全文获取类型
收费全文 | 24845篇 |
免费 | 51篇 |
国内免费 | 88篇 |
专业分类
系统科学 | 97篇 |
丛书文集 | 259篇 |
教育与普及 | 60篇 |
理论与方法论 | 112篇 |
现状及发展 | 10654篇 |
研究方法 | 1121篇 |
综合类 | 12261篇 |
自然研究 | 420篇 |
出版年
2013年 | 179篇 |
2012年 | 395篇 |
2011年 | 798篇 |
2010年 | 176篇 |
2008年 | 455篇 |
2007年 | 469篇 |
2006年 | 471篇 |
2005年 | 483篇 |
2004年 | 485篇 |
2003年 | 433篇 |
2002年 | 416篇 |
2001年 | 738篇 |
2000年 | 702篇 |
1999年 | 507篇 |
1992年 | 445篇 |
1991年 | 338篇 |
1990年 | 389篇 |
1989年 | 379篇 |
1988年 | 382篇 |
1987年 | 385篇 |
1986年 | 337篇 |
1985年 | 489篇 |
1984年 | 364篇 |
1983年 | 280篇 |
1982年 | 309篇 |
1981年 | 266篇 |
1980年 | 323篇 |
1979年 | 746篇 |
1978年 | 559篇 |
1977年 | 559篇 |
1976年 | 502篇 |
1975年 | 572篇 |
1974年 | 644篇 |
1973年 | 626篇 |
1972年 | 680篇 |
1971年 | 718篇 |
1970年 | 910篇 |
1969年 | 772篇 |
1968年 | 784篇 |
1967年 | 740篇 |
1966年 | 660篇 |
1965年 | 460篇 |
1964年 | 128篇 |
1959年 | 264篇 |
1958年 | 481篇 |
1957年 | 318篇 |
1956年 | 293篇 |
1955年 | 245篇 |
1954年 | 258篇 |
1948年 | 214篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
81.
LANE RE 《Advancement of science》1948,5(18):96-118
82.
Liu F Thirumangalathu S Gallant NM Yang SH Stoick-Cooper CL Reddy ST Andl T Taketo MM Dlugosz AA Moon RT Barlow LA Millar SE 《Nature genetics》2007,39(1):106-112
Fungiform taste papillae form a regular array on the dorsal tongue. Taste buds arise from papilla epithelium and, unusually for epithelial derivatives, synapse with neurons, release neurotransmitters and generate receptor and action potentials. Despite the importance of taste as one of our five senses, genetic analyses of taste papilla and bud development are lacking. We demonstrate that Wnt-beta-catenin signaling is activated in developing fungiform placodes and taste bud cells. A dominant stabilizing mutation of epithelial beta-catenin causes massive overproduction of enlarged fungiform papillae and taste buds. Likewise, genetic deletion of epithelial beta-catenin or inhibition of Wnt-beta-catenin signaling by ectopic dickkopf1 (Dkk1) blocks initiation of fungiform papilla morphogenesis. Ectopic papillae are innervated in the stabilizing beta-catenin mutant, whereas ectopic Dkk1 causes absence of lingual epithelial innervation. Thus, Wnt-beta-catenin signaling is critical for fungiform papilla and taste bud development. Altered regulation of this pathway may underlie evolutionary changes in taste papilla patterning. 相似文献
83.
Edwin Y.B.Pun 《复旦学报(自然科学版)》2007,(5)
1 Results Rare earth doped waveguide amplifiers and devices have been demonstrated in silica, crystal and other glass hosts. These rare earth doped optical waveguide devices are based on inorganic materials. Many processing steps are required and can lead to long fabrication time and low yield.Polymer materials offer many distinct properties compared to inorganic materials, such as ease of fabrication, low production costs, simple processing steps, and compatibility with micro-fabrication technologies. ... 相似文献
84.
tRNase Z: the end is not in sight 总被引:1,自引:0,他引:1
Although the enzyme tRNase Z has only recently been isolated, a plethora of data has already been acquired concerning the
enzyme. tRNase Z is the endonuclease that catalyzes the removal of the tRNA 3′ trailer, yielding the mature tRNA 3′ end ready
for CCA addition and aminoacylation. Another substrate cleaved by tRNase Z is the small chromogenic phosphodiester bis(p-nitrophenyl)phosphate (bpNPP), which is the smallest tRNase Z substrate known so far. Hitherto the biological function as
tRNA 3′-end processing enzyme has been shown only in one prokaryotic and one eukaryotic organism, respectively. This review
summarizes the present information concerning the two tRNase Z substrates pre-tRNA and bpNPP, as well as the metal requirements
of tRNase Z enzymes.
