全文获取类型
收费全文 | 45944篇 |
免费 | 96篇 |
国内免费 | 117篇 |
专业分类
系统科学 | 354篇 |
丛书文集 | 1082篇 |
教育与普及 | 118篇 |
理论与方法论 | 244篇 |
现状及发展 | 20269篇 |
研究方法 | 1711篇 |
综合类 | 21685篇 |
自然研究 | 694篇 |
出版年
2013年 | 285篇 |
2012年 | 574篇 |
2011年 | 1300篇 |
2010年 | 247篇 |
2008年 | 745篇 |
2007年 | 778篇 |
2006年 | 838篇 |
2005年 | 826篇 |
2004年 | 774篇 |
2003年 | 829篇 |
2002年 | 753篇 |
2001年 | 1355篇 |
2000年 | 1236篇 |
1999年 | 803篇 |
1992年 | 797篇 |
1991年 | 676篇 |
1990年 | 715篇 |
1989年 | 667篇 |
1988年 | 692篇 |
1987年 | 712篇 |
1986年 | 689篇 |
1985年 | 855篇 |
1984年 | 699篇 |
1983年 | 589篇 |
1982年 | 493篇 |
1981年 | 511篇 |
1980年 | 665篇 |
1979年 | 1421篇 |
1978年 | 1213篇 |
1977年 | 1204篇 |
1976年 | 875篇 |
1975年 | 994篇 |
1974年 | 1370篇 |
1973年 | 1203篇 |
1972年 | 1221篇 |
1971年 | 1477篇 |
1970年 | 1942篇 |
1969年 | 1502篇 |
1968年 | 1367篇 |
1967年 | 1447篇 |
1966年 | 1254篇 |
1965年 | 907篇 |
1964年 | 243篇 |
1959年 | 571篇 |
1958年 | 850篇 |
1957年 | 668篇 |
1956年 | 572篇 |
1955年 | 503篇 |
1954年 | 561篇 |
1948年 | 334篇 |
排序方式: 共有10000条查询结果,搜索用时 990 毫秒
771.
772.
Cohausz O Blenn C Malanga M Althaus FR 《Cellular and molecular life sciences : CMLS》2008,65(4):644-655
Poly(ADP-ribose) (PAR) has been identified as a DNA damage-inducible cell death signal upstream of apoptosis-inducing factor
(AIF). PAR causes the translocation of AIF from mitochondria to the nucleus and triggers cell death. In living cells, PAR
molecules are subject to dynamic changes pending on internal and external stress factors. Using RNA interference (RNAi), we
determined the roles of poly(ADP-ribose) polymerases-1 and -2 (PARP-1, PARP-2) and poly(ADP-ribose) glycohydrolase (PARG),
the key enzymes configuring PAR molecules, in cell death induced by an alkylating agent. We found that PARP-1, but not PARP-2
and PARG, contributed to alkylation-induced cell death. Likewise, AIF translocation was only affected by PARP-1. PARP-1 seems
to play a major role configuring PAR as a death signal involving AIF translocation regardless of the death pathway involved.
Received 7 November 2007; received after revision 19 December 2007; accepted 21 December 2007
O. Cohausz, C. Blenn: These two authors contributed equally to this work. 相似文献
773.
774.
Molecular and Cellular Basis of Regeneration and Tissue Repair 总被引:2,自引:0,他引:2
The Xenopus tadpole is a favourable organism for regeneration research because it is suitable for a wide range of micromanipulative procedures and for a wide range of transgenic methods. Combination of these techniques enables genes to be activated or inhibited at specific times and in specific tissue types to a much higher degree than in any other organism capable of regeneration. Regenerating systems include the tail, the limb buds and the lens. The study of tail regeneration has shown that each tissue type supplies the cells for its own replacement: there is no detectable de-differentiation or metaplasia. Signalling systems needed for regeneration include the BMP and Notch signalling pathways, and perhaps also the Wnt and FGF pathways. The limb buds will regenerate completely at early stages, but not once they are fully differentiated. This provides a good opportunity to study the loss of regenerative ability using transgenic methods. 相似文献
775.
