全文获取类型
收费全文 | 8543篇 |
免费 | 83篇 |
国内免费 | 152篇 |
专业分类
系统科学 | 122篇 |
丛书文集 | 394篇 |
教育与普及 | 303篇 |
理论与方法论 | 24篇 |
现状及发展 | 724篇 |
研究方法 | 1163篇 |
综合类 | 6034篇 |
自然研究 | 14篇 |
出版年
2018年 | 17篇 |
2017年 | 32篇 |
2016年 | 19篇 |
2015年 | 26篇 |
2014年 | 49篇 |
2013年 | 37篇 |
2012年 | 553篇 |
2011年 | 704篇 |
2010年 | 189篇 |
2009年 | 108篇 |
2008年 | 674篇 |
2007年 | 722篇 |
2006年 | 744篇 |
2005年 | 760篇 |
2004年 | 538篇 |
2003年 | 508篇 |
2002年 | 465篇 |
2001年 | 379篇 |
2000年 | 557篇 |
1999年 | 203篇 |
1998年 | 52篇 |
1997年 | 35篇 |
1996年 | 21篇 |
1995年 | 18篇 |
1994年 | 29篇 |
1993年 | 25篇 |
1992年 | 16篇 |
1991年 | 31篇 |
1990年 | 37篇 |
1989年 | 36篇 |
1988年 | 29篇 |
1987年 | 30篇 |
1986年 | 40篇 |
1985年 | 31篇 |
1984年 | 17篇 |
1983年 | 22篇 |
1982年 | 31篇 |
1981年 | 23篇 |
1980年 | 14篇 |
1979年 | 20篇 |
1971年 | 18篇 |
1970年 | 39篇 |
1966年 | 18篇 |
1959年 | 104篇 |
1958年 | 176篇 |
1957年 | 124篇 |
1956年 | 115篇 |
1955年 | 117篇 |
1954年 | 114篇 |
1948年 | 28篇 |
排序方式: 共有8778条查询结果,搜索用时 171 毫秒
901.
The S receptor kinase determines self-incompatibility in Brassica stigma 总被引:37,自引:0,他引:37
The self-incompatibility possessed by Brassica is an intraspecific reproductive barrier by which the stigma rejects self-pollen but accepts non-self-pollen for fertilization. The molecular/biochemical bases of recognition and rejection have been intensively studied. Self-incompatibility in Brassica is sporophytically controlled by the polymorphic S locus. Two tightly linked polymorphic genes at the S locus, S receptor kinase gene (SRK) and S locus glycoprotein gene (SLG), are specifically expressed in the papillar cells of the stigma, and analyses of self-compatible lines of Brassica have suggested that together they control stigma function in self-incompatibility interactions. Here we show, by transforming self-incompatible plants of Brassica rapa with an SRK28 and an SLG28 transgene separately, that expression of SRK28 alone, but not SLG28 alone, conferred the ability to reject self (S28)-pollen on the transgenic plants. We also show that the ability of SRK28 to reject S28 pollen was enhanced by SLG28. We conclude that SRK alone determines S haplotype specificity of the stigma, and that SLG acts to promote a full manifestation of the self-incompatibility response. 相似文献
902.
A comprehensive analysis of protein-protein interactions in Saccharomyces cerevisiae 总被引:85,自引:0,他引:85
Uetz P Giot L Cagney G Mansfield TA Judson RS Knight JR Lockshon D Narayan V Srinivasan M Pochart P Qureshi-Emili A Li Y Godwin B Conover D Kalbfleisch T Vijayadamodar G Yang M Johnston M Fields S Rothberg JM 《Nature》2000,403(6770):623-627
Two large-scale yeast two-hybrid screens were undertaken to identify protein-protein interactions between full-length open reading frames predicted from the Saccharomyces cerevisiae genome sequence. In one approach, we constructed a protein array of about 6,000 yeast transformants, with each transformant expressing one of the open reading frames as a fusion to an activation domain. This array was screened by a simple and automated procedure for 192 yeast proteins, with positive responses identified by their positions in the array. In a second approach, we pooled cells expressing one of about 6,000 activation domain fusions to generate a library. We used a high-throughput screening procedure to screen nearly all of the 6,000 predicted yeast proteins, expressed as Gal4 DNA-binding domain fusion proteins, against the library, and characterized positives by sequence analysis. These approaches resulted in the detection of 957 putative interactions involving 1,004 S. cerevisiae proteins. These data reveal interactions that place functionally unclassified proteins in a biological context, interactions between proteins involved in the same biological function, and interactions that link biological functions together into larger cellular processes. The results of these screens are shown here. 相似文献
903.
