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排序方式: 共有188条查询结果,搜索用时 15 毫秒
91.
McGrew MJ Sherman A Ellard FM Lillico SG Gilhooley HJ Kingsman AJ Mitrophanous KA Sang H 《EMBO reports》2004,5(7):728-733
An effective method for genetic modification of chickens has yet to be developed. An efficient technology, enabling production of transgenic birds at high frequency and with reliable expression of transgenes, will have many applications, both in basic research and in biotechnology. We investigated the efficiency with which lentiviral vectors could transduce the chicken germ line and examined the expression of introduced reporter transgenes. Ten founder cockerels transmitted the vector to between 4% and 45% of their offspring and stable transmission to the G2 generation was demonstrated. Analysis of expression of reporter gene constructs in several transgenic lines showed a conserved expression profile between individuals that was maintained after transmission through the germ line. These data demonstrate that lentiviral vectors can be used to generate transgenic lines with an efficiency in the order of 100-fold higher than any previously published method, with no detectable silencing of transgene expression between generations. 相似文献
92.
It is generally thought that cell growth and metabolism regulate cell division and not vice versa. Here, we examined Saccharomyces cerevisiae cells growing under conditions of continuous culture in a chemostat. We found that loss of G1 cyclins, or inactivation of the cyclin-dependent kinase Cdc28p, reduced the activity of glutamate synthase (Glt1p), a key enzyme in nitrogen assimilation. We also present evidence indicating that the G1 cyclin-dependent control of Glt1p may involve Jem1p, a DnaJ-type chaperone. Our results suggest that completion of START may be linked to nitrogen metabolism.Communicated by C. P. Hollenberg 相似文献
93.
In order to avoid the metabolic burden of protein expression during cell growth, and to avoid potential toxicity of recombinant proteins, microbial expression systems typically utilize regulated expression vectors. In contrast, constitutive expression vectors have usually been utilized for isolation of protein expressing mammalian cell lines. In mammalian systems, inducible expression vectors are typically utilized for only those proteins that are toxic when overexpressed. We developed a tetracycline regulated expression system in CHO cells, and show that cell pools selected in the uninduced state recover faster than those selected in the induced state even though the proteins showed no apparent toxicity or expression instability. Furthermore, cell pools selected in the uninduced state had higher expression levels when protein expression was turned on only in production cultures compared to pools that were selected and maintained in the induced state through production. We show a titer improvement of greater than twofold for an Fc-fusion protein and greater than 50% improvement for a recombinant antibody. The improvement is primarily due to an increase in specific productivity. Recombinant protein mRNA levels correlate strongly with protein expression levels and are highest in those cultures selected in the uninduced state and only induced during production. These data are consistent with a model where CHO cell lines with constitutive expression select for subclones with lower expression levels. 相似文献
94.
Benjamin Baiser Dominique Gravel Alyssa R. Cirtwill Jennifer A. Dunne Ashkaan K. Fahimipour Luis J. Gilarranz Joshua A. Grochow Daijiang Li Neo D. Martinez Alicia McGrew Timothe Poisot Tamara N. Romanuk Daniel B. Stouffer Lauren B. Trotta Fernanda S. Valdovinos Richard J. Williams Spencer A. Wood Justin D. Yeakel 《Global Ecology and Biogeography》2019,28(9):1204-1218
95.
Sir2 blocks extreme life-span extension 总被引:18,自引:0,他引:18
Sir2 is a conserved deacetylase that modulates life span in yeast, worms, and flies and stress response in mammals. In yeast, Sir2 is required for maintaining replicative life span, and increasing Sir2 dosage can delay replicative aging. We address the role of Sir2 in regulating chronological life span in yeast. Lack of Sir2 along with calorie restriction and/or mutations in the yeast AKT homolog, Sch9, or Ras pathways causes a dramatic chronological life-span extension. Inactivation of Sir2 causes uptake and catabolism of ethanol and upregulation of many stress-resistance and sporulation genes. These changes while sufficient to extend chronological life span in wild-type yeast require severe calorie restriction or additional mutations to extend life span of sir2Delta mutants. Our results demonstrate that effects of SIR2 on chronological life span are opposite to replicatve life span and suggest that the relevant activities of Sir2-like deacetylases may also be complex in higher eukaryotes. 相似文献
96.
