全文获取类型
收费全文 | 832篇 |
免费 | 4篇 |
国内免费 | 8篇 |
专业分类
系统科学 | 21篇 |
丛书文集 | 1篇 |
教育与普及 | 1篇 |
理论与方法论 | 8篇 |
现状及发展 | 112篇 |
研究方法 | 149篇 |
综合类 | 506篇 |
自然研究 | 46篇 |
出版年
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 7篇 |
2015年 | 11篇 |
2014年 | 14篇 |
2013年 | 9篇 |
2012年 | 99篇 |
2011年 | 147篇 |
2010年 | 37篇 |
2009年 | 7篇 |
2008年 | 80篇 |
2007年 | 79篇 |
2006年 | 56篇 |
2005年 | 64篇 |
2004年 | 51篇 |
2003年 | 39篇 |
2002年 | 46篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1970年 | 5篇 |
1969年 | 2篇 |
1967年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有844条查询结果,搜索用时 15 毫秒
71.
72.
Protein-protein interactions may impose constraints on both structural and regulatory evolution. Here we show that protein-protein interactions are negatively associated with evolutionary variation in gene expression. Moreover, interacting proteins have similar levels of variation in expression, and their expression levels are positively correlated across strains. Our results suggest that interacting proteins undergo similar evolutionary dynamics, and that their expression levels are evolutionarily coupled. These patterns hold for organisms as diverse as budding yeast and fruit flies. 相似文献
73.
Krakow D Robertson SP King LM Morgan T Sebald ET Bertolotto C Wachsmann-Hogiu S Acuna D Shapiro SS Takafuta T Aftimos S Kim CA Firth H Steiner CE Cormier-Daire V Superti-Furga A Bonafe L Graham JM Grix A Bacino CA Allanson J Bialer MG Lachman RS Rimoin DL Cohn DH 《Nature genetics》2004,36(4):405-410
The filamins are cytoplasmic proteins that regulate the structure and activity of the cytoskeleton by cross-linking actin into three-dimensional networks, linking the cell membrane to the cytoskeleton and serving as scaffolds on which intracellular signaling and protein trafficking pathways are organized (reviewed in refs. 1,2). We identified mutations in the gene encoding filamin B in four human skeletal disorders. We found homozygosity or compound heterozygosity with respect to stop-codon mutations in autosomal recessive spondylocarpotarsal syndrome (SCT, OMIM 272460) and missense mutations in individuals with autosomal dominant Larsen syndrome (OMIM 150250) and the perinatal lethal atelosteogenesis I and III phenotypes (AOI, OMIM 108720; AOIII, OMIM 108721). We found that filamin B is expressed in human growth plate chondrocytes and in the developing vertebral bodies in the mouse. These data indicate an unexpected role in vertebral segmentation, joint formation and endochondral ossification for this ubiquitously expressed cytoskeletal protein. 相似文献
74.
Thibault ST Singer MA Miyazaki WY Milash B Dompe NA Singh CM Buchholz R Demsky M Fawcett R Francis-Lang HL Ryner L Cheung LM Chong A Erickson C Fisher WW Greer K Hartouni SR Howie E Jakkula L Joo D Killpack K Laufer A Mazzotta J Smith RD Stevens LM Stuber C Tan LR Ventura R Woo A Zakrajsek I Zhao L Chen F Swimmer C Kopczynski C Duyk G Winberg ML Margolis J 《Nature genetics》2004,36(3):283-287
With the availability of complete genome sequence for Drosophila melanogaster, one of the next strategic goals for fly researchers is a complete gene knockout collection. The P-element transposon, the workhorse of D. melanogaster molecular genetics, has a pronounced nonrandom insertion spectrum. It has been estimated that 87% saturation of the approximately 13,500-gene complement of D. melanogaster might require generating and analyzing up to 150,000 insertions. We describe specific improvements to the lepidopteran transposon piggyBac and the P element that enabled us to tag and disrupt genes in D. melanogaster more efficiently. We generated over 29,000 inserts resulting in 53% gene saturation and a more diverse collection of phenotypically stronger insertional alleles. We found that piggyBac has distinct global and local gene-tagging behavior from that of P elements. Notably, piggyBac excisions from the germ line are nearly always precise, piggyBac does not share chromosomal hotspots associated with P and piggyBac is more effective at gene disruption because it lacks the P bias for insertion in 5' regulatory sequences. 相似文献
75.
Instrumental observations and reconstructions of global and hemispheric temperature evolution reveal a pronounced warming during the past approximately 150 years. One expression of this warming is the observed increase in the occurrence of heatwaves. Conceptually this increase is understood as a shift of the statistical distribution towards warmer temperatures, while changes in the width of the distribution are often considered small. Here we show that this framework fails to explain the record-breaking central European summer temperatures in 2003, although it is consistent with observations from previous years. We find that an event like that of summer 2003 is statistically extremely unlikely, even when the observed warming is taken into account. We propose that a regime with an increased variability of temperatures (in addition to increases in mean temperature) may be able to account for summer 2003. To test this proposal, we simulate possible future European climate with a regional climate model in a scenario with increased atmospheric greenhouse-gas concentrations, and find that temperature variability increases by up to 100%, with maximum changes in central and eastern Europe. 相似文献
76.