Molecular and Cellular Basis of Regeneration and Tissue Repair 总被引:3,自引:0,他引:3
Rossi L Salvetti A Batistoni R Deri P Gremigni V 《Cellular and molecular life sciences : CMLS》2008,65(1):16-23
Planarians possess amazing abilities to regulate tissue homeostasis and regenerate missing body parts. These features reside on the presence of a population of pluripotent/totipotent stem cells, the neoblasts, which are considered as the only planarian cells able to proliferate in the asexual strains. Neoblast distribution has been identified by mapping the cells incorporating bromodeoxyuridine, analyzing mitotic figures and using cell proliferation markers. Recently identified molecular markers specifically label subgroups of neoblasts, revealing thus the heterogeneity of the planarian stem cell population. Therefore, the apparent totipotency of neoblasts probably reflects the composite activities of multiple stem cell types. First steps have been undertaken to understand how neoblasts and differentiated cells communicate with each other to adapt the self-renewal and differentiation rates of neoblasts to the demands of the body. Moreover, the introduction of molecular resource database on planarians now paves the way to renewed strategies to understand planarian regeneration and stem cell-related issues. 相似文献
776.
Shin JM Vagin O Munson K Kidd M Modlin IM Sachs G 《Cellular and molecular life sciences : CMLS》2008,65(2):264-281
Inhibition of gastric acid secretion is the mainstay of the treatment of gastroesophageal reflux disease and peptic ulceration;
therapies to inhibit acid are among the best-selling drugs worldwide. Highly effective agents targeting the histamine H2 receptor
were first identified in the 1970s. These were followed by the development of irreversible inhibitors of the parietal cell
hydrogen-potassium ATPase (the proton pump inhibitors) that inhibit acid secretion much more effectively. Reviewed here are
the chemistry, biological targets and pharmacology of these drugs, with reference to their current and evolving clinical utilities.
Future directions in the development of acid inhibitory drugs include modifications of current agents and the emergence of
a novel class of agents, the acid pump antagonists.
Received 30 May 2007; received after revision 15 August 2007; accepted 13 September 2007 相似文献
777.
Beside its role as a neurotransmitter in the central nervous system, serotonin appears to be a central physiologic mediator
of many gastrointestinal (GI) functions and a mediator of the brain-gut connection. By acting directly and via modulation
of the enteric nervous system, serotonin has numerous effects on the GI tract. The main gut disturbances in which serotonin
is involved are acute chemotherapy-induced nausea and vomiting, carcinoid syndrome and irritable bowel syndrome. Serotonin
also has mitogenic properties. Platelet-derived serotonin is involved in liver regeneration after partial hepatectomy. In
diseased liver, serotonin may play a crucial role in the progression of hepatic fibrosis and the pathogenesis of steatohepatitis.
Better understanding of the role of the serotonin receptor subtypes and serotonin mechanisms of action in the liver and gut
may open new therapeutic strategies in hepato-gastrointestinal diseases.
Received 15 August 2007; received after revision 1 November 2007; accepted 5 November 2007 相似文献
778.
Hochrainer K Kroismayr R Baranyi U Binder BR Lipp J 《Cellular and molecular life sciences : CMLS》2008,65(13):2105-2117
Small HERC proteins are defined by the presence of one RCC1-like domain and a HECT domain. Having evolved out of one common ancestor, the four members of the family exhibit a high degree of homology in genomic organization and amino acid sequence, thus it seems possible that they might accomplish similar functions. Here we show that small HERC proteins interact with each other and localize to the same cellular structures, which we identify as late endosomes and lysosomes. We demonstrate interaction of HERC3 with the ubiquitin-like proteins hPLIC-1 and hPLIC-2 and we establish interaction of HERC5 with the metastasis suppressor Nm23B. While hPLIC proteins are not ubiquitinated by HERC3, HERC5 plays an important role in ubiquitination of Nm23B. In summary, although small HERC proteins are highly homologous showing the same subcellular distribution, they undergo different molecular interactions. 相似文献
779.
Bile acids and bile alcohols in the form of their conjugates are amphipathic end products of cholesterol metabolism with multiple physiological functions. The great variety of bile acids and bile alcohols that are present in vertebrates are tabulated. Bile salts have an enterohepatic circulation resulting from efficient vectorial transport of bile salts through the hepatocyte and the ileal enterocyte; such transport leads to the accumulation of a pool of bile salts that cycles between the liver and intestine. Bile salt anions promote lipid absorption, enhance tryptic cleavage of dietary proteins, and have antimicrobial effects. Bile salts are signaling molecules, activating nuclear receptors in the hepatocyte and ileal enterocyte, as well as an increasing number of G-protein coupled receptors. Bile acids are used therapeutically to correct deficiency states, to decrease the cholesterol saturation of bile, or to decrease the cytotoxicity of retained bile acids in cholestatic liver disease. 相似文献
780.