Received 29 March 2007; received after revision 15 May 2007; accepted 21 May 2007 相似文献
85.
Dhar-Chowdhury P Malester B Rajacic P Coetzee WA 《Cellular and molecular life sciences : CMLS》2007,64(23):3069-3083
Glycolysis is an evolutionary conserved metabolic pathway that provides small amounts of energy in the form of ATP when compared
to other pathways such as oxidative phosphorylation or fatty acid oxidation. The ATP levels inside metabolically active cells
are not constant and the local ATP level will depend on the site of production as well as the respective rates of ATP production,
diffusion and consumption. Membrane ion transporters (pumps, exchangers and channels) are located at sites distal to the major
sources of ATP formation (the mitochondria). We review evidence that the glycolytic complex is associated with membranes;
both at the plasmalemma and with membranes of the endo/sarcoplasmic reticular network. We examine the evidence for the concept
that many of the ion transporters are regulated preferentially by the glycolytic process. These include the Na+/K+-ATPase, the H+-ATPase, various types of Ca2+-ATPases, the Na+/H+ exchanger, the ATP-sensitive K+ channel, cation channels, Na+ channels, Ca2+ channels and other channels involved in intracellular Ca2+ homeostasis. Regulation of these pumps, exchangers and ion channels by the glycolytic process has important consequences
in a variety of physiological and pathophysiological processes, and a better understanding of this mode of regulation may
have important consequences for developing future strategies in combating disease and developing novel therapeutic approaches.
Received 20 July 2007; received after revision 30 July 2007; accepted 17 August 2007 相似文献
86.
E. Häfliger 《Cellular and molecular life sciences : CMLS》1948,4(6):223-225
Summary The action of DDT on honey-bees depends to a high extent on the temperature (see graph). At 36°C (breeding temperature) DDT has a far weaker insecticidal action than at 20°C (laboratory temperature). This shows that the insecticidal properties of DDT diminish with the raise of temperature.This resistance to DDT at higher temperature is most propitious for bee-keeping and also explains the fact why in agricultural practice there has been no corroborated case of poisoning of bees, though in laboratory tests DDT avered itself to be toxic to bees. 相似文献
87.
陶娥 《长春师范学院学报》2007,(3)
由于民间文学的社会功能是多方面的,东北地区的民间文学在东北旅游文化中能起到传播知识、净化灵魂、陶冶情操、娱乐休闲等教益作用。 相似文献
88.
Pyruvate dehydrogenase kinase regulatory mechanisms and inhibition in treating diabetes, heart ischemia, and cancer 总被引:2,自引:2,他引:0
The fraction of pyruvate dehydrogenase complex (PDC) in the active form is reduced by the activities of dedicated PD kinase
isozymes (PDK1, PDK2, PDK3 and PDK4). Via binding to the inner lipoyl domain (L2) of the dihydrolipoyl acetyltransferase (E2
60mer), PDK rapidly access their E2-bound PD substrate. The E2-enhanced activity of the widely distributed PDK2 is limited
by dissociation of ADP from its C-terminal catalytic domain, and this is further slowed by pyruvate binding to the N-terminal
regulatory (R) domain. Via the reverse of the PDC reaction, NADH and acetyl-CoA reductively acetylate lipoyl group of L2,
which binds to the R domain and stimulates PDK2 activity by speeding up ADP dissociation. Activation of PDC by synthetic PDK
inhibitors binding at the pyruvate or lipoyl binding sites decreased damage during heart ischemia and lowered blood glucose
in insulin-resistant animals. PDC activation also triggers apoptosis in cancer cells that selectively convert glucose to lactate.
Received 25 August 2006; received after revision 20 November 2006; accepted 20 December 2006 相似文献
89.
90.