A bacteriolytic agent that detects and kills Bacillus anthracis 总被引:17,自引:0,他引:17
The dormant and durable spore form of Bacillus anthracis is an ideal biological weapon of mass destruction. Once inhaled, spores are transported by alveolar macrophages to lymph nodes surrounding the lungs, where they germinate; subsequent vegetative expansion causes an overwhelming flood of bacteria and toxins into the blood, killing up to 99% of untreated victims. Natural and genetically engineered antibiotic-resistant bacilli amplify the threat of spores being used as weapons, and heighten the need for improved treatments and spore-detection methods after an intentional release. We exploited the inherent binding specificity and lytic action of bacteriophage enzymes called lysins for the rapid detection and killing of B. anthracis. Here we show that the PlyG lysin, isolated from the gamma phage of B. anthracis, specifically kills B. anthracis isolates and other members of the B. anthracis 'cluster' of bacilli in vitro and in vivo. Both vegetative cells and germinating spores are susceptible. The lytic specificity of PlyG was also exploited as part of a rapid method for the identification of B. anthracis. We conclude that PlyG is a tool for the treatment and detection of B. anthracis. 相似文献
77.
Coulomb blockade and the Kondo effect in single-atom transistors 总被引:7,自引:0,他引:7
Park J Pasupathy AN Goldsmith JI Chang C Yaish Y Petta JR Rinkoski M Sethna JP Abruña HD McEuen PL Ralph DC 《Nature》2002,417(6890):722-725
Using molecules as electronic components is a powerful new direction in the science and technology of nanometre-scale systems. Experiments to date have examined a multitude of molecules conducting in parallel, or, in some cases, transport through single molecules. The latter includes molecules probed in a two-terminal geometry using mechanically controlled break junctions or scanning probes as well as three-terminal single-molecule transistors made from carbon nanotubes, C(60) molecules, and conjugated molecules diluted in a less-conducting molecular layer. The ultimate limit would be a device where electrons hop on to, and off from, a single atom between two contacts. Here we describe transistors incorporating a transition-metal complex designed so that electron transport occurs through well-defined charge states of a single atom. We examine two related molecules containing a Co ion bonded to polypyridyl ligands, attached to insulating tethers of different lengths. Changing the length of the insulating tether alters the coupling of the ion to the electrodes, enabling the fabrication of devices that exhibit either single-electron phenomena, such as Coulomb blockade, or the Kondo effect. 相似文献
78.
VEGF regulates haematopoietic stem cell survival by an internal autocrine loop mechanism 总被引:49,自引:0,他引:49
Gerber HP Malik AK Solar GP Sherman D Liang XH Meng G Hong K Marsters JC Ferrara N 《Nature》2002,417(6892):954-958
Vascular endothelial growth factor (VEGF) is a principal regulator of blood vessel formation and haematopoiesis, but the mechanisms by which VEGF differentially regulates these processes have been elusive. Here we describe a regulatory loop by which VEGF controls survival of haematopoietic stem cells (HSCs). We observed a reduction in survival, colony formation and in vivo repopulation rates of HSCs after ablation of the VEGF gene in mice. Intracellularly acting small-molecule inhibitors of VEGF receptor (VEGFR) tyrosine kinase dramatically reduced colony formation of HSCs, thus mimicking deletion of the VEGF gene. However, blocking VEGF by administering a soluble VEGFR-1, which acts extracellularly, induced only minor effects. These findings support the involvement in HSC survival of a VEGF-dependent internal autocrine loop mechanism (that is, the mechanism is resistant to inhibitors that fail to penetrate the intracellular compartment). Not only ligands selective for VEGF and VEGFR-2 but also VEGFR-1 agonists rescued survival and repopulation of VEGF-deficient HSCs, revealing a function for VEGFR-1 signalling during haematopoiesis. 相似文献
79.
Identifying the genes involved in polygenic traits has been difficult. In the 1950s and 1960s, laboratory selection experiments for extreme geotaxic behavior in fruit flies established for the first time that a complex behavioral trait has a genetic basis. But the specific genes responsible for the behavior have never been identified using this classical model. To identify the individual genes involved in geotaxic response, we used cDNA microarrays to identify candidate genes and assessed fly lines mutant in these genes for behavioral confirmation. We have thus determined the identities of several genes that contribute to the complex, polygenic behavior of geotaxis. 相似文献
80.
Walder RY Landau D Meyer P Shalev H Tsolia M Borochowitz Z Boettger MB Beck GE Englehardt RK Carmi R Sheffield VC 《Nature genetics》2002,31(2):171-174
Familial hypomagnesemia with secondary hypocalcemia (OMIM 602014) is an autosomal recessive disease that results in electrolyte abnormalities shortly after birth. Affected individuals show severe hypomagnesemia and hypocalcemia, which lead to seizures and tetany. The disorder has been thought to be caused by a defect in the intestinal absorption of magnesium, rather than by abnormal renal loss of magnesium. Restoring the concentrations of serum magnesium to normal values by high-dose magnesium supplementation can overcome the apparent defect in magnesium absorption and in serum concentrations of calcium. Life-long magnesium supplementation is required to overcome the defect in magnesium handling by these individuals. We previously mapped the gene locus to chromosome 9q in three large inbred kindreds from Israel. Here we report that mutation of TRPM6 causes hypomagnesemia with secondary hypocalcemia and show that individuals carrying mutations in this gene have abnormal renal magnesium excretion. 相似文献