in a mixed mammalian muscle preparation, the perfused rat hindlimb. The method is suitable for the characterization of the kinetic parameters of sugar and amino acid transport and its regulation by hormones, contractile activity, hypoxia, etc. Insulin stimulates sugar transport by increasing the Vmax. of the process 2-3 fold, but its affinity is unchanged. Starvation increases the affinity of sugar transport in perfused skeletal muscle. 相似文献
58.
59.
Inbred corn varieties differing in their tolerance to the maize dwarf mosaic virus infection also differ in varietal character and host response to simazine. Oh 7B, a tolerant cv., has less total soluble and globulin proteins than the sensitive variety, H 55, but more Kjeldahl nitrogen, albumin protein and a doubling of catalase activity. Virus inoculation in Oh 7B causes a reduction in all three protein fractions, Kjeldahl nitrogen and catalase activity. Deleterious virus-simazine interaction does not occur with either variety and the observed varietal and host response differences in protein may account for the conflicting reports of other workers. 相似文献
60.