Coyote-lamb interactions in 65-ha pastures were observed during a study of Komondor dogs guarding sheep. Vulnerability of lambs to coyote predation was related to total time lambs were exposed to coyotes in the enclosures and total time present in the flock. Lambs were most vulnerable during the first two weeks of exposure (P < 0.001, X2 = 49.3), and were somewhat less vulnerable in the next 4 weeks of exposure. If the lambs survived 6 weeks of exposure, their chances of succumbing to predation were small. Lambs were most vulnerable if they were added to an established flock. Orphan lambs were more vulnerable than ewe-reared lambs. Even though the coyotes in this study were persistent in attacking lambs, their success was limited for at least 3 reasons. First, the lambs sometimes refused to run from the coyotes. In addition, they occasionally actively defended themselves by foot-stomping, butting and approaching the coyote. Finally, no lambs were killed while in close proximity to a guardian dog. Based on this study, predation might best be reduced by minimizing introductions of new lambs, and especially orphan lambs, to established flocks, and by using a guardian dog, if possible. 相似文献
97.
The use of stone-tools to open palm nuts (Elaeis guineensis) was studied in a group of 16 chimpanzees (Pan troglodytes) released from captivity to a natural island setting in Liberia. The behaviour was started by one female of the group; it
then spread to 12 others over periods varying from a few seconds to a few weeks. Nut-cracking soon spread to three other sites,
both spontaneously and with human encouragement. Both nuts and tools were carried distances of several hundred meters. Social
interaction at cracking sites was rich and varied, ranging from fights over possession of tools to unsolicited sharing of
nuts. Nut-crackers showed selectivity in schoosing “good” nuts and varied their methods according to the qualities of the
nuts. Individual differences in technique emerged. These are the first detailed behavioural data on palm-nut-cracking, and
they show many parallels with nut-cracking of other species by chimpanzees of the Tai Forest, Ivory Coast. This is another
example of hammer-stone use from a limited region of West Africa: southeastern Guinea, eastern Liberia, and western Ivory
Coast. This suggests limited cultural diffusion of the custom. 相似文献
98.
Emergence,propagation or disappearance of novel behavioral patterns in the habituated chimpanzees of Mahale: a review 总被引:1,自引:1,他引:0
Toshisada Nishida Takahisa Matsusaka William C. McGrew 《Primates; journal of primatology》2009,50(1):23-36
Each local population of chimpanzees shows cultural variation, but little is known about how behavioral variations first emerge,
and how often variants spread to other individuals and then become fixed as a local culture in chimpanzee society. Although
field studies of chimpanzees are still too short to answer these questions definitively, it may stimulate further study in
various sites to summarize the developments observed over the past 40 years at Mahale, Tanzania. Innovative patterns were
operationally defined as new behavioral patterns performed by M group chimpanzees from 1981 onwards. Innovations included
patterns of feeding (n = 8), human-directed behavior (n = 3), hygiene behavior (n = 4), maternal carrying of infants (n = 2), courtship (n = 2), play (n = 6), intimidation displays (n = 3), and quasi-grooming (n = 4). Although most patterns were repeated later by other individuals, six patterns were never seen performed by another
individual, and eight patterns were performed by one or a few individuals but social transmission was unlikely. Thus, innovation
was not rare, but emergence of fashion or establishment of traditions seems to occur rarely in chimpanzee society. 相似文献
99.
Renuka Ramachandra Stephanie McGrew Keith Elmslie 《Journal of visualized experiments : JoVE》2013,(82)
Sensory neurons transmit signals from various parts of the body to the central nervous system. The soma for these neurons are located in the dorsal root ganglia that line the spinal column. Understanding the receptors and channels expressed by these sensory afferent neurons could lead to novel therapies for disease. The initial step is to identify the specific subset of sensory neurons of interest. Here we describe a method to identify afferent neurons innervating the muscles by retrograde labeling using a fluorescent dye DiI (1,1''-dioctadecyl-3,3,3'',3''-tetramethylindocarbocyanine perchlorate). Understanding the contribution of ion channels to excitation of muscle afferents could help to better control excessive excitability induced by certain disease states such as peripheral vascular disease or heart failure. We used two approaches to identify the voltage dependent ion channels expressed by these neurons, patch clamp electrophysiology and immunocytochemistry. While electrophysiology plus pharmacological blockers can identify functional ion channel types, we used immunocytochemistry to identify channels for which specific blockers were unavailable and to better understand the ion channel distribution pattern in the cell population. These techniques can be applied to other areas of the nervous system to study specific neuronal groups. 相似文献
100.