全文获取类型
收费全文 | 36409篇 |
免费 | 124篇 |
国内免费 | 101篇 |
专业分类
系统科学 | 324篇 |
丛书文集 | 690篇 |
教育与普及 | 74篇 |
理论与方法论 | 127篇 |
现状及发展 | 16510篇 |
研究方法 | 1347篇 |
综合类 | 17045篇 |
自然研究 | 517篇 |
出版年
2013年 | 244篇 |
2012年 | 473篇 |
2011年 | 1016篇 |
2010年 | 226篇 |
2008年 | 553篇 |
2007年 | 606篇 |
2006年 | 657篇 |
2005年 | 663篇 |
2004年 | 720篇 |
2003年 | 614篇 |
2002年 | 531篇 |
2001年 | 1016篇 |
2000年 | 1013篇 |
1999年 | 632篇 |
1992年 | 615篇 |
1991年 | 511篇 |
1990年 | 548篇 |
1989年 | 507篇 |
1988年 | 520篇 |
1987年 | 528篇 |
1986年 | 534篇 |
1985年 | 700篇 |
1984年 | 530篇 |
1983年 | 481篇 |
1982年 | 410篇 |
1981年 | 406篇 |
1980年 | 512篇 |
1979年 | 1125篇 |
1978年 | 928篇 |
1977年 | 906篇 |
1976年 | 744篇 |
1975年 | 846篇 |
1974年 | 1123篇 |
1973年 | 948篇 |
1972年 | 992篇 |
1971年 | 1156篇 |
1970年 | 1503篇 |
1969年 | 1170篇 |
1968年 | 1102篇 |
1967年 | 1115篇 |
1966年 | 951篇 |
1965年 | 740篇 |
1964年 | 234篇 |
1959年 | 428篇 |
1958年 | 686篇 |
1957年 | 515篇 |
1956年 | 436篇 |
1955年 | 404篇 |
1954年 | 418篇 |
1948年 | 290篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Myelin sheaths: glycoproteins involved in their formation,maintenance and degeneration 总被引:8,自引:0,他引:8
Quarles RH 《Cellular and molecular life sciences : CMLS》2002,59(11):1851-1871
Myelin sheaths are formed around axons by extending, biochemically modifying and spiraling plasma membranes of Schwann cells
in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS). Because glycoproteins are
prominent components of plasma membranes, it is not surprising that they have important roles in the formation, maintenance
and degeneration of myelin sheaths. The emphasis in this review is on four integral membrane glycoproteins. Two of them, protein
zero (P0) and peripheral myelin protein-22 (PMP-22), are components of compact PNS myelin. The other two are preferentially
localized in membranes of sheaths that are distinct from compact myelin. One is the myelin-associated glycoprotein, which
is localized at the inside of sheaths where it functions in glia-axon interactions in both the PNS and CNS. The other is the
myelin-oligodendrocyte glycoprotein, which is preferentially localized on the outside of CNS myelin sheaths and appears to
be an important target antigen in autoimmune demyelinating diseases such as multiple sclerosis.
Received 8 April 2002; received after revision 13 May 2002; accepted 22 May 2002 相似文献
942.
RAGE is a multiligand receptor of the immunoglobulin superfamily: implications for homeostasis and chronic disease 总被引:19,自引:0,他引:19
Bucciarelli LG Wendt T Rong L Lalla E Hofmann MA Goova MT Taguchi A Yan SF Yan SD Stern DM Schmidt AM 《Cellular and molecular life sciences : CMLS》2002,59(7):1117-1128
Receptor for AGE (RAGE) is a member of the immunoglobulin superfamily that engages distinct classes of ligands. The biology of RAGE is driven by the settings in which these ligands accumulate, such as diabetes, inflammation, neurodegenerative disorders and tumors. In this review, we discuss the context of each of these classes of ligands, including advance glycation end-products, amyloid beta peptide and the family of beta sheet fibrils, S100/calgranulins and amphoterin. Implications for the role of these ligands interacting with RAGE in homeostasis and disease will be considered. 相似文献
943.
Morphine 6 glucuronide stimulates nitric oxide release in mussel neural tissues: evidence for a morphine 6 glucuronide opiate receptor subtype 总被引:1,自引:0,他引:1
Mantione K Zhu W Rialas C Casares F Cadet P Franklin AL Tonnesen J Stefano GB 《Cellular and molecular life sciences : CMLS》2002,59(3):570-574
We have previously demonstrated that Mytilus edulis pedal ganglia contain opiate alkaloids, i.e., morphine and morphine 6 glucuronide (M6G), as well as mu opiate receptor subtype
fragments exhibiting high sequence similarity to those found in mammals. Now we demonstrate that M6G stimulates pedal ganglia
constitutive nitric oxide (NO) synthase (cNOS)-derived NO release at identical concentrations and to similar peak levels as
morphine. However, the classic opiate antagonist, naloxone, only blocked the ability of morphine to stimulate cNOS-derived
NO release and not that of M6G. CTOP, a mu-specific antagonist, blocked the ability of M6G to induce cNOS-derived NO release
as well as that of morphine, suggesting that a novel mu opiate receptor was present and selective toward M6G. In examining
a receptor displacement analysis, both opiate alkaloids displaced [3H]-dihydromorphine binding to the mu opiate receptor subtype. However, morphine exhibited a twofold higher affinity, again
suggesting that a novel mu opiate receptor may be present.
Received 1 November 2001; received after revision 1 February 2002; accepted 1 February 2002 相似文献
944.