904.
The Ras-MAPK (mitogen-activated protein kinase) signal transduction pathway is well known to control cellular proliferation and differentiation in response to extracellular signals, but its other functions are less understood. In Caenorhabditis elegans this pathway regulates several developmental events, such as vulval induction and progression of meiosis, but its function in the nervous system is unknown. Here we report that the Ras-MAPK pathway is involved in olfaction in this organism. Mutational inactivation and hyperactivation of this pathway impairs efficiency of chemotaxis to a set of odorants. Experiments in which let-60 ras was expressed using a heat-shock promoter and a cell-specific promoter show that a normal activity of LET-60 Ras is required in mature olfactory neurons. Application of the odorant isoamylalcohol to wild-type animals leads to the activation of MAP kinase in olfactory neurons within 10 seconds. This induction is dependent on the function of the nucleotide-gated channel TAX-2/TAX-4 and the voltage-activated calcium channel subunit UNC-2. These results suggest a dynamic regulatory role for the Ras-MAPK pathway in perception and transmission of sensory signals in olfactory neurons. 相似文献
905.
Myoglobin-like aerotaxis transducers in Archaea and Bacteria 总被引:14,自引:0,他引:14
Haem-containing proteins such as haemoglobin and myoglobin play an essential role in oxygen transport and storage. Comparison of the amino-acid sequences of globins from Bacteria and Eukarya suggests that they share an early common ancestor, even though the proteins perform different functions in these two kingdoms. Until now, no members of the globin family have been found in the third kingdom, Archaea. Recent studies of biological signalling in the Bacteria and Eukarya have revealed a new class of haem-containing proteins that serve as sensors. Until now, no haem-based sensor has been described in the Archaea. Here we report the first myoglobin-like, haem-containing protein in the Archaea, and the first haem-based aerotactic transducer in the Bacteria (termed HemAT-Hs for the archaeon Halobacterium salinarum, and HemAT-Bs for Bacillus subtilis). These proteins exhibit spectral properties similar to those of myoglobin and trigger aerotactic responses. 相似文献
906.
907.
Inhibitor of neurite outgrowth in humans 总被引:82,自引:0,他引:82
Prinjha R Moore SE Vinson M Blake S Morrow R Christie G Michalovich D Simmons DL Walsh FS 《Nature》2000,403(6768):383-384
908.
YidC mediates membrane protein insertion in bacteria 总被引:13,自引:0,他引:13
Samuelson JC Chen M Jiang F Möller I Wiedmann M Kuhn A Phillips GJ Dalbey RE 《Nature》2000,406(6796):637-641
The basic machinery for the translocation of proteins into or across membranes is remarkably conserved from Escherichia coli to humans. In eukaryotes, proteins are inserted into the endoplasmic reticulum using the signal recognition particle (SRP) and the SRP receptor, as well as the integral membrane Sec61 trimeric complex (composed of alpha, beta and gamma subunits). In bacteria, most proteins are inserted by a related pathway that includes the SRP homologue Ffh, the SRP receptor FtsY, and the SecYEG trimeric complex, where Y and E are related to the Sec61 alpha and gamma subunits, respectively. Proteins in bacteria that exhibit no dependence on the Sec translocase were previously thought to insert into the membrane directly without the aid of a protein machinery. Here we show that membrane insertion of two Sec-independent proteins requires YidC. YidC is essential for E. coli viability and homologues are present in mitochondria and chloroplasts. Depletion of YidC also interferes with insertion of Sec-dependent membrane proteins, but it has only a minor effect on the export of secretory proteins. These results provide evidence for an additional component of the translocation machinery that is specialized for the integration of membrane proteins. 相似文献
909.
Oncogene inactivation in a mouse model 总被引:4,自引:0,他引:4
910.