全文获取类型
收费全文 | 20515篇 |
免费 | 115篇 |
国内免费 | 236篇 |
专业分类
系统科学 | 436篇 |
丛书文集 | 382篇 |
教育与普及 | 73篇 |
理论与方法论 | 107篇 |
现状及发展 | 7698篇 |
研究方法 | 947篇 |
综合类 | 10640篇 |
自然研究 | 583篇 |
出版年
2015年 | 144篇 |
2014年 | 176篇 |
2013年 | 318篇 |
2012年 | 580篇 |
2011年 | 1169篇 |
2010年 | 421篇 |
2009年 | 360篇 |
2008年 | 622篇 |
2007年 | 697篇 |
2006年 | 704篇 |
2005年 | 648篇 |
2004年 | 493篇 |
2003年 | 383篇 |
2002年 | 393篇 |
2001年 | 545篇 |
2000年 | 584篇 |
1999年 | 433篇 |
1992年 | 308篇 |
1991年 | 268篇 |
1990年 | 276篇 |
1989年 | 241篇 |
1988年 | 225篇 |
1987年 | 253篇 |
1986年 | 217篇 |
1985年 | 267篇 |
1984年 | 255篇 |
1983年 | 169篇 |
1982年 | 196篇 |
1981年 | 172篇 |
1980年 | 227篇 |
1979年 | 507篇 |
1978年 | 398篇 |
1977年 | 441篇 |
1976年 | 281篇 |
1975年 | 350篇 |
1974年 | 524篇 |
1973年 | 451篇 |
1972年 | 441篇 |
1971年 | 481篇 |
1970年 | 553篇 |
1969年 | 497篇 |
1968年 | 460篇 |
1967年 | 511篇 |
1966年 | 438篇 |
1965年 | 338篇 |
1959年 | 162篇 |
1958年 | 237篇 |
1957年 | 186篇 |
1955年 | 158篇 |
1954年 | 138篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
201.
Lin-Hua Jiang Fatema Mousawi Xuebin Yang Sėbastien Roger 《Cellular and molecular life sciences : CMLS》2017,74(20):3697-3710
The ability of cells to migrate to the destined tissues or lesions is crucial for physiological processes from tissue morphogenesis, homeostasis and immune responses, and also for stem cell-based regenerative medicines. Cytosolic Ca2+ is a primary second messenger in the control and regulation of a wide range of cell functions including cell migration. Extracellular ATP, together with the cognate receptors on the cell surface, ligand-gated ion channel P2X receptors and a subset of G-protein-coupled P2Y receptors, represents common autocrine and/or paracrine Ca2+ signalling mechanisms. The P2X receptor ion channels mediate extracellular Ca2+ influx, whereas stimulation of the P2Y receptors triggers intracellular Ca2+ release from the endoplasmic reticulum (ER), and activation of both type of receptors thus can elevate the cytosolic Ca2+ concentration ([Ca2+]c), albeit with different kinetics and capacity. Reduction in the ER Ca2+ level following the P2Y receptor activation can further induce store-operated Ca2+ entry as a distinct Ca2+ influx pathway that contributes in ATP-induced increase in the [Ca2+]c. Mesenchymal stem cells (MSC) are a group of multipotent stem cells that grow from adult tissues and hold promising applications in tissue engineering and cell-based therapies treating a great and diverse number of diseases. There is increasing evidence to show constitutive or evoked ATP release from stem cells themselves or mature cells in the close vicinity. In this review, we discuss the mechanisms for ATP release and clearance, the receptors and ion channels participating in ATP-induced Ca2+ signalling and the roles of such signalling mechanisms in mediating ATP-induced regulation of MSC migration. 相似文献
202.
203.
204.
205.
206.
207.
Dominique Eladari Régine Chambrey Nicolas Picard Juliette Hadchouel 《Cellular and molecular life sciences : CMLS》2014,71(15):2879-2895
Sodium absorption by the distal part of the nephron, i.e., the distal convoluted tubule, the connecting tubule, and the collecting duct, plays a major role in the control of homeostasis by the kidney. In this part of the nephron, sodium transport can either be electroneutral or electrogenic. The study of electrogenic Na+ absorption, which is mediated by the epithelial sodium channel (ENaC), has been the focus of considerable interest because of its implication in sodium, potassium, and acid–base homeostasis. However, recent studies have highlighted the crucial role played by electroneutral NaCl absorption in the regulation of the body content of sodium chloride, which in turn controls extracellular fluid volume and blood pressure. Here, we review the identification and characterization of the NaCl cotransporter (NCC), the molecule accounting for the main part of electroneutral NaCl absorption in the distal nephron, and its regulators. We also discuss recent work describing the identification of a novel “NCC-like” transport system mediated by pendrin and the sodium-driven chloride/bicarbonate exchanger (NDCBE) in the β-intercalated cells of the collecting system. 相似文献
208.
综述了域上或交换代数上的线性(-)代数的相应的簇(范畴)的 Groebner-Shirshov 基理论的新成果,如:结合代数(包括群(半群)代数),自由代数的张量积,李代数,Di-代数,pre-李代数,Rota-Baxter代数,metabelian李代数,L-代数,半环代数,范畴代数,等.以上结果包含了许多应用,尤其是给出了一些著名结论的新的证明. 相似文献
209.
Juan C. Mayo Rosa M. Sainz Pedro González-Menéndez David Hevia Rafael Cernuda-Cernuda 《Cellular and molecular life sciences : CMLS》2017,74(21):3927-3940
Melatonin is a well-known, nighttime-produced indole found in bacteria, eukaryotic unicellulars, animals or vascular plants. In vertebrates, melatonin is the major product of the pineal gland, which accounts for its increase in serum during the dark phase, but it is also produced by many other organs and cell types. Such a wide distribution is consistent with its multiple and well-described functions which include from the circadian regulation and adaptation to seasonal variations to immunomodulatory and oncostatic actions in different types of tumors. The discovery of its antioxidant properties in the early 1990s opened a new field of potential protective functions in multiple tissues. A special mention should be made regarding the nervous system, where the indole is considered a major neuroprotector. Furthermore, mitochondria appear as one of the most important targets for the indole’s protective actions. Melatonin’s mechanisms of action vary from the direct molecular interaction with free radicals (free radical scavenger) to the binding to membrane (MLT1A and MLT1B) or nuclear receptors (RZR/RORα). Receptor binding has been associated with some, but not all of the indole functions reported to date. Recently, two new mechanisms of cellular uptake involving the facilitative glucose transporters GLUT/SLC2A and the proton-driven oligopeptide transporter PEPT1/2 have been reported. Here we discuss the potential importance that these newly discovered transport systems could have in determining the actions of melatonin, particularly in the mitochondria. We also argue the relative importance of passive diffusion vs active transport in different parts of the cell. 相似文献
210.
Technical communication (TC) is an important activity in order to provide the users of technical artifacts with necessary information concerning the operation and maintenance of the products they are using. In the current working procedures of TC, however, the users become too passive. They are just receivers of information. Further, there is no effective feedback from the users to the producers of the information. In order to overcome those problems we here propose an application of social media (SM) in future TC. By using SM as a complementary channel for TC it becomes possible for technology firms to boost their competitive advantage and to improve the quality and completeness of their TC. This technique, however, is still more of a potential and less of a reality. Several problems, mostly concerning security and confidentiality remain to be solved. The empirical base for this work comes from TIC, an EU-funded development project involving several Swedish technology companies. Published research results are somewhat scattered but several sources coherently indicate both the need and potential for SM as a vehicle in TC. By scanning the net it is further possible to identify a number of seemingly successful applications of SM in such applications. 相似文献