HIV-1 superinfection despite broad CD8+ T-cell responses containing replication of the primary virus 总被引:21,自引:0,他引:21
Altfeld M Allen TM Yu XG Johnston MN Agrawal D Korber BT Montefiori DC O'Connor DH Davis BT Lee PK Maier EL Harlow J Goulder PJ Brander C Rosenberg ES Walker BD 《Nature》2002,420(6914):434-439
Early treatment of acute HIV-1 infection followed by treatment interruptions has shown promise for enhancing immune control of infection. A subsequent loss of control, however, allows the correlates of protective immunity to be assessed. Here we show that sudden breakthrough of plasma viraemia occurred after prolonged immune containment in an individual infected with HIV-1 at a time when 25 distinct CD8+ T-cell epitopes in the viral proteins Gag, RT, Integrase, Env, Nef, Vpr, Vif and Rev were being targeted. Sequencing of the virus in plasma and cells showed that superinfection with a second clade-B virus was coincident with the loss of immune control. This sudden increase in viraemia was associated with a decline in half of the CD8+ T-cell responses. The declining CD8+ T-cell responses were coupled with sequence changes relative to the initial virus that resulted in impaired recognition. Our data show that HIV-1 superinfection can occur in the setting of a strong and broadly directed virus-specific CD8+ T-cell response. The lack of cross-protective immunity for closely related HIV-1 strains, despite persistent recognition of multiple CD8 epitopes, has important implications for public health and vaccine development. 相似文献
945.
946.
Wabnitz H Bittner L de Castro AR Döhrmann R Gürtler P Laarmann T Laasch W Schulz J Swiderski A von Haeften K Möller T Faatz B Fateev A Feldhaus J Gerth C Hahn U Saldin E Schneidmiller E Sytchev K Tiedtke K Treusch R Yurkov M 《Nature》2002,420(6915):482-485
Intense radiation from lasers has opened up many new areas of research in physics and chemistry, and has revolutionized optical technology. So far, most work in the field of nonlinear processes has been restricted to infrared, visible and ultraviolet light, although progress in the development of X-ray lasers has been made recently. With the advent of a free-electron laser in the soft-X-ray regime below 100 nm wavelength, a new light source is now available for experiments with intense, short-wavelength radiation that could be used to obtain deeper insights into the structure of matter. Other free-electron sources with even shorter wavelengths are planned for the future. Here we present initial results from a study of the interaction of soft X-ray radiation, generated by a free-electron laser, with Xe atoms and clusters. We find that, whereas Xe atoms become only singly ionized by the absorption of single photons, absorption in clusters is strongly enhanced. On average, each atom in large clusters absorbs up to 400 eV, corresponding to 30 photons. We suggest that the clusters are heated up and electrons are emitted after acquiring sufficient energy. The clusters finally disintegrate completely by Coulomb explosion. 相似文献
947.
Long-term in vivo imaging of experience-dependent synaptic plasticity in adult cortex 总被引:36,自引:0,他引:36
Do new synapses form in the adult cortex to support experience-dependent plasticity? To address this question, we repeatedly imaged individual pyramidal neurons in the mouse barrel cortex over periods of weeks. We found that, although dendritic structure is stable, some spines appear and disappear. Spine lifetimes vary greatly: stable spines, about 50% of the population, persist for at least a month, whereas the remainder are present for a few days or less. Serial-section electron microscopy of imaged dendritic segments revealed retrospectively that spine sprouting and retraction are associated with synapse formation and elimination. Experience-dependent plasticity of cortical receptive fields was accompanied by increased synapse turnover. Our measurements suggest that sensory experience drives the formation and elimination of synapses and that these changes might underlie adaptive remodelling of neural circuits. 相似文献
948.
The relatively short length of most instrumental climate records restricts the study of climate variability, and it is therefore essential to extend the record into the past with the help of proxy data. Only since the late 1940s have atmospheric data been available that are sufficient in quality and spatial resolution to identify the dominant patterns of climate variability, such as the Pacific North America pattern and the Pacific Decadal Oscillation. Here we present a 301-year snow accumulation record from an ice core at a height of 5,340 m above sea level-from Mount Logan, in northwestern North America. This record shows features that are closely linked with the Pacific North America pattern for the period of instrumental data availability. Our record extends back in time to cover the period from the closing stages of the Little Ice Age to the warmest decade in the past millennium. We find a positive, accelerating trend in snow accumulation after the middle of the nineteenth century. This trend is paralleled by a warming over northwestern North America which has been associated with secular changes in both the Pacific North America pattern and the Pacific Decadal Oscillation. 相似文献
949.
Navigating the signalling network in mouse cardiac myocytes 总被引:6,自引:0,他引:6
Cardiac myocytes have a complex network of signals that regulates their essential role in the rhythmic pumping of the heart. This network is an appealing model system in which to study the basic principles underlying cellular signalling mechanisms. Progress in this effort has come through the establishment of standardized myocyte isolation and culture procedures and characterization of important signalling responses. 相似文献
950.
Analysis of the mouse transcriptome based on functional annotation of 60,770 full-length cDNAs 总被引:6,自引:0,他引:6
Okazaki Y Furuno M Kasukawa T Adachi J Bono H Kondo S Nikaido I Osato N Saito R Suzuki H Yamanaka I Kiyosawa H Yagi K Tomaru Y Hasegawa Y Nogami A Schönbach C Gojobori T Baldarelli R Hill DP Bult C Hume DA Quackenbush J Schriml LM Kanapin A Matsuda H Batalov S Beisel KW Blake JA Bradt D Brusic V Chothia C Corbani LE Cousins S Dalla E Dragani TA Fletcher CF Forrest A Frazer KS Gaasterland T Gariboldi M Gissi C Godzik A Gough J Grimmond S Gustincich S Hirokawa N Jackson IJ Jarvis ED Kanai A 《Nature》2002,420(6915